JPS639279Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a protection device for a power converter such as a thyristor Leonard device that protects the power converter from overcurrent during a power outage or instantaneous power outage.

Generally, in a power converter such as a thyristor Leonard device, the thyristor may cause a DC short circuit due to a delay in the start-up of the control power supply of the power converter and disturbances in the synchronous power supply when the power is restored after an AC power outage. This may cause damage to the thyristor. Therefore, in order to prevent damage to the thyristor due to this DC short circuit, a no-fuse breaker or arm fuse is built into the motor armature circuit to protect the thyristor. An overcurrent flows until the fuse blows or the fuse blows.
As this is repeated, stress accumulates in the thyristor, resulting in a shortened lifespan of the thyristor. Furthermore, if the no-fuse breaker or fuse blows out, there is a problem in that the power converter cannot be restarted promptly when power is restored.

The present invention was developed in view of the above problems, and its purpose is to prevent erroneous firing of the thyristor by starting the firing of the thyristor after the control power supply is established when the power is restored after a power outage. An object of the present invention is to provide a protection device for a power conversion device.

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

As shown in Fig. 1, in the main circuit of the thyristor Leonard device, 12 thyristors are connected from an AC power source (not shown) through a power transformer 1, a no-fuse breaker 2, a main contactor 3, an AC reactor 4, and a quick-break fuse 5. AC power is supplied to a thyristor stack 6 composed of thyristors, and the thyristor stack 6 controls the phase of the DC voltage obtained by three-phase full-wave rectification, thereby controlling the DC motor 7. In addition, a field unit 8 connected to the connection point between the no-fuse breaker 2 and the main contactor 3
A field current is supplied to the field winding 7a of the motor 7 by.

A control circuit (not shown) that controls the gates of the thyristors constituting the above-mentioned thyristor stack 6 is powered by a transformer 9 from the primary side of the main contactor 3.
A DC voltage of ±15V is generated via the automatic voltage regulator 10, and a voltage of +/-15V is generated via the transformer 9, which consists of a diode stack 11 and a smoothing filter 12.
DC +24V is generated by the 24V power supply 42. The time constant of the smoothing filter 12 is made as small as possible,
The output voltage of this +24V power supply 42 is made to attenuate rapidly during a power outage.

In the power conversion device having the above-mentioned main circuit and power supply circuit, the protection device for the power conversion device for detecting a power outage and gating and cutting off the thyristor is as shown in FIG. 2 and as shown in FIG. A resistor 21 is connected between the output terminal A of the +24V power supply 42 and the OV point.
22 series circuits are connected, resistor 21 and resistor 22
The connection point between the two terminals is connected to the negative input terminal of the comparator 24 via the resistor 23. Further, the anode of a diode 25 is connected to the output terminal A of the +24V power supply 42, the cathode of this diode 25 is connected to a capacitor 26, and the capacitor 26 is connected to an OV
Connected to points. One fixed terminal of a variable resistor 27 is connected to the connection point between the cathode of the diode 25 and the capacitor 26, and the other fixed terminal of the variable resistor 27 is connected to the OV point. A movable terminal of variable resistor 27 is connected to the + input terminal of comparator 24 via resistor 28 . Furthermore, the connection point between the cathode of the diode 25 and the capacitor 26 is connected to the comparator 24.
connected to the power terminal of the

A Zena diode 29 is connected to the output terminal of the comparator 24.
The cathode of this Zena diode 29 is connected
The anode of is connected to the transistor 31 via the resistor 30.
connected to the base of The emitter of this transistor 31 is connected to the OV point, and the transistor 31
The collector of is connected to the anode of a diode 33 via a resistor 32. The connection point between the anode of this diode 33 and the resistor 32 is connected via the resistor 34 to the output terminal B of the +15V power supply shown in FIG. connected to.
Further, the cathode of the diode 33 is connected to the base of one of the two Darlington-connected transistors 36, and the emitter of the other transistor 36 is connected through the diode 37.
Connected to OV point. These two transistors 3
6 is connected to the emitter of the transistor 38, the collector of the transistor 38 is connected to one terminal of the primary winding of the pulse transformer 39, and the other terminal of the primary winding of the pulse transformer 39 is connected to the emitter of the transistor 38. It is connected to the output terminal A of the +24V power supply 42. The secondary winding of the pulse transformer 39 is connected to a gate circuit (not shown) of a thyristor constituting the thyristor stack 6 shown in FIG. A phase shift circuit 41 is connected to the base of the above-mentioned transistor 38, and the output signal from this phase shift circuit 41 controls on/off of the transistor 38, causing firing from the secondary side of the pulse transformer 39 to the gate of the thyristor. A pulse is output. Note that this circuit consisting of the transistor 38 and the pulse transformer 39 is provided for each thyristor constituting the thyristor stack 6, and the secondary winding of each pulse transformer is connected to the gate of each thyristor. Additionally, the collector of the transistor 36 is connected to the cathode of a diode 40, and the anode of the diode 40 is connected to a phase control circuit (not shown) for shifting the phase of the thyristor to α-max (maximum delayed phase angle). .

