JP4844180B2 - Power converter and control method thereof - Google Patents

Description

  The present invention relates to a power converter configured by two sets of three-phase voltage type PWM converters that share a DC unit and whose AC output terminals are connected via a reactor, and in particular, circulates between the three-phase voltage type PWM converters. It relates to the suppression of zero-phase current.

  As a method of increasing the capacity of a power converter, a method of connecting AC output terminals of two sets of three-phase voltage type PWM converters in parallel via a reactor as shown in FIG.

  In this configuration, since no transformer is interposed between the two sets of three-phase voltage type PWM converters, a zero-phase current circulates through both converters. This zero-phase current includes not only a zero-phase current that can flow in principle with switching, but also a low-frequency zero-phase current including a direct current that should not flow theoretically due to variations in switching timing. Since the zero-phase current only increases the loss of the converter, it is necessary to reduce the zero-phase current as much as possible in order to improve device efficiency.

  As a method for reducing the zero-phase current, Patent Document 1 proposes a method for adding a current detection value of each phase and controlling the output voltage in accordance with the value to reduce the zero-phase current. Since a DC component can also flow in the zero-phase current, the current detector that detects the zero-phase current is preferably a Hall CT.

Japanese Patent No. 3251628 (FIG. 1 and description of paragraph (0011))

  When the power converter starts operation, a loss occurs in the semiconductor switching element and the filter reactor, and the ambient temperature rises. When the ambient temperature rises, the temperature of the current detector also rises, and the output of the current detector changes due to temperature drift. Therefore, an error is superimposed on the detected value.

  When the zero-phase current circulating through two sets of three-phase voltage type PWM converters having a common DC section is suppressed by the method described in Patent Document 1, the DC current detection value and temperature included in the detection value of the current detector Since it cannot be distinguished from the offset due to drift, the zero phase is caused to flow by an error included in the detected value.

  An object of the present invention is to reduce a current detection error due to temperature drift and to suppress a zero-phase current circulating through two sets of three-phase voltage type PWM converters.

  The power converter of the present invention includes two sets of three-phase voltage type PWM converters that share a direct current section and whose AC output terminals are connected via a reactor, and each three-phase voltage type PWM converter has a current detector. The zero-phase output voltage of the three-phase voltage type PWM converter is changed using the difference in the output of the current detector.

  The power converter of the present invention can detect the zero-phase current with high accuracy. Further, by controlling the zero-phase current using the detected value, the zero-phase current circulating through the two sets of three-phase voltage type PWM converters can be accurately suppressed.

  Details of the present invention will be described with reference to the drawings.

  This embodiment will be described with reference to FIG. The power converter shown in FIG. 1 is a parallel multiplex converter. 1 is a main circuit of the power converter of this embodiment, 100 is a logic unit of the power converter of this embodiment, 8 is an AC power source, and 20 is a load. The power converter according to the present embodiment converts AC power obtained from the AC power supply 8 into DC power and supplies the DC power to the load 20.

  The main circuit 1 of the power converter includes three-phase voltage type PWM converters 2 and 3 that share a direct current section, a transformer 7, filter reactors 4 and 5, and a direct current capacitor 6. The terminal voltage of the DC capacitor 6 is the voltage detector 12, the AC output phase current of the three-phase voltage type PWM converter 2 is the current detector 13, 14, 15, and the AC output phase current of the three-phase voltage type PWM converter 3. Are the current detectors 16, 17 and 18, the zero-phase current circulating through the three-phase voltage type PWM converters 2 and 3 is detected by the current detectors 10 and 11, and the secondary side voltage of the transformer 7 is detected by the voltage detector 19. The detected value is input to the logic unit 100.

  The logic unit 100 calculates the gate signals Gate1 and Gate2 of the IGBTs of the three-phase voltage type PWM converters 2 and 3 so that the DC voltage of the three-phase voltage type PWM converters 2 and 3 follows the command value Vdcref. Specifically, the phase detector 101 calculates the phase of the secondary side voltage of the transformer 7 and outputs the voltage phase to the current controllers 102 and 107. The current controllers 102 and 107 perform α-β conversion and dq conversion on the phase current of each PWM converter using the voltage phase, and the effective current of the PWM converter converts the DC capacitor voltage in the DC voltage controller 106. The voltage d-axis component and the q-axis component are calculated so that the reactive current of the PWM converter becomes 0 so as to follow the active current command value calculated so as to follow the command value Vdcref, and these values are converted to the inverse dq. Conversion, two-phase to three-phase conversion are performed to calculate a three-phase voltage command value.

  The α-β conversion of current is shown in (Expression 1). Since the zero phase component is canceled at the time of α-β conversion, the above control is independent of the zero phase.

  The output value of the current controller 107 is input to the PWM calculator 109. The PWM calculator 109 compares the output values of the carrier and the current controller 107 and calculates the gate signal Gate2. The gate signal Gate2 is input to the three-phase voltage type PWM converter 3 to turn on / off the IGBT.

  The zero-phase current control unit, which is the point of the present invention, will be described. The zero-phase current circulating through the three-phase voltage PWM converters 2 and 3 is detected by the current detector 10 and the current detector 11. The current detector 10 and the current detector 11 are the same type of current detector. The current direction of the current detector 10 and the current detector 11 is opposite to the zero-phase current circulating through the three-phase voltage PWM converters 2 and 3.

  When the converter is operated, the temperature of surrounding electrical components such as the reactor rises, and the temperature of the current detectors 10 and 11 also rises. Therefore, an offset is superimposed on the current detection value due to the influence of temperature drift. If the current detector is the same type, the effect of temperature drift shows a similar trend. The principle of offset cancellation by temperature drift in the current detection value will be described with reference to FIG.

  2A and 2B show current detection values of the current detector 10 and the current detector 11. Offsets due to temperature drift are superimposed on the output values of the current detector 10 and the current detector 11. In the parallel multiple converter, the output currents of the three-phase voltage type PWM converters 2 and 3 are substantially equal, and the heat generation in the filter reactors 4 and 5 is also substantially equal. Therefore, the temperature changes of the current detectors are also substantially equal, and the offset due to the temperature drift included in the detection values of the current detectors 10 and 11 is also substantially equal. Since the current directions of the current detector 10 and the current detector 11 are opposite to the zero-phase current circulating through the three-phase voltage type PWM converters 2 and 3, the sign of the true current detection value is reversed.

  The result of subtracting the output values of the current detector 10 and the current detector 11 by the subtractor 103 is shown in FIG. Since the subtractor output value has the same temperature drift in the detection values of the current detectors 10 and 11, most of the offset due to the drift is canceled and becomes a value twice the true current detection value. For the above reasons, the zero-phase current can be detected with high accuracy.

  The zero-phase current calculated by the subtractor 103 is input to the zero-phase current controller 104, and the zero-phase current controller 104 calculates a zero-phase voltage adjustment for reducing the output value of the subtractor 103, and Output. The adder 105 adds the output values of the zero-phase current controller 104 and the current controller 102, calculates a new voltage command value, and inputs the output to the PWM calculator 108 to obtain the gate signal Gate1. The gate signal Gate1 is input to the three-phase voltage type PWM converter 2, and the zero-phase current can be reduced by outputting a desired alternating voltage from the three-phase voltage type PWM converter 2 by turning on and off the IGBT.

  In this embodiment, the power converter is a parallel multiple converter. However, as shown in FIG. 4, the power converter receives an active current command value from an external active current command value generator 200 and accommodates power between transmission lines. The same applies to. According to the present embodiment, in a power converter having two sets of three-phase voltage type PWM converters that share a DC part and whose AC output terminals are connected via a reactor, zero phase that circulates through the PWM converter The current can be detected with high accuracy, and as a result, the zero-phase current can be controlled with high accuracy.

  This embodiment will be described with reference to FIG. The difference between the present embodiment and the first embodiment is only that the zero-phase current is calculated from the sum of the phase currents. According to the present embodiment, since the number of current detectors can be reduced, the apparatus can be simplified.

  Only differences from the first embodiment will be described below. In FIG. 3, the same functional parts as those in FIG. In this embodiment, the current detectors 13, 14, 15, 16, 17, 18 are the same type of current detector. The AC phase current of the three-phase voltage type PWM converter 2 is detected by current detectors 13, 14, 15. The output of the current detector is input to the current controller 102 and the adder 112. The adder 112 adds the outputs of the current detectors 13, 14, and 15 to calculate a zero phase component. The output of the adder 112 is input to the subtracter 103. Similarly, the AC phase current of the three-phase voltage type PWM converter 3 is detected by the current detectors 16, 17 and 18. The output of the current detector is input to the current controller 107 and the adder 113.

  The adder 113 adds the outputs of the current detectors 16, 17, and 18 to calculate a zero phase component. The output of the adder 113 is input to the subtracter 103. Here, with respect to the zero-phase current circulating through the three-phase voltage type PWM converters 2 and 3, the current detectors 13, 14, and 15 and the current detectors 16, 17, and 18 have different current directions. By taking the difference, the offset can be canceled out, and a value double the true zero-phase current detection value can be obtained. Therefore, the zero-phase current can be detected with high accuracy, and the zero-phase current can be suppressed with high accuracy by performing the zero-phase current suppression control using this value.

  According to the present embodiment, in a power converter having two sets of three-phase voltage type PWM converters that share a DC part and whose AC output terminals are connected via a reactor, zero phase that circulates through the PWM converter The current can be detected with high accuracy, and as a result, the zero-phase current can be controlled with high accuracy. Furthermore, since the number of zero-phase current detection current detectors can be reduced, the apparatus can be simplified.

  The present embodiment will be described with reference to FIG. The difference between the present embodiment and the first embodiment is that the method for reducing the offset of the current detector is different. Hereinafter, only differences from the first embodiment will be described. Further, in FIG. 5, the same functional parts as those in FIG.

  The outputs of the current detector 10 and the current detector 11 are input to the adder 110 and added. Since the true current detection value has the opposite sign, it is canceled by adding the current detection value, and only the offset value remains. Since the sum of the current detection values is the sum of the offset values of the current detector 10 and the current detector 11, the offset average value of the current detectors 10 and 11 can be calculated by multiplying the multiplier 114 by 1/2. The subtractor 111 subtracts the output of the multiplier 114 from the output of the current detector 10 to obtain a zero-phase current with most of the offset canceled. Therefore, the zero-phase current can be detected with high accuracy.

  In this embodiment, the parallel number of the three-phase voltage type PWM converter is set to 2. However, even if the parallel number is other than 2, the offset can be calculated by dividing the sum of the zero-phase current detection values by the parallel number. As in the example, the zero-phase current can be detected with high accuracy. According to the present embodiment, in a power converter having two sets of three-phase voltage type PWM converters that share a DC part and whose AC output terminals are connected via a reactor, zero phase that circulates through the PWM converter The current can be detected with high accuracy, and as a result, the zero-phase current can be controlled with high accuracy.

FIG. 3 is an explanatory diagram of a power converter according to the first embodiment. FIG. 3 is an explanatory diagram of the principle of reducing the current detector offset according to the first embodiment. Explanatory drawing of the power converter of Example 2. FIG. Explanatory drawing of another power converter of Example 1. FIG. Explanatory drawing of the power converter of Example 3. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Main circuit, 2, 3 ... Three-phase voltage type PWM converter, 4, 5 ... Filter reactor, 6 ... DC capacitor, 7, 9 ... Transformer, 8 ... AC power supply 10, 11, 13, 14, 15, 16, 17, 18 ... current detector, 12, 19 ... voltage detector, 20 ... load, 100 ... logic unit, 101 ... phase detector, 102, 107 ... current controller, 103, 111 ... subtractor, 104 ... Zero phase current controller, 105, 110, 112, 113 ... adder, 106 ... DC voltage controller, 108, 109 ... PWM calculator, 114 ... multiplier, 200 ... active current command value generator.

Claims (1)

It is a power converter composed of two sets of three-phase voltage type PWM converters that share a DC part and whose AC output terminals are connected via a reactor,
Detecting the two sets of the current detector to detect the two sets of the zero-phase current of the three-phase voltage-PWM converter collectively respectively, the two sets of three-phase voltage type PWM converter AC output phase currents, respectively and two sets of three of the current detector, wherein using the output of the two sets of the current detector for detecting an AC output phase currents, the two sets of three-phase voltage-type PWM converter two sets of controlling individually a current controller, a subtractor for subtracting the output of the two sets of the current detector for detecting the zero-phase current, a zero-phase current controller for calculating a zero-phase voltage adjustment amount to reduce the output value of the subtracter Have
Using the output of the zero-phase current controller and the output of one of the two sets of current detectors that detect the zero-phase current , the zero-phase output voltage of one of the three-phase voltage type PWM converters is changed. A featured power converter.

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