CA2082553C - Power conversion system - Google Patents
Power conversion systemInfo
- Publication number
- CA2082553C CA2082553C CA002082553A CA2082553A CA2082553C CA 2082553 C CA2082553 C CA 2082553C CA 002082553 A CA002082553 A CA 002082553A CA 2082553 A CA2082553 A CA 2082553A CA 2082553 C CA2082553 C CA 2082553C
- Authority
- CA
- Canada
- Prior art keywords
- power
- commutated
- line
- converting means
- diode
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/66—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal
- H02M7/68—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters
- H02M7/72—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/75—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means
- H02M7/757—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/01—Arrangements for reducing harmonics or ripples
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
- H02J3/1821—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators
- H02J3/1835—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control
- H02J3/1842—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control wherein at least one reactive element is actively controlled by a bridge converter, e.g. active filters
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/12—Arrangements for reducing harmonics from ac input or output
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
- H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
- H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/145—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means
- H02M7/155—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only
- H02M7/162—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only in a bridge configuration
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/20—Active power filtering [APF]
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/40—Arrangements for reducing harmonics
Abstract
A power conversion system of this invention comprises line-commutated power converting means in which a line-commutated power conversion circuit that performs line-commutated commutation and a coupling diode are coupled to form a DC circuit and for converting DC power into AC
power or AC power into DC power. Further the system comprises self-commutated power converting means in which a self-commutated power conversion circuit coupled to the coupling diode in order to form a DC circuit and for reducing reactive power, or the reactive power and harmonics generated by the line-commutated converting means.
Accordingly their respective strengths can be made use of and their mutual weaknesses can complement each other.
power or AC power into DC power. Further the system comprises self-commutated power converting means in which a self-commutated power conversion circuit coupled to the coupling diode in order to form a DC circuit and for reducing reactive power, or the reactive power and harmonics generated by the line-commutated converting means.
Accordingly their respective strengths can be made use of and their mutual weaknesses can complement each other.
Description
2~'82~53 POWER CONVERSION SYSTEM
Background of the Invention Field of the Invention The invention relates to a power conversion system in which a line-commutated power conversion system and a self-commutated power conversion system are coupled.
Description of the Related Art Line-commutated power conversion systems are widely used for conversion from AC power to DC power or from DC
power to AC power. By way of example, large-scale systems are used in power conversion systems for DC power transmission.
However, large-scale line-commutated power conversion systems require LC filters consisting of a reactor and a capacitor in order to reduce harmonics and compensate lagging reactive power, but in addition to the problem that the space required for the LC filter is large, there are problems of overcurrent in the LC filter caused by ingress of harmonics from the outside and the occurrence of antiresonance caused by the LC filter and the reactance of the system.
Further, in line-commutated conversion systems, a switching device is commutated using the system voltage so that there is also a problem in that commutation failure is caused and the system damaged if the voltage of the system should drop or voltage distortion occur during inverter operation.
Active filters and reactive power adjusting devices using voltage type self-commutated power conversion systems instead of LC filters have recently appeared together with advances in self-¢ommutated power conversion technology.
By way of examples, active filters _nd re_ctive power adjusting devices, products classed from sever_l NVA to sever_l tens of NVA have been produced starting with the device disclosed in the "Toshiba Review" ~Vol. 43, No. 4, pp. 339 to 342) for example. The power conversion circuit is of the voltage type self-commutated type. The primary problem in systems using thi~ voltage type self-commutated power convorsion system is overcurrent protection in the switching device during a DC short-circuit.
The problQms associated with a main circuit become particularly apparent _t higher c_pacities. To elabor_te, should the GTO (G_te Turn-Off) thyristors be ON at the same time due to a control irregul_rity or the like, the charge of the DC capacitor is dischargQd through the GTo thyristors. If there is a rapid rise in the short-circuit current it is impossible to use the current circuit-brea~;ng function of the GTO thyristor at this time _nd there is a risk of overcurrent bre_kdown of the GTO thyristor. Protective fuses _re inserted to prevent the risk.
However, protective fuses are not av_ilable for higher voltages ~nd some customers do not like to use them for re_sons of gu_r_nteeing long-term reliability, and there is a demand for devices to replace them.
8umm_ry of the Invention It is therefore an object of the invention to provide _ power conversion system comprising a line-commutated power converter and a self-commutated power converter, wherein their respective strengths can be made use of and their respective wea~ne~ses can be complemented by each other.
To achieve the above object, a power conversion system comprising line-commutated power converting means ~n~5~
in which a line-commutated power conversion circuit and a coupling diode are coupled to form a DC circuit and for converting DC power into AC power or AC power into DC power, and self-commutated power converting means in which a self-commutated power conversion circuit is coupled to the coupling diode in order to form a DC circuit and for reducing reactive power, or the reactive power and harmonics generated by the line-commutated converting means.
According to the above-structured power conversion system of the invention, the line-commutated power converting means governs the power conversion from DC power to AC power or from AC power to DC power and the self-commutated power converting means reduces the reactive power, or the reactive power and harmonics generated by the line-commutated power converting means, and both operate more or less independently, but during the rare direct current short-circuiting of the self-commutated power converting means, conduction by said coupling diode is blocked so that the line-commutated power converting means and the self-commutated power converting means operate in series. Thus the overcurrent in the self-commutated power converting means side is limited by the constant current control function of the line-commutated power converting means and the short-through is safely removed by the turn-off action of the switching devices by the intrinsic circuit-breaking function. This makes it possible to make self-commutated power converting means fuseless and smaller in scale.
5 !5 3 -3a-In accordance with the present invention, there is provided a power conversion system comprising line-commutated power converting means for converting from DC power to AC
power or from AC power to DC power; self-commutated power converting means for reducing reactive power by the line-commutated power converting means; and a coupling means for forming a first closed circuit with the line-commutated power converting means and a second closed circuit with the self-commutated power converting means, wherein the line-commutated power converting means comprises a circuit breaker, a trans-former, a reverse-conducting bridge connected power converter, a reactor and a DC capacitor, the coupling means is a diode, the first closed circuit comprises a load, the diode, the DC
reactor, and the reverse-blocking bridge connected power converter, and the second closed circuit comprises the DC
capacitor, the diode, and the reverse-conducting bridge connected power converter.
In accordance with the present invention, there is further provided a power conversion system comprising line-commutated power converting means for converting from DC powerto AC power or from AC power to DC power; self-commutated power converting means for reducing reactive power by the line-commutated power converting means; and a coupling means for forming a first closed circuit with the line-commutated power converting means and a second closed circuit with the self-commutated power converting means, wherein the line-commutated power converting means comprises a circuit breaker, -3b-a transformer, a reverse-blocking bridge connected power converter, and a DC reactor, the self-commutated power converting means comprises a circuit breaker, a transformer, a reverse-conducting bridge connected power converter, a reactor and a DC capacitor, the coupling means is a diode, the first closed circuit comprises a DC power source, the diode, the DC
reactor, and the reverse-blocking bridge connected power converter, and the second closed circuit comprises a DC power source, the diode, and the reverse-conducting bridge connected power converter.
In accordance with the present invention, there is further provided a power conversion system comprising a pair of self-commutated power converters having AC terminals which are respectively connected to a first AC system and a second AC system and DC terminals, and being provided in common with a series circuit comprising a DC capacitor between the DC
terminals and a coupling diode inserted with polarity such as to block the discharge current of the DC capacitor; and a pair of line-commutated power converters that perform line-commutated commutation, having AC terminals being respectivelyconnected to the first AC system and second AC system, and which are connected such that the coupling diode is contained in series and such that DC current flows through the coupling diode.
