JPS63268496A - Control of potential type inverter - Google Patents

Abstract

PURPOSE:To reduce the distortion of output voltage waveform of an inverter and to prevent the inverter against the occurrence of torque ripple, by operating ON-ready compensatory voltage and adding it to a voltage command in accordance with the direction of current vector. CONSTITUTION:A compensatory voltage arithmetic circuit 7 operates compensatory voltage vector components fd and fq for compensating voltage drop by the ON-ready of a PWM inverter 1 on the rotating field coordinate from an exciting current command signal id, a torque current command signal iq and a phase reference signal omega1t from an integrating circuit 3. The output signals fd and fq are added with adders 8 and 9 to the voltage command signals v*d and v*q of the output of voltage arithmetic circuits 5 and 6.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of compensating for voltage drops due to on-delays in pulse width modulated inverters (hereinafter referred to as PWM inverters).

[Conventional technology]

In a PWM inverter, the positive side and negative side switching elements constituting the inverter are alternately controlled to be conductive to perform PWM control of the output voltage. However, since the switching element has a switching delay due to the turn-off time, a short-circuit prevention period (hereinafter referred to as on-delay) is provided to prevent the positive side and the negative side from conducting at the same time. Therefore, there is a problem in that waveform distortion occurs in the output voltage of the inverter due to the influence of on-delay.

Conventionally, as a countermeasure to this problem, as described in Japanese Patent Publication No. 59-8152, the output current polarity of the inverter is detected for each phase, and based on this polarity signal, the waveform distortion of the inverter output voltage due to the influence of on-delay is detected. A method is known in which a compensating means is provided to compensate for this. However, in this method, it is difficult to detect the polarity of the output current due to waveform distortion, so on-delay compensation is not sufficiently performed, resulting in the occurrence of torque ripple.

[Problem that the invention seeks to solve]

The above conventional technology determines the compensation voltage according to the polarity of the output current of the PWM inverter, but because it is difficult to correctly detect the current polarity due to waveform distortion near zero of the output current, the compensation voltage is not determined correctly and the output There was a problem in that the voltage waveform was not a sine wave and torque ripple occurred. Also.

The hardware configuration is complicated because it is necessary to detect the polarity of the output current of the inverter.

An object of the present invention is to compensate for the output voltage waveform distortion of a PWM inverter using a method that does not directly detect the polarity of the output current, and to make the output voltage waveform a sine wave.

[Means for solving problems]

The above purpose is based on the direction of the current vector of the AC motor.
The compensation voltage for the voltage drop due to on-delay is determined by the coordinate reference signal ω1 of the rotating magnetic field coordinate system and the current reference signal i 41
．． This can be achieved by calculating from "Lq" and adding it to the voltage command.

[Effect]

In the conventional on-delay compensation for output voltage waveform distortion, the compensation voltage was determined based on the polarity of the output current of the inverter. However, as shown in Figure 10, the output current of the inverter has a large waveform distortion, which makes it difficult to correctly detect the current polarity due to the current detection error near zero. However, distortion torque ripple occurs.

Therefore, if the on-delay compensation voltage is calculated from the current reference signal of the rotating magnetic field coordinate system and the coordinate reference signal, the above-mentioned problem can be avoided since there is no need to detect the polarity of the output current (eliminating the output voltage waveform distortion). Figures 11 and 12
The principle of calculating the compensation voltage to be added to the voltage command in the rotating magnetic field coordinate system will be explained using the drawings. FIG. 11 shows the characteristics of on-delay voltage drop with respect to the output current of the inverter.

