JPH0783600B2 - Power converter control circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a control circuit of a power conversion device configured to control a DC output voltage at a constant level and to control an input current to be in phase with a power supply voltage. Is.

[Conventional technology]

Figure 9 shows, for example, the 1994 National Meeting of the Institute of Electrical Engineers, No.6
(547) is a block diagram showing a control circuit of a conventional power converter shown in "Examination of control characteristics of PWM converter". In the figure, 1 is a power converter, and in this embodiment, a PWM converter (hereinafter simply referred to as a converter ) 1 is used.
2 is an AC filter reactor provided on the AC input side of the converter 1, 3 is an AC power supply for supplying a power supply voltage V _S and an input current I _S , 4 is a DC filter capacitor provided on the DC output side of the converter 1, 5 Is a load, 6a is a power supply voltage V _S detection circuit, 6b is a DC output voltage V _D detection circuit, 6c is an input current I _S detection circuit, and 6d is a load current I _L detection circuit. Ten
1-119 (excluding 10,105,106,110,117,118) intended to constitute a control circuit, 101 is a reference voltage generating circuit is a reference voltage V _DR generated, 102 and a detection value V _D of the reference voltage V _DR and the detection circuit 6b A subtractor that subtracts to obtain a voltage deviation value, 103 is a voltage control circuit that outputs a voltage control signal according to the voltage deviation value, and 119 is a feedforward signal obtained by multiplying the detection value I _L of the detection circuit 6d by a constant K _L. A feedforward control circuit for generating, 107 is an adder for adding the voltage control signal and the feedforward signal to obtain a peak value command I _m of the input current, 10
8 is a sine wave generation circuit that generates a sine waveform sin θ in phase with the power supply voltage V _S based on the detection value V _S of the detection circuit 6a, and 109 is an input current obtained by multiplying the crest value command I _m and the sine waveform sin θ. A multiplier for obtaining the command value I _SS , 111 is a subtracter for subtracting the detection value I _S of the detection circuit 6c and the input current command value I _SS to obtain a current deviation value, 1
12 is a current control circuit that outputs a current control signal according to the current deviation value, 113 is an adder that adds the detection value V _S of the detection circuit 6a to the current control signal to compensate for disturbance of the power supply voltage V _S , 115 is, for example, A carrier wave generating circuit for generating a carrier wave such as a triangular wave, 114 compares the output of the adder 113 with the carrier wave, and the converter 1
A PWM modulation (pulse width modulation) circuit that determines the switching time of a switching element (not shown) that constitutes
The drive circuit drives the converter 1 according to the output pulse width of the PWM modulation circuit 114.

Next, the operation will be described. The converter 1 converts the input AC power into DC power and supplies it to the load 5. The capacitor 4 is provided for smoothing to absorb the fluctuation of the DC output voltage V _D of the converter 1. The control circuit controls the DC output voltage V _D so as to match the reference voltage V _DR, and also makes the input current I _S a sine wave in phase with the power supply voltage V _S , with a power factor of 100% and a harmonic. Performs control with few waves and low distortion. In order to keep the DC output voltage V _D constant, the voltage control circuit 103 outputs a voltage control signal for correcting the peak value of the input current I _S. If the response of this voltage control is slow, the control becomes impossible when the DC output voltage V _D obtained at the capacitor drops sharply.
In 7, the feedforward signal having the value of K _L I _L is applied to the voltage control signal so that the peak value command I _m can respond instantaneously. Input current command value I
_{The SS} is obtained in the multiplier 109 by multiplying the peak value command I _m by the power supply voltage V _S and the in-phase sine waveform sin θ. This input current peak value I _SS is subtracted from the input current I _S in the subtractor 111 to obtain a current deviation value, and the current control circuit 112 follows this current deviation value and outputs it as a current control signal. This current control signal is supplied to the PWM modulation circuit 114 after the disturbance due to the power supply voltage V _S is compensated by adding the power supply voltage V _S in the adder 113. The PWM modulation circuit 114 is
A PWM having a pulse width corresponding to the voltage deviation value and the current deviation value is obtained by comparing the disturbance-compensated current control signal with a carrier wave such as a 1-2 KHz triangular wave from the carrier wave generation circuit 115.
A signal is output and supplied to the drive circuit 116, and the drive circuit 116 controls switching of the switching element of the converter 1 in response to this.

[Problems to be solved by the invention]

Since the control circuit of the conventional power converter is configured as described above, that is, in order to prevent the control circuit from becoming uncontrollable due to a drop due to a sudden change in the DC output voltage V _D , the load current I _L
Since the input current command value I _SS is obtained by adding the detected value of 1 to the voltage control signal as a feedforward signal, the load current I _L is considerably large when the load 5 is a single-phase inverter or the like. Although with ripples, the ripples to appear in the input current command value I _SS, harmonics of the input current waveform I _S of the converter 1 has a problem such as increasing.

The present invention has been made in order to solve the above problems, and obtains a control circuit of a power conversion device capable of improving a decrease in a DC output voltage due to a sudden change of a load and reducing an influence of a ripple of a load current. The purpose is to

[Means for solving problems]

The control circuit of the power conversion device according to the present invention obtains an average value of the detected values of the load current and produces a feedforward signal according to the degree of this average value.

[Action]

In the control circuit of the power conversion device according to the present invention, the feedforward signal based on the average value of the detected values of the load current reduces the harmonics of the input current command value.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. First
In the figure, the same parts as those in FIG. 9 are designated by the same reference numerals, and the description thereof will be omitted. In FIG. 1, 104 is an averaging circuit provided between the detection circuit 6b and the subtractor 102, and 105 is the detector 6d.
And an adder 107, an averaging circuit 106, a filter for passing the output of the averaging circuit 105, a switch 118 for switching between the output of the averaging circuit 105 and the output of the filter 106, and supplying it to the adder 107, 117 Is a limiter provided between the adder 107 and the multiplier 109, and 110 is a low-pass filter provided between the detection circuit 6c and the subtractor 111.

FIG. 2 shows a concrete circuit configuration of the inverter 1. In the figure, D _{1 to} D ₄ are rectifying diodes in a bridge configuration,
S _{1 to} S ₄ are switching elements such as transistors that are connected in reverse parallel to the rectifying diodes D _{1 to} D ₄ and have a bridge structure. The converter 1 is configured as a voltage type converter in which the switching elements S _{1 to} S ₄ are switched by a drive signal from the drive circuit 116 in a plurality of circuits in one cycle.

Next, the operation of the circuit shown in FIG. 1 will be described. In the present invention, the input current command value I _SS is obtained from the voltage measure loop described later and the feedforward signal I _LS of the load current I _L and the power supply voltage V _S, and will be described later according to this input current command value I _SS. With the current minor loop, the input current I _S is made to respond instantaneously, and the DC output voltage V _D that matches the reference voltage V _DR is obtained.

First, the voltage measure loop will be described. The voltage measure loop is a voltage control system composed of the circuits 101 to 109, 117 and 118, and its configuration is shown in FIG. In FIG. 3, moving average circuit 10 is used as averaging circuits 104 and 105.
4,105 are used. Here, the moving average is to sample a detected value at every sampling time T _S in digital control and average a fixed arbitrary number of sample data from the newer sample value. For example, as shown in FIG. 4, when the waveform of the DC output voltage V _D having a ripple having a constant period, assuming averaging every six data DC at _{KT S t <(K + 1} ) T S Output voltage V
The moving average value of _D is Becomes Furthermore, for (K + 1) T _S t <(K + 2) T _S Becomes In this way, if the number of data to be averaged is determined according to the ripple cycle, the moving average value becomes substantially constant, and the influence of ripple on the control operation is eliminated.

In FIG. 3, the subtractor 102 detects a voltage deviation value from the average value of the DC output voltage V _D obtained from the moving average circuit 104 and the DC reference voltage V _{DR (K),} and applies it to the voltage control circuit 103.
This voltage control circuit 103 has a proportional term part 1 that is multiplied by a constant K _p.
Integral term part 103b in which a multiplication value obtained by multiplying 03a by a constant K _I and a value obtained by delaying this multiplication value by delay element Z ^-1 are added.
It consists of and. The voltage control signal output from the voltage control circuit 103 and the feedforward signal I _{LS (K)} obtained from the switch 118 are added in the adder 107.

Here, how to obtain the feedforward signal I _{LS (K)} will be described with reference to the flowchart of FIG. A moving average circuit is used as the average circuit 105.
First, in step ST (1), the detected value I of the load current I _L is detected.
_The moving average value I _{LA (K)} is calculated using _{L (K)} , and then step ST
By (2), the difference between the moving average value I _{LA (K)} and the feed-forward signal I _{LA (K-1)} one sampling before is obtained, and it is judged whether or not the difference is larger than a predetermined set value I _LO. To do. If the difference is larger than the set value I _LO , the switch 118 is closed to the contact b side in step ST (3) and the moving average value I _{LA (K)} at that time is added as the feed forward signal I _{LS (K).} Add to vessel 107. If the difference does not exceed the set value I _LO , the switch 118 is closed to the contact a side in step ST (4), and the moving average value I _{LA (K)} at that time is set to a filter having a predetermined first-order lag characteristic. No signal I _{LF (K)} through 106,
This signal I _{LF (K)} is added to the adder 107 as the feed forward signal I _{LS (K)} in step ST (5).

Here, the simulation waveform when the load 5 is a single-phase inverter and the set value I _LO is 25% of the rated current is the sixth waveform.
Shown in the figure. FIG. 7A shows the waveform of the load current I _{L (K)} input to the single-phase inverter, which has many harmonics. The figure (b) shows the waveform of the moving average value I _{LA (K)} of the load current, and the figure (c) shows the waveform of the feedforward signal I _{LS (K)} . It can be seen that this feedforward signal I _{LS (K)} follows the sudden change of the load current I _{L (K)} at high speed.

