JPH05252795A - Digital current controller for inverter - Google Patents

Abstract

PURPOSE:To prevent the occurrence of deviation in an inverter output current waveform by detecting the state of continuity between inverter switching elements, counting the continuity time and giving the result as a compensation signal for voltage command value. CONSTITUTION:A sensor 14 detects the state of continuity between elements at the positive polarity side of two switches connected in series of an inverter 3 and inputs a detection signal to a counter 15. The counter 15 counts the conducting time between switches by a detection signal and inputs the counted value (v) to a current control arithmetic unit (IC) 11. Therefore, the IC 11 performs the current control arithmetic operations from a current command value (i')of speed control arithmetic unit 8, a digital value (i)of an A/D converter 10 and a count value V of the counter 15 and calculates a voltage command value (v). That is, compensation calculation for dead time is performed by the current value (v) for the voltage command value obtained from the current command value (i') and the digital value (i), a final voltage command value (v') is obtained, and the voltage command value (v') is input to the PWM equipment 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a plurality of switching elements connected in series and connected in parallel to convert DC power into AC power and supply the output current of an inverter to a load. The present invention relates to a digital control device, and more particularly to a digital current control device for an inverter, which is capable of eliminating a distortion of an output current waveform of the inverter by obtaining a voltage command value having a more dead time compensation effect.

[0002]

2. Description of the Related Art In general, an inverter has been widely used as a means for driving an induction motor for an elevator, for example. This inverter is configured by connecting a plurality of sets in which a plurality of switching elements are connected in series and connected in parallel, and converts the DC power from the converter into AC power and supplies the AC power to the induction motor. Further, in this case, the inverter is usually designed to digitally control its output current by a digital current controller. FIG. 2 is a block diagram showing an example of the overall configuration of a conventional digital current control device for an induction motor inverter of this type.

In FIG. 2, the main circuit comprises a three-phase AC power supply 0 for R, S, and T and a diode.
A converter 1 for converting AC power from the DC power into DC power,
The smoothing capacitor 2 for smoothing the DC output from the converter 1 and three pairs of the smoothing capacitor 2 with two switching elements connected in series at both ends are connected in parallel to convert DC power to AC power. It is composed of an inverter 3 and an induction motor 4 which is driven by the AC power converted by the inverter 3 to rotate.

On the other hand, the digital current controller detects the rotational position by the rotation sensor 5 directly connected to the rotary shaft of the induction motor 4 and the output signal 5a of the rotation sensor 5, and outputs the position signal θ.
A position detector 6 for outputting a differentiator 7 for converting the position signal θ from the position detector 6 to the speed signal omega, the speed command value omega ^* And the speed signal ω from the differentiator 7 are input to perform speed control calculation, and the current command value i ^* A / D for converting the current value detected by the speed control arithmetic unit 8 for outputting the current value and the current value detected by the current detector 9 provided in the main circuit line of the inverter 3 and the induction motor 4 and outputting it as the digital value i. The current command value i ^* from the D converter 10 and the speed control arithmetic unit 8 And the digital value i from the A / D converter 10 are input to perform current control calculation, and the voltage command value v ^* And a voltage command value v ^* from the current control arithmetic unit 11 Is compared with the carrier signal from the carrier generation circuit 13 and outputs the gate signal of the switching element of the inverter 3 to the PWM device 12.

By the way, in such a digital current controller, in order to prevent a short circuit between the main circuits of the inverter 3,
Dead time is added to the gate signal of the switching element of the inverter 3 and the result is output. Therefore, the voltage command value v ^* Between the output voltage and the actual output voltage causes a distortion in the output current waveform.

Therefore, in order to solve such a problem, various dead time compensating devices have been proposed recently, and one example thereof is as follows. That is, in the current control arithmetic unit 11, the current command value i ^* Dead time compensation is performed by superimposing a constant voltage according to the polarity of the.

However, in the dead time compensation of such a digital current control device, although the dead time compensation effect is obtained to some extent, some distortion remains in the output current waveform at the zero cross point, and the induction motor. Nowadays, high precision control is required, but it cannot be said to be sufficient.

[0008]

As described above, in the digital current control device of the inverter having the conventional dead time compensating device, the dead time compensating effect is not sufficient and the output current waveform of the inverter is distorted. There was a problem that it would occur.

An object of the present invention is to provide an extremely reliable inverter digital current control device capable of obtaining a voltage command value having a further dead time compensation effect and eliminating distortion of the output current waveform of the inverter. To provide.

