JPS6117214B2 - - Google Patents

Description

Detailed Description of the Invention The present invention is a controlled rectifier used in power supplies for aluminum electrolysis, etc., and is a controlled rectifier that connects multiple three-phase bridge control rectifiers in parallel to form 12 or more phases. This invention relates to a protection method for a controlled rectifier when the margin angle is insufficient.

When the controlled rectifier performs a reverse conversion operation, commutation will fail unless there is a certain commutation margin angle due to the turn-off characteristics of the controlled rectifier used. For this reason, the commutation margin angle has been conventionally detected to protect the controlled rectifier when the commutation margin angle is insufficient.

FIG. 1 shows a block diagram of a conventionally used forced ignition method to protect a controlled rectifier when commutation margin angle is insufficient.

In Figure 1, 1 is a reverse pressure detection circuit that detects the reverse pressure period between the anode and cathode of the controlled rectifier, and 2 is a circuit that detects whether the reverse pressure period signal from the reverse pressure detection current 1 is generated for a certain period of time. A flow margin angle insufficient detection circuit, 3 a phase control circuit, and 4 a timing and phase for generating a forced firing pulse (hereinafter referred to as a strong point pulse) when commutation margin angle is insufficient according to a firing command from the phase control circuit 3; A forced firing pulse generation circuit determines and generates a strong point pulse based on a commutation margin angle shortage signal from the commutation margin angle shortage detection circuit, 5 is a firing pulse from the phase control circuit 3 and a commutation margin angle shortage detection circuit. An AND element outputs a signal to the OR element 6 based on the AND condition of the insufficient commutation margin angle signal from the circuit 2 and the NOT signal. 7 is an interface between the firing command from the control circuit and the firing pulse signal to the gate of the control rectifier. be.

During normal operation, a firing command is generated from the phase control circuit 3, and a firing signal is applied to the gate of the control rectifying element via the AND element 6, the OR element 6, and the interface 7. When an abnormality occurs, that is, when a commutation margin angle shortage signal is generated from the commutation margin angle shortage detection circuit 2, the AND element 5 cuts off the firing command from the phase control circuit 3, and at the same time, the forced firing is performed from the strong point pulse generation circuit 4. A pulse is generated in the phase following the phase in which commutation operation is attempted during normal operation. That is, the high voltage side of the phases of the control rectifier connected to the R phase, S phase, and T phase of the AC power supply side are connected to the U phase, V phase, and W phase, respectively, and the low voltage side is connected to the X phase, Y phase, and Z phase, respectively. Under normal conditions, U, Z, V, X, W, and Y are ignited in this order, and the high pressure side is commutated in the order of U to V, V to W, and W to U, and the low pressure side is commutated from X to Y, and Y. The current is commutated in the order of Z to Z, and Z to X. For example, if a commutation margin angle shortage occurs when commutating from V phase to W phase, a strong point pulse is applied to U phase, and the U phase and becomes energized, resulting in a so-called bypass pair (hereinafter referred to as BPP) state. After that, if the output of the commutation margin angle insufficient detection circuit is turned off after a certain period of time, the phase control circuit 3
A firing command is generated through the AND element 5, and the normal state is restored.

The above is a protection method when the margin angle is insufficient for a six-phase controlled rectifier configured with one three-phase bridge controlled rectifier. By the way, FIG. 2 shows a 12-phase control rectifier in which two three-phase bridge control rectifiers 11A and 11B are connected in parallel. The following explanation is for simplicity
The explanation will be given for 12 phases, but the same explanation can be given for two or more phases.

In Figure 2, 9 is an AC bus, 10A, 10B are rectifier transformers that receive power from the AC bus, 11A, 11
B is a three-phase bridge control rectifier, and 12 is a load. Using the previously described strong point pulse protection scheme in a 12-phase controlled rectifier, e.g.
The three-phase bridge control rectifier 11A shown in the figure (assuming 11A is on the leading phase side). If the commutation margin angle is insufficient and a strong point pulse occurs, the three-phase bridge control rectifier 11A (hereinafter referred to as A bridge) on the commutation failure side becomes BPP and the output voltage becomes zero, but the normal three-phase The bridge control rectifier 11B (hereinafter referred to as the B bridge) continues to perform inverse conversion operation. The phase voltage waveform and DC voltage waveform at this time are shown in FIG. As is clear from the figure, since the DC voltage of the B bridge 11B is lower than that of the A bridge 11A, the load current concentrates on the A bridge 11A. Therefore, when attempting to return the A-bridge 11A after a certain period of time, the commutation overlap angle increases and the commutation fails again. Furthermore, if the B bridge is turned off and only the A bridge remains in the BPP state, the load current will continue to flow only through the A bridge, which may destroy the element in the case of a large inductance load.

The purpose of the present invention is to solve the problem when a certain three-phase bridge rectifier becomes insufficient in commutation margin angle in a controlled rectifier in which a plurality of three-phase bridge control rectifiers are connected in parallel to form 12 or more phases. It is an object of the present invention to provide a protection method for a controlled rectifier that promptly protects the controlled rectifier and enables continuous operation of the controlled rectifier.

The present invention will be explained below with reference to the drawings.

