JPH0449347B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an overcurrent protection circuit for an inverter that prevents each transistor in a transistor inverter from being damaged by overcurrent.

[Prior art]

Traditionally, thyristors have been used as control elements in inverters used as control power supplies for variable operation of large induction motors or stabilized power supplies for large electronic computers, but as the capacity of power transistors has increased in recent years, , transistor inverters that use power transistors as control elements in place of thyristors are being developed.

A conventional transistor inverter is configured as shown in FIG. 1, for example. In the figure, 1 is a connection terminal connected to a commercial AC power supply, and 2 is a connection terminal that rectifies and smoothes the AC that has passed through the connection terminal 1. Rectifier circuit consisting of thyristor 2a, reactor 2b, and capacitor 2c, 3a, 3b, 3c, 3d
are NPN type first to fourth transistors, a flywheel diode 4 is connected in antiparallel to the collector and emitter of each transistor 3a to 3d, respectively, and the collector of the first and second transistors 3a and 3b is connected to the rectifier circuit 2. The collectors of the third and fourth transistors 3c and 3d are connected to the emitters of the first and second transistors 3a and 3b.
The emitters of transistors 3a to 3d are connected to the negative output terminal of the rectifier circuit 2 via a current detector 5 consisting of a shunt, a DC transformer, etc.
The base of is connected to the base control terminal of the control circuit described later, and the rectifier circuit 2 and each transistor 3a
~3d, each diode 4 constitutes a transistor inverter 6.

7 is a transformer in which both ends of the primary winding 7a are connected to the emitters of the first and second transistors 3a and 3b; 8 is a load connected to the secondary winding 7b of the transformer 7; 9 is a control circuit; Gate control terminal 9a
A gate control section that outputs a gate control signal to the gate of the thyristor 2a through the gate, and a gate control section that outputs a gate control signal to the gate of the thyristor 2a, and a gate control section that outputs a gate control signal to the gate of the thyristor 2a.
a base control section that outputs a base control signal to the base of the base, and an overcurrent protection section 10 as shown in FIG.
It is made up of.

Next, in FIG. 2, 10a is a DC reference power supply, 10b is a comparison circuit that compares the reference voltage from the reference power supply 10a and the voltage based on the primary current of the inverter 6 detected by the detector 5, and 10c
is a stop circuit, which includes a display section, and outputs a stop signal to the base control section when the voltage due to the primary side current is higher than the reference voltage, and outputs a stop signal to the base control signal to each of the transistors 3a to 3d. The output is stopped, the switching of each transistor 3a to 3d is stopped, and an abnormality is displayed on the display section. An overcurrent protection section 10 is constituted by a reference power supply 10a, a comparator circuit 10b, and a stop circuit 10c. ing.

Then, the base control signal from the base control section of the control circuit 9 is transmitted to the first and fourth transistors 3a and 3d.
base and the second and third transistors 3b, 3
The first and fourth transistors 3a, 3d and the second and third transistors 3b3c alternately turn on and off,
By turning on the fourth transistors 3a and 3d, the DC current from the rectifier circuit 2 is transferred to the collector and emitter of the first transistor 3a, and to the primary winding 7 of the transformer 7.
a, flows through the collector and emitter of the fourth transistor 3d, the detector 5, and the rectifier circuit 2, and by turning on the second and third transistors 3b and 3c, the rectifier circuit 2
DC current flows through the collector and emitter of the second transistor 3b, the primary winding 7a of the transformer 7, and the third
The current flows through the collector and emitter of the transistor 3c, the detector 5, and the rectifier circuit 2, and the inverter 6 converts the direct current from the rectifier circuit 2 into alternating current, which is then supplied to the load 8.

At this time, since the primary current of the inverter 6 detected by the detector 5 is a steady current, the
Comparison circuit 10 is detected by detector 5 based on the next-side current.
The voltage value applied to b is lower than the reference voltage value from the reference power supply 10a, and the stop circuit 10c is not activated by the comparison signal from the comparison circuit 10b, and no stop signal is output from the stop circuit 10c, and the above-mentioned Each base control signal continues to be output from the base control section, and the inverter 6 continues to operate normally.

