JPS639280Y2 - - 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.

In general, in power conversion devices such as thyristor Leonard devices, due to the nature of the thyristor, once the thyristor is ignited, it will not be extinguished unless the circuit is opened or a reverse voltage is applied, so if a power outage occurs during regenerative operation, normal commutation will not occur. Failure to do so will cause a DC short circuit and damage the thyristor. Therefore, in order to prevent damage to the thyristor due to this DC short circuit, a power outage is detected and the gate of the thyristor is cut off. However, in the past, power outages were detected using the output voltage of an automatic voltage regulator to generate control power for the thyristors. Immediately after, the output voltage of the automatic voltage regulator did not drop immediately, causing a time delay in detecting a power outage. Therefore, due to the delay in gate opening and closing of the thyristor, normal commutation of the thyristor may not occur during regenerative operation, causing a DC short circuit and overcurrent flowing, which may damage the thyristor. become. In this case, a no-fuse breaker or an arm fuse is installed in the motor armature circuit to protect the thyristor, but an overcurrent flows during the time until the no-fuse breaker breaks or the fuse blows out each time a power outage occurs, and this is repeated. Accumulation of stress in the thyristor has resulted in a shortened lifespan of the thyristor. Furthermore, if the no-fuse breaker or fuse blows out every time a power outage occurs, 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-mentioned problems, and its purpose is to detect a power outage without delay and promptly gate or disconnect the thyristor, thereby preventing overcurrent from flowing through the thyristor. By preventing the no-fuse breaker or fuse from opening or breaking,
An object of the present invention is to provide a protection device for a power converter that can quickly restart the power converter when power is restored.

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 disconnecting the thyristor is shown in FIG. 1 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 is connected to the negative input terminal of the operational amplifier 24 via the resistor 23. Furthermore, +24V power supply 4
The anode of a diode 25 is connected to the output terminal A of 2, the cathode of this diode 25 is connected to a capacitor 26, and the capacitor 26 is
Connected to Ov point. 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. variable resistance 2
The movable terminal of 7 is connected to the operational amplifier 24 via the resistor 28.
Connected to the + input terminal of the Further, a connection point between the cathode of the diode 25 and the capacitor 26 is connected to the power supply terminal of the operational amplifier 24.

The output terminal of the operational amplifier 24 is connected to the cathode of a Zena diode 29, and the anode of the Zena diode 29 is connected to the base of a transistor 31 via a resistor 30. This transistor 3
The emitter of transistor 31 is connected to the Ov point, and the collector of transistor 31 is connected to diode 3 through resistor 32.
Connected to the anode of 3. This diode 33
The connection point between the anode and the resistor 32 is connected to the output terminal B of the +15V power supply shown in FIG. 1 via the resistor 34, and is also connected to the capacitor 35,
Furthermore, this capacitor 35 is connected to the Ov point. 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 to the Ov point via the diode 37. The connection point of the collectors of these two transistors 36 is connected to the emitter of a transistor 38, and the collector of the transistor 38 is connected to one terminal of the primary winding of a pulse transformer 39. The other terminal is the output terminal A of the +24V power supply 42.
connected to. 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.
Further, 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 then input to an operational amplifier 24, which operates as a comparator, via a - input terminal. In addition, the output voltage of the +24V power supply 42 is connected to the capacitor 2 via the diode 25.
6 to generate a voltage with almost no ripples, this voltage is used as the power input of the operational amplifier 24, and the voltage obtained by dividing the voltage by the variable resistor 27 is used as the reference voltage for power failure detection via the resistor 28. The signal is input to the operational amplifier 24 via the +input terminal of the operational amplifier 24. When the AC power supply voltage is normal, the voltage input to the operational amplifier 24 through the - input terminal of the operational amplifier 24 is higher than the voltage input through the + input terminal of the operational amplifier 24. The output is Ov. Therefore, the transistor 31 is turned off, 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 turns the transistor 36 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 transistor 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 operational amplifier 24 is rapidly reduced. At this time, the voltage at the + input terminal of the operational amplifier 24 is
Because it decreases with a constant time constant due to the discharge of 6,
At the beginning of a power outage, the operational amplifier 24 +
The voltage at the input terminal becomes greater than the voltage at the -input terminal. Furthermore, since the power supply voltage of the operational amplifier 24 is the charging voltage of the capacitor 26, the operational amplifier 24 can operate even at this point. At this time, the output of the operational amplifier 24 becomes high level, and this signal is applied to the base of the transistor 31 via the Zener diode 29 and the resistor 30, turning the transistor 31 on. When the transistor 31 is turned on, the charge in the capacitor 35 passes through the resistor 32 and the transistor 31 for 1 msec.
The transistor 36 is rapidly discharged within a short period of time, and the base potential of the transistor 36 rapidly decreases, and the transistor 36 is turned off. Therefore, the primary side of the pulse transformer 39 is turned off, and the pulse transformer 39
The ignition pulse is prohibited from being output from the secondary side of the thyristor to the thyristor gate, and the thyristor gate is cut off. 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, approximately 20 to 30 minutes after the power outage occurred,
Since the main conductor cuts off the regenerative current after 30msec, there is no long-term overcurrent, which prevents damage to the thyristor.

As explained above, in the protection device for a power conversion device according to the present invention, the protection device responds to the magnitude relationship between the DC voltage that rapidly changes to the AC power supply voltage and the charging voltage of the capacitor that is charged by the DC voltage. Since the thyristor is gated and disconnected by the output signal of the operational amplifier that outputs the signal, it is possible to prevent unnecessary thyristors from igniting and forming a short circuit during an AC power outage. It is possible to prevent overcurrent from flowing through the thyristor, prevent the no-fuse breaker or fuse from blowing, and prevent the thyristor from deteriorating.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the main circuit and control power supply circuit of a power converter equipped with a protection device for a power conversion 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... Operational amplifier, 25... Diode, 26... Capacitor, 31, 36, 38... Transistor, 41
...Phase shift circuit.

Claims (1)

[Scope of utility model registration request] a thyristor stack that converts alternating current supplied from an alternating current power supply into direct current; a switching transistor connected in series to a transistor connected to a pulse transformer for generating gate pulses applied to each thyristor of the thyristor stack; and the above-mentioned alternating current. A rectifier circuit that rectifies the alternating current of the power source to generate a direct current voltage corresponding to the voltage of the alternating current power source, and in which the direct current voltage disappears in a first time in the event of a power outage of the alternating current power source, and an anode connected to the output terminal of the rectifier circuit. A capacitor connected through a diode facing the rectifier circuit and holding the voltage for a second time longer than the first time of the rectifier circuit, and a first voltage corresponding to the output voltage of the rectifier circuit. An operation that takes one input, a second voltage corresponding to the voltage of the capacitor mentioned above as the other input, and uses the voltage of the capacitor as the power source, and the output disappears when the first voltage becomes lower than the second voltage. A protection device for a power conversion device, comprising an amplifier and a circuit that turns off the switching transistor in response to disappearance of the output of the operational amplifier.