In accordance with the present invention, there is further provided a power conversion system comprising a pair of voltage type self-commutated converters that perform self-r~ 28516-5 commutated commutation and have AC terminals being respect-ively connected to a first AC system and a second AC system and DC terminals, one end of a DC capacitor being connected to one end of the DC terminals of a coupling diode bridge, the other end of the coupling diode bridge being connected as DC
terminals; and a pair of line-commutated converters that perform line-commutated commutation, have AC terminals being respectively connected to the first AC system and the second AC system, and are connected such that DC circuits are formed through the DC terminals of the coupling diode bridge and such that their DC currents flow through the coupling diode bridge.
Brief Description of the Drawinqs Fig. 1 is a diagram of a power conversion system illustrating first embodiment of the invention;
Fig. 2 is a diagram illustrating one example of a reverse blocking type bridge connected converter;
_ -4- 2~825~3 Fig. 3 is a diagram showing paths along which current flows during DC short-circuiting of the reverse conducting type bridge connected converter;
Fig. ~ is ~ diagram illustrating one ex~mple of a reverse conducting type bridge connected converter;
Fig. 5 is a diagram of a power conversion system illustrating second embodiment of the invention;
Fig. 6 is a diagram of a power conversion system illustrating third embodiment of the invention;
Fig. 7 is a diagram of a power conversion system illustrating fourth emboaiment of the invention;
Fig. 8 is a ~iagram of a power conversion system illustrating fifth embodiment of the invention;
Fig. 9 i~ ~ diagram of ~ power conversion system illustrating sixth embodiment of the invention;
Fig. 10 is a diagram of a power conversion system illustrating seventh emboaiment of the invention;
Fig. 11 is a diagram of a power conversion system illustrating eighth embodiment of the invention Fig. 12 is a diagr~m showing paths along which current flows during DC short-circuiting of a reverse conaucting type bridge connected converter of the eighth embodiment in Fig. 11;
Fig. 13 i8 a diagram of a power conversion system illustrating ninth embodiment of the invention;
Fig. 14 is a aiagram of a power conversion system illustrating tenth embodiment of the invention;
Fig. 15 is a diagram of a power conversion system illustrating eleventh embodiment of the invention.
Detailed Description of the Preferrea Embodiments Preferred embodiments of the invention will now be describea referring to the accompanying drawings.
As shown in Fig. 1, a power conversion system of a first embodiment comprises a line-commutated power conversion apparatus 100 and a voltage type self-commutated power conversion apparatus 200. Both ~~5~ ~n82553 apparatus 100 and 200 are coupled by a eoupling diode 107.
The line-commutated power eonver~ion apparatus comprises a circuit breaker 101, a transformer 102, a reverse bloe~; n7 type bridge eonnected power eonverter 103 having a positive terminal 104 and a negative terminal 105, a DC reaetor 106 and the eoupling diode 107.
Also the voltage type self-eommutated power 10eonver~ion apparatus 200 eomprises a eireuit breaker 201, a tran~former 202, a eoupling reaetor 203, a reverse eondueting type bridge eonneeted power eonverter 204 having a positive terminal 205 and a negative terminal 206, a DC eapaeitor 207 and the eoupling diode 107.
15Further, the reverse bloeking type bridge eonneeted power eonverter 103 may be a thyristor rectifier as shown in Fig. 2.
As the eoupling diode 107 is eonneeted in the direetion of DC eurrent flow, the normal operation of the line-eommutated power eonver~ion apparatus 100 is not influeneed by the eoupling diode 107.
on the other hand as the eoupling diode 107 is inserted with the polarity in Fig. 1 in the voltage type self-eommutated power conversion apparatus 200, the capacitor 207 is charged but there is no pathway for diseharging in the voltage type self-eommutated power eonversion apparatus 200.
Consequently the voltage type ~elf-commutated power eonversion apparatus 200 does not operate alone.
However, if the line-eommutated power eonversion apparatus 100 is operated and a current Il flows in the coupling diode 107, th~ voltage type ~elf-eommutated power eonversion apparatus 200 operates in exactly the same way as when there is no coupling diode provided that the eurrent in the diseharge direetion flowing in the DC
eapaeitor 207 is less than the eurrent Il.
However, if for some reason the reverse eondueting type bridge eonneeted power eonverter 204 suffer~
_ -6- ~0825~3 commutation failure, the terminals 205 and 206 ~re short-circuited, and the charge of the capacitor 207 attempts to flow through the short-circuit path. Further if this value is about to ~Ycee~ the current Il, the current in the coupling diode 107 is zero and the coupling diode 107 enters the reverse blocking state.
As result, a~ shown in Fig. 3, the discharge current Ic flows through the circuit of the line-commutated power conversion apparatus 100 and the increase in current is restricted. 8ubsequently, a protective operation is ¢arried out by a signal from a commutation failure detection circuit ~not shown). The co lutation failure detection ¢ircuit protects the power conversion ~ystem from the overcurrent caused by the commutation failure.
Further, a choice is made depending on the cause of the commutation failure as to whether to restart the operation or to ~top the voltage-type self-commutated power conversion apparatus 200 and only operate the line-commutated power conversion system 100, 80 preventing a drop in the wor~ing efficiency of the power conversion system.
Now the operation of protecting the reverse conducting type bridge connected power converter 204 will be described.
Referred to Fig. 4, the GTO thyristors 211, 214 and 216 are fired, currents Iu, Iv and Iw flow into terminals U, V and W respectively. If curront Iw is flowing, and the GTO thyristor 215 is fired by accident, a DC short-circuit occurs between the GTO thyristor 215 and the GTO
thyristor 216.
As described above, as the current Il flows through the point of short-circuit, the current I1 flows into the GTO thyristor 215 and the currents Iw and Il flow into the GTO thyristor 216. If the maximum current value at which the GTO thyristor can be turned off by its gate is In~ and the value of current Iw plus current Il is equal to I~ or less, the GTO thyristor can be provided with an OFF signal and can be turned off safely. However, if 7- 2~82~53 the value of current Iw plus current I1 i~ more th_n the I~ and the GTO thyristor is provided with the CFF
signal, it will be dQstroyed due to overcurrent.
Accordingly, for safe operation, the current Il must satisfy the following expression.
Iw I Il < I~
Consequently, if the GTO thyristors 215 _nd 216 are turned off, the short-circuit iq removed. The GTO
thyri~tor 216 can then also be turned off safely and the system can be restarted immediately.
A method of providing ON signal to other GTO
thyristors of pha~es which did not ~hort-circuit at the s~me time after detecting the ~hort-circuited condition as a method of decreasing current value flowing in a ~hort-circuited portion.
Next _ second embodiment will be de~cribed with reference to Fig. 5.
As shown in Fig. 5, in this embodiment a DC power source 120 has been connecte~ instead of the load. The line-commut~ted power conversion apparatus 100 freely converts from AC to DC and from DC to AC by changing the firing control angle of the thyristor.
Next a third embodiment will be dQscribed with reference to Fig. 6.
A voltage type self-commutated power conversion apparatus in Fig. 6 also has the function of reducing harmonics a8 well a8 the function of adjusting reactive power while supplying active power to the system by converting DC power to AC power.
The power conversion system shown in Fig. 1, Fig. S
and Fig. 6 have various other ~lternative~. The embodiment~ ~hown below illu~trate alternatives of the power conversion system in Fig. 1, but similar alternatives are also pos~ible for the power conversion systems in Fig. 5 and Fig. 6.
Fig. 7 show~ a fourth embodiment of the invention.
This embodiment shows that the position where the -8- 2082~53 coupling diode 107 is inserted can be varied freely in the clo~ed circuit constituted by the rever~e blocking type bridge connected power converter 103, DC reactor 106, load 110, and the coupling diode 107 in the power conver~ion systQm in Fig. 1. It also shows that the function of coupling reactor 203 is included in the leakage reactance of tran~former 208 and the function of circuit breaker 201 is included in the circuit breaker 101 .
