JP2004147475A - Rectifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that, in conventional circuits so constituted that a chopper circuit is connected with the output of a rectifying circuit and a switching element is thereby caused to carry out soft switching, the secondary winding of a transformer used is connected in series with a diode and thereby the charges in a capacity for soft switching are regenerated to the direct-current output, in this case a diode of high breakdown voltage is required, and the price and loss of the equipment are increased. <P>SOLUTION: A rectifier is so constituted that a series circuit of a reactor and a switching element is connected between the direct-current output terminals of an N-phase (N is a natural number not less than 2) diode bridge circuit which is fed with N-phase alternating-current power as input, a series circuit of a diode and a capacitor both the ends of which are direct-current output is connected in parallel with the switching element, and a load is connected in parallel with the capacitor. In this rectifier, a series circuit comprising a capacitor, a diode, the primary winding of a transformer, and a switching element is connected in parallel with the above switching element. Further, a series circuit of a diode and the secondary winding of the transformer is connected between the direct-current output terminals of the rectifier. A voltage clamping means is connected in parallel with the primary winding of the transformer. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a so-called PWM rectifier circuit that generates a direct current from an AC power supply using a switching element and a diode, and more particularly to a soft switching circuit technology applied to a rectifier circuit.
[0002]
[Prior art]
FIG. 3 shows an embodiment based on the prior art. Here, an embodiment using a single-phase AC power supply will be described. The conventional example shown in FIG. 3 is described in Power Electronics Specialists Conference 1999 "IMPROVING THE OPERATION OF ZVT DC-DC CONVERTERS" Paulo J. et al. M. It is disclosed on pages 293-297 by Menegaz et al. "IMPROVING THE OPERATION OF ZVT DC-DC CONVERTERS" FIG. In No. 2, a snubber circuit is formed by the diode Dsx and the capacitor Csx, but is not shown in FIG. 3 because it has no relation to the main operation and effect of the present invention.
[0003]
The circuit configuration illustrated in FIG. 3A includes a diode bridge circuit including diodes 2 to 5 and a rectifier circuit including a chopper circuit including the reactor 21, the diode 6, and the switching element 15. Here, when the switching element 15 is turned on, the AC power supply is short-circuited through the diode bridge circuit and the reactor 21, and the reactor 21 stores energy and increases the AC input current.
Next, when the switching element 15 is turned off, the energy stored in the reactor 21 is supplied through the diode 6 to the capacitor 33 and the load 33 which become a DC output. As described above, the input current can be controlled by the on / off control of the switching element 15, so that the harmonics of the input current can be reduced and the AC voltage can be converted to the DC voltage.
[0004]
The capacitor 31, the diodes 7, 10, 11, the transformer 22, and the switching element 17 form a soft switching circuit of a chopper circuit. FIG. 3B shows an example of an operation waveform according to the related art. Here, by turning on the switching element 17, the current flowing through the path of the reactor 21 → the diode 6 → the capacitor 33 → the diode bridge circuit 40 → the AC power supply 1 → the reactor 21 in the period t 1 becomes the leakage inductance of the transformer 22. Under the influence of the above, the current is gradually commutated to the path of the reactor 21 → the diode 7 → the primary winding 22a of the transformer 22 → the switching element 17 → the diode bridge circuit 40 → the AC power supply 1 → the reactor 21. At this time, since the current flowing through the switching element 17 gradually increases from zero, soft switching at the time of turning on the switching element 17 is established. Next, when the current flowing through the switching element 17 becomes equal to the value of the current flowing through the reactor 21, the period t2 starts, and the diode 6 is turned off. At this time, since the current of the diode 6 gradually becomes zero, the surge voltage and the reverse recovery loss at the time of the reverse recovery are reduced.
At the same time, the electric charge stored in the capacitor 31 (or the parasitic capacitance of the switching element 15) is discharged through the path of the capacitor 31 → the diode 7 → the primary winding 22a of the transformer 22 → the switching element 17 → the capacitor 31. Is regenerated to the output side through the secondary winding 22b of the transformer 22 and the diode 10. Further, when the switching element 15 is turned on after the voltage of the switching element 15 becomes zero in the period t3, the switching element 15 receives a difference current between the current flowing through the primary winding 22a of the transformer 22 and the current flowing through the reactor 21. Therefore, the current flowing through the switching element 15 gradually increases from a current value of zero or less at which the parasitic diode 12 flows the current. Therefore, the switching element 15 performs soft switching at the time of turn-on.
The reactor 21 → the diode 7 → the primary winding 22a of the transformer 22 → the switching element 17 → the diode bridge circuit 40 → the AC power supply 1 → the current flowing in the route of the reactor 21 is the reactor 21 → the switching element 15 → the diode bridge circuit 40 → While gradually commutating to the path from the AC power supply 1 to the reactor 21, the energy stored in the leakage inductance of the transformer 22 is supplied to the output side via the secondary winding 22b of the transformer 22 and the diode 10, The current flowing through the switching element 17 gradually decreases to zero. Since the switching element 17 is turned off after the current becomes zero, soft switching at the time of turn-off is established.
On the other hand, when the switching element 15 is turned off, a current flows through the capacitor 31, so that the voltage of the switching element 15 gradually increases, so that the turn-off loss is reduced. Thus, soft switching of the switching elements 15 and 17 is established, and loss and noise can be reduced.
[0005]
[Problems to be solved by the invention]
In the related art, when the switching element 17 is turned off, during a period t4, a path of the primary winding 22a of the transformer 22 → the diode 11 → the capacitor 33 → the parasitic diode 12 of the switching element 15 → the diode 7 → the primary winding 22a of the transformer 22. Accordingly, a reset voltage is generated in the primary winding 22a of the transformer 22 which is clamped by the DC output voltage (voltage of the capacitor 33). Here, in order to regenerate all the electric charges stored in the capacitor 31 to the DC output side, the turns ratio of the transformer 22 needs to be 2 or more.
[0006]
Therefore, a voltage that is twice the turns ratio of the DC output voltage is generated in the secondary winding 22b of the transformer 22, and a high voltage is applied to the diode 10. In order to safely operate the diode 10 without damaging it, a diode with a high withstand voltage is required, and the device becomes expensive and the loss increases. In view of the above, an object of the present invention is to use a diode with a low withstand voltage, and to reduce the cost and the loss of the device.
[0007]
[Means for Solving the Invention]
As a first means for solving the above problem, a series circuit of a reactor and a switching element is provided between DC output terminals of an N-phase diode bridge circuit to which an N-phase (N is a natural number of 2 or more) AC power supply is input. In a rectifier in which a series circuit of a diode and a capacitor whose both ends become a DC output in parallel with the switching element, and a load connected in parallel with the capacitor, a capacitor, a diode, and a transformer are connected in parallel with the switching element. A primary circuit of the transformer and a series circuit composed of switching elements are connected to each other, and a series circuit of a diode and a secondary winding of the transformer is connected in parallel with the primary winding of the transformer between the DC output terminals of the rectifier. Is connected to voltage clamp means.
[0008]
As a second means, N (N is a natural number of 2 or more) series circuits of a diode and a switching element are connected in parallel, and an internal connection point of the series circuit of the diode and the switching element is connected to an N-phase AC power supply. A rectifier in which a reactor having a DC output at both ends is connected between parallel connection points of a series circuit of the diode and the switching element, and a load is connected in parallel with the capacitor. The anode terminal of the diode is connected to each of the internal connection points of the diode and the switching element in the series circuit of the switching element and the switching element in which the capacitor is connected in parallel, the cathodes of the respective diodes are connected collectively, and the cathode terminal of the diode and the DC A series circuit of a primary winding of a transformer and a switching element between one of the output terminals The series circuit of the secondary winding of the diode and the transformer between the DC output terminals of the rectifier device, the voltage clamping means in parallel with the primary winding of the transformer, respectively coupled.
[0009]
【Example】
FIG. 1 shows an embodiment according to claim 1. Here, an embodiment using a single-phase AC power supply will be described. In the circuit configuration shown in FIG. 1A, a rectifier circuit is composed of a diode bridge circuit 40 composed of diodes 2 to 5 and a chopper circuit composed of a reactor 21, a diode 6, and a switching element 15, as in the conventional technology. The diodes 7, 9, 10, the switching element 17, the transformer 22, and the voltage clamp element 30 constitute a soft switching circuit. In the present invention, the same operation as in the related art is performed during the periods t1 to t3, and the soft switching of the switching elements 15, 17 and the diode 6 is established.
In a period t4, the voltage clamped by the voltage clamp element 30 to the primary winding 22a of the transformer 22 through the path of the primary winding 22a of the transformer 22 → the voltage clamp element 30 → the diode 9 → the primary winding 22a of the transformer 22 An equal reset voltage is generated. The secondary winding 22b of the transformer 22 generates a voltage that is twice the turns ratio of the primary winding, and the diode 10 receives the sum of the DC output voltage and the secondary winding voltage of the transformer 22. Here, by setting the clamp voltage of the voltage clamp element 30 low, the voltage applied to the diode 10 can be reduced.
Therefore, a diode with a low withstand voltage can be used as the diode 10, and the cost and the loss of the device can be reduced. However, even if the clamp voltage of the voltage clamp element 30 is set low, the reset period is sufficiently long, so that the transformer 22 can be sufficiently reset, and magnetic saturation does not occur.
[0010]
FIG. 2 shows an embodiment according to the second aspect. Here, an embodiment using a single-phase AC power supply will be described. In the circuit configuration shown in FIG. 2A, a rectifier circuit is formed by the reactor 21, the diodes 2 to 5, and the switching elements 15 and 16. The rectifier circuit includes a switching element 15 and a capacitor 31 in parallel with the diode 3 of the diode bridge circuit composed of diodes 2 to 5, a switching element 16 and a capacitor 32 in parallel with the diode 5, and a diode 2 and a diode 3. The AC power supply 1 is connected between the series connection point and the series connection point of the diodes 4 and 5 via the reactor 21, and the capacitor 33 and the load 34 are connected between the DC terminals of the diode bridge circuit. is there. Here, the diode 3 can be replaced with a parasitic diode of the switching element 15, and the diode 5 can be replaced with a parasitic diode of the switching element 16.
[0011]
The diodes 7 to 10, the switching element 17, the transformer 22, and the voltage clamp element 30 constitute a soft switching circuit. The configuration of the soft switching circuit is such that the anode of the diode 8 is connected to the series connection point of the diodes 2 and 3, the anode of the diode 7 is connected to the series connection point of the diodes 4 and 5, and the cathode of the diodes 7 and 8 is connected to the primary winding of the transformer 22. The other terminal of the transformer is connected to one terminal of the line 22a, the drain terminal of the switching element 17 having the diode 13 connected in parallel, the source terminal of the switching element 17 is connected to the negative terminal of the DC output, and the diode 9 and the voltage clamp element 30 are connected. In this configuration, the series circuit is connected in parallel with the primary winding 22a of the transformer 22, and the diode 10 and the secondary winding series circuit of the transformer 22 are connected in parallel with the capacitor 33 which is a DC output. The diode 13 can be replaced by a parasitic diode of the switching element 17.
[0012]
The operation will be described below. When the AC power supply voltage is positive, the switching element 15 is turned on, so that the AC input current increases in the path of AC power supply 1 → reactor 21 → switching element 15 → diode 5 → AC power supply 1, and energy is stored in the reactor 21. Can be Next, when the switching element 15 is turned off, the energy of the reactor 21 is supplied to the DC output side through the route of the reactor 21 → the diode 2 → the capacitor 33 → the diode 5 → the AC power supply 1 → the reactor 21. Therefore, when the AC power supply voltage is positive, the switching element 15 is turned on / off to control the input current to a high power factor and convert the input current to a DC voltage. When the AC power supply voltage is negative, the switching element 16 is turned on and off in the same manner, so that the input current can be converted to a DC voltage while controlling it at a high power factor.
[0013]
Here, in claim 2, diodes 7 and 8 are connected instead of the diode 7 in claim 1, and the diode 8 is connected when the AC power supply voltage is positive, and the diode 7 is connected when the AC power supply voltage is negative. Plays the role of the diode 7. Since the switching element 15 is turned on and off when the AC power supply voltage is positive, the charge stored in the capacitor 31 is regenerated to the DC output side by the same operation as in claim 1. However, since the current always flows through the diode 5 when the AC power supply voltage is positive, no charge is stored in the capacitor 32.
Similarly, when the AC power supply voltage is negative, the electric charge stored in the capacitor 32 is regenerated to the load side as in the first aspect. Therefore, the operation of the rectifier circuit according to the second aspect is the same as that of the first aspect, and the switching elements 15, 16, 17 and the diodes 2, 4 perform the soft switching operation.
[0014]
Further, since the sum of the DC output voltage and the secondary winding voltage of the transformer 22 is applied to the diode 10 as in the first embodiment, the diode 10 is set by setting the clamp voltage of the voltage clamp element 30 low. The applied voltage can be reduced. However, since the reset period is sufficiently long even if the clamp voltage of the voltage clamp element 30 is set low, the transformer 22 can be sufficiently reset, and does not magnetically saturate. Therefore, a diode having a low withstand voltage can be used as the diode 10, and the cost and the loss of the device can be reduced.
[0015]
【The invention's effect】
According to the present invention, in a rectifier circuit that converts an AC voltage into a DC voltage by a switching operation, it is possible to achieve soft switching and reduce the voltage applied to the diode, thereby improving the efficiency, cost, and cost of the device. Noise can be generated. Here, an example in the case of a single-phase AC power supply has been described, but it goes without saying that a similar effect can be obtained in a three-phase AC power supply.
[Brief description of the drawings]
FIG. 1 shows an embodiment of the invention according to claim 1;
FIG. 2 shows an embodiment of the invention according to claim 2;
FIG. 3 shows an embodiment according to the prior art.
[Explanation of symbols]
1 …………………… AC power supplies 2 to 13 ………………… Diodes 15 to 17 …………………… Switching Element 21 …………………………………………………………………………………………………………… Transformer 22a ... Transformer primary winding, 22b ... Transformer secondary winding 30 Voltage clamp elements 31, 32 Capacitor or parasitic capacitance 33 Capacitor 34 ... Load 40 ... Diode bridge circuit t1 to t4 ..................... Period

Claims (2)

A series circuit of a reactor and a switching element is connected between the DC output terminals of an N-phase diode bridge circuit that receives an N-phase (N is a natural number of 2 or more) AC power supply. In a rectifier in which a series circuit with a capacitor and a load in parallel with the capacitor are connected,
In parallel with the switching element, a capacitor, a diode, a primary circuit of a transformer and a series circuit including a switching element are connected, and a diode and a secondary winding of the transformer are connected between DC output terminals of a rectifier. A rectifier, wherein a voltage clamp means is connected to the series circuit of the above in parallel with the primary winding of the transformer. N (N is a natural number of 2 or more) series circuits of a diode and a switching element are connected in parallel, and a reactor is connected between an internal connection point of the series circuit of the diode and the switching element and an N-phase AC power supply. A capacitor having a DC output at both ends between the parallel connection points of the series circuit with the switching element, a load in parallel with the capacitor, in a rectifier in which each is connected,
An anode terminal of the diode is connected to each of the internal connection points of the diode and the switching element in a series circuit of the switching element in which the N diodes and the capacitor are connected in parallel, and the cathodes of the respective diodes are collectively connected. A series circuit of a primary winding of a transformer and a switching element is provided between the cathode terminal and one of the DC output terminals, and a series circuit of a diode and a secondary winding of the transformer is provided between the DC output terminals of the rectifier. A voltage clamp means connected in parallel with a primary winding of the transformer.

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