FIG. 4 shows a configuration diagram of an embodiment of the present invention. Blocks in the figure with the same numbers as those in FIG. 1 indicate the same functions. In Fig. 4, 6 _{and 7} are OR elements that take an OR condition between the commutation margin angle shortage signal from the commutation margin angle detection circuit 2 and the commutation margin angle shortage signal from another control rectifier connected in parallel; A strong point pulse generation phase when the commutation margin angle is insufficient due to the firing command of the phase control circuit 3,
This logic control circuit determines the ignition phase for bypass pair release, generates a strong point pulse with the signal from the OR element ₆₇ , and generates a bypass pair release pulse after a certain period of time when the commutation margin angle is insufficient.

Next, the operation of the present invention will be explained. As shown in Figure 2, two 3-phase bridge control rectifiers are connected in parallel to form a 12-phase controlled rectifier, and each control rectifier has a commutation margin as shown in Figure 3. It has a protection device in case of insufficient horn.
When the commutation margin angle insufficient detection circuit 2 of the A bridge 11A operates due to some kind of malfunction, the OR element 6 ₇
A signal is sent to the AND elements 5 ₁ to 5 ₆ through the circuit, and the signal from the phase control current 3 is cut off. At the same time, the commutation margin angle shortage signal is sent to the commutation margin angle shortage logic control circuit 8. A strong point pulse is generated and the A bridge 11A enters the BPP state. At the same time, the commutation margin angle incorrect signal is sent to the OR element ₆₇ of the commutation margin insufficient protection device of the B bridge 11B, and the B bridge 11B also enters the BPP state. Thereafter, after an appropriate time delay, each commutation margin angle insufficient logic control circuit 8 generates a firing pulse to release BPP and turns off the commutation margin angle insufficient signal, and AND elements 5 ₁ to 5 ₆ The firing command of the phase control circuit 3 passes through the OR elements 6 ₁ to 6 again.
₆ and returns to normal operation.

FIG. 5 shows the phase voltage waveform and DC voltage waveform when the operation of the present invention is performed, assuming that the A bridge 11A is on the leading phase side. This is the case when the commutation margin angle becomes insufficient during commutation from the V ₁ phase to the W ₁ phase, and at this point, a commutation margin angle shortage signal is generated, and the A bridge 11
Strong point pulses are generated in the _U1 phase and _U2 phase of the A and B bridges 11B. After that, a BPP release pulse was generated in the _Y1 phase and _Y2 phase, and normal operation was restored. Fifth
In the figure, the BPP release pulse is controlled so that the firing angles of the A bridge 11A and the B bridge 11B are the same. ，
The same effect can be obtained even if they are generated simultaneously in the B bridge 11B.

In addition, the commutation margin angle shortage logic control circuit 8 shown in FIG. 4 is replaced with the forced firing pulse generation circuit 4 shown in FIG. BPP can also be canceled by turning off the signal and receiving a firing command from the phase control circuit. In this case, the firing phase when BPP is released is determined by the phase control circuit.

As is clear from the above explanation, in a controlled rectifier in which a plurality of three-phase bridge control rectifiers are connected in parallel to form 12 or more phases, a certain
When the phase bridge control rectifier becomes insufficient in commutation margin angle, a forced ignition pulse is generated in the control rectifier,
When the BPP is turned on and the other healthy three-phase bridge control rectifiers are also generated a strong point pulse and turned on to the BPP, and then the BPP is released after an appropriate time,
It is possible to restore the normal state to a controlled rectifier with insufficient commutation margin angle without concentrating current or shutting down the operation, improving system reliability and designing an economical controlled rectifier. Since it is possible, the effect is great.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a conventional protection system for a controlled rectifier when commutation margin angle is insufficient, and Figure 2 is a controlled rectifier in which two 3-phase bridge control rectifiers are connected in parallel to form 12 phases. The configuration diagram of the device, Figure 3 shows the phase voltage and direct voltage waveform of the 12-phase controlled rectifier when the conventional protection method is used, and Figure 4 shows one implementation of the protection method of the controlled rectifier of the present invention. An example block diagram, FIG. 5, is a phase voltage and DC voltage waveform diagram when the embodiment of the present invention shown in FIG. 4 is carried out. DESCRIPTION OF SYMBOLS 1... Reverse pressure detection circuit, 2... Commutation margin angle deficiency detection circuit, 3... Phase control circuit, 4... Forced firing pulse generation circuit, 5, 5 ₁ to 5 ₆ ... AND element, 6, 6 ₁ to
6 ₇ ...OR element, 7...Interface, 8...Logic control circuit when commutation margin angle is insufficient, 9...AC bus,
10-1, 10-2... Rectifier transformer, 11A,
11B...6-phase bridge control rectifier, 12...Load.

Claims (1)

[Claims] 1. In a controlled rectifier in which multiple 3-phase bridge control rectifiers are connected in parallel to form 12 or more phases, when the commutation margin angle of any 3-phase bridge control rectifier is insufficient, the 3-phase bridge control rectifier is A protection method for a controlled rectifier, characterized in that the control rectifier is connected to a bypass pair, and another healthy three-phase bridge control rectifier is also connected to the bypass pair, and then the bypass pair is released.