JP2010119278A - Rectifying device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rectifying device suppressing harmonics by simple control. <P>SOLUTION: A full-wave rectifying circuit 2 rectifies an AC power supply input from a first input terminal 2a and a second input terminal 2b. An anode terminal of a first diode 11 is connected to the first input terminal 2a of the full-wave rectifying circuit 2. The anode terminal of a second diode 12 is connected to the second input terminal 2b of the full-wave rectifying circuit 2. A transistor 31 is connected between cathode terminals of the first diode 11 and the second diode 12 and negative side output terminals of the full-wave rectifying circuit 2. A controller 41 turns on the transistor 31 once per half cycle of the AC power supply, when no current flows through the full-wave rectifying circuit. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a rectifier.

  Conventionally, in a rectifier, for the purpose of reducing harmonics, an anode terminal of a rectifier diode is connected to each AC input terminal of each phase of a diode bridge circuit, and a cathode terminal of the rectifier diode is connected to a positive electrode of a semiconductor switching element. The negative electrode of the switching element is connected to the negative output terminal of the full-wave rectifier circuit, and the control circuit turns on and off the semiconductor switching element at high speed (see, for example, Patent Document 1).

  In the rectifier disclosed in Patent Document 1, since the semiconductor switching element is turned on during a period in which a current flows through the diode bridge circuit, a reverse recovery current flows in the diode and noise is generated. FIG. 5 is a graph in which noise generated by the reverse recovery current is recorded. In FIG. 5, the noise N is three times or more the peak value of the AC input current, and there is a concern about adverse effects on peripheral electronic components. For this reason, the rectifier disclosed in Patent Document 1 employs a high-speed diode as the positive arm of the diode bridge circuit for the purpose of reducing noise due to the reverse recovery current.

However, even if the noise due to the reverse recovery current is reduced, it is not eliminated, and when the number of times of switching increases, the noise filter must be enlarged. Furthermore, an expensive high-speed diode is required, which causes an increase in cost.
JP 2007-274818 A

  An object of the present invention is to provide a rectifier that can suppress harmonics with simple control.

  The rectifier according to the first invention includes a full-wave rectifier circuit, a first diode, a second diode, switch means, and a controller. The full-wave rectifier circuit rectifies the AC power input from the first input terminal and the second input terminal. The anode terminal of the first diode is connected to the first input terminal of the full-wave rectifier circuit. The anode terminal of the second diode is connected to the second input terminal of the full-wave rectifier circuit. The switch means is connected between the cathode terminals of the first diode and the second diode and the negative output terminal of the full-wave rectifier circuit. The control unit turns on the switch means at a predetermined timing. Further, the control unit turns on the switch means once every half cycle of the AC power supply when no current is flowing through the full-wave rectifier circuit.

  In this rectifier, since the switch means is only turned on once, the rectifier for switching the switch means at a frequency of several kHz to several hundred Hz as described in the publicly known technology (Japanese Patent Laid-Open No. 2007-274818) In comparison, harmonics can be easily suppressed and noise is also reduced.

  The rectifier according to the second invention is the rectifier according to the first invention, wherein the full-wave rectifier circuit is a bridge circuit composed of four or six diodes. The diode used for the positive arm of the bridge circuit is a rectifier diode. In this rectifier, since the reverse recovery current of the diode does not flow, there is no damage to the component due to the reverse recovery current, and the cost of the component is not finally increased.

  The rectifier according to the third invention is the rectifier according to the second invention, further comprising a capacitor connected between the output terminals of the full-wave rectifier circuit, the number of which is only one.

  In this rectifier, since the generation of harmonics is suppressed, there is no need to employ a voltage doubler system in which capacitors connected in series with each other are connected between the output terminals of the full-wave rectifier circuit. The capacitor connected between the output terminals only needs to have one smoothing capacitor.

  In the rectifier according to the first invention, harmonics can be easily suppressed, noise is reduced, and the cost is low.

