JPS6392275A - Overcurrent control circuit for inverter - Google Patents

Abstract

PURPOSE:To prevent a switching element from being destructed, by providing a comparator with which a limit circuit is operated only when overcurrent flows. CONSTITUTION:An overcurrent limit circuit of an inverter provides a current transformer to an AC output circuit, supplies the detected voltage to an amplitude regulation circuit 10 regulating the amplitude of a sinusoidal signal 9 through a rectification circuit 6 and an error amplifier 7 and controls the inverter so that the detected voltage may be the same as the reference voltage of a power source 8. The overcurrent limitation is performed with AC feedback circuits 11-12, a PWM modulation circuit 14, a logical circuit 15, etc. At this moment, on the output side of the abovementioned rectification circuit 6 provided is a comparator 16, to which a reference voltage power source 17 is connected and its comparative output is inputted into the logical 15. The limit circuit is thereby operation only when overcurrent flows, limiting the absolute maximum current, so that a switching element of the inverter circuit can be prevented from being destructed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an inverter overcurrent control circuit that can effectively protect an inverter-based power supply circuit against overload current.

[Background of the invention]

A conventionally known inverter has a structure as shown in FIG. 3, and an overcurrent limiting circuit for a conventional inverter has a structure as shown in FIG. 4.

That is, the conventional inverter shown in FIG.
For example, transistors, thyristors, or mechanical switching elements (2-1), (2-2), (2
-3), (2-4), etc. are connected, and by repeating on and off operations by this switch circuit 2, an alternating current (rectangular wave) is generated, and a fundamental wave component is added to this alternating current output circuit. Filters 6 and 4 are interposed to extract the . Further, as an overcurrent limiting circuit of this inverter, a current transformer 5 for detecting load current is provided in the above-mentioned AC output circuit, and the voltage detected by the current transformer 5 is converted into DC by a rectifier circuit 6 shown in FIG. death,
This is input to the e side of the error amplifier 7. By inputting the reference voltage from the power supply 8 to the e side of the error amplifier 7, the difference voltage between the voltage from the rectifier circuit 6 and the voltage from the power supply 8 is obtained from the error amplifier 7. , is supplied to an amplitude adjustment circuit 10 that adjusts the amplitude of the sine wave signal 9 that controls the output voltage of the inverter, and at this time, when the detected voltage from the current transformer 5 becomes υ larger than the reference voltage, the voltage of the inverter is is controlled so that the detected voltage becomes the same as the power supply 80 reference voltage. Reference numerals 11 and 12 are AC feedback circuits for stably operating the error amplifier 7, 13 is a triangular wave generation circuit for carrier waves, and 14 is a PWM modulation circuit. The logic circuit 15 inputs the output from the circuit 10 to generate a pulse width modulation signal, and each switch element (2-1) of the #J switch circuit 2,
(2-2), (2-3), and (2-4) are controlled to limit the overcurrent of the inverter.

However, the peak current setting value of this overcurrent limiting circuit is
When the effective current value is about 1.4, if the peak current value is nearly three times the effective current flowing in a capacitor input rectifier circuit load, the AC feedback is limited to a value lower than the rated current. Circuits 11 and 12 can bring the current close to the effective current, but the response to excessive current due to other load short circuits is delayed, and for this reason, the switch
There was a problem that 2-1), (2-2), (2-3), and (2-4) were destroyed.

[Purpose of the invention]

The present invention has been made by focusing on such conventional problems, and is an inverter that is capable of limiting the absolute maximum current when an excessive current flows to prevent destruction of the switching elements in the inverter circuit. The purpose is to provide an overcurrent limiting circuit.

[Embodiments of the invention]

The inverter overcurrent limiting circuit according to the present invention will be explained in detail below based on FIG. 1, but the main structure of the overcurrent limiting circuit in this embodiment is similar to that of the conventional overcurrent limiting circuit shown in FIG. , so the same parts are given the same reference numerals as in the conventional example.

A description of the same structure will be omitted.

That is, in this embodiment, a comparator 16 is connected to the output side of a rectifier circuit B that rectifies the detected voltage, a reference voltage power supply 17 is connected to this comparator 16, and the output from this comparator 16 is A circuit configured to connect to the logic circuit 15 is used.

Next, to describe its operation, first, the AC feedback circuit 11
．． Set the time constant of 12 to several times the period of the output frequency,
Avoid being limited by the peak value for load currents with large peak values, such as capacitor input rectified load currents. However, if this continues, if an excessive current such as a load short-circuit current occurs, the slow response may exceed the withstand current of the switch element in the inverter circuit, causing the switch element to be destroyed.

Therefore, in this embodiment, a comparator 16 that can instantaneously compare the reference voltage from the reference voltage power source 17 and the voltage from the rectifier circuit 6 is set to a level that does not operate at the peak voltage value of the capacitor input rectifier load. Only when an excessive current flows, the limiting circuit is activated to limit the absolute maximum current as shown in Figure 2, thereby reducing the switching elements (2-1), (2-2), and (2) in the inverter circuit.
-3) and (2-4) can be effectively prevented.

[Summary of the invention]

As described above, the present invention includes a conversion circuit that converts a DC power source into a pulse width modulated AC output by controlling the opening and closing of a plurality of switch elements that are opened and closed by a control signal whose pulse width is modulated, and a conversion circuit that extracts a fundamental wave component. In the inverter, the inverter is equipped with a filter circuit that outputs an AC output, and a detection circuit that extracts a voltage proportional to the output current using a current transformer built into the conversion circuit. a rectifying circuit that rectifies the signal from the rectifying circuit; an error amplifier having a current feedback circuit that inputs the respective signals from the reference voltage power source and obtains a difference signal between the two; and an error amplifier that rectifies the output from the rectifying circuit and the reference voltage. This is an inverter overcurrent control circuit characterized by having a two-stage overcurrent limiting circuit having a comparator that limits the pulse width.

〔Effect of the invention〕

Therefore, according to this overcurrent control circuit, the comparator
Only when an excessive current flows can the limiting circuit be activated to limit the absolute maximum current.
Even if an excessive current occurs due to a short circuit on the load side, etc., it is possible to prevent the inverter circuit from breaking down.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of an overcurrent limiting circuit according to the present invention, FIG. 2 is an explanatory diagram of overcurrent control waveforms,
FIG. 3 is a block diagram of a conventional inverter main circuit, and FIG. 4 is a block diagram of a conventional overcurrent limiting circuit connected to the above inverter main circuit. 6... Rectifier circuit 7... Error amplifier 8.
...Power supply 9...Sine wave signal 10...
・Amplitude adjustment circuit 11.12... AC feedback circuit 13... Triangular wave generation circuit 14... PW
M modulation circuit 15...Logic circuit 16...Comparator 17...31st flash of reference voltage power supply

Claims (1)

[Claims] A conversion circuit that converts a DC power source into a pulse width modulated AC output by controlling the opening and closing of multiple switch elements that are opened and closed by pulse width modulated control signals, and a filter circuit that extracts a fundamental wave component and outputs an AC output. , an inverter equipped with a detection circuit that extracts a voltage proportional to the output current by a current transformer incorporated in the conversion circuit, wherein the overcurrent control circuit of the inverter includes a rectifier circuit that rectifies the signal detected by the current transformer. An error amplifier having an AC feedback circuit that inputs each signal from the reference voltage power source and obtains a difference signal between the two, compares the output from the rectifier circuit with the reference voltage, and limits the pulse width. An overcurrent control circuit for an inverter, comprising a two-stage overcurrent limiting circuit having a comparator.