Also in this system the transformer 208 is connected to the DC winding side of the tran~former 102. This allows the freguency of occurrence of commutation failure in the line-commutated power conversion apparatus to be reduced as far as possible by preventing the ~ystem voltage from falling due to reactive power supplied by the voltage type self-commutated power conversion apparatus and reducing the distortion of the system voltage by a harmonic reducing function. However in this case lea~age reactance of transformer is set at low level. Of course, it i8 po~sible to reduce the freguency of commutation failure and the like as well, but this depen~ on the sises and proportions of the impedance of the tran~former 102 and the impe~Ancq on the system side.
Large capacity system~ require duplication of the reverse conducting type bridge connected power converter 204. A fifth embodiment through a ~eventh embodiment are shown in Fig. 8 to Fig. 10.
In the fifth embodiment in Fig. 8, two coupling diodes 107 are inserted in seriQs, and series circuits consisting of reverse conducting type bridge connected power converters 2041 and 2042 and DC capacitor~ 2071 and 2072 are connected to these with the polarity depicted.
Waveform synthesis with a tran~former 209 using two reverse conducting type bridge connected converters in this way i8 a technigue g~nerally widely usQd for duplicate inverters. Even if one of the reverse conducting type bridge connected power converters 2041 or 2042, or both, cau~es a DC short circuit, the conduction 9 20~553 of one or both of the coupling diode~ 1071 or 1072 is bloc~ed as in Fig. 1, the line-commutated power conversion apparatus 100 and the voltage type self-commutated power conversion apparatus 200 are connected in series and it proves possible to move the protection operation while the rise in the ~hort circuit current is limited.
In the sixth embodiment in Fig. 9, the positional relationship between the DC capacitor 207 and the reverse conducting type bridge connecter power converter 204 has been reversed. Coupling reactor 203 may be inserted on the AC winding sidQ of the transformer as in Fig. 9, or it can be inserted in the DC w;n~;ng side as in Fig. 1, or omitted if a high-impedance transformer is used.
lS In the sQventh embodiment in Fig. 10 is a format effective in large capacity power conversion systems a~
in Fig. 8: a plurality of serial circuits consisting of a DC reactor 106 and coupling diode 107 are connected in parallel, and reverse conducting type bridge connected power converters 204 and DC capacitors 207 are connected to the coupling diodes. In this case too, the DC
capacitors may be divided as in Fig. 8 and Fig. 9.
The insulating transformers 102, 202 and 209 in the embodiments in Fig. 1 to Fig. 10 are used normally when connected to the system. It i8 clear that there is no need to provide insulating transformers in both the line-commutated power conversion apparatus 100 and the voltage type self-commutated power conversion apparatu~ 200 although, in principle, the AC side must be insulated since the two apparatu~ are coupled by the coupling diode 107 in the direct current portion.
Example~ have been given in the preceding ~escription in which the voltage type self-commutated power conversion apparatus has been used as a reactive power adjusting device, active filter or invertor, but it is clear that in principle it can also be used to convert from AC power to DC power. In addition to the device commutation power converter shown in Fig. 4, a converter 20825~3 using impulse eommutation type or another type self-commutated power eonversion apparatus can be appropriately used as the reverse eon~ucting type bridge eonnected power converter.
Next an eighth embodiment of this invention will be described with referenee to Fig. 11.
A power conversion system of thi~ embodiment as shown in Fig. 11 eompri~e~ a fir~t AC line 300a, a sQeond AC
line 300b, ~ line-commutated power conversion apparatus 400, a self-commutated power convQrsion apparatus 500.
The interiors of line-eommutated power conversion apparatus 400 and ~elf-eommutated power eonversion apparatus 500 are symmetrieal a~ between the ~ide a~soeiated with AC line 300a and the side assoeiatQd with AC line 300b. The referenee numerals of the eonstituent devieQs are therefore distinguished by the suffixes a and b.
The power souree terminals of eireuit breakers 401 and 501 are respeetively eonneeted to AC lines 300a and 300b. The load terminal of eireuit breaker 401 i8 eonneeted to the input terminal of a transformer 402 and the load terminal of eireuit breaker 501 is eonneeted to the input terminal of a transformer 501.
The output terminal of transformer 402 is eonneeted to the AC terminal of a reverse bloç~;~g type bridge eonneeted power converter 403 while the output terminal of transformer 502 is eonnected to the AC terminal of a rever~e conducting type bridge eonnected power converter 504 through a reactor 503.
The reverse bloc~;ng type bridge connected power eonverter ~03 has a positive eleetrode terminal 404 and a negative eleetrode terminal 405.
The negative electrode terminal 405 and one end of reactor 406 are connected. The positive electrode terminal 404 and the anode of a coupling diode 407 are eonneeted. The po~itive eleetrode terminal 404 is eonneeted to the other end of reaetor 406. The eathode of eoupling diode 407 is eonneeted to the negative 2~i~2~3 electrode terminal 405 of reverse blor~tng type bridge connected power converter 403, forming a pair.
A sQries circuit consisting of a DC cap_citor 507 and coupling diode 407 i~ connected between positive electrode terminal 505 and negative electrode terminal 506 of reverse conducting type bridge connected power converter 504 with _ polarity ~uch _~ to bloc~ di~ch_rge of DC cap_citor 507.
The oper_tions of the line-commut_ted power conversion apparatus 400 and 8elf-commutated power conversion apparatus 500 are the same a~ the opQrations described in the first embodiment. Con~equently the operations are not described in this embodiment in detail.
15Howover, if for ~ome reason there is a f_ilure of commut_tion of the reverse conducting type bridge connected power converter 504a on the sidQ of AC line 300_, when terminal~ 505_ _nd 506_ go into a ~hort-circuited condition, the di~charge current of DC
20capacitor 507 trie~ to flow through the ~hort-circuit with the result that its value tries to exceed Il.
However, when thi~ happen~, the current of coupling diode 407 goe~ to zero, 80 that ¢oupling diode 407 goes into _ bloc~ing condition.
25A~ _ re~ult, a8 shown in Fig. 13, in which identical parts to those of Fig. 11 are given the ~_me reference numerals, discharge current Ic flow~ through the circuit of line-commutated power conversion apparatu~ 400 which ~uppresses thi~ di~charge current Ic to Il. The GTO
30thyri~tor of the healthy reverse conducting type bridge connected power converter 504b i8 therefore turned off by _ sign_l gener_ted by a commut_tion f_ilure detection circuit (not shown). An OFF sign_l i~ ~imultaneou~ly supplied to the GTO thyristor of the faulty reverse 35conducting type bridge connected power converter 504_.
The difference between thi~ embodiment _nd the embodiment de~cribed in Fig. 1 is a current value flowing in the short-circuit portion.
Though the eurrent value is the value I1 ~ Im in the embodiment deseribed in Fig. 1, the eurrent value in this embodiment i~ the value Il ~ Im ~ I~. NOW I~ means a direct eurrent flowing the reverse conducting type bridge eonneeted power eonverter 504b.
Con~equently the eurrent value deseribed in thi~
embodiment ha~ two eases due to the direction of flowing of the direet eurrent. One i8 that the curront value i8 larger than the value Il + I~ and the other is that it is lower than the value Il ~ Im-It may be seleeted whether the operation of rever~e eondueting type bridge eonnected power eonverter 504b stop or not at the same time to short-eireuit in order to deerease the eurrent flowing at the short-eireuit portion as large as possible.
Also in ease of Fig. 11, it is effeetive to turn on all of GTO thyristors in the reverse eondueting type bridge eonneeted power eonverter whieh short-eireuited and to disperse the short-eireuit eurrent.
The Fig. 13 i8 a diagram showing a ninth embodiment of thi~ invention. The differenee from Fig. 11 lies in that a single-phase diode bridge 410 is employed for eoupling instead of eoupling diode 407. The single-phase diode bridge ~10 has DC terminals 411 and 412 and AC
2 5 terminal~ 413 and 414. Ordinary operation in this ease is the same a~ in Fig. 11.
