JP2006166499A - Power converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power converter for controlling continuously operating converters as an input DC voltage of an inverter is controlled within a target value even if an output from an electric motor as a load of the inverter is unbalanced in a transformer-less system having a plurality of the converters connected in series. <P>SOLUTION: The power converter is included in the transformerless system having the n converters 5 connected in series, and is provided with a DC voltage detecting means 6 for detecting a DC voltage from each converter, a first output voltage instruction calculating means 13 for calculating a first output voltage instruction as a common output voltage instruction for the converters, based on the DC voltages from all the converters, and a second output voltage instruction calculating means 16 for calculating a second output voltage instruction so as to match the DC voltage of each converter with each predetermined value. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a power conversion device.

  In AC train systems such as the Shinkansen, electric power is supplied from a single-phase AC line to the motor via a transformer, converter and inverter. By using a transformer, the high voltage of the overhead wire is reduced and further insulated, thereby facilitating the insulation of each electrical device. However, the installation of a transformer is not always preferable from the viewpoint of the weight of the apparatus and the viewpoint of noise generated during operation of the transformer itself, and is expected to be realized in a transformerless system that does not use a transformer.

  In the transformerless system, the converter is directly connected to the high-voltage overhead line, so that it is necessary to connect only the required number of the multiple converters in series according to the rated voltage of the overhead line. However, when the AC sides of such a plurality of converters are connected in series with each other, if an imbalance occurs in the output of the electric motor that is the load of the inverter, the input DC voltage of the inverter rises, and the overvoltage detection operates. It may become out of control.

As a transformerless system in which the converters connected in series are directly connected to the overhead line, `` Leon M. Tolbert, Frang Zheng Peng, Tim Cunnyngham, and John N. Chiasson, '' Charge Balance Control Schemes for Cascade Multilevel Converter in Hybrid Electric Vehicles ", IEEE Transactions on Industrial Electronics, Vol. 49, No. 5, October 2002" (Non-Patent Document 1), "Sibylle Diekerhoff, Uwe Schaefer,""Transformerless Drive System for Main Line Rail Vehicle Propulsion", EPE 2001- Graz, August 27-29, 2001 (Non-Patent Document 2), "M. Steiner, R. Deplazes, H. Stemmler," A New Transformerless Topology for AC-Fed Traction Vehicles using Multi-Star Induction Motors ", EPE'99-Lausanne, September 9-9, 1999 "(Non-Patent Document 3). However, Non-Patent Document 1 assumes that the DC link voltage is a fixed value, and Non-Patent Documents 2 and 3 do not discuss a control method when an imbalance occurs in the load output of the inverter.
Leon M. Tolbert, Frang Zheng Peng, Tim Cunnyngham, and John N. Chiasson, "Charge Balance Control Schemes for Cascade Multilevel Converter in Hybrid Electric Vehicles", IEEE Transactions on Industrial Electronics, Vol. 49, No. 5, 2002 10 Moon Sibylle Diekerhoff, Uwe Schaefer, "Transformerless Drive System for Main Line Rail Vehicle Propulsion", EPE 2001-Graz, August 27-29, 2001 M. Steiner, R. Deplazes, H. Stemmler, "A New Transformerless Topology for AC-Fed Traction Vehicles using Multi-Star Induction Motors", EPE'99-Lausanne, September 7-9, 1999

  The present invention has been made in view of the above-described problems of the prior art, and is unbalanced in the converter load, that is, the motor output that is the load of the inverter, in a transformerless system in which a plurality of converters are connected in series. An object of the present invention is to provide a power conversion device that allows operation to be continued while controlling an input DC voltage of an inverter within a target value even in a situation where the occurrence of the inverter occurs.

  The present invention provides a power conversion device in which AC input sides of a plurality of n converters are connected in series with each other, both ends thereof are connected to an AC power source, and each load is connected to the DC side of each of the converters. DC voltage detection means for detecting a DC voltage, first output voltage command calculation means for calculating a first output voltage command serving as a common output voltage command for the converter based on the detected DC voltage of all converters, Second output voltage command calculation means for calculating a second output voltage command based on the detected DC voltage of the converter so that the DC voltage of each of the converters matches a predetermined value; and the first output PWM control means for PWM-controlling the gate of each converter according to the output of the voltage command calculation means and the output of the second output voltage command calculation means.

