GB2073513A - A circuit arrangement for supplying a synchronous motor from a DC voltage source - Google Patents

Abstract

To ensure that a synchronous motor supplied from a DC source operates at maximum torque and efficiency, the static windings W1 to W4 are connected to the DC voltage supply V0 in a cyclic sequence by cyclically applying a control voltage to valves V1 to V4 in accordance with the position of the motor rotor and within an electric angular region which is substantially symmetrical with respect to the crest of the negative half wave of the AC voltage U1-U4 induced in a static winding which is not connected to the DC supply voltage. <IMAGE>

Description

SPECIFICATION A circuit arrangement for supplying a synchronous motor from a DC voltage source The invention originates from a circuit arrangement according to the preamble to the main claim.

Synchronous motors are usually supplied from an AC voltage source wherein the poly-phase winding supplied from the source generates a rotating field by which the pole system of the rotor is driven.

Moreover, the pole system of the rotor is either supplied with DC current through slip rings or is formed as a permanent magnet system. If only a DC voltage source is available for supplying the synchronous motor, it is known to connect the stator windings of the synchronous motor cyclically to the DC voltage.

Thus, for example, a three-phase generator without a transformer is known from the publication "Intermetal, 100 typical circuits with semiconductor components", Freiburg 1967, Example No. 30, and how it can be used in association with synchronous motors when the speed of the drives separated from one another need to be exactly equal and moreovervari- able. This makes the production of a so-called "electric wave" possible. Thus, "electric gearboxes" may also be constructed if the frequency, by which the first generator is controlled, is reduced and a second generator is controlled by it. Then, drives are provided with a fixed speed relationship.

However, the known circuit arrangement does not disclose any means for the cyclic step-by-step switching of the statorwindings of the synchronous motor. Moreover, the problems of starting the motor, limiting the current and regulating the speed are not taken into account.

As opposed to this, the circuit arrangement in accordance with the invention comprising the characterising features of the main claim has the advantage that the step-by-step switching of the stator windings is controlled by the position of the rotor so that the synchronous motor behaves entirely like a permanently energised DC motor.

Advantageous further developments of the circuit arrangement set forth in the main claim are made possible by the measures set forth in the subclaims.

Thus, the respective connected winding is connected up during an electrical angle of 360" divided by the phase number of the motor, which is located symmetrically with respect to the crest of the negative half-wave of the induced AC voltage. In that way, the synchronous motor delivers its maximum torque and has the highest efficiency.

By using a ring counter for the cyclic step-by-step connection of the statorwindingsto a terminal circuit at the counter input, the spurious signals occurring during switching over of the stator windings, do not affect the step-by-step connection of the ring counter.

Furthermore, in a preferred embodiment of the circuit arrangement in accordance with the invention, means are provided which cause starting current limiting and further means are provided which permit a speed regulation of the synchronous motor.

Embodiments of the invention are illustrated in the drawing. There is shown in: Figure 1 the principle circuit diagram of a synchronous motor provided with switching valves in the supply lines to the stator windings; Figure 2 the circuit diagram of an electronic circuit arrangement for the cyclic step-by-step connection of the stator windings; Figure 3 various signal curves as they occur in the circuit arrangement according to Figure 2; Figures 4 to 6 circuit diagrams of circuit arrangements for the starting current limiting of the synchronous motor; Figure 7 the circuit diagram of a circuit arrangement for current limiting and speed regulation of the synchronous motor; Figures 8 and 9 circuits for a control device with improved starting characteristics; Figure 10 shows a time diagram for that purpose.

The circuit diagram of a circuit arrangement which serves for the supply of a synchronous motor from a DC voltage source is illustrated in Figure 1.

Moreover, the synchronous motor is referenced 10 and has stator windings W1, W2, W3, W4 which are connected in a starwherein the centre point leads to one terminal of the supply DC voltage UO. The other ends of the stator windings W1, W2, W3, W4 are connected through electric valves V1, V2, V2, V4to a collector line which is connected to the other pole of the supply DC voltage UO. In the embodiment according to Figure 1, the electric valves V1, V2, V3, V4 are illustrated as transistors to the collector emitter paths of which are applied the control voltages U1, U2, U2, U4 when each valve is blocked.However, other electrical or electronic switching elements can, of course, also be used as valves. In the illustrated embodiment, the rotor of the synchronous motor 10 is formed as a permanent magnet the poles of which are referenced N and S.

By controlling the valves V1, V2, V3, V4 cyclically, the stator winding W" W2, W3, W4 can then be connected successively to the supply DC voltage UO whereby, with the circuit arrangement in accordance with the invention, one winding is connected and the others are disconnected and the step-by-step connection of the valves V1, V2, V3, V4 is undertaken in accordance with the voltages which result from the difference between the supply DC voltage and the AC voltages induced in the stator windings and can be derived as U1, U2, U3, U4.

An embodiment of a circuit arrangement in accordance with the invention for the cyclic changing over of the stator windings Wt, W2, W3, W4 is illustrated in Figure 2. On its input side, the circuit arrangement is influenced by the voltages U1, U2, U3, U4 and delivers control signals on its output side for the valves V1, V2, V3, V4.The voltages U1, U2, U3, U4 lead respectively to positive inputs to comparators 11, 12, 13, 14 the negative inputs to which are so connected to a respective positive in put to another comparator that in the first comparator 11, the voltage U, is compared with the voltage U4, in the second comparator 12 the voltage U2 is compared with the voltage U1, in the third comparator 13 the voltage U3 is compared with the voltage U2 and in the fourth comparator 14 the voltage U4 is compared with the voltage U3. The outputs from the comparators 11, 12, 13, 14 lead to first inputs to AND gates 15, 16, 17, 18 the further inputs to which lead to the output control lines for the valves V1, V2, V3, V4.Moreover, the first AND gate 15 is connected to the output control line for V2, the second AND gate 16 is connected to that for V3, the third AND gate 17 to that for V4 and the fourth AND gate 18 to that for V1. The outputs from the AND gates 15, 16, 17, 18 lead to a 4-input OR gate 19 the output from which is connected to one input to an AND gate 20. The output from the AND gate 20 is in communication with a dynamic setting input to a monostable sweep stage 21 which has the unstable time tvi. On the one hand, the non-inverting output from the monostable sweep stage 21 is connected through an inverter 22 to the further input to the AND gate 20 and on the other hand is connected to the dynamic counter input 230 to counter23.The counter 23 has four counting states corresponding to the phase number = 4 of the synchronous motor 10 illustrated in Figure 1.Each counting state 1 to 4 generates a signal at one of the counter output lines 1 to 4 wherein the output line 1 is connected to the control input for the valve V,,the output line 2 is connected to that for the valve V2, the output line 3 to that for the valve V3 and the output line 4 to that for the valve V4. With each control of the input 230, the counter is advanced by one position in the sequence 1-2-34-1 and the control of the valves is also switched step-by-step therewith in the same sequ ence.

The method of operation of the circuit illustrated in Figure 2 will now be explained with the aid of the diagrams illustrated in Figure 3. Figure 3a shows the voltages U1, U2, U3, U4 induced in the stator windings W1,-W2, W3, W4 which occur when no connection of a statorwinding has taken place. In orderto utilize the maximum torque and the highest efficiency of the synchronous motor, each winding is connected up in accordance with the invention, corresponding to an angle of 90" (with a four-phase motor) symmetrically with respect to the crest of the negative half wave of the induced AC voltage that is to say with respect to the minimum of the voltages U1, U2, U3, U4.Thus, it follows directly from Figure 3a, that the start of the connection for the statorwinding W, for example coincides with the instant at which the voltage U3 becomes greater than U2. Correspondingly, advance of the connection from the first winding W, to the second winding W2 takes place when the voltage U4 becomes greaterthan U3. Expressed generally, the i-te winding is connected and the (i-1 )-te winding is disconnected in an n-phase synchronous motor (n is an even number), when

wherein U represents the voltage induced in the i-te winding and i = i + k. n when k = 0,1, 2 . . . (Exam- ple: n = 4, connection of W4 when U6 > Us or if k = 1 when U2 > U,).

This is expressed in Figure 3b where the particular state Z of the counter 23 is plotted. As is apparent, the control signal is gated with the countercondition "1" during the connecting up period for the winding W1 previously referred to. If the voltage U4 becomes greater than U3, the counter moves into the state 2 whereupon the valve V2 is actuated in accordance with the circuit according to Figure 2.

As stated, the step-by-step connection of the counter 23 is effected by controlling the input 230 through the monostabie sweep stage 21. For this purpose, the changeoverrequ rements are first of all established in the comprators 11, 12, 13, 14 accord- ing to a comparison of the voltages U1, U2, U3, U4 and on achieving a changeover point, for example when U3 becomes greater than U2, a control signal at the output from the comparator 13 is transmitted to the AND gates 15, 16, 17, 18, thus for example the AND gate 17. The AND gate 17 then switches when the state "4" is simultaneously read into the counter 23 which, as Figure 3b shows, is the case before reaching the changeover requirement U3 greater than U2.Thus, by connecting the AND gates 15,16, 17, 18 to the counter output signal, a preparation of the AND gates 15, 16, 17, 18 is effected in such a manner that a signal for the step-by-step switching of the counter 23 through the AND gates 15, 16, 17, 18 is only provided when, on the one hand, the counter 23 was in the preceding counter state and on the other hand the changeover requirement established from the voltages U1, U2, U3, U4 is reached.

