JPH066978A - Power converter - Google Patents

Abstract

PURPOSE:To enhance overload capacity of power converter while suppressing noise. CONSTITUTION:The power converter comprises a hysteresis comparator 7 performing ON/OFF control of a switch element SW to produce an output current Id while following up a current command Is, wherein a hysteresis width correcting section 10 corrects hysteresis width of the hysteresis comparator 7 according to the magnitude of input current such that the hysteresis width is increased to lower the switching frequency (loss) for high input current, i.e., overload, whereas the hysteresis width is decreased to increase switching frequency for low input current.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter using a semiconductor switch element, and more particularly to a power converter using a hysteresis comparator to perform switching control following a current command.

[0002]

2. Description of the Related Art AC-DC conversion and active filters,
In a power converter for DC / AC conversion such as an inverter, a semiconductor switch is used as a main circuit switch element, and voltage, current, and frequency controlled outputs are obtained by the switching control.

Among these, in the current follow-up control system using the hysteresis comparator, the deviation between the current command value and the detected current is used as the input of the hysteresis comparator, and switching control of the main circuit switch element is performed so that the output follows the current command value. To do.

FIG. 4 shows a conventional AC-DC power converter. The AC input of the AC power supply 1 is converted into DC by the rectifier 2, and this DC output is boosted by the boost chopper 3 to obtain a DC output.

The voltage control of the DC output is performed by setting the DC voltage set value Vs.
The deviation between the DC detection value Vf and the DC detection value Vf is proportional-integrated (PI) calculated by the voltage control amplifier 4. This calculation output is the multiplier 5
Of the AC power supply 1 obtained from the absolute value circuit 6 is applied to the multiplicand input of the multiplier 5.

The output of the multiplier 5 which becomes a full-wave rectified voltage waveform is made into a current command, and the deviation between this current command Is and the output current Id of the chopper 3 is inputted to the hysteresis comparator 7, and with respect to the current command Is. When the output current Id exceeds the hysteresis width ΔI, an inverted output is obtained from the comparator 7. The ON / OFF output of the hysteresis comparator 7 is used as an ON / OFF control signal of the switch SW of the step-up chopper 3 via the gate circuit 8.

In the above conventional structure, the current command Is and the detected current Id are as shown in FIG. 5, and the input current from the AC power source 1 to the rectifier 2 side becomes an equivalent sine wave and the fundamental wave power factor is set to 1. Obtained AC-DC power conversion.

FIG. 6 shows another conventional power converter, which is a case of a current tracking type PWM inverter. Also in this case, switching control of each switch is performed by the hysteresis comparator 9 based on the deviation between the sine wave current command Is and the detected current Id.

[0009]

In the conventional power converter of the hysteresis comparator type, the hysteresis width of the hysteresis comparator is set to be small, and the higher the switching frequency of the switch element, the higher the high frequency component of the input or output current is reduced. Input / output characteristics are improved. Further, in terms of configuration, it is possible to achieve downsizing and noise reduction by reducing the capacity of the DC reactor of the chopper.

On the other hand, as the switching frequency becomes higher,
It is limited by the switching characteristics of the switching element used, the surge voltage absorption circuit, the applied voltage, and the magnitude of the current.

For this reason, the switching frequency of the switch element, the surge voltage absorbing circuit, etc. are designed with a relatively large margin in consideration of the worst conditions such as the fluctuation of the input voltage and the overload withstanding capability.

For example, when the overload resistance is large or the input voltage fluctuation is large, a restriction on the upper limit of the switching frequency and a large surge voltage absorption circuit are required, which makes it difficult to reduce noise, reduce cost, and reduce size. ing.

An object of the present invention is to provide a power conversion device that solves the above problems.

[0014]

In order to solve the above-mentioned problems, the present invention provides a power converter having a hysteresis comparator for performing switching control of a main circuit switch element in accordance with a current command. It is characterized in that a hysteresis width correcting means for decreasing or increasing the hysteresis width of the hysteresis comparator according to the increase or decrease of the output current is provided.

[0015]

When the input or output current of the device is low such as a normal load, the hysteresis width is reduced to increase the switching frequency, and in the high current state such as an overload, the hysteresis width is increased to decrease the switching frequency.

[0016]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. 4 is different from FIG. 4 in that a hysteresis width correction unit 10 that corrects the hysteresis width of the hysteresis comparator 7 according to the input current of the device is provided.

The absolute value circuit 11 includes an AC power source 1 and a rectifier 2
Detects the absolute value of the input current to the low-pass filter 12
Removes the high frequency component from the absolute value signal to obtain the absolute value of the fundamental wave component.

The hysteresis width correction circuit 13 generates a hysteresis width correction signal according to the level of the absolute value signal and corrects the hysteresis width of the hysteresis comparator 7 with this correction signal.

The hysteresis width correction characteristic of the hysteresis width correction circuit 13 is illustrated in FIG. In the figure, the hysteresis width is reduced up to the current I ₁ which is the rated input current of the power converter, and the hysteresis width is proportional to the increase of the input current I for the overload current from the current I ₁ to the maximum rated input current I _2. This is the case where the polygonal line characteristic is set so that it is increased and is limited to a constant hysteresis width when the current is I ₂ or more.

In this embodiment, the hysteresis width is corrected depending on whether the load of the device is small and the input current is within the rated range or the overload range. FIG. 3 shows changes in the output current waveform depending on the magnitude of the input current. When the input current Is ₂ is relatively small, the hysteresis width is small and the switching frequency is high, and when the input current Is ₁ is large, the hysteresis width is large and the switching frequency is low.

As a result, in the overload state, the switching frequency of the switch element of the chopper 3 is lowered, the switching loss of the element is reduced, and the withstand capability of the device and the surge voltage absorbing circuit are increased. Similarly, when the input current increases due to the fluctuation of the input voltage, the switching frequency is lowered to reduce the switching loss.

On the other hand, in the normal load state, the hysteresis width can be reduced and the switching frequency can be increased to reduce noise.

In the embodiment, the case of AC-DC conversion is shown, but the same action and effect can be obtained by applying the current-following power converter using a hysteresis comparator such as the PWM inverter illustrated in FIG. You can

In the embodiment, the hysteresis width correction characteristic diagram of the broken line characteristic is shown, but the design may be changed as appropriate such as one having a quadratic curve characteristic and one having a linear characteristic.

Further, the current detection for determining the hysteresis width may be output current detection of the device.

[0026]

As described above, according to the present invention, when the hysteresis comparator is used to perform switching control that follows the current command, the hysteresis width of the hysteresis comparator is adjusted according to the increase or decrease of the input or output current of the device. Since it is designed to decrease, for example, in an overload state, the switching frequency of the switch element is reduced to increase the switch element withstand voltage and the surge voltage absorption circuit withstand voltage.
Increases the overload resistance without increasing the device cost or increasing the size. Moreover, in a normal load state, the switching frequency is increased to reduce noise and reduce output ripple.

[Brief description of drawings]

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

FIG. 2 is a hysteresis width correction characteristic diagram in the embodiment.

FIG. 3 is an output current waveform diagram of the example.

FIG. 4 is a circuit diagram of a conventional example.

FIG. 5 is a conventional output current waveform diagram.

FIG. 6 is a circuit diagram of a conventional example.

[Explanation of symbols]

 2 ... Rectifier 3 ... Step-up chopper 4 ... Voltage control amplifier 5 ... Multiplier 6, 11 ... Absolute value circuit 7 ... Hysteresis comparator 8 ... Gate circuit 10 ... Hysteresis width correction part 12 ... Low pass filter 13 ... Hysteresis width correction circuit

Claims (1)

[Claims] 1. A power conversion device equipped with a hysteresis comparator that controls switching of a main circuit switch element by following a current command, and increases or decreases the hysteresis width of the hysteresis comparator according to an increase or decrease in the input or output current of the device. An electric power conversion device comprising: