JP2006191743A - Three-level pwm power converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably conduct neutral-point potential control without being influenced by the ripple of an input current, a detection delay or the like even if the input current is small. <P>SOLUTION: This three-level PWM power converter performs polarity switching on the basis of the operation command (power running/regeneration) of an inverter in place of an input current detection value, by paying attention to the fact that a power factor at the input side of an AC electric vehicle is operated so as to be 1.0 or -1.0 in the AC electric vehicle, and conducts the neutral-point potential control. Thus, the balance of voltages of smoothing capacitors 6, 7 can be kept without being influenced by the ripple of the input current, the detection delay or the like even if the input current is small. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a power converter that outputs three-level voltage, and more particularly to a neutral point potential control system.

FIG. 6 shows a conventional example of a three-level power converter. This is an example applied to an AC electric vehicle, and is described in Patent Document 1.
In FIG. 6, 4 is a three-level PWM rectifier whose AC side is connected to the single-phase AC power supply 1 via the transformer 2 and the reactor 3, and the voltage of the smoothing capacitor 6 and the smoothing capacitor 7 connected to the DC side thereof. Rectification or regenerative operation is performed so that the sum becomes the specified voltage. Reference numeral 5 denotes a three-level inverter whose DC side is connected to the smoothing capacitors 6, 7. The inverter operates during powering, converts the DC power of the smoothing capacitors 6, 7 into AC power, and supplies the induction machine 8 with power. . Further, a regenerative operation is performed during braking (regeneration), and the rotational energy of the induction machine 8 is converted into DC power and supplied to the smoothing capacitors 6 and 7.
Although the terminal voltages Edp and Edn of the smoothing capacitors 6 and 7 are ideally equal, the smoothing capacitor voltages Edp and Edn are unbalanced due to variations in characteristics of the semiconductor switch elements constituting the power converter. As a result, the output voltage of the inverter 5 is unbalanced between positive and negative, so that a desired voltage cannot be output, and either one of the smoothing capacitors 6 and 7 becomes an overvoltage, which may damage the device. Therefore, neutral point potential control is performed to equalize the smoothing capacitor voltages Edp and Edn. The circuit configuration and control device of the three-level PWM rectifier 4 performing neutral point potential control will be described below.

  As shown in FIG. 7, the three-level PWM rectifier 4 includes a U-phase leg 100 and a V-phase leg 200. The U-phase leg is a connection point between the semiconductor switches 101a, 101b, 101c, and 101d, and the diodes 102a, 102b, 102c, and 102d connected in reverse parallel to the smoothing capacitors 6 and 7 (hereinafter referred to as neutral points). It consists of a diode 103a connected between z1 and the cathode side of the diode 102b, and a diode 103b connected to the neutral point z1 and the anode side of the diode 102c, and the V-phase leg is similarly switched to the semiconductor switches 201a, 201b, 201c, 201d, diodes 202a, 202b, 202c, 202d connected in antiparallel to these, diode 203a connected between neutral point z1 and the cathode side of diode 202b, neutral point z1 and diode It consists of a diode 203b connected to the anode side of 202c. The semiconductor switches 101a, 101b, 101c, 101d, and 201a, 201b, 201c, 201d are turned on / off based on the gate signals PWMU, PWMV of each phase output from the control device 20, and are opposed to the input voltage Vc Is output to maintain the sum of the smoothing capacitor voltages Edp and Edn at a specified voltage.

  The control device 20 includes a voltage command calculation unit 21, an adder 22, subtracters 23 and 24, a polarity inverter 25, a gate signal generation unit 26, and a neutral point potential control unit 30. The adder 22 adds the terminal voltages Edp and Edn of the smoothing capacitors 6 and 7 detected by the voltage detectors 12 and 13 and outputs the result to the voltage command calculation unit 21 as a collective DC voltage Ed. Based on the input voltage Vs detected by the voltage detector 10, the input current Is detected by the current detector 11, and the DC voltage Ed, the voltage command calculation unit 21 outputs an output voltage command vcsol that matches the DC voltage Ed with a specified voltage. Output. Then, the subtractor 24 performs a correction process by neutral point potential control on the output voltage command vcsol, which is used as a U-phase voltage command vusol, and the polarity inverter 25 reverses the polarity of the output voltage command vcsol This is the V-phase voltage command vvsol. The gate signal generators 26U and 26V output gate signals PWMU and PWMV to the PWM rectifier 4 based on the U-phase and V-phase voltage commands vusol and vvsol, and turn on / off each semiconductor switch.

The neutral point potential controller 30 includes a voltage command correction amount calculator 31, a polarity determiner 32, and a multiplier 33. The voltage command correction amount calculation unit 31 is a proportional controller or the like, and outputs a voltage command correction amount vccmp corresponding to the difference voltage ΔEd between the smoothing capacitor voltage Edp and Edn calculated by the subtracter 23. The polarity determiner 32 outputs `` 1 '' as the current polarity signal Issign when the polarity is positive based on the input current detection value Is (positive direction from the single-phase AC power supply to the PWM rectifier). If is negative, "-1" is output. The multiplier 33 multiplies the voltage command correction amount vccmp and the current polarity signal Issign, and outputs the result to the subtracter 24 as the voltage command correction amount vccmp1. The subtracter 24 subtracts the voltage correction amount vccmp1 from the output voltage command vcsol, and outputs the result as a U-phase voltage command vusol.
Thus, for example, when the differential voltage ΔEd between the smoothing capacitors 6 and 7 is positive (Edp> Edn) and the input current is positive during powering, the voltage command correction amount vccmp1 becomes a positive value, and the U-phase voltage command Is biased to the negative side, and the period during which the upper arm of the U phase is turned on becomes shorter. As a result, the charging period of the smoothing capacitor 6 is shortened, the terminal voltage Edp is reduced, and the smoothing capacitor voltages Edp and Edn can be balanced. If the differential voltage △ Ed is positive (Edp> Edn) and the input current is negative, the differential voltage △ Ed is negative (Edp <Edn) and input by biasing the U-phase voltage command to the positive side. When the current is positive, bias the U-phase voltage command to the positive side.When the differential voltage △ Ed is negative (Edp <Edn) and the input current is negative, the U-phase voltage command is biased to the negative side. As a result, the smoothing capacitor voltages Edp and Edn can be balanced. The operation of neutral point potential control during regeneration is the reverse of that during powering.
Republished WO97 / 25766 (Fig. 1)

  In the conventional example, neutral point potential control is performed based on the polarity of the input current detection value Is, and therefore there is a difference between the actual current value and the detection value due to input current ripple, detection delay, etc. There is a possibility that the neutral point potential control is reversed and the voltage difference between the smoothing capacitors 6 and 7 is further increased. Further, when the input current is small and the polarity cannot be determined, the control becomes impossible, and there is a possibility that the voltages of the smoothing capacitors 6 and 7 cannot be balanced.

The reason why neutral point potential control is the reverse of the original operation and the voltage difference between the smoothing capacitors 6 and 7 is increased or becomes uncontrollable is determined by determining the polarity based on the detected value of the input current. It is because it is doing.
The present invention focuses on the fact that an AC electric vehicle is operated so that its power factor on the input side is 1.0 or -1.0. Instead of an input current detection value, an operation command (power running / regeneration) of the converter is used. ), Switching the polarity and performing neutral point potential control, without being affected by input current ripple, detection delay, etc., and even when the input current is small, the voltage balance of the smoothing capacitors 6 and 7 is balanced. It is intended to be able to plan.

  According to the present invention, neutral point potential control can be performed stably without being affected by input current ripple, detection delay, and the like, and even when the input current is small.

When powering (power factor 1.0 operation) and the differential voltage △ Ed is positive (Edp> Edn), by biasing the U-phase voltage command to the negative side, both the input voltage and current are positive. The charging period of the smoothing capacitor 6 is shortened by the path shown in FIG. 1 (AC input U → diode 102b → diode 102a → smoothing capacitor 6 → diode 203a → semiconductor switch 201b → AC input V), and both the input voltage and current are negative. In this period, the period for charging the smoothing capacitor 7 in the path shown in FIG. 2 (AC input V → semiconductor switch 201c → diode 203b → smoothing capacitor 7 → diode 102d → diode 102c → AC input U) becomes longer. The voltage Edp and Edn can be balanced. When the differential voltage ΔEd is negative (Edp <Edn), the smoothing capacitor voltages Edp and Edn can be balanced by biasing the U-phase voltage command to the positive side.
Also, when regenerating (power factor -1.0) and the differential voltage △ Ed is positive (Edp> Edn), the input voltage is positive and the current is negative by biasing the U-phase voltage command to the positive side. In the period, the period during which the smoothing capacitor 6 is discharged becomes longer by the path shown in FIG. 3 (AC input V → semiconductor switch 201c → diode 203b → smoothing capacitor 6 → semiconductor switch 101a → semiconductor switch 101b → AC input U). In the period in which the voltage is negative and the current is positive, the smoothing capacitor 7 in the path (AC input U → semiconductor switch 101c → semiconductor switch 101d → smoothing capacitor 7 → diode 203a → semiconductor switch 201b → AC input V) shown in FIG. The period during which is discharged becomes shorter, and the smoothing capacitor voltages Edp and Edn can be balanced. When the differential voltage ΔEd is negative (Edp <Edn), the smoothing capacitor voltages Edp and Edn can be balanced by biasing the U-phase voltage command to the negative side. Thus, neutral point potential control can be performed by the differential voltage ΔEd and the operation mode.

FIG. 5 shows a first embodiment. This is an example in which the present invention is applied to a three-level power converter for an AC electric vehicle. The difference between the present invention and the configuration of the conventional three-level power converter shown in FIG. 6 is that a neutral point potential control unit 40 shown in FIG. This is the point where point potential control is performed. In the neutral point potential control unit 40, the same components as those in FIG.
The neutral point potential control unit 40 includes a voltage command correction amount calculation unit 31, a multiplier 33, and a changeover switch 41. The changeover switch 41 outputs “1” as the operation mode flag rmode when the operation command is power running, and outputs “−1” when the operation command is regeneration. The multiplier 33 multiplies the voltage command correction amount vccmp by the operation mode flag rmode, and outputs the result to the subtractor 24 as the voltage command correction amount vccmp1. Thus, neutral point potential control can be performed by switching the polarity based on the operation command (power running / regeneration) instead of the input current detection value.

  In a multilevel converter / inverter system, it is important to reliably control the neutral point voltage in order to solve the problems of ensuring the output performance of the apparatus and equalizing the voltage applied to the elements. In particular, the neutral point voltage can be reliably controlled as compared with the conventional method in which the polarity of the current is detected by detecting the zero point of the current, so that the present invention can be applied to an industrial inverter as well as a vehicle-mounted converter.

It is a figure which shows the path | route of electric current Is when input voltage / input current is positive polarity at the time of power running. It is a figure which shows the path | route of electric current Is when input voltage / input current is negative polarity at the time of power running. It is a figure which shows the path | route of electric current Is when input voltage is positive polarity / input current is negative polarity at the time of regeneration. It is a figure which shows the path | route of electric current Is when input voltage is negative polarity / input current is positive polarity at the time of regeneration. 1 is a circuit diagram showing a first embodiment of the present invention. It is a circuit diagram which shows the prior art example of a 3 level power converter device. 3 shows details of the three-level PWM rectifier 4.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Single phase alternating current power supply 2 ... Transformer 3 ... Reactor 4 ... PWM rectifier 5 ... 3 level inverter 6, 7 ... Smoothing capacitor 8 ... Induction machine 10 ... Voltage Detector 11 ... Current detector 12, 13 ... Voltage detector 20 ... Control device 21 ... Voltage command calculator 22 ... Adder 23, 24 ... Subtractor 25 ... Polarity inverter 26... Gate signal generator
DESCRIPTION OF SYMBOLS 30 ... Neutral point electric potential control part 31 ... Voltage command correction amount calculating part 32 ... Polarity determination device 33 ... Multiplier 40 ... Neutral point electric potential control part 41 ... Changeover switch 100・ ・ ・ U phase leg 200 ・ ・ ・ V phase leg
101a, 101b, 101c, 101d, 201a, 201b, 201c, 201d ... Semiconductor switches 102a, 102b, 102c, 102d, 202a, 202b, 202c, 202d, 103a, 103b, 203a, 203b ... Diodes

Claims (2)

In a three-level power converter in which a series circuit of a first DC smoothing capacitor and a second DC smoothing capacitor is connected to the DC side, and an AC power source is connected to the AC side via a reactor.
A three-level power conversion device comprising means for correcting an output voltage command of the three-level power conversion device based on a difference voltage between the two DC smoothing capacitor voltages and an operating state command. The three-level power converter according to claim 1, wherein a power running command or a regenerative command is used as the operation state command.

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