JP3028268B2 - 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 in a system in which a plurality of power converters are operated in parallel.

[0002]

2. Description of the Related Art A power conversion device using a semiconductor switching device is provided with a plurality of parallel power conversion devices in order to limit the capacity of the semiconductor switching device to be used and to improve the reliability of the power conversion device system for an important load. I often drive . As described in Japanese Patent Application Laid-Open No. 61-157235 and Japanese Patent Application Laid-Open No. 1-295631, the sharing of the load current between the power converters that are operated in parallel is performed by two or more power converters. It is contemplated to balance the output or input current.

[0003]

However, in the prior art, no consideration has been given to suppressing the circulating current between the power converters, which not only increases the loss of the switching elements in the power converter but also increases the power conversion. On the AC side of the apparatus, there is a problem that the AC reactor is DC-excited and overheated because of zero-phase current.

[0004] That is, a power converter using a semiconductor switching element is reversely connected to the semiconductor switching element in either a single-phase or a three-phase or a half-bridge or a full-bridge. A positive arm and a negative arm consisting of a freewheel diode are connected in series between the positive and negative poles of the DC line, and the connection point between the positive and negative arms is connected to an AC power supply or AC load. ing.

When the power converter having the above-described configuration is a pulse width modulation (hereinafter abbreviated as PWM) control method using a semiconductor switching element having an on / off function such as a gate turn-off thyristor or a bipolar power transistor. In general, there are irregularities in the time from when an on / off drive signal is input to each switching element until the switching operation is actually started and the switching speed of the switching element.

Accordingly, the pulse width of the switching element of the positive side arm and the pulse width of the switching element of the negative side arm are different. Since the integral value of the pulse width is an AC voltage, a difference occurs between the AC positive voltage and the negative voltage. For example, if the pulse width of the positive switching element is large, the AC waveform moves from the zero potential to the positive side. It has moved, and the DC component is superimposed on the positive side of the AC voltage. That is, a potential difference occurs between the zero-point potential on the AC side and the midpoint on the DC side. This potential difference causes a circulating current to flow through another power converter circuit operating in parallel.

As described above, the circulating current is caused by the difference in pulse width in the PWM control of the switching elements of the positive and negative arms, so that the converter, the inverter, the single phase, It can occur in any of the three phases.

The above-described circulating current can be prevented by providing a transformer between the AC power supply and the AC input terminal or between the AC load and the AC output terminal of the power converter to insulate DC, but a transformer is provided. As a result, there is a problem that the device becomes large.

An object of the present invention is to provide a parallel system of power converters that reduces a circulating current flowing between power converters of a PWM control system operated in parallel by using a PWM signal.

[0010]

The present invention achieves the above object.
To formed, based on the PWM signal obtained by comparing the command signal and the carrier signal corresponding to the waveform of the AC voltage to be output Dzu
Input and output terminals of the plurality of reverse power conversion device that is controlled have
In parallel operation reverse power converter system for a system formed by connecting in parallel between, provided to the AC output of the inverse power conversion device
A DC current detecting means for detecting a DC current component is to reduce the direct current component in accordance with the output of the DC current detection means
In this way, a reverse power conversion device provided with a correction means for correcting one of a command signal and a carrier signal is proposed.

[0011] The present invention also relates to a method for controlling the voltage on the AC side of a converter.
Command signal and carrier signal according to the voltage waveform to be generated
Are controlled based on the PWM signal obtained by comparing
Number of forward power converters are connected in parallel between the input and output terminals.
In a continuous power converter for a parallel operation system
And a positive current component provided at the DC output terminal of the forward power converter.
DC difference current detection means for detecting the difference between the current component and the negative electrode current component
And the DC difference current is reduced according to the output of the DC difference current detection means.
Either the command signal or the carrier signal to reduce
A forward power conversion device provided with correction means for correcting
You.

[0012] The present invention further provides a method for controlling the AC side voltage of the converter.
Command signal and carrier signal according to the voltage waveform to be generated
Is controlled based on the PWM signal obtained by comparing
AC power converter and DC output of AC power converter
And a plurality of reverse power converters
AC input terminal and DC output terminal of force converter are common
Connected to the storage battery and the AC input of the reverse power converter.
Power conversion for parallel operation system with outputs connected in parallel
In the device, the DC output terminal of the forward power converter and the DC
Positive current provided between output terminal and storage battery connection point
DC current detection method for detecting the difference between the current component and the negative electrode current component
Stage and reduce the DC difference current according to the output of the DC difference current detection means.
Either the command signal or the carrier signal to reduce
A reverse power conversion device provided with correction means for correcting
You.

[0013]

Direct current component included in the AC output current detected by the DC current detecting means of the action reverse power converter, between the inverse power conversion devices that are operated in parallel, <br/> control based on the PWM signal It is generated by a DC voltage generated due to a difference in pulse width between the positive and negative switching elements .

Assuming that the direction of the detected direct current component toward the load is positive, this is when the pulse width of the positive side switching element is larger than that of the negative side. did
Therefore, in order to reduce the direct current component, the pulse width of the positive side switching element may be reduced. Like that PW
In order to change the M signal, the relative position of the command signal with respect to the carrier signal may be changed according to the magnitude of the detected direct current component. That is, a value corresponding to the magnitude of the DC current component may be subtracted from the command signal, and the value may be added to the carrier signal. As a result, a signal in which the pulse width of the positive side switching element is reduced is output from the switching element driving means, and the DC current component is reduced, thereby achieving the object of the present invention .

In the case of a forward power converter, the output of the DC difference current detector is generated for the same reason as the DC current component included in the AC output current detected by the DC current detector of the reverse power converter . Therefore, as in the case of the forward power converter , the relative position of the command signal with respect to the carrier signal may be changed according to the magnitude of the detected DC difference current.

[0016]

FIG. 1 shows an embodiment of the present invention. FIG. 1 shows a parallel system of two single-phase inverters. The inverters 1A and 1B are half-bridge type single-phase PWM control inverters. The main circuit of the inverter 1A is composed of DC capacitors 4 and 5, transistors 6 and 7, diodes 8 and 9 and an AC reactor 10 which are respectively reversely connected.

A control circuit is provided on the load side of the AC reactor 10 so as to detect a difference between an output current to the load and a return current from the load, a drive circuit 12 for the transistors 6, 7 and a command signal. Generating means 13, carrier signal generating means 14, subtractor 15 for subtracting the output of Hall CT 11 from the output of carrier signal generating means 14, and subtracter 1
5 and a comparator 16 for comparing the output of the command signal generating means 13 and outputting a signal to the transistor driving means 12.

The inverter 1B has exactly the same circuit configuration as the inverter 1A. Although not shown in detail, the DC input is connected to a common DC power supply 2 and the AC output is also directly connected to a common load 3. .

When the pulse width of the transistor 6 of the positive arm of the inverter 1A is larger than the pulse width of the transistor 7 of the negative arm, the AC voltage waveform is shifted from the zero potential to the positive side, and the DC component is reduced. It is superimposed on the positive side. With this DC component, the transistor 6
A connection point of the input terminal of the AC load 3 with the single-phase inverter 1B, a diode of the positive arm of the single-phase inverter 1B,
A circulating current flows through a circuit that returns to the transistor 6 of the power conversion device via a connection point at the output terminal of the DC power supply 2.

FIG. 4 shows an example of an output waveform of each part of the control circuit . Here, the hole CT11 assumes that the current in the direction of the arrow in FIG. 1 is positive. In the above example, since the circulating current flows from the inverter 1A to the inverter 1B, the output of the hall CT11 due to the circulating current becomes positive, and its waveform is shown by the line a in FIG. This output is output to the carrier signal generation means 14.
The output of the adder 15 to be added to the output of FIG.
The output of the hall CT11 from the horizontal axis e (0 level) upward
The waveform c moves by an amount corresponding to a. When this waveform c is compared with the output b of the command signal generating means 13 by the comparator 16, an output represented by a waveform d is obtained. This output is PW
The signal becomes an M signal, and the transistor driving means 12 drives the transistors 6 and 7 by this signal. Since this PWM signal increases the pulse width of the switching element on the negative side, it reduces the DC component superimposed on the positive side of the AC,
As a result, the circulating current is also reduced.

If there is no imbalance in the pulse widths of the positive side switching element and the negative side switching element as described above, the output of the Hall CT 11 is zero, and the comparator 16 outputs the command signal generating means 13 and the carrier signal generating means 14. The outputs are compared as they are, and a PWM signal in which the positive and negative are balanced is output.

Another embodiment will be described with reference to FIG. FIG. 2 shows a parallel system of two single-phase converters. Converters 21A and 21B are half-bridge type single-phase PWM converters. The main circuits of the converters 21A and 21B include an AC reactor 22 installed at an input end, transistors 23 and 24, and diodes 25 and 26 reversely connected thereto.
And DC capacitors 27 and 28.

These operations are as follows. The difference between the feedback of the DC output voltage of the converters 21A and 21B and the output reference voltage 31 is amplified by the operational amplifier 32. This output and
The output of the synchronous sine wave generating means 33 for generating a sine wave synchronized with the input AC voltage is multiplied by a multiplier 34. Here, as the converter output value increases, the error output of the operational amplifier 32 decreases, and the output of the multiplier 34 also decreases.
You. The output value of the multiplier 34 indicates an input current command.

The difference between the output of the multiplier 34 and the feedback of the AC input current by the current transformer 20 is amplified by the operational amplifier 35. The output of the operational amplifier 35 is a single-phase PWM converter.
It becomes an AC voltage command signal.

The output of the hall CT 11 for detecting the common current of the converter output and the output of the carrier signal generating means 14 are added by an adder 36, and the output of the operational amplifier 35 and the comparator 16 are added.
To compare. Here, the hole CT assumes that the current in the direction of the arrow in the figure is positive. The output of the comparator 16 becomes a PWM signal, and the transistor driving means 12 drives the transistors 23 and 24 by this signal. The converter 21A and the converter 21B have exactly the same circuit configuration, the AC input is connected to a common AC power supply 18, and the DC output is also a common load 19.
It is connected to the.

If the actual input current detection value of the current transformer 20 is smaller than the output of the multiplier 34 (input current command) , the output of the operational amplifier 35 (AC voltage command of the converter ) becomes smaller and the AC voltage of the converter becomes lower. Therefore, the input current increases. Conversely, if the actual input current detection value of the current transformer 20 is larger than the output of the multiplier 34, the output of the operational amplifier 35 increases and the AC voltage of the converter increases, so that the input current decreases. Therefore, at the output of the multiplier 34
Control is performed so that a certain input current command matches an actual input current detection value of the power converter by the current transformer 20.

Further, when the output voltage of the converter becomes lower than the reference voltage 31, the output of the operational amplifier 32 increases and the output of the multiplier 34 (input current command) also increases.
Then, the input current of the converter increases, and the DC voltage of the output also increases. Conversely, when the output voltage of the converter becomes higher than the reference voltage 31, the output of the operational amplifier 32 decreases and the output of the multiplier 34 (input current command) also decreases.
Then, the input current of the converter decreases, and the DC voltage of the output also decreases. Therefore, control is performed so that the DC output voltage and the reference voltage 31 match.

In the converters 21A and 21B, if the pulse widths of the switching elements of the positive and negative arms are equal, there is no imbalance between the AC zero potential and the DC potential, so that no circulating current flows. Therefore, the output of the hall CT11 is zero, and the comparator 16 compares the output of the command signal generating means 13 with the output of the operational amplifier 35 as it is.
Since both the output of the multiplier 34 and the output of the current transformer 20 do not ideally include a DC component, the comparator 16 outputs a P
It outputs a WM signal.

Here, assuming that the pulse width of the positive side arm of converter 21A becomes large and the zero-point potential on the AC side with respect to the DC side potential becomes larger than that of converter 21B, the circulating current flows in the positive direction of hall CT11. The flow hall CT11 output has a positive signal. This signal is added to the output of the command signal generator 13 by the adder 36. Therefore, the output of the operational amplifier 35 is shifted to the negative side relative to the command signal, and the PWM signal output from the comparator 16 is also shifted to the negative side. Then
The zero-point potential on the AC side with respect to the DC side potential of converter 21A is reduced, and the circulating current is suppressed. Each of these signals
The correspondence between the waveforms is as shown in FIG.

A third embodiment will be described with reference to FIG. FIG. 3 shows a parallel system of two three-phase uninterruptible power supplies.
The uninterruptible power supply 41A includes a rectifier 51A that converts an AC input into a DC output, an inverter 52A that converts the DC into an AC, and a transformer 53 that insulates the AC output from a load.
A, a hole CT11A for detecting a common current of an external input line to a DC line connecting the rectifier 51A and the inverter 52A, and a rectifier when a positive output of the hole CT11A (the direction of the arrow in the drawing is positive) is generated. And a control circuit 54A for controlling the zero-point potential on the AC side relative to the DC-side potential of 51A to decrease. The uninterruptible power supply 41B has the same configuration as the uninterruptible power supply 41A, with B added to the reference numeral.

Uninterruptible power supply 41A and uninterruptible power supply 4
1B is connected to a common AC power supply 42, a common storage battery 43, and a common load 44. In this case, the rectifiers 51A and 51B of the two uninterruptible power supplies form a parallel system. Since the circulating current between the two rectifiers can be detected by the holes CT11A and 11B, the circulating current can be suppressed by the same principle as that described with reference to FIG.

In this embodiment, the rectifiers 51A, 51B are used to replace the detector holes CT11A, 11B for detecting the circulating current with the rectifiers 51A, 51B.
, But can be installed on the wiring branched from the output and connected to the storage battery 43. The outputs of the rectifiers 51A and 51B are wires through which power is always flowing.
Since only the charging current of the storage battery 43 always flows through the wiring connected to the power supply and the current flows only for a short time even during a power failure, the wire or copper bar is small, so that a small detector can be used. It has the effect of becoming.

The above description has been made in connection with the case where two units are connected in parallel. However, even when three or more units are operated in parallel, the same operation can be performed.

[0034] In addition, it has dealt with the example of a single-phase half-bridge configuration in the embodiment, a single-phase full-bridge configuration, your
And in any of the three phases.

[0035]

In the parallel system of the power conversion device of the PWM control system for converting from AC to DC or from AC to DC, the pulse width is generated due to the difference in pulse width of the switching elements constituting the positive and negative arms. By detecting the circulating current and controlling the PMW signal according to the circulating current, the circulating current can be suppressed. As a result, an increase in the converter capacity and DC excitation of the AC reactor can be prevented .
There is an effect that the power converter and the AC reactor can be reduced in size.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of another embodiment of the present invention.

FIG. 3 is a diagram showing a configuration of a third embodiment of the present invention.

FIG. 4 is a diagram illustrating a waveform example of each circuit of the control circuit.

[Explanation of symbols]

 1A, 1B Single-phase inverter 2 DC power supply 3 Load 4, 5, 27, 28 Capacitor 6, 7, 23, 24 Transistor 8, 9, 25, 26 Diode 10 AC reactor 11, 11A, 11B Hall CT 12 Transistor driving means 13 Command signal generating means 14 Carrier signal generating means 15 Subtractor 16 Comparator 18 Single-phase AC power supply 19 Load 20 Current transformer 21A, 21B Single-phase converter 22 AC reactor 31 Reference voltage source 32, 35 Operational amplifier 33 Synchronous sine wave generating means 34 Multiplier 36 Adder 41A, 41B Uninterruptible power supply 42 Three-phase AC power supply 43 Storage battery 44 Load 51A, 51B Rectifier 52A, 52B Inverter 53A, 53B Transformer 54A, 54B Rectifier control circuit

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Satoru Inukai 3-1-1, Sachimachi, Hitachi-shi, Ibaraki Hitachi, Ltd. Hitachi Plant (72) Tomoaki Mino 3-1-1, Sachimachi, Hitachi-shi, Ibaraki 1 Hitachi, Ltd. Hitachi Plant (72) Inventor Yoshihiro Taniguchi 3-1-1, Yukimachi, Hitachi, Ibaraki Prefecture Hitachi, Ltd. Inside Hitachi Plant (56) References JP-A-61-157235 (JP, A JP-A-4-33574 (JP, A) JP-A-5-300748 (JP, A) JP-A-1-295631 (JP, A) JP-A-5-308777 (JP, A) JP-A-62 95979 (JP, A) JP-A-3-32366 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02M ^7/ 00-7/98

Claims (3)

(57) [Claims] 1. A group PWM signal obtained by comparing the command signal corresponding to the waveform of the AC voltage to be output and the carrier signal Dzu
Input and output terminals of the plurality of reverse power conversion device that is controlled have
In parallel operation reverse power converter system for a system formed by connecting in parallel between the, and the DC current detection means for detecting a DC current component provided to the AC output of the inverse power converter, the DC current detection means A reverse power conversion device comprising: a correction unit that corrects one of the command signal and the carrier signal so as to reduce the DC current component according to an output . 2. An electric power to be generated as an AC side voltage of a converter.
Parallel formed by connecting in parallel between a plurality of forward power conversion device is controlled based on a PWM signal obtained by comparing the command signal and the carrier signal corresponding to the waveform of the pressure between the input terminal and the output terminal
In order power converter for operating the system, a DC difference current detecting means for detecting a difference between the provided cathode current component and the negative electrode current component to the direct current output end of the forward power converter, the output of the DC difference current detector A forward power conversion device comprising: a correction unit configured to correct one of the command signal and the carrier signal so as to reduce the DC difference current accordingly . 3. An electric power to be generated as an AC side voltage of a converter.
Inverse power conversion apparatus for converting a forward power converter is controlled based on a PWM signal obtained by comparing the carrier signal and the command signal corresponding to the pressure waveform, the DC output of the forward power converter into an AC output A parallel operation system comprising a plurality of forward power converters, wherein an AC input terminal and a DC output terminal of the plurality of forward power converters are respectively connected to a common AC input and a storage battery, and an AC output of the reverse power converter is connected in parallel. Power conversion equipment
Oite the location, Oyo DC output terminal and the DC output ends of the forward power converter
A DC difference current detecting means for detecting a difference between the positive current component and the negative electrode current component provided between the connection point of the fine the storage battery,
The DC difference current according to the output of the DC difference current detection means;
A reverse power conversion device comprising: a correction unit configured to correct one of the command signal and the carrier signal so as to decrease the power signal.