JPH0937552A - Pwm converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To dispense with a large-scale transformer in a converter main circuit by forming a current control system in which the current commands of each phase obtained from a voltage control system are respectively compared with the input current detection signals of each phase of a converter main circuit. SOLUTION: In control devices 51 , 52 , as shown in the control device 52 the DC component of the current detection signal IV of a V-phase is adjusted by an offset adjustment value IOSET to pass it through an amplifier 73 , thereby obtaining a current detection signal IV1 in which the DC component is zero, and the current detection signal 1V1 is compared with the current command IV5 of a multiplier 11V. When a lag is generated in the switching time of the semiconductor element of converter main circuits 31 , 32 and a circulating current is generated between the main circuits 31 , 32 , the AC component and the DC component are detected by a Hall transformer connected to each phase and the DC component is controlled so as to be zero together with the AC component. As a result, the circulating current of AC and DC components between the converter main circuits 31 , 32 is suppressed and the DC component becomes zero and for that reason, the AC input side of the main circuit 31 , 32 dispenses with a transformer.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to PWs connected in parallel.
The present invention relates to an M converter, and particularly to a control device that suppresses a DC circulating current.

[0002]

2. Description of the Related Art FIG. 2 shows a parallel device configuration of two PWM converters for supplying DC power to a load with a common DC side.

Three-phase AC power supply 1 to two transformers 2 ₁ and 2 ₂
AC power is supplied to the converter main circuits 3 ₁ and 3 ₂ through. The converter main circuits 3 ₁ and 3 ₂ include bridge-connected semiconductor switches SU1 to SZ1 and SU2 to SZ2 and smoothing capacitors CD1 and CD2, and each semiconductor switch is a PW.
The power is converted under M control to supply DC power to the common load 4.

The control devices 5 ₁ and 5 ₂ of the converter main circuits 3 ₁ and 3 ₂ have a current control system in a minor loop of a voltage control system, as represented by the control device 5 _2.
Obtain the WM gate signal.

Input currents I _U and I _{W of the} converter main circuit 3 _2
Are detected by Hall current transformers 6 _U2 and 6 _W2 , respectively, and the detection signals are adjusted to have a DC component of zero by an offset adjustment value I _0SET , and a current detection signal I _U1 having a zero DC component is output through amplifiers 7 ₁ and 7 _2. , I _W1 . V-phase current detection signal I
_V1 is obtained by adding both detection signals I _U1 and I _W1 by the adder 8.

The DC output voltages of the converter main circuits 3 ₁ , 3 ₂ are detected by the voltage detector 9, the detected voltage is compared with the DC voltage set value V _SET, and the difference is amplified by the error amplifier 10.

The multipliers 11 _U , 11 _V , and 11 _W multiply the respective phase voltages detected by the detection transformer 12 and the output of the error amplifier 10 to generate currents (power factor 1.0) synchronized with the respective phase voltages. Obtain the command values I _US , I _VS , and I _WS .

The respective current command values I _US , I _VS , I _WS are compared with the current detection values I _U1 , I _V1 , I _W1 of the respective phases and amplified by the error amplifiers 13 _U , 13 _V , 13 _W , The PWM signal generator 14 generates a PWM gate signal for each phase.

[0009]

SUMMARY OF THE INVENTION In the conventional configuration,
If the switching time of the semiconductor elements of the converter main circuits 3 ₁ , 3 ₂ is deviated, the converter main circuit 3 ₁ ,
A circulating current is generated during 3 ₂ .

The circulating current has an AC component and a DC component. The AC component is a component that can be detected and controlled by the Hall current transformer connected between the two AC phases.

However, if the DC component circulates in the V phase to which the Hall current transformer is not connected, it cannot be detected,
Since it becomes uncontrollable, transformers 2 ₁ and 2 ₂ are provided on the AC input side of the converter main circuits 3 ₁ and 3 ₂ .

For example, when the transformers 2 ₁ and 2 ₂ are not provided,
Path indicated by the arrow, the converter main circuit 3 ₁ AC input V phase → the converter main circuit 3 _first DC positive-side → converter main circuit 3 _second DC positive-side → converter main circuit 3 ₂ of the DC negative-side → converter main circuit 3 _{When a} DC component flows through the AC input V phase path of ₂ , the converter main circuit 3 ₁ supplies power to the converter main circuit 3 ₂ and an imbalance occurs in the input power (current) between the converter main circuits. To do.

As described above, since the circulation of the DC component is unavoidable in the converter main circuits 3 ₁ and 3 ₂ common to the AC input and the DC side, the transformer 2 _{1 is} provided on the input side of both converter main circuits 3 ₁ and 3 _2. 2 ₂ are provided to cut the direct current component.

In this configuration, each converter main circuit requires a large transformer corresponding to the power conversion capacity, which leads to an increase in size and cost of the device.

[0015]

According to the present invention, a converter control device has a current control system in a minor loop of a voltage control system to obtain a PWM gate signal, and the current control system is provided for each phase obtained from the voltage control system. It is characterized in that the current command and the input current detection signals of the respective phases of the main circuit of the converter are compared with each other.

The current control system is configured to detect the current for each phase, and when the circulating current of the AC component and the DC component is about to flow between the converter main circuits, the circulating current is suppressed by the current control system.

By suppressing the circulating current by the current control system,
No transformer is required on the AC input side of the converter main circuit.

[0018]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. 2 is different from FIG. 2 in that the transformers 2 ₁ and 2 ₂ are omitted from the main circuit and the alternating current is directly applied from the power source 1 to the converter main circuits 3 ₁ and 3 ₂ , and the control device 5 ₁ ,
5 of ₂ the V-phase current is also in view of obtaining a current detection signal offset adjustment for each phase is detected.

In order to detect the AC input current of each phase of the converter main circuits 3 ₁ , 3 ₂ , Hall current transformers 6 _U1 , 6 _V1 , 6 _W1 , 6 _U2 , 6 _V2 , are _added to the U, V, W phases, respectively. Provide 6 _W2 .
The current detector may be any detector that can detect the direct current component.

In the control devices 5 ₁ and 5 ₂ , as represented by the control device 5 ₂ , the DC component is adjusted to zero by the offset adjustment value I _0SET of the V-phase current detection signal I _V , and the amplifier 7 ₃ To obtain a current detection signal I _V1 having a DC component of zero. This current detection signal I _V1 is compared with the current command I _VS of the multiplier 11 _V.

In the present embodiment, the converter main circuit 3
_1, deviation occurs in the 3 switching time of the _second semiconductor element,
If circulating current between the converter main circuit 3 _1, 3 ₂ is about to occur, the AC component and the DC component is detected by the Hall current transformer that is connected to each phase, the DC component with the AC component to zero Controlled.

[0022] Thus, the converter main circuit 3 _1, 3 circulating current of the AC and DC components of between ₂ is suppressed, the converter main circuit 3 ₁ since the DC component becomes zero, 3 the _second AC input side transformer No need for vessels. Further, it is possible to prevent imbalance in the input power (current) between the converter main circuits.

The same configuration is adopted when three or more PWM converters are connected in parallel. Also, single-phase PWM
Even when the converters are connected in parallel, the circulating current (AC and DC components) can be suppressed by detecting the current of each phase.

[0024]

As described above, according to the present invention, since the current control system of the converter control device is configured to detect the current for each phase, the circulating currents of the AC component and the DC component flow between the converter main circuits. In this case, the circulating current can be suppressed by the current control system, which has the effect of eliminating the need for a transformer on the AC input side of the converter main circuit.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention.

FIG. 2 is a circuit diagram of a conventional example.

[Explanation of symbols]

3 ₁ 3 ₂ ... Converter main circuit 4 ... Load 5 ₁ 5 ₂ ... Control device 6 _U1 , 6 _W2 ... Hall current transformer 7 ₁ , 7 ₂ , 7 ₃ ... Amplifier 9 ... Voltage detector 10 ... Error amplifier 11 _U , 11 _V , 11 _W ... Multiplier 12 ... Detection transformer 13 _U , 13 _V , 13 _W ... Error amplifier

Claims (1)

[Claims] 1. In a PWM converter connected in parallel, an AC input side of a main circuit of each converter is directly connected to an AC power source, and a converter control device has a current control system in a minor loop of a voltage control system and a PWM gate signal. And a current control system for comparing each phase current command obtained from the voltage control system with each phase input current detection signal of the main circuit of the converter.