JPH0731150A - Switching power supply - Google Patents

Abstract

PURPOSE:To improve the input power factor by connecting an AC three-phase power supply with a star-connection of single phase rectifying circuits and power factor improving circuits and smoothing the output therefrom through a smoothing capacitor. CONSTITUTION:The voltages between the phases U, V, W and the neutral point n of an AC three-phase power supply 1 are full-wave rectified through single phase rectifying circuits (SD) 2A, 2B, 2C and fed to power factor improving circuits (PD) 6A, 6B, 6C. When the switching elements (Tr) 3 in the PDs 6A, 6B, 6C are turned ON by a drive signal delivered from a control circuit 10, current is fed from the SDs 2A, 2B, 2C and electromagnetic energy is stored in an inductance 4. When the Tr 3 is turned OFF, the electromagnetic energy stored in the inductances 4 of of the PDs 6A, 6B, 6C is superposed on the current from the SDs 2A, 2B, 2C and fed through a diode 5 to a smoothing capacitor 7 thus feeding an output voltage V0. Consequently, the input current becomes sinusoidal and the input power factor can be improved nearly to 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply device having a three-phase AC power supply as an input power supply and having a power factor improving function of an input power factor.

[Object of the Invention]

[0002]

2. Description of the Related Art FIG. 1 shows an example of a circuit in the prior art. In this switching power supply device, a three-phase rectifier circuit 2 for rectifying a three-phase AC power supply 1 is connected to a power factor correction circuit 6 composed of a step-up chopper circuit composed of a switching element 3, an inductance 4 and a diode 5. A smoothing capacitor 7 is connected between the output terminals of the power factor correction circuit 6 to supply power to the load 20. Then, the output voltage V0 is detected and the switching circuit 3 is controlled by the drive circuit through the control circuit 10. As described above, in the switching power supply device including the power factor correction circuit 6, the electromagnetic energy is accumulated in the inductance 4 when the switching element 3 of the power factor correction circuit 6 is turned on by the drive signal (2). When the switching element 3 is off, the smoothing capacitor 7 is charged through the diode 5 in which the accumulated electromagnetic energy and the output from the three-phase rectifier circuit 2 are superposed to bring the AC voltage waveform and the current waveform close to each other. To improve the power factor.

[0003]

In the above-mentioned prior art, since the three-phase rectifier circuit 2 rectifies the voltage, the output current waveform of the three-phase rectifier circuit 2 is a voltage for three phases having a phase difference of 120 °. The pulses corresponding to the above are intermittently formed, and even if the power factor correction circuit 6 is provided, the input power factor is set to 0.
It cannot be improved above 95.

Therefore, an object of the present invention is to provide a power supply device capable of improving the input power factor in a device using a three-phase AC power supply as an input power supply.

[0005]

The present invention includes a power factor correction circuit for rectifying a three-phase AC power supply voltage by a rectifier circuit and switching a switching element to bring a current waveform close to the voltage waveform of the power supply voltage. In a switching power supply device that supplies a DC output smoothed by a smoothing capacitor to a load, a single-phase rectifier circuit and a power factor correction circuit are connected to each of the three phases to rectify each of the three-phase voltages. In addition, the power factor is improved by the power factor correction circuit to supply power to the load.

[0006]

The structure and operation of the present invention will be described with reference to FIG. In FIG. 2, single-phase rectifier circuits 2A, 2B,
2C is star-connected, and the three phase inputs except the neutral point terminal N commonly connected in the star connection are connected to the (3) line U, V, and W phases of the three-phase AC power supply 1 Connecting. Single-phase rectifier circuit 2A,
After the 2B and 2C, the single-phase power factor correction circuit 6A,
6B and 6C are connected and a common smoothing capacitor 7 is connected to obtain a DC output voltage V0 and supply it to the load 20. Further, the control circuit 10 controls the switching element 3 of each of the power factor correction circuits 6A, 6B, 6C so that the output voltage V0 becomes constant and the phase voltage waveform and the phase current waveform of each phase come close to each other.

