JPH11299245A - Control method of converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the losses caused by a switching element with its stable operation, by keeping constant the ratio of a modulating wave to a carrier, controlling the power factor at 1, and performing constant-DC-voltage control. SOLUTION: The control portion of this converter has a dead-time adjusting circuit 21 as well as a PWM control signal generator 12 and a PLL control circuit 10 including a power factor detector 9. One arm, which is connected to a phase with the minimum and maximum absolute value of a three-phase AC voltage, controls a switching element in PWM to suppress higher-harmonic currents. Also, the other two phases are commutated continuously to give to this converter a DC voltage characteristic similar to the diode-bridge converter. Then, when the DC voltage is increased, the PLL control circuit 10 detects a power-factor angle from the power supply voltage and AC current and adjusts the value of the power factor to 1. On the other hand, the dead-time adjusting circuit 21 adjusts the value of a Y-axis component from the input AC current and the power-factor angle of the power factor sensor 9 to make the vaue zero. Thereby, stable operation is maintained and the losses of the switching element can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter for converting AC power into DC power by pulse width modulation of a switching element, and more particularly to a control method of a power converter suitable as a converter.

[0002]

2. Description of the Related Art A typical example of a converter for converting AC power into DC power is a well-known diode bridge circuit. However, this diode bridge circuit has a problem that the power supply current includes many harmonics, and further has a problem that power regeneration cannot be performed because it does not have an inversion function.

On the other hand, as a converter circuit which can cope with the problem of the diode bridge circuit, for example, PW
There is an M (pulse width modulation) power converter. But this P
The WM power converter requires a control device that is unnecessary in the diode bridge circuit, and similarly, the diode bridge circuit has a problem that a switching element that does not exist in principle causes a switching loss.

Therefore, as one method for reducing such problems of the PWM power converter, a simple control method in which instantaneous current value control is omitted is disclosed in the following literature.

[0005] 1990, IEEJ Transactions D, 110, 7
No. "Power factor control type three-phase voltage type PWM power converter" The following describes the conventional technology disclosed in this document. This conventional technology converts DC power converted by a converter device into AC power of a variable frequency. FIG. 12 shows a circuit configuration diagram of the inverter device, in which 1 is a three-phase AC power supply, 2 is a converter section for converting three-phase AC to DC, and 3 is for smoothing a DC voltage. The capacitor 4 is an inverter unit. Here, converter unit 2 includes self-extinguishing type switching elements 2a to 2f.
And diodes 2g to 2l connected in anti-parallel to these switching elements. Similarly, the inverter unit 4 also has the self-extinguishing type switching elements 4a to 4f.
And diodes 4g to 4l (ells) connected in anti-parallel to the respective switching elements. The output of the inverter 4 on the AC side is connected to an induction motor 5.

[0006] Next, reference numeral 6 denotes a reactor which functions to suppress a PWM frequency component in harmonics included in the AC current, and 7 denotes an AC voltage / current detector, which is a current transformer 7a (hereinafter referred to as CT). ) And instrument transformer 7b (hereinafter referred to as PT)
8 is a DC voltage detector, 9 is a power factor detector, and 9 is a power factor based on the AC voltage and AC current detected by the AC voltage / current detector 7. The function of detecting is as follows.

[0007] Further, reference numeral 10 denotes a PLL control circuit which outputs a phase command value α for keeping the power factor constant, and 11 denotes a DC voltage control circuit which converts a DC voltage detected by the DC voltage detector 8 into a set value. 12 is a sine-wave PWM control signal generator that outputs firing (ON) / extinguishing (OFF) commands 12a to 12f for the switching elements 2a to 2f. , 13 are sine-wave PWM control signal generators on the inverter side.
firing (ON) / extinguishing (OFF) commands 13a to 4f
13f is output.

FIG. 10 shows an AC power supply voltage ER, a current IR,
A vector diagram for one phase showing the relationship between the AC reactor voltage drop EX and the converter voltage EC. If the modulation factor M is equal to or greater than the critical modulation factor MC determined by the load state, the power is always adjusted by adjusting the phase command value α. It is said that control to set the rate to 1 is possible.

When the load fluctuation on the inverter side is small, the modulation factor M may be fixed to a value close to 1, and in this case, the DC voltage control circuit 11 for adjusting the modulation factor M is not necessarily required. Is not required.

Therefore, according to the converter section 2 of the inverter device shown in FIG. 12, the higher harmonic current can be suppressed as compared with the diode bridge circuit, and the AC current control required in the ordinary PWM power converter is omitted. can do.

[0011]

In the above prior art, it cannot be said that sufficient consideration has been given to maintaining operation stability and improving efficiency, and as described below, the operation when the operation state fluctuates. And the loss of the switching element.

According to the above conventional example, the harmonic current can be suppressed more than the diode bridge circuit, and the ordinary PWM
The AC current control required in the power converter can also be omitted. However, when it is necessary to continue the operation even when the AC power supply voltage drops or becomes unbalanced, the inductance value of the AC reactor 6 is increased to suppress the overcurrent, or the element constituting the converter unit 2 There is a problem that it is necessary to increase the capacity of the component so that it can sufficiently withstand an overcurrent.

Further, in the above-mentioned prior art, the DC voltage control can be omitted. In this case, even if the load fluctuation on the inverter side is normally small, for example, it is directly connected to the AC motor of the inverter load transiently. For example, when the load torque of the applied machine suddenly increases, there is a problem that the DC voltage drop becomes large and operation becomes impossible.

An object of the present invention is to maintain continuous operation during power supply fluctuations and load fluctuations without controlling AC current and DC voltage, and to sufficiently obtain high efficiency by reducing loss due to switching elements. PWM that can be used
An object of the present invention is to provide a power converter.

[0015]

An object of the present invention is to provide a PWM power converter in which a switching element and a diode element which are antiparallel to each other are connected as one arm between a three-phase AC power supply and a DC smoothing circuit having a capacitor. In the three-phase AC power supply, for the arm connected to the phase in which the absolute value of the phase voltage is the minimum and the maximum, the pulse width modulation control of the switching element, and for the arm connected to the remaining two phases Is achieved by controlling the diode to flow in the forward conversion operation state and controlling the switching element to continuously flow in the reverse conversion state.

Although a converter circuit using a diode bridge as shown in FIG. 13 is well known, FIG.
As shown in the figure, the waveform of the AC power supply current of each phase becomes a distorted waveform far away from the sine waveform, and almost no current flows near the point where the absolute value of the phase voltage is minimum (point A).
Near the point where the absolute value of the phase voltage becomes maximum (point B), two peaks including the maximum value are formed. As a result, the harmonic component of the current causes a failure in the load, causing a serious accident. Therefore, in the present invention, for the arm connected to the phase in which the absolute value of the phase voltage is the minimum and the phase in which the absolute value is the maximum, the switching element is subjected to pulse width modulation control to reduce the flow rate of the current flowing through the switching element. Adjust to bring the current waveform closer to a sine wave.

On the other hand, the converter circuit based on the diode bridge does not control anything, but the DC voltage is automatically adjusted to be substantially constant even when the load on the DC side is suddenly changed, so that stable operation can be continued without the AC reactor. Has advantages. According to the present invention, a DC voltage characteristic close to that of a diode bridge converter circuit can be obtained by continuously arcing a two-phase arm that is not performing PWM control. As a result, when the ignition command to the self-extinguishing type switching element is completely blocked and the operation shifts to the same operation as the diode bridge converter circuit, or when the ignition command is restarted, there is almost no change in the capacitor voltage. Therefore, the operation can be continued even when the DC load suddenly changes. Further, since the two-phase switching elements of the three-phase AC power supply are continuously arc-turned, the switching operation frequency is reduced, and accordingly, the switching loss is reduced and the efficiency is improved.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment will be described with reference to FIG. The main circuit is the same as that shown in FIG.
Is shown as DC load 76. The control part is shown in FIG.
In addition to the PLL control circuit 10 including the power factor detector 9 and the PWM control signal generator 12, a dead time adjusting circuit 21 is added. It should be noted that the DC voltage detector 8 and the DC voltage control circuit 11 are described on the assumption that the load fluctuation is small, and therefore are omitted in the drawing. FIGS. 8 and 9 are diagrams for explaining the operation of the PWM control signal generator 12. FIG. FIG.
This is a pulse width modulation waveform for three phases of one cycle. For the arm connected to the phase having the minimum and maximum absolute values of the three-phase AC voltage, the switching element performs pulse width modulation control to reduce the harmonic current. Suppression is performed, and the other two phases are continuously arced to have a DC voltage characteristic close to that of the diode bridge converter circuit. FIG. 9 is a diagram illustrating the relationship between the modulated wave of the R phase and the carrier. The modulation wave and the carrier are fixed, and the modulation rate is set to 1 or more in order to continuously flow the switching element. The PWM of the S phase and the T phase is the same as in FIG.
Control.

FIG. 10 shows a vector diagram of the R phase. Here, ER is a power supply voltage vector, IR is an AC current vector, EX is a reactor voltage vector, and EC is a converter input voltage vector. In order to maintain IR at a power factor of 1, the EC vector must be on the line of A.
That is, when the load increases, the phase delay α increases and the EC vector increases, and when the load decreases, the phase delay α decreases and the EC vector decreases. In this method, since the modulation rate is fixed, for example, when the DC voltage rises, the converter input vector becomes large as in EC ', and the relation of the power factor 1 cannot be maintained. Further, for example, when the phase α becomes α ′, the voltage drop vector of the reactor becomes larger, as indicated by EX ″, and the IR becomes a current larger than the value determined by the load accordingly. Even if the relationship of 1 is maintained, the smoothing capacitor is charged except for the amount consumed by the load, and the voltage of the capacitor rises. When the load is reduced, the voltage drop of the reactance is reduced, and the EX vector is reduced. This means that since the modulation factor is fixed, the DC voltage increases as the load decreases.

FIG. 11 is a diagram showing a relationship between the converter input voltage vector EC 'and the power supply voltage vector ER, the reactance voltage vector EX and the current vector IR when the DC voltage of FIG. 12 rises. Here, the direction of the power supply voltage vector ER is defined as the X axis, and the direction of the reactance voltage drop vector EX is defined as the Y axis. In such a state, the control system of FIG. 1 controls as follows. PLL control circuit 1
0 synchronizes the converter voltage with the power supply voltage by detecting the zero crossing of the power supply voltage. The power factor detector 9 detects the power factor angle θ from the power supply voltage and the AC current, and the power factor adjusting unit 20 adjusts the phase command value α so that θ is zero (power factor 1). This corresponds to the power factor control of the X-axis direction component in FIG. On the other hand, the dead time adjustment circuit 21
Calculates the Y-axis component from the AC current and the power factor angle θ of the power factor detector 9 by the Y-axis component calculator 22, so that the dead time k is adjusted by the dead time adjustment unit 23 so that the Y-axis component becomes zero. Adjust so that The fact that the Y-axis component is zero means that
The DC voltage of the capacitor 3 is controlled to a predetermined value. FIG. 11 shows a regenerative operation vector diagram. In the case of a power running operation, the power factor angle θ is in the opposite direction.

As described above, according to the present embodiment, power factor 1 control and DC voltage constant control can be performed, so that stable operation can be continued with respect to power supply fluctuations and load fluctuations. Further, since the switching frequency is reduced, the switching loss of the switching element can be reduced, and the reactor inserted between the switching element and the AC power supply can be reduced.

A second embodiment will be described with reference to FIG. FIG.
The difference is that PT7b and CT7b are used to monitor the R-phase and T-phase voltages in order to perform the dq conversion of the PLL control.
7a, and dq conversion units 100 and 101
The point is that a DC voltage detector 8 for performing DC voltage control is provided as a countermeasure for performing a -q conversion and as a measure against a large load fluctuation. Further, the PWM control signal generator 12 includes a carrier wave unit 109, a PWM unit 108, and a modulated wave creation unit 107.
It consists of. Note that the power factor adjusting unit 20 is
5, the PI compensation unit 106 corresponds to the dead time adjustment unit 23. The converter is operated by the well-known PLL control circuit 10 while synchronizing with the power supply voltage. First, PL
In the L control, the dq converter 100 calculates an invalid component Vd from the phase voltages of the R and T phases. Next, by the phase command value θd * that makes the invalid component Vd zero in the PI compensating unit 104, si
The n / cos generator 103 generates a phase reference signal, and performs dq conversion based on the signal. On the other hand, the d-q converter 101 calculates an invalid component Id for the R-phase and T-phase currents,
The compensating unit 105 controls θ so that the ineffective component Id becomes zero and controls the power supply voltage and the AC current to have a power factor of 1. Further, the PI compensating unit 106 controls the DC voltage detector 8 so that the voltage Ed across the capacitor 3 becomes the command value Ed *.
Is performed based on the feedback signal and the invalid component Id, and the dead time is adjusted by the output k. Modulated wave creating section 107 creates a modulated wave based on output signals θ and k of PI compensating sections 105 and 106. PWM unit 10
8 is a PWM signal 12 by comparison with the carrier unit 109.
a to 12f to generate the gate terminals 2a to 2
f.

The modulated wave adjusts the dead time and phase according to FIGS. FIG. 3 shows the phase relationship between the power supply voltage, the modulated wave, and the AC current waveform, which is the state shown in the vector diagram of FIG. The alternating current has a leading phase of + θ due to the voltage drop vector of the reactor. At this time,
As shown in FIG. 4A, the phase of the modulated wave y is advanced by + θ in order to make the power supply voltage and the alternating current have a power factor of 1, and the slope is at the zero point of the modulated wave y and the negative side is the base. K is added to the slope, and k is subtracted on the plus side. k is an output signal of the PI compensator 106 in FIG. In other words, since the chopping is changed by changing the value of k, an effect equivalent to adjusting the dead time can be obtained. (B) shows another method, in which a straight line passing through a zero point and a waveform before and after advancing the phase of a modulated wave is formed, and chopping is adjusted by changing the slope of the modulated wave. As described above, according to the present embodiment, the DC voltage is fed back to adjust the dead time, so that the DC voltage constant control can be performed at a high speed with respect to a sudden load change, so that stable operation can be continued. .

FIG. 5 shows a third embodiment. In this figure, P
The output of the I compensation unit 106 acts on the carrier unit 109 to adjust the dead time. When switching the upper and lower arms of the R phase as shown in FIG. 6A, an arm short circuit occurs, an overcurrent flows, and the switching element may be damaged. Here, Ed is the voltage across capacitor 3. As a countermeasure, a dead time Td is provided as shown in FIG. 6B to prevent an arm short circuit. The same measures are taken for the S phase and the T phase.
The carrier in FIG. 9 exists in two phases without overlap as shown in FIG. 7, and generates a PWM signal by comparison with a modulated wave. At this time, the dead time is a time Td in which the carrier waves do not overlap. Therefore, DC voltage control can be realized by directly changing the dead time Td of the carrier. Here, the R phase has been described, but the S phase and T
Similar control is performed for the phases.

As described above, according to the present embodiment, the DC voltage control can be performed by directly adjusting the dead time Td of the carrier, and therefore can be easily realized without changing the system configuration. .

[0026]

According to the present invention, the modulation rate is fixed, and
PWM control with a modulation factor of greater than 1 is performed. For power factor 1 control, the phase is adjusted to make the AC current vector and the power supply voltage vector in-phase, and for DC voltage control, the size of the dead time is changed. Adjust. By performing such control, power factor 1 control and DC voltage constant control can be performed, so that stable operation can be continued with respect to power supply fluctuations and load fluctuations. Also,
Since the switching frequency is reduced, the switching loss of the switching element can be reduced, and the reactor inserted between the switching element and the AC power supply can be reduced.

[Brief description of the drawings]

FIG. 1 is a basic control block diagram showing a first embodiment of the present invention.

FIG. 2 is a control block diagram showing a second embodiment of the present invention.

FIG. 3 is a phase relationship diagram between a modulated wave, an AC voltage, and a current waveform.

FIG. 4 is an adjustment diagram of a dead time of a modulated wave according to the present invention.

FIG. 5 is a control block diagram showing a third embodiment of the present invention.

FIG. 6 shows a conventional PW applied to upper and lower arm terminals of an R phase.
M signal diagram.

FIG. 7 is a diagram illustrating a dead time adjustment by an R-phase carrier according to the present invention.

FIG. 8 is a PWM signal waveform operation diagram for one cycle of the present invention.

FIG. 9 is an operation diagram of an R-phase modulated wave and a carrier wave according to the present invention.

FIG. 10 is a conventional R-phase vector diagram.

FIG. 11 is a vector diagram showing an R-phase control method according to the present invention.

FIG. 12 is a diagram of a conventional converter / inverter device disclosed in a document.

FIG. 13 is a known diode bridge circuit diagram.

FIG. 14 is a phase current waveform diagram of a known diode bridge circuit diagram.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Three-phase AC power supply, 2 ... Converter part, 3 ... Smoothing capacitor, 4 ... Inverter part, 6 ... Reactor, 7 ... AC voltage / current detector, 7a ... Current transformer, 7b ... Measurement transformer, 8 ... DC voltage detector, 9 ... Power factor detector, 10 ... PL
L control circuit, 11 DC voltage control circuit, 12 PWM control signal generator, 13 PWM control signal generator on the inverter side, 20 power factor adjustment unit, 21 dead time adjustment circuit,
22: Y-axis component calculator, 23: dead time adjustment unit, 7
6 DC load, 100, 101 dq converter, 103
... sin / cos generator, 104, 105, 106 ... PI compensator, 107 ... modulated wave generator, 108 ... PWM unit, 109
... Carrier part.

Claims (4)

[Claims] 1. A pulse width modulated power conversion device connected between a three-phase AC power supply and a DC smoothing circuit having a capacitor by using a self-extinguishing type switching element and a diode element which are reversely connected to each other as arms. For the arm connected to the phase of the minimum and maximum of the insulation value of the phase voltage of the AC power supply, the switching element performs pulse width modulation control, and the pulse width modulation control sets the ratio between the carrier wave and the modulation wave to a constant value. In a fixed manner, the remaining two-phase connected arms are controlled so as to flow through the diode element during the forward conversion operation and through the switching element during the reverse conversion operation. The power factor angle is calculated by adjusting the phase of the output voltage of the converter by calculating the read power factor angle and performing the PLL control to make the AC power source and the power source voltage have a power factor of 1. Luo retrieves the value of the vertical component, converter control method characterized by performing a control to constant voltage DC voltage by adjusting the dead time to the vertical component to zero. 2. The method according to claim 1, wherein the dead time is adjusted.
A converter control method, characterized in that the slope of the modulated wave is changed to a slope obtained by subtracting a constant at the base slope on the plus side and changing the slope to a slope obtained by adding a constant at the base slope to the plus side. 3. The method according to claim 1, wherein the dead time is adjusted.
A converter control method characterized in that the slope of the modulated wave is changed to a slope that is a straight line connecting the points before and after the phase adjustment and the zero point. 4. The method according to claim 1, wherein the dead time is adjusted.
A converter control method characterized by changing the time difference between two non-overlapping carrier waves.