Each of the output signals from the AND gates 15, 16,17,18 controls,throughthe OR gate 19, one input to the AND gate 20 which, in its turn, acts on the control in put to the monostable sweep stage 21.

Moreover, the gating of the non-inverting output from the monostable sweep stage 21 through the inverter 22 with the further input to the AND gate 20 has the effect of maintaining the input 230 to the counter 23 at a positive signal during the period of the unstable time of the monostable sweep stage 20 as is illustrated in Figure 3c. Thus, spurious voltages occurring during changing overofthewindings, do not lead to an unwanted step-by-step switching of the counter 23 before the next definite changeover requirement is reached.Moreover, Figure 3c repres ends the output voltage at the non-inverting output from the monostable sweep stage 21 wherein the unstable time is reference tvi. Moreover, this unstable time is so calculated that all transient states after the changing over of the stator winding are damped during the unstable time and the monostable sweep stage 21 and with itthe counter 23 can be released forthe next changeover operation.

Figures 3d,3e,3f,3g show the control signals appiied to the output terminals forthe valve V1, V2, V3, V4. In the example referred to above, in which switching to the stator winding W, occurs when U3 is greater than U2, this means that the valve V, remains open until the next changeover requirement (U4 greater than U3). Thereafter, there is a step-by-step con nection to V2, then to V3 etc.

Finally, the voltage U1 forthe stator winding W, is illustrated for example in Figure 3h wherein contrary to Figure 3a the connection and disconnection of the statorwindings is undertaken. This means that, due to the control of the valve V1, the voltage U, drops to zero at the instantofconnection of the stator winding W, until the stator winding W2 is connected. As is explained below, it is possible in an advantageous form of the circuit arrangement in accordance with the invention, to delay the connecting instant for the individual windings, thus in the illustrated example for the stator winding W1, by a predeterminable amount of tV2 in order to effect speed regulation of the synchronous motor in this way.

In the synchronous motor driven in accordance with the invention, an opposing voltage increasing with an increase in speed is built up as in a DC motor so that the current falls. If it is then desired to dimension the switching elements for the current at higher speed then it is necessary to limit the current during the starting phase of the motor.

In a first further development of the circuit arrangement in accordance with the invention (Figure 4) a known series resistor 24 is connected forthis purpose in the supply line to the centre point of the stator windings W1, W2, W3, W4 as is illustrated in Figure 4. Moreover, the series resistor 24 can be shunted by an electromechanical or electronic switch 25 either dependent on current or dependent on speed.

According to a further form of the circuit arrangement in accordance with the invention (Figure 5) the synchronous motor 10 is connected to the tapping of a voltage divider which consists of a series element 26 and a capacitor 27. Moreover, by means of the adjustable series element 26, for example a series transistor, the voltage UO is limited and the motor current is indirectly limited thereby. In this arrangement, the capacitor 27 serves for smoothing the peaks occurring in the free wheeling phase and thus completely effects an improvement in the efficiency of the synchronous motor.

Finally, an embodiment of a circuit arrangement in accordance with the invention is illustrated in Figure 6 in which the DC voltage for supplying the synchronous motor 10 is derived from an AC voltage U wherein the supply DC voltage UO at the capacitor 27 is adjustable by a controllable rectifier 28.

A limitation of the starting current can be achieved by timing the respective operated valves V1, V2, V3, V4 by the counter 23 and the maximum value or the average value of the current, for example, is thus limited. However, proceeding in that manner, a more reliable comparison of the voltages U1, U2, U2, U4 is no longer possible due to the timing. Thus, the timing must be set shortly before an expected cut-off point of the voltage value. An arrangement is illustrated in Figure 7 in which both the starting current is limited by timing and the speed of the synchronous motor 10 can be adjusted. Forthis purpose, the control signal for one valve V is converted into a modified control signal V'. The control signal V' can be derived from the output from an AND gate 30 the inputs to which are connected to an AND gate 31 or to an OR gate 32.On the one hand, the AND gate 31 is connected on its input side to the control signal for the valve V and on the other hand is connected to the inverted output from a monostable sweep stage 33 which has an unstable time tV2 which is adjustable in accordance with the difference between a set speed n5011 and an actual speed n jS; as is shown by the summing point 35. On its input side, the OR gate 32 is connected to the inverted output from a monosyllable sweep stage 34 which is controlled by the control signal for the valve V and is connected to the output from a timing device 36 which is controllable in accordance with the difference between a maximum current imax and an actual current as is illustrated by the summing point 37.