  In the present invention, the first output voltage command calculation means includes a common DC voltage calculation means for calculating a common DC voltage according to a predetermined relationship based on the DC voltages detected by the n converters, and the common DC voltage and the predetermined voltage. An output current command calculating means for calculating an output current command such that a deviation from the DC voltage command is zero, an AC current detecting means for detecting an AC current flowing on the AC side of the n converters, and the output current command Current control means for calculating the first output voltage command so that the detected AC current matches the detected AC current, and the second output voltage command calculation means includes the detected DC voltage of each converter DC difference voltage calculating means for calculating a difference voltage from the common DC voltage, and a DC voltage for generating a second output voltage command to each converter so that the DC difference voltage of each converter becomes zero. It can be assumed to have a separate control unit.

  In the power conversion device of the present invention, voltage feedforward calculation means for calculating a feedforward value of the converter output voltage based on the detected DC voltage and output current command of each converter, and the first output voltage command A third output voltage command calculating means for calculating a third output voltage command of each converter in accordance with an output of the calculating means and an output of the second output voltage command calculating means and supplying the third output voltage command to the PWM control means; and the voltage feedforward calculation. Converter output side voltage command means for correcting the third output voltage command by adding the output of the means to the output of the third output voltage command calculation means.

  In the power converter of the present invention, the DC voltage average value calculating means for calculating the average value based on the DC voltages detected by all the converters, and the converter output current based on the DC voltage average value and the DC voltage command. Current feedforward calculation means for calculating the feedforward value of the output, and n outputs for correcting the first output voltage command by adding the output of the current feedforward calculation means and the output of the first output current command calculation means Common converter output current command means may be provided.

  According to the present invention, the inverter DC voltage is controlled within the target value even in a situation where an unbalance occurs in the converter load, that is, the motor output that is the load of the inverter, in a transformerless system in which a plurality of converters are connected in series. Thus, it is possible to provide a power conversion device that continues the operation.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. 1 and 2 are block diagrams showing the configuration of a power conversion device according to an embodiment of the present invention. Single-phase alternating current fed from the substation is collected by the pantograph 1 and the wheels 2. The AC input sides of a plurality of n converters 5 are connected in series, and both ends thereof are connected to the pantograph 1 and the wheel 2, respectively. A filter capacitor 7 for smoothing and a converter load are connected to the DC side of each converter 5. The converter load is a main motor (M) 9 and a VVVF inverter 8 that drives the main motor 9.

Based on the AC-side current detected by the current detector 4, the converter control unit 10 of the converter 5 generates an alternating current so that each filter capacitor voltage Vdc1,..., Vdcn detected by the voltage detector 6 has a predetermined value. The output voltage command Vc ^* is controlled. The input to the converter control unit 10 is an output current Ic that is a current on the AC side of the converter 5 and voltages Vdc1,..., Vdcn of the filter capacitor 7.

The filter capacitor voltage average value calculation unit 11 receives the filter capacitor voltages Vdc1,..., Vdcn of each converter 5 and calculates the average value as shown in Equation (1).

In the present embodiment, the common DC voltage Vdccom indicates an average value VdcAVE of filter capacitor voltages. The calculation formula of the common DC voltage Vdccom may be obtained by weighting each filter capacitor voltage with a weighting factor according to the situation as follows.

The voltage control unit 13 receives the difference voltage between the filter capacitor voltage average value VdcAVE, which is the output of the subtractor 12, and the DC voltage command Vdc ^* , which is the target value, so that the deviation becomes zero. The effective current amplitude command value IPA ^* is calculated as shown in Equation 3.

  Here, KpAVR and KiAVR are a proportional gain and an integral gain of DC voltage control. S is a Laplace operator.

  The phase estimation unit 31 calculates the phase θs of the power supply voltage based on the overhead line voltage V1 by a well-known single-phase PLL technique.

The current command calculation unit 27 calculates the converter output current command Ic ^* by the equation (4) based on the power supply voltage phase θs and the effective current amplitude command IPA ^* of the converter 5. However, here, it is assumed that the power factor at the pantah point = 1. In the present embodiment, it is assumed that the power factor at the punter point is 1. However, even if the power factor at the punter point is not 1, the same effect can be obtained.

The current control unit 16 calculates the first output voltage command Vccmp as shown in Equation 5 so that the output current Ic detected by the current detector 4 matches the output current command Ic ^* of the converter 5.

