JP2007184998A - Power converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To acquire a power converter for instantaneously reducing a switching frequency during an abnormality such as a short circuit in a load, and preventing a main semiconductor element from an overheat without new additional circuits. <P>SOLUTION: The power converter uses a self-excited semiconductor switch 2 with an instantaneous value controlled switching system for following a current instruction Is, and is provided with a hysteresis width correcting means 11 for correcting a hysteresis width for determining the switching frequency in response to the magnitude of the current instruction. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a power conversion device using a self-excited semiconductor switch applied to, for example, an uninterruptible power supply, an inverter for driving a motor, and the like, and in particular, an electric power having an instantaneous value control type switching system that follows a current command. The present invention relates to a conversion device.

FIG. 6 shows an AC-DC power converter using a hysteresis comparator system provided with a conventional hysteresis width correcting means (see, for example, Patent Document 1).
A conventional power conversion device is a device that converts an AC input of an AC power supply 21 into DC by a rectifier 22 and boosts the DC output by a boost chopper 23 to obtain a DC output. In the voltage control of the DC output, the voltage control amplifier 24 performs a proportional control calculation on the deviation of the DC voltage set value Vs from the DC detection value Vf. This output and full-wave rectification of the AC power supply 21 are integrated by a multiplier 25 to generate a current command Is. The current command Is, the output current Id of the chopper 23 and the deviation are input to the hysteresis comparator 27, and an inverted output is obtained from the comparator 27 when the output current Id exceeds the hysteresis width ΔI with respect to the current command Is. The on / off output of the hysteresis comparator 27 is converted into an on / off control signal for the switch SW of the boost chopper 23 via the gate circuit 28. Here, the hysteresis width ΔI includes a hysteresis width correction means 29 that increases or decreases the hysteresis width according to the input current. The hysteresis correction circuit 29c is a circuit that passes the absolute value obtained by passing the input current through the absolute value circuit 29a, passes through the low-pass filter 29b, and increases or decreases the hysteresis width according to the output with the characteristic shown on the boundary of the rated current of the device. When the input current is less than the rated current, the hysteresis width ΔI is decreased to increase the switching frequency, and in a high current state such as an overload, the hysteresis width ΔI is increased to decrease the switching frequency. This acts to reduce switching loss when the current is large, such as during overload.
The hysteresis width correcting means 29 operates in the same manner even when correction is made in accordance with the output current in an inverter circuit that converts direct current into alternating current.

Japanese Patent Laid-Open No. 6-6978 (FIG. 1)

For example, when the output circuit in the inverter circuit causes a load-side short circuit, the current change rate becomes very high, so the switching frequency of the main circuit semiconductor element rises transiently. As a result, the switching loss increases and the main circuit semiconductor element Because there is a possibility of the worst element failure,
In a load short circuit or the like, it is necessary to instantaneously lower the switching frequency to prevent the semiconductor element from overheating. However, since the hysteresis width adjusting means in the conventional current follow-up type hysteresis comparator system is a circuit that corrects according to the result of the input current or output current, the correction amount does not operate excessively due to the current ripple as shown in FIG. The low-pass filter circuit 29b is necessary, and there is a problem that the response of correction for reducing the switching frequency is delayed. Further, the circuit of the conventional example shown in FIG. 6 has a problem that the cost increases because a dedicated input current sensor is required for correcting the hysteresis width.

  The present invention has been made to solve the above-described problems, and at the time of abnormality such as a load short circuit, the switching frequency is instantaneously lowered to prevent overheating of the main circuit semiconductor element, and without adding a new circuit. It aims at providing the power converter device which can achieve this.

  The power converter according to the present invention uses a self-excited semiconductor switch having an instantaneous value control type switching system that follows the current command, and the magnitude of the current command is larger than the hysteresis width that determines the switching frequency. A hysteresis width correcting means for correcting the hysteresis width according to the height is provided.

  According to the present invention, the correction means for increasing / decreasing the switching frequency is performed based on the current command, so that the delay element of the filter circuit is not required, and an excessive increase in the switching frequency can be suppressed at a high speed. Since instantaneous current control always has a reference current command, there is no need to provide a new circuit.

Embodiment 1.
Hereinafter, the power converter in Embodiment 1 of this invention is demonstrated based on FIG.
FIG. 1 shows an embodiment in which the present invention is applied to an inverter circuit in a three-phase uninterruptible power supply. In FIG. 1, 1 is a DC power source, 2 is an IGBT element, 3 is a reactor, 4 is a capacitor, 5 is a load, 6 is a current sensor, 7 is a U-phase AC current command (Isu), and 8 is a U-phase hysteresis width. (ΔIu), 9 is a hysteresis comparator, 10 is a gate circuit, 11 is a hysteresis width correction means, and 12 is a U-phase hysteresis width correction amount (ΔIhu). The reactor 3 and the capacitor 4 constitute a filter circuit, and a stable AC voltage is supplied to the load 5. The hysteresis comparator 9 compares the deviation between the current command Is and the current detection value detected by the current sensor 6 and the hysteresis width, and gives an on / off signal to the gate circuit 10 that drives the IGBT element 2. The IGBT element 2 is turned on / off, and a current that follows the current command can flow.

  Next, the operation of the present invention will be described by taking the U phase as an example, but the same applies to the V phase and the W phase. Reference numeral 7 denotes a U-phase AC current command Isu, which is generated from voltage control for controlling the AC voltage of the capacitor 4 to be constant, and inputs a deviation from the U-phase current detection value detected by the current sensor 6 to the hysteresis comparator 9. . Here, the hysteresis width 8 (ΔIu) of the U phase is a value determined from the switching frequency and the like in the rated state, and the hysteresis width correction amount 12 (ΔIhu) of the U phase calculated by the hysteresis width correction means 11 is added to this value. The result of adding is input to the hysteresis comparator 9. An example of the configuration of the hysteresis width correcting means 11 is shown in FIG. In FIG. 2, the absolute value circuit 11a is passed through the current command Is, and the correction start current reference 11b (Ik) is subtracted therefrom. The correction start current reference Ik is a current that serves as a reference for lowering the switching frequency, and is determined by restrictions on the IGBT element 2 and the like. Next, a lower limiter 11c of 0 is provided so that the subtraction result does not become negative, and the correction gain 11d (G) is integrated to obtain a hysteresis width correction amount 12 (ΔIh). The value of the correction gain 11d is a value determined from a circuit constant, a switching frequency limit value, and the like.

  As described above, the hysteresis width input to the hysteresis comparator 9 by the hysteresis width correction unit 11 shown in the first embodiment is such that the current command amplitude increases with the correction start reference current Ik as a boundary, as shown in FIG. To work. This situation will be described in the uninterruptible power supply. FIG. 4 is a schematic block diagram showing a circuit for generating a current command, and voltage feedback control is performed so that the AC voltage of the filter capacitor 4 shown in FIG. 1 is constant. In FIG. 4, the deviation between the voltage command and the voltage feedback of the capacitor 4 is passed through a voltage controller 13 constituted by proportional integration or the like, and a current limiter 14 is provided for this value to generate a current command Is. Further, the voltage control is performed at a high speed because the waveform control of the AC waveform is performed. Next, the waveform shown in FIG. 5 shows the movement of each part waveform when a load short circuit occurs. If a short circuit occurs on the load side when the voltage of the capacitor 4, the current command of the inverter, and the current are output at a constant level, the voltage of the capacitor 4 will suddenly decrease to near zero, and as a result, let's recover the drop in voltage. Since the voltage controller 13 operates, the inverter current command reaches the limiter instantaneously. Next, as the current command increases, the above-described hysteresis width correction means operates to increase the hysteresis width and operate to suppress an excessive increase in the switching frequency of the IGBT element 2.

  As described above, according to the first embodiment of the present invention, since the hysteresis width correcting means for increasing / decreasing the hysteresis width according to the current command amount is provided, the transient switching frequency rise of the main circuit element can be increased at high speed. It is possible to suppress the main circuit element from overheating.

  In the first embodiment, the case of a three-phase PWM inverter has been described. Can obtain the same effect. Further, in the circuit shown in the conventional example of FIG. 6, by correcting the hysteresis width by Is that is a current command, it is not necessary to detect the AC input current as in the conventional example, and it is possible to correct at high speed. It becomes.

  In the first embodiment, the correction start current reference 11b (Ik) is provided, and the hysteresis width is linearly corrected on the basis of the correction start current reference 11b (Ik). However, the correction amount is appropriately designed based on the circuit constant, the tolerance of the main circuit element, and the like. Is done.

BRIEF DESCRIPTION OF THE DRAWINGS It is a system block diagram which shows the power converter device in Embodiment 1 of this invention. It is a block diagram which shows the hysteresis width correction | amendment means of the power converter device in Embodiment 1 of this invention. It is a figure which shows the hysteresis width characteristic of the power converter device in Embodiment 1 of this invention. It is a block diagram which shows the voltage control circuit of the power converter device in Embodiment 1 of this invention. It is a figure which shows each part waveform at the time of the load short circuit of the power converter device in Embodiment 1 of this invention. It is a block diagram which shows the hysteresis width correction | amendment means of the conventional power converter device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 DC power supply 2 IGBT element 3 Reactor 4 Capacitor 5 Load 6 Current sensor 7 Current command 8 Hysteresis width 9 Hysteresis comparator 10 Gate circuit 11 Hysteresis width correction means 12 Hysteresis width correction amount 13 Voltage controller 14 Current limiter

Claims (4)

  In a power converter using a self-excited semiconductor switch equipped with an instantaneous value control type switching system that follows a current command, a hysteresis width is set according to the magnitude of the current command with respect to the hysteresis width that determines the switching frequency. A power converter comprising a hysteresis width correcting means for correcting.   Hysteresis width correction means passes an absolute value circuit to the current command, subtracts the correction start current reference from this, provides a zero lower limiter so that the subtraction result does not become negative, integrates the correction gain, and corrects the hysteresis width The power conversion device according to claim 1, wherein the power conversion device is an amount.   The power conversion device according to claim 2, wherein the correction start current reference is a current that serves as a reference for lowering the switching frequency, and is determined by a restriction of the IGBT element. The current command is generated by passing a deviation between the voltage command and the voltage feedback of the capacitor through a voltage controller configured by proportional integration, and providing a current limiter for this value. 4. The power conversion device according to any one of 3.

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