By the way, during the normal operation of the inverter 6, due to a malfunction of the base control section, for example, the first
If an abnormality occurs in which the third transistors 3a and 3c turn on at the same time, the inverter 6
When the output of
The voltage becomes higher than the reference voltage value by a, and the comparator circuit 10b
The stop circuit 10c is activated by the comparison signal from
A stop signal is output from the stop circuit 10c, the output of the base control signal from the base control section is stopped, each transistor 3a to 3d is turned off, and the operation of the inverter 6 is stopped.
An abnormality is displayed on the display section c.

However, when a flow divider is used as the detector 5,
It is necessary to insulate the output signals of the shunts so that they are not directly input to the bases of the transistors 3a to 3d, which is very complicated. Since the current flow device becomes a delay element, when an overcurrent occurs, the output of the base control signal from the base control section cannot be stopped instantaneously, resulting in damage to the transistors 3a to 3d, etc.

It is also conceivable to use a fuse as the detector 5, but the fuse cannot instantly stop the output of the base control signal from the base control section when an overcurrent occurs.

Furthermore, when the load 8 is a capacitor input type load, when starting the load, a large charging current is required to charge the capacitor immediately after turning on the start switch, etc., so the inverter 6 The primary side current also increases, causing the overcurrent protection section 10 to operate in the same way as described above, causing the inverter 6 to stop operating, which tends to cause the inconvenience that the load cannot be started.

[Purpose of the invention]

The present invention has been made with the above-mentioned points in mind, and it is an object of the present invention to instantly stop an inverter when an overcurrent occurs and to enable starting of a capacitor input type load.

[Structure of the invention]

This invention provides an inverter that converts direct current to alternating current by switching a plurality of transistors;
A first using Hall elements provided on the primary side and the secondary side of the inverter, respectively, and outputting a voltage signal proportional to the current flowing through the primary side and the secondary side, respectively.
A second current detector compares the output voltage values of the two current detectors with each of the two reference voltage values, and generates a comparison signal using the voltage signals from the two current detectors each having a value greater than or equal to the reference voltage value. First and second comparison circuits that output pulses, first and second pulse generation circuits that output pulses based on both of the comparison signals, and switching of each of the transistors for a predetermined period of time using pulses from either of the pulse generation circuits. The transistor is characterized by comprising a first stop circuit that stops the switching, and a second stop circuit that counts both the numbers of pulses and stops switching of each of the transistors when one of the numbers of pulses reaches a set value. This is an overcurrent protection circuit for inverters.

〔Effect of the invention〕

Therefore, according to the inverter overcurrent protection circuit of the present invention, first and second current detectors using Hall elements are provided on the primary and secondary sides of the inverter consisting of a plurality of transistors, and both standards are A first stop circuit is provided that stops switching of each transistor of the inverter for a predetermined period of time by either pulse from both pulse generating circuits based on voltage signals from both current detectors having a voltage value or higher. By providing a second stop circuit that stops switching each transistor when the number reaches a set value, the inverter can be stopped instantly when an overcurrent occurs, thereby preventing damage to the transistors, etc. In addition, even if the load is a capacitor input type, it can be started easily and is practical.

〔Example〕

Next, the present invention will be explained in detail with reference to the drawings from FIG. 3 showing one embodiment thereof.

First, in FIG. 3, the same symbols as in FIG.
A first current detector using a Hall element is provided between both emitters c and 3d and the negative output terminal of the rectifier circuit 2; one end and the fourth transistor 3
A second current detector using a Hall element is provided between the collector of d, and both current detectors 11, 1
2 outputs a voltage signal proportional to the current flowing through the primary and secondary sides of the inverter 6.

13 is a rectifier that rectifies the AC voltage signal output from the second current detector 12, and 14 is a control circuit that connects the thyristor 2 via the gate control terminal 14a.
a gate control section that outputs a gate control signal to the gate of transistor a; a base control section that outputs a base control signal to the base of each transistor 3a to 3d via four base control terminals 14b to 14e; The overcurrent protection section 15 is configured as follows.

Next, in Fig. 4, 15a and 15a' are two DC reference power supplies, and 15b and 15b' are two reference power supplies 1.
5a, 15a' reference voltage and first current detector 1
1 and the output voltage values of the rectifier 13, respectively, and output comparison signals;
15c and 15c' are first and second pulse generation circuits each consisting of a monostable multivibrator that outputs high-level pulses in response to voltage signals from the first current detector 11 and rectifier 13, each having voltages higher than both reference voltage values, and 15d, This is a first stop circuit, and base control is performed from the base control unit to each transistor 3a to 3d during a predetermined output period of the pulse, that is, a high level period, by a pulse from one of the pulse generating circuits 15c and 15c'. The output of the signal is stopped, and the switching of each transistor 3a to 3d is stopped.

15e, 15e' are both pulse generating circuits 15c, 1
Count the number of pulses from 5c', and set the counted pulse numbers to the first and second setting devices 1, respectively.
The first and second counters output the first and second command signals when the values set by 5f and 15f' are reached. Reference numeral 15g is a stop section, and includes a display section. The output of the base control signal from the base control section to each transistor 3a to 3d is completely stopped, and each transistor 3a to 3
d is stopped, and an abnormality is displayed on the display section. Both counters 15e, 15e', both setters 15f, 15f', and a stop section 15g constitute a second stop circuit 15h. The overcurrent protection section 15 is constituted by the circuit surrounded by the one-dot chain line in FIG.

Next, the operation of the above embodiment will be explained.

Now, the first and fourth transistors 3 are controlled by the base control signal from the base control section of the control circuit 14.
a, 3d and second and third transistors 3b, 3
c repeats on and off alternately, and inverter 6
For example, when the first and third transistors 3 are operating normally, due to a malfunction of the control circuit 14, etc.
When transistors a and 3c are turned on at the same time, the output of the inverter 6 is short-circuited due to the simultaneous turning on of the first and third transistors 3a and 3c, and an overcurrent flows to the primary side of the inverter 6. The voltage value of the voltage signal to the first comparison circuit 15b is the reference power supply 15a.
becomes higher than the reference voltage value, and the first comparator circuit 15
The first pulse generating circuit 15 receives the comparison signal from b.
The output of c is inverted to high level and a high level pulse is output, and the pulse causes the first stop circuit 1
5d is activated, the first stop circuit 15d stops the output of the base control signal from the base control section to each of the transistors 3a to 3d for the output period of the pulse, and the switching of each transistor 3a to 3d is stopped and the inverter is turned off. 6 is stopped only during the high level period of the pulse.

Then, the first stop circuit 15d, in which the output of the first pulse generating circuit 15c is inverted to high level and then inverted to low level again after a predetermined period of time, stops operating, and the output from the base control section is transmitted to each transistor 3a to
The base control signal is output again to the inverter 3d, but if the overcurrent continues to flow to the primary side of the inverter 6 due to the simultaneous turning on of the first and third transistors 3a and 3c, the above operation is not performed. The number of pulses from the first pulse generating circuit 15c is repeatedly counted by the first counter 15e, and when the count value of the first counter 15e reaches the set value by the first setting device 15f, the first counter 15e outputs the pulse number. The stop part 15g is activated by the command signal,
The second stop circuit 15h completely stops outputting the base control signal from the base control section to each of the transistors 3a to 3d.
The switching of d is stopped and the operation of the inverter 6 is completely stopped, and an abnormality is displayed on the display section of the stop section 15g.

Next, the load 8 becomes overloaded and the inverter 6
When an overcurrent flows through the primary winding 7a of the transformer 7, which is the secondary side of the 15a' becomes higher than the reference voltage value, and as in the case where an overcurrent occurs on the primary side of the inverter 6, a high-level pulse is output from the second pulse generation circuit 15c', and the pulse causes the first stop circuit 15d to be output. Accordingly, the output of the base control signal from the base control section to each of the transistors 3a to 3d is stopped, and the operation of the inverter 6 is stopped only during the high level period of the pulse.

Furthermore, even after the pulse from the second pulse generation circuit 15c' is inverted to low level, the inverter 6
If overcurrent continues to flow to the next side, the second
The second pulse generating circuit 15 is controlled by the counter 15e'.
The number of pulses from c' is counted, and when the count value of the second counter 15e' reaches the set value by the second setter 15f', the second stop circuit 15h controls the number of pulses from the base control section to each of the transistors 3a to 3d. The base control signal output is completely stopped, the switching of each transistor 3a to 3d is stopped, and the operation of the inverter 6 is completely stopped, and an abnormality is displayed on the display section of the stop section 15g.

Also, if the load 8 is a capacitor input type,
When the inverter 6 operates, the load 8 is passed through the transformer 7.
Immediately after the start of energization, the load 8
Since a large charging current is required to charge the capacitor, an overcurrent flows through the secondary side of the inverter 6, that is, the primary winding 7a of the transformer 7, and as described above, the first stop circuit 15d is activated and the The output of the base control signal from the base control section to each of the transistors 3a to 3d is stopped for a predetermined period of time, but when the first stop circuit 15d repeats the output and stop of the output of the base control signal by the base control section several times, As the charging current of the capacitor gradually decreases, the voltage value of the voltage signal from the second current detector 12 rectified by the rectifier 13 eventually becomes lower than the reference voltage value from the reference power supply 15a', Both the second stop circuits 15d and 15h cease to operate, the inverter 6 continues to operate normally, and the load 8 is started.

Therefore, according to the embodiment, since the current detectors 11 and 12 are used, a delay element such as a DC current transformer can be removed, and the inverter 6 can be stopped instantly when an overcurrent occurs. Therefore, damage to the transistors 3a to 3d, etc. can be prevented.

Further, since the first stop circuit 15d and the second stop circuit 15h are provided, even if the load 8 is of a capacitor input type, it can be started easily, which is very practical.

In the above embodiment, the case where the inverter 6 is of a full-bridge type using transistors has been described, but it goes without saying that it may be of a half-bridge type.

[Brief explanation of the drawing]

Fig. 1 is a wiring diagram of a conventional inverter overcurrent protection circuit, Fig. 2 is a partial wiring diagram of Fig. 1, and Fig. 3 and the following drawings are an embodiment of the inverter overcurrent protection circuit of the present invention. 3 is a wiring diagram, and FIG. 4 is a partial wiring diagram. 3a to 3d...transistor, 6...inverter,
11, 12...Current detector, 15b, 15b'...Comparison circuit, 15c, 15c'...Pulse generation circuit, 15d
...first stop circuit, 15h...second stop circuit.

Claims (1)

[Claims] 1. An inverter that converts direct current to alternating current by switching a plurality of transistors, and is provided on the primary and secondary sides of the inverter and outputs a voltage signal proportional to the current flowing through the primary and secondary sides, respectively. The first and second current detectors each using a Hall element, and the output voltage values of the two current detectors are compared with two reference voltage values, and each of the two current detectors is higher than the reference voltage value. first and second comparison circuits that output comparison signals based on voltage signals from the first and second comparison circuits, first and second pulse generation circuits that output pulses based on both of the comparison signals, and pulses from either of the pulse generation circuits. a first stop circuit that stops switching of each of the transistors for a predetermined time; and a second stop circuit that counts both pulse numbers and stops switching of each of the transistors when either of the pulse numbers reaches a set value. An inverter overcurrent protection circuit comprising: