EP0585551A2 - Speed control device for AC or three phase motor - Google Patents

Abstract

A capacitor is arranged in each rotation speed stage of the control device. This capacitor can be connected into the supply strand of the motor, without forming switching sparks, via a semiconductor switch without contacts and, immediately downstream thereof, via a relay having a switching contact which is arranged in parallel with the respective semiconductor switch. The capacitors in the switching stages which can be constructed either to be identical to one another or to be different from one another are connected in parallel into the supply strand of the motor. The setting of the respectively desired rotation speed level can be carried out by means of a manually operable sequencing switch, in the form of a rotary switch or slide switch. <IMAGE>

Description

The invention relates to a device for speed control of AC or three-phase motors, in particular motors for driving fans, which is provided with means for gradually changing the voltage applied to the motor and with a switch for setting the desired speed level.

Devices for speed control of the aforementioned type and purpose are generally known. Transformers with secondary taps are used as a means of changing the voltage applied to the motor.

In the case of controls for fan drives, five speed levels can generally be set and, for example, with an input voltage of 220/240 volts on the transformer, output voltages of 60, 105, 130, 160 and 220 volts can be tapped from its transformer taps.

Controls of this type have proven themselves, but they are expensive to set up and, moreover, have poor efficiencies. At most, transformers achieve an efficiency of 80 percent. Also, at least for larger outputs, the transformers must be provided with ribs for heat dissipation or even be equipped with special cooling systems.

The object of the present invention is therefore to provide a control of the type and intended use which is simpler and less expensive to manufacture, and which is also to be characterized by better efficiencies than the controls according to the prior art.

This object is achieved according to the invention in that, in the control device according to the preamble of claim 1, the control takes place via one capacitor at each speed level, which can be switched on in parallel in the supply line of the motor, and in that each capacitor is initially connected via a contactless semiconductor switch and directly can then be applied to the supply voltage via a relay with a switching contact arranged in parallel with the respective semiconductor switch.

The invention is therefore that capacitors have taken the place of a transformer with a number of secondary taps corresponding to the desired number of switching stages. Depending on the desired switching level, these capacitors can gradually be switched in parallel to one another. A practically loss-free speed control is thereby realized.

As is known, considerable switching sparks usually occur when switching capacitors, which can easily lead to burning or welding of the switching contacts. This is now prevented in the invention in that each capacitor in parallel to each other is assigned a contactless semiconductor switch and the switching contact of a switching relay and that first the contactless semiconductor switch is switched on by applying a control voltage and then immediately afterwards by triggering the relay the relay contact of this switching stage in Closing position is brought.

It is therefore characteristic of the control according to the invention that when a speed stage is switched, its capacitor is first connected to the supply voltage via the contactless semiconductor switch and immediately afterwards a second current path is created by closing the relay contact of this switching stage and is maintained during operation. Since at the moment the relay contact of each switching stage is closed, its capacitor is already connected to the supply voltage via the contactless semiconductor switch, the switching contact is present of the assigned relay at most only slight potential differences (forward voltage of the semiconductors) and consequently no switching sparks or contact welding can occur when the relay switch contact is actuated into its closed position.

A speed control has thus been created which can be designed for any number of switching stages, each switching stage being assigned a capacitor and the latter being able to be applied to the supply voltage in succession via a contactless semiconductor switch and then via the switching contact of a relay. The capacitors of the individual switching stages can be connected in parallel with one another with the result that when the second and each subsequent speed stage are switched on, the capacitances of the capacitors assigned to these stages add up to one another.

An expedient development of the invention provides that the contactless semiconductor switch and the relay with the switch contact parallel to the semiconductor switch can be controlled in each speed stage via their in turn arranged switching contacts and that the switching contact serving to control the relay of each speed level immediately after actuating the Switch contact is actuated to control the associated semiconductor switch in its closed position.

According to this embodiment, it is therefore ensured that the compulsory law after the control of the contactless semiconductor switch of a switching stage Relay of this switching level is also controlled and the relay contact is therefore actuated in its closed position and short-circuits the electronic current path.

It has proven to be particularly expedient if the switch for setting the desired speed level is designed as a sequential switch with inevitable actuation of the contacts serving to actuate the relays in the individual switching stages after prior actuation of the contacts for actuating the respective semiconductor switch in their closed positions. This switch can be a rotary or slide switch.

Another advantageous further development of the invention provides that the switching functions of the switch for setting the desired speed level depending on environmental conditions are triggered by means of a sensor system.

Fig. 1

in einem Prinzipschaltbild eine Einrichtung zur Drehzahlsteuerung eines Einphasen-Wechselstrommotors und

Fig. 2

in einem Schaubild die jeweils aufeinanderfolgende Betätigung eines Schaltkontaktes zum Ansteuern des kontaktlosen Halbleiterschalters und nachfolgend eines Schaltkontaktes zum Ansteuern eines Schaltrelais in verschiedenen Schaltstufen.

An embodiment of the speed control according to the invention will be explained below with reference to the accompanying drawing. Show in schematic views.