Considering the ease where short-eireuit oeeur~ in the ux pole of reverse eonducting bridge connected eonverter 504a as in Fig. 11, entry of the DC eurrent I~
of reverse eondueting type bridge eonneeted power eonverter 504b is bloeked by single-phase diode bridge 410, ~o the GTO thyristor eurrent of the ux pole beeome~
Iu, ~ Il while the other GTO thyristor eurrents are Il. If a seleetive turn-off proeedure i~ adopted 80 long a~
I~ ~ Il, Il ean be bigger than in Fig. 11. Now the ux pole means the portion eonstituted in the bridge eonneeted eireuit of Fig. 4 by GTO thyristors 211 and -13- ~8~5~
212, diode~ 217 and 218 and fuReR 223 and 224, and formR
one pha~e.
Fig. 1~ ~how~ yet a tenth embodiment of thi~
invention. In thi~ embodiment, two ~elf-commutated power conver~ion apparatu_ a~ in Fig. 11 are provided.
Further, in thi~ embodiment, eoupling reaetor 503a and tran~former 502a are integrated and substituted by high-induetanee tran_former~ 508. The primary winding~
of two high-induetanee transformers 508 are eonneeted in _erie~. Voltage eompo~ition u~ing a tran~former i8 often carried out, in order to reduce waveform distort~on on the AC side of a plurality of reverRe eonducting type bridge eonnected power eonverter~ 504 in a voltage type ~elf-commutated power eonverter.
Cireuit-breaker 501a i~ eonnected to the ~eeondary ~ide of transformer 402a of line-commutated power conversion apparatu~ 400. A reaetor 408 is in~erted between thi~ ~eeondary side and reverse bloeking type bridge eonneeted power eonverter 403a. Thi~ i~ provided with the aim of deerea~ing outflow of higher harmonic current to the sy~tem and reducing the frequency of commutation failure of reverse bloeking type bridge connected power converter 403a, by reducing the voltage drop generated in AC line 300a and the higher harmonic~
generated by reverse blocking bridge eonnqcted converter 403a in self-commut~ted power conver~ion apparatu~ S00.
Fig. 15 ~how~ an eleventh emho~;ment in which two ~elf-commutated coupling RyRtem~ as in Fig. 13 are employed. In this caRe alRo, the primarie~ of tran~former~ 502 are connected in ~eries.
In the above de~cription, GTO thyri_tors are employed as rever~e conducting type bridge connected power converter 50~, but other devices could al~o be u~ed.
Furthermore, apart from device-commutated power converter~, impul~e commutation or another Relf-commutated commutation type power eonverter could be employed.
-14- 20~2~3 In the embodiments of Fig. 11 to Fig. 15, the coupling diode or switching device was shown by a single symbol, but these could be appropriately used in series or in p~r~llel depending on the voltage or current.
As described above, according to the eighth embodiment through the eleventh embodiment, the self-commutated power conversion apparatus reduces the reactive power and generation of higher harmonics, which are the weakne~ses of the line-commutated power conversion apparatus and prevents commutation failure due to drop of system voltage and/or distortion. The line-commutated power conversion apparatus prevents overcurrent breakdown on short-circuiting, which is the weakness of the self-commutated power conversion lS apparatus.
In those embodiment in Fig. 1 to Fig. 15, the devices used in the coupling diode and the reverse conducting type bridge connected power converter have been represented by a single symbol, and these may be used in series, in parallel or in series and parallel as appropriate depending on the circuit voltage current. The line-commutated power conversion apparatus is not limited to a six-phase construction and it may be embodied as a twelve-phase or other multi-phase construction.
Thus benefits are exhibited which cannot be attained simply by arranging a line-commutated power conversion apparatu~ and ~elf-commutated power conversion apparatus in parallel. Thus the embodiments offer great benefits in particular in contributing to implementation of large self-commutated power conversion apparatus.
Background of the Invention Field of the Invention The invention relates to a power conversion system in which a line-commutated power conversion system and a self-commutated power conversion system are coupled.
Description of the Related Art Line-commutated power conversion systems are widely used for conversion from AC power to DC power or from DC
power to AC power. By way of example, large-scale systems are used in power conversion systems for DC power transmission.
However, large-scale line-commutated power conversion systems require LC filters consisting of a reactor and a capacitor in order to reduce harmonics and compensate lagging reactive power, but in addition to the problem that the space required for the LC filter is large, there are problems of overcurrent in the LC filter caused by ingress of harmonics from the outside and the occurrence of antiresonance caused by the LC filter and the reactance of the system.
Further, in line-commutated conversion systems, a switching device is commutated using the system voltage so that there is also a problem in that commutation failure is caused and the system damaged if the voltage of the system should drop or voltage distortion occur during inverter operation.
Active filters and reactive power adjusting devices using voltage type self-commutated power conversion systems instead of LC filters have recently appeared together with advances in self-¢ommutated power conversion technology.
By way of examples, active filters _nd re_ctive power adjusting devices, products classed from sever_l NVA to sever_l tens of NVA have been produced starting with the device disclosed in the "Toshiba Review" ~Vol. 43, No. 4, pp. 339 to 342) for example. The power conversion circuit is of the voltage type self-commutated type. The primary problem in systems using thi~ voltage type self-commutated power convorsion system is overcurrent protection in the switching device during a DC short-circuit.
The problQms associated with a main circuit become particularly apparent _t higher c_pacities. To elabor_te, should the GTO (G_te Turn-Off) thyristors be ON at the same time due to a control irregul_rity or the like, the charge of the DC capacitor is dischargQd through the GTo thyristors. If there is a rapid rise in the short-circuit current it is impossible to use the current circuit-brea~;ng function of the GTO thyristor at this time _nd there is a risk of overcurrent bre_kdown of the GTO thyristor. Protective fuses _re inserted to prevent the risk.
However, protective fuses are not av_ilable for higher voltages ~nd some customers do not like to use them for re_sons of gu_r_nteeing long-term reliability, and there is a demand for devices to replace them.
8umm_ry of the Invention It is therefore an object of the invention to provide _ power conversion system comprising a line-commutated power converter and a self-commutated power converter, wherein their respective strengths can be made use of and their respective wea~ne~ses can be complemented by each other.
To achieve the above object, a power conversion system comprising line-commutated power converting means ~n~5~
in which a line-commutated power conversion circuit and a coupling diode are coupled to form a DC circuit and for converting DC power into AC power or AC power into DC power, and self-commutated power converting means in which a self-commutated power conversion circuit is coupled to the coupling diode in order to form a DC circuit and for reducing reactive power, or the reactive power and harmonics generated by the line-commutated converting means.
According to the above-structured power conversion system of the invention, the line-commutated power converting means governs the power conversion from DC power to AC power or from AC power to DC power and the self-commutated power converting means reduces the reactive power, or the reactive power and harmonics generated by the line-commutated power converting means, and both operate more or less independently, but during the rare direct current short-circuiting of the self-commutated power converting means, conduction by said coupling diode is blocked so that the line-commutated power converting means and the self-commutated power converting means operate in series. Thus the overcurrent in the self-commutated power converting means side is limited by the constant current control function of the line-commutated power converting means and the short-through is safely removed by the turn-off action of the switching devices by the intrinsic circuit-breaking function. This makes it possible to make self-commutated power converting means fuseless and smaller in scale.
