JPS62254662A - Control device of power converter - Google Patents

Abstract

PURPOSE:To generate high quality AC, by imparting a frequency command signal, DC intensity, the intensity of AC flowing through a load and its polarity to the control part of a power converter, and controlling ON/OFF of the power converter in correspondence with the amount of the current. CONSTITUTION:A power converter drives a PWM type inverter with DC, which is obtained by rectifying AC, and supplies AC to a load. A DC level IDC, a current signal IU flowing through a load and a frequency command signal 17 are inputted to the control part of a the power converter. The frequency command signal 17 is inputted to a PWMsignal generating part 18 and a voltage- polarity judging circuit 19. The DC level of current level IDC is judged by a DC-level judging circuit 21. When the value is small, a selector 22 selects the voltage polarity judging circuit 19. When the current starts to flow, the selector 22 selects the current polarity jduging circuit 20. A shortcircuit preventing period is formed by a short-circuit-preventing. period forming circuit 23 and added to the selected signal. The result and the PWM signal 18 undergo logic operation 24. Pulses UP and UN, which drive the positive and negative sides of the PWM signal, are outputted. Thus the high quality AC close to a sine wave is supplied to the load.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a power converter that converts direct current (DC) to alternating current (AC), in which a pure sine wave current is applied to the AC side.

The present invention relates to a control device for a power converter that conducts voltage.

[Conventional technology]

Figure 4 is, for example, a connection diagram of a control device for a power converter used as a motor control device, which was presented in the ``Power Semiconductor Elements, Forward Conversion, Chopper 9 Inverter, and Power Applications'' section of the 1981 National Conference of the Institute of Electrical Engineers of Japan. It is.

In the figure, 1 is a 3-phase AC power supply, 2 is a 3-phase rectifier using a diode bridge connected to the 3-phase AC power supply, and 3 is a 3-phase rectifier connected to the 3-phase AC power supply.
A smoothing capacitor 5 smoothes the output voltage of the phase rectifier 2, a transistor inverter 5 supplies three-phase AC power to the induction motor 6, and a period td 10 prevents the transistors in the upper and lower arms of the transistor inverter 5 from firing at the same time. (hereinafter referred to as short circuit prevention period td)
7 is a correction circuit; 7 is a base amplifier circuit that supplies a base current to the inverter 5; 9 is a control circuit.

FIG. 5 is an explanatory diagram of the td correction circuit 10 in FIG. 4. In FIG. 5, 11 is a voltage detection circuit, 12 is a td
The creation circuit 13 is a td correction circuit.

The td generation circuit 12 includes a first td generation circuit 12a and a second td generation circuit 12C having an inverter 12b on the input side. Further, the td correction circuit 13 has inverters 13a and 13b on one input side, respectively.

13d, an integrator 13e for adding/subtracting and integrating the outputs of the AND gates 13C and 13d, and a comparator 13f provided on the output side of the integrator 13e.

Figure 6 is an analog representation of the waveform generated by a general PWM transistor inverter.
is a frequency command signal, the amplitude represents the output voltage value, and the period represents the output voltage period (frequency).

The VTR uses a triangular wave to determine the conduction angle (conduction angle) of the output transistor, and if VRy (No. 8 and the VTR signal are compared to obtain the conduction angle signal), the conduction angle (conduction angle) of the positive transistor T is Tau and negative transistor T
The conduction angle of - becomes TRU-.

By the way, since normal transistors have a switching delay, td is provided so that the upper and lower transistors do not become conductive at the same time. UP81 shows this situation.
, Ups2, the conduction angle of the positive transistor 1T is Upst, and the conduction angle of the negative transistor is UP82.

Now, the conduction angle of a PWM circuit is usually determined by the polarity of the load current. Therefore, if the current flows in the direction shown by the solid line in Figure 5 (in the area where the load current is positive), the conduction angle of the transistor is UP81, and the current flows in the direction shown by the dotted line (in the area where the load current is negative). When it flows, it looks like Up82 K
Become.

Therefore, when the output voltage is expressed equivalently, as shown in Fig. 5(b), the command voltage (dotted line) is a step-like DC voltage [2 The waveform shown by the dashed dotted line (FIG. 6(b)) is superimposed once and has a circular shape, resulting in a waveform shown by the dashed dotted line.

FIG. 7 is a signal waveform diagram of each part in FIG. 5 to explain the operation, (a) is the input (g A,
f output signal B, (c) is the output signal T of the first td generation circuit 12a, (d) is the output signal T-1 of the second td generation circuit 12e, (e) is the detection signal of the voltage detection circuit 11 V
, (f), the output signal Δv1(g) of the integrator 13e is a current flowing from the transistor inverter 5 to the load.

Now, suppose that the voltage detection circuit 11 outputs the detection signal V shown in FIG.
Since the AND gate 13C performs AND logic with the inverted signal inverted through the integrator 13e, the integrator 13e starts integrating.

Next, at the timing of T2,
Since neither C nor 13d is output, the integrator 13e stops integrating. Ando at the timing of T8) 13d
Since the output from the integrator 13e starts subtraction. Then, at the timing of T4, Ando again)
Both 13c and 13d have no output and stop subtraction.

When one integrator 13e operates as described above, the integrator output has a waveform as shown in FIG. 7(f).

Therefore, the output signal ΔV of the integrator 13e is
When multiplied by 3fK, the output signal B of the comparator 13f corrects td and becomes Tahalus, as shown in FIG. 7(b).

If td is created from the output signal B of this comparator 13f and used as the base signal of the transistor, the conduction angle of the positive side transistor is the output signal T+ of the first td creation circuit 12a.
become that way. This conduction angle is exactly equal to the TRU signal as shown in the waveform of FIG. 6(a), and the total output is the corrected td.

[Problem that the invention seeks to solve]

Since the conventional power converter control device is configured as described above, by creating td and correcting td by detecting the inverter voltage, it is possible to control the inverter output current without distortion. , which attempts to control the motor, which is the load, so that it does not cause unstable operation, but by increasing the switching frequency of the main transistor,
When increasing the PWM modulation frequency, the voltage detection circuit 11
There were problems such as poor responsiveness and complicated circuitry.

This invention was made to solve the above-mentioned problems, and provides a stable sine wave current no matter how high the PWM modulation frequency becomes, thereby ensuring stable operation of the power converter. The purpose is to obtain a control device for a power converter.

[Means for solving problems]

A control device for a power converter according to the present invention includes a voltage polarity signal that gives an AC voltage polarity to a power converter, an amount of DC current flowing between a DC power source and a pulse width modulation type power converter, and an amount of DC current flowing between the power converter and a load. The power converter is equipped with means for determining the conduction polarity of the power converter in accordance with the current polarity of the alternating current flowing through the power converter.

[For production]

For example, the power converter control device of the present invention determines the polarity of the transistor that conducts based on the voltage polarity when the current of the motor, which is the load, is very small, and determines the polarity of the transistor that conducts based on the current polarity when the load becomes heavy. decide, and
By determining whether a light load or a heavy load is determined by the DC current flowing between the DC power supply and the power converter, a highly stable sine wave current can be supplied to the load no matter how high the PWM modulation frequency becomes. This has the effect of not only ensuring stable operation of the power converter but also reducing hysteresis loss when the load is an electric motor.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. 1, in which the same parts as in FIG. 4 are denoted by the same reference numerals.

In FIG. 1, 4 is a DC current detector that detects a DC current flowing between a DC power source produced by rectifying a three-phase AC power source and a transistor inverter 5 as a power converter;
16 is an alternating current detector that detects the alternating current of each phase flowing through a three-phase induction motor as a load; T is a base amplifier circuit; and 9 is a control circuit.

FIG. 2 is a diagram showing details of the control circuit 9. In FIG. 2, 17 is a frequency command section, and 18 is a frequency command section 1.
Frequency command signal from 7 #) Create PWM signal P
WM signal generation section, 19 is a voltage polarity discrimination circuit for discriminating voltage polarity from the frequency command signal from the frequency command section 17; 20 is a polarity discrimination circuit for discriminating the polarity of the alternating current of the motor; A DC current level determination circuit for determining the level, 22 is a DC current level determination circuit 21
23 is a short-circuit prevention period creation circuit that sets a short-circuit prevention period for the current or voltage polarity signal, 24 is a logic circuit section that logically processes the PWM number and polarity signal and sets the firing timing of the transistor.

The portions indicated by dashed lines are the V and W phase circuit sections, respectively, and have the same circuit configuration as the U phase.

Next, the operation of the embodiment having the above configuration will be explained with reference to FIGS. 2 and 3.

For example, if the PWM inverter 5 wants to output a voltage as shown in FIG. 3(a), the output from the voltage polarity determination circuit 19 will be as shown in FIG. 3(C). The current flowing through an induction motor usually lags (during power running) and advances (during power running).
(during regeneration) Since it is mostly a load, there is a difference between the voltage phase and current phase.

Therefore, assuming a lagging load, the current flows as shown in FIG. 3(b). Therefore, the signal output from the current polarity determining circuit 20 is as shown in FIG. 3(d). By the way, P
WM) The signal that determines the conduction phase of the lunge transformer 5 should be selected essentially based on the current polarity, as shown in FIG. 6 above.

However, when the induction motor 6 is under no load, almost only the no-load excitation current flows as the motor current, so a high-performance current detector is required to detect the alternating current polarity. becomes impossible to distinguish.

Therefore, when the motor current is very small, the signal from the DC current level determiner 21 causes the analog switch 22 to select the voltage polarity signal.

Then, since the PWM (PWM) range inverter 5 performs switching using a voltage polarity signal which is a self-oscillation signal, the inverter 5 operates even in a no-load state.

When a certain amount of current begins to flow, the analog switch 22 is operated to select the voltage polarity signal. Then, regardless of the load condition of the induction motor 6, the PWM tractor/
The register parter 5 operates stably. FIG. 3(e) shows this situation, and FIG. 3(f) shows the PWM signal when the current polarity is selected.

In addition, the short-circuit prevention period td stage setting in the short-circuit prevention period creation circuit 23, PWM at the time of polarity switching) The upper and lower arm transistors (+ and - transistors) of the lunge inverter are for preventing short circuits. el has little effect on waveform distortion.

Further, although the embodiment has shown a transistor inverter, the same effect can be obtained even if the inverter is configured with other switching elements such as a thyristor.

〔Effect of the invention〕

As described above, according to the present invention, when the load is very light, the signal that determines the conduction phase of the transistor of the PWM (transistor inverter) determines which transistor conducts based on the voltage polarity, and when the load is normal or heavy, the signal determines the conduction phase of the transistor. Since the configuration is configured such that the transistor to be made conductive is determined, it is possible to supply a high-quality sinusoidal current to the load and reduce switching loss and pace amplifier circuit loss.

[Brief explanation of drawings]

Fig. 1 is a connection diagram of a power converter to which a control device according to an embodiment of the present invention is applied, Fig. 2 is a block diagram showing the configuration of the control device, and Fig. 3 is for explaining the operation of Fig. 1. Fig. 4 is a connection diagram of a power converter using a conventional control device, Fig. 5 is a block diagram of a short-circuit prevention period correction circuit, Fig. 6 is an explanatory diagram of inverter operation, Fig. 7 This figure is a signal waveform diagram for explaining the operation of FIG. 4. 2 is a DC power supply (3-phase diode bridge), 5 is a power converter (transistor inverter), 4 is a DC current detector, 6 is a load (3-phase induction motor), 16 is an AC current detector, 11 is a frequency command 18 is a PWM Gi number creation part, 19 is a voltage polarity determination circuit, 20 is a 11th current polarity determination circuit, 21 is a DC current level determination circuit, 22 is an analog switch, 23 is a short circuit prevention period creation circuit, 24 is a Logic circuit section. In addition, in the figures, the same reference numerals indicate the same or equivalent parts. Patent applicant: Mitsubishi Electric Corporation (2 others)

Claims (1)

[Claims] In a control device for a power converter that converts direct current into alternating current by sequentially conducting the switching elements of a power converter using a pulse width modulation method configured by connecting a plurality of switching elements in a bridge connection, a DC current level determination circuit that determines the level of the DC current flowing through the power converter, an AC current polarity determination circuit that determines the polarity of the AC current flowing from the power converter to the load, and a voltage polarity determination circuit that determines the voltage polarity from the frequency command signal. a circuit, a selection means for selecting whether to use the voltage polarity determination circuit or the alternating current polarity determination circuit based on a signal from the DC current level determination circuit, and a circuit selected by the selection means. A short-circuit prevention period creation circuit that sets a short-circuit prevention period in an output signal, and a PWM signal created from the frequency command signal and the output signal of the short-circuit prevention period creation circuit are logically processed to set the firing timing of the switching element. A control device for a power converter, characterized by comprising a logic circuit.