In order to effect a current limiting in the above described manner, the difference between the actual current iisi and the maximum current imax is first of all formed atthe summing point 37 and the timing device 36 is controlled in accordance with the said difference. The control signal for the valve V sets the monostable sweep stage 34 for a predetermined time which, for example, amounts to 0.8 times the connecting time for one winding. Then, due to the gating of the output signals from the elements 34,36 in the OR gate 32, there is a guarantee that after the unstable time of the monostable sweep stage 34 has elapsed the OR gate 32 becomes conductive in any case, that is to say the timing device 36 becomes effective only during a first portion of the connecting time for the particular winding.Then follows a stabilising time in which the transition phenomena produced by the timing are damped sothatthe ring counter 23 can be prepared for the next connecting step.

In order to adjust the speed of the synchronous motor 10, it is possible, on the one hand, to adjust either the linear element 26 of Figure 5 or the controllable rectifier 28 of Figure 6 in such a manner that the voltage UO is varied until the desired speed is set.

On the other hand, it is also possible to undertake speed regulation by pulse length control. For that purpose, the difference between the actual speed n and a set speed nSOIl is produced at the summing point 35 of Figure 7 and the unstable time of the monostable sweep stage 33 is adjusted in accordance with that difference. As long as the monostable sweep stage 33 is in its set condition, the control signal for the valves V is not passed on through the AND gate 31 and the AND gate 30. As has already been been referred to in the description of Figure 3h, this delay in the control signal V causes a variation in the voltage curve of, for example, U, as is illustrated in dotted lines in Figure 3h.The effective connecting up time for the stator winding W1, for example, is thereby shortened and the speed correspondingly reduced. In the embodiment according to Figure 7, the speed of the synchronous motor 10 is regulated on the basis of the comparison between the set and actual speed. However, it is clearly also possible, by feeding a control signal to the summing point 35, to apply a control to the synchronous motor 10 instead of a regulation.

Since in the stationary position of the synchronous motor driven in accordance with the invention, no information is available concerning the position of the rotor, a special control is required for starting up.

To this end in accordance with the invention, a rotary field of very low frequency is generated first of all, preferably slightly rising during the period, and is then converted to the normal operation described in detail above. In so doing, the conversion can either take place at a particular speed or in accordance with switching means which detect when the induced vol tages U1, U2, U3, U4 permit a position detection. In a further preferred form of the invention, a starting up control is provided by bringing the rotor into a defi nite position before starting up by switching in one valve for a long period, then switching off the valve and simultaneously switching in the next valve irethe cycle.With an appropriate design of the com parators 11,12,13, 14, this causes the next but one valve to be already switched in automatically.

The above described indirect signalling of the pole wheel position depends on the comparison of the electromotively induced voltages in the windings through which the current is not flowing. For example, the transistorT, conducts until U4 > U2, then T1 is blocked and T2 becomes conductive until U, > U4 etc. This detection of the pole wheel position by comparing the phase voltages requires not additional components at the motor. It functions with very low rotational speeds but not when stationary.

Thus, special measures are required for starting.

As proposed above, the counter can be moved step-by-step in very slow steps (about 0.5 seconds) by an auxiliary pulse for starting so that the rotor can be properly orientated. As soon as the sense of rotation, the condition of the counter and the voltage intersection point coincide, the motor proceeds under automatic control and accelerates with maximum torque up to operational speed. With this arrangement, a starting delay of more than one second is produced in the most unfavourable case.

For particular uses, this starting delay is unacceptable (for example with fuel pumps for injection engines). A non-delayed start can be provided in accordance with the invention by bringing the rotor into a definite position when the motor is stationary from which a fresh start can take place without a delay.

Each starting operation assumes a particular position of the pole wheel and starts when the counter is set in a particular position and one motor winding is connected to the supply voltage through the appropriate transistor (for example T,.to which example the further operation relates). When within a predetermined time, U4 > U3, T1 is blocked and T2 becomes conductive. Thus, the motor normally runs from the first step to automatic control.When a particular period has been exceeded, until U4 > U3 (stopping of the motor due to mis-matching of the starting position of the pole wheel) or when directly after the intersection point U4 > U2 already U, > U4 (reverse movement due to mis-matching at the starting position of the pole wheel) starting up is interrupted and a positioning operation is initiated. During the positioning, the transistors T2 and T4 are made conductive successively for about 0.5 seconds and the pole wheel is so orientated that automatic control of starting can take place with the counter position T,.