5 !5 3 -3a-In accordance with the present invention, there is provided a power conversion system comprising line-commutated power converting means for converting from DC power to AC
power or from AC power to DC power; self-commutated power converting means for reducing reactive power by the line-commutated power converting means; and a coupling means for forming a first closed circuit with the line-commutated power converting means and a second closed circuit with the self-commutated power converting means, wherein the line-commutated power converting means comprises a circuit breaker, a trans-former, a reverse-conducting bridge connected power converter, a reactor and a DC capacitor, the coupling means is a diode, the first closed circuit comprises a load, the diode, the DC
reactor, and the reverse-blocking bridge connected power converter, and the second closed circuit comprises the DC
capacitor, the diode, and the reverse-conducting bridge connected power converter.
In accordance with the present invention, there is further provided a power conversion system comprising line-commutated power converting means for converting from DC powerto AC power or from AC power to DC power; self-commutated power converting means for reducing reactive power by the line-commutated power converting means; and a coupling means for forming a first closed circuit with the line-commutated power converting means and a second closed circuit with the self-commutated power converting means, wherein the line-commutated power converting means comprises a circuit breaker, -3b-a transformer, a reverse-blocking bridge connected power converter, and a DC reactor, the self-commutated power converting means comprises a circuit breaker, a transformer, a reverse-conducting bridge connected power converter, a reactor and a DC capacitor, the coupling means is a diode, the first closed circuit comprises a DC power source, the diode, the DC
reactor, and the reverse-blocking bridge connected power converter, and the second closed circuit comprises a DC power source, the diode, and the reverse-conducting bridge connected power converter.
In accordance with the present invention, there is further provided a power conversion system comprising a pair of self-commutated power converters having AC terminals which are respectively connected to a first AC system and a second AC system and DC terminals, and being provided in common with a series circuit comprising a DC capacitor between the DC
terminals and a coupling diode inserted with polarity such as to block the discharge current of the DC capacitor; and a pair of line-commutated power converters that perform line-commutated commutation, having AC terminals being respectivelyconnected to the first AC system and second AC system, and which are connected such that the coupling diode is contained in series and such that DC current flows through the coupling diode.
In accordance with the present invention, there is further provided a power conversion system comprising a pair of voltage type self-commutated converters that perform self-r~ 28516-5 commutated commutation and have AC terminals being respect-ively connected to a first AC system and a second AC system and DC terminals, one end of a DC capacitor being connected to one end of the DC terminals of a coupling diode bridge, the other end of the coupling diode bridge being connected as DC
terminals; and a pair of line-commutated converters that perform line-commutated commutation, have AC terminals being respectively connected to the first AC system and the second AC system, and are connected such that DC circuits are formed through the DC terminals of the coupling diode bridge and such that their DC currents flow through the coupling diode bridge.
Brief Description of the Drawinqs Fig. 1 is a diagram of a power conversion system illustrating first embodiment of the invention;
Fig. 2 is a diagram illustrating one example of a reverse blocking type bridge connected converter;
_ -4- 2~825~3 Fig. 3 is a diagram showing paths along which current flows during DC short-circuiting of the reverse conducting type bridge connected converter;
Fig. ~ is ~ diagram illustrating one ex~mple of a reverse conducting type bridge connected converter;
Fig. 5 is a diagram of a power conversion system illustrating second embodiment of the invention;
Fig. 6 is a diagram of a power conversion system illustrating third embodiment of the invention;
Fig. 7 is a diagram of a power conversion system illustrating fourth emboaiment of the invention;
Fig. 8 is a ~iagram of a power conversion system illustrating fifth embodiment of the invention;
Fig. 9 i~ ~ diagram of ~ power conversion system illustrating sixth embodiment of the invention;
Fig. 10 is a diagram of a power conversion system illustrating seventh emboaiment of the invention;
Fig. 11 is a diagram of a power conversion system illustrating eighth embodiment of the invention Fig. 12 is a diagr~m showing paths along which current flows during DC short-circuiting of a reverse conaucting type bridge connected converter of the eighth embodiment in Fig. 11;
Fig. 13 i8 a diagram of a power conversion system illustrating ninth embodiment of the invention;
Fig. 14 is a aiagram of a power conversion system illustrating tenth embodiment of the invention;
Fig. 15 is a diagram of a power conversion system illustrating eleventh embodiment of the invention.
Detailed Description of the Preferrea Embodiments Preferred embodiments of the invention will now be describea referring to the accompanying drawings.
As shown in Fig. 1, a power conversion system of a first embodiment comprises a line-commutated power conversion apparatus 100 and a voltage type self-commutated power conversion apparatus 200. Both ~~5~ ~n82553 apparatus 100 and 200 are coupled by a eoupling diode 107.
The line-commutated power eonver~ion apparatus comprises a circuit breaker 101, a transformer 102, a reverse bloe~; n7 type bridge eonnected power eonverter 103 having a positive terminal 104 and a negative terminal 105, a DC reaetor 106 and the eoupling diode 107.
Also the voltage type self-eommutated power 10eonver~ion apparatus 200 eomprises a eireuit breaker 201, a tran~former 202, a eoupling reaetor 203, a reverse eondueting type bridge eonneeted power eonverter 204 having a positive terminal 205 and a negative terminal 206, a DC eapaeitor 207 and the eoupling diode 107.
15Further, the reverse bloeking type bridge eonneeted power eonverter 103 may be a thyristor rectifier as shown in Fig. 2.
As the eoupling diode 107 is eonneeted in the direetion of DC eurrent flow, the normal operation of the line-eommutated power eonver~ion apparatus 100 is not influeneed by the eoupling diode 107.
on the other hand as the eoupling diode 107 is inserted with the polarity in Fig. 1 in the voltage type self-eommutated power conversion apparatus 200, the capacitor 207 is charged but there is no pathway for diseharging in the voltage type self-eommutated power eonversion apparatus 200.
Consequently the voltage type ~elf-commutated power eonversion apparatus 200 does not operate alone.
However, if the line-eommutated power eonversion apparatus 100 is operated and a current Il flows in the coupling diode 107, th~ voltage type ~elf-eommutated power eonversion apparatus 200 operates in exactly the same way as when there is no coupling diode provided that the eurrent in the diseharge direetion flowing in the DC
eapaeitor 207 is less than the eurrent Il.
However, if for some reason the reverse eondueting type bridge eonneeted power eonverter 204 suffer~
_ -6- ~0825~3 commutation failure, the terminals 205 and 206 ~re short-circuited, and the charge of the capacitor 207 attempts to flow through the short-circuit path. Further if this value is about to ~Ycee~ the current Il, the current in the coupling diode 107 is zero and the coupling diode 107 enters the reverse blocking state.
As result, a~ shown in Fig. 3, the discharge current Ic flows through the circuit of the line-commutated power conversion apparatus 100 and the increase in current is restricted. 8ubsequently, a protective operation is ¢arried out by a signal from a commutation failure detection circuit ~not shown). The co lutation failure detection ¢ircuit protects the power conversion ~ystem from the overcurrent caused by the commutation failure.
Further, a choice is made depending on the cause of the commutation failure as to whether to restart the operation or to ~top the voltage-type self-commutated power conversion apparatus 200 and only operate the line-commutated power conversion system 100, 80 preventing a drop in the wor~ing efficiency of the power conversion system.
Now the operation of protecting the reverse conducting type bridge connected power converter 204 will be described.
Referred to Fig. 4, the GTO thyristors 211, 214 and 216 are fired, currents Iu, Iv and Iw flow into terminals U, V and W respectively. If curront Iw is flowing, and the GTO thyristor 215 is fired by accident, a DC short-circuit occurs between the GTO thyristor 215 and the GTO
thyristor 216.
As described above, as the current Il flows through the point of short-circuit, the current I1 flows into the GTO thyristor 215 and the currents Iw and Il flow into the GTO thyristor 216. If the maximum current value at which the GTO thyristor can be turned off by its gate is In~ and the value of current Iw plus current Il is equal to I~ or less, the GTO thyristor can be provided with an OFF signal and can be turned off safely. However, if 7- 2~82~53 the value of current Iw plus current I1 i~ more th_n the I~ and the GTO thyristor is provided with the CFF
signal, it will be dQstroyed due to overcurrent.
