JPH0731153A - Power converter - Google Patents

Abstract

PURPOSE:To provide a power converter in which lowering of power conversion efficiency, heating and power loss of circuit elements are prevented while suppressing current noise caused by a rectangular high frequency voltage. CONSTITUTION:Half-wave switch circuits 25, 26 are connected in series with the output terminals of a full-wave rectifier circuit 22 through a diode 23. The switch circuits 25, 26 are switched alternately to generate a rectangular high frequency voltage which is applied to a series circuit of a capacitor 38, an inductor 39, and a load 40 thus feeding a part of resonance energy to the load. A smoothing capacitor 32 is connected through a capacitor 33 and a forward diode 34 with the joints of half-wave switch circuits and a reverse polarity diode 35 is also connected through a capacitor 33 with the joint.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC / AC power converter applied to, for example, a discharge lamp lighting device.

[0002]

2. Description of the Related Art In a power converter of this type, an input terminal of a full-wave rectifier circuit 2 is connected to a commercial AC power source 1, as shown in FIG. Then, the first and second smoothing capacitors 3 and 4
Is provided, one end of the first smoothing capacitor 3 is connected to the positive side of the output terminal of the full-wave rectification circuit 2, and the other end is connected to the negative side of the output terminal of the full-wave rectification circuit 2 through the diode 5 in the reverse direction. Connected. Also, one end of the second smoothing capacitor 4 is connected to the positive electrode side of the output terminal of the full-wave rectification circuit 2 through the diode 6 in the forward direction, and the other end is connected to the negative side of the output terminal of the full-wave rectification circuit 2. ing. The cathode of the diode 5 is connected to the anode of the diode 6 via the diode 7 in the forward direction and further via the inductor 8.

Further, a capacitor 9 is connected to the output terminal of the full-wave rectifier circuit 2 and a pair of half-wave switch circuits 10,
11 series circuits are connected. The half-wave switch circuits 10 and 11 are switch elements 12 and 1 such as transistors.
3 and the diodes 14 and 15 are connected in parallel. Each half-wave switch circuit 10, 11 constitutes a half-bridge type inverter circuit, and the drive circuit for the switch elements 12, 13 is a well-known drive circuit (not shown).

Capacitors 16 and 17 are connected in parallel to the half-wave switch circuits 10 and 11, respectively.

A load 20 is connected in parallel to the other half-wave switch circuit 11 via a capacitor 18 and an inductor 19.

In this conventional device, when the output voltage of the full-wave rectifier circuit 2 is higher than the series voltage of the smoothing capacitors 3 and 4, the positive terminal of the output terminal of the full-wave rectifier circuit 2 → the first smoothing capacitor. 3 → Diode 7 → Inductor 8 → Second smoothing capacitor 4 → Charging current flows through the path on the negative electrode side of the output terminal of the full-wave rectifier circuit 2 to charge the smoothing capacitors 3 and 4. At the same time, the output voltage of the full-wave rectifier circuit 2 is directly supplied to the load side.

When the output voltage of the full-wave rectifier circuit 2 is lower than the series voltage of the smoothing capacitors 3 and 4 and higher than the individual voltage of the smoothing capacitors 3 and 4, the smoothing capacitors 3 and 4 are supplied to the smoothing capacitors 3 and 4 respectively. Although the charging is stopped, the direct supply of the output voltage of the full-wave rectifier circuit 2 to the load side is continued.

When the output voltage of the full-wave rectifier circuit 2 is lower than the individual voltage of the smoothing capacitors 3 and 4, the smoothing capacitors 3 and 4 are in parallel and discharge.

In this device, when the switch elements 12 and 13 are alternately opened and closed, a rectangular voltage is generated at the connection point of the switch elements 12 and 13. Capacitor 1 for this rectangular voltage
8. Resonance is generated by the inductor 19, and if the switching frequency of each switch element 12, 13 is set to an appropriate point in the vicinity of this resonance, the oscillation of the inverter circuit is continued.

[0010]

In this conventional device, when the switch element 13 is closed, the load 20 → the inductor 19 is closed.
→ Current flows through the path of capacitor 18 → switch element 13. When the switch element 13 is opened in this state, the current path is cut off at that moment, but the current tends to flow continuously because of the inductance component due to the inductor 19. As a result, the current interrupted by the opening of the switch element 13 first flows in the direction of charging the capacitor 9 via the capacitor 16 until the voltage across the capacitor 16 becomes zero, and the voltage across the capacitor 16 becomes zero. After that, the current flows in the direction of charging the capacitor 9 via the diode 14.

Due to such operation, a large current suddenly flows to the capacitor 16 and the diode 14 from the moment the switch element 13 is opened. This abrupt current change actually induces resonance with the capacitor 16 due to the existence of an inductance component in the wiring, resulting in a noisy current waveform as shown in FIG. 4 (c). . 4A shows the opening / closing timing of the switch element 13, and FIG. 4B shows the voltage waveform across the switch element 13.

The vibration induced by such a steep current change is not easily attenuated because the resistance component for absorbing the vibration does not exist in the circuit.

The generation of current noise associated with the opening / closing operation of the switch element 13 has been described above, but it similarly occurs during the opening / closing operation of the switch element 12.

As described above, in the conventional device, current noise is generated at a higher frequency that is much higher than the switching frequency of the inverter, which adversely affects semiconductor elements such as switching elements and diodes, and also generates extra vibration energy. Therefore, there is a problem that the power conversion efficiency is reduced. Then, the decrease in power conversion efficiency is specifically manifested as an increase in temperature of the semiconductor element or the like. For this reason, there is a problem that the size of the element and the size of the heat dissipation plate are increased.

Therefore, the present invention provides a power conversion device capable of preventing the generation of current noise, thereby preventing a decrease in power conversion efficiency, heat generation of circuit elements, and power loss.

[0016]

The invention according to claim 1 is
A frequency at which a pair of half-wave switch circuits connected in series to a DC power supply are alternately opened and closed to generate a rectangular high-frequency voltage, and this high-frequency voltage is applied to an LC resonance circuit to alternately open and close each half-wave switch circuit. In the DC-AC power converter that creates a resonance state for supplying a part of the resonance energy to the load at this time, the capacitor and the first rectifying element are provided in the forward direction at the voltage or current fluctuation point. A smoothing capacitor connected thereto and a second rectifying element having a polarity opposite to that of the first rectifying element connected via the capacitor at a voltage or current variation point are provided.

[0017]

In the invention having such a structure, the vibration energy generated at the fluctuation point of the voltage or the current is reduced to the smoothing capacitor as an electric charge through the capacitor and the first rectifying element. The electric charge lost in the capacitor due to this reduction is replenished via the second rectifying element.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, an input terminal of a full-wave rectifier circuit 22 is connected to a commercial AC power source 21. The output terminal of the full-wave rectifier circuit 22 is connected to a capacitor 23 and a series circuit of a pair of half-wave switch circuits 25 and 26 via a diode 23 in the forward direction.

The half-wave switch circuits 25 and 26 are composed of switching elements 27 and 28 such as transistors and a diode 2.
It is composed of 9, 30 parallel circuits. Each half-wave switch circuit 25, 26 constitutes a half-bridge type inverter circuit, and the drive circuit for the switch elements 27, 28 is a well-known drive circuit although not shown.

The cathode of the diode 23 is connected to the cathode of the diode 31, and the anode of the diode 31 is connected to one end of the smoothing capacitor 32. The other end of the smoothing capacitor 32 is connected to the negative side of the output terminal of the full-wave rectifier circuit 22.

A voltage or current fluctuation point, for example, a connection point between the half-wave switch circuits 25 and 26 is connected via a capacitor 33, and a diode 34 which is a first rectifying element is connected in a forward direction to the smoothing capacitor 32. It is connected to one end.

A diode 35, which is a second rectifying element, is connected to the half-wave switch circuit 26 via the capacitor 33 in parallel with the diode 34 having a polarity opposite to that of the diode 34. The connection point of each of the half-wave switch circuits 25 and 26 is connected to the connection point of the positive electrode side of the output terminal of the full-wave rectification circuit 22 and the anode of the diode 23 via an inductor 36 and a capacitor 37 in series. ing.

A capacitor 3 is provided in the half-wave switch circuit 26.
The load 40 is connected in parallel via the inductor 8 and the inductor 39.

In the embodiment having such a configuration, when the power is turned on, the capacitor 24 is passed through the diode 23.
Will charge. The capacitor 24 is a capacitor for absorbing the high frequency current of the inverter and has a sufficiently small capacity with respect to the frequency of the commercial AC power supply 21. Therefore, a large inrush current does not flow when the power is turned on.

When a voltage is generated across the capacitor 24, the inverter circuit starts operating and the switch element 27,
28 alternately starts the switching operation.

For example, the switch element 28 starts the opening / closing operation at the timing shown in FIG.
The rectangular high-frequency voltage shown in (b) is generated. The upper part of this rectangular high frequency voltage is not flat at all,
When the current flows into the capacitor 4, the voltage of the capacitor 24 slightly increases, and the increased amount also appears in the rectangular voltage.

The rectangular high-frequency voltage is also generated when the switch element 27 is opened and closed, and in this case, the phase is different from that of the switch element 28 by 180 degrees.

With respect to the rectangular high frequency voltage, when the voltage rises, a current flows through the path of the capacitor 33 → diode 34 → smoothing capacitor 32 to charge the smoothing capacitor 32.

When the rectangular high-frequency voltage falls, a current flows through the path of the diode 35 → capacitor 33 to replenish the lost charge of the capacitor 33.

Thus, the capacitor 33 and the diode 3
The circuit composed of 4, 35 functions as a kind of current pump and has a function of converting the energy of the high frequency voltage into the charge energy of the smoothing capacitor 32.

Thus, even if vibration is generated by the energy of the high frequency voltage, it is consumed as current pumping energy to the smoothing capacitor 32, so the vibration is quickly absorbed. Therefore, the waveform of the current flowing by the opening / closing operation of the switch element 28 is as shown in FIG. 2C, and no current noise is generated.

The series circuit of the inductor 36 and the capacitor 37 becomes a current resonance state based on the high frequency voltage, and changes the potential between the output terminal of the full wave rectification circuit 22 and the diode 23. Due to this voltage fluctuation, the voltage temporarily becomes lower than the input voltage, or temporarily becomes higher than the potential of the capacitor 24, so that the input current from the power supply side is drawn.

The path of the capacitor 38, the inductor 39 and the load 40 cuts the direct current component by the capacitor 38 based on the high frequency voltage and transmits the alternating current component, and the current is sine wave smoothed by the current limiting action of the inductor. Load 4
Supply to 0. At this time, the capacitor 38 and the inductor 3
The relationship with 9 may or may not be in a resonance state.

As described above, even if a rectangular high-frequency voltage is generated by the switching operation of the switch elements 27 and 28, it is possible to prevent the generation of vibrations and the generation of current noise, so that the circuit elements such as the switch elements 27 and 28 generate heat. And power loss can be reduced, and therefore, a circuit element having a small capacity can be used, and a heat dissipation plate to be used can also be made small.

Further, the vibration which is about to be generated by the rectangular high frequency voltage is absorbed by the smoothing capacitor 32 as charge energy and reused, so that the power conversion efficiency can be improved.

Further, since the capacitor capacitance acts on the rectangular high frequency voltage, the rising and falling slopes of the voltage become large, and the switching loss of the switch elements 27 and 28 can be reduced. That is, the voltage rises at the moment when the switch element 28 opens, and the crossing area of the portion where the flowing current drops to zero, that is, W = I ×
V can be reduced.

[0038]

As described above, according to the present invention, it is possible to prevent the generation of current noise due to the generation of a rectangular high frequency voltage, thereby preventing the reduction of power conversion efficiency and the heat generation and power loss of circuit elements.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention.

FIG. 2 is a waveform diagram for explaining the operation of the half-wave switch circuit of the same embodiment.

FIG. 3 is a circuit configuration diagram showing a conventional example.

FIG. 4 is a waveform diagram for explaining the operation of the half-wave switch circuit of the conventional example.

[Explanation of symbols]

 25, 26 ... Half-wave switch circuit 32 ... Smoothing capacitor 33 ... Capacitor 34 ... Diode (first rectifying element) 35 ... Diode (second rectifying element)

Claims (1)

[Claims] 1. A pair of half-wave switch circuits connected in series to a DC power source are alternately opened and closed to generate a rectangular high-frequency voltage, and the high-frequency voltage is applied to an LC resonance circuit to each half-wave switch circuit. In the DC-AC power converter that creates a resonance state for the frequency of alternately opening and closing, and supplies a part of the resonance energy at this time to the load, the capacitor and the first rectifying element at the voltage or current fluctuation point. A smoothing capacitor connected through the capacitor in the forward direction, and the first capacitor connected through the capacitor to a variation point of the voltage or current.
And a second rectifying element having a polarity opposite to that of the second rectifying element.