[0010]

In order to achieve the above object, according to the present invention, a plurality of sets of a plurality of switching elements connected in series are connected in parallel to convert DC power into AC power. In a device for digitally controlling the output current of an inverter supplied to a load, a current detection means for detecting the output current of the inverter and a speed command value and a speed signal of the load are input to perform a speed control calculation. And a current control calculation means for inputting the current value detected by the current detection means and the current command value from the speed control calculation means to perform current control calculation and outputting a voltage command value. PWM means for comparing the voltage command value from the current control calculation means with the carrier signal from the carrier generation means and outputting the gate signal of the switching element of the inverter, Converter provided between the switching elements of the inverter and detecting the conduction state between the switching elements, and the conduction signal between the switching elements is counted by the detection signal from the conduction detecting means, and the count value is calculated as the current. And a dead time compensating means composed of counting means for outputting to the control computing means as a compensation signal of the voltage command value. An induction motor is used as the load.

[0011]

Therefore, in the inverter digital current control device of the present invention, the conduction state between the switching elements of the inverter is detected by the conduction detecting means, and the conduction time between the switching elements is counted by the counting means by this detection signal. .. Since the count value is given to the current control calculation means as a compensation signal for the voltage command value, the actual output voltage of the inverter can be recognized, so that the voltage command value can be processed for dead time compensation. , The output current waveform of the inverter is not distorted.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing an example of the overall configuration of a digital current control device for an induction motor inverter according to the present invention. The same parts as those in FIG. 2 are designated by the same reference numerals and the description thereof will be omitted. Now, only different parts will be described.

That is, as shown in FIG. 1, the digital current control apparatus of the present embodiment is mounted between two switching elements of the inverter 3 connected in series, the switching elements having the negative polarity side, and the positive electrodes of the switching elements. The sensor 14 which is a conduction detecting means for detecting that the elements on the sex side are in the conduction state, and the conduction time between the switching elements is counted by the detection signal from the sensor 14, and the count value v
To the current control arithmetic unit 11 with the voltage command value v ^* In this configuration, a dead time compensating device including a counter 15 which is a counting means for outputting as a compensation signal is provided.
Next, the operation of the digital current control device for the induction motor inverter of the present embodiment configured as described above will be described.

In FIG. 1, the AC power converted by the inverter 3 is input to the induction motor 4 to rotate the induction motor 4. The output signal 5 a from the rotation sensor 5 directly connected to the rotation shaft of the induction motor 4 is input to the position detector 6, and the position signal θ is input from the position detector 6 to the differentiator 7. In the differentiator 7, the position signal θ is converted into the speed signal ω and input to the speed control arithmetic device 8.

On the other hand, in the speed control arithmetic unit 8, the speed command value ω ^* And the speed signal and ω perform speed control calculation,
Current command value i ^* Is input to the current control arithmetic unit 11.
The current value of the inverter 3 detected by the current detector 9 is converted from analog to digital by the A / D converter 10, and the digital value i is input to the current control arithmetic unit 11. Further, the sensor 14 detects that the positive polarity side elements of the two switching elements of the inverter 3 connected in series are in a conductive state, and the detection signal is input to the counter 15. In the counter 15, the conduction time between the switching elements is counted by the detection signal from the sensor 14, and the count value v is sent to the current control arithmetic unit 11 as the voltage command value v ^*. Is input as a compensation signal of.

As a result, in the current control arithmetic unit 11,
Current command value i ^* from the speed control arithmetic unit 8 And the digital value i from the A / D converter 11 and the count value v from the counter 15 are used for current control calculation, and the voltage command value v ^* Is calculated. That is, the current command value i ^* The dead time compensation calculation is performed by the count value v with respect to the voltage command value obtained from the digital value i and the final voltage command value v ^*. Is obtained, and this voltage command value v ^* Is P
It is input to the WM device 12.

In the PWM device 12, the voltage command value v ^* from the current control calculation device 11 is given ^. And the carrier signal from the carrier generation circuit 13 are compared, and the inverter 3
The gate signal is output to the switching element.

In this case, since the current control arithmetic unit 11 can recognize the actual output voltage of the inverter 3 by reading the count value v from the counter 15, the voltage command having a further dead time compensation effect. Value v ^* Can be calculated and distortion of the output current waveform can be eliminated.