In the protection device for the power converter configured as described above, when the AC power supply voltage is normal, the voltage obtained by dividing the output voltage of the +24V power supply 42 by the resistor 21 and the resistor 22 is the voltage that is obtained by dividing the output voltage of the +24V power supply 42 by the resistor 23. The signal is input to a comparator 24 which operates as a comparator via a - input terminal. In addition, the output voltage of the +24V power supply 42 is made into a voltage with almost no ripple by the capacitor 26 via the diode 25, and this voltage is used as the power input of the operational amplifier 24, and is divided by the variable resistor 27. The obtained voltage is used as the reference voltage for power failure detection by the comparator 2 via the resistor 28.
It is input to the comparator 24 through the + input terminal of No. 4. When the AC power supply voltage is normal, this operational amplifier 24
Since the voltage input through the - input terminal of comparator 24 is higher than the voltage input through the + input terminal of comparator 24, the output of comparator 24 is OV. Therefore, the transistor 31 is turned off, and the capacitor 35 is charged by the +15V power supply, that is, the output voltage of the automatic voltage regulator 10, and the charging voltage of the capacitor 35 causes the transistor 3 to be charged.
6 is turned on. When the transistor 36 is turned on, the transistor 38 is turned on and off by the output signal from the phase shift circuit 41, and a firing pulse is output from the pulse transformer 39 to the gate of the thyristor.

Now, if the AC power supply fails, the +24V power supply 42
Because the time constant of the smoothing circuit 12 is small, the output voltage of is rapidly attenuated, and therefore the voltage at one input terminal of the comparator 24 is rapidly reduced. At this time, the voltage at the +input terminal of the comparator 24 decreases with a constant time constant due to the discharge of the capacitor 26, so at the beginning of a power outage, the voltage at the +input terminal of the comparator 24 decreases from the -input terminal. greater than the voltage. Further, since the power supply voltage of the comparator 24 is the charging voltage of the capacitor 26, the comparator 24 can operate even at this point. At this time, the output of the comparator 24 becomes high level, and the Zener diode 29 and resistor 30
This signal is applied to the base of transistor 31 via , turning transistor 31 on. When the transistor 31 is turned on, the charge in the capacitor 35 is rapidly discharged through the resistor 32 and the transistor 31 in a short period of time, usually within 1 msec, and the base potential of the transistor 36 is rapidly reduced, causing the transistor 36 is turned off. Therefore, the primary side of the pulse transformer 39 is turned off, and the firing pulse is prohibited from being output from the secondary side of the pulse transformer 39 to the gate of the thyristor.
Performs thyristor gate and disconnection. At this time, if the thyristor Leonard device shown in Figure 1 is performing regenerative operation, only the thyristor that was firing at the moment the gate was cut off will continue to flow regenerative current, and the other thyristors will be turned off. Since it does not arc, it will not lead to a DC short circuit. In addition, since the power supply voltage has dropped to zero due to a power outage, there is a risk that the regenerative current will become an overcurrent, but since the current flows through the AC reactor and power transformer, it can be suppressed to below the peak on-current of the thyristor. Furthermore, since the main contactor cuts off the regenerative current approximately 20 to 30 msec after a power outage occurs, overcurrent does not occur for a long period of time, and damage to the thyristor can be prevented.

