DE3135764A1 - STABILIZATION CIRCUIT FOR A REGULATED INVERTER MOTOR SYSTEM - Google Patents

Description

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The invention relates to a controller for stabilizing an inverter-controlled motor in the event of transient surges or malfunctions, which significantly improves the dynamic behavior of the inverter-motor system, and in the steady-state State when the operating conditions are suitable for causing the system to oscillate.

Inverter motor systems tend to operate at low frequencies under certain operating conditions to oscillate, with the inverter acting as a negative terminating resistor for the DC voltage busbar, over which it receives its excitation voltage. The invention aims to give the inverter a more positive resistance value. and thus reduce the tendency to vibrate.

Also, the inverter motor may turn off abruptly have changing load torques, which have significant deviations of the nominal DC voltage of the busbar in the steady state. The invention is also intended reduce the effect of sudden load torque changes on the DC voltage of the busbar, thereby also reducing Deviations from the nominal DC voltage of the busbar are prevented.

The reason for the undesirable voltage changes in the . The busbar is to be ascribed to the filter, which consists of a series-connected choke and a 'parallel-connected Capacitor consists, and is usually arranged in the DC voltage supply, which the busbar voltage generated. During normal operation in a steady state no current with an arithmetic mean value flows to the filter capacitor, and the entire current is supplied to the Inverter and from there to the motor windings. In the event of a sudden drop in, for example, the load torque at the motor, the motor current also drops abruptly, and the inductor current flows to the filter capacitor, whereby it

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charges it to a significantly higher voltage. Because the DC busbar is connected in parallel to the capacitor the busbar voltage also increases significantly. This high power voltage can also save one harmful influence on the motor destroy the switching devices in the inverter (which can be transistors). To prevent this, oversized switching devices are mostly used, their performance characteristics • Sufficient to handle even the strongest busbar voltages

1Ό to withstand the very sudden change in load could occur.

The controller according to the invention achieves a considerably improved dynamic behavior and overcomes the question of instability by regulating the DC bus voltage for the stability of the engine, while keeping it at the same time avoids the need for oversized switching devices. According to the invention, the negative Resistance of the inverter a more positive value in order to eliminate the tendency to oscillate. At the same time cares the invention that the engine torques in the. Change time to the deviation of the busbar DC voltage to decrease from the setpoint ·.

The regulator according to the invention regulates one through .the output AC voltage an inverter controlled AC motor, whereby the inverter is controlled by an adjustable • Busbar DC voltage is excited, which is applied from a controlled DC voltage supply. The regulator

30 · includes devices for setting a nominal voltage ■ ■ for a target amplitude and a target frequency of the inverter generated alternating voltage. It also has devices that use the nominal voltage of the output voltage of the inverter impress a target amplitude and target frequency at a target level. Stabilization devices / which indicate an undesirable change in the

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addressing rail direct voltage, are used to change the inverter frequency to the electrical load to control parallel to the DC voltage control rail, whereby the busbar voltage ratio is kept constant.

The invention is explained in more detail below. All in the Features and measures contained in the description can be essential to the invention. The drawings show:

Fig..1 is a circuit diagram of a controller according to the invention with the way in which this is coupled to the inverter-overhead motor system in order to operate it regulate and stabilize,

2 and 3 parts of the controller of FIG. 1 in other exemplary embodiments the invention.

According to FIG. 1, the lines L ₁ , L2 and L ₃ are routed from a conventional three-phase network and thus emit a three-phase voltage, ie three alternating voltages offset from one another by 120 ° with a frequency of 60 Hz. The individual three phase voltages form a concatenated voltage , 'which is applied to one of the lines L-, L ₂ and L ₃ opposite each other of the lines. The alternating voltage present on these lines is converted into direct voltage by a controlled rectifier bridge 10 of known design. The bridge has a group of six controlled semiconductor rectifiers (SCR) 11-16 which, when controlled by the switching current of a rectifier regulator 17, rectify the applied AC voltage and allow a rectified voltage to be applied to the positive and negative output terminals 18 and 19 of the bridge Size is determined by the conduction angle of the controlled semiconductor rectifier for each half cycle of the applied AC voltage.

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The individual controlled semiconductor rectifiers in the bridge 10 can during a positive switching period of the control applied AC voltage when its anode is positive with respect to the cathode. The control takes place but not during a positive half cycle until a switching or control current from the rectifier control 17 is applied to the gate of the controlled semiconductor rectifier. Now they control or switch on, which makes them of a working current can flow through until the end of the positive half-cycle. The larger the phase angle or the Time delay between the start of the positive half-period and the activation of the controlled semiconductor rectifier the smaller the conduction angle and the lower the proportion of the mean electrode voltage, which is rectified and given to the consumer. Of course, the rectified voltage is at terminal 18 compared to terminal 19 positive.

