JP2002330581A - Dc power supply device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a DC power supply device, which makes output-current ripple in the low-current region small, even if a small DC passive filter is used. SOLUTION: Switching frequency is made higher in the low output-current region than that at the rated output current, by continuously making variable control of the switching frequency relative to the chopper output current, so that loss of the power semi-conductor device, calculated from the relation of the output current of a chopper converter device to the switching frequency, becomes the rated one or less, and the switching frequency becomes optimum.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC power supply, and more particularly, to a DC power supply suitable for reducing a DC output and reducing the size of a DC filter.

[0002]

2. Description of the Related Art A conventional example of a DC power supply using a chopper converter is disclosed in a document of the 6th Institute of Electrical Engineers of Japan Ibaraki Branch Presentation "Sine-wave AC / DC converter using IGBT + two-quadrant chopper accelerator power supply. IGBT of the chopper conversion device by comparing the magnitude of a carrier wave (triangular wave) with a constant frequency and a modulated wave (chopper output voltage command).
There is disclosed a triangular wave comparison pulse width modulation system for controlling the ON / OFF of the signal.

FIG. 2 shows an example of the above-mentioned conventional control method (in the case of a step-down chopper of one polarity output voltage = 1-quadrant chopper circuit method). In FIG. 2, a modulated wave VC is obtained by comparing an arithmetic output of an automatic current control circuit (hereinafter, ACR) and an output voltage average value Voave by an automatic voltage control circuit (hereinafter, AVR), and is constant with the modulated wave VC. Carrier TR of frequency
An on / off signal of the power semiconductor device (for example, IGBT) for the chopper converter 4 is generated based on the magnitude relationship with I. In this prior art, the switching period T of the carrier wave TRI and the input stage DC voltage EDC of the chopper converter 4 are used.
Is constant, the output voltage average value Voave of the chopper converter 4 is output in proportion to the ON conduction time Ton of the IGBT, and the relationship is expressed by the following equation (1).

Voave = EDC × (Ton / T) (Equation 1) Further, when the load 7 is a coil and its inductance is L, the relationship is expressed by Equation (2).

ΔI = EDC × {1− (Ton / T)} × Ton / L (2) In order to satisfy the low ripple DC output characteristic, the DC reactor 5 It is necessary to reduce the output current ripple ΔI by installing a DC passive filter 15 or the like constituted by series resonance with the DC capacitor 6. The gain characteristic of the DC passive filter 15 is as follows.
Assuming that the output current value of the chopper converter is Iout, and the ripple rate is calculated by equation (3), the ripple rate is determined so as to satisfy the following condition: ripple rate = ΔI / Iout <ripple specified value (expression 3) .

When the switching period T is constant, the value of the output current ripple ΔI is determined by the equation (2) to be the value of the output current ripple at the rated output current and the minimum value of the output current (intermittent limit current value of the DC reactor 5). It is almost the same as time. Therefore, according to the equation (3), the ripple rate becomes largest when the output current Iout is the minimum value.

Therefore, the output current Iout of the DC power supply
In order to suppress the ripple rate included in the DC current from the low current range to the rated current range, the gain characteristic of the DC passive filter 15 is determined under the condition that the output current Iout is the minimum value. Can satisfy the specifications. However, this means that as the output current Iout increases, the ripple ratio decreases proportionally, so that in a region where the output current value is large, the DC passive filter is excessively installed, and the DC power supply device is large and the cost is high. It was supposed that a filter was installed.

[0008]

In the above prior art, the ripple rate is larger in the low output current region than in the case of the rated output current, and the specified ripple value is satisfied in the entire operation range of the rated output current. In this case, there is a problem that the size of the DC passive filter is large and the cost is high.

An object of the present invention is to variably control the switching frequency of a chopper converter according to the magnitude of an output current command value or an output current detection value, thereby reducing the output current ripple generated in the prior art even in a low current region. An object of the present invention is to provide a DC power supply device that can be smaller and satisfy a specified value with a small-sized DC passive filter.

[0010]

In the low output current region of the chopper converter, the power loss of the power semiconductor device is small as compared with the case of the rated output current. Therefore, even if the switching frequency is higher than the switching frequency at the time of the rated output current, the element does not break down due to heat generation.

Therefore, in the DC power supply of the present invention, the switching is performed so that the loss of the power semiconductor device calculated from the relationship between the output current of the chopper converter and the switching frequency is equal to or lower than the rated value and the optimum switching frequency. The frequency is continuously variably controlled with respect to the chopper output current value. That is, in the low output current region, the switching frequency is set higher than the switching frequency at the time of the rated output current.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. As shown in FIG. 1, AC power supplied from an AC power supply 1 is converted by a forward converter 2 into DC power. The converted DC power is once converted to predetermined DC power by the chopper converter 4 via the DC filter 3. The DC power output from the chopper converter 4 is supplied to the electromagnet of the load 7 via a DC passive filter 15 configured by a series resonance of the DC reactor 5 and the DC capacitor 6. Here, the chopper converter 4 includes a load 7
A modulated wave VC generated via the automatic current control circuit 13 and the automatic voltage control circuit 12 so that an output current corresponding to the output current command circuit 14 for energizing the electromagnet flows through the carrier current command circuit 16 The level with the carrier TRI output from the carrier oscillation circuit 11 is determined by the comparator 10.
IG of the chopper converter 4
A BT on / off pulse is generated, and the IGBT is turned on / off via the driver circuit 9.

The average output voltage Voa of the chopper converter 4
ve is expressed by Equation (4), where Ton is the ON conduction time of the IGBT, T is the switching period of the carrier wave, and EDC is the input stage DC voltage of the chopper converter 4.

Voave = EDC × (Ton / T) (Equation 4) The equation (Equation 4) holds when the step-down chopper of the one-polarity output voltage = 1-quadrant chopper circuit system. Further, when the load 7 is a coil, the output current ripple ΔI
When the inductance is L, it is expressed by (Equation 5).

ΔI = EDC × {1− (Ton / T)} × Ton / L (Equation 5) Here, if Ton / T = Don duty (Don duty: IGBT ON time), Voave = EDC × Don duty (Equation 6) ΔI = EDC × {1− (Don duty)} × Don duty × T / L (Equation 7)

From the equation (6), the Don duty is constant under the condition that the average output voltage Voave of the chopper converter 4 is a constant value, and the output current ripple ΔI is obtained from the equation (7) under the condition of the constant Don duty. Is proportional to the switching period T. That is, by reducing the switching cycle T (increase the switching frequency fsw), the output current ripple Δ
I can be reduced.

On the other hand, the IGBT loss includes a steady loss Psat.
And the switching loss Psw. The IGBT collector current Ic and the switching frequency fsw (= 1 / T, T: switching cycle) are determined so that the junction temperature rise of the IGBT due to the loss of the two becomes less than the rated use. There is a need to. Here, the steady loss Psat and the switching loss P
The sw is proportional to the IGBT collector current Ic and the switching frequency fsw. When the switching frequency fsw is constant, the loss of the IGBT increases as the IGBT collector current Ic increases, while when the IGBT collector current Ic is constant, the switching occurs. It increases as the frequency fsw increases. Therefore, in this embodiment, when the IGBT collector current Ic is small, the IGBT collector current Ic
Is operated with a higher switching frequency fsw than in the case where is larger.

Here, the carrier frequency command circuit 16 receives the output current command value Ipat and determines the switching frequency fsw at which the IGBT generation loss and the output current ripple are optimal from the relationship between the IGBT collector current Ic and the switching frequency fsw. The output (carrier frequency pattern command) is input to the carrier oscillation circuit 11 via the voltage / frequency converter 17. In the carrier wave oscillation circuit 11,
The frequency (switching cycle T) of the carrier TRI is variably controlled according to the input carrier frequency pattern command.

According to this embodiment, the switching frequency of the IGBT is variably controlled by the output current command value, and the output current ripple can be controlled to be small even in a low output current region.

In the above embodiment, the case where the power semiconductor device is an IGBT using a step-down chopper in which the polarity of the output voltage is unidirectional is described. However, if the power semiconductor device is a self-extinguishing type power semiconductor device, a power semiconductor device other than the IGBT Alternatively, the same effect can be obtained even in the case of a bipolar two-quadrant chopper, a quadrant chopper system of more than two quadrants, and a case where the chopper converter is a parallel n-multiplexer.

In the above embodiment, the switching frequency fsw is calculated by inputting the output current command value Ipat to the carrier frequency command circuit 16, but the output current detection value Iout may be input.

[0022]

As described above, according to the DC power supply of the present invention, since the switching frequency is variably controlled by the output current of the chopper converter, the output current ripple in the low output current region can be reduced. Further, according to the DC power supply device of the present invention, a small-sized passive filter can satisfy the specified ripple value in a range from a low output current range to a rated output current range.

[Brief description of the drawings]

FIG. 1 shows a DC power supply circuit of the present invention.

FIG. 2 shows a block diagram of a prior art DC power supply circuit.

FIG. 3 shows an explanatory diagram of pulse width modulation.

[Description of Signs] 1 ... AC power supply, 2 ... Self-excited forward converter, 3 ... DC filter, 4 ... Chopper converter, 5 ... DC reactor, 6 ...
DC capacitor, 7: load, 8: DC current detector, 9:
Driver circuit, 10: Comparator, 11: Carrier oscillation circuit, 12: Automatic voltage control circuit, 13: Automatic current control circuit, 14: Output current command circuit, 15: DC passive filter, 16: Carrier frequency command circuit, 17: Voltage / Frequency converter.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Hiroshi Kubo 3-1-1, Sachimachi, Hitachi-shi, Ibaraki Pref. Hitachi, Ltd. Hitachi Works (72) Inventor Masaaki Yabuki 3-2-2, Sachimachi, Hitachi-shi, Ibaraki No. 1 Hitachi Engineering Co., Ltd. F-term (reference) 5H730 AS01 BB11 BB57 DD02 FD01 FD31 FF02 FG05 FG07 FG22

Claims (3)

[Claims] 1. A forward power converter using a power semiconductor device to convert AC to DC, and a chopper converter for converting DC converted by the forward power converter into predetermined DC power using the same power semiconductor device. A DC power supply device comprising a device and a DC passive filter for reducing output ripple, comprising a control circuit for continuously variably controlling the switching frequency of the chopper converter with respect to the chopper output current value. Characteristic DC power supply. 2. The direct-current power supply according to claim 1,
A DC power supply device, wherein a switching frequency of the chopper converter is higher than a switching frequency at a rated output current in a low output current region. 3. The DC power supply according to claim 2,
A DC power supply, wherein a switching element of the chopper converter is an IGBT.