  In the rectifier according to the second aspect of the invention, since the reverse recovery current of the diode does not flow, there is no damage to the component due to the reverse recovery current, and the cost of the component is not finally increased.

  In the rectifier according to the third aspect of the present invention, the capacitor connected between the output terminals of the full-wave rectifier circuit is only required to have one smoothing capacitor, so that downsizing and cost reduction of parts are achieved.

  Embodiments of the present invention will be described below with reference to the drawings. The following embodiments are specific examples of the present invention and do not limit the technical scope of the present invention.

(Configuration of rectifier)
FIG. 1 is a circuit diagram of a rectifier according to an embodiment of the present invention. In FIG. 1, the first input terminal 2a and the second input terminal 2b of the full-wave rectifier circuit 2 are connected to an AC power source. A reactor 1 is connected between the AC power source and the first input terminal 2a. The full-wave rectifier circuit 2 is a bridge circuit in which four rectifier diodes 21, 22, 23, and 24 are bridge-connected, and full-wave rectifies an AC input voltage input from the first input terminal 2a and the second input terminal 2b. Then, a DC voltage is supplied to the load 6 from the positive output terminal and the negative output terminal via the smoothing capacitor 5.

  As shown in FIG. 1, the anode terminal of the first diode 11 is connected to the first input terminal 2a. The anode terminal of the second diode 12 is connected to the second input terminal 2b. The cathode terminals of the first diode 11 and the second diode 12 are connected to the collector of a transistor 31 that is a switch means. The emitter of the transistor 31 is connected to the negative output terminal of the full-wave rectifier circuit 2. The base of the transistor 31 is connected to the control unit 41 via a signal line.

  A bipolar transistor, a field effect transistor (FET), an insulated gate bipolar transistor (IGBT), or the like is selected as the transistor 31 serving as the switch means. Note that a switch means other than a transistor may be employed. For example, a thyristor or a triac is selected.

(Current flow)
FIG. 2A is a circuit diagram of the rectifier that shows the flow path of the AC input current when the positive voltage of the AC power supply is applied to the first input terminal and the transistor is off. FIG. 2B is a circuit diagram of the rectifying device showing a reverse recovery current flow path when the positive voltage of the AC power supply is applied to the first input terminal and the transistor is turned on. FIG. 2C is a circuit diagram of the rectifier that shows the flow path of the AC input current when the positive voltage of the AC power supply is applied to the first input terminal and the transistor is turned on.

  In FIG. 2A, when the transistor 31 is not turned on, the AC input current is supplied from the AC power source to the first input terminal 2a, the rectifier diode 21, the positive output terminal, the load 6, the negative output terminal, and the rectifier diode 24. The second input terminal 2b flows through the AC power supply path.

  In FIG. 2B, when the transistor 31 is turned on, the current accumulated in the rectifier diode 21 is changed from the anode of the rectifier diode 21 to the first diode 11, the transistor 31, the smoothing capacitor 5, the positive output terminal, and the rectifier diode. It flows in 21 routes. This is a reverse recovery current and causes noise. The reverse recovery current is a phenomenon in which an AC input current flows through the rectifier diode 21 so that a current is accumulated therein, and the accumulated current flows to the transistor 31 when the transistor 31 is turned on. In other words, when no AC input current flows through the rectifier diode 21, no reverse recovery current flows even when the transistor 31 is turned on.

  In FIG. 2C, when the transistor 31 is on, the AC input current is supplied from the AC power source to the first input terminal 2a, the first diode 11, the transistor 31, the negative output terminal, the rectifier diode 24, and the second input. It flows through the terminal 2b and the path of the AC power supply.

  FIG. 3A is a circuit diagram of the rectifier that shows the flow path of the AC input current when the positive voltage of the AC power supply is applied to the second input terminal and the transistor is turned off. FIG. 3B is a circuit diagram of the rectifying device showing the flow path of the reverse recovery current when the positive voltage of the AC power supply is applied to the second input terminal and the transistor is turned on. FIG. 3C is a circuit diagram of the rectifier device showing a flow path of the AC input current when the positive voltage of the AC power supply is applied to the second input terminal and the transistor is turned on.

  3A, when the transistor 31 is not turned on, the AC input current is supplied from the AC power source to the second input terminal 2b, the rectifier diode 22, the positive output terminal, the load 6, the negative output terminal, and the rectifier diode 23. The first input terminal 2a flows through the AC power supply path.

  In FIG. 3B, when the transistor 31 is turned on, the current accumulated in the rectifier diode 22 flows from the anode of the rectifier diode 22 to the second diode 12, transistor 31, smoothing capacitor 5, positive output terminal, rectifier diode. It flows through 22 routes. This is a reverse recovery current and causes noise. The reverse recovery current is a phenomenon in which an AC input current flows through the rectifier diode 22 so that current is accumulated therein, and the accumulated current flows through the transistor 31 when the transistor 31 is turned on. In other words, when no AC input current flows through the rectifier diode 22, no reverse recovery current flows even if the transistor 31 is turned on.

  In FIG. 3C, when the transistor 31 is on, the AC input current is supplied from the AC power source to the second input terminal 2b, the second diode 12, the transistor 31, the negative output terminal, the rectifier diode 23, and the first input. It flows through the terminal 2a and the path of the AC power supply.

(Operation of rectifier)
The rectified voltage that has been full-wave rectified by the full-wave rectifier circuit 2 is smoothed by the smoothing capacitor 5 to become a low ripple DC voltage. Since the input current of the full-wave rectifier circuit 2 flows when the DC voltage charged in the smoothing capacitor 5 becomes lower than the AC input voltage, it becomes a distorted waveform that flows only near the peak of the AC input voltage.

  At that time, when the transistor 31 is turned on, a current flows through the AC power source, the first diode 11 (or the second diode 12), the transistor 31, the negative output terminal of the full-wave rectifier circuit 2, and the AC power source. As a result, the current flows at the timing when the current of the AC power source does not flow with the full-wave rectifier circuit 2 alone.

  In general, if the on / off operation of the transistor 31 is controlled so that the input current of the full-wave rectifier circuit 2 becomes a sine wave and the voltage phase and the current phase coincide, the power factor of the rectifier is improved and the full-wave rectifier circuit The lower order harmonics of the input current of 2 are reduced. For example, in the rectifier disclosed in Patent Document 1 described in the background art, the carrier frequency for on / off control is set to a high frequency of several kHz to several hundred kHz.

  In this case, although the harmonics are reduced, the semiconductor switching element is turned on when a current is flowing through the full-wave rectifier circuit. Therefore, the diode on the positive side arm of the full-wave rectifier circuit is shown in FIG. A large reverse recovery current flows, which causes noise.

  On the other hand, in the rectifier according to the present embodiment, the control unit 41 performs control to turn on the transistor 31 once every half cycle of the AC power supply when no current flows through the full-wave rectifier circuit 2. . Specifically, the control unit 41 detects a zero cross of the AC input voltage via a zero cross detection circuit (not shown), and inputs a pulse signal having a time width of 2 ms to 4 ms rising from the zero cross point to the base of the transistor 31. To do. As a result, the collector-emitter conducts, and the input current flows through the path of the AC power supply, the first diode 11 (or the second diode 12), the transistor 31, the negative output terminal of the full-wave rectifier circuit 2, and the AC power supply. Since the transistor 31 is on when no current flows through the rectifier diodes 21 and 22 of the positive-side arm of the full-wave rectifier circuit 2, no reverse recovery current flows when the transistor 31 is on, and noise is generated. Is avoided.

  FIG. 4 is a graph showing a current waveform of an AC input current input to the rectifier according to the present embodiment. In FIG. 4, the upper waveform is an AC input current that flows when the transistor 31 is turned on, and the middle waveform is a current waveform of the transistor. In the upper waveform, if the transistor 31 is not turned on, the waveform A is a waveform B indicated by a dotted line.

