JPS63287373A - Controller for power converter - Google Patents

Abstract

PURPOSE:To suppress direct current, by varying the short-circuiting-proof period of a positive side arm and a negative side arm, according to the polarity of the direct current of each phase. CONSTITUTION:An inverter 1 is PWM-controlled based on the output signal of the output signal of a micro-processor 6 which is PWM-modulated by a PWM generating circuit 5, and its output is fed to an AC motor 2. Into the processor 6, motor current is taken in every sample period via a two-phase converter 4 through the detectors 3U, 3V of the current. The processing section of the processor 6 is composed of a differentiating circuit 20, a DC component arithmetic circuit 21, a two-phase/three-phase conversion circuit 8, an output voltage command circuit 7, and adders 9U-9W. Through the difference of the two-phase AC flow of inverter output current, the scale of direct current is detected, and according to the scale, pulse width is changed, and in the output voltage of the inverter 1, DC voltage component is contrived not to be included. As a result, an output voltage distortion along with a short-circuiting-proof period can be perfectly compensated for.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a control device for a power conversion device.

[Conventional technology]

Generally, the time-averaged output voltage for each carrier period of a pulse width modulated inverter is ideal (due to the short-circuit prevention period provided to prevent the positive and negative arms of the inverter from firing at the same time). It does not produce a typical sine wave output, but has some distortion. Therefore, if an AC motor is driven with this distorted output voltage, torque ripple will occur.

A control method is known that compensates for the distortion of the output voltage of the inverter and obtains a sine wave output. The conventional control device is
For example, Japanese Patent Publication No. 59-8152, Japanese Patent Publication No. 61-1094
As described in No. 92, etc., the amount of output voltage distortion based on the short-circuit prevention period is added to the output voltage command according to the polarity of the inverter's output current, and the required sine wave output voltage is obtained from the inverter. ing.

[Problem that the invention seeks to solve]

The conventional control method improves the output waveform to an ideal sine wave by compensating for the distortion of the inverter output voltage due to the short-circuit prevention period. However, no consideration was given to the problem that the DC current on the output side increases due to the difference in the short-circuit prevention period between the positive arm and the negative arm of the inverter. When the load is an electric motor, there is a problem in that when the direct current increases, the torque ripple increases.

An object of the present invention is to provide an inverter control device that can prevent direct current from flowing on the output side of the inverter.

[Means for solving problems]

The present invention is achieved by changing the pulse width so that the maximum value or minimum value of each two-phase alternating current amount of the output current of the inverter becomes equal.

[Effect]

The actual short-circuit prevention period between the positive side arm and the negative side arm of the PWM inverter is the period obtained by subtracting the element storage time from the set short-circuit prevention period (hereinafter referred to as the actual short-circuit prevention period). The actual short-circuit prevention period differs between each arm due to the inherent characteristics of the device, and the output includes a DC voltage component.

Figure 5 shows the principle of obtaining on/off signals for the positive arm and negative arm by comparing the output voltage command for one phase and the carrier triangular wave when the short circuit prevention period is ideally compensated. A case is shown in which the actual short-circuit prevention period tdp of the positive side arm and the actual short-circuit prevention period t, ds of the negative side arm are different for each set short-circuit period tds. When tdp of the positive arm is smaller than tdN of the negative arm, the average output voltage of the positive arm becomes larger than that of the negative arm, and a DC voltage component is generated, as shown by the solid line. In order to prevent this, this can be accomplished by applying an output voltage command as shown by the broken line to cancel out this DC voltage component, and turning on signals for the positive side arm and the negative side arm shown by the broken line. Furthermore, if the load has low DC resistance, such as an AC motor, a large DC current will flow even with a small DC voltage component.

Figure 6 shows the difference between the actual short-circuit prevention period tdp of the positive arm and the actual short-circuit prevention period tdN of the negative arm, the DC voltage component Edu included in the inverter output with respect to tdu, and the DC current flowing to the load due to this DC voltage component. The characteristics of Idc are shown. The magnitude of the DC voltage component Edυ is determined by the DC power supply voltage Ed of the PWM inverter and the carrier frequencies fc and t.
It is proportional to the size of du. The DC current Idc increases in proportion to the reciprocal of the DC resistance of the load. When an AC motor is used as a load, the DC current due to the difference in the actual short-circuit prevention period between the positive arm and the negative arm flows as ild and rzd, as shown in FIG. When this is expressed on a space vector diagram, as shown in FIG. 8, the magnitude of the DC current has the effect of moving the original origin O of the space vector to 0', and can be detected from the two-phase AC flow rate. Therefore, in the present invention, each of the two-phase alternating current amounts lα and i of the output current of the inverter is
The magnitude of the DC current is detected from the difference in magnitude between the maximum values of β, i a wax and i β wax, or the minimum values, i a win and i β min, and the pulse width is changed according to the magnitude, and the inverter's This ensures that the output voltage does not include a DC voltage component. In addition, the magnitude of the DC current is detected and compensated according to the difference in the actual short-circuit prevention period between each arm, making it possible to prevent DC current, thereby reducing output voltage distortion caused by the short-circuit prevention period. Since complete compensation can be achieved, the output current of the inverter can be made into a sine wave.

〔Example〕

An embodiment of the present invention is shown in FIG.

In FIG. 1, inverter 1 is microprocessor 6
PWM control is performed based on the output signal obtained by PWM-modulating the output signal in the PWM generation circuit 5, and the output voltage is supplied to the AC motor 2. The microprocessor 6 has
Detect the current of the AC motor 2 with current detectors 3U and 3V,
This detection signal is input to the two-phase converter 4, and its output, the two-phase AC output, is taken in every sampling period.

In order to make the explanation easier to understand, in 22, the arithmetic processing contents of the microprocessor are represented by analog circuits.

The arithmetic processing section of the microprocessor 6 includes a differentiator circuit 2 that performs a differential operation on the two-phase alternating current flow taken in every sampling period.
0, a DC component calculation circuit 21 that calculates a DC component from the output signal of this differentiation circuit 20 and the two-phase AC flow rate, and a DC component calculation circuit 21 that converts the output signal of this DC component calculation circuit 21 into a three-phase AC flow rate.
A phase-to-three-phase conversion circuit 8, an output voltage command circuit 7 that calculates the output voltage of the inverter, and an adder 9U that adds the output signal of the output voltage command circuit 7 and the output signal of the two-phase to three-phase conversion circuit 8. It is composed of ~9W.

The differentiating circuit 20 includes a dead time circuit 14.15 that holds the value of the two-phase flow rate one sample period before, an adder 16.17 that adds the output signal of the open circuit during dead time, and the two-phase AC flow rate.
The output signal of this adder is input, and it is composed of a proportional gain of 18.19 having a magnitude that is the reciprocal of the sampling period Ts. Further, the DC component calculation circuit 21 includes a divider 10.11 that divides the output signal of the differentiating circuit 20 by the primary angular frequency W1.
and.

It is composed of adders 12 and 13 that mutually add the output signal of this divider and the two-phase alternating current amount.

Next, the operation will be explained.

FIG. 7 shows that the direct currents 11d and ld due to the difference in the actual short-circuit prevention period between the positive side arm and the negative side arm of the inverter 1 are
This is based on the assumption that the current flows in the AC motor 2. DC current Iud flowing through each phase.

If the positive directions of Ivd and Iwd are taken as shown in the figure, the relational expression of DC currents Izd and Izd is given by the following equation.

Therefore, the detection signal iu of the current detector 3U and 3V.

iv is given by the following formula. iu and iv represent alternating current components.

Furthermore, from iu and iv, the two-phase alternating current amounts iα and iu are expressed as follows.

These relationships can be expressed in a space vector diagram.

It will look like Figure 8. The dimensions αd and Iβd obtained by converting the DC currents Ild and Izd into the two-phase AC flow coordinate system are (1)
, is given by the following equation from equation (3).

That is, when looking at the magnitude of the direct current on a space vector diagram, it can be seen that it is a vector Idc that moves the origin O of the coordinate system of the two-phase alternating current to O-'.

As a result, the current iα in the two-phase alternating current coordinate system.

iu maximum value iamax, iβwax and minimum value icz
min.

The magnitude of each iuwin changes depending on the magnitude of the DC current. That is, the magnitude of the direct current may be detected and compensated so that the maximum value or the minimum value of the two-phase alternating current flow becomes equal. Therefore.

In the differentiating circuit 20, AC components jα and iβ of the two-phase AC quantities iα and iu are determined. Its size iαZiβ' is given by the following equation. Engineering 1 is W! , the magnitude of the flow vector i, the phase angle, and ω1 is the primary angular frequency.

In the DC component calculation circuit 21, the output signal i of the differentiating circuit 20
αt, iβ' are divided by ω1 in a divider 10.11 to obtain iα, −1β, and an adder 12.13 divides iα
, iβ, and the DC components αd and Iβd are as shown in the following equation.

Next, in order to find the magnitude of the DC current in each phase, phase 2-3
In the phase converter 8, the sum of Iαd and Iβd is 1Iud,
It is converted to Ivd and Iwd. Iud.

Ivd and Iwd are given by the following equations.

By adding compensation to the output voltage command of each phase based on the above ■υd, Ivd, and Iwd, the output voltage command as shown by the broken line in Figure 4 is obtained, and the positive side arm and negative side arm of each phase are By changing the pulse width of the arm, it is possible to suppress the DC current due to the DC voltage component due to the difference in the actual short circuit prevention period.

Another embodiment of the invention is shown in FIG.

In FIG. 2, the same parts as in FIG. 1 are designated by the same numbers, and their explanations will be omitted. The difference from FIG. 1 is that a proportional gain 22.23 and an adder 24.2 are used to compensate for the calculation error of the differentiating circuit 20 and to perform highly accurate DC current calculations.
5 was provided.

The differentiating circuit 20 differentiates the two-phase alternating current amounts iα and iβ based on the following equation.

Here, Ts is the sampling period and t is time.

Therefore, when the sampling period Ts becomes large, a correct differential value cannot be obtained and a calculation error occurs. The magnitude of this calculation error becomes an error in the magnitude of the direct current. From equation (9), jαZiβ' determined from equation (5) becomes as follows.

Ts 2 2':;-ω14t Sin ωtt+'+'-□Ts
2 2 ωzTs 丑ω+It・Cos ω1+ψ−□Divider 10.1
1, by dividing iα' and iβ' by the primary angular frequency ω1, the output signal becomes as follows.

The proportional gain 22.23 receives the output signal of the adder 16.17, has a negative magnitude, and its output signal is expressed by the following equation.

Therefore, adder 24.25 adds equation (12), which is the output signal of divider 10.11, and equation (13), which is the output signal of gain 22°23. ,i
Correctly calculate and output α. As a result, adder 12.
13, the DC current component ■αd included in iα, jβ,
Iβd can be calculated with high precision without being affected by the sampling period Ts.

Another embodiment of the invention is shown in FIG.

In FIG. 3, the same parts as those in FIG. 2 are given the same numbers, and their explanations will be omitted. The difference from Figure 2 is that PWM
This is because the generation circuit 5 is operated by the arithmetic processing of the microprocessor 6.

The PWM generation calculation circuit 30U, 30V, 30W is ■
The calculation contents are illustrated for only the phases. The output signal of the output voltage command circuit 7 is added to the output signal of the carrier triangular wave generation circuit 26 in adders 27 to 29.
The output signals of 7 are input to comparators 31 and 32. PWM
The generation calculation circuit 30U includes a comparator 31, a NOT circuit 32 that inverts the output signal of the comparator 31, and a dead time circuit 33 that delays the output signal of the comparator 31 by a predetermined time.
A dead time circuit 34 which delays the output 4F of the NOT circuit 32 by a predetermined time, an AND circuit 35 which outputs the AND of the output signal of the comparator 31 and the output 48 of the dead time circuit 34, and a NOT circuit. 32 output number 11 and dead time circuit 3
The dead time circuits 33 and 34 are configured to have variable delay times according to the polarity of the output signal of the 2-phase to 3-phase conversion circuit 8. In other words, when the output signal of the 2-phase to 3-phase conversion circuit 8 is of positive polarity, the dead time is The delay time of the circuit 34 is increased from the predetermined value. Conversely, when the output signal of the 2-phase to 3-phase conversion circuit 8 is of negative polarity, the short-circuit prevention period on the negative side is increased so that the on-pulse width of the negative side arm is narrowed. In order to do this, dead time circuit 3
3 is increased from the predetermined value.

As described above, by varying the short-circuit prevention period of the positive side arm and the negative side arm according to the output signal of the 2-phase to 3-phase conversion circuit, that is, the polarity of the DC current of each phase, the positive side and negative side The actual short-circuit prevention period of the side arms is the same, and the output of the inverter does not include a DC voltage component, thereby preventing DC current from flowing to the AC motor.

Furthermore, according to this embodiment, since there is no need to superimpose a DC bias voltage on the output voltage command, the ratio of the magnitude of the output voltage command to the magnitude of the carrier triangular wave can be close to 1.0. This has the effect of increasing the output voltage range of the inverter.

Another embodiment of the invention is shown in FIG.

In FIG. 4, parts that are the same as those in FIG. 3 are given the same numbers, so their explanation will be omitted. The difference from Fig. 3 is that the two-phase -
The output signal of the three-phase conversion circuit 8 is added to the output signal of the carrier triangular wave generation circuit 26 in adders 37-39, respectively, and the output signals are inputted to the adders 27-29. This embodiment also provides the same effects as the embodiment shown in FIG. 2.

〔Effect of the invention〕

According to the present invention, it is possible to suppress the generation of DC voltage and the DC current based on the difference between the positive side arm and the negative side arm of the short circuit prevention period of the PWM inverter.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the first embodiment of the present invention, Figs. 2 to 4 are block diagrams showing the second to fourth embodiments of the present invention, and Fig. 5 shows the output voltage of the PWM inverter. Figure 6 is a characteristic diagram showing the relationship between DC voltage and DC current for the difference in the short termination prevention period of the upper and lower arms, and Figure 7 is a waveform diagram showing the relationship between the ON signal of the upper and lower arms. FIG. 8 is an equivalent circuit diagram illustrating a state in which a DC current due to a voltage component flows through an AC motor, and FIG. 8 is a space vector diagram showing the relationship between two-phase AC amount and DC current. DESCRIPTION OF SYMBOLS 1...Inverter, 2...AC motor, 3...Current detector, 5...PWM' generation circuit, 6...Microprocessor Eto-on voltage door LT No. Figure 3

Claims (1)

[Claims] 1. A power converter that supplies alternating current with variable voltage and variable frequency; a load device that is supplied with power by the power converter; and a power converter that is provided for each phase of the power converter and that a pulse width control means for performing pulse width control based on the power conversion device; a means for detecting a direct current included in the output of the power conversion device; and a means for compensating the direct current; 1. A control device for a power conversion device, characterized in that the control device for a power conversion device is configured to compensate by changing a pulse width so that the maximum value or the minimum value of each two-phase alternating current amount of the output amount of the conversion device becomes equal. 2. In claim 1, the AC component of the two-phase AC amount is calculated based on the two-phase AC amount of the output amount of the power conversion device and the differential value of the two-phase AC amount, and the calculation result and the A control device for a power converter, characterized in that the magnitude of a direct current component included in the output of the power converter is detected by adding the two-phase alternating current amounts to each other. 3. In claims 1 and 2, a DC voltage bias signal is calculated based on a detection signal of DC current included in the output of the power conversion device, and the DC voltage bias signal and the voltage command are calculated. A control device for a power conversion device, characterized in that the direct current is compensated for by performing pulse width control based on the result of adding the signals. 4. In claims 1 and 2, a short-circuit prevention period between the positive side arm and the negative side arm of the power conversion device is set based on a detection signal of a DC current included in the output of the power conversion device. A control device for a power conversion device, characterized in that the DC current is compensated by varying the magnitude of the value. 5. Claims 1 and 2, in which the carrier triangular wave of the pulse width control means is made asymmetric based on the detection signal of the DC current included in the output of the power converter, so that the DC current is A control device for a power converter, characterized in that it compensates for current.