Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
1999-12-22
2001-01-09
Riley, Shawn (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S132000
Reexamination Certificate
active
06172882
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a partial resonance PWM converter.
PRIOR ART
Japanese Patent Laid-Open Publication Hei 6-284749 discloses an inverter, wherein two main switches connected in series with each other are connected in parallel with a DC power supply, two auxiliary switches connected in series with each other are respectively connected in parallel with these main switches, and a connection point of the two main switches and a connection point of the two auxiliary switches are connected with each other via an inductor and a capacitor which are connected in series with each other, so as to pick up an output at the connection point of the two main switches. Diodes are respectively connected in parallel with each of the main switches and the auxiliary switches in the opposite direction of a polarity of the DC power supply. The inverter described in this Laid-Open Publication intends to reduce and inhibit the voltage surge and the switching loss which occur at the main switch device, by taking advantage of a resonance current generated from the series circuit composed of the inductor and the capacitor. In this inverter, the main switch may be switched after making a current through the main switch device zero by turning on the auxiliary switch just before the main switch is switched. Thus the voltage surge occurring at the main switch is inhibited and a snubber circuit may also be omitted, thereby high efficiency and low noise may be established. Herefrom, this inverter is referred as a snubberless inverter in this Laid-Open Publication.
In the operation of this device, there is a problem that turn-on loss and current surge/voltage surge can be caused from making the main switch turn on at hard switching and also switching loss can potentially be increased due to occurrence of the turn-off loss at the auxiliary switch depending on a turn-off timing of the auxiliary switch device.
As another prior art, there is “Novel Zero-Current-Transition PWM Converter” described in “IEEE TRANSACTION ON POWER ELECTRONICS, Vol.9, No.6, November 1994”, page 601 to 606. This circuit includes a basic circuit of a boost up converter wherein a main switch, with which a diode is connected in parallel, and an inductor are connected in series with a DC power supply, a connection point of the inductor and the main switch device is connected to a negative electrode of the DC power supply, and an output capacitor is connected between the connection point and the negative electrode via an output diode. A series resonance circuit composed of second inductor and a capacitor, and an auxiliary circuit composed of an auxiliary switch device, second diode and a third diode are additionally incorporated in the basic circuit to allow the main switch to be turned off at zero current so that voltage surge may be controlled to reduce turn-off loss. In this circuit, the auxiliary switch is turned on just before the main switch is turned off so as to generate an resonance current. Then the diode connected in parallel with the main switch device is turned on by the generated resonance current. During the above course, the main switch device is turned so as to make the zero current turn-off possible. According to these actions, the voltage surge occurring at the main switch device is controlled so that a snubber circuit may be omitted and turn-off loss may also be reduced. Therefore a partial resonance PWM boost converter characterized by high efficiency and low noise can be constructed.
As a problem of this device, it is pointed that turn-off loss is caused due to the fact that some current inevitably passes when the auxiliary switch device is turned off. Further, in the case where a continuous current is applied to the first inductor, a recovery current of the output diode passes through the main switch device when the main switch is turned on. This results in generated turn-on loss and noise. Thus this type of circuit is limited in facilitating high efficiency and low noise.
DISCLOSURE OF INVENTION
It is an object of the present invention to solve the problem described above and to provide a partial resonance PWM boost converter wherein, by controlling a switching timing of an auxiliary switch device and a main switch device, the zero current turn-on and zero current turn-off at the auxiliary switch device and the main switch device can be achieved, and the switching loss occurring at the main switch and the auxiliary switch can also be made substantial zero, so that voltage surge and current surge can be reduced to make the lower noise possible.
To achieve the aforementioned object, the present invention provides a new converter. In this converter, a series circuit composed of first and second main switch devices is connected in parallel with a DC power supply, and diodes are connected in parallel with each of the main switch devices in the opposite direction of a polarity of the DC power supply. An output circuit is located at a juncture of these main switch devices, and the main switch devices are alternatively switched to output AC or DC power. Another series circuit composed of first and second auxiliary switch devices is connected in parallel with the DC power supply, and diodes are connected in parallel with each of the auxiliary switch devices in the opposite direction of the polarity of the DC power supply. A series resonance circuit composed of a capacitor and an inductor is inserted between the juncture of the first and second main switch devices and a juncture of the first and second auxiliary switch devices. The auxiliary switch is turned on just before the main switch device is switched so as to generate a resonance at the series resonance circuit. During resonance, at least in the main switch devices, a switching timing is controlled to make the main switch device turn off when the diode connected in parallel with each of the main switch devices is turned nearly to ON condition or during ON condition of the diode. Preferably, in the auxiliary switch device, a switching timing may additionally be controlled to make the auxiliary switch device turn off during ON condition of the diode connected in parallel with each of the auxiliary switch devices. This enables the main switch device and the auxiliary switch device to be turned on at zero current and be also turned off at zero current so that switching loss can be reduced.
In another embodiment of the present invention, a series circuit composed of first and second main switch devices and a series circuit composed of first and second capacitors are respectively connected in parallel with a DC power supply. Diodes are respectively connected in parallel with each of the main switch devices in the opposite direction of a polarity of the DC power supply. Two auxiliary switch devices are connected in series between a connection point of the first and second main switch devices and a connection point of the first and second capacitors. In this connection, a bi-directional switch device composed of the auxiliary switches and diodes respectively connected in parallel with each of the auxiliary switches, and a series resonance circuit composed of an inductor and a capacitor are inserted in series. With making the connection point of the main switch devices an power output, the main switch devices are alternatively switched so as to output an AC or DC power. In the converter according to this embodiment, a switching timing is controlled to make the auxiliary switch device turn on just before the main switch is switched, and then to make the main switch device and the auxiliary switch device turn on at zero current and also turn off at zero current by detecting a current which passes through the main switch device and the auxiliary switch device. Thus the switching loss can be reduced and the noise caused from voltage surge and current surge can also be reduced.
In other embodiment of the present invention, there is provided a PWM boost converter, wherein an inductor and a main switch device are connected in series with a DC power supply, o
Ito Kazuyuki
Okita Yoshihisa
Tanaka Katsuaki
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Riley Shawn
TDK Corporation
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