Referring again to FIG. 3, the output value of the adder 107 is the effective value command I of the current for the DC side of the converter 1.
Indicates _{me (K)} . In order to convert this effective value command I _{me (K)} into the input current command value I _{SS (K)} for the AC side, the multiplier 119 multiplies the average value V _{D (K)} of the DC output voltage V _D and , _{Divided by} the effective value V _{Se (K)} of the power supply voltage V _S. This multiplier
The output of 119 is limited by the limiter 117 to the allowable current of the converter 1 or less, and then applied to the multiplier 109. Multiplier 109
, The output of limiter 117 has a waveform in phase with power supply voltage V _S. The input current specified value I _{SS (K)} is obtained by multiplying by.

Next, the current minor loop will be described. This current minor loop is a current control system composed of the respective circuits 111 to 113 in FIG. 1, and its configuration is shown in FIG.
In FIG. 7, the detected value of the input current I _S becomes the detected value I _{S (K)} from which the ripple component has been removed by the low-pass filter 110 (see FIG. 1) and is added to the subtractor 111 to input the input current command value I _{S. The} current deviation value is obtained by subtracting from _{SS (K)} . This current deviation value is supplied to the current control circuit 112. The current control circuit 112 includes an integral term part 112a for adding a multiplication value multiplied by a constant G _I and a signal delayed by the delay element Z ⁻¹ , and a proportional term part for multiplying the constant G _p. And 112b. The output of the subtractor 111 is added to the integral term part 112a, and the detected value I _{S (K)} is added to the proportional term part 112b, and the output of the integral term part 112a and the output of the proportional term part 112b are added. To be done. The addition output is added to the detected value V _{S (K)} of the power supply voltage V _S in the adder 113, and the control signal V _{CS (K)} is obtained. This control signal V _{CS (K)} is
By being supplied to the M modulation circuit 114 and compared with the carrier wave, the switching elements S _{1 to} S ₄ constituting the converter 1 are
Is controlled.

The current minor loop as described above reduces the delay,
By increasing the gain, it is possible to make an instantaneous response.

By the operation described above, the DC output voltage V _D is controlled to be constant, and the input current I _S is controlled to be a sine wave current having the same phase as the power supply voltage V _S and a low distortion rate. Further, by using the averaging circuits 104 and 105 as moving average circuits, when the load 5 is a single-phase inverter or the like, a ripple having a frequency twice the output frequency is removed. Further, the feedforward signal I _LS is also filtered by the filter 106 so that ripples due to sampling for averaging are removed, so that the input current command value I _SS has few harmonics.

In the above embodiment, in the feedforward control system for giving the detected value of the load current I _L to the control circuit, when the fluctuation of the moving average value I _LA of the load current exceeds an arbitrary set value I _LO , the moving average is calculated. Although the value I _LA is used as the feed-forward signal I _LS of the load current directly without passing through the filter 106, if the moving average value of the load current does not fluctuate significantly, the moving average value is directly calculated. It is not necessary to use the feed forward signal of the switch circuit 11 as shown in FIG.
8 can be omitted, and the same effect as in the above embodiment can be obtained.

Further, in the above embodiment, the voltage control circuit 103 and the current control circuit 1
The case where 12 and 12 are constituted by a digital control system has been described, but the control circuit of the present invention may be wholly or partly an analog control circuit, and has the same effect as the above embodiment.

〔The invention's effect〕

As described above, according to the present invention, since the detection current averaging circuit is used in the load current feedforward control system, the influence of the load current ripple can be reduced, and the input current of the power converter can be reduced. Has the effect of making a sinusoidal current that is in phase with the power supply voltage and has a low distortion.

[Brief description of drawings]

1 is a block diagram of a control circuit for a power converter according to an embodiment of the present invention, FIG. 2 is a circuit diagram of a converter in the same embodiment, FIG. 3 is a block diagram of a voltage control circuit, and FIG. 4 is a sample. Explanatory drawing of principle of moving average in value control, 5th
FIG. 6 is a flow chart for obtaining a feedforward signal of load current, FIG. 6 is a waveform diagram obtained by simulation, FIG. 7 is a block diagram of a current control circuit, and FIG. 8 is a block diagram showing another embodiment of the present invention. , FIG. 9 is a block diagram of a control circuit of a conventional power converter. 1 is a power converter (converter), 3 is an AC power supply, 5 is a load, 103 is a voltage control circuit, 105 is an averaging circuit, and 112 is a current control circuit. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (2)

[Claims] 1. A voltage control system provided in a power converter for converting input AC power into DC power and outputting the DC power, and a current control for controlling a DC output voltage constant and an input current in phase with a power supply voltage. In the control circuit of the power converter that has a system and is provided with the detection value of the load current, an averaging circuit that averages the detection values of the load current is provided, and the output fluctuation of this averaging circuit does not exceed a predetermined set value. In this case, the output of this averaging circuit is fed to the control circuit through a low pass filter,
When the output fluctuation of the averaging circuit exceeds a predetermined set value, the output of the averaging circuit is directly applied to the control circuit without passing through the low-pass filter. Control circuit 2. A control circuit for a power converter according to claim 1, wherein a moving average circuit is used as the averaging circuit.