JP2602902B2 - Power converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Purpose of the Invention] (Industrial application field) The present invention relates to a power converter for protecting an inverter.

(Prior Art) FIG. 3 shows a conventional protection device for a voltage-source inverter.
In FIG. 3, 1 is a three-phase AC power supply 2 is a contactor and 3 is a converter for converting three-phase AC to DC.
3a to 3f. 4 is a capacitor for smoothing the DC voltage converted by the converter, 5 is an inverter for converting the DC power converted by the converter into AC power of a variable frequency, and transistors 5a to 5f
Are connected by a bridge, and each transistor 5a
Diodes 5g to 5l are connected between the collector and the emitter of ~ 5f. 6 is an AC motor, 7 is a current detector for detecting the current of the DC bus, 7a is a current detection value signal detected by the current detector, 8 is a reference value generation circuit for creating a reference value, 8a is a reference value signal, 9 Is a comparison circuit that compares the current detection value signal with the reference value signal, 9a is an overcurrent detection signal generated as a result of the comparison, 10 is a hold circuit that holds the overcurrent detection signal, and 10a is an inverter that holds the overcurrent detection signal A signal 11 is an inverter control device, and 11a is a base signal given to the bases of the transistors 5a to 5f of the inverter by the inverter control device. 11b is an inverter operation start command signal given from the host microcomputer to the inverter control device.

The overcurrent protection operation in the device configured as described above will be described. If a short circuit occurs at the output terminals U, V, W of the inverter 5, or if the upper and lower transistors of one arm in the inverter, for example, 5g and 5j are simultaneously turned on, the DC voltage as the converter output is short-circuited through the turned on transistor. Therefore, a very large short-circuit current flows and the transistor is destroyed. In order to prevent this, the short-circuit current is detected and the base signal 11a of the transistors 5a to 5f is quickly detected.
And the transistors 5a to 5f are turned off to interrupt the short-circuit current. Therefore, the input current on the DC side of the inverter 5 is detected by the current detector 7. The current detection value signal 7a output from the current detector 7 is a voltage proportional to the absolute value of the input current on the DC side of the inverter. A reference current determined by the ratings of the transistors 5a to 5f is generated by a reference value generating circuit 8 and is used as a reference signal.
8a. The reference value signal 8a and the current detection value signal 7a are compared by the comparison circuit 9, and when the magnitude of the current detection value signal exceeds the reference value signal, the output of the comparison circuit, the overcurrent detection signal 9a, is activated and the short circuit current is reduced. Is detected. This overcurrent detection signal is held by the hold circuit 10 and used as an inverter stop signal 10a. When the inverter stop signal becomes active, the inverter control device cuts off the base signal 11a. As a result, the transistors 5a to 5f are turned off, the short-circuit current is cut off, and the transistors are protected.

Next, an operation start sequence of the inverter will be described. First, the contactor 2 is turned on. The smoothing capacitor 4 is charged through the converter 3 and the converter 3
When the output DC voltage is established, the inverter operation start command signal becomes active from the host microprocessor, and the inverter control device 11 outputs a base signal to start the operation of the inverter.

(Problems to be Solved by the Invention) As described above, it is necessary to operate at high speed from the detection of the short-circuit current to the interruption of the base signal. Therefore, the current detection value signal, the reference value signal, the overcurrent detection signal, and the inverter stop signal are generated. Must be a voltage signal. However, noise is generated in the current detection signal due to the surge when the contactor is turned on,
The overcurrent detection signal is held by the hold circuit,
After that, since the inverter stop signal is held, the operation of the inverter is not started even if the operation start command is output from the host microprocessor.

An object of the present invention is to provide a power converter that protects an inverter when an overcurrent is detected when an inverter operation start command signal is output.

[Configuration of the invention]

(Means for Solving the Problems) A converter that converts AC power into DC and outputs the DC power, and an inverter that is connected to the converter via a capacitor and converts DC power into AC power and supplies the AC power to the electric motor;
A current detector connected to the input side of the inverter and detecting a DC current; detecting an abnormality when an output signal of the current detector exceeds a predetermined value, and stopping the inverter when an operation start command signal is output to the inverter; A power conversion device having a comparison unit that outputs a signal.

(Operation) The overcurrent detection signal is obtained by the logical product of the inverter operation start command signal and the overcurrent detection signal, and the signal obtained by holding this is used as the inverter stop signal.

(Example) FIG. 1 shows an example of the present invention. FIG. 1 shows an AND element 12 inserted between the comparison circuit 9 and the hold circuit 10 shown in FIG. 3, and an overcurrent detection signal 9a and an inverter operation start command signal 11
In this configuration, the logical product of b is newly input to the hold circuit 10 as the overcurrent detection signal 12a.

Even though the current detection signal 7a generates noise due to the surge when the contactor 2 is turned on and the overcurrent detection signal 9a is output, the inverter operation start command signal is not output. The output of the element 12, which is the logical product of the signal 9a, is not output. When the inverter operation start command signal 11b is output, the inverter control device 11 generates a base signal and starts the inverter operation.

Next, another embodiment is shown in FIG. In FIG.
3 is a converter on the power supply side for adjusting reactive power,
Thereby, the three-phase alternating current is converted to direct current. Reference numeral 13 denotes a control device on the power supply side, reference numeral 13a denotes a base signal, and reference numeral 13b denotes an operation start command signal given to the converter 3 from the host microprocessor. Reference numeral 14 denotes a logical sum element, and reference numeral 14a denotes a logical sum of an operation start instruction signal 13b on the power supply side and an operation start instruction signal 11b on the electric motor side, which are obtained by 14. Also, in this case,
To detect a short circuit on the power supply side, the current detector 7 is provided between the connection point between the smoothing capacitor 4 and the DC bus. As shown in FIG. 2, the logical sum of the logical sum of the operation start command signals 11b and 13b on both the electric motor side and the power supply side and the overcurrent detection signal 9a is used as the overcurrent detection signal 12a, so that the above-mentioned embodiment is realized. As described in the explanation, the problem caused by the surge when the contactor is turned on is solved. Although the converter components in FIGS. 1 and 2 are described as being composed of transistors, a self-extinguishing element such as GTO may be used.

〔The invention's effect〕

As described above, the present invention uses the logical product of the overcurrent detection signal obtained by comparing the current detection signal and the reference value signal with the operation start command signal as the overcurrent detection signal, so that the Even if noise occurs in the current detection signal due to the surge, the overcurrent detection signal is not output, and the operation of the inverter can be started by the operation start command signal output.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of an embodiment based on the present invention, FIG. 2 is a block diagram showing another embodiment, and FIG. 3 is a block diagram of a conventional apparatus. 3 Converter 5 Inverter 6 Motor 7 Current detector 9 Comparison circuit 12 AND device

Claims (1)

(57) [Claims] A converter for converting AC power into DC power and outputting the DC power; an inverter connected to the inverter via a capacitor to convert DC power into AC power and supplying the AC power to a motor; and an input side of the inverter. A current detector that detects a DC current, detects an abnormality when an output signal of the current detector exceeds a predetermined value, and outputs an inverter stop signal when an operation start command signal is output to the inverter. A power conversion device comprising: a comparison unit.