JP2007274818A - Rectifying device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rectifying device where a power factor is improved, harmonics are reduced and miniaturization and high efficiency are achieved. <P>SOLUTION: The device is provided with a full wave rectifying circuit 3 which bridge-connects first high speed diodes 31 and 32 used for a positive side arm and first rectification diodes 34 and 35 used for a negative side arm and converts AC voltage into DC voltage, second rectification diodes 61 and 62 where anode terminals are connected to AC input terminals of respective phases in the full wave rectifying circuit 3 and cathode terminals are mutually connected, a power semiconductor switching element 64 where positive electrodes are connected to the cathode terminals of the second rectification didoes 61 and 62 and negative electrodes are connected to a negative side output terminal of the full wave rectifying circuit 3 and a control circuit 7 which turns on/off at high speed the power semiconductor switching element 64 so that a power factor viewed from an AC power supply 1-side is improved. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a rectifier, and more particularly to a rectifier having improved loss and power factor characteristics.

  In order to convert AC power into DC power, a full-wave rectifier circuit using a diode bridge is widely used. However, since the current flowing from the AC power supply on the input side is distorted, there is a problem that the power factor is bad and harmonics flow out to the power supply system. When an input reactor is inserted to suppress this current distortion, the power factor is improved to some extent, but there is a problem that the volume and weight of the input reactor become very large with respect to the full-wave rectifier circuit.

For such a technical problem, a series circuit composed of a boosting reactor and a power semiconductor switching element at the output end of a full-wave rectifier circuit that rectifies the voltage of the AC power supply, a high speed diode at both ends of the power semiconductor switching element, A series circuit consisting of a smoothing capacitor connected in parallel with the load is provided, and the power semiconductor switching element is controlled so that the current waveform of the AC power supply matches the sine wave to improve the power factor and reduce harmonics. A rectifying device has been proposed (see, for example, Patent Document 1).
Japanese Patent Laying-Open No. 2004-282958 (page 6-8, FIG. 1)

  According to the technique disclosed in Patent Document 1, it is possible to improve the power factor and reduce harmonics, but there are problems with respect to the following points.

  That is, when a current flows through the newly added high-speed diode, a forward voltage (for example, 1.2 V) is generated and a conduction loss is generated. In the full-wave rectifier circuit, there are two diodes in the current path that flows from the AC power supply to the AC power supply and returns to the AC power supply. However, when the technique of Patent Document 1 is adopted, a high-speed diode provided to improve the power factor In addition to the above, there are three diodes in the current path, and the conduction loss increases.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a rectifier that can improve power factor, reduce harmonics, and reduce the size and increase the efficiency. .

In order to achieve the above object, a rectifier of the present invention is configured by bridging a first high-speed diode used for a positive arm and a first rectifier diode used for a negative arm, A full-wave rectifier circuit that converts an AC voltage supplied from a polyphase AC power source into a DC voltage;
A second rectifier diode having an anode terminal connected to an AC input terminal of each phase of the full-wave rectifier circuit and a cathode terminal connected to each other, and a positive electrode to the cathode terminal of the second rectifier diode, The power semiconductor switching element having a negative electrode connected to the negative output terminal of the full-wave rectifier circuit, and the power semiconductor switching element are turned on / off at high speed so as to improve the power factor viewed from the AC power supply side. And a control circuit.

  ADVANTAGE OF THE INVENTION According to this invention, the rectifier which can improve a power factor, reduce a harmonic, can be reduced in size, and can be highly efficient can be provided.

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

  FIG. 1 is a circuit configuration diagram of a rectifier according to Embodiment 1 of the present invention.

  The AC voltage supplied from the AC power source 1 is full-wave rectified by the full-wave rectifier circuit 3 via the input reactor 2. The full-wave rectifier circuit 3 has a configuration in which high-speed diodes 31 and 32 of the positive arm and rectifier diodes 34 and 35 of the negative arm are bridge-connected, and smoothed from the positive output terminal P and the negative output terminal N. A DC voltage is supplied to the load 5 via the capacitor 4. Here, the fast diode means a diode having a shorter recovery time and a smaller reverse recovery loss than a normal rectifier diode.

  A power factor correction circuit 6 is connected between each phase output of the input reactor 2 and the negative output terminal N of the full-wave rectifier circuit 3. The power factor correction circuit 6 is connected to rectifier diodes 61 and 62 having anode electrodes connected to the respective phase outputs of the input reactor 2 and cathode terminals thereof connected to each other, and to the cathode terminals of the rectifier diode 61 and the rectifier diode 62. The electrodes are constituted by power switching elements 64 each having a negative electrode connected to the negative output terminal N of the full-wave rectifier circuit 3.

  The power switching element 64 is turned on so that the input power factor of the full-wave rectifier circuit 3 is improved by a control signal from the control circuit 7 (not shown) and the input current of the full-wave rectifier circuit 3 becomes a sine wave. / Off controlled. The carrier frequency for this on / off control is usually set to a high frequency of, for example, several kHz to several hundred kHz. For this reason, a high-frequency reverse voltage is applied to the high-speed diodes 31 and 32, and reverse recovery loss occurs. Accordingly, high-speed diodes 31 and 32 are high-speed diodes with low reverse recovery loss. On the other hand, since the rectifier diodes 34 and 35 operate at a commercial frequency (for example, 50 Hz) of the AC power supply 1, rectifier diodes having a low forward voltage are used.

  Hereinafter, the operation of the rectifier having the configuration shown in FIG. 1 will be described.

  The rectified voltage obtained by full-wave rectifying the voltage of the AC power source 1 through the input reactor 2 by the full-wave rectifier circuit 3 is smoothed by the smoothing capacitor 4 to be a low ripple DC voltage. Here, the current flowing from the AC power source 1, that is, the input current of the full-wave rectifier circuit 3 flows when the DC voltage charged in the smoothing capacitor 4 becomes lower than the voltage of the AC power source 1. That is, the input current of the full-wave rectifier circuit 3 becomes a distorted waveform that flows only near the peak of the voltage of the AC power supply 1.

  Here, when the power semiconductor switching element 64 is turned on, the AC power source 1 → the point A of the power factor correction circuit 6 → the power semiconductor switching element 64 → the negative output terminal N of the full-wave rectifier circuit 3 → the AC power source 1 Current flows through the path. As a result, the current can be passed during the period when the current of the AC power supply 1 does not flow with the full-wave rectifier circuit 3 alone.

  Therefore, if the on / off operation of the power semiconductor switching element 64 is controlled so that the input current of the full-wave rectifier circuit 3 is a sine wave and the voltage phase and the current phase coincide with each other, the power factor of the rectifier can be increased. It is possible to improve and reduce low-order harmonics of the input current of the full-wave rectifier circuit 3. Note that the input current of the full-wave rectifier circuit 3 in the above description includes a current flowing into the power semiconductor switching element 64 via the rectifier diodes 61 and 62. This indicates that the control circuit 7 performs on / off control of the power semiconductor switching element 64 so that the power factor of the device viewed from the AC power source 1 is improved to about 1.

  In this way, by reducing the lower harmonics of the input current of the full-wave rectifier circuit 3, the pulsating component of the input current is substantially only the carrier frequency of the power semiconductor switching element 64. Therefore, the inductance value of the input reactor 2 can be reduced, the input reactor 2 can be made smaller and lighter, and the apparatus can be made more efficient.

  Moreover, since there are only two diodes in the current path of the main current returning from the AC power supply 1 to the AC power supply 1, the conduction loss of the diode can be reduced as compared with the technique disclosed in Patent Document 1. Furthermore, the reverse recovery loss of the diode can be reduced by using the high speed diodes 31 and 32 to which the high frequency reverse voltage is applied as a high speed diode with a small reverse recovery loss due to the reverse recovery current.

  FIG. 2 shows a circuit configuration diagram of a rectifier according to Embodiment 2 of the present invention. In each part of the second embodiment, the same parts as those in the circuit configuration diagram of the rectifier according to the first embodiment shown in FIG. The second embodiment differs from the first embodiment in that an anode terminal is connected to the positive electrode of the power switching element 64 in the power factor correction circuit 6A, and a cathode terminal is connected to the positive output point P of the full-wave rectifier circuit 3. The high-speed diode 65 is provided.

  Consider a case where the power semiconductor switching element 64 changes from an on state to an off state. At this time, the main current depends on the energy accumulated in the input reactor 2, the AC power source 1 → the positive output terminal P of the full wave rectifier circuit 3 → the parallel circuit of the smoothing capacitor 4 and the load 5 → the negative side of the full wave rectifier circuit 3. A current flows through the path of the output terminal N → the AC power source 1. Here, since there is a wiring parasitic inductance L in the wiring from the rectifier diodes 61 and 62 to the power semiconductor switching element 64 of the power factor correction circuit 6A, Ldi in the transient state where the power semiconductor switching element 64 shifts to the OFF state. A surge voltage corresponding to / dt is generated and applied to the power semiconductor switching element 64. At this time, when the voltage between the positive and negative electrodes of the power semiconductor switching element 64 exceeds the voltage across the smoothing capacitor 4, the high-speed diode 65 is turned on. Therefore, the voltage between the positive and negative electrodes of the power semiconductor switching element 64 is clamped to the voltage across the smoothing capacitor 4.

  Thus, the high-speed diode 65 functions to suppress the surge voltage applied to the power semiconductor switching element 64 and protect the overvoltage of the power semiconductor switching element 64. Therefore, the current capacity of the high speed diode 65 can be selected to be sufficiently smaller than that of the high speed diodes 31 and 32. Note that a path is formed to flow current from the AC power source 1 to the parallel circuit of the smoothing capacitor 4 and the load 5 through the rectifier diodes 61 and 62 and the high speed diode 65 of the power factor correction circuit 6A. The voltage drop in the forward direction is large due to the series connection. Accordingly, the main current flows to the parallel circuit of the smoothing capacitor 4 and the load 5 through the positive output terminal P of the full-wave rectifier circuit 3 that passes through only one of the high-speed diodes 31 and 32. That is, since a main current does not flow through the high-speed diode 65, a small-capacitance element can be applied as described above.

  As described above, according to the second embodiment of the present invention, the overvoltage protection of the power semiconductor switching element can be performed by adding the high-speed diode having a low loss.

  FIG. 3 shows a circuit configuration diagram of a rectifier according to Embodiment 3 of the present invention. In each part of the third embodiment, the same parts as those in the circuit configuration diagram of the rectifier according to the first embodiment shown in FIG. The difference between the second embodiment and the first embodiment is that the AC power supply 1A and the input reactor 2A have a three-phase configuration. The full-wave rectifier circuit 3A is provided with a high-speed diode 33 and a rectifier diode 36 for the added phase. And a point in which a rectifier diode 63 is provided in a direction in which current flows from the phase added to the input side of the power factor correction circuit 6B to the point A.

  When the AC power supply 1A has three phases, the full-wave rectifier circuit 3A is configured by a three-phase bridge, and the rectifier diode of the power factor correction circuit 6B is also provided with rectifier diodes 61, 62, and 63 for three phases for each phase. It becomes. Since the function of each component is basically the same as that of the single phase of the first embodiment, the description thereof is omitted.

  Also in the rectifier according to Embodiment 3 of the present invention configured as described above, the power factor viewed from the AC power source 1A is improved by turning on / off the power semiconductor switching element 64 at high speed, and the input reactor 2A is The device can be made small and light, and the efficiency of the apparatus can be increased.

  Further, as shown in the second embodiment, a high-speed diode having an anode terminal connected to the positive electrode of the power switching element 64 in the power factor correction circuit 6B and a cathode terminal connected to the positive output point P of the full-wave rectifier circuit 3A. By providing this, it becomes possible to suppress the surge voltage applied to the power semiconductor switching element 64.

  A unipolar diode is preferably used as the high-speed diode in the first to third embodiments described above. As the unipolar diode, a Schottky barrier diode (SBD) or a junction controlled barrier Schottky diode (JBS) can be applied.

  Unlike a bipolar diode, a unipolar diode has no minority carrier accumulation and no reverse recovery charge is formed, so that a reverse recovery current essentially does not flow. The unipolar diode has a charge stored in the junction capacitance, but the charge / discharge current of the junction capacitance is small. Therefore, the loss of the high speed diode can be greatly reduced. Further, the application of the unipolar diode prevents the reverse recovery current from flowing into the power semiconductor switching element 64 in the switching-on transient state, so that the turn-on loss of the power semiconductor switching element 64 can be reduced.

  For the unipolar diode, SBD can be used practically. For example, an element breakdown voltage of 200 V or less is practical in an SBD constructed in a silicon semiconductor, whereas an SBD constructed in a wide gap semiconductor has a high breakdown voltage of, for example, 200 V or more. As the unipolar diode, JBS having the same characteristics as SBD can be used.

  Further, in the first to third embodiments described above, if a high-speed diode made of a wide gap semiconductor is applied to the high-speed diode, the loss can be further reduced. As this wide gap semiconductor, SiC (silicon carbide), GaN (gallium nitride), and diamond are applicable.

  A high-speed diode made of a wide-gap semiconductor can increase the breakdown electric field strength by an order of magnitude compared to a silicon semiconductor, and can realize a high breakdown voltage of the high-speed diode. For example, a unipolar diode can be practically used in a wide gap semiconductor even if it is a high-speed diode having a high breakdown voltage that can be used only in a bipolar diode in a silicon semiconductor.

  In a high-speed diode formed using a wide gap semiconductor, the breakdown electric field strength can be increased by an order of magnitude compared to a silicon semiconductor, and a high-voltage diode with a high breakdown voltage can be realized. For example, even with high breakdown voltage high-speed diodes that can only be used with bipolar diodes as high-speed diodes in silicon semiconductors, unipolar diodes can be used in wide-gap semiconductors, greatly reducing reverse recovery loss, Loss can be reduced. Further, as described above, the turn-on loss of the power semiconductor switching element 64 can be reduced.

  Furthermore, in the rectifiers of the first to third embodiments, if a wide gap semiconductor is applied to the power semiconductor switching element 64, the loss can be further reduced.

  In a power semiconductor switching element formed using a wide gap semiconductor, the breakdown electric field strength can be increased by an order of magnitude compared to a silicon semiconductor, and a drift layer for maintaining a breakdown breakdown voltage can be provided. Since the thickness can be reduced to about 10, the conduction loss of the power semiconductor switching element can be reduced. In addition, since the wide gap semiconductor can increase the saturation electron drift velocity about twice as much as that of the silicon semiconductor, a high frequency of about 10 times can be realized. As the wide gap semiconductor, SiC (silicon carbide), GaN (gallium nitride), diamond, or the like is applicable.

The circuit block diagram of the rectifier which concerns on Example 1 of this invention. The circuit block diagram of the rectifier which concerns on Example 2 of this invention. The circuit block diagram of the rectifier which concerns on Example 3 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 1A AC power supply 2, 2A Input reactor 3, 3A Full wave rectifier circuit 4 Smoothing capacitor 5 Load 6, 6A, 6B Power factor improvement circuit 7 Control circuit

31, 32, 33 High-speed diodes 34, 35, 36 Rectifier diodes

61, 62, 63 Rectifier diode 64 Power semiconductor switching element 65 High-speed diode

Claims (9)

The first high-speed diode used for the positive arm and the first rectifier diode used for the negative arm are connected in a bridge to convert AC voltage supplied from a single-phase or multi-phase AC power source into DC voltage. A full-wave rectifier circuit,
A second rectifier diode having an anode terminal connected to the AC input terminal of each phase of the full-wave rectifier circuit and a cathode terminal connected to each other;
A power semiconductor switching element having a positive electrode connected to a cathode terminal of the second rectifier diode and a negative electrode connected to a negative output terminal of the full-wave rectifier circuit;
A rectifier comprising: a control circuit for turning on / off the power semiconductor switching element at high speed so as to improve a power factor seen from the AC power supply side.   The second high-speed diode having an anode terminal connected to a positive electrode of the power semiconductor switching element and a cathode terminal connected to a positive output terminal of the full-wave rectifier circuit is provided. Rectifier.   The rectifier according to claim 1, wherein the first high-speed diode is a unipolar diode.   The rectifier according to claim 1 or 2, wherein the second high-speed diode is a unipolar diode. The rectifier according to claim 3 or 4, wherein the unipolar diode is a Schottky barrier diode or a junction controlled barrier Schottky diode.   The rectifier according to claim 1, wherein the first high-speed diode is formed of a wide gap semiconductor.   The rectifier according to claim 1 or 2, wherein the second high-speed diode is formed of a wide gap semiconductor.   The rectifier according to any one of claims 1 to 7, wherein the power semiconductor switching element is formed of a wide gap semiconductor. The rectifier according to any one of claims 6 to 8, wherein the wide gap semiconductor is SiC (silicon carbide), GaN (gallium nitride), or diamond.

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