Accordingly, for safe operation, the current Il must satisfy the following expression.
Iw I Il < I~
Consequently, if the GTO thyristors 215 _nd 216 are turned off, the short-circuit iq removed. The GTO
thyri~tor 216 can then also be turned off safely and the system can be restarted immediately.
A method of providing ON signal to other GTO
thyristors of pha~es which did not ~hort-circuit at the s~me time after detecting the ~hort-circuited condition as a method of decreasing current value flowing in a ~hort-circuited portion.
Next _ second embodiment will be de~cribed with reference to Fig. 5.
As shown in Fig. 5, in this embodiment a DC power source 120 has been connecte~ instead of the load. The line-commut~ted power conversion apparatus 100 freely converts from AC to DC and from DC to AC by changing the firing control angle of the thyristor.
Next a third embodiment will be dQscribed with reference to Fig. 6.
A voltage type self-commutated power conversion apparatus in Fig. 6 also has the function of reducing harmonics a8 well a8 the function of adjusting reactive power while supplying active power to the system by converting DC power to AC power.
The power conversion system shown in Fig. 1, Fig. S
and Fig. 6 have various other ~lternative~. The embodiment~ ~hown below illu~trate alternatives of the power conversion system in Fig. 1, but similar alternatives are also pos~ible for the power conversion systems in Fig. 5 and Fig. 6.
Fig. 7 show~ a fourth embodiment of the invention.
This embodiment shows that the position where the -8- 2082~53 coupling diode 107 is inserted can be varied freely in the clo~ed circuit constituted by the rever~e blocking type bridge connected power converter 103, DC reactor 106, load 110, and the coupling diode 107 in the power conver~ion systQm in Fig. 1. It also shows that the function of coupling reactor 203 is included in the leakage reactance of tran~former 208 and the function of circuit breaker 201 is included in the circuit breaker 101 .
Also in this system the transformer 208 is connected to the DC winding side of the tran~former 102. This allows the freguency of occurrence of commutation failure in the line-commutated power conversion apparatus to be reduced as far as possible by preventing the ~ystem voltage from falling due to reactive power supplied by the voltage type self-commutated power conversion apparatus and reducing the distortion of the system voltage by a harmonic reducing function. However in this case lea~age reactance of transformer is set at low level. Of course, it i8 po~sible to reduce the freguency of commutation failure and the like as well, but this depen~ on the sises and proportions of the impedance of the tran~former 102 and the impe~Ancq on the system side.
Large capacity system~ require duplication of the reverse conducting type bridge connected power converter 204. A fifth embodiment through a ~eventh embodiment are shown in Fig. 8 to Fig. 10.
In the fifth embodiment in Fig. 8, two coupling diodes 107 are inserted in seriQs, and series circuits consisting of reverse conducting type bridge connected power converters 2041 and 2042 and DC capacitor~ 2071 and 2072 are connected to these with the polarity depicted.
Waveform synthesis with a tran~former 209 using two reverse conducting type bridge connected converters in this way i8 a technigue g~nerally widely usQd for duplicate inverters. Even if one of the reverse conducting type bridge connected power converters 2041 or 2042, or both, cau~es a DC short circuit, the conduction 9 20~553 of one or both of the coupling diode~ 1071 or 1072 is bloc~ed as in Fig. 1, the line-commutated power conversion apparatus 100 and the voltage type self-commutated power conversion apparatus 200 are connected in series and it proves possible to move the protection operation while the rise in the ~hort circuit current is limited.
In the sixth embodiment in Fig. 9, the positional relationship between the DC capacitor 207 and the reverse conducting type bridge connecter power converter 204 has been reversed. Coupling reactor 203 may be inserted on the AC winding sidQ of the transformer as in Fig. 9, or it can be inserted in the DC w;n~;ng side as in Fig. 1, or omitted if a high-impedance transformer is used.
lS In the sQventh embodiment in Fig. 10 is a format effective in large capacity power conversion systems a~
in Fig. 8: a plurality of serial circuits consisting of a DC reactor 106 and coupling diode 107 are connected in parallel, and reverse conducting type bridge connected power converters 204 and DC capacitors 207 are connected to the coupling diodes. In this case too, the DC
capacitors may be divided as in Fig. 8 and Fig. 9.
The insulating transformers 102, 202 and 209 in the embodiments in Fig. 1 to Fig. 10 are used normally when connected to the system. It i8 clear that there is no need to provide insulating transformers in both the line-commutated power conversion apparatus 100 and the voltage type self-commutated power conversion apparatu~ 200 although, in principle, the AC side must be insulated since the two apparatu~ are coupled by the coupling diode 107 in the direct current portion.
Example~ have been given in the preceding ~escription in which the voltage type self-commutated power conversion apparatus has been used as a reactive power adjusting device, active filter or invertor, but it is clear that in principle it can also be used to convert from AC power to DC power. In addition to the device commutation power converter shown in Fig. 4, a converter 20825~3 using impulse eommutation type or another type self-commutated power eonversion apparatus can be appropriately used as the reverse eon~ucting type bridge eonnected power converter.
Next an eighth embodiment of this invention will be described with referenee to Fig. 11.
A power conversion system of thi~ embodiment as shown in Fig. 11 eompri~e~ a fir~t AC line 300a, a sQeond AC
line 300b, ~ line-commutated power conversion apparatus 400, a self-commutated power convQrsion apparatus 500.
The interiors of line-eommutated power conversion apparatus 400 and ~elf-eommutated power eonversion apparatus 500 are symmetrieal a~ between the ~ide a~soeiated with AC line 300a and the side assoeiatQd with AC line 300b. The referenee numerals of the eonstituent devieQs are therefore distinguished by the suffixes a and b.
The power souree terminals of eireuit breakers 401 and 501 are respeetively eonneeted to AC lines 300a and 300b. The load terminal of eireuit breaker 401 i8 eonneeted to the input terminal of a transformer 402 and the load terminal of eireuit breaker 501 is eonneeted to the input terminal of a transformer 501.
The output terminal of transformer 402 is eonneeted to the AC terminal of a reverse bloç~;~g type bridge eonneeted power converter 403 while the output terminal of transformer 502 is eonnected to the AC terminal of a rever~e conducting type bridge eonnected power converter 504 through a reactor 503.
The reverse bloc~;ng type bridge connected power eonverter ~03 has a positive eleetrode terminal 404 and a negative eleetrode terminal 405.
The negative electrode terminal 405 and one end of reactor 406 are connected. The positive electrode terminal 404 and the anode of a coupling diode 407 are eonneeted. The po~itive eleetrode terminal 404 is eonneeted to the other end of reaetor 406. The eathode of eoupling diode 407 is eonneeted to the negative 2~i~2~3 electrode terminal 405 of reverse blor~tng type bridge connected power converter 403, forming a pair.
A sQries circuit consisting of a DC cap_citor 507 and coupling diode 407 i~ connected between positive electrode terminal 505 and negative electrode terminal 506 of reverse conducting type bridge connected power converter 504 with _ polarity ~uch _~ to bloc~ di~ch_rge of DC cap_citor 507.
The oper_tions of the line-commut_ted power conversion apparatus 400 and 8elf-commutated power conversion apparatus 500 are the same a~ the opQrations described in the first embodiment. Con~equently the operations are not described in this embodiment in detail.
15Howover, if for ~ome reason there is a f_ilure of commut_tion of the reverse conducting type bridge connected power converter 504a on the sidQ of AC line 300_, when terminal~ 505_ _nd 506_ go into a ~hort-circuited condition, the di~charge current of DC
20capacitor 507 trie~ to flow through the ~hort-circuit with the result that its value tries to exceed Il.
