JP2012175767A - Electric power conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power conversion device capable of improving distortion of a current waveform by performing switching in proper timing according to the current.SOLUTION: An electric power conversion device 10 includes a reactor 12 connected to respective phase lines of a three-phase AC power source; two smoothing capacitors 14a, 14b connected in series between DC terminals of a three-phase rectifier 13; switching elements SW1, SW2, and SW3 each corresponding to each phase and having one end connected to an output end of each reactor 12 and the other end connected to a middle point between the two smoothing capacitors 14a, 14b; and a switching control part 15. The switching control part 15 switches the switching elements SW1, SW2, and SW3 within a predetermined angle range within an angle range of -30° or more and +60° or less when a zero-cross point of a voltage waveform of each phase is 0°, and the predetermined angle range is varied according to a maximum amplitude of a last half-wave current waveform in each phase.

Description

  The present invention relates to, for example, a power converter that rectifies a three-phase AC voltage and converts it into a DC voltage.

As a power converter that rectifies three-phase AC voltage and converts it to DC voltage, a three-phase rectifier circuit consisting of six diodes connected in a three-phase bridge and a smoothing connected between the DC output terminals of the three-phase rectifier circuit A configuration including a capacitor is generally used.
Conventionally, in such a power converter, for example, methods disclosed in Patent Literature 1 and Patent Literature 2 have been proposed as methods for suppressing harmonics included in a current waveform.

  In Patent Document 1, a single-phase rectifier circuit in which four diodes are connected in a single-phase bridge is connected to each phase of a three-phase AC power supply, and a semiconductor switching element is provided between the DC output terminals of the single-phase DC circuit. In addition, it is disclosed that a semiconductor switching element is turned on and off in a period of about 30 degrees or more and less than 60 degrees before and after the zero-cross point of each phase voltage to obtain an effect of suppressing harmonic components contained in the input current.

  In Patent Document 2, in a three-phase full-wave rectifier circuit known as a general passive system, a short-circuit switch for short-circuiting each phase of a three-phase AC power supply is provided, and a predetermined delay time is set from the zero-cross point of each phase. It is disclosed that a short-circuit switch is turned on and turned off after a predetermined time to obtain an effect of suppressing harmonic components contained in the input current and an effect of improving the power source power factor.

JP-A-9-182441 (FIGS. 2 and 3) International Publication No. 2005/006531 (FIGS. 6 and 7)

  However, in the methods disclosed in Patent Document 1 and Patent Document 2, since switching is performed uniformly regardless of the current waveform, switching cannot be performed at an appropriate timing according to the current state. .

  The present invention has been made in view of such circumstances, and by performing switching at an appropriate timing according to the current, the distortion of the current waveform before and after the zero cross point of each phase voltage is improved. An object of the present invention is to provide a power conversion device that can be used.

In order to solve the above problems, the present invention employs the following means.
The present invention is a power conversion device that rectifies and converts a three-phase AC voltage output from a three-phase AC power source into a DC voltage, the reactor connected to each phase line of the three-phase AC power source, and the reactor A three-phase rectifier for rectifying the AC voltage output from the two-phase rectifier, two smoothing capacitors connected in series between the DC terminals of the three-phase rectifier, and one end connected to the output end of each of the reactors. Switching element provided corresponding to each phase where the other end is connected to the middle point of the capacitor, and an angle range between -30 degrees and +60 degrees when the zero cross point of the voltage waveform of each phase is 0 degrees Switching control means for switching the switching element in a predetermined angle range in accordance with the maximum amplitude of the immediately preceding half-wave current waveform in each phase. Providing a power conversion device for changing the serial predetermined angular range.

  According to the present invention, when the zero-cross point of the voltage waveform of each phase is 0 degree, the switching element provided corresponding to each phase in a predetermined angle range within an angle range of −30 degrees to +60 degrees In addition, since the predetermined angle range is determined according to the maximum amplitude of the immediately preceding half-wave current waveform in each phase, it is possible to set an appropriate angle range according to the current situation at that time. it can. As a result, it is possible to avoid an excessive increase in current and a shortage of the current increase amount, and it is possible to effectively improve the distortion of the current waveform.

  In the power conversion device, the switching control means has a maximum amplitude at which current can be output and an angle range corresponding to the maximum amplitude in the range of 0 degrees to less than 60 degrees, and the maximum amplitude The angle range may be determined based on the ratio of the measured value of the current amplitude to.

  Thus, since the angle range is determined based on the ratio of the measured value of the current amplitude to the immediately preceding maximum amplitude, an appropriate angle range can be determined according to the current increase / decrease.

  In the power converter, the switching control unit may predict a zero cross point of a current waveform in an angle range of −30 degrees or more and less than 0 degree, and may perform switching at the predicted position of the zero cross point.

  Thus, since the zero cross point of the current waveform is predicted and the switching element is turned on at the predicted position of the zero cross point, distortion of the current waveform can be alleviated without being turned on and off excessively.

  According to the present invention, by performing switching at an appropriate timing according to the current, it is possible to improve the distortion of the current waveform before and after the zero cross point of each phase voltage.

It is a circuit diagram showing a schematic structure of a motor drive device to which a power converter according to an embodiment of the present invention is applied. It is a figure for demonstrating the on-off timing of the switching element which concerns on one Embodiment of this invention. It is a figure for demonstrating the determination method of the angle range which performs switching.

Hereinafter, an embodiment in which a power conversion device according to the present invention is applied to a motor drive device will be described with reference to the drawings.
FIG. 1 is a circuit diagram illustrating a schematic configuration of a motor driving device to which a power conversion device 10 according to the present embodiment is applied. As shown in FIG. 1, the power conversion device 10 according to the present embodiment converts rectified three-phase AC power from a three-phase AC power supply 11 into DC power. In the motor drive device shown in FIG. 1, the electric power converted into direct current by the power conversion device 10 is converted again into three-phase alternating current power by the inverter 20 and supplied to the motor 30. Thereby, the motor 30 is driven.

  The power conversion apparatus 10 includes a reactor 12 connected to each phase line (R phase, T phase, S phase) of the three-phase AC power supply 11, a three-phase rectifier 13 that rectifies an AC voltage output from each reactor 12, and Between the DC output terminals of the three-phase rectifier 13, two smoothing capacitors 14a and 14b connected in series are provided. The three-phase rectifier 13 includes six diodes connected in a three-phase bridge. Further, the power converter 10 has one end connected to the output end of each reactor 12 corresponding to each phase (R phase, T phase, S phase), and the other end at the midpoint of the two smoothing capacitors 14a, 14b. Switching elements SW1, SW2, and SW3 are provided. Switching of the switching elements SW1, SW2, and SW3 is controlled by the switching control unit 15. The switching element SW1 corresponds to the R phase, the switching element SW2 corresponds to the T phase, and the switching element SW3 corresponds to the S phase. The zero cross and the current of the voltage of each phase output from the three-phase AC power supply 11 are detected by the voltage detection unit 16 and the current detection unit 17, respectively. The detected zero-cross signal and the measured current are input to the switching control unit 15.

  In FIG. 1, the configuration of the power conversion device 10 is mainly shown, and the internal configuration of the inverter 20, the control device that controls the inverter 20, and various sensors that are necessary for controlling the inverter 20 are omitted. These descriptions are also omitted.

Next, the on / off timing of the switching elements SW1, SW2, and SW3 by the switching control unit 15 will be described with reference to FIG.
FIG. 2 is a diagram showing an example of an R-phase current waveform and the on / off timings of the switching elements SW1, SW2, and SW3 corresponding to the phase voltages.

As shown in FIG. 2, the switching control unit 15 according to the present embodiment has a predetermined angle range within an angle range of −30 degrees to +60 degrees when the zero-cross point of the voltage waveform of each phase is set to 0 degrees. Thus, switching of the switching elements SW1, SW2, and SW3 is performed. In FIG. 2, the switching element is turned on when the pulse is on, and the switching element is turned off when the pulse is off.
Since the relationship between the ON / OFF timing of the switching element with respect to the voltage waveform of each phase is the same, in the following description, the switching element SW1 corresponding to the R phase will be described as a representative example.

  The switching control unit 15 turns on the switching element SW1 once at a predetermined timing in an angle range of −30 degrees to less than 0 degrees in the R phase voltage waveform, and the predetermined number of times in a predetermined angle range of 0 degrees to 60 degrees. The switching element SW1 is turned on (three times in this embodiment).

  First, in the angle range of −30 degrees or more and less than 0 degrees, the switching control unit 15 predicts the next zero-cross point in the current waveform based on the measurement current input from the current detection unit 17. The zero cross point is predicted based on the maximum amplitude of the current waveform in the immediately preceding half cycle or one cycle. When the next zero cross point is predicted, the switching control unit 15 turns on the switching element SW1 once at the predicted timing of the zero cross point. When the switching element SW1 is turned on, the current flowing in the R phase increases, so that the actual zero cross point appears later than the predicted zero cross point.