Next, when the AC power is restored, +24V power supply 42
The output voltage rises, the capacitor 26 is instantly charged via the diode 25, and the comparator 24
Power is supplied to the In addition, the voltage obtained by dividing the output voltage of the +24V power supply 42 by the resistors 21 and 22 is
3 and the negative input terminal of the comparator 24, and the voltage obtained by dividing the charging voltage of the capacitor 26 by the variable resistor 27 is input to the resistor 28.
to the + input terminal of the comparator 24 through the comparator 2
4 is input. At this time, since the voltage at the - input terminal of the comparator 24 is higher than the voltage at the + input terminal, the output voltage of the comparator 24 becomes OV, and the transistor 31 is turned off. In addition, when the AC power supply is restored, the output voltage of the +15V power supply also rises.
Since the transistor 31 is turned off, the capacitor 35 is charged with a time constant determined by the resistance value of the resistor 34 and the capacitance value of the capacitor 35. After a certain period of time, the charging voltage of the capacitor 35 increases to the transistor 3.
Transistor 3 rises to a value that turns on transistor 6.
6 is turned on. By turning on the transistor 36, the pulse amplifier 38 is controlled on and off by the output signal from the phase shift circuit 41, and a firing pulse is output from the pulse transformer 39 at the gate of the thyristor. Further, when the transistor 36 is turned on, the collector of the transistor 36 becomes OV, and this signal is input to the phase control circuit via the diode 40 to cancel the α-max shift of the thyristor. That is, when the AC power supply is restored after a power outage, the gate of the thyristor is released when a delay time determined by a delay circuit including a resistor 34 and a capacitor 35 has elapsed.

As explained above, in the protection device for a power conversion device according to the present invention, the voltage obtained by dividing the charging voltage of the capacitor charged by the DC voltage obtained by rectifying the AC power supply voltage, and the When the AC power supply fails, the thyristor gate is immediately activated by the output signal of the delay circuit, which operates based on the output signal of the comparator, which outputs a signal depending on the magnitude relationship with the voltage obtained by dividing the DC voltage. When the AC power supply is restored and a certain period of time has elapsed until the control power supply is established, the thyristor gate is released.
When the AC power supply is restored after a power outage, it can prevent overcurrent from flowing to the thyristor due to DC short circuit caused by erroneous ignition of the thyristor, prevent the no-fuse breaker or fuse from operating, and prevent deterioration of the thyristor. can be prevented and also
The power conversion device can be quickly restarted when power is restored.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a main circuit and a control power supply circuit of a power conversion device equipped with a protection device for a power exchange device according to the present invention, and FIG. 2 is a circuit diagram showing an embodiment of the protection device for a power conversion device according to the present invention. FIG. 6... Thyristor stack, 11... Diode stack, 12... Smoothing filter, 24... Comparator, 25... Diode, 26, 35... Capacitor, 31, 36, 38... Transistor, 3
4...Resistance.

Claims (1)

[Claims for Utility Model Registration] A thyristor stack that converts alternating current supplied from an alternating current power source into direct current, and a transistor connected in series to a pulse transformer for generating gate pulses applied to each thyristor of the thyristor stack. A first switching transistor that rectifies and stabilizes the alternating current of the above-mentioned alternating current power supply.
a constant voltage circuit that generates a DC voltage; and a constant voltage circuit that rectifies the AC of the AC power supply to generate a second DC voltage corresponding to the voltage of the AC power supply, and in the event of a power outage of the AC power supply, the DC voltage disappears in a first time. and a capacitor connected to the output terminal of the rectifier circuit via a diode with an anode facing the rectifier circuit side and holding a voltage for a second time longer than the first time of the rectifier circuit. , a third voltage corresponding to the output voltage of the rectifier circuit is used as one input, a fourth voltage corresponding to the charging voltage of the capacitor is used as the other input, and the charging voltage of the capacitor is used as the power source, a comparator whose output disappears when the voltage becomes lower than a fourth voltage; a circuit which turns off the switching transistor in response to the disappearance of the output of the comparator; and a third circuit from the rectifier circuit. Protection of a power conversion device, comprising: a delay circuit that operates when the output of a comparator is inverted due to the application of a voltage; and a circuit that turns on the switching transistor by the output of the delay circuit. Device.