  In the case of waveform B, the generated harmonics cannot satisfy the power supply harmonic specification values (IEC61000-3-2, 61000-3-12) by the International Electrotechnical Commission (IEC), but in the case of waveform A, the power supply The harmonic specification value can be satisfied.

<Features>
(1)
In the rectifier according to the present embodiment, the control unit 41 turns on the transistor 31 at the zero cross point of the AC input voltage, so that the waveform of the AC input current approaches the AC input voltage and harmonics can be reduced. Further, it is possible to avoid reverse recovery current from flowing from the rectifier diodes 21 and 22 forming the positive arm of the full-wave rectifier circuit 2. Furthermore, since noise is reduced, the noise filter is reduced in size and the cost is reduced.

(2)
In this rectifier, since the generation of harmonics is suppressed, for example, it is not necessary to employ a voltage doubler system in which capacitors connected in series with each other are connected between the output terminals of the full-wave rectifier circuit. As a result, the capacitor connected between the output terminals of the full-wave rectifier circuit is only required to have one smoothing capacitor, so that downsizing is achieved.

  As described above, according to the present invention, noise reduction, size reduction, and cost reduction are realized in the rectifier, which is useful as a rectifier for fan motor control of an air conditioner.

The circuit diagram of the rectifier concerning one embodiment of the present invention. (A) The circuit diagram of the rectifier which shows the flow path of alternating current input when the positive voltage of alternating current power supply is applied to the 1st input terminal, and the transistor is OFF. (B) The circuit diagram of the rectifier which shows the flow path | route of a reverse recovery current when the positive voltage of alternating current power supply is applied to the 1st input terminal, and the transistor is ON. (C) The circuit diagram of the rectifier which shows the flow path of alternating current input when the positive voltage of alternating current power supply is applied to 1 input terminal, and the transistor is ON. (A) The circuit diagram of the rectifier which shows the flow path of an alternating current input current when the positive voltage of alternating current power supply is applied to the 2nd input terminal, and the transistor is OFF. (B) The circuit diagram of the rectifier which shows the flow path | route of a reverse recovery current when the positive voltage of alternating current power supply is applied to the 2nd input terminal, and the transistor is ON. (C) The circuit diagram of the rectifier which shows the flow path of alternating current input current when the positive voltage of alternating current power supply is applied to the 2nd input terminal, and the transistor is ON. The graph which shows the electric current waveform of the alternating current input input into the rectifier which concerns on this embodiment. The graph which recorded the noise which arose by the reverse recovery current in the conventional rectifier.

Explanation of symbols

2 full wave rectifier circuit 2a first input terminal 2b second input terminal 5 smoothing capacitor 11 first diode 12 second diodes 21, 22, 23, 24 rectifier diode 31 transistor 41 control unit

Claims (3)

A full-wave rectifier circuit (2) for rectifying the AC power input from the first input terminal (2a) and the second input terminal (2b);
A first diode (11) having an anode terminal connected to the first input terminal (2a) of the full-wave rectifier circuit (2);
A second diode (12) having an anode terminal connected to the second input terminal (2b) of the full-wave rectifier circuit (2);
Switch means (31) connected between the cathode terminals of the first diode (11) and the second diode (12) and the negative output terminal of the full-wave rectifier circuit (2);
A control unit (41) for turning on the switch means (31) at a predetermined timing;
With
The control unit (41) turns on the switch means (31) once in a half cycle of the AC power source when no current flows through the full-wave rectifier circuit (2).
Rectifier. The full-wave rectifier circuit (2) is a bridge circuit composed of four or six diodes (21, 22, 23, 24),
The diode (21, 22) used for the positive side arm of the bridge circuit is a rectifier diode,
The rectifier according to claim 1. A capacitor (5) connected between output terminals of the full-wave rectifier circuit (2);
There is only one capacitor (5),
The rectifier according to claim 2.

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