Fig. 1

in a block diagram a device for speed control of a single-phase AC motor and

Fig. 2

in a diagram, the successive actuation of a switching contact for controlling the contactless semiconductor switch and subsequently a switching contact for controlling a switching relay in different switching stages.

In the device for speed control of a single-phase AC motor M shown in the basic circuit diagram according to FIG. 1, two successive switching stages 1 and 2 are shown. It is without further the equipment with further switching stages possible, which can be identical to each other. This is indicated by the dots arranged to the right of switching stage 2 in the circuit diagram.

Each of the switching stages of the device for speed control is equipped with a capacitor C1, C2 ... which can be switched into the supply line of the motor M and also has a contactless semiconductor switch T1, T2 ... (in a special arrangement with passive components) and a relay R1, R2 ... with a switching contact K1, K2 ... arranged in parallel to the semiconductor switch of the relevant switching stage. Finally, the semiconductor switches T1, T2 ... via switching contacts S1.1, S2.1 ... and the relays R1, R2 ... via the switch contacts S1.2, S2.2. .. controllable, by means of a switch, not shown, which can be designed as a manually operated sequential switch in the form of a rotary or slide switch.

When the first switching stage is switched on, the contact S1.1 is brought into the closed position by means of the sequential switch and thereby the contactless semiconductor switch T1 is switched to continuity, with the result that a circuit from L to the contactless semiconductor switch T1, the capacitor C1 and the motor M. N closes. Immediately after the contactless semiconductor switch T1 has switched, as shown in the diagram in FIG. 2, the switch contact S1.2 of the first stage is in the closed position, as a result of which the relay R1 is actuated and its switch contact K1 arranged in parallel with the semiconductor switch T1 Closed position actuated, which then forms a current path parallel to the semiconductor switch T1. In view of the existence of a current path via the semiconductor switch T1 at the time the switch contact K1 closes, there are only slight potential differences thereon, so that no switching sparks can occur at the switch contact K1 when switching. The current path formed via the closed switching contact K1 ensures the further supply of the motor M via the capacitor C1 if the semiconductor switch T1 drops after the aforementioned parallel current path has been established via K1.

The structure of the second switching stage, and any other switching stages that may be present, is the same as switching stage 1. If the second switching stage is to be switched on, the contactless semiconductor switch T2 is first activated and closed for continuity by closing the switch contact S2.1, whereupon the relay R2 is actuated by immediately following actuation of the switch contact S2.2 and the switch contact K2 is thereby closed. The capacitor C2 of the switching stage 2 is then connected in parallel to the capacitor C1 of the switching stage 1 and the total capacitance switched into the supply line of the motor M is equal to the sum of the capacitances of the capacitors C1 and C2.

The diagram according to FIG. 2 illustrates analogously to switching stage 1 for switching stage 2 and a third switching stage indicated in this diagram the closing of the switching contact S2.2 applying the relay R2 to the supply voltage immediately after the closing of the switching contact S2.1 to apply the contactless semiconductor switch T2 to the supply voltage.

In FIG. 1 the contactless semiconductor switches T1, T2 are illustrated in the same way as the switch contacts K1, K2 of the relays R1, R2 as switch contacts which can be actuated between a closed and an open position, merely for the sake of clarity. In fact, however, the semiconductor switches are contactless switching elements in connection with passive components which are switched to continuity by application to a special supply voltage as a result of actuation of the assigned switching contacts S1.1, S2.1.

Switching off or switching to a lower speed level takes place in reverse order.

Claims (4)

Device for speed control of AC or three-phase motors, in particular motors for driving fans, which is provided with means for gradually changing the voltage applied to the motor and with a switch for setting the desired speed level in each case,
characterized,
that the control takes place via a capacitor (C1, C2 ...) at each speed level (1, 2 ...), which can be switched on in parallel in the supply line of the motor (M), and that each capacitor (C1, C2 ...) first via a contactless semiconductor switch (T1, T2 ...) and immediately afterwards via a relay (R1, R2 ...) with the switch contact (K1, K2 ...) can be applied to the supply voltage. Device according to claim 1, characterized in that in each speed stage (1, 2 ...) the contactless semiconductor switch (T1, T2 ...) and the relay (R1, R2 ...) with that to the semiconductor switch (T1, T2 ...) parallel switching contact (K1, K2 ...) can be controlled via switching contacts (S1.1, S1.2; S2.1, S2.2; ...) which are arranged parallel to each other and that the switching contact (S1 .2, S2.2 ...) the relay (R1, R2 ...) of each speed level immediately after actuation of the switch contact (S1.1, S2.1 ...) to control the assigned semiconductor switch (T1, T2 ...) is operated in its closed position. Device according to claim 1 or 2, characterized in that the switch for setting the desired speed level (1, 2 ...) as a sequence switch with inevitable actuation of those used to control the relays (R1, R2 ...) in the individual switching stages Contacts (S1.2, S2.2 ...) after actuation of the contacts (S1.1, S2.1 ...) to control the respective semiconductor switch (T1, T2 ...) is formed in their closed positions. Device according to one of claims 1 to 3, characterized in that the switching functions of the switch for setting the desired speed level (1, 2 ...) are triggered as a function of ambient conditions by means of a sensor system.

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