WO2008103630A1

WO2008103630A1 - Adjusting commutation of a brusheless dc motor to increase motor speed

Info

Publication number: WO2008103630A1
Application number: PCT/US2008/054213
Authority: WO
Inventors: Robert D. Keefover; Donald Podwoiski
Original assignee: Borgwarner Inc.
Priority date: 2007-02-21
Filing date: 2008-02-18
Publication date: 2008-08-28

Abstract

One exemplary embodiment includes a method of increasing motor speed of a brushless direct current motor having a rotor and multiple stator phase windings. A rotor position is detected, and motor torque and/or motor speed is determined. An adjustment commutation command corresponding to the detected rotor position is selected, when motor torque is determined to be within a low-end motor torque range and/or when motor speed is determined to be within a high-end motor speed range. Voltage is applied to the multiple phase windings in accordance with the selected adjustment commutation command to increase motor speed.

Description

ADJUSTING COMMUTATION OF A BRUSHLESS DC MOTOR TO INCREASE MOTOR SPEED

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims the benefit of U.S. Provisional

Application No. 60/890,858, filed February 21 , 2007.

TECHNICAL FIELD

[0002] The field to which the disclosure generally relates includes control of a switched reluctance machine and, more particularly, to speed control of a brushless direct current motor.

BACKGROUND

[0003] Polyphase brushless direct current (BLDC) motors convert electrical energy into mechanical energy, and are used in a wide variety of applications, including automotive turbocharger actuators. Typical BLDC motors include a stationary outside portion called a stator, and a rotating inner portion called a rotor. The stator includes a plurality of phase windings wound around a plurality of poles. The rotor includes permanent magnets responsive to electricity flowing through the phase windings, and is mounted on a shaft supported by bearings so that the rotor is free to rotate within the stator to produce mechanical energy. A controller and a power output stage together control rotation of the rotor by sequentially energizing the phase windings with electrical current to produce a rotating magnetic field. Under magnetic attraction, the rotor magnets follow the rotation of the field and, therefore, the rotor rotates.

SUMMARY OF EXEMPLARY EMBODIMENTS OF THE INVENTION [0004] One exemplary embodiment of the invention includes a method of increasing motor speed of a brushless direct current motor having a rotor, and multiple stator phase windings. According to the method, a rotor position is detected, and motor torque and/or motor speed is determined. An adjustment commutation command corresponding to the detected rotor position is selected, when motor torque is determined to be within a low-end motor torque range and/or when motor speed is determined to be within a high-speed motor speed range. Voltage is applied to the multiple phase windings in accordance with the selected adjustment commutation command to increase motor speed.

[0005] Other exemplary embodiments of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the exemplary embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Exemplary embodiments of the present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: [0007] FIG. 1 is a schematic view of an exemplary embodiment of a motor system including a motor and control electronics;

[0008] FIG. 2 is a schematic cross-sectional view of an exemplary embodiment of the motor of FIG. 1 ;

[0009] FIG. 3 is a graphical view of an exemplary embodiment of six- step commutation plots, which highlight normal commutation at peak torque;

[0010] FIG. 4 is a schematic view of another exemplary embodiment of a motor system including a motor and control electronics, which are hardwired together for adjusted motor commutation;

[0011] FIG. 4A is a graphical view of an exemplary embodiment of six- step adjusted commutation plots, which highlight advanced commutation;

[0012] FIG. 4B is a graphical view of an exemplary embodiment of six- step adjusted commutation plots, which highlight delayed commutation;

[0013] FIG. 5A is a graphical view of an exemplary embodiment of six- step adjusted commutation plots, which highlight software-enabled advanced commutation in a clockwise direction;

[0014] FIG. 5B is a graphical view of an exemplary embodiment of six- step adjusted commutation plots, which highlight software-enabled delayed commutation in a clockwise direction;

[0015] FIG. 6A is a graphical view of an exemplary embodiment of six- step adjusted commutation plots, which highlight software-enabled advanced commutation in a counterclockwise direction;

[0016] FIG. 6B is a graphical view of an exemplary embodiment of six- step adjusted commutation plots, which highlight software-enabled delayed commutation in a counterclockwise direction; [0017] FIG. 7A is a graphical view of an exemplary embodiment of plots of motor speed, current, output power, and efficiency for a high iron loss motor operated according to normal and adjusted commutation; and

[0018] FIG. 7B is a graphical view of an exemplary embodiment of plots of motor speed, current, output power, and efficiency for a low iron loss motor operated according to normal and adjusted commutation.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS [0019] The following description of the embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.

[0020] FIG. 1 illustrates an exemplary motor system 10 to provide controlled rotational power to any suitable device, such as a variable turbine geometry (VTG) actuator for a VTG turbocharger, or an exhaust gas recirculation (EGR) valve actuator for an EGR equipped exhaust system. The motor system 10 generally includes a motor 12 to provide rotational power and electronic controls 14 to control operation of the motor 12. In general, the electronic controls 14 include a power output stage 16 including switches Q1 - Q6 for selectively communicating electrical power from a power source 18 to the motor 12, a controller 20 for receiving suitable input signals and processing the input signals with suitable software to generate motor commutation command signals, and a driver 22 for converting commutation command signals received from the controller 20 into suitable switching signals for use by the power output stage 16. Below, the structure and basic function of the system 10 will be described, then normal motor commutation, followed by adjusted motor commutation.

The System

[0021] Referring to FIG. 2, the motor 12 may be any suitable motor, but is preferably an exemplary three-phase brushless direct current motor in a Y configuration. In the exemplary motor 12, a rotor 24, such as a permanent magnet rotor, includes an iron yoke 26 surrounded by five alternating magnetic pole pairs (N, S) 28. The rotor 24 may be disposed inside of a laminated stator 30 having nine poles including three coil center poles 32a, 32b, 32c and six outside winding poles 34. Each coil center pole 32a, 32b, 32c carries a respective stator phase winding 36a, 36b, 36c thereon and corresponding to respective phase lines A, B, C. The stator 30 may also carry three rotor position sensors: a first phase sensor or HED A 38a, a second phase sensor or HED B 38b, and a third phase sensor or HED C 38c, which may be magnetically operated devices such as hall effect devices or any other suitable position sensing devices.

[0022] Referring to FIG. 1 , the controller 20, in general, receives the rotor position signals from the motor 12 and processes this input with software to produce output in the form of commutation command signals. The controller 20 may be used to detect a rotor position from rotor position pulses generated from the multiple rotor position sensors 38a, 38b, 38c, and to identify a discrete normal commutation command and a discrete adjustment commutation command corresponding to the detected rotor position. The controller 20 may also be used to determine motor torque, such as from output signals received from any suitable motor torque sensor(s) (not shown), another controller, or the like.

[0023] The controller 20 may include any suitable processor(s) (not separately shown) configured to execute control logic that provides at least some of the functionality for motor phase switching or commutation. In this respect, the processor may encompass one or more processing units, microprocessors, micro-controllers, discrete logic circuit(s) having logic gates for implementing logic functions upon data signals, application specific integrated circuits (ASIC) with suitable logic gates, complex programmable logic devices (CPLD), programmable or field-programmable gate arrays (PGA/FPGA), any combinations of the aforementioned, and the like. The processor(s) may be interfaced with any suitable memory (not separately shown), which can include any medium configured to provide at least temporary storage of data and/or software or instructions that provide at least some of the functionality of the phase switching and that may be executed by the processor. The controller 20 may also include any other suitable devices or modules, such as ancillary devices like clocks, power supplies, and the like.

[0024] The gate driver 22 receives the command signals from the controller 20 and amplifies the signals and sends them to appropriate gate pins of corresponding switches Q1 -Q6 in the power output stage 16 to energize the corresponding motor phase windings 36a, 36b, 36c. In other words, from an output of the controller 20, the gate driver 22 generates suitable current and voltage to turn suitable power output stage switches on and off to commutate the motor 12. Any suitable gate driver may be used, such as an IGBT or MOSFET driver, and may be integrated with the controller 20 or the power output stage 16.

[0025] The power output stage 16 may be coupled between the voltage source 18 and the motor 12 and may be controlled by the controller 20 via the gate driver 22 to sequentially energize the motor phase windings 36a, 36b, 36c. In other words, each of the motor phase windings 36a, 36b, 36c may be connected to the power output stage 16 and electricity may be supplied to the power output stage 16 from the DC voltage source 18, such as one or more DC batteries, fuel cell(s), generator(s), power converter(s), and/or the like. The power output stage 16 may also be termed a power converter or a multiphase power bridge.

[0026] In the exemplary power output stage 16, two of the commutation switches Q1 -Q6 commutate the phase windings 36a, 36b, 36c of the motor 12 at any given instant. The switches Q1 -Q6 are disposed across high and low sides of the power output stage 16, and communicate with respective motor phase windings 36a, 36b, 36c through respective phase lines A, B, C. The first phase line A and phase winding 36a are connected between a first high side switch Q1 and a first low side switch Q2, the second phase line B and phase winding 36b are connected between a second high side switch Q3 and a second low side switch Q4, and the third phase line C and phase winding 36c are connected between a third high side switch Q5 and a third low side switch Q6. The switches Q1 -Q6 may be any suitable switching devices, such as IGBTs, MOSFETs, or any other suitable semiconductor or transistor devices. Those skilled in the art will recognize that the switches Q1 -Q6 can include integrated freewheeling diodes as shown, or separate diodes. Motor Commutation

[0027] The motor 12 may be controlled using electronic commutation, which is the manner in which the phase windings 36a, 36b, 36c are turned on and off to produce useful torque at the rotor 24. The control electronics 14 control flow of electrical current into the phase windings 36a, 36b, 36c based on rotor position, rotor speed, motor torque, and other factors. In normal operation, the controller 20 receives various input signals, including rotor position signals from the position sensors 38a, 38b, 38c, and processes such signals with software, lookup tables, and the like stored in its memory to generate sequential commutation command output signals for output to the gate driver 22.

[0028] There are two primary commutation methods typically used for motor control: sine-wave commutation and six-step commutation. Preferably, the motor 12 may be controlled with six-step commutation, which involves generating and communicating rectangular pulse currents through only one electrical path including only two of the phase windings 36a, 36b, 36c at any given time. Thus, six-step commutation may be also known as two-phase-on commutation.

[0029] The six steps of commutation include sequentially energizing the following phase pairs: phase A to phase B; phase A to phase C; phase C to phase B; phase C to phase A; phase B to phase A; and phase B to phase C. Each commutation step involves energizing one of the phase windings 36a, 36b, 36c to "positive" power (current entering the winding) and another to "negative" power (current exiting the winding), with the third phase winding in a non-energized condition. [0030] Each set of six steps represents 360 electrical degrees of rotation, so that each step may be equivalent to 60 electrical degrees. Thus, six step commutation includes increments of 60 electrical degrees. Electrical degrees are related to mechanical degrees as follows:

@e = Np x Θm , where

Θe = electrical degrees,

Np = number of pole pairs, and

Θm = mechanical degrees.

Accordingly, a six-step commutation cycle occurs every 72 mechanical degrees, or five times per revolution of the rotor 24.

[0031] The motor phase windings 36a, 36b, 36c are sequentially energized with electrical current to produce a rotating magnetic field. The magnetic field attracts (or repulses) the rotor magnets, which thus follow (or lead) the rotation of the field and, therefore, cause the rotor 24 to rotate. As the rotor 24 rotates, each magnetic pole pair (N, S) passes each magnetic position sensor to turn the position sensors 38a, 38b, 38c on and off (or high and low) and thereby provide rotor position signals for energizing the phase windings 36a, 36b, 36c in a predetermined sequence to maintain rotor rotation. As will be described below, when the motor 12 is energized and the rotor 24 rotates, the rotor position sensors 38a, 38b, 38c produce rotor position signals that are output to the controller 20 of the control electronics 14.

[0032] The commutation command signals are determinative of which of the phase windings 36a, 36b, 36c are to be energized at any given moment, and are further determinative of the magnitude of current to be applied to the phase windings 36a, 36b, 36c so as to variably control motor speed and/or torque. Those skilled in the art will recognize that the magnitude of the current may be controlled wherein the gate driver 22 interprets current magnitude signals and produces output signals to suitable power output stage switches Q1 -Q6 according to a duty cycle to achieve the commanded current magnitude.

[0033] Based on signals received from the gate driver 22, suitable pairs of the power output stage switches Q1 -Q6 are activated and deactivated to selectively apply phase voltages to one or more of the phase windings 36a, 36b, 36c. In turn, these applied phase voltages cause phase currents to flow through the phase windings 36a, 36b, 36c to energize the phase windings 36a, 36b, 36c and rotate the rotor 24. The phase windings 36a, 36b, 36c inherently include inductances and resistances, wherein rotation of the rotor 24 produces back electromagnetic force (EMF) voltages in the phase windings 36a, 36b, 36c.

[0034] Preferably, the three position sensors 38a, 38b, 38c provide rotor position information and are equidistantly spaced 120 mechanical degrees apart and 60 mechanical degrees from respective coil center poles 32a, 32b, 32c. The position sensors 38a, 38b, 38c are activated and deactivated by rotation of the rotor 24 and its permanent magnets, including the ten magnet poles or five pole pairs (N,S). These sensors 38a, 38b, 38c preferably operate on a 50% duty cycle to produce six different three-bit logic states at 60 electrical degree intervals as the rotor 24 turns, per electrical cycle. In other words, for every 60 electrical, or 12 mechanical, degrees of rotation, one of the three position sensors 38a, 38b, 38c changes state. At this rate, it takes six state changes or steps to complete an electrical cycle. At each state change of the sensors 38a, 38b, 38c, phase winding energization may be updated by the controller 20. Whenever the rotor magnetic pole pairs (N, S) pass the position sensors 38a, 38b, 38c, the position sensors 38a, 38b, 38c generate a high or low signal indicating the N or S pole is passing the position sensors 38a, 38b, 38c.

[0035] For a motor without any position sensors, such as a sensorless brushless direct current motor (not shown), the control electronics 14 can be used to sense motor terminal voltages and determine the speed and position of a rotor based on sensed back EMF voltages in a nonenergized phase winding of the sensorless motor. The controller 20 may receive selected phase terminal voltage signals and determines a time instant for a back EMF zero crossing event. The controller 20 may further use the detected back EMF zero crossing event to estimate or detect an operating position the motor rotor and to determine when to turn on a corresponding phase. In another example, a single position sensor or encoder device could instead be used to estimate or detect position of the rotor. Back EMF rotor position detection and position encoding devices and techniques are well known to those of ordinary skill in the art, and those of ordinary skill in the art realize that such techniques could be used to yield signal states SS1 -SS6.

Normal Commutation

[0036] Based on the combination of the three sensor signals, a preferred sequence of normal commutation may be determined as illustrated with respect to Table 1 below. Table 1 is an exemplary look up table that may be stored in controller memory and used by the controller processor.

TABLE 1

[0037] For example, the motor 12 depicted in FIG. 2 is shown at a given instant in time when the rotor 24 is rotating clockwise and its position triggers position sensor 36a, but not sensors 36b and 36c, to yield signal state SS1 in look up Table 1 . Accordingly, the controller 20 would cross-reference signal state SS1 with the clockwise commutation command V_A-c and thereafter output a suitable VA-_C command to the gate driver 22. Those skilled in the art will recognize that the V_A-c command may be in any suitable binary, hexadecimal, or other computer readable format.

[0038] The gate driver 22 receives the V_A-c command and processes it to generate suitable corresponding switching commands for the power output stage 16. More particularly, the gate driver 22 instantaneously and simultaneously activates switches Q1 and Q6 and deactivates any other switches that may be on. Those skilled in the art will recognize that delays may be provided between deactivation of switches and activation of other switches to avoid short circuiting the power output stage. In any case, this switching initiates a power circuit from the voltage source 18 through switch Q1 , away from the power output stage 16 through phase line A, through phase winding 36a into the motor 12, through phase winding 36c out of the motor 12 and, back toward the power output stage 16 through phase line C, and through switch Q6 to ground to complete the circuit.

[0039] This energization of the motor 12 rotates the rotor 24 further clockwise, wherein the position sensor 38a remains activated and the position sensor 38c becomes activated. Activation of the position sensor 38c results in a change in signal state from SS1 to SS2. Under normal commutation, the controller 20 cross-references signal state SS2 with the corresponding clockwise commutation command VA-B and outputs the VA-B command to the gate driver 22.

[0040] Again, the gate driver 22 receives the V_A-B command and processes it to generate suitable corresponding switching commands for the power output stage 16. More particularly, the gate driver 22 instantaneously and simultaneously activates switches Q1 and Q4 and deactivates switch Q6 which was previously activated. This switching initiates a power circuit from the voltage source 18 through switch Q1 , away from the power output stage 16 through phase line A, through phase winding 36a into the motor 12, out of the motor 12 through phase winding 36b, back toward the power output stage 16 through phase line B, and through switch Q4 to ground to complete the circuit.

[0041] Such energization of the motor 12 further rotates the rotor 24 clockwise, wherein the position sensor 38a is no longer activated and the position sensor 38c remains activated. This sequential energization of the phase windings 36a, 36b, 36c repeats and yields plots similar to that shown in FIG. 3.

[0042] FIG. 3 illustrates plots of normalized motor torque vs. rotor position in electrical degrees for each of the six different energized phase pairs A-C, A-B, C-B, C-A, B-A, B-C, which correspond to the Table 1 signal states SS1 , SS2, SS3, SS4, SS5, SS6 for clockwise rotation of the rotor 24. The position sensors 38a, 38b, 38c typically change state about 30 electrical degrees before the peak of each plotted phase pair energization. Also, when phase winding currents are in phase with respective back EMF voltages, maximum motor torque may be achieved for optimal motor efficiency. With normal commutation, the position sensors 38a, 38b, 38c are routed to corresponding position sensor inputs, including a first phase input 40a, second phase input 40b, and third phase input 40c, in the motor controller 20 according to Table 2 below.

Table 2

[0043] As may be seen in FIG. 3, normal commutation results in operation of the motor 12 at peak torque and efficiency. The Y-axis depicts the percentage or factor of motor torque with a single energized phase winding. In other words, a reading of 1 .0 on the Y-axis represents a factor of torque output of the motor 12 for any one of the three phase windings 36a, 36b, 36c. As one example, when current flowing into one energized phase winding and out of the other energized phase winding momentarily peaks, motor torque also peaks at about a factor of 1 .73, or 173% of single phase torque.

Adjusted Commutation In developing the present invention, it was discovered that the speed of the motor 12 may be increased by adjusting commutation in a simple and cost effective manner compared to prior motor control techniques. In some applications, and over a relatively low torque range, motor speed is increased so as to increase response time of some device powered by the motor 12. As demonstrated by the steady state equations below, motor speed may be increased by effectively lowering the torque constant of the motor 12.

Tm = Kt - Im and Va = Im- Rm + Kt ■ com Eq. 1 and Eq. 2 substituting and solving for motor speed yields: COm = Va I Kt - (R_n, - Tm) I K² Eq. 3 solving for motor current yields:

Im = Tm I Kt , where Eq . 4 com = Motor Speed (rad/s); l_m = Motor Current (amps);

K_t = Motor Torque Constant (Nm/amp);

K_t = K_e = Back EMF Constant (V/rad/sec);

R_m = Motor Resistance (ohms);

T_m = Motor Torque (Nm); and

Vg = Applied Terminal Voltage (volts). [0045] From Equation 3, ωm = Va I K₁ - (Rm - Tm)/ K² , it may be observed that if the motor torque constant K_t is lowered, then the motor speed will increase because of the inverse relationship therebetween. Likewise, from Equation 4, L_n = TmI Kt , it may be reasoned that if the motor torque constant K_t is decreased, then the motor current l_m will increase because of the inverse relationship therebetween. But in solving for T_m, it may be seen that motor torque will decrease if the motor torque constant K_t is decreased because of the direct relationship therebetween. Adjustment of commutation in the manner described herein results in increased motor speed at the expense of reduced torque and increased current consumption.

[0046] Nonetheless, it may be desired to increase the speed of the motor 12 by effectively lowering the torque constant of the motor 12 by adjusting the commutation of the motor 12. Adjustment of motor commutation may be carried out by either advancing or retarding motor commutation. In adjusted commutation operation, the motor 12 may be commutated in similar fashion as that described above, except the relationship between the rotor position signal states and the commutation command signals may be adjusted to either advance or retard motor commutation to increase motor speed at the expense of motor efficiency and power. This may be accomplished by physically altering the hardwiring of the outputs of the position sensors 38a, 38b, 38c to the motor controller 20, and is preferably accomplished by modifying functionality within the motor controller 20 as will be described further below.

[0047] But first, two examples illustrate the effectiveness of adjusting motor commutation wherein the physical hard wiring of the position sensors 38a, 38b, 38c to the controller 20 may be altered to change the motor-to- controller phase relationship.

[0048] In a first example, the outputs of the position sensors 38a, 38b,

38c may be structurally rerouted, such as by hardwiring, to the controller HED inputs 40a, 40b, 40c as shown in Table 3 below and in FIG. 4. It is also contemplated that the position sensor outputs could instead be functionally rerouted to the HED inputs in any suitable manner, including changes in software switch settings, hardware switching, or the like.

Table 3

[0049] In FIG. 4, a motor system 1 10 includes the control electronics 14 and the motor 12, which may be rerouted to the controller 20 in a different manner. The motor output of the position sensor 38a may be communicated to the sensor input 40c of the motor controller 20, the output of the position sensor 38b may be communicated to the sensor input 40a of the controller 20, and the output of the position sensor 38c may be communicated to the sensor input 40b of the controller 20. This rerouting effectively advances commutation of the motor 12 by advancing a commutation command relative to a position sensor signal state.

[0050] For example, and referring again to Table 1 and the motor 12 in its position shown in FIG. 2, under normal wiring the actual signal state output of A1 -BO-CO would be seen by the controller 20 as actual input of A1 -BO-CO or SS1 to generate a VA-_C commutation command over 150-90 electrical degrees. But according to the altered wiring of Table 3 and FIG. 4, the actual signal output of A1 -BO-CO would be seen by the controller 20 as modified or advanced input of A0-B0-C1 (per SS3) to generate a V_C-B command over 150- 90 electrical degrees as shown in FIG. 4A. The plot of V_C-B over 150-90 electrical degrees happens to fall on the negative side of the abscissa or X- axis, thereby indicating that the rerouting according to Table 3 and FIG. 4 results not only in advanced commutation but also a reversal in rotational direction of the rotor 24 of the motor 12. Subsequently, the next actual signal output of A1 -B0-C1 would be seen by the controller 20 as modified input of A0-B1 -C1 or SS4 to generate a V_C-A command over 90-30 electrical degrees.

[0051] The reversal in rotational direction of the rotor due to the rerouting may be overcome by changing one or more software switch settings in the controller, or motor hardware switch(es), or the like. Those skilled in the art will recognize that motor controllers are often provided with soft switches for reversing motor direction. Such switch(es) may be activated substantially simultaneously as any rerouting of the position sensor signals to the controller. Accordingly, commutation may be advanced via sensor signal rerouting without any directional change in rotor rotation to yield an advanced commutation plot like that shown in FIG. 5A instead of FIG. 4A.

[0052] In a second example, the outputs of the position sensors 38a,

38b, 38c may be structurally rerouted, such as by hardwiring, to the controller HED inputs 40a, 40b, 40c as shown in Table 4 below. It is also contemplated that the position sensor outputs could instead be functionally rerouted to the HED inputs in any suitable manner, including changes in software settings, switching, or the like.

Table 4

[0053] Although not shown in the drawings, position sensor 38a output of the motor 12 may be communicated to the sensor input 40b of the motor controller 20, position sensor 38b output may be communicated to the sensor input 40c, and position sensor 38c output may be communicated to the sensor input 40a. This rerouting effectively retards or delays commutation of the motor 12 by retarding or delaying a commutation command relative to a position sensor signal state.

[0054] For example, and referring again to Table 1 and the motor 12 in its position shown in FIG. 2, under normal wiring the actual signal state output of A1 -BO-CO would be seen by the controller 20 as actual input of A0-B1 -C0 or SS1 to generate a V_A-c commutation command over 150-90 electrical degrees according to the look up table. But according to the altered wiring of Table 4, the actual signal output of A1 -BO-CO would be seen by the controller 20 as modified or delayed input of A0-B1 -C0 (per SS5) to generate a V_B-A command over 150-90 electrical degrees as shown in FIG. 4B. The plot of V_B- _A over 150-90 electrical degrees happens to fall on the negative side of the abscissa, thereby indicating that the rerouting results not only in delayed commutation but also a reversal in rotational direction of the rotor 24 of the motor 12. Subsequently, the next actual signal output of A1 -B0-C1 would be seen by the controller 20 as modified input of A1 -B1-C0 or SS6 to generate a VB-_C command over 90-30 electrical degrees.

[0055] Again, the reversal in rotational direction of the rotor due to the rerouting may be overcome by changing one or more software switch settings in the controller, or motor hardware switch(es), or the like. Any suitable motor reversal switch(es) may be activated substantially simultaneously as any rerouting of the position sensor signals to the controller. Accordingly, commutation may be delayed via sensor signal rerouting without any directional change in rotor rotation to yield a delayed commutation plot like that shown in FIG. 5B instead of FIG. 4B.

[0056] Instead of physically rewiring the system 10, the functionality of the motor controller 20 may be modified to adjust commutation of the motor 12. For example, the motor controller 12 may include one or more commutation adjustment look up tables stored in controller memory and used by the controller processor. More specifically, Table 5 below depicts one way to generate advanced or delayed commutation command signals according to clockwise motor direction. Table 5 is a lookup table similar to Table 1 , but with advanced and delayed commutation command signals in addition to normal commutation command signals.

[0057] In an exemplary adjusted commutation mode, the controller 20 would invoke the look up table above, receive an actual signal state from the motor 12 and cross reference that signal state with a corresponding advanced or delayed commutation command from the look up table. Then, that commutation command would be output to the gate driver 22 for use in commutating the motor 12.

[0058] One manifestation of the controller 20 applying the advanced commutation sequence of Table 5 may be represented by the advanced commutation plot of FIG. 5A. As shown in FIG. 5A, and compared to FIG. 3 over 150-90 electrical degrees, instead of winding pair A-C being energized, commutation may be advanced to energize the subsequent winding pair A-B in the commutation sequence. Then, over 90-30 electrical degrees, instead of winding pair A-B being energized as in FIG. 3, commutation may be advanced to energize the next subsequent winding pair C-B in the commutation sequence, and so on.

[0059] One manifestation of delayed commutation may be represented by the advanced commutation plot of FIG. 5B. As shown in FIG. 5B, and compared to FIG. 3 over 150-90 electrical degrees, instead of winding pair A- C being energized, commutation may be delayed to energize the preceding winding pair B-C in the commutation sequence. Then, over 90-30 electrical degrees, instead of winding pair A-B being energized as in FIG. 3, commutation may be delayed to energize the next preceding winding pair A-C in the sequence, and so on.

[0060] Table 6 below is similar to Table 5 above, but depicts one way to generate advanced or delayed commutation command signals according to counterclockwise motor direction.

[0061] One manifestation of the controller 20 applying the advanced commutation sequence of Table 6 may be represented by the advanced commutation plot of FIG. 6A. As shown in FIG. 6A, instead of winding pair A- C being energized over 90-150 electrical degrees, commutation may be advanced to energize the subsequent winding pair B-C in the commutation sequence. Then, over 150-210 electrical degrees, instead of winding pair B-C being energized, commutation may be advanced to energize the next subsequent winding pair B-A in the commutation sequence, and so on.

[0062] One manifestation of delayed commutation may be represented by the advanced commutation plot of FIG. 6B. As shown in FIG. 6B, instead of winding pair A-C being energized over 90-150 electrical degrees, commutation may be delayed to energize the preceding winding pair A-B in the commutation sequence. Then, over 150-210 electrical degrees, instead of winding pair B-C being energized, commutation may be delayed to energize the next preceding winding pair A-C in the sequence, and so on.

[0063] Referring to FIGS. 7A and 7B, the exemplary adjusted commutation mode is preferably carried out when motor torque is below a motor torque threshold value and/or when motor speed is above a motor speed threshold value. FIGS. 7A and 7B illustrate exemplary plots of the effects of normal commutation and adjusted commutation as a function of motor speed, current, and efficiency vs. motor torque. More specifically, FIG. 7A is a plot for an exemplary motor having relatively high iron loss of about 5 W/kg, whereas FIG. 7B is a plot for an exemplary motor having relatively low iron loss of about 1 W/kg.

[0064] FIGS. 7A and 7B illustrate the following plots according to exemplary normal commutation: lines 50a, 50b are plots of motor speed; lines 52a, 52b are plots of motor current; lines 54a, 54b are plots of motor output power; and lines 56a, 56b are plots of motor efficiency.

[0065] FIGS. 7A and 7B also illustrate the following plots according to exemplary adjusted (advanced or delayed) commutation: lines 60a, 60b are plots of motor speed; lines 62a, 62b are plots of motor current; lines 64a, 64b are plots of motor output power; and lines 66a, 66b are plots of motor efficiency.

[0066] Point 55a and point 55b represent exemplary intersections where the plot of adjusted commutation motor speed crosses the plot of normal commutation motor speed. The intersections correspond to particular exemplary motor torque values along the abscissas and motor speed values along the ordinates.

[0067] An exemplary low-end motor torque range may be defined between the intersections 55a, 55b and the ordinates or Y-axes. For example, in FIG. 7A, intersection 55a corresponds to about 16 Nm and, in FIG. 7B, intersection 55b corresponds to about 30 Nm. Thus, the exemplary low-end motor torque range covers from about 0 to about 30 Nm or, in other words, from about 0% to about 25% of maximum motor torque. Another exemplary low-end motor torque range covers from about 0% to about 50% of maximum motor torque.

[0068] An exemplary high-end motor speed range may be defined above the speed values corresponding to the intersections 55a, 55b, on the opposite side of the abscissas or X-axes. For example, in FIGS. 7A and 7B, intersections 55a and 55b correspond to about 7,800 RPM, and the maximum motor speed is between about 10,500 RPM as shown in FIG. 7A to about 17,000 RPM as shown in FIG. B. Thus, the exemplary high-end motor speed range covers from about 7,800 RPM to about 17,000 RPM or, in other words, from about 40% to about 100% of maximum motor speed. [0069] In development of the present invention, it was discovered that it may be beneficial to apply adjusted motor commutation commands preferably where motor torque is determined to be within its low-end motor torque range. Accordingly, the controller 20 may select one or more adjustment commutation commands instead of normal commutation commands when motor torque is determined to be within a low-end motor torque range. Thereafter, voltage may be applied to the multiple phase windings in accordance with the selected adjustment commutation command(s) to increase motor speed.

[0070] More particularly, it is preferable to apply adjusted motor commutation commands where motor torque is less than the torque values corresponding to the intersections 55a, 55b and/or where motor speed is greater than the speed values corresponding to the intersections 55a, 55b. In other words, it is preferable to apply adjusted commutation for a high iron loss motor below its intersection 55a at about 16 Nm and/or above its intersection 55a at about 7,800 RPM and, for a low iron loss motor below its intersection 55b at about 30 Nm and/or above its intersection at about 7,800 RPM. As shown in FIGS. 7A, 7B, over a low-end motor torque range and/or high-end motor speed range, and during adjusted commutation, current draw may be higher, efficiency may be lower, while motor output power may be about equal.

[0071] The method may be performed as part of a computer program and the various commutation commands and signal states may be stored in memory as a look-up table or the like. The computer program may exist in a variety of forms both active and inactive. For example, the computer program can exist as software program(s) comprised of program instructions in source code, object code, executable code or other formats; firmware program(s); or hardware description language (HDL) files. Any of the above may be embodied on a computer readable medium, which include storage devices and signals, in compressed or uncompressed form. Exemplary computer readable storage devices include conventional computer system RAM (random access memory), ROM (read only memory), EPROM (erasable, programmable ROM), EEPROM (electrically erasable, programmable ROM), and magnetic or optical disks or tapes. The above description of embodiments of the invention is merely exemplary in nature and, thus, variations thereof are not to be regarded as a departure from the spirit and scope of the invention.

Claims

CLAIMS What is claimed is:

1 . A method of increasing motor speed of a brushless direct current motor having a rotor and multiple stator phase windings, the method comprising: detecting a rotor position; determining at least one of motor torque or motor speed; selecting an adjustment commutation command corresponding to the detected rotor position, when motor torque is determined to be within a low-end motor torque range and/or motor speed is determined to be within a high-end motor speed range; and applying voltage to the multiple phase windings in accordance with the selected adjustment commutation command to increase motor speed.

2. The method of claim 1 , wherein the adjustment commutation command is identified from a lookup table, which cross-references rotor position states to adjustment commutation commands.

3. The method of claim 1 , wherein the low-end motor torque range is defined between about 0% and about 50% of maximum motor torque and wherein the high-end motor speed range is defined between about 40% and 100% of maximum motor speed.

4. The method of claim 3, wherein the low-end motor torque range is defined between about 0% and about 25% of maximum motor torque.

5. The method of claim 1 , wherein the low-end motor torque range is defined between an ordinate and an intersection of plots of normal commutation motor speed and adjusted commutation motor speed and wherein the high-end motor speed range is defined above the intersection.

6. The method of claim 1 , wherein the adjustment commutation command is an advanced commutation command.

7. The method of claim 1 , wherein the adjustment commutation command is a delayed commutation command.

8. A method of increasing motor speed of a brushless direct current motor having a rotor, multiple stator phase windings, and multiple rotor position sensors, the method comprising: detecting a rotor position from rotor position pulses generated from the multiple rotor position sensors; routing the rotor position pulses to corresponding rotor position inputs of control electronics for the motor; determining at least one of motor torque or motor speed; rerouting the rotor position pulses among the corresponding rotor position inputs, when motor torque is determined to be within a low-end motor torque range or when motor speed is determined to be within a high- end motor speed range; and applying voltage to the multiple phase windings in accordance with the rerouted rotor position pulses to increase motor speed.

9. The method of claim 8, wherein the rerouting step includes: rerouting a first phase position sensor output to a third phase position sensor input of the control electronics; rerouting a second phase position sensor output to a first phase position sensor input of the control electronics; and rerouting a third phase position sensor output to a second phase position sensor input of the control electronics.

10. A system, comprising: a brushless direct current motor having a rotor and multiple stator phase windings disposed about the rotor; and control electronics, including: a controller to process input to generate motor commutation command signals; a power output stage that selectively communicates electrical power to the motor; and a driver to convert commutation command signals from the controller into switching signals for the power output stage; wherein the controller detects rotor position, measures motor torque, and selects an adjustment commutation command corresponding to the detected rotor position, when motor torque is determined to be within a low-end motor torque range and/or when motor speed is determined to be within a high-end motor speed range, and wherein the power output stage applies voltage to the multiple phase windings in accordance with the selected adjustment commutation command to increase motor speed.

1 1 . The system of claim 10, wherein the motor includes three phase windings and three rotor position sensors to enable the controller to detect rotor position.

12. The system of claim 10, wherein the power output stage includes three pairs of switches including three high side switches and three low side switches.

13. The system of claim 10, wherein the controller includes a lookup table, which cross-references rotor position to adjustment commutation commands.

14. The system of claim 10, wherein the low-end motor torque range is defined between about 0% and about 50% of maximum motor torque and wherein the high-end motor speed range is defined between about 40% and 100% of maximum motor speed.

15. The system of claim 14, wherein the low-end motor torque range is defined between about 0% and about 25% of maximum motor torque.

16. The system of claim 10, wherein the low-end motor torque range is defined between an ordinate and an intersection of plots of normal commutation motor speed and adjusted commutation motor speed and wherein the high-end motor speed range is defined above the intersection.

17. The system of claim 10, wherein the adjustment commutation command is an advanced commutation command.

18. The system of claim 10, wherein the adjustment commutation command is a delayed commutation command.

19. A system, comprising: a brushless direct current motor having a rotor, multiple stator phase windings disposed about the rotor, and multiple rotor position sensors disposed about the rotor; and control electronics, including: a controller to receive input including from the multiple rotor position sensors and to process the input to generate motor commutation command signals; an power output stage that selectively communicates electrical power to the motor; and a driver to convert commutation command signals from the controller into switching signals for the power output stage; wherein the controller detects rotor position from rotor position pulses generated from the multiple rotor position sensors, routes the rotor position pulses to corresponding rotor position inputs of control electronics for the motor, determines motor torque, and reroutes the rotor position pulses among the corresponding rotor position inputs when motor torque is determined to be within a low-end motor torque range and/or when motor speed is determined to be within a high-end motor speed range, and wherein the power output stage applies voltage to the multiple phase windings in accordance with the rerouted rotor position pulses to increase motor speed.

20. A computer usable medium embodying instructions executable by a processor to enable a method of increasing motor speed of a brushless direct current motor having a rotor, multiple stator phase windings, the method comprising: detecting a rotor position; determining at least one of motor torque or motor speed; selecting an adjustment commutation command corresponding to the detected rotor position, when motor torque is determined to be within a low-end motor torque range and/or motor speed is determined to be within a high-end motor speed range; and applying voltage to the multiple phase windings in accordance with the selected adjustment commutation command to increase motor speed.

21 . A computer usable medium embodying instructions executable by a processor to enable a method of increasing motor speed of a brushless direct current motor having a rotor, multiple stator phase windings, and multiple rotor position sensors, the method comprising: detecting a rotor position from rotor position pulses generated from the multiple rotor position sensors; routing the rotor position pulses to corresponding rotor position inputs of control electronics for the motor; determining at least one of motor torque or motor speed; rerouting the rotor position pulses among the corresponding rotor position inputs when motor torque is determined to be within a low-end motor torque range and/or when motor speed is determined to be within a high-end motor speed range; and applying voltage to the multiple phase windings in accordance with the rerouted rotor position pulses to increase motor speed.