From this characteristic, the voltage drop Vzu depends on the polarity of the inverter output current, that is, the motor current 1u, and is almost constant with respect to its magnitude. Therefore, the compensation voltage for compensating the voltage drop has a rectangular waveform related to the polarity of the output current. Becomes the property of FIG. 12 shows (a), (b), and (c) the compensation voltage Vfi.
This is a waveform when u, Vffiv, and Vffilf are approximated as complete rectangular waves depending on the current polarity. Compensation can be achieved by adding these compensation voltages to the voltage command (sine wave) of each phase, but the compensation voltage includes a zero-phase component shown in (e) in the same figure, which is unrelated to the generation of harmonic current. Therefore, by subtracting it, the compensation voltages shown in (f), (g), and (h) of the same figure are obtained. Even if this voltage is added to the voltage command (sine wave) of each phase, the on-delay voltage drop can be similarly compensated for. Such a compensation voltage can be calculated from the current command signal (DC signal) in the rotating magnetic field coordinate system and the coordinate reference signal as described later, so it is possible to perform compensation by adding this to the original voltage command. can.

〔Example〕

Hereinafter, an embodiment of the present invention will be explained with reference to FIG. 1.6 In FIG. It is an induction motor connected. 3 is an integrating circuit for commanding the phase reference ω1t from the primary angular frequency command ω16 of the induction motor 2; 4 is an oscillator that outputs a sine wave signal with a constant amplitude and a frequency proportional to the output signal from the integrating circuit 3; , its output signal is applied to the coordinate converter 10.

5 is a voltage calculation circuit that outputs a voltage command Va'' for the electric motor 2 in response to the excitation current command signal id, and 6 is a voltage calculation circuit that outputs a voltage command Vl for the electric motor 2 in response to the torque current command signal iq*. 7 is a compensation voltage vector for compensating the voltage drop due to on-delay of the PWM inverter 1 on the rotating magnetic field coordinates from the excitation current command signal idl, the torque current command signal j-, and the phase reference signal ωt from the integrating circuit 3. 8 is an adder that adds the output signal vd* of the voltage calculation circuit 5 on the rotating magnetic field coordinate system and the output signal fa of the compensation voltage calculation circuit 7; 9 is the rotating magnetic field an adder that adds the output signal vq* of the voltage calculation circuit 6 on the coordinate system and the output signal fq of the compensation voltage calculation circuit 7; 10 is the output signal Va''+ of the adders 8 and 9;
fa and vq+fq are converted from the rotating magnetic field coordinates to the stator coordinate voltage command Vu”p based on the output sine wave signal of the oscillator 4.
A coordinate converter 11 is a switching element that composes the PWM inverter 1 and compares the output signal Vll"t VV"j v- of the coordinate converter 10 with a carrier signal for pulse width modulation. This is a PWM pulse generation circuit that generates a PWM signal to turn on and off the .

The basic operation of this embodiment is as follows. As is well known, this control method is a control method for the induction motor 2 called vector control using a PWM inverter, in which the excitation current command signal i- and the torque current command signal iq* in the rotating magnetic field coordinate system are used.
The voltage commands V −, V q” of the induction motor 2 are calculated from , and the voltage commands are converted from the rotating magnetic field coordinate system to the stator coordinate system based on the output sine wave signal of the oscillator 4 to obtain a sinusoidal voltage command Vu”. , Vv", and V- with the carrier signal to control the output voltage of each phase according to the PWM signal obtained. On the other hand, the voltage drop due to the on-delay of the PWM inverter 1 is compensated by the compensation voltage in the rotating magnetic field coordinate system. Feedback is compensated by the signal from the arithmetic circuit.

Next, a method of compensating for voltage drops due to on-delay in the rotating magnetic field coordinate system will be explained with reference to FIGS. 2, 3, 4, and 5.

The on-delay compensation voltage of ° in the rotating magnetic field coordinate system can be determined based on the compensation voltage in the stator coordinate system. Compensation voltages Vzu, V□v, and Viw in the stator coordinate system are converted from three-phase to two-phase, and the magnitudes fα and fβ on the α-β axis are determined by the following equations.

Here, X represents the magnitude of the on-delay voltage, and Sfn represents the polarity of each phase current of the induction motor 2.

Figure 2 shows the compensation voltage V for three phases according to the calculation formula (1).
zu, Vzvp Compensation voltage fα for two phases of Vzw.