As described above, in the present embodiment, three sets of two switching elements connected in series are connected in parallel, and the DC power from the converter 1 is converted into AC power for induction motor 4. A device for digitally controlling the output current of the inverter 3 supplied to the current detector 9, a current detector 9 for detecting the output current of the inverter 3, and an A / D converter 10 for analog / digital converting the current value from the current detector 9,
Speed command value ω ^* And the speed signal ω of the induction motor 4 are input to perform speed control calculation, and the current command value i ^* , The current value from the A / D converter 10 and the current command value i ^* from the speed control arithmetic device 8 ^. Input and to perform the current control calculation and set the voltage command value v ^* And a voltage command value v ^* from the current control arithmetic unit 11 And the carrier signal from the carrier generation circuit 13 are compared to output the gate signal of the switching element of the inverter 3, and the PWM device 12 and the inverter 3
Sensor 14 provided between the switching elements and detecting the conduction between the switching elements, and the conduction time between the switching elements is counted by the detection signal from the sensor 14, and the count value v is the current control arithmetic unit. 11 voltage command value v ^* And a dead time compensating device comprising a counter 15 for outputting as a compensation signal.

Therefore, since the sensor 14 is installed between the switching elements of the inverter 3 and the counter 15 which operates by the detection signal thereof is installed so that the current control arithmetic unit 11 can recognize the actual output voltage of the inverter 3, it is further improved. Voltage command value v ^{* with} dead time compensation effect Can be calculated, and the distortion of the output current waveform can be eliminated. As a result, it is possible to sufficiently meet the demand for highly accurate control of the induction motor 4.

In the above embodiments, the case where the present invention is applied to an induction motor inverter in which the load is an induction motor has been described, but the present invention is not limited to this, and other inverters in which the load is other than the induction motor are also applicable. The present invention can be similarly applied.

[0023]

As described above, according to the present invention, a plurality of sets in which a plurality of switching elements are connected in series are connected in parallel, and DC power is converted into AC power and supplied to a load. In a device for digitally controlling the output current of an inverter, a current detection means for detecting the output current of the inverter and a speed control calculation by inputting a speed command value and a speed signal of a load to output a current command value. A current control calculation means for inputting a current value detected by the current detection means and a current command value from the speed control calculation means to perform a current control calculation and outputting a voltage command value, and a current control calculation means. PWM means for comparing the voltage command value from the carrier signal from the carrier generating means and outputting the gate signal of the switching element of the inverter,
Continuity detection means provided between switching elements of the inverter for detecting that the switching elements are in a conductive state, and the conduction signal between the switching elements is counted by a detection signal from the conduction detection means, and the count value is calculated as a current. Since the dead time compensating means including the counting means for outputting as the compensation signal of the voltage command value to the control calculating means is provided, the voltage command value having a further dead time compensating effect is obtained to obtain the output current of the inverter. An extremely reliable inverter digital current control device capable of eliminating waveform distortion can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a digital current control device for an induction motor inverter according to the present invention.

FIG. 2 is a block diagram showing an example of the overall configuration of a conventional digital current control device for an induction motor inverter.

[Explanation of symbols]

0 ... Three-phase AC power supply, 1 ... Converter, 2 ... Smoothing capacitor, 3 ... Inverter, 4 ... Induction motor, 5 ... Rotation sensor, 6 ... Position detector, 7 ... Differentiator, 8 ... Speed control arithmetic unit, 9 ... Current detector, 10 ... A / D converter, 11 ...
Current control arithmetic device, 12 ... PWM device, 13 ... Carrier generation circuit, 14 ... Sensor, 15 ... Counter.

Claims (2)

[Claims] 1. An apparatus for digitally controlling an output current of an inverter, which comprises a plurality of switching elements connected in series and connected in parallel and which converts DC power into AC power and supplies the AC current to a load. The current detection means for detecting the output current of the inverter, the speed control calculation means for inputting the speed command value and the speed signal of the load to perform speed control calculation, and outputting the current command value, and the current detection means. A current control calculation unit that inputs a detected current value and a current command value from the speed control calculation unit to perform a current control calculation and outputs a voltage command value; and a voltage command value from the current control calculation unit. PWM means for comparing the carrier signal from the carrier generating means and outputting the gate signal of the switching element of the inverter; Provided between the device counts the conduction time between the switching element conduction detecting means and a detection signal from the conduction detecting means for detecting that between the switching elements is conductive,
A digital current control device for an inverter, comprising: a dead time compensating unit including a counting unit that outputs the count value to the current control calculating unit as a compensation signal of a voltage command value. 2. The digital current control device for an inverter according to claim 1, wherein the load is an induction motor.