A filter 20, with a series-connected choke 21 and a parallel-connected capacitor 22 filters the rectified voltage of the bridge and forms a fil-. tered DC voltage, which is generated via the DC voltage rail on the inverter on lines 26 • and 27 25 is present. A positive DC bus voltage is therefore on line 26 opposite line 27, which is connected to the ground of the reference voltage. and in export example is 0 V. By controlling the conduction angle of the controlled semiconductor rectifiers 11-16, the abutting the inverter 25 via the busbars 26, 27 Busbar DC voltage controlled.

The inverter 25 is of a known circuit design. It comprises three pairs of two-pole NPN power transistors 31-36, each pair being connected in series to busbars 26,27. The three nodes 37, 38, 39 of the three pairs of transistors are connected to the windings of an asynchronous motor 41, the output shaft 42 of which is a

mechanical load 43 drives. By applying the control current to the phases of the six two-pole transistors 31-36 At certain times, the DC voltage on the DC voltage busbar is converted into an AC voltage, the Andes. Windings of the motor is applied, whereby the motor 41 is absorbed by the windings AC current runs at a speed that is directly proportional to the frequency of the inverter output voltage. For example, if the basic control current is applied to transistors 31 and 35 at the same time in order to saturate them, Current flows from line 26 in the following order via the emitter-collector path of transistor 31, node 37, one winding of motor 41, node 38 and the emitter-collector path of transistor x 35 to line 27 or to ground. When transistors 31 and 35 block and transistors 32 and 34 instead through, current flows through the same motor winding in the opposite direction. The control circuit for supplying the Basic control flow for switching the transistors 31- 36 in the right order, at the right time and at the right frequency to make the required change • voltage to operate the motor 41 and the load 43

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aim is known to those skilled in the art. The control circuit is in the exemplary embodiment represented by block 45 marked "inverter control circuit". Mostly Such a control circuit comprises the logic circuit and a controlled oscillator which is dependent on a control voltage applied via a line 47, programmed periodically recurring clock pulses or Basic control signals for transistors 31-36 are generated to determine the frequency of the inverter output voltage and therefore the speed of the motor. The repetition frequency the clock pulse is a function of the control voltage of line 47. Therefore, the inverter frequency is regulated by changing the magnitude of this control voltage.

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The emitter-collector path of the six individual power transistors 31-36 is assigned by a respective one Reverse polarity feedback diode 51-56 shunted, whereby the diodes serve to supply the reactive current of the motor. · To lead back to the filter capacitor 22. The feedback diodes 51-56 also cause the terminal voltage to be clamped of the motor so that it is never higher than the DC busbar voltage.

Although it is not shown in the drawing, the individual transistors 31-36 are preferably also through a Conventional attenuator placed in parallel, so that the induction voltage the motor windings cannot damage the transistors when they are controlled by the inverter 45 can be switched off during normal operation.

• Although the individual two-pole power transistors 31 36 each as conventional NPN transistors for simplicity In the drawing, they are preferably known in practice as power Darlington transistors executed. In the Darlington circuit, the individual transistors 31 - 36 consist of a combination of two transistors, which however only have the three connections as in the drawing, namely. base, emitter and collector. Of course, in addition to: the two-pole power transistors, other switching devices such as Thyristors, field effect transistors, etc. are used.

To control the rectifier regulator 17 for setting the amplitude of the output voltage of the inverter as well as for the control, the control circuit 45 for the frequency regulation of the inverter voltage is on Node 57 between the fixed resistor 58 and the 'Po-

3.5 tentiometer 59 an adjustable setpoint or reference voltage

at. The output target voltage of the voltage divider 58, 59 ■ determines the working conditions in the steady

stood and sets a target amplitude and target frequency for the Mo.tor 41 of the alternating voltage generated by the inverter 25 The setpoint is chosen so that it fulfills the speed requested by the mechanical load 43, A comparison circuit 61 compares the target voltage with a voltage proportional to the busbar DC voltage Voltage (because of the gain factor K62) and generates an error voltage that is a function of the difference of the compared tensions is. K62 sets the gain between the busbar DC voltage and the Target voltage fixed. The rectifier regulator 17 responds to the fault voltage and generates corresponding keyed Control current pulses that are applied to the gates of the controlled semiconductor rectifiers 11-16 in order to increase the to regulate the controlled semiconductor rectifier as required in order to regulate the busbar DC voltage on the lines 26 and 27 with the size required to generate the inverter output voltage and they to hold at the target amplitude. If the busbar 0 DC voltage vcm required steady state level 'strives to deviate, the fault voltage changes and causes the rectifier regulator 17 to adjust the conduction angle changes as necessary to readjust the busbar DC voltage until the correct ampli ■ tuden level for the steady state is restored.

In the meantime, the control voltage for regulating the control circuit 45 is generated in that in the adding circuit 63 the nominal tension is added to a tension proportional to the spring tension. K64 represents a transfer function and shows the gain in the control loop. The value of K64 is determined according to the best investment performance selected. A value that is too small damages the positive characteristics of the controller, while a value that is too high Value for K64 can lead to instability. The control voltage is thus a function of the error voltage and the Target voltage, from which it follows that the programmed

Clock or basic control signals for the transistors 31-36 have a frequency that is used to set the frequency the inverter output voltage is used to set the target level in the steady state. Since both the amplitude and the frequency of the inverter output voltage can also be determined by the nominal voltage, these two characteristic curves have the inverter voltage has a fixed ratio to each other / if there is no fault voltage. This Relationship for the steady state can through the gain 62 can be set. A fixed ratio is desirable to prevent the engine from overheating 41 and to ensure that the motor has a constant output torque regardless of its speed gives away.

If there is a normal change in the load requirement and thus a different engine speed · for the steady-state. or constant condition, the potentiometer 59 ^{can be adjusted to:} change the setpoint voltage as far as necessary to change the control voltage as required, whereby the frequency of the · inverter voltage to a level •. is set, which is required to operate the motor 41 at the new target speed. At the same time, the new setpoint voltage changes the DC busbar voltage as necessary to maintain the same fixed ratio of amplitude and frequency of the inverter output voltage.

Although of course the engine speed can also be adjusted manually of the potentiometer 59 can be changed, the target voltage can be measured by measuring a parameter or a Characteristic of the plant-to be tapped into which the controlled inverter-motor system is built in to increase the motor speed depending on the scanned data ' to control automatically.

It should also be noted that the DC power supply (namely, rectifier bridge 10 and filter 20) in

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Can work depending on a single-phase instead of a three-phase AC voltage. In the case of single-phase operation, the line L ₃ and the semiconductor rectifiers 13 and 16 would be omitted. Of course, a voltage that is positive with respect to line 27 is still generated on line 26 on the DC voltage busbar. It should also be noted that the construction of the DC power supply and the inverter can take many different forms. For example, the aercqelte global voltage busbar could be represented by a DC voltage converter supplied by a direct voltage busbar.

If the mechanical load on the motor 41 suddenly changes without the stabilization circuit according to the invention found out, it would be the voltage of the DC voltage rail change. For the sake of explanation it is assumed that the load torque on the motor 41 suddenly drops or does not apply altogether, whereby a suddenly dropped arithmetic

20. Busbar direct current to the inverter got. The filter choke current then flows to the filter capacitor 22, which is thereby charged to a voltage which is considerably higher than the nominal busbar voltage. The tendency of the busbar voltage to rise is however according to the invention compensated that the engine speed as a function of the increasing Busbar voltage is increased so that the inverter motor system is not adversely affected and stable operation results. The invention serves practical in addition, in the event of sudden abnormal mechanical load changes on the motor 41, an electrical load on the DC voltage busbar 26, 27 maintain, which causes the busbar DC voltage to be maintained remains a relatively fixed value.

Protection against sudden or transient changes of the load torque results from the regulation of the alternating

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converter frequency so that it is a function of the busbar DC voltage and changes directly with it. When the busbar voltage is tending, when it is falling Increasing the load torque also increases the error voltage and causes the control voltage to rise, whereupon the inverter control circuit 4.5 triggers a frequency increase in its output voltage. As a result, increased The motor speed also increases and this in turn increases the electrical load on the DC voltage main rail,. ' thereby compensating for the decreased electrical load that occurred when the mechanical load was reduced is, - That is, the engine is accelerated whenever the mechanical load drops, resulting in a reduced change in the electrical load on the DC busbar appears. The error voltage then falls to zero through the control loop of the DC voltage busbar and the system works again at the frequency and voltage specified by the setpoint voltage. Of the Gain for the ratio of junction change or deviation of the busbar voltage versus the The resulting frequency deviation of the inverter is set by the gain factor K64 and can be differently and independently of the permanent gain factor 62.

Of course, when the motor 41 has a sudden increase in Load torque, which means that it has a higher electrical Load and a decreased DC bus voltage, the fault voltage drops and also causes a Drop in inverter frequency and motor speed, so that the electrical load on the DC voltage busbar drops and the busbar voltage increases. .

In the operation of the invention according to FIG. 1, the rectifier regulator is used 17 under normal continuous operating conditions to reduce the error voltage to zero. The busbar

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Internal DC voltage is then calculated with the gain factor K62 related to the nominal voltage '. Now that's the one The control voltage that determines the inverter frequency is equal to the target voltage. Therefore, the ratio of the busbar DC voltage to the inverter frequency can be set using K62. Under settling conditions is the fault voltage not zero. The degree of amplification is determined by K64 the size of the control voltage deviation from the zero value, which occurs at a given fault voltage. Thus, K64 determines the size of the frequency deviation from. Frequency value in the steady state, the under conditions occurs. The ratio of the deviation of the busbar DC voltage from the continuous setpoint to the deviation the inverter frequency from the continuous setpoint is therefore controlled by the gain factor K64. Thus, the ■ Ratio of the continuous busbar DC voltage to the inverter sequence regardless of the ratio of the busbar DC voltage deviation to the inverter frequency deviation can be set under transient conditions.

It should be noted that the invention can be embodied in various forms in order to avoid a deviation in the frequency, To achieve control voltage that is proportional to the deviation of the busbar DC voltage from its nominal value. In the exemplary embodiment in FIG. 1, transient changes in the busbar voltage result in changes in the transient error voltage, which then serve to change the inverter frequency. The stabilization device according to the invention can of course respond directly to a transient change in the busbar DC voltage. this is shown in the embodiment of FIG. In contrast The control loop is sweet in relation to the embodiment of FIG from the DC voltage busbar to the inverter, the comparison circuit 61 does not turn on. According to the embodiment of FIG. 2, a band filter 6 5 is connected upstream of K64, to eliminate any idle state effect of the control system

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switch. With this filter, the stabilization circuit only speaks to transient changes in the busbar voltage at. That is, in normal operation when the inverter-motor system is under other continuous operating conditions works, there is no voltage across the filter 65 at the adder 63 and that the inverter frequency is finally determined by the nominal voltage. However, if the busbar voltage has an undesirable transient surge experiences, this change is passed through the filter 65 to the adder 63. That is, the adder. link 63 practically not on relatively slow changes in the busbar voltage, but only on relatively addresses quick changes. The control voltage generated by the adder is therefore changed, and according to the invention, the inverter frequency is also changed to accommodate the sudden change in busbar voltage.

Every transient change in the busbar DC voltage appears naturally also as. Settling change in the motor voltage or the inverter output voltage, what is practically the same. Therefore, the invention can be used to provide a feedback loop from the AC motor 41 to create the inverter 25 in order to

25. to regulate the frequency as a function of transient surges in the inverter output voltage. This is shown in the exemplary embodiment in FIG. The three-phase voltage generated by the inverter 25 is rectified by a rectifier, resulting in a direct voltage, the magnitude of which is the same as the busbar direct voltage applied to the inverter. In addition, each Einschwingveränderung the DC bus voltage indicates as a Einschwingveränderung the output voltage of the rectifier 67. Thus it can be a DC voltage to the comparison circuit 61, and the system operates in practice as ₅ in FIG. 1.
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It is clear from this that the invention not only stabilizes the operation of an inverter motor system, but also Even the transistors of the inverter do not need to be oversized because of an increase in the busbar DC voltage is avoided depending on a sudden drop in the load torque.

In addition to the exemplary embodiments described above, others are also possible without falling within the scope of the invention to leave.

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Claims (15)

- tit - sl <rels for? <'»£ Cteretelfz- Wc U c r ~ Hc f cran la <λ £ ^v patent claims · ' Regulator for regulating one through the output voltage an inverter controlled AC motor / .5 where the inverter is powered by an adjustable DC busbar voltage is applied, which is supplied via a DC voltage busbar from a regulated DC voltage source, is applied, characterized in that it comprises the following assemblies: a device (57-59) for generating a nominal voltage for a target amplitude and a target frequency for the alternating voltage generated by the inverter (25), Devices (61, 17, 62, 64, 63, 45). For use the nominal voltage to the output voltage of the inverter with a nominal amplitude and the frequency of the Build up the inverter output voltage to a target level, - And stabilization devices (62, 61, 64, 63, 45), which in response to an undesired change in the Saitimelschiene DC voltage change the inverter frequency in order to regulate the electrical load on the DC voltage rail, so that the busbar voltage is proportionate stay constant. . ■ 2. Regulator for regulating a through the output voltage an inverter controlled AC motor, whereby the inverter is powered by a controllable busbar DC voltage is acted upon, the via a busbar from e ^ iner regulated power supply applied, characterized in that it comprises the following components: · Means (57-59) for generating a reference voltage representing a desired amplitude and time duration of a desired frequency by the inverter (25) generated AC voltage, a device (61) for comparing the nominal voltage with a voltage proportional to the busbar DC voltage Voltage to generate an error voltage that is a ". ■ -5- Is a function of the difference between the compared voltages, a device (17) for using the error voltage to build up the output voltage of the inverter (25) with the target duration amplitude, Devices (63, 45) for using the nominal voltage to build up the frequency of the inverter output voltage at a steady set level and stabilization devices (62, 61, 64, 63, 45) that • 10 as a function of a transient change in the busbar DC voltage change the inverter frequency to accommodate the electrical load on the DC busbar to be regulated in such a way that the busbar voltage remains relatively constant » 15th 3. Regulator according to claim 2, characterized in that the Stabilization devices have a control circuit (61-64, 45) from the DC voltage busbar to the inverter having. 4. Regulator according to claim 2 ,. characterized in that a Transient change in the busbar voltage is identified as a transient change in the fault voltage and in that the stabilizing devices (62, 61, 64, 63, 45) are controlled by the error voltage will. 5. Regulator according to claim 2, characterized in that the stabilizing devices ■ (62, 61, 64, 63, 45) a Filters (65) included so that they only respond to the transitional '• fluctuations in the busbar co-spanning. 6. Regulator for regulating an AC motor controlled by the output voltage of an inverter, the inverter being acted upon ^{by a controllable direct voltage busbar / which is applied via a direct voltage busbar 4} from a regulated direct voltage source, thereby marked- net that it comprises the following components: a device (57-59) for generating a target voltage, for a target amplitude and target frequency of the output voltage generated by the inverter, devices. (17, 61-64, 45) for using the target voltage in order to build up an inverter output voltage with the target amplitude and the target frequency at a target level and
Stabilizing devices (61-64, 45) with a control loop from the DC voltage busbar to the inverter in order to regulate its frequency as a function of transition changes in the DC busbar voltage and thereby compensate for the changes and generate a relatively constant busbar voltage. 7. Regulator for regulating an AC motor controlled by the output voltage of an inverter, the inverter being acted upon by a controllable busbar DC voltage which is applied via a busbar from a regulated DC voltage supply, characterized in that it has the following modules includes:
Devices (57-59) for generating a target voltage for a continuous target amplitude and a continuous target frequency of the output voltage generated by the inverter (25), a device (61) which compares the target voltage with a voltage proportional to the busbar DC voltage in order to generate a fault voltage which has a Is a function of the difference between the compared voltages, a device (17) for using the error voltage for regulating the busbar DC voltage as required, to give the inverter output voltage the continuous setpoint amplitude to impress, Devices (63, 45) for using the nominal voltage «, in order to impress the frequency with the continuous target level on the inverter output voltage, -7- (4- wherein the system has a certain degree of amplification for the steady-state steady-state conditions, which is the ratio the busbar DC voltage is determined by the inverter frequency, and. Stabilization devices (61-64, 45), which are dependent on to change the inverter frequency "from a transient deviation of the busbar DC voltage, to regulate the electrical load on the DC voltage busbar, so that the busbar voltage remain relatively constant, whereby the plant under transient conditions has an amplification factor which can be set for the steady state • independently of the gain level so that a different relationship between the deviation of the busbar DC voltage and the deviation of the Inverter frequency can be obtained. 8. Regulator for regulating a through the output voltage an inverter controlled AC motor, · whereby the inverter by .. a controllable collective. DC voltage is applied to the rail via a. Busbar from a regulated DC voltage supply supply is available,. characterized in that it comprises the following modules: Devices (57-59) for generating a target voltage which has a target amplitude and a target frequency of the Inverter (25) represents generated alternating voltage, devices (17, 61-64, 45) for using the target voltage, to build up an inverter output voltage with the target amplitude and frequency at the target level and Stabilizing devices (61-64, 45) including a control loop from the AC motor to the inverter to control the inverter frequency depending on transient changes in the inverter output voltage, to compensate for these changes and a relatively constant inverter output voltage to create. _G_ 9. Regulator for regulating an AC motor controlled by the output voltage of an inverter, wherein the inverter is acted upon by a controllable busbar DC voltage, which via a DC voltage busbar is applied from a regulated DC voltage source, characterized in that it comprises the following building blocks: Devices (57-59) for generating a nominal voltage, • the nominal amplitude and nominal frequency of the inverter (25) represents alternating voltage generated, ·. a device (61) for comparing the nominal voltage with a voltage proportional to the busbar DC voltage Voltage to produce an error voltage which is a function of the difference in the voltages compared,. a device (17), which the error voltage to. Structure of the inverter output voltage with the target amplitude is used and Devices (63, 45), which the error voltage and the Use setpoint voltage to set the frequency of the inverter output voltage to build up to the target level, whereby the fault voltage prevents the operation of the inverter motor system stabilized in that it causes a change in the inverter frequency whenever the busbar voltage experiences an undesirable change in amplitude, which reduces the electrical load on the DC voltage busbar is regulated to the busbar voltage keep the ratio constant. 10. Regulator for regulating an AC motor controlled by the output voltage of an inverter, wherein the inverter is acted upon by a controllable DC busbar voltage, which is supplied via a DC voltage busbar from a regulated DC voltage source is applied, and the amplitude of the alternating. rectifier output voltage is determined by the magnitude of the busbar DC voltage, while the frequency of the Inverter output voltage is determined by the clock pulses applied to the inverter. indicates that it comprises the following modules: Devices (57-59) for generating a target voltage, the target amplitude and a target frequency of the inverter output voltage represents . a comparison circuit (61) for comparing the target voltage with a voltage proportional to the busbar DC voltage Voltage to generate an error voltage that is a function of "the difference between the compared Tension is a regulator (17), which depends on the error voltage regulates the DC voltage supply in order to set the busbar DC voltage to the level which is required to build up the inverter output voltage with the target amplitude, an adder (63) for generating a control voltage from the error voltage and the target voltage, and an inverter control circuit (45), the periodically recurring as a function of the control voltage Sends clock pulses to the inverter (25) to generate an inverter output voltage with the desired frequency build up and thereby set a certain target level for the engine speed, where the error voltage causes the inverter frequency to move in the same direction and together with the fluctuations in the DC busbar voltage changed to increase the electrical load on the busbar regulate, whereby the busbar voltage is proportionate kept constant and the operation of the inverter motor plant is stabilized. . . -. 11. Regulator according to claim 10, characterized in that the inverter control circuit (140) and logic circuits comprises a controlled oscillator to periodically recurring clock pulses for regulating the frequency of the inverter (25) includes. 12. Regulator according to claim 10, characterized in that the regulated DC voltage supply is a phase-controlled Semiconductor rectifier bridge (10) and a filter (20) comprises in order to be removed from an alternating current network AC voltage obtained to develop a DC busbar voltage. 13. Regulator according to claim 10, characterized in that • the adder (63) contains a summing circuit to which the setpoint voltage and a voltage proportional to the error voltage is applied, both through the summing circuit ■ can be added to generate the control voltage. 14. Regulator according to claim 10, characterized in that ■ the adder (63) is responsive to relatively rapid error voltage changes generated by transient changes in the busbar voltage. 15. Regulator for regulating a through the output voltage of a Inverter controlled AC motor, whereby the inverter is powered by an adjustable busbar DC voltage is applied, which is applied via a DC voltage busbar from a regulated DC voltage source, characterized in that, that it comprises the following building blocks: Devices (57-59) for generating a target voltage which represents a continuous target amplitude and continuous target frequency of the inverter output voltage, a device (61) for comparing the target voltage with a voltage proportional to the busbar DC voltage in order to generate an error voltage which is a function of the difference between the compared tensions is,
a device (17) which uses the error voltage to build up an inverter output voltage to the continuous setpoint amplitude, «Β β a
9 "WHERE" Devices (63-45) that use the setpoint voltage to build the frequency of the inverter output voltage to the continuous setpoint level,
and means (61-64, 45) to stabilize the inverter-motor system under transient conditions by changing the inverter frequency each time the busbar voltage experiences an undesired change in amplitude, whereby the electrical load on the DC voltage busbar is regulated by the busbar voltage in proportion keep constant. -12-