JPS6361861B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an overcurrent protection circuit for an inverter device that drives an AC motor.

[Prior art]

Conventionally, there has been a device of this type as shown in FIG. In this figure, 1 is an AC power supply, 2 is a converter that takes this AC power supply 1 as an input, 3 is a capacitor connected to the output of this converter 2, and 4
is the inverter connected to this capacitor 3, 5
is an AC motor connected to the output of this inverter 4, 6 is a current detector inserted between the capacitor 3 and the inverter 4, 7 is a current signal that is the output of this current detector 6, and 8 is an overcurrent level. signal, 9
is a comparator, which inputs the current signal 7 and overcurrent level signal 8, compares them, and outputs an output cutoff signal 10.
Output. 11 is a first base signal; 12 is a base drive circuit which receives the output cutoff signal 10 and the first base signal 11;
3 is output to inverter 4.

Next, the operation will be explained.

AC power supply 1 is converted to DC by converter 2,
The signal is smoothed by a capacitor 3 and supplied to an inverter 4 made up of transistors. The transistor of the inverter 4 receives the second base signal 1
3, the AC motor 5 is sequentially turned on and off, and the AC voltage is supplied to the AC motor 5, which is a load, to drive the AC motor 5. Here, the current detector 6
detects direct current and outputs a current signal 7. Comparator 9 receives current signal 7 and overcurrent level signal 8
When the current signal 7 becomes larger than the overcurrent level signal 8, an output cutoff signal 10 is output.
Here, since the output cutoff signal 10 is not output during normal operation, the first base signal 11 is directly amplified by the base drive circuit 12, becomes the second base signal 13, and is supplied to the inverter 4. Although the transistor is turned on and off, the output current of the inverter 4 increases due to an accident such as the AC motor 5 being locked, and when the current signal 7 increases and becomes larger than the overcurrent level signal 8, an output cutoff signal is generated. 10 is output, the base drive circuit 12 stops outputting the second base signal 13 that had been output until then, stops the operation of the transistor of the inverter 4, and the converter 2,
It works to prevent the capacitor 3, inverter 4, etc. from being damaged by overcurrent.

Since the overcurrent protection circuit of a conventional inverter device is configured as described above, for example, when an AC power supply 1
Using a three-phase AC power source as a reference, select converter 2, capacitor 3, inverter 4, etc. based on this input, and set the overcurrent level to the limit that will not damage converter 2, capacitor 3, inverter 4, etc. Naturally, when a single-phase AC power source is input, the peak current of the converter 2 will increase compared to when a three-phase AC power source is input, and the ripple current of the capacitor 3 will also increase, so that up to the above overcurrent level. When the output current increases, the converter 2 and the capacitor 3 have the drawback of being damaged by the current flow.

[Summary of the invention]

This invention was made to eliminate the drawbacks of the conventional ones as described above, and it determines whether the input power source is single-phase or three-phase, and changes the overcurrent level based on the determination result. Therefore, even if converters, capacitors, inverters, etc. are selected based on the three-phase AC power input, if an inverter device is used with a single-phase AC power input and an overcurrent occurs due to an accident, each component may be damaged. It is an object of the present invention to provide an overcurrent protection circuit for an inverter device that can prevent such problems from occurring.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. In FIG. 2, 81 is a single-phase overcurrent level signal, which is input to the comparator 9 via the first contact 111. 82 is a three-phase overcurrent level signal,
It becomes an input to the comparator 9 via the second contact 112.
14 is a single-phase/three-phase input discrimination circuit connected to the AC power supply 1, and 101 and 102 are a single-phase input signal and a three-phase input signal that are outputs of the single-phase/three-phase input discrimination circuit 14. The same reference numerals as in FIG. 1 indicate the same parts.

Next, the operation will be explained.

The operation when the output cutoff signal 10, which is the output of the comparator 9, is not output is exactly the same as that shown in FIG. 1, so a description thereof will be omitted. The difference is that it determines whether the input power source is single-phase or three-phase, and switches the overcurrent level signal. This difference will be explained below.

The single-phase/three-phase input determination circuit 14 determines whether the input power source of the inverter device is single-phase or three-phase. Output. Here, the first contact 1
11 is closed only when the single-phase input signal 101 is output, and inputs the single-phase overcurrent level signal 81 to the comparator 9, and the second contact 112 is closed when the single-phase input signal 101 is output.
02 is output, and the three-phase overcurrent level signal 82 is input to the comparator 9. Therefore, the comparator 9 outputs an output cutoff signal 10 to stop the inverter 4 when the current signal 7 exceeds the single-phase overcurrent level signal 81 during single-phase input, and when the current signal 7 exceeds the single-phase overcurrent level signal 81, the comparator 9 outputs an output cutoff signal 10 to stop the inverter 4. outputs an output cutoff signal 10 to stop the inverter 4 when the current signal 7 becomes higher than the three-phase overcurrent level signal 82. Therefore, during single-phase input, the overcurrent level that provides overcurrent protection is the single-phase overcurrent level, and during three-phase input, the overcurrent level is automatically set to the three-phase overcurrent level. A switch is made.

In the above embodiment, single-phase input and three-phase input are discriminated by the single-phase/three-phase input discrimination circuit 14, but any means can be used as long as it can discriminate between single-phase input and three-phase input. For example, the determination results may be input manually.

Further, in the above embodiment, the overcurrent level signal 8 is divided into a single-phase overcurrent level signal 81 and a three-phase overcurrent level signal 82 to change the overcurrent level at the time of single-phase input and at the time of three-phase input. However, this can be done by any means as long as the overcurrent level changes; for example, by amplifying the current signal 7 with an amplifier and switching the gain between single-phase and three-phase. The overcurrent level can be changed even when the current is on, and similar effects can be expected.

〔Effect of the invention〕

As explained above, according to the present invention, the single-phase/three-phase input determining means determines whether the input power source is single-phase or three-phase, and based on the determination result, the overcurrent level changing means determines whether the input power source is single-phase or three-phase. Since the level is changed, converters, capacitors, inverters, etc. are selected based on the three-phase AC power input, so if an inverter device is used with a single-phase input and an overcurrent occurs due to an accident, etc. However, since damage to each component can be prevented, there is an advantage that a highly reliable device can be obtained while maintaining the versatility of the device.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an overcurrent protection circuit of a conventional inverter device, and FIG. 2 is a diagram showing an overcurrent protection circuit of an inverter device according to an embodiment of the present invention. In the figure, 1 is an AC power supply, 2 is a converter, 3 is a capacitor, 4 is an inverter, 5 is an AC motor, and 6
is a current detector, 7 is a current signal, 8 is an overcurrent level signal, 9 is a comparator, 10 is an output cutoff signal, 11 is a first base signal, 12 is a base drive circuit, 13
is a second base signal, 14 is a single-phase/three-phase input discrimination circuit, 81 is a single-phase overcurrent level signal, 82 is a three-phase overcurrent level signal, 101 is a single-phase input signal,
102 is a three-phase input signal, 111 is a first contact, 1
12 is a second contact. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. Either a single-phase or three-phase AC power source can be used as the input AC, and the single-phase or three-phase AC power is converted to DC using a converter, smoothed using a capacitor, and then converted to AC using an inverter and output as an AC load. an inverter device including at least the converter, a capacitor, and an inverter for driving the converter, the capacitances of the converter and the capacitor are set based on when three-phase AC power is input, and the current flowing into the inverter is an overcurrent. In the overcurrent protection circuit of the inverter device, which stops the operation of the inverter when
An inverter comprising three-phase input determining means and overcurrent level changing means for changing an overcurrent level for overcurrent protection based on the determination result of the single-phase/three-phase input determining means. Equipment overcurrent protection circuit.