JPS6361863B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an overcurrent protection circuit for a power conversion device.

[Prior Art] A conventional device of this type is shown in FIG. In this figure, 1 is an AC power supply, 2 is a contact A, 3 is a converter that inputs the AC power supply 1, 4 is a capacitor connected to the output of the converter 3, and 5 is a load connected in parallel to this capacitor 4. , 6 is a current detector inserted between the capacitor 4 and the load 5, 7 is a current signal that is the output of this current detector 6, 8 is an overcurrent level signal, and 9 is the current signal 7 and the overcurrent level. This is an overcurrent protection circuit that receives a signal 8 as an input and outputs an output cutoff signal 10.

Next, the operation will be explained.

AC power source 1 is converted to DC by converter 3, smoothed by capacitor 4, and supplied to load 5. Here, the current detector 6 detects a direct current and outputs a current signal 7. Overcurrent protection circuit 9
compares the current signal 7 and the 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, during normal operation, that is, when the output cutoff signal 10 is not output, the contact A2 is in a closed state and power is being supplied to the load 5, but due to an accident such as a short circuit between both ends of the load 5. When the load current increases and the current signal 7 increases and becomes larger than the overcurrent level signal 8, the output cutoff signal 10 is output, and the contact A2 is opened to stop supplying power to the load 5, and the converter 3 and capacitor 4 It works to prevent damage caused by overcurrent.

Since the overcurrent protection circuit of a conventional power conversion device is configured as described above, for example, converter 3 and capacitor 4 are
and set the overcurrent level to the limit that will not damage converter 3, capacitor 4, etc.
When a single-phase AC power source is input, the peak current of the converter 3 naturally increases compared to when a three-phase AC power source is input, and the ripple current of the capacitor 4 also increases, so the output current increases to the above-mentioned overcurrent level. In this case, the converter 3 and capacitor 4 had the disadvantage of being damaged by overcurrent.

[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, select converters and capacitors based on the input of three-phase AC power,
The purpose of the present invention is to provide a current carrying protection circuit for a power converter that can prevent damage to the components even if an overcurrent occurs due to an accident or the like when the power converter is used when a single-phase AC power source is input. There is.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 2, 1 to 7, 9, and 10 are the same as in FIG. 1, 81 is a single-phase overcurrent level signal that is input to the overcurrent protection circuit 9 through the first contact 111, is a three-phase overcurrent level signal that is input to the overcurrent protection circuit 9 via the second contact 112, and these constitute overcurrent level changing means. 11 is a single-phase/three-phase input discrimination circuit connected to the AC power source 1; 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 11;

Next, the operation will be explained.

That is, the operation in a state where the output cutoff signal 10 which is the output of the overcurrent protection circuit 9 is not output is as follows.
Since it is exactly the same as FIG. 1, the explanation will be omitted. The difference is that it is determined whether the input AC power supply 1 is single-phase or three-phase, and the overcurrent level signal is switched. The differences will be explained below.

A single-phase/three-phase input determination circuit 11 determines whether the input power source of the power converter is single-phase or three-phase. Output. Here, the first contact 11
1 is closed only when the single-phase input signal 101 is output, inputs the single-phase overcurrent level signal 81 to the overcurrent protection circuit 9, and the second contact 112 is closed when the three-phase input signal 102 is output. The three-phase overcurrent level signal 82 is input to the overcurrent protection circuit 9. Therefore, when the overcurrent protection circuit 9 receives a single-phase input, the current signal 7 becomes the single-phase overcurrent level signal 8.
1, output cutoff signal 10 is output, contact A2 is opened to stop the power converter, and during three-phase input, current signal 7 becomes excessive than three-phase overcurrent level signal 82. At this time, the output cutoff signal 10 is output, contact A2 is opened, and the power converter is stopped. Therefore, during single-phase input, the overcurrent level that provides overcurrent protection becomes the single-phase overcurrent level, and during three-phase input, the overcurrent level becomes the three-phase overcurrent level.

In the above embodiment, the single-phase/three-phase input discrimination circuit 11 discriminates between single-phase input and three-phase input, but this single-phase/three-phase input discrimination circuit 11 includes:
Any means may be used as long as it can determine whether it is a single-phase input or a three-phase input; for example, the determination result may be input manually.

Further, in the above embodiment, the overcurrent level signal 8 is changed to change the overcurrent level between single-phase input and three-phase input, but any method may be used as long as the overcurrent level changes. For example, current signal 7
By amplifying this with an amplifier and switching its gain between single-phase and three-phase, the overcurrent level can be changed, and a similar effect can be expected.

〔Effect of the invention〕

As explained above, in the present invention, the single-phase/three-phase input discrimination circuit discriminates whether the input power source is single-phase or three-phase, and the overcurrent level is changed by the overcurrent level changing means based on the discrimination result. Therefore, select converters, capacitors, etc. based on the case when three-phase AC power is input, and prevent damage to the above components even if overcurrent occurs due to an accident when using a power conversion device with single-phase input. Therefore, it is possible to obtain a highly reliable device while maintaining its versatility.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an overcurrent protection circuit of a conventional power converter, and FIG. 2 is a diagram showing an overcurrent protection circuit of a power converter according to an embodiment of the present invention. In the figure, 1 is an AC power supply, 2 is a contact A, 3 is a converter, 4 is a capacitor, 5 is a load, 6 is a current detector, 7 is a current signal, 8 is an overcurrent level signal, 9 is an overcurrent protection circuit, 10 is an output cutoff signal, 11 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 the first contact, and 112 is the 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 an input, and the single-phase or three-phase AC power source is converted to DC by a converter, smoothed by a capacitor, and then the power is supplied to the load. A power conversion device, in which the capacities of the converter and the capacitor are set based on the input of three-phase AC power, and the power conversion device shuts off the output of the power conversion device when the load current becomes an overcurrent. In the overcurrent protection circuit, a single-phase/three-phase input discriminating means for discriminating whether the input AC power source is a single-phase input or a three-phase input; An overcurrent protection circuit for a power conversion device, comprising: overcurrent level changing means for changing an overcurrent level of the overcurrent protection circuit. 2. The overcurrent protection circuit for a power conversion device according to claim 1, wherein the overcurrent protection circuit shuts off input to the power conversion device when the load current becomes an overcurrent. 3. Overcurrent protection for a power conversion device according to claim 1, wherein the overcurrent protection circuit shuts off both the input and output of the power conversion device when the load current becomes an overcurrent. circuit.