JP5427787B2 - Three-phase rectifier - Google Patents

Description

  The present invention relates to a three-phase rectifier that rectifies a voltage of a three-phase AC power source and converts it into a DC voltage.

  A rectifier circuit that rectifies the voltage of a three-phase AC power source and converts it into a DC voltage has three series circuits in which a pair of diodes are connected in series, and the interconnection point of each diode in these series circuits is a three-phase AC Connected to each phase line of power supply. A smoothing capacitor is connected to the output terminal of the rectifier circuit, and a load is connected to the smoothing capacitor.

  The three-phase AC voltage is composed of three phase voltages whose phases are different from each other by 120 °. With these phase voltages, a current flows through the positive diode of each series circuit to the smoothing capacitor, and each of the series circuits is supplied from the smoothing capacitor. Current flows through the negative diode.

  As an example of such a rectifier circuit, in order to suppress harmonic components contained in the input current, a reactor is inserted and connected to each phase line on the input side, and a plurality of switch means for forming a closed circuit for these reactors are connected. However, there is one that employs a three-phase active filter system that causes the input current waveform to follow a sine wave by switching these switch means at high frequency (for example, Patent Document 1). In this method, a virtual neutral point is provided as a short-circuit target, the withstand voltage of the short-circuit element can be lowered, and the voltage applied to the reactor is also low, so the di / dt is small and good active filter characteristics can be realized.

  Similarly, a reactor is inserted and connected to the input line on the AC power supply side, and a switch element for forming a closed circuit is connected to this reactor. When this switch element is turned on, a forced current is passed from the AC power supply to the reactor, and the forced current is supplied to the reactor. There is a DC power supply device in which the power factor is improved by flowing into a smoothing capacitor through a rectifier circuit by switching off a switch element (for example, Patent Document 2).

Japanese Patent No. 2857094 JP 2002-199730 A

  The above-described three-phase active filter type rectifier circuit of Patent Document 1 performs high-frequency switching, and thus has problems such as generation of high-frequency switching noise and the necessity of using a component that can handle high-frequency current as a reactor. .

  The DC power supply device of Patent Document 2 is a harmonic reduction means effective for a single-phase AC power supply, but cannot be applied to a three-phase AC power supply.

  The three-phase rectifier of the present invention uses only a small reactor, and has the object of reducing high-frequency switching noise and improving the harmonic reduction effect.

The three-phase rectifier of this invention is
A series circuit for U phase in which a pair of diodes are connected in series and an interconnection point between both diodes is connected to a U phase line of a three-phase AC power supply, and a pair of diodes connected in series is an interconnection point between the two diodes. V-phase series circuit connected to the V-phase line of the phase AC power supply, a series circuit for W-phase in which a pair of diodes are connected in series, and an interconnection point of both diodes is connected to the W-phase line of the three-phase AC power supply A first rectifier circuit that converts the voltage of the three-phase AC power source into a DC voltage and outputs the DC voltage;
A U-phase reactor, a V-phase reactor, and a W-phase reactor respectively provided on the U-phase line, the V-phase line, and the W-phase line of the three-phase AC power source;
A series circuit of a pair of capacitors to which the output voltage of the first rectifier circuit is applied;
A bidirectional U-phase switch connected between an interconnection point of both diodes of the U-phase series circuit and an interconnection point of the capacitors;
A bidirectional V-phase switch connected between an interconnection point of both diodes of the V-phase series circuit and an interconnection point of the capacitors;
A bidirectional W-phase switch connected between an interconnection point of both diodes of the W-phase series circuit and an interconnection point of the capacitors;
The V-phase switch flows into the V-phase reactor during a 0-degree to 60-degree period and a 120-degree to 180-degree period of a half cycle of the U-phase current flowing into the U-phase reactor through the U-phase switch. In the 0-degree to 60-degree period and the 120-180 degree period of the half cycle of the V-phase current, the 0-degree to 60-degree period of the half-cycle of the W-phase current flowing into the W-phase reactor through the W-phase switch and Control means for turning on and off at a timing not synchronized with each other in a period of 120 ° to 180 °;
A second rectifier circuit connected to a three-phase diode bridge for converting a voltage of the three-phase AC power source into a DC voltage;
A smoothing capacitor for output to which an output voltage of the second rectifier circuit and a voltage generated in a series circuit of the capacitors are applied;
A DC reactor provided in a current path between the second rectifier circuit and a series circuit of the capacitors and the smoothing capacitor;
The voltage generated in the series circuit of each capacitor is output.

  According to the three-phase rectifier of the present invention, a small-sized reactor can be used, and high-frequency switching noise is reduced, and the effect of reducing harmonics is improved.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. FIG. 2 is a waveform diagram showing the waveform of each phase current and the on / off pattern of each switch in one embodiment. FIG. 3 is a waveform diagram for explaining the on / off pattern asynchronization in FIG. FIG. 4 is a waveform diagram showing a state in which the phase current in one embodiment differs depending on the size of the load. FIG. 5 is a diagram showing the relationship between the magnitude of the load and the on / off timing data in one embodiment. FIG. 6 is a Fourier analysis diagram of different phase currents according to the size of the load in one embodiment. FIG. 7 is a diagram in which the limit value of each harmonic order is added to the Fourier analysis diagram of FIG. FIG. 8 is a block diagram illustrating a configuration of a modified example of the embodiment.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 1, a three-phase rectifier 10 is connected to three phase lines R, S, and T of a three-phase AC power source 1, and an output voltage of the three-phase rectifier 10 (capacitors 14 and 15 described later) The voltage generated in the series circuit) is applied to the output smoothing capacitor 3 via the DC reactor 2. If the capacitances of the capacitors 14 and 15 are increased, the output smoothing capacitor 3 can be dispensed with. In this case, both ends of the series circuit of the capacitors 14 and 15 are output as they are. However, it is more advantageous in terms of cost to provide the smoothing capacitor 3 and reduce the capacitance of the capacitors 14 and 15 than to use only the large capacitors 14 and 15.

  A load 4 is connected to the smoothing capacitor 3. Further, current sensors 5u, 5v, 5w are provided in each phase line between the three-phase AC power source 1 and the three-phase rectifier 10, and a current detection circuit 6 is connected to these current sensors. The current detection circuit 6 detects the phase currents Iu, Iv, and Iw via the current sensors 5u, 5v, and 5w.

  The DC reactor 2, the smoothing capacitor 3, the current sensors 5 u, 5 v, 5 w, and the current detection circuit 6 are devices attached to the three-phase rectifier 10.

  The three-phase rectifier 10 has a rectifier circuit 12. The rectifier circuit 12 includes a pair of diodes 12u1 and 12u2 connected in series, and a connection circuit between the two diodes connected to the U-phase line of the three-phase AC power supply 1, and a pair of diodes 12v1 and 12v2 connected in series. A series circuit for V phase in which the connection point between the two diodes is connected to the V phase line of the three-phase AC power source 1, and a pair of diodes 12w1 and 12w2 are connected in series. It has a W-phase series circuit connected to the W-phase line of the power source 1 and converts the three-phase AC voltage of the three-phase AC power source 1 into a DC voltage for output.

  A plurality of U-phase reactors 11u, V-phase reactors 11v, and W-phase reactors 11w for reducing harmonics are provided on the respective phase lines between the three-phase AC power supply 1 and the rectifier circuit 12.

  The output voltage of the rectifier circuit 12 is applied to a series circuit of a pair of capacitors 14 and 15 having the same capacity. The DC voltage generated in the series circuit of the capacitors 14 and 15 becomes the output of the three-phase rectifier 10.

  A bidirectional U-phase switch 13u is connected between an interconnection point of the capacitors 14 and 15 (hereinafter referred to as a virtual neutral point) and an interconnection point of each diode in the U-phase series circuit of the rectifier circuit 12. Is connected. A bidirectional V-phase switch 13v is connected between the virtual neutral point and the interconnection point of each diode in the V-phase series circuit of the rectifier circuit 12. A bidirectional W-phase switch 13w is connected between the virtual neutral point and the interconnection point of each diode in the W-phase series circuit of the rectifier circuit 12.

  Each of the U-phase switch 13u, the V-phase switch 13v, and the W-phase switch 13w includes a series circuit of two N-type MOSFETs 21 and 22, and a drive circuit 23 for driving the MOSFETs 21 and 22 on and off. .

  Each drive circuit 23 drives the MOSFETs 21 and 22 on and off at the same timing in accordance with a command from the control unit 30. When the MOSFETs 21 and 22 are turned on, currents flowing from the U-phase reactor 11u, the V-phase reactor 11v, and the W-phase reactor 11w to each virtual neutral point are between the drain and source of the MOSFET 21, and between the source and drain of the MOSFET 22. , And a parasitic diode of the MOSFET 22, and currents flowing from the respective virtual neutral points to the U-phase reactor 11 u, the V-phase reactor 11 v, and the W-phase reactor 11 w are between the drain and source of the MOSFET 22 and the source − of the MOSFET 21. It flows between the drains and through the parasitic diode of MOSFET 21.

  The control unit 30 operates according to the output voltage of the rectifier circuit 12 and controls each drive circuit 23. The U-phase switch 13u, the V-phase switch 13v, and the W-phase switch 13w are turned on / off with respect to the MOSFETs 21 and 22. It has a memory (storage means) 30a in which timing data is stored, and has the following means (1) and (2) as main functions.

(1) A load detection section (load detection means) for detecting the magnitude of the load 4 from each phase current detected by the current detection circuit 6.
(2) The phase currents Iu, Iv, Iw flowing from the three-phase AC power source 1 to the U-phase reactor 11u, the V-phase reactor 11v, and the W-phase reactor 11w are monitored, and the phase currents Iu, Iv, Iw Control section (control means) for turning on and off the MOSFETs 21 and 22 of the U-phase switch 13u, the V-phase switch 13v, and the W-phase switch 13w in the half-cycle period of 0 ° to 60 ° and 120 ° to 180 ° . Specifically, in the 0 ° to 60 ° period and 120 ° to 180 ° period of the half cycle of each phase current Iu, Iv, Iw, and in the load detection section of the on / off timing data in the memory 30a. Based on the ON / OFF timing data matching the detected load size, the MOSFETs 21 and 22 of the U-phase switch 13u, the V-phase switch 13v, and the W-phase switch 13w are turned on and off. When there is no on / off timing data matching the magnitude of the load detected in the load detection section in the memory 30a, the on / off timing data corresponding to the magnitude of the load detected in the load detection section is stored in the memory 30a. Are calculated by linear interpolation from the on / off timing data, and the MOSFETs 21 and 22 of the U-phase switch 13u, V-phase switch 13v, and W-phase switch 13w are turned on / off based on the calculated on / off timing data. To do.

Next, the operation will be described.
As shown in FIG. 2, the MOSFETs 21 and 22 of the U-phase switch 13u are turned on and off during the 0 ° to 60 ° period and the 120 ° to 180 ° period of the half cycle of the phase current Iu. In the period of 0 ° to 60 °, the ON period is gradually shortened and the OFF period is gradually lengthened as the distance from the zero cross point is 0 °. In the 120 ° to 180 ° period, as the zero cross point approaches 180 °, the on period gradually increases and the off period gradually decreases. A forced current flows from the three-phase AC power source 1 to the U-phase reactor 11u during the on period of the MOSFETs 21 and 22 (current increase period). The forced current flows between the rectifier circuit 12 and the DC reactor 2 during the off period of the MOSFETs 21 and 22. And flows into the smoothing capacitor 3. ILu in FIG. 2 indicates a current flowing through the U-phase reactor 11u.

  Similarly, the MOSFETs 21 and 22 of the V-phase switch 13v are turned on and off during the 0 ° to 60 ° period and the 120 ° to 180 ° period of the half cycle of the phase current Iv. The MOSFETs 21 and 22 of the W-phase switch 13w are turned on and off during the 0 ° to 60 ° period and the 120 ° to 180 ° period of the half cycle of the phase current Iw.

  By performing ON / OFF control of the U-phase switch 13u, the V-phase switch 13v, and the W-phase switch 13w, a U-phase reactor 11u, a V-phase reactor 11v, and a W-phase reactor 11w are provided. The generation of high frequency switching noise can be reduced as compared with the conventional rectifier circuit that performs high frequency switching while obtaining the effect of reducing harmonics, and as a result, the reactor for U phase 11u, the reactor for V phase 11v, and for W phase A three-phase active filter that employs a low-frequency reactor having a small size and a large current / inductance capacity can be configured as the reactor 11w. If the U-phase reactor 11u, the V-phase reactor 11v, and the W-phase reactor 11w are reduced in size, the equipment on which the three-phase rectifier 20 is mounted can be reduced in size.

