JP2838133B2 - Power converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter such as a converter or an inverter which can appropriately limit an input current at the time of starting.

[0002]

2. Description of the Related Art A power converter such as a converter or an inverter having a control circuit as shown in FIG. 1 is known.
This power conversion device is configured to connect a power conversion circuit 3 such as a converter or an inverter between a power supply 1 and a load 2, and to control the power conversion circuit 3 based on an output voltage and an input current. . In order to control the power conversion circuit 3, a current detector 4 as input current detection means, a voltage detection line 5 as output voltage detection means, a reference voltage source circuit 6, a switch 7 as start command generation means, Output voltage controller (hereinafter, referred to as AVR) 8, input current controller (hereinafter, referred to as ACR) 9, PWM (pulse width modulation)
Pulse generator 10 and switching element drive circuit 11
And a start-up current limiting filter 12.

In this embodiment, a power supply 1 is a three-phase AC power supply, and a power conversion circuit 3 is a step-up type three-phase converter. As shown in FIG. 2, six switching elements Q1, Q2, Q
3, Q4, Q5, Q6 and six diodes D1, D2
, D3, D4, D5, and D6 in a three-phase bridge connection, and the reactors L1, L
2 and L3, and a capacitor C1 between the DC output lines.
Having. The reactors L1, L2, L3 have a power storage function and a switching noise removing function.
Since the converter circuit of FIG. 2 is well known, detailed description will be omitted.

A reference voltage source 6 generates a reference voltage Er as an output voltage command value. The reference voltage source 5 is connected to the AVR 8 via the start switch 7 and the RC filter 12. Therefore, when the start switch 7 is turned on, the reference voltage Er is corrected by the filter 12 so that the corrected reference voltage E
r ', which is input to AVR 8 via line 13.

The AVR 8 comprises, for example, a comparator 8a and a compensator 8b as shown in FIG. The comparator 8a generates an output (error signal) corresponding to the difference between the voltage detection value E0 given from the voltage detection line 5 and the corrected reference voltage (command value) Er 'given from the reference voltage line 13, and compensates. The compensator 8b compensates for the output of the comparator 8a by proportional compensation or proportional integral compensation.
And outputs a signal indicating the amount of operation.

As shown in FIG. 4, the ACR 9 includes a comparator 9a and a compensator 9b connected to the current detector 4 and the AVR 8.
Consisting of The comparator 9a forms an error signal between the current detection value and a current reference value (current command value) composed of the first operation amount given from the AVR 8. Compensator 9b is a comparator 9a
And outputs a second manipulated variable by performing proportional compensation or proportional integral compensation on the error signal obtained from the second operation amount.

[0007] The PWM pulse generator 10 connected to the ACR 9 as a switch control signal forming circuit switches the switching elements Q 1 -Q of the power conversion circuit 3 based on the second manipulated variable.
A PWM pulse for turning on / off 6 is formed by a known method. Note that the switching elements Q1 to Q6
The off time corresponds to the second manipulated variable. The switching element drive circuit 11 controls on / off of the switching elements Q1 to Q6 of the power conversion circuit 3 based on the output of the PWM pulse generation circuit 10 by a known method. Although FIG. 1, FIG. 3 and FIG. 4 are apparently shown as a single phase, circuits for three phases are actually provided.

In the power converter of FIG. 1, the output voltage of the power conversion circuit 3 operates so as to follow a reference voltage (output voltage command value). That is, the first manipulated variable is determined by the AVR 8, and the first manipulated variable is used as a reference current value (input current command value) to determine the second manipulated variable that causes the input current Ii to follow the first manipulated variable. Control.

[0009]

The filter 1
2 shows a step-like reference voltage (output voltage command value) Er supplied when the start switch 6 is turned on, as shown in FIGS.
(A) has the effect of changing the correction reference voltage Er 'to rise exponentially. Thus, the input current Ii gradually rises as shown in FIGS. 5 and 6B. FIG. 5 shows a case where the load 2 is light, and FIG.
Indicates a heavy time. As is clear from the comparison between FIG. 5B and FIG. 6B, the effect of suppressing the rise of the input current is obtained regardless of the size of the load 2, but the slope of the envelope of the input current Ii changes. ing. As shown in FIG. 6B, when the rising slope of the input current Ii becomes steep under heavy load, the load on the power supply at the time of startup increases.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a power converter capable of stabilizing a rising slope of an input current at the time of startup regardless of a change in load.

[0011]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a power supply terminal, a power conversion circuit connected to the power supply terminal, and having a power conversion switch; Current detection means for detecting an input current flowing through the power conversion circuit, voltage detection means for detecting an output voltage of the power conversion circuit, start command generation means, and a reference voltage in response to a start command of the start command generation means. A reference voltage source circuit for generating the voltage, the current detection unit, the voltage detection unit, the reference voltage source circuit, and the power conversion circuit are connected to each other, and the detection voltage obtained from the voltage detection unit follows the reference voltage. Calculating a first operation amount for limiting the first operation amount by a limit value whose absolute value changes with time in response to the start command to obtain a current reference value;
A second manipulated variable for causing the current detection value obtained from the current detection means to follow the current reference value is obtained.
And a control circuit for controlling the power conversion switch by forming an on / off control signal for the power conversion switch based on the operation amount of the power conversion switch. The control circuit includes an output voltage controller (AVR), a current reference signal forming circuit having a limiting action, an input current controller (ACR), and a switch control signal forming circuit. be able to.

[0012]

In the present invention, the first manipulated variable is limited by a limit value, and this is used as a reference current value (input current command value) in input current control.
By making the rising slope of the reference current value at start-up constant by the limit value, the slope of the input current also becomes constant irrespective of the magnitude of the load. In addition, since this inclination can be set arbitrarily, the rise of an arbitrary input current can be easily obtained.

[0013]

Next, a power converter according to an embodiment of the present invention will be described with reference to FIGS. FIG. 7 shows a power converter according to the embodiment. Since the power converter shown in FIG. 7 is a modification of a part of the power converter shown in FIG. 1, parts in FIG. 7 that are common to FIG. 1 are denoted by the same reference numerals, and description thereof is omitted. The circuit of FIG. 7 eliminates the filter 12 from the circuit of FIG. This corresponds to a circuit to which the generation circuit 14 is connected. The limiter circuit 15 and the limit value generating circuit 14 function as a reference current signal forming circuit for giving a reference current value (input current command value) to the ACR 9. The start command generator 7a controls the start switch 7 to be turned on by the start command signal, and also supplies the limit command circuit 14 with the start command signal.

The limit value generating circuit 14 outputs a voltage indicating a limit value which increases with a slope with time in response to a start signal, and includes a reference voltage source 21 and an operational amplifier as shown in FIG. 22, an input resistor Ri, an integrating capacitor Cf, and a start switch 23. The inverting input terminal of the operational amplifier 22 is connected via an input resistor Ri to a reference voltage source 21 for generating a negative reference voltage. The non-inverting input terminal of the operational amplifier 22 is connected to the ground. The integrating capacitor Cf and the start switch 23 are connected between the inverting input terminal and the output terminal of the operational amplifier 22, respectively. This limit value generating circuit 14
The switch 23 is turned off in response to the start command signal of the start command generator 7a shown in FIG. 7, and the integration of the negative reference voltage is started to generate the ramp voltage shown in FIG. That is, if the slope is A, the output of the limit value generation circuit 14 is the slope A
With the linear function At with respect to time t. This limit value increases to a value sufficiently higher than the normal AVR8 output value.

As shown in FIG. 8, the limiter circuit 15
It has two input terminals 24 and 25 and an output terminal 26, and determines the smaller one of the first operation amount (AVR output) given to one input terminal 24 and the limit value given to the other input terminal 25. Output to the output terminal 26. A buffer amplifier 27, a resistor 28, and a diode 29 are provided between the input terminals 24 and 25 and the output terminal 26 of the limiter circuit 15.
And are connected. One input terminal 24 is connected to an output terminal 26 via a buffer amplifier 27 and a resistor 28. The input terminal 25 is connected to the output terminal 26 via a diode 29. The input terminal 25 is connected to the output terminal of the limit value generating circuit 14. When the voltage shown in FIG. 9E supplied from limit value generating circuit 14 is lower than the output voltage of the buffer amplifier, diode 29 is turned on, and the voltage of output terminal 26 is substantially equal to the output voltage of limit value generating circuit 14. Be the same. On the other hand, when the output voltage of the limit value generating circuit 14 becomes higher than the output voltage of the buffer amplifier 27, the diode 29 enters a reverse bias state and turns off. Therefore, one input terminal 2
The first operation amount (AVR output) of No. 4 is output without being limited to the limit value. Note that the limit value generating circuit 14 and the limiter circuit 15 form a current reference signal for input current control by limiting the first operation amount obtained from the AVR 8.

FIG. 9 is a waveform diagram showing a state at the time of starting points A to G in FIG. Immediately after starting at t0, the output voltage E0
9 is lower than the reference voltage Er.
High-level output as shown in (D) (first manipulated variable)
e is obtained. However, since the limiter circuit 15 is provided, the output of FIG. 9D is not directly input to the ACR 9, but the limit value of FIG. 9E is selected and becomes the output of the limiter circuit 15. The output of the limiter circuit 15 shown in FIG. 9 (F) functions as a current reference value in the ACR 9, and the input current Ii in FIG. 9 (G) follows the current reference value in FIG. 9 (F). As a result, the rising slope of the input current Ii is limited to the limit value. Figure 10 shows the slope of the limit value.
When the output signal e of the AVR 8 is in the restricted area as shown in FIG. Although the final stable level of the output signal e of the AVR 8 varies depending on the magnitude of the load 2, the limit gradient in the limiter circuit 15 is the same, so that the ACR 9
Does not become abnormally high at startup.

FIGS. 11A, 11B, and 11C show waveforms at the start of the input current Ii when the load 2 is a heavy load, a medium load, and a light load.

Since the adjustment of the limit value can be arbitrarily performed, the rising waveform of the input current Ii can be arbitrarily adjusted.

[0019]

[Modifications] The present invention is not limited to the above-described embodiment, and for example, the following modifications are possible. (1) The power conversion circuit 3 is, for example, a bridge-type inverter, or a rectifier circuit for rectifying the bridge-type inverter and its output, or another type of AC-DC.
Alternatively, a DC-DC converter can be used. (2) The entire system can be configured as an uninterruptible power supply circuit. (3) AVR8, ACR9, PWM pulse generator 1
A part or all of the zero, the limiter circuit 13, and the limit value generating circuit 14 can be configured as a digital circuit such as a microprocessor. In this case, an A / D converter is connected to the current detector 4 and the output voltage detection line 5. (4) Instead of controlling the switches 7 and 23 by the start command generator 7a, the switches 7 and 23
Can be a mechanical switch that works together.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a conventional power converter.

FIG. 2 is a circuit diagram showing an example of the power conversion circuit of FIG.

FIG. 3 is a block diagram showing the AVR of FIG. 1;

FIG. 4 is a block diagram showing the ACR of FIG. 1;

FIG. 5 is a waveform diagram showing a reference voltage value and an input current at the time of startup when the load of FIG. 1 is light;

FIG. 6 is a waveform chart showing a reference voltage value and an input current at the time of startup when the load of FIG. 1 is heavy.

FIG. 7 is a block diagram illustrating a power converter according to an embodiment.

FIG. 8 is a circuit diagram showing a limiter circuit and a limit value generation circuit of FIG. 7;

FIG. 9 is a waveform diagram showing states at points A to G in FIG. 7;

FIG. 10 is a diagram showing a state of a limit value generation circuit.

FIG. 11 is a waveform chart showing input currents in three types of loads.

[Explanation of symbols]

 3 Power conversion circuit 15 Limiter circuit 14 Limit value generation circuit

Claims (2)

(57) [Claims] 1. A power supply terminal, a power conversion circuit connected to the power supply terminal and having a power conversion switch, and current detection means for detecting an input current flowing from the power supply terminal to the power conversion circuit, Voltage detection means for detecting an output voltage of the power conversion circuit; start command generation means; a reference voltage source circuit for generating a reference voltage in response to a start command of the start command generation means; A first operation amount that is connected to the voltage detection unit, the reference voltage source circuit, and the power conversion circuit and causes the detection voltage obtained from the voltage detection unit to follow the reference voltage; A current reference value is obtained by limiting the first manipulated variable by a limit value that changes with time in response to a start command, and a current detection value obtained from the current detection means follows the current reference value. And a control circuit for controlling the power conversion switch by forming an on / off control signal for the power conversion switch based on the second operation amount. Conversion device. 2. The control circuit is coupled to the voltage detection means and the reference voltage source circuit,
An output voltage for obtaining and outputting a first manipulated variable for causing the detection voltage to follow the reference voltage based on the detection voltage obtained from the voltage detection means and a reference voltage provided from the reference voltage source circuit; A control unit coupled to the output voltage controller and the start command generating means, wherein the first operation amount is limited by a limit value whose absolute value changes with time in response to the start command. A current reference signal forming circuit for forming a current detection signal; and a second current detection circuit coupled to the current detection means and the current reference signal formation circuit, for causing a current detection value obtained from the current detection means to follow the current reference signal. An input current controller for obtaining an operation amount, connected between the input current controller and the power conversion switch element, for turning on and off the power conversion switch according to the second operation amount; Power converter according to claim 1, characterized in that it consists of a switch control signal forming circuit for forming a switch control signal for obtaining.