However, when thi~ happen~, the current of coupling diode 407 goe~ to zero, 80 that ¢oupling diode 407 goes into _ bloc~ing condition.
25A~ _ re~ult, a8 shown in Fig. 13, in which identical parts to those of Fig. 11 are given the ~_me reference numerals, discharge current Ic flow~ through the circuit of line-commutated power conversion apparatu~ 400 which ~uppresses thi~ di~charge current Ic to Il. The GTO
30thyri~tor of the healthy reverse conducting type bridge connected power converter 504b i8 therefore turned off by _ sign_l gener_ted by a commut_tion f_ilure detection circuit (not shown). An OFF sign_l i~ ~imultaneou~ly supplied to the GTO thyristor of the faulty reverse 35conducting type bridge connected power converter 504_.
The difference between thi~ embodiment _nd the embodiment de~cribed in Fig. 1 is a current value flowing in the short-circuit portion.
Though the eurrent value is the value I1 ~ Im in the embodiment deseribed in Fig. 1, the eurrent value in this embodiment i~ the value Il ~ Im ~ I~. NOW I~ means a direct eurrent flowing the reverse conducting type bridge eonneeted power eonverter 504b.
Con~equently the eurrent value deseribed in thi~
embodiment ha~ two eases due to the direction of flowing of the direet eurrent. One i8 that the curront value i8 larger than the value Il + I~ and the other is that it is lower than the value Il ~ Im-It may be seleeted whether the operation of rever~e eondueting type bridge eonnected power eonverter 504b stop or not at the same time to short-eireuit in order to deerease the eurrent flowing at the short-eireuit portion as large as possible.
Also in ease of Fig. 11, it is effeetive to turn on all of GTO thyristors in the reverse eondueting type bridge eonneeted power eonverter whieh short-eireuited and to disperse the short-eireuit eurrent.
The Fig. 13 i8 a diagram showing a ninth embodiment of thi~ invention. The differenee from Fig. 11 lies in that a single-phase diode bridge 410 is employed for eoupling instead of eoupling diode 407. The single-phase diode bridge ~10 has DC terminals 411 and 412 and AC
2 5 terminal~ 413 and 414. Ordinary operation in this ease is the same a~ in Fig. 11.
Considering the ease where short-eireuit oeeur~ in the ux pole of reverse eonducting bridge connected eonverter 504a as in Fig. 11, entry of the DC eurrent I~
of reverse eondueting type bridge eonneeted power eonverter 504b is bloeked by single-phase diode bridge 410, ~o the GTO thyristor eurrent of the ux pole beeome~
Iu, ~ Il while the other GTO thyristor eurrents are Il. If a seleetive turn-off proeedure i~ adopted 80 long a~
I~ ~ Il, Il ean be bigger than in Fig. 11. Now the ux pole means the portion eonstituted in the bridge eonneeted eireuit of Fig. 4 by GTO thyristors 211 and -13- ~8~5~
212, diode~ 217 and 218 and fuReR 223 and 224, and formR
one pha~e.
Fig. 1~ ~how~ yet a tenth embodiment of thi~
invention. In thi~ embodiment, two ~elf-commutated power conver~ion apparatu_ a~ in Fig. 11 are provided.
Further, in thi~ embodiment, eoupling reaetor 503a and tran~former 502a are integrated and substituted by high-induetanee tran_former~ 508. The primary winding~
of two high-induetanee transformers 508 are eonneeted in _erie~. Voltage eompo~ition u~ing a tran~former i8 often carried out, in order to reduce waveform distort~on on the AC side of a plurality of reverRe eonducting type bridge eonnected power eonverter~ 504 in a voltage type ~elf-commutated power eonverter.
Cireuit-breaker 501a i~ eonnected to the ~eeondary ~ide of transformer 402a of line-commutated power conversion apparatu~ 400. A reaetor 408 is in~erted between thi~ ~eeondary side and reverse bloeking type bridge eonneeted power eonverter 403a. Thi~ i~ provided with the aim of deerea~ing outflow of higher harmonic current to the sy~tem and reducing the frequency of commutation failure of reverse bloeking type bridge connected power converter 403a, by reducing the voltage drop generated in AC line 300a and the higher harmonic~
generated by reverse blocking bridge eonnqcted converter 403a in self-commut~ted power conver~ion apparatu~ S00.
Fig. 15 ~how~ an eleventh emho~;ment in which two ~elf-commutated coupling RyRtem~ as in Fig. 13 are employed. In this caRe alRo, the primarie~ of tran~former~ 502 are connected in ~eries.
In the above de~cription, GTO thyri_tors are employed as rever~e conducting type bridge connected power converter 50~, but other devices could al~o be u~ed.
Furthermore, apart from device-commutated power converter~, impul~e commutation or another Relf-commutated commutation type power eonverter could be employed.
-14- 20~2~3 In the embodiments of Fig. 11 to Fig. 15, the coupling diode or switching device was shown by a single symbol, but these could be appropriately used in series or in p~r~llel depending on the voltage or current.
As described above, according to the eighth embodiment through the eleventh embodiment, the self-commutated power conversion apparatus reduces the reactive power and generation of higher harmonics, which are the weakne~ses of the line-commutated power conversion apparatus and prevents commutation failure due to drop of system voltage and/or distortion. The line-commutated power conversion apparatus prevents overcurrent breakdown on short-circuiting, which is the weakness of the self-commutated power conversion lS apparatus.
In those embodiment in Fig. 1 to Fig. 15, the devices used in the coupling diode and the reverse conducting type bridge connected power converter have been represented by a single symbol, and these may be used in series, in parallel or in series and parallel as appropriate depending on the circuit voltage current. The line-commutated power conversion apparatus is not limited to a six-phase construction and it may be embodied as a twelve-phase or other multi-phase construction.
Thus benefits are exhibited which cannot be attained simply by arranging a line-commutated power conversion apparatu~ and ~elf-commutated power conversion apparatus in parallel. Thus the embodiments offer great benefits in particular in contributing to implementation of large self-commutated power conversion apparatus.
Claims (4)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A power conversion system comprising:
line-commutated power converting means for converting from DC power to AC power or from AC power to DC power;
self-commutated power converting means for reducing reactive power by the line-commutated power converting means;
and a coupling means for forming a first closed circuit with the line-commutated power converting means and a second closed circuit with the self-commutated power converting means, wherein the line-commutated power converting means comprises a circuit breaker, a transformer, a reverse-conducting bridge connected power converter, a reactor and a DC capacitor, the coupling means is a diode, the first closed circuit comprises a load, the diode, the DC reactor, and the reverse-blocking bridge connected power converter, and the second closed circuit comprises the DC capacitor, the diode, and the reverse-conducting bridge connected power converter.
line-commutated power converting means for converting from DC power to AC power or from AC power to DC power;
self-commutated power converting means for reducing reactive power by the line-commutated power converting means;
and a coupling means for forming a first closed circuit with the line-commutated power converting means and a second closed circuit with the self-commutated power converting means, wherein the line-commutated power converting means comprises a circuit breaker, a transformer, a reverse-conducting bridge connected power converter, a reactor and a DC capacitor, the coupling means is a diode, the first closed circuit comprises a load, the diode, the DC reactor, and the reverse-blocking bridge connected power converter, and the second closed circuit comprises the DC capacitor, the diode, and the reverse-conducting bridge connected power converter.
2. A power conversion system comprising:
line-commutated power converting means for converting from DC power to AC power or from AC power to DC power;
self-commutated power converting means for reducing reactive power by the line-commutated power converting means;
and a coupling means for forming a first closed circuit with the line-commutated power converting means and a second closed circuit with the self-commutated power converting means, wherein the line-commutated power converting means comprises a circuit breaker, a transformer, a reverse-blocking bridge connected power converter, and a DC reactor, the self-commutated power converting means comprises a circuit breaker, a transformer, a reverse-conducting bridge connected power converter, a reactor and a DC capacitor, the coupling means is a diode, the first closed circuit comprises a DC power source, the diode, the DC reactor, and the reverse-blocking bridge connected power converter, and the second closed circuit comprises a DC power source, the diode, and the reverse-conducting bridge connected power converter.
line-commutated power converting means for converting from DC power to AC power or from AC power to DC power;
self-commutated power converting means for reducing reactive power by the line-commutated power converting means;
and a coupling means for forming a first closed circuit with the line-commutated power converting means and a second closed circuit with the self-commutated power converting means, wherein the line-commutated power converting means comprises a circuit breaker, a transformer, a reverse-blocking bridge connected power converter, and a DC reactor, the self-commutated power converting means comprises a circuit breaker, a transformer, a reverse-conducting bridge connected power converter, a reactor and a DC capacitor, the coupling means is a diode, the first closed circuit comprises a DC power source, the diode, the DC reactor, and the reverse-blocking bridge connected power converter, and the second closed circuit comprises a DC power source, the diode, and the reverse-conducting bridge connected power converter.
3. A power conversion system comprising:
a pair of self-commutated power converters having AC
terminals which are respectively connected to a first AC
system and a second AC system and DC terminals, and being provided in common with a series circuit comprising a DC
capacitor between the DC terminals and a coupling diode inserted with polarity such as to block the discharge current of the DC capacitor; and a pair of line-commutated power converters that perform line-commutated commutation, having AC terminals being respectively connected to the first AC system and second AC
system, and which are connected such that the coupling diode is contained in series and such that DC current flows through the coupling diode.
a pair of self-commutated power converters having AC
terminals which are respectively connected to a first AC
system and a second AC system and DC terminals, and being provided in common with a series circuit comprising a DC
capacitor between the DC terminals and a coupling diode inserted with polarity such as to block the discharge current of the DC capacitor; and a pair of line-commutated power converters that perform line-commutated commutation, having AC terminals being respectively connected to the first AC system and second AC
system, and which are connected such that the coupling diode is contained in series and such that DC current flows through the coupling diode.
4. A power conversion system comprising:
a pair of voltage type self-commutated converters that perform self-commutated commutation and have AC terminals being respectively connected to a first AC system and a second AC system and DC terminals, one end of a DC capacitor being connected to one end of the DC terminals of a coupling diode bridge, the other end of the coupling diode bridge being connected as DC terminals; and a pair of line-commutated converters that perform line-commutated commutation, have AC terminals being respectively connected to the first AC system and the second AC system, and are connected such that DC circuits are formed through the DC
terminals of the coupling diode bridge and such that their DC
currents flow through the coupling diode bridge.
a pair of voltage type self-commutated converters that perform self-commutated commutation and have AC terminals being respectively connected to a first AC system and a second AC system and DC terminals, one end of a DC capacitor being connected to one end of the DC terminals of a coupling diode bridge, the other end of the coupling diode bridge being connected as DC terminals; and a pair of line-commutated converters that perform line-commutated commutation, have AC terminals being respectively connected to the first AC system and the second AC system, and are connected such that DC circuits are formed through the DC
terminals of the coupling diode bridge and such that their DC
currents flow through the coupling diode bridge.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JPP03-294059 | 1991-11-11 | ||
| JP29405991A JPH05134775A (en) | 1991-11-11 | 1991-11-11 | Power conversion system |
| JP3339202A JPH05176460A (en) | 1991-12-24 | 1991-12-24 | System linkage unit |
| JPP03-339202 | 1991-12-24 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2082553A1 CA2082553A1 (en) | 1993-05-12 |
| CA2082553C true CA2082553C (en) | 1998-12-08 |
Family
ID=26559663
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002082553A Expired - Fee Related CA2082553C (en) | 1991-11-11 | 1992-11-10 | Power conversion system |
Country Status (4)
| Country | Link |
|---|---|
| US (1) | US5371664A (en) |
| EP (1) | EP0542507B1 (en) |
| CA (1) | CA2082553C (en) |
| DE (1) | DE69211815T2 (en) |
Families Citing this family (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2695221B1 (en) * | 1992-08-25 | 1994-11-04 | Alsthom Gec | Active filter for traction unit powered by single-phase catenary. |
| JPH07298627A (en) * | 1994-04-27 | 1995-11-10 | Toshiba Corp | Controller for power converter |
| US5814975A (en) * | 1995-06-05 | 1998-09-29 | Westinghouse Electric Corporation | Inverter controlled series compensator |
| SE506199C2 (en) * | 1996-03-26 | 1997-11-17 | Asea Brown Boveri | Method and apparatus for determining the short-circuit power of an AC power network connected to a high-voltage direct current transmission |
| SE520611C2 (en) * | 1997-03-24 | 2003-07-29 | Abb Ab | Electric power transmission system |
| DE19726161A1 (en) * | 1997-06-20 | 1998-12-24 | Alsthom Cge Alcatel | Method for operating a DC link converter connected in parallel to supply an asynchronous motor and associated circuit arrangement |
| US9099936B2 (en) | 2013-03-14 | 2015-08-04 | General Electric Company | High voltage direct current (HVDC) converter system and method of operating the same |
| EP3334023A1 (en) * | 2016-12-07 | 2018-06-13 | General Electric Technology GmbH | Improvements in or relating to line commutated converters |
| CN108574286A (en) * | 2018-05-09 | 2018-09-25 | 华中科技大学 | The idle work optimization and fault ride-through method of mixed type transverter MMC-PLUS |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3609508A (en) * | 1969-02-20 | 1971-09-28 | Kazimir Borisovich Gusakovsky | Controlled valve-type converter |
| SU813587A1 (en) * | 1979-06-07 | 1981-03-15 | Донецкий Ордена Трудового Красногознамени Политехнический Институт | Device for compensating for single-phase earthing full current |
| US4346421A (en) * | 1979-07-02 | 1982-08-24 | Sangamo Weston, Inc. | Fault detector |
| DE3029358A1 (en) * | 1980-08-01 | 1982-03-11 | Siemens AG, 1000 Berlin und 8000 München | DEVICE FOR BRIDGING SHORT-TERM NETWORK OUTPUTS FOR INTERMEDIATE VOLTAGE CONVERTERS |
| SU1119120A2 (en) * | 1983-06-24 | 1984-10-15 | Азербайджанский Научно-Исследовательский Институт Энергетики Им.И.Б.Есьмана | Reactive power compensator |
| JPH074067B2 (en) * | 1986-01-24 | 1995-01-18 | 株式会社明電舍 | Reactive power processing circuit of current source GTO inverter |
| DE3725515C2 (en) * | 1987-07-29 | 1995-02-09 | Licentia Gmbh | Quenching procedure for controllable power converters |
| JPS6442715A (en) * | 1987-08-10 | 1989-02-15 | Meidensha Electric Mfg Co Ltd | Power converter |
-
1992
- 1992-11-04 US US07/971,157 patent/US5371664A/en not_active Expired - Fee Related
- 1992-11-10 CA CA002082553A patent/CA2082553C/en not_active Expired - Fee Related
- 1992-11-10 DE DE69211815T patent/DE69211815T2/en not_active Expired - Fee Related
- 1992-11-10 EP EP92310262A patent/EP0542507B1/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| EP0542507A2 (en) | 1993-05-19 |
| EP0542507A3 (en) | 1994-02-02 |
| DE69211815D1 (en) | 1996-08-01 |
| EP0542507B1 (en) | 1996-06-26 |
| CA2082553A1 (en) | 1993-05-12 |
| US5371664A (en) | 1994-12-06 |
| DE69211815T2 (en) | 1996-10-31 |
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| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKLA | Lapsed | ||
| MKLA | Lapsed |
Effective date: 20031110 |