JPH04101669A - Output short circuit protective method for voltage type inverter - Google Patents

Abstract

PURPOSE:To protect main circuit elements against breakdown due to a large current occurring at the time of output short circuit by conducting specific main circuit elements in an inverter circuit during output short circuit detection interval thereby forming a closed circuit of short circuit detection current and preventing actuation of the inverter circuit upon detection of short circuit. CONSTITUTION:During an interval when an initial charging circuit 21 is functioning, a controller 15 provides specific main circuit elements in a three- phase inverter circuit 10 with ON pulses. Consequently, a short circuit detection current flows on a path (c) from a capacitor 22 in a DC circuit. When the interval for providing the ON pulse is set longer than the interval during which DC current detectors l3', 14' can detect the current, output short circuit is detected when the short circuit detection current exceeds an overcurrent set level because the path (c) passes through the current detectors l3', l4'. Consequently, the controller 15 stops operation of the inverter circuit 10 and protect the main circuit element against breakdown.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a voltage source inverter for driving an AC motor, etc., which is designed to prevent damage to main circuit elements due to a short circuit on the output side. Concerning output short circuit protection method.

(Prior art) Fig. 3 shows a self-extinguishing element (for example, a bipolar transistor, IGBT, etc.) as a main circuit element of an inverter circuit.
This figure shows a known voltage source inverter using . In the figure, 10 is a three-phase inverter circuit using self-extinguishing elements 118 to If, 13.14 is a current detector (CT),
15 is a three-phase inverter circuit 100 control device, and 16 is a rust conduction motor.

On the other hand, 30 is a converter circuit, which is composed of a diode rectifier 20, an initial charging circuit 21, and a smoothing capacitor 22. This converter circuit 30 rectifies AC power supply (commercial power supply) voltage and outputs DC voltage. It is composed of

Here, the function of the initial charging circuit 21 will be briefly explained. Now, when the AC power supply voltage is input to the rectifier 20,
Since the load of the rectifier 20 is the capacitor 22, a very large rush current will flow transiently if no measures are taken. Therefore, in order to suppress this rush current, the initial charging circuit 21 performs the function of starting up the capacitor voltage with a fixed time constant. Specifically, when the m power is turned on, the switch 21a is temporarily opened. By inserting the resistor 21b into the DC circuit, the above-mentioned time constant is increased and the charging current is limited.

PWM control is generally used as a control method for this type of inverter. In this PWM MIll, a turning-off pulse is applied to a self-turning off element constituting an inverter circuit to turn the self-turning off element on and off, thereby controlling the magnitude and frequency of the output voltage of the inverter.

Figure 4 shows the calculation method for PWM pulses, which are point-extinguishing pulses.
WM pulse is shown. PWM pulse calculation is performed by comparing the magnitude of the inverter output voltage reference signal (sine wave in this figure) with the triangular wave that is the modulation signal, and in the range where the sine wave is large, the self-extinguishing element is turned on (ignition). A signal is output, and in a range where the triangular wave is large, an off signal that turns off (extinguishes) the self-arc-extinguishing element is output. This on-
By applying an off signal to the positive side element and applying a signal inverted to this signal to the negative side element, the self-extinguishing elements connected in series are turned on and off with each other to control the inverter.

By the way, in such a device, if an overcurrent failure occurs for some reason on the output side of the inverter,
It is important to protect the elements without destroying them.

The conventional overcurrent protection method is to install current detectors 13 and 14 on the output side of the inverter as shown in Figure 3.
These outputs are input to the control device 15, and the control device 15 determines whether the detected current value has reached the failure level and outputs a command to stop the inverter, etc. Aiming to protect Ilf or the entire inverter 6 (Problem to be solved by the invention) Among overcurrent failures in an inverter, an output short circuit is a failure that leads to destruction of main circuit elements. This accident occurs when the inverter is operated with the output lines of the inverter short-circuited due to a wiring error or disconnection. For example, as shown in Figure 5, the location a on the output side of the inverter
When an output short circuit occurs, a power supply short circuit occurs due to the self-extinguishing elements +1a and lle as shown in the path in the figure. In addition, in FIG. 5, 12 is an AC power supply and a capacitor 2.
This is a DC power supply equivalent to 2nd grade.

Figure 6 shows the relationship between the PWM pulse when starting the inverter and the short-circuit current. As is clear from the figure, the PWM pulse when starting the inverter has a small amplitude of the reference signal, so the on-off period is almost equal. It becomes a pulse. Therefore, the short circuit current caused by the output short circuit described above becomes a very narrow current, and a problem arises in that the current detectors 13 and 14 attached to the output side of the inverter cannot detect this current.

If short-circuit current cannot be detected in this way, the conventional overcurrent protection function will not work, leading to a serious problem in that the main circuit elements will be destroyed by this short-circuit current.

The present invention has been made to solve the above problems,
The purpose is to provide an output short-circuit protection method for a voltage source inverter that can prevent damage to main circuit elements from large currents generated during output short-circuits.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a converter circuit connected to an AC power supply, an inverter circuit connected to this converter circuit via a DC intermediate circuit, and a converter circuit connected to an AC power source. In a voltage source inverter equipped with a circuit control device, an output short circuit detection period is set within a period until the voltage of the DC intermediate circuit is established, and a specific main circuit constituting the inverter circuit is detected during this output short circuit detection period. The circuit elements are made conductive to form a closed circuit for short-circuit detection current from the DC intermediate circuit to the output side of the inverter circuit via the main circuit element, and the short-circuit is detected by an output short-circuit detection means provided in this closed circuit. The presence or absence of an output short circuit is detected by detecting the magnitude of the current, and when a short circuit is detected, the control device stops the activation of the inverter circuit.