  Next, for an angle range of 0 ° to 60 ° in the voltage waveform, a predetermined angle range in which the switching element SW1 is on / off controlled is changed according to the maximum amplitude of the immediately preceding half-wave current waveform. For example, the switching control unit 15 has a maximum output current amplitude and an angle range corresponding to the maximum amplitude, and is 0 degrees or more and 60 degrees or less based on a ratio of a measured value of the current amplitude to the maximum amplitude. A predetermined angle range within the range is determined.

  For example, now, in the motor driving apparatus shown in FIG. 1, if the maximum amplitude at which current can be output is defined as 30A, 30A and the corresponding angular range (for example, 0 degrees or more and less than 60 degrees) Are associated with each other. As shown in FIG. 3, when the maximum amplitude of the immediately preceding half-wave current waveform is 10A, the angle range is determined based on the ratio between the maximum amplitude 30A and the immediately preceding maximum amplitude 10A. In this case, since the amplitude is one third, the angle range is also one third of 60 degrees, and the predetermined angle range for turning on / off the switching element SW1 is determined to be 0 degree or more and less than 20 degrees. .

  When the switching control unit 15 determines the angle range in this manner, the switching control unit 15 turns on the pulse three times in the determined angle range. At this time, the pulse width is set according to the angle range and a preset number of pulses. Specifically, the angle range is set to a value divided by the number of pulses. In this case, the narrower the angle range, the narrower the pulse width. By doing so, the balance between the angle range and the pulse width can be maintained.

  The pulse width is not limited to the above aspect. For example, each pulse width may be changed in three pulses. FIG. 2 shows a case where the width of the first pulse is set wider than the widths of the other pulses. By doing in this way, it becomes possible to relieve the distortion of the current waveform without turning it on and off excessively.

  Then, as described above, every time the zero cross point of the voltage waveform comes in each phase, that is, every half cycle, on / off control of the switching elements SW1, SW2, SW3 is performed in an angle range of −30 degrees to 60 degrees. As a result, distortion in the current waveform can be improved.

  As described above, according to the power conversion device 10 according to the present embodiment, when the zero-cross point of the voltage waveform of each phase is set to 0 degrees, the predetermined range within the angle range of −30 degrees to +60 degrees is set. The switching elements SW1, SW2 and SW3 provided corresponding to the respective phases in the angular range are controlled to be turned on / off, and the predetermined angular range is determined according to the maximum amplitude of the half-wave current waveform immediately before in each phase. Therefore, an appropriate angle range can be set according to the current situation. As a result, it is possible to avoid an excessive increase in current and a shortage of the current increase amount, and it is possible to effectively improve the distortion of the current waveform.

DESCRIPTION OF SYMBOLS 10 Power converter 11 Three-phase alternating current power supply 12 Reactor 13 Three-phase rectifier 14a, 14b Smoothing capacitor 15 Switching control part 16 Voltage detection part 17 Current detection part 20 Inverter 30 Motor SW1, SW2, SW3 Switching element

Claims (3)

A power conversion device that rectifies and converts a three-phase AC voltage output from a three-phase AC power source into a DC voltage,
A reactor connected to each phase wire of the three-phase AC power source;
A three-phase rectifier for rectifying the AC voltage output from the reactor;
Two smoothing capacitors connected in series between the DC terminals of the three-phase rectifier,
One end is connected to the output end of each of the reactors, the switching element provided corresponding to each phase that the other end is connected to the middle point of the two smoothing capacitors,
Switching control means for switching the switching element in a predetermined angular range within an angular range of −30 degrees to +60 degrees when the zero-crossing point of the voltage waveform of each phase is 0 degree,
The said switching control means is a power converter device which changes the said predetermined angle range according to the maximum amplitude of the half wave current waveform immediately before in each phase.   The switching control means has a current output maximum amplitude and an angle range corresponding to the maximum amplitude in the range of 0 degrees to less than 60 degrees, and a measured value of the current amplitude with respect to the maximum amplitude. The power converter according to claim 1, wherein the angle range is determined based on a ratio of   3. The power conversion according to claim 1, wherein the switching control unit predicts a zero cross point of a current waveform in an angle range of −30 degrees or more and less than 0 degree, and performs switching at the predicted position of the zero cross point. apparatus.

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