The waveforms of various parts when converted to fβ are shown. Further, FIG. 3 shows fα and fβ in a space vector diagram. Third
In the figure, the composite vector of fα and fβ is 1 in the μ° direction.
A total of 6 points (A, B, C, D) every π/3 for ~■
, E, F). Each point of this composite vector is shown in correspondence with FIG. As a result, it can be seen that the composite vector can be found as six points because the values of fα and fβ change every π/3. Note that the maximum value y of the composite vector can be calculated from equation (1), and is 4/3
It becomes x.

In this way, the compensation voltage on the α-β axis is in the μ° direction 1~■
It is calculated as 6 points for .

Therefore, from the above conditions, the direction of the current vector μ0 (■ ~
Compensation voltage f, + in the rotating magnetic field coordinate system for
, fq are shown in FIG.

Therefore, in order to compensate for the on-delay voltage of the PWM inverter in the rotating magnetic field coordinate system, according to the direction of the current vector μ0 (ω1 is 10), from the CO3, SIN table (BIAS(N); N = each section center phase angle) −
By reading the value corresponding to (ω1 = 10) and adding it to vq*, linearization of the PWM inverter can be achieved.

FIG. 5 is an operational waveform of the on-delay compensation voltage according to the present invention. On the rotating magnetic field coordinate system, the current vector μ° direction (ωl
When the compensation voltages fd and fq calculated according to t10) are converted to the stator coordinate system, the compensation voltages for three phases VfuP
+ vp HV□, it is possible to obtain l.

FIG. 6 is a specific configuration diagram of the compensation voltage calculation circuit of FIG. 1. In FIG. 6, 12 is the torque current command signal iq
13 is an arctangent circuit that calculates the direction θ of the current vector μ from the output signal of the divider 12; 14 is the output signal θ of the arctangent circuit 13;
An adder 15 adds the primary speed ω1t of the induction motor 2 and outputs a signal (ω1t+0) in the direction of the current vector μ−, and 15 represents the output signal (ωit+O) of the adder 14 and the on-delay compensation voltage f, + ROM circuit that stores the relationship between
6 is a ROM circuit that stores the relationship between the output signal (ω1t+fJ) of the adder 14 and the on-delay compensation voltage f.

Compensation for voltage drop due to on-delay is performed as follows. Torque current command signal iq* in the rotating magnetic field coordinate system,
Direction of current vector μ based on excitation current command signal id* and primary phase angle ω1t of motor 2 (ω1 is 10)
, and correspondingly calculate the compensation voltages fa and fq in ROM.
Read from the table and obtain the voltage command V d ” HV q
In this way, the on-delay is compensated by forward control according to the direction of the current vector μ, so the output voltage becomes a sine wave and the generation of torque ripple can be prevented.The above is done using a microprocessor. This can be realized by the arithmetic processing shown in FIG.

The operation will be explained below. In block 7a, the direction O of the current vector μ in the rotating magnetic field coordinate system is calculated.

In block 7b, the direction of the space vector is divided into six sections, and the central angle θk of the section where the current vector exists is determined. In block 7c, the compensation voltage existing on the phase angle of the center of the section is projected onto the rotating coordinate, and each axis component element d,
Calculate fq. In block 7d, compensation voltage components d,
Add fq. On-delay compensation can be achieved by performing the operations in blocks 7a to 7d above.

As described above, since the voltage drop due to on-delay is compensated according to the direction of the current vector μ on the rotating magnetic field coordinate system, it is not affected by the waveform distortion of each phase current of the motor 2 as in the conventional case. Torque ripple can be prevented from occurring. Further, since the compensation voltage is calculated according to the direction of the current vector μ, there is no need to detect the current of the induction motor 2, and therefore the hardware configuration is simplified.

FIG. 8 shows another embodiment of the present invention. Components that are the same as those in FIG. 1 are given the same numbers, so their explanation will be omitted. The difference from FIG. 1 is that the on-delay compensation voltage is added to the voltage command in the stator coordinate system.