  The ON / OFF control period of 0 ° to 60 ° and the 120 ° to 180 ° period are periods in which the ON / OFF control of one phase has little influence on the current waveforms of the other two phases. By selecting this period, the effect of reducing high-frequency switching noise and the effect of reducing harmonics are increased.

  On the other hand, among the three U-phase switch 13u, V-phase switch 13v, and W-phase switch 13w, there is a period in which the on / off control of the two switches overlaps. The current increase is superimposed on the remaining one phase, which causes an increase in harmonics. In order to eliminate this problem, the three U-phase switches 13u, the V-phase switch 13v, and the W-phase switch 13w are turned on and off at timings that are not synchronized with each other. That is, as indicated by the hatched lines in FIG. 3, the on-periods of the U-phase switch 13u, the V-phase switch 13v, and the W-phase switch 13w are shifted from each other. Increases further.

  Further, the levels of the phase currents Iu, Iv, and Iw vary depending on the magnitude of the load as shown in FIG. Therefore, as on / off timing data for determining on / off timings t1, t2, t3, t4, t5, t6... Of the U-phase switch 13u, V-phase switch 13v, and W-phase switch 13w, the load A plurality of types prepared for different sizes are stored in the memory 30 a of the control unit 30.

  That is, as shown in FIG. 5, for example, for three loads A, B, and C, on / off timing data for obtaining the maximum phase current Amax, on / off timing data for obtaining the maximum phase current Bmax, and the maximum phase On / off timing data for obtaining the current Cmax is stored in the memory 30a. Then, the magnitude of the load 4 is detected from the detection current of the current detection circuit 6, and on / off timing data matching the detected load is read from the memory 30a.

  However, the actual load 4 has various sizes. As shown in FIG. 4, there is no on / off timing data for the load H between the load B and the load C in the memory 30a. Therefore, when there is no on / off timing data in the memory 30a that matches the magnitude of the detected load, the on / off timing data corresponding to the magnitude of the detected load is included in each on / off timing data in the memory 30a. Calculated based on straight line interpolation.

  Specifically, as shown in FIG. 5, when looking at the load H between the loads B and C, the timing t1 in the case of the load B and the timing t1 in the case of the load C are connected by a straight line. The point corresponding to the load H is calculated as the timing t1 in the case of the load H. Based on the calculated ON / OFF timing data, ON / OFF control of the U-phase switch 13u, the V-phase switch 13v, and the W-phase switch 13w is executed.

  As an example of how the phase current varies depending on the size of the load, the phase current Iua at a predetermined load and the phase current Iub at a half load of the predetermined load are shown as Fourier (FFT) analysis diagrams. This is shown in FIG. Further, FIG. 7 shows the limit value (IEC) of each harmonic order corresponding to IEC61000-3-2 added to the Fourier analysis diagram of FIG. 6, which is suitable for any load / order.

  The on / off timing for shifting the on periods of the U-phase switch 13u, the V-phase switch 13v, and the W-phase switch 13w may be set based on on / off timing data in the memory 30a. However, if there is a switch that is turned on during actual control, the other switches may be turned on until the switch is turned off.

  Further, although the current sensors 5u, 5v, 5w and the current detection circuit 6 are used as load detection means, a resistor 7 is inserted and connected to the energization line between the smoothing capacitor 3 and the load 4 as shown by a broken line in FIG. The current detection circuit 8 may be connected to both ends of the resistor 7 so that the current flowing through the load 4 is detected from the voltage generated in the resistor 7 and the size of the load 4 is detected based on the detected current.

  Further, as shown in FIG. 8, a general rectifier in which a smoothing capacitor 3 is connected to a rectifier circuit (second rectifier circuit) 9 having a three-phase diode bridge connection similar to the rectifier circuit 12 via a DC reactor 2. When the device already exists, the three-phase rectifier 10 of the present invention may be newly connected in parallel to the rectifier circuit 9.

  The rectifier circuit 9 includes a pair of diodes 9u1 and 9u2 connected in series, and a connection circuit between the two diodes is connected to a U-phase line of the three-phase AC power supply 1, and a pair of diodes 9v1 and 9v2 are connected in series. A series circuit for V phase in which the connection point between the two diodes is connected to the V phase line of the three-phase AC power source 1, and a pair of diodes 9w1 and 9w2 are connected in series. It has a W-phase series circuit connected to the W-phase line of the power source 1 and converts the three-phase AC voltage of the three-phase AC power source 1 into a DC voltage for output.

  In other words, the three-phase rectifier 10 can be retrofitted to existing equipment for the purpose of reducing harmonics. In this case, among the phase currents, a part of the current near the center where the amplitude of the half wave is large (60 ° to 120 ° period or 240 ° to 300 ° period) is a U-phase reactor 11u, a V-phase reactor 11v, Since it flows toward the rectifier circuit 9 without passing through the W-phase reactor 11w, the U-phase reactor 11u, the V-phase reactor 11v, and the W-phase reactor 11w may have a smaller magnetic flux capacity than the current capacity. it can. That is, the U-phase reactor 11u, the V-phase reactor 11v, and the W-phase reactor 11w are further reduced in size.

  In addition, the present invention is not limited to the above embodiment, and various modifications can be made without departing from the scope of the invention.

  The three-phase rectifier of the present invention can be mounted on equipment connected to a three-phase AC power source.

  DESCRIPTION OF SYMBOLS 1 ... Three-phase alternating current power supply, 2 ... DC reactor, 3 ... Smoothing capacitor, 4 ... Load, 10 ... Three-phase rectifier, 11u, 11v, 11w ... Reactor, 12 ... Rectifier circuit, 13u ... U-phase switch, 13v ... V-phase switch, 13w ... W-phase switch, 14, 15 ... capacitor, 21,22 ... MOSFET, 23 ... drive circuit, 30 ... control unit, 30a ... memory (storage means)

Claims (3)

A series circuit for U phase in which a pair of diodes are connected in series and an interconnection point between both diodes is connected to a U phase line of a three-phase AC power supply, and a pair of diodes connected in series is an interconnection point between the two diodes. V-phase series circuit connected to the V-phase line of the phase AC power supply, a series circuit for W-phase in which a pair of diodes are connected in series, and an interconnection point of both diodes is connected to the W-phase line of the three-phase AC power supply A first rectifier circuit that converts the voltage of the three-phase AC power source into a DC voltage and outputs the DC voltage;
A U-phase reactor, a V-phase reactor, and a W-phase reactor respectively provided on the U-phase line, the V-phase line, and the W-phase line of the three-phase AC power source;
A series circuit of a pair of capacitors to which the output voltage of the first rectifier circuit is applied;
A bidirectional U-phase switch connected between an interconnection point of both diodes of the U-phase series circuit and an interconnection point of the capacitors;
A bidirectional V-phase switch connected between an interconnection point of both diodes of the V-phase series circuit and an interconnection point of the capacitors;
A bidirectional W-phase switch connected between an interconnection point of both diodes of the W-phase series circuit and an interconnection point of the capacitors;
The V-phase switch flows into the V-phase reactor during a 0-degree to 60-degree period and a 120-degree to 180-degree period of a half cycle of the U-phase current flowing into the U-phase reactor through the U-phase switch. In the 0-degree to 60-degree period and the 120-180 degree period of the half cycle of the V-phase current, the 0-degree to 60-degree period of the half-cycle of the W-phase current flowing into the W-phase reactor through the W-phase switch and Control means for turning on and off at a timing not synchronized with each other in a period of 120 ° to 180 °;
A second rectifier circuit connected to a three-phase diode bridge for converting a voltage of the three-phase AC power source into a DC voltage;
A smoothing capacitor for output to which an output voltage of the second rectifier circuit and a voltage generated in a series circuit of the capacitors are applied;
A DC reactor provided in a current path between the second rectifier circuit and a series circuit of the capacitors and the smoothing capacitor;
And a voltage generated in a series circuit of the capacitors as an output. A plurality of on / off timing data for determining the on / off timing of the U-phase switch, the V-phase switch, and the W-phase switch according to the magnitude of the load of the device is stored by the control means. Stored storage means,
The three-phase rectifier according to claim 1, further comprising: The control means turns the U-phase switch, the V-phase switch, and the W-phase switch on and off to match the load size of the device among the on / off timing data in the storage means. Based on the timing data, or on / off timing data corresponding to the load size of the device is calculated from each on / off timing data in the storage means, and on / off based on the calculated on / off timing data. To
The three-phase rectifier according to claim 2.

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