JP3478663B2 - Switching power supply - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for reducing a commercial ripple current at the output of a rectifier in a switching power supply with three-phase input power factor correction. FIG. 1 shows a circuit configuration of a conventional rectifier with three-phase input power factor correction. In the figure, converters 2a, 2b and 2c with single-phase input power factor correction are connected to the respective lines UV, VW and WU of the three-phase AC power supply 1, and their output terminals are connected in parallel. Connected to form a rectifier with three-phase input power factor improvement. At this time, the current I of each phase of the three-phase AC power supply 1 is
U, IV, and IW are the sums of the input currents IU-V, IV-W, and IW-U of the converter with end-phase input power factor correction, and IU = IU-V + IW-.
U, IV = IV-W + IU-V, IW = IW-U + IV-W. (2) FIG. 2 shows one converter having a single-phase input power factor improvement, wherein 2a, 2b and 2c all have the same circuit configuration. 2a, 2b, and 2c are line voltage V, respectively.
UV, VV-W, and VW-U are input voltages Vin. In FIG. 2, the power conversion system is a forward converter system, and its control is performed by an input current detector 1.
The input current Iin and the input voltage Vin detected in step 1 are input to the pulse oscillator 13. Using the input voltage Vin as a reference waveform, the pulse width is controlled so that the input current Iin has the same phase and a similar waveform as the reference waveform, and a pulse signal is applied to the switching element 8 through the drive circuit 12; Switching element 8
Is turned ON and OFF. Since the switching element 8 switches the input voltage Vin which is not smoothed, the switching element 8
To -2, a voltage n times the number of turns of the transformer 6 of the full-wave rectified input voltage Vin is applied. Therefore, on the output side,
Ripple current of twice the cycle (100 Hz) of the commercial flows. FIG. 1 shows a converter 2 with a single-phase input power factor improvement.
a, 2b, and 2c have outputs connected in parallel;
The input voltages VU-V, VV-W, and VW-U of b and 2c each have a phase difference of 2π / 3 (rad). Therefore, a ripple current of 300 Hz flows in the output as shown in FIG. When a three-phase input rectifier is used as a power source for a communication device or the like, commercial ripple current appearing at the output of the rectifier adversely affects the communication device or the like as noise. (3) Conventionally, there is a method of adding a commercial reactor to the output side of the rectifier or increasing the capacity of the output electrolytic capacitor, but there are problems in efficiency, cost, and mounting. FIG. 3 shows waveforms of the input voltage Vin and the input current Iin. Since the power conversion system shown in FIG. 2 is a forward converter system, the output voltage V0 is converted to V0 / n on the input side via the transformer 6. (N is the turns ratio of the transformer 6.) At this time, the conduction angle θ at which the input current Iin flows is
FIG. 1 shows a period during which the input voltage Vin is higher than V0 / n.
In order to obtain a conduction angle of (rad) for each of the phase currents Iu, IV, and IW, θ ≧ 2π / 3 (rad). Therefore, the input voltage Vin is input to the pulse oscillator 3 and the conduction angle is 2π / 3.
Shape the waveform so that FIG. 4 shows the waveforms of the input current Iin (only IU-V and IU-W are shown in the figure) and the output ripple current.
The output ripple current has a peak value at a point where the input currents IU-V, IV-W and IW-U of 2a, 2b and 2c in FIG. 1 overlap.
(In FIG. 4, IU-V and IW-U overlap at point a.) FIG. 5 shows an embodiment of an output ripple current reduction circuit according to the present invention. The basic configuration of the circuit shown in FIG. 5 is the same as that of the conventional single-phase input power factor improving circuit shown in FIG. FIG. 5 is obtained by adding 16 and 17 to FIG. Reference numeral 17 denotes each phase voltage of the three-phase AC power supply,
Reference numeral 6 denotes a circuit for performing full-wave rectification of each phase voltage and detecting only a ripple component. (4) The ripple component detected by the ripple component detector 16 corresponds to the pulse oscillator 13 to which the input voltage Vin is input.
Within the range, and becomes the reference voltage. Control is performed such that the input current Iin has the same phase and similar waveform with respect to this reference voltage. FIG. 6A shows the ripple component detected by the ripple component detector 16 and FIG.
The waveform shaped to π / 3 is (b), and the pulse oscillator 13
The waveform obtained by adding (a) and (b) is shown in (c). FIG. 1 shows a converter 2 with a single-phase input power factor improvement.
When a, b, and c are configured by the circuit of FIG. 5, the output ripple current is reduced as shown by the thick line in FIG. According to the present invention, the power factor of a three-phase input switching power supply can be improved and the output commercial ripple current can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a converter with three-phase input power factor improvement. FIG. 2 is a converter with a single-phase input power factor improvement. FIG. 3 shows the input voltage Vi of a converter with a single-phase input power factor improvement.
n, input current Iin waveform. FIG. 4 is an output ripple current waveform of a converter with three-phase input power factor improvement. FIG. 5 is a converter with a single-phase input power factor improvement of the present invention for reducing an output ripple current. FIG. 6 is a reference voltage waveform of the circuit of the present invention for reducing the output ripple current. (5) FIG. 7 is a waveform of the circuit of the present invention in which the output ripple current is reduced. [Description of Signs] 1 Three-phase AC power supply 2a, 2b, 2c Converter with single-phase input power factor improvement 3 Load 4 Rectifier diode 5 Input capacitor 6 Transformer 7 Output rectifier diode 8 Output commutation diode Reference Signs List 9 output choke 10 output electrolytic capacitor 11 input current detector 12 drive circuit 13 pulse oscillator 14 error amplifier 15 error amplifier reference voltage 16 ripple component detector 17 three-phase AC phase voltage detector

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Claims (1)

(57) [Claim 1] A switching power supply for improving a power factor of a three-phase input by providing a converter with a single-phase input power factor correction for each phase of a three-phase input. A single-phase input power factor improving converter of a phase inputs a DC input voltage and a DC input current to a pulse oscillator, and uses the input voltage as a reference waveform, and the DC input current has a similar waveform in phase with the DC input voltage. Thus, in a three-phase input switching power supply that improves the power factor of a commercial input current by controlling the pulse oscillator , each phase voltage of the three-phase input is subjected to full-wave rectification, and a ripple is generated.
The pulse generator detects only the component and adds the ripple component to the DC input voltage in the pulse oscillator as a reference waveform, and the pulse oscillator is configured such that the DC input current has the same phase and a similar waveform as the reference waveform. A three-phase input switching power supply characterized by controlling the power factor to improve the power factor and reducing the output commercial ripple current.