  However, Kp is a proportional gain.

The correction voltage control unit 26 receives a difference voltage between each converter filter capacitor voltage Vdc1,..., Vdcn, which is an output of the subtractor 19, and the average DC voltage VdcAVE. Therefore, the correction voltage control unit 26 calculates the correction voltage values VsA1,..., VsAn of each converter 5 as shown in Equation 6 so that the difference voltage becomes zero.

  However, Kvdc is a proportional gain.

In the correction voltage calculating unit 28, the voltage amplitude correction value VsA1 of each converter 5, ..., based on VsAn and the power supply voltage phase [theta] s, the second output voltage command for each converter 5 ^Vs1 *, ..., the number of Vsn ^* 7 Calculate as in the equation.

In the adder 17, the second output voltage command ^Vs1 of all the units first output voltage command Vccmp and each converter 5 *, ..., by adding the Vsn ^*, output voltage command value ^Vc1 for each converter 5 *, ..., Vcn ^* Can be calculated.

The PWM control unit 18 generates a gate signal to each converter by triangular wave comparison PWM control or the like so that an output voltage that matches the output voltage command value Vc1 ^* ,..., Vcn ^* of each converter 5 is obtained.

With such a configuration, the following operational effects can be obtained. An output current command Ic ^* common to all units is calculated according to the average DC voltage of the converter 5 calculated by the filter capacitor voltage average value calculation unit 11. The current controller 16 adjusts the output voltage of the converter 5 so that a current that matches the output current command Ic ^* flows. The correction voltage control unit 26 adjusts the output voltage of each converter 5 so that the DC voltage of each converter 5 matches the average DC voltage. That is, the average DC voltage of all converter loads is adjusted by the converter input current, and each individual DC voltage is adjusted by the converter output voltage.

  Therefore, when the load output of each converter is unbalanced according to the above setting, that is, when the output of the motor 9 is unbalanced, the average direct current voltage is controlled to a predetermined value by the output current, and the unbalance of each direct current voltage is controlled. By correcting this, the DC voltage of each converter 5 can be controlled to a predetermined value at high speed while reducing mutual interference.

  FIG. 3 shows changes in DC voltage, load output, output voltage and output current when the load output of half of the converters is reduced to 50%. It can be confirmed that the DC voltage is controlled within the target value.

Next, the torque correction control unit 23 will be described in detail. The torque correction control unit 23, output voltage command ^Vc1 of each converter 5 *, ..., a difference voltage between the maximum voltage Vcmax the Vcn ^* and the converter can output is input, the output voltage command ^Vc1 *, ..., Vcn ^* maximum Torque correction values T1 cmp,..., Tncmp of each inverter 8 are calculated as shown in Equation 9 so that the difference voltage becomes 0 or less when the voltage Vcmax is exceeded.

  However, KpP is a proportional gain for torque correction.

Here, although based on the output voltage, it may be considered as a modulation rate. That is, when the output voltage command exceeds the maximum output voltage, it is the same as when the modulation rate exceeds 1. Further, the same effect can be obtained by using the difference voltage between the detected RMS value of the converter output voltage and the RMS value of the maximum output voltage, not based on the difference voltage between the converter output voltage command Vdc ^* and the maximum voltage Vcmax. .

By the torque control unit 30 of the inverter 8 to be realized by the vector control system PWM control is well known, the torque command ^T1 *, ..., Tn ^* are corrected as number 10 formula.

  Here, whether it is converter load output or inverter power, the same effect as the motor output is exhibited.

With the above configuration, the load output of the converter 5 whose output voltage exceeds the maximum output voltage is adjusted by the torque correction controller 23 according to the output voltage command Vc ^* and the maximum output voltage Vcmax of the converter 5. As a result, when the output voltage of the converter 5 exceeds the maximum output voltage, the failure of the control due to the increase of the output voltage can be prevented by suppressing the converter load output in the decreasing direction.

  FIG. 4 shows that control has failed because the load output of half of the converters 5 has decreased to 25% and the output voltage of the converter has exceeded the maximum output voltage. On the other hand, in the present embodiment, as shown in FIG. 5, when the converter output voltage exceeds the maximum output voltage, the load output is adjusted, control failure is prevented, and stable operation continuation is realized. .

Next, the voltage FF calculation unit will be described in detail. The voltage FF calculator 22 calculates the voltage feedforward terms VfA1,..., VfAn as follows based on the electric power Pi1,..., Pin of each inverter and the converter output current command Ic ^* .

  Here, Kv is a predetermined conversion gain.

The adder 21 adds the voltage feedforward terms VfA1,..., VfAn to the voltage amplitude correction values VsA1,. Therefore, the correction voltage commands Vs1 ^* ,..., Vsn ^* of each converter 5 output from the correction voltage calculation unit 28 are as follows.

  Note that the same effect can be obtained even if the output voltage feedforward value is calculated based on the converter load output or the motor output.

  With the configuration as described above, the output voltage feedforward value VfA is calculated by the voltage FF calculation unit 22 according to the load output of each converter. Thereby, even if the load output of each converter changes rapidly, the fluctuation | variation of DC voltage can be suppressed. As a result, it is possible to avoid the converter 5 from being stopped due to overvoltage, so that the reliability characteristics of the system can be improved.

  FIG. 6 shows the effect of the output voltage feedforward, and it can be seen from the comparison with FIG. 5 that the fluctuation of the DC voltage is suppressed after the voltage feedforward control is turned on.

Next, the converter average power calculation unit 25 will be described in detail. The converter average power calculation unit 25 receives each converter output power Pi1,..., Pin, and calculates the average power value PiAVE ^* as follows.

The current FF calculation unit 20 calculates the converter current amplitude feedforward term IFA ^* based on the average power value PiAvE ^* and the DC voltage command Vdc ^* as shown in Equation 14.

  However, KpI is a proportional gain of current feedforward control.

The adder 14 adds the converter current feedforward term IFA ^* to the current amplitude command IPA ^* and corrects it. Therefore, Equation 4 is corrected to Equation 15 to calculate converter output current command Ic ^* .

  With the above configuration, an output current feedforward value common to all units is calculated according to the converter average load output calculated by the average power calculation unit 25, and when the converter load output is unbalanced, the load output average is calculated. An output current command corresponding to the value can be calculated. Therefore, it is possible to quickly suppress the jump of the DC voltage when the load suddenly changes.

  FIG. 7 shows the effect of output current feedforward. Comparison with FIG. 6 shows that the jump of the DC voltage is further suppressed after the current feedforward control is turned on. As a result, the converter can be prevented from being stopped due to overvoltage, and the reliability of the system can be further improved.

In the present embodiment, the average DC voltage VdcAVE is used as the common DC voltage Vdccom. However, similar effects can be obtained by using the maximum converter DC voltage detected as shown in Equation 16 instead of using the average DC voltage.

  In particular, in this case, since the output current is controlled not by the average but by the maximum voltage, it is possible to more reliably avoid the converter 5 from being stopped due to overvoltage, and the effect of improving the reliability of the system can be obtained.

  When the load output of the converter is unbalanced, for example, when the load is an inverter and a motor, and the output of the motor is unbalanced, the power conversion device configured as described above generates an average DC voltage by the output current of the converter. Control to a predetermined value to eliminate individual DC voltage imbalance by correcting the converter output voltage, reduce mutual interference caused by DC voltage imbalance of each converter, and quickly to a predetermined value And can be controlled.

  In addition, the power conversion device according to the present embodiment prevents the failure of control due to the increase in the output voltage of the converter by suppressing the converter load output in a decreasing direction when the output voltage of the converter exceeds the maximum output voltage. be able to.

  Furthermore, the power conversion device according to the present embodiment can quickly suppress the jump of the DC voltage at the time of sudden load change by calculating the output current command according to the average value of the load output. As a result, even if the converter load output changes suddenly, fluctuations in the DC voltage can be suppressed. As a result, it is possible to prevent a certain converter from being stopped due to overvoltage. Can be improved.

  Instead of the control based on the modulation factor in the above embodiment, an actual voltage may be used.

The block diagram 1 of the power converter device of one embodiment of this invention. The block diagram 2 of the power converter device of one embodiment of this invention. The power converter device of the said embodiment WHEREIN: The graph which shows the change of DC voltage, load output, an output voltage, and output current when the load output of a half converter reduces to 50%. As a comparative example, a graph showing changes in DC voltage, load output, output voltage and output current when the load output of half of the converters is reduced to 25%. In the power conversion device of the above embodiment, when the load output of half of the converters is reduced to 25% and the load output is adjusted when the converter output voltage exceeds the maximum output voltage, the DC voltage, the load output A graph showing changes in output voltage and output current. FIG. 6 is a graph showing changes in DC voltage, load output, output voltage, and output current when voltage feedforward control is further applied from the operating conditions of FIG. 5 in the power conversion device of the embodiment. FIG. 7 is a graph showing changes in DC voltage, load output, output voltage, and output current when output current feedforward control is further entered from the operating conditions of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pantograph 2 Wheel 3 Converter input voltage detector 4 Converter input current detector 5 Converter 6 Filter capacitor voltage detector 7 Filter capacitor 8 Inverter 9 Electric motor 10 Converter control part 11 Filter capacitor voltage average value calculation part 12 Subtractor 13 DC voltage control Unit 14 Adder 15 Subtractor 16 Current control unit 17 Adder 18 PWM control unit 19 Subtractor 20 Current FF calculation unit 21 Adder 22 Voltage FF calculation unit 23 Torque correction control unit 24 Subtractor 25 Average power calculation unit 26 Correction voltage Control unit 27 Current command calculation unit 28 Correction voltage calculation unit 29 Subtractor 30 Inverter torque control unit 31 Phase estimation unit 32 Voltage detector

Claims (9)

In the power conversion apparatus in which the AC input sides of a plurality of n converters are connected in series with each other, both ends thereof are connected to an AC power source, and each load is connected to the DC side of each of the converters
DC voltage detection means for detecting the DC voltage of each converter;
First output voltage command calculation means for calculating a first output voltage command serving as a common output voltage command for the converter based on the detected DC voltage of all converters;
A second output voltage command calculation means for calculating a second output voltage command based on the detected DC voltage of each converter so that the DC voltage of each converter matches a predetermined value;
A power conversion device comprising: PWM control means for PWM-controlling the gate of each converter in accordance with the output of the first output voltage command calculation means and the output of the second output voltage command calculation means. The first output voltage command calculation means includes common DC voltage calculation means for calculating a common DC voltage according to a predetermined relationship based on DC voltages detected by n converters, the common DC voltage and a predetermined DC voltage command, Output current command calculating means for calculating an output current command so that the deviation of the output becomes zero, AC current detecting means for detecting an AC current flowing on the AC side of the n converters, and the output current command detected Current control means for calculating the first output voltage command so that the alternating current matches,
The second output voltage command calculation means includes DC difference voltage calculation means for calculating a difference voltage between the detected DC voltage of each converter and a common DC voltage, and the DC difference voltage of each converter becomes zero. The power converter according to claim 1, further comprising direct current voltage individual control means for generating a second output voltage command to each converter.   The power converter according to claim 2, wherein the common DC voltage calculation unit calculates an average value based on DC voltages of the n converters.   The power converter according to claim 2, wherein the common DC voltage calculation means is a maximum DC voltage calculation means for obtaining a maximum voltage based on a DC voltage detected by each of the converters.   Modulation rate calculation means for calculating the modulation rate of each converter, and load output control means for controlling the output of the load connected to each converter so that the modulation rate of each converter does not exceed 1. The power conversion device according to claim 1, wherein: The load is an electric motor,
The load output control means corrects the torque of the motor load based on a difference voltage between the output voltage command and the overvoltage set value when an output voltage command of each converter exceeds an overvoltage set value. The power conversion device according to claim 5. Voltage feedforward calculation means for calculating a feedforward value of the converter output voltage based on the detected DC voltage and output current command of each converter;
A third output voltage command calculating means for calculating a third output voltage command for each converter in accordance with an output of the first output voltage command calculating means and an output of the second output voltage command calculating means and supplying the third output voltage command to the PWM control means; ,
The converter AC output voltage command means for correcting the third output voltage command by adding the output of the voltage feedforward calculation means to the output of the third output voltage command calculation means. The power converter according to 1 or 2. DC voltage average value calculating means for calculating the average value based on the detected DC voltage of all converters, and current feedforward for calculating the feedforward value of the converter output current based on the DC voltage average value and the DC voltage command. Computing means;
N converter common output current command means for correcting the first output voltage command by adding the output of the current feedforward calculation means and the output of the first output current command calculation means. The power conversion device according to claim 2. The power converter according to claim 1, wherein the AC power supply is a single-phase AC.

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