In orderto prepareforthe rapid starting in accordance with the invention, the positioning is carried out in a servo operated programme after each time the motor becomes stationary (for example stopping of the fuel pump when the combustion engine is switched off by the ignition key) and thereafter the equipment is switched off.

A new start usuaily zakes place without any starting delay. If the servo positioning has been upset by any condition and the rapid start does not function, an addition positioning operation is initiated auto magically.

In afurtherform oftheinvention,the positioning operation is initiated by an additional signal, a seat or door contact, before the real starting by the ignition key.

Claims (21)

1. Acircuit arrangement for supplying a synchronous motor from a DC voltage source in which the stator windings of the synchronous motor are connected to the DC voltage in a cyclic sequence, characterised in that, the AC voltages induced in the stator windings which are not connected is meas- - ured and the connection of a respective stator winding is undertaken during a predetermined electrical angular region at least substantially symmetrical with respect to the crest of the negative half wave of the AC voltage induced in a respective stator winding.

2. A circtuit arrangement according to claim 1, characterized in that, the electrical angular region is 36001n with an n-phase synchronous motor.

3. Acircuit arrangement according to claim 1 or 2, characterised in that, the instants for connecting and disconnecting the respective stator winding are determined by comparing the voltages induced in the non-connected stator windings.

4. Acircuit arrangement according to claim 3, characterised in that, in an n-phase synchronous motor (n even number) the i-te winding is connected and the (i-1 )-te winding is disconnected (i = i + k.n fork=0,1,2,3,...;in),when Us+ 2 > U1 + 2-1 2 wherein U represents the voltage induced in the i-te winding.

5. Acircuit arrangement according to one of the preceding claims, characterised in that, a counter is used for cyclically switching the statorwindings and counts forward in accordance with the comparators comparing the induced AC voltages and the outputs from which are connected on the one hand to the valves effecting the connecting and disconnecting of the statorwindings and are connected on the other hand to switching meansby means of which the output signals from all the comparators until one becomes blocked and the respective unblocked comparator delivers the next counting pulse.

6. A circuit arrangement according to claim 5, characterised in that, after each counting pulse, the counter input to the ring counter is blocked for a predetermined period oftime.

7. Acircuit arrangement according to one of the preceding claims, characterised in that, a series resistor which can be shunted is connected in the current supply to the synchronous motor.

8. A circuit arrangement according to one of claims 1 to 6, characterised in that, the synchronous motor is connected to a tapping from a voltage divider which includes a controllable linear element, preferably a linear transistor.

9. A circuit arrangement according to one of claims 1 to 6, characterised in that, the supply DC voltage to the synchronous motor is derived from an AC current supply through a controllable rectifier.

10. A circuit arrangement according to one of the preceding claims characterised in that, the supply DC voltage to the synchronous motor is pulsed.

11. A circuit arrangement according to claim 10, characterised in that, the duty ratio is determined by comparing the actual current with the maximal permissible current.

12. A circuit arrangement according to claim 10 or 11, characterised in that, the synchronous motor is only pulsed during a first portion, preferably 80%, of the connection time of the particular stator winding.

13. Acircuit arrangement according to one of the preceding claims, characterised in that, the connecting time for the respective stator windings is adjustable in accordance with the difference between the set speed and the actual speed of the synchronous motor.

14. Acircuit arrangement according to claim 13, characterised in that, the instant at which the respective stator winding is connected, is delayed.

15. A circuit arrangement according to one of the preceding claims, characterised in that, furthermore an oscillator, preferably of lower or slightly rising frequency, is provided to which the counter can be switched over for a short period of time for starting the synchronous motor from stationary.

16. A circuit arrangement according to one of claims 1 to 14, characterised in that, when setting the synchronous motor in operation, first of all a stator winding is connected statically and is then switched over cyclically to the next winding.

17. A circuit arrangement according to one of claims 1 to 16, characterised in that, means are provided which, when the rotor is stationary, brings the latter into a definite rest position with respect to the stator.

18. Acircuit arrangement according to claim 17, characterised in that, a servo control is provided which carries out the positioning in a servo programme during stopping of the motor.

19. A circuit arrangement according to claim 18, characterised in that, at least two phase conducting transistors are provided for the positioning operation and which are made conductive successively, each for about 0.5 seconds.

20. A circuit arrangement according to one of claims 17 to 19, characterised in that, at least one additional contact, for example a seat or door contact, is provided for initiating the positioning operation.

21. A circuit arrangement for supplying a synchronous motor from a DC voltage source substantially as herein described with reference to Fig. 1 or any one of Figs. 2 to 10 ofthe accompanying drawings.