(Function) In the present invention, the voltage of the DC circuit of the converter circuit,
That is, an output short circuit detection period is provided within the period until the voltage of the smoothing capacitor is established.

During this output short circuit detection period, for example, the operating period of an initial charging circuit provided in the DC circuit is used, and a specific main circuit element of the inverter circuit is made conductive during this period, and output is output from the DC circuit via the main circuit element. Forms a closed circuit for short-circuit detection current to the side.

If a short circuit occurs on the output side of the inverter, the short circuit detection current will exceed the overcurrent setting level at the time of short circuit detection, so the short circuit detection means will detect this and determine that it is an output short circuit, and the inverter circuit will be activated. To prevent destruction of main circuit elements by stopping operation, that is, without starting the inverter circuit.

At this time, the voltage of the DC circuit has not yet been established and is below the steady state value, so even if an output short circuit occurs, the value of the short circuit detection current is small and it will not destroy the main circuit elements. .

In addition, as an output short circuit detection means, it is preferable to provide a current detector on the output side of the inverter circuit or in the above-mentioned DC circuit.When provided in the DC circuit, not only the output short circuit but also the top and bottom of the inverter circuit can be detected. It is also possible to detect arm short-circuit accidents.

(Example) The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the present invention, which is substantially the same as the conventional example except that the current detectors on the output side of the three-phase inverter circuit IO are DC current detectors 13' and 14'. Because of the configuration, each component is given the same number.

In this embodiment, the initial charging circuit 2 of the converter circuit 30
1 is operating as an output short circuit detection period, and during this period, an on-pulse is applied from the control device 15 to a specific main circuit element of the three-phase inverter circuit 10. In the example shown in FIG. 1, on-pulses are given to self-extinguishing elements 11a, lie, and Ilf.

In this way, the self-extinguishing elements +1a, Ile, ll given the on-pulse from the capacitor 22 of the DC circuit
The Himeji detection current flows through path C (indicated by a broken line) including induction motor [6] through f. Here, if the period during which the on-pulse is applied (output short circuit detection period) is set to be a sufficient time longer than the time during which the DC current detectors +3' and +4' can detect the current, the path C is the current detector 13', +4', an output short circuit can be detected when this short circuit detection current exceeds a preset overcurrent setting level for detecting a short circuit. When an output short circuit is detected, if the control device 15 stops the operation of the inverter circuit 10 without starting it, it is possible to prevent the main circuit elements from being destroyed.

Normally, when the inverter is in a short-circuited state, the DC voltage of the converter circuit 30 is applied to the main circuit elements, and a large current of five to six times the rated current flows through the main circuit elements, causing their destruction. In this embodiment, the current in the path C is passed in a low state where the DC voltage of the converter circuit 30 has not yet been established, so even if a short circuit occurs on the output side, the voltage applied to the element is low and the current is large. It also doesn't flow easily. Therefore, there is no risk of element destruction during the output short circuit detection period.

FIG. 2 shows another embodiment of the present invention, which differs from the embodiment shown in FIG. 1 in that a DC current detector 17 is provided on the DC side of the inverter circuit 10, and other aspects are the same as in FIG. 1. Since the configuration is as follows, detailed description will be omitted.

According to this configuration, as in FIG. 1, it is possible to reliably detect an output short circuit by flowing the short circuit detection current of path C during the output short circuit detection period, and also to detect a short circuit generated inside the inverter (for example, on the positive side, A short circuit that occurs when one of the negative side elements is in a broken state and a normal element is turned on can be detected by the DC current detector 17, and the normal element can be detected by stopping the inverter by the control device [15]. Destruction can be prevented.

Note that the present invention can also be applied to voltage source inverters that use elements that cannot self-extinguish in the inverter circuit, such as ordinary thyristors, and can be applied not only to three-phase inverters but also to single-phase inverters. .

(Effects of the Invention) As described above, according to the present invention, an output short circuit of a voltage source inverter can be reliably detected without making any major changes to the conventional circuit configuration, and the main circuit elements or Destruction of the main circuit can be prevented.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing one embodiment of the present invention, Fig. 2 is a circuit diagram showing another embodiment of the invention, Fig. 3 is a circuit diagram showing a conventional technique, and Fig. 4 is a circuit diagram showing a PWM pulse. FIG. 5 is a waveform diagram explaining the generation principle, FIG. 5 is an explanatory diagram at the time of output short circuit, and FIG. 6 is a waveform diagram showing the relationship between PWM pulse and short circuit current at startup. lO...Three-phase inverter circuit 11a-Ilf...Self-extinguishing element 12...DC power supply +3', +4'...DC current detector 15...
Control device 16... Induction motor 17... DC current detector 20... Rectifier 21... Initial charging circuit 22... Smoothing capacitor 30... Converter circuit a... Short circuit point b. Short circuit current Path C...Short circuit detection current path

Claims (3)

[Claims] (1) In a voltage source inverter comprising a converter circuit connected to an AC power source, an inverter circuit connected to a DC circuit of this converter circuit, and a control device for this inverter circuit, the voltage of the DC circuit is established. An output short circuit detection period is set within a period of A closed circuit is formed for the short-circuit detection current leading to , and an output short-circuit detection means provided in this closed circuit detects the magnitude of the short-circuit detection current to detect the presence or absence of an output short-circuit, and when a short-circuit is detected, the control device A method for protecting an output short circuit of a voltage source inverter, characterized by stopping activation of an inverter circuit. (2) The output short-circuit protection method for a voltage source inverter according to claim (1), wherein the output short-circuit detection means is a current detector provided on the output side of the inverter circuit. (3) The output short-circuit protection method for a voltage source inverter according to claim (1), wherein the output short-circuit detection means is a current detector provided in the DC circuit.