The voltages between the U, V, and W phases of the three-phase AC power source 1 and the neutral point terminal N are the single-phase rectifier circuits 2A, 2B, respectively.
Full-wave rectification by 2C, power factor correction circuits 6A, 6B, 6
Supplied to C. When the switching element 3 of each power factor correction circuit 6A, 6B, 6C is turned on by the drive signal from the control circuit 10, the current from the single-phase rectifier circuits 2A, 2B, 2C flows and the electromagnetic energy is stored in the inductance 4. Therefore, when the switching element 3 is off, the electromagnetic energy stored in the inductance 4 of each power factor correction circuit 6A, 6B, 6C and the current from the single-phase rectification circuits 2A, 2B, 2C are superposed and the diode 5 is added. Through smoothing capacitor 7
To supply the output voltage V0.

As described above, in the above-described embodiment, the single-phase rectifier circuit 2 converts the phase voltages of the lines U, V, and W of the three-phase AC power source 1.
Each rectifying circuit 2 by rectifying by A, 2B, 2C
It is possible to prevent the currents from A, 2B, and 2C from becoming intermittent, and to smooth the smoothing capacitor 7 through the power factor correction circuits 6A, 6B, and 6C connected to the subsequent stages of the single-phase rectifier circuits 2A, 2B, and 2C. Since the output voltage V0 is supplied by charging the input current waveform, the input current waveform becomes a sine wave, and the input power factor can be increased to nearly 1.

The present invention is not limited to the above embodiments, but various modifications can be made within the scope of the present invention. For example, the power factor correction circuit may use a step-up / down chopper circuit instead of the step-up chopper circuit.
An insulating converter may be used instead of the non-insulating type (4) chopper.

[0010]

INDUSTRIAL APPLICABILITY The present invention uses a power factor correction circuit for rectifying by a three-phase AC power supply rectifying circuit and switching a switching element to bring a current waveform close to a voltage waveform of each phase of the three-phase AC power supply. In a switching power supply that supplies DC output after smoothing with a smoothing capacitor, obtain a DC output by connecting a star-connected single-phase rectifier circuit and a power factor correction circuit to each of the three phases and smoothing with a smoothing capacitor. With such a configuration, it is possible to provide a switching power supply device capable of improving the input power factor in a device using a three-phase AC power supply as an input power supply. Further, in the configuration of the present invention, the terminals are commonly connected in a star-shaped connection, and the terminals correspond to the neutral points of the star-shaped three-phase AC power supply.
Therefore, there is an advantage that the three-phase AC power supply can be used regardless of whether it is a three-phase three-wire power supply or a three-phase four-wire power supply.

[Brief description of drawings]

FIG. 1 Example of power factor correction circuit for conventional three-phase AC input

FIG. 2 is an example of a power factor correction circuit for three-phase AC input of the present invention.

[Explanation of symbols]

 1 Three-Phase AC Power Supply 2 Three-Phase Rectifier Circuit 2A, 2B, 2C Single-Phase Rectifier Circuit 3 Switching Element 4 Choke 5 Diode 6 Conventional Power Factor Correction Circuit 6A, 6B, 6C Power Factor Correction Circuit (5) 7 Smoothing capacitor 20 load

Claims (1)

[Claims] 1. A power factor correction circuit for rectifying a three-phase AC power source voltage by a rectifier circuit and switching a switching element to bring a current waveform close to a voltage waveform of the power source voltage. In a power supply device that smoothes the output and supplies a DC voltage, three sets of single-phase rectifier circuits and three sets of power factor correction circuits connected to this output are three-phase star-connected at the input side, Rectify for each phase voltage of each layer,
The outputs of the three sets of power factor correction circuits connected to the output side are connected to a set of smoothing capacitors to supply power to the load, and the voltage waveform of the phase voltage and the phase current waveform are brought close to each other to obtain the power factor. A switching power supply device characterized in that it is configured to improve.