20 converts the output signals fv and fq of the compensation voltage calculation circuit 7 into a compensation voltage vzup l vzvp tVtwp from the rotating magnetic field coordinate to the stator coordinate based on the sine wave signal of the oscillator 4.
Coordinate converters 21 to 23 convert output signals Vu'', Vv'', VIF'' of the coordinate converter 10 and the coordinate converter 20
This is an adder for adding the output signals VfuP, HVF, and HViWP of respectively f. Even if the on-delay compensation voltage is converted from the rotating magnetic field coordinate system to the stator coordinate system and added to the voltage command in the stator coordinate system, the generation of torque ripple can be prevented in the same way as in the above-described control.

FIG. 9 shows another embodiment of the present invention. Components that are the same as those in FIG. 1 are given the same numbers, so their explanation will be omitted. The difference from FIG. 1 is that a control loop for excitation current and torque current is provided. 25 to 27 are current detectors for detecting the primary currents lu Hly and i (output current of the inverter 1) of the U-phase, ■-phase, and W-phase of the induction motor 2; 28;
29 is a coordinate converter that converts the output signals of the current detectors 25 to 27 into two-phase signals of two current components it and iq in the rotating magnetic field coordinate system of the motor 2, and 29 is an excitation current command value i- and a coordinate converter 28 30 is an adder that outputs a deviation signal between the torque current command value iq and the output signal iq of the coordinate converter 28; 31 is an adder that outputs a deviation signal between the output signal i of the adder 29; Accordingly, voltage command value vd* of electric motor 2
32 is a torque current control unit that outputs a voltage command value vq* of the electric motor 2 according to the deviation of the adder 30.

By providing the excitation current and torque current control loops in the rotating magnetic field coordinate system, each actual current value can be accurately controlled to match each current command value. Even in that case, the compensation voltage can be calculated and compensated in the same manner as in FIG. 1 using each command value or actual value. In this case as well, as described above, since the instantaneous value (detected value) of the motor current is not used, it is not affected by current waveform distortion.

〔Effect of the invention〕

According to the present invention, since the on-delay compensation voltage is calculated according to the direction of the current vector μ- and added to the voltage command, the distortion of the output voltage waveform of the inverter is reduced and the occurrence of torque ripple can be prevented.

Furthermore, since the instantaneous detected value of the motor current is not used, the compensation voltage can be calculated correctly without being affected by waveform distortion.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram of a PWM inverter device showing an embodiment of the present invention, FIGS. 2 to 5 are diagrams for explaining the present invention in detail, and FIG. 6 is the compensating voltage calculation of FIG. 1. A circuit configuration diagram of the circuit, FIG. 7 is a flowchart of the calculation processing contents when the calculation in FIG. 6 is performed by a microprocessor, FIGS. 8 and 9 are other embodiments of the present invention, and FIGS. The figure is a diagram for explaining the present invention in detail. 1... PWM inverter, 2... induction motor, 3...
... Integral circuit, 4... Oscillator, 5, 6... Voltage calculation circuit, 7... Compensation voltage calculation circuit, 8, 9... Adder, 10... Coordinate converter, 11...・PWM generation circuit,
12...Divider. 13... Arctangent circuit, 15.16... ROM circuit,
25-27... Current detector, 28... Coordinate converter,
29.30... Adder, 31... Excitation current control section,
Figure 2 Figure 3 Figure 4 Figure 4 Figure 1 Theta Figure 11 Mountain

Claims (1)

[Claims] 1. A voltage source inverter that supplies alternating current of variable voltage and variable frequency to an alternating current motor, and two current component command values i_(d^*) and i_(q^*) of the rotating magnetic field coordinate system of the alternating current motor.
); an arithmetic circuit that outputs two voltage component command values v_(d^*) and v_(q^*) of the AC motor; and an arithmetic circuit that outputs the output signal of the arithmetic circuit in the stator coordinate system. A device comprising a coordinate converter that converts the voltage command into a voltage command, and a PWM control circuit that controls the output voltage of the voltage source inverter based on the output signal of the coordinate converter, wherein the current in the rotating magnetic field coordinate system of the AC motor is Component command value i_(d^*
) and i_(q^*) and the coordinate reference signal ω_1t of the AC motor to calculate the on-delay compensation voltage of the voltage source inverter and add it to the voltage command value of the rotating magnetic field coordinate system of the AC motor. A method of controlling a voltage source inverter characterized by: