JPH0984351A - Power converter - Google Patents

Abstract

(57) Abstract: In a power conversion device in which an arm is composed of a plurality of semiconductor elements connected in parallel, the operation can be performed according to the number of faulty parallel semiconductor elements and the operation is not stopped. SOLUTION: An element failure determination circuit 6 for determining the number of failure parallels of the semiconductor element, and a current reference value of the power converter is lowered in response to the element failure determination circuit 6 according to the number of failure parallels of the semiconductor element. An overcurrent level changing circuit that responds to the current reference changing circuit 13 and the element failure determination circuit 6 and lowers the protection level of the overcurrent protection circuit that protects the power converter from an overcurrent according to the number of faulty parallel semiconductor devices. 1
A power conversion device comprising 1-3, which lowers an output current of the power conversion device and also lowers an overcurrent protection level in accordance with the number of faulty parallels of the semiconductor element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is composed of at least a plurality of semiconductor elements connected in parallel in each arm constituting an electric power converter, and is used, for example, in a DC arc furnace for converting AC into DC and electrolysis. The present invention relates to a large-current power conversion device for power supply equipment.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram showing a conventional example in which a thyristor rectifier is used as an example of a power converter.
In FIG. 4, 1 is an AC bus, 2 is a circuit breaker for shutting off power supply equipment, 3 is a transformer for a thyristor rectifier (hereinafter, simply referred to as rectifier), and 4 is a rectifier for converting AC of the transformer into DC. Each bridge-connected arm is composed of a plurality of parallel-connected thyristors (hereinafter referred to as semiconductor elements). Reference numeral 5 is a load connected to the DC circuit of the rectifier 4, 6 is an element failure determination circuit for determining the number of faulty parallel semiconductor elements, 7 is a current reference setting apparatus for setting the output current value of the rectifier 4, and 8 is the rectifier 4 Of the current reference signal I set by the current reference setting unit 7
Ref and the current feedback signal IF.B. detected by the current detector 8 are applied, and the constant current control circuit 10 performs control for keeping the output current of the rectifier 4 constant. 4 is a gate control circuit for controlling the gate of the semiconductor device, 11 is an overcurrent protection level setter 11-1 for setting the overcurrent protection level, and the output current IF.B. of the rectifier 4 detected by the current detector 8. Is compared with the value set by the level setter 11-1 and outputs an overcurrent detection signal, which is an overcurrent protection circuit composed of a comparison calculator 11-2, and 12 is a failure signal detected by the element failure determination circuit 6. And overcurrent protection circuit 11
This is a protection circuit that performs protection interlocking by the overcurrent signal detected in 1. In case of a serious failure, the circuit breaker 2 is cut off to protect the system.

[0003]

When an element failure occurs, the number of parallel failed arms of the rectifier 4 decreases, so that the current sharing value of a healthy semiconductor element of the arm in which the element failure occurs increases. Therefore, since it is difficult to output the rated output of the rectifier 4 only with sound elements, there is a redundancy (usually 1
It was necessary to have a redundant number of pieces).

Further, since the rated output cannot be continued when the number of elements in two parallels fails, it is necessary to treat it as a serious failure and stop the system. An object of the present invention is to provide no redundant number, and even if a semiconductor element failure such as 1 parallel number element failure, 2 parallel number element failure, or 3 parallel number element failure occurs, depending on the number of semiconductor element failure parallels. , The operation can be continued by reducing the output current of the rectifier 4, and even if there is a redundant number, the output current is not reduced and the operation is continued up to the redundant number even if a semiconductor element failure occurs. It is an object of the present invention to provide a power conversion device capable of continuing the operation by decreasing the output current of the rectifier 4 in accordance with the number of faulty parallel semiconductor devices when the fault of the semiconductor devices exceeds the above.

[0005]

In order to achieve the above object, the invention according to claim 1 provides a power conversion device in which each arm comprises at least a plurality of semiconductor elements connected in parallel. An element failure determination circuit for determining the number of failure parallels, a current reference changing circuit that responds to the element failure determination circuit and decreases the current reference value of the power conversion device according to the number of failure parallels of the semiconductor element, and the element failure A faulty parallel number of the semiconductor element, which is provided with an overcurrent level changing circuit which responds to the discrimination circuit and lowers a protection level of the overcurrent protection circuit for protecting the power converter from an overcurrent according to the faulty parallel number of the semiconductor element. According to the above, the output current of the power conversion device is reduced and the overcurrent protection level is also reduced.

According to a second aspect of the present invention, in an electric power conversion device in which each arm is composed of at least a plurality of semiconductor elements connected in parallel, an element failure determination circuit for determining the number of failure parallel connections of the semiconductor elements. A current detection value changing circuit for increasing the detection value of the output current of the power conversion device according to the number of faulty parallels of the semiconductor element in response to the element failure determining circuit, and outputting the output of the current detection value changing circuit. It is given as a current feedback signal to a constant current control circuit that controls the output current of the power conversion device, and is also given to an overcurrent protection circuit that protects the power conversion device from overcurrent. It is characterized in that the output current of the power conversion device is reduced and the overcurrent protection level is also reduced.

Further, the invention according to claim 3 is the
In a power converter comprising at least a plurality of semiconductor elements connected in parallel, an element failure determination circuit for determining the number of failure parallels of the semiconductor element, and a failure parallel of the semiconductor element in response to the element failure determination circuit. The current detection value changing circuit for increasing the detection value of the output current of the power conversion device according to the number, and the protection level of the overcurrent protection circuit for protecting the power conversion device from overcurrent in response to the element failure determination circuit. The semiconductor device includes an overcurrent level changing circuit that lowers according to the number of faulty parallel semiconductor devices, and outputs the output of the current detection value changing circuit as a current feedback signal to a constant current control circuit that controls the output current of the power conversion device. It is characterized in that the output current of the power conversion device is reduced and the overcurrent protection level is also reduced according to the number of faulty parallel semiconductor devices.

Furthermore, the invention corresponding to claim 4 is the invention corresponding to any one of claims 1 to 3,
The element failure determination circuit is characterized in that the operation of the power conversion device is stopped when the limit of the number of failure parallel connections of the semiconductor elements is determined.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below with reference to FIGS. 1 to 3 in which the same parts as those in FIG.
In addition, in FIGS. 1 to 3, the same reference numerals as those in FIG.
Since they have the same function, their explanation is omitted.

FIG. 1 is a block diagram showing an embodiment of the invention corresponding to claim 1. In FIG. In FIG. 1, 13 is a current reference value IRef set by the current reference setting unit 7 according to the number of semiconductor device failure parallels detected by the device failure determination circuit 6,
[(Number of parallels-Number of fault parallels) / Number of parallels] = (Number of healthy parallels /
It is a current reference changing circuit that lowers the current reference value to the current value that can be passed by the healthy parallel number of semiconductor elements by multiplying by Iset. Reference numeral 11 denotes an overcurrent level changing circuit 11-4 that lowers the overcurrent protection level according to the number of fault parallels from the element failure determination circuit 6, and the changed overcurrent protection level and the rectifier 4 detected by the current detector 8. Is an overcurrent protection circuit including a comparison calculator 11-2 for comparing and calculating the output current IF.B.

Here, the parallel number is 10P (the parallel number is 10).
The rectifier 4 composed of the arms of
When operating with Ref = 1PU (100%), for example, if a failure of 1P (the number of parallels is 1) occurs, the output of the current reference changing circuit 13 is Iset = IRef x (9 /
10) = (9/10) IRef, and the constant current control circuit 9
This reduces the output current IF.B. of the rectifier 4 to 90%.

Further, since the overcurrent protection level is lowered by the overcurrent level changing circuit 11-4 to the overcurrent protection level in the case where the number of semiconductor elements is 9P (9 in parallel), the semiconductor elements are connected in 9P (parallel). (Over several 9) can be protected against overcurrent.

Similarly, the number of parallel faults is 2P (two parallel numbers).
If the failure occurs, the IF.B. is lowered to 80% and the overcurrent protection level is also lowered to the value at 8P (8 in parallel), so that the semiconductor element can be protected against overcurrent at 8P.

As described above, according to the invention according to claim 1, even if the number of failed parallel elements is 1 or 2, the operation is performed by decreasing the output current of the rectifier according to the number of failed parallel elements. You can continue. This makes it possible to provide a redundant rectifier, so that it is possible to provide a small-sized, inexpensive and highly reliable rectifier.

FIG. 2 is a block diagram showing an embodiment of the invention corresponding to claim 2. In FIG. In FIG. 2, 14 is the value IF.B. detected by the current detector 8 according to the number of element failures detected by the element failure determination circuit 6 [number of parallels / (number of parallels-number of parallels in failure)] = (parallel Number / healthy parallel number) to obtain Id,
It is a current detection value changing circuit for increasing the value of the current detection signal by the number of faulty parallel semiconductor devices.

For example, in the rectifier 4 in which the number of parallel semiconductor elements forming the arm is 10P (the number of parallels is 10),
When a fault with a parallel number of 1P (parallel number of 1) occurs, if IRef = 1PU (100%) of the current reference setting unit, Id = IF.B. x (10/9) = (10/9 ) IF.B.
Since the constant current control circuit 9 keeps Id at 100%, the output current IF.B. of the rectifier 4 drops to 90%. Further, since the overcurrent protection level is set for Id, the IF.B. changes, so that the overcurrent protection level is lowered with respect to the rating of the rectifier 4. Therefore, overcurrent protection can be performed when the number of semiconductor elements is 9P (9 in parallel).

Similarly, the number of parallel faults is 2P (two parallel numbers).
If a failure occurs, the IF.B. will drop to 80%, the overcurrent protection level will also drop to the value at 8P (8 in parallel), and the overcurrent protection when the semiconductor element is 8P (8 in parallel). You can

As described above, according to the invention corresponding to claim 2, even if the number of parallel faults is one or two, the output current of the rectifier 4 is reduced according to the number of faulty parallel elements, and overcurrent protection is performed. By lowering the level, the same effect as that of the invention according to claim 1 can be obtained.

FIG. 3 is a block diagram showing an embodiment of the invention corresponding to claim 3. In FIG. In FIG. 3, as in FIG. 2, 14 indicates the value IF.B. detected by the current detector 8 according to the number of element failures detected by the element failure determination circuit 6 [the number of parallel /
(Parallel number-fault parallel number)] = (parallel number / healthy parallel number) to obtain Id, and the current detection value changing circuit increases the value of the current detection signal by the fault parallel number of the semiconductor element.

Further, as in FIG. 1, reference numeral 11 denotes an overcurrent level changing circuit 11-4 which lowers the overcurrent protection level in accordance with the number of fault parallels from the element fault discriminating circuit 6 and a changed overcurrent protection level. It is an overcurrent protection circuit composed of a comparison calculator 11-2 which compares the output current IF.B. of the rectifier 4 detected by the current detector 8 and outputs an overcurrent signal.

Here, the parallel number is 10P (the parallel number is 10).
The rectifier 4 composed of the arm of
When operating with Ref = 1PU (100%), for example, if a failure of 1P (1 parallel number) occurs,
Id = IF.B. × (10/9) = (10/9) IF.B. Since the constant current control circuit 9 keeps Id at 100%, the output current IF.B. of the rectifier 4 is 90. In addition, the overcurrent protection level is lowered to the overcurrent protection level when the semiconductor element is 9P (9 in parallel) by the overcurrent level changing circuit 11-4.
Overcurrent protection at P (9 in parallel) is possible.

Similarly, the fault parallel number is 2P (parallel number 2).
If the failure occurs, the IF.B. is lowered to 80% and the overcurrent protection level is also lowered to the value at 8P (8 in parallel), so that the semiconductor element can be protected against overcurrent at 8P.

As described above, according to the invention according to claim 3, even if the number of faulty parallels is 1 or 2, the output current of the rectifier 4 is reduced according to the number of faulty parallel elements, and the overcurrent protection level is also increased. By lowering, it is possible to obtain the same effect as that of the invention according to claim 1.

The inventions corresponding to claims 1 to 3 are:
In principle, it is possible to operate up to one healthy semiconductor device parallel number, but since there are restrictions due to load conditions, etc., a limit is set on the healthy semiconductor device parallel number, and if the parallel number is less than the limit. If the operation of the power converter is stopped, efficient operation is possible. Although this limit value varies depending on the system, it is considered that the operation can be performed up to a failure of 5 to 30% of the total number of parallel semiconductor devices. Therefore, the operation is continued up to 70% to 95% of the rated output of the power converter,
By stopping the power conversion device when the limit value is exceeded, the system can be used efficiently and effectively.

[0025]

As described above, according to the present invention, when the arm of the power conversion device is composed of a plurality of semiconductor elements connected in parallel, the output current of the power conversion device is changed according to the number of faulty parallel connections. By limiting and also lowering the overcurrent protection level of the power converter according to the number of parallel failures, the safe operation can be continued up to the limit of the number of parallel failures.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a power conversion device of the invention corresponding to claim 1. FIG.

FIG. 2 is a configuration diagram showing an embodiment of a power conversion device of the invention corresponding to claim 2;

FIG. 3 is a configuration diagram showing an embodiment of a power conversion device of the invention corresponding to claim 3;

FIG. 4 is a configuration diagram of a conventional power conversion device.

[Explanation of symbols]

1 ... AC bus 2 ... Circuit breaker 3 ... Rectifier transformer 4 ... Rectifier 5 ... Load 6 ... Element failure determination circuit 7 ... Current reference setting device 8 ... Current detector 9 ... Constant current control circuit 10 ... Gate control circuit 11 ... Overcurrent protection circuit 11-1 ... Overcurrent level setter 11-2 ... Comparison calculator 11-3 ... Overcurrent level change circuit 12 ... Protection circuit 13 ... Current reference change circuit 14 ... Current detection value change circuit

Claims (4)

[Claims] 1. A power converter in which each arm comprises at least a plurality of semiconductor elements connected in parallel,
An element failure determination circuit for determining the failure parallel number of the semiconductor element, and a current reference changing circuit that responds to the element failure determination circuit and lowers the current reference value of the power converter according to the failure parallel number of the semiconductor element, The semiconductor device includes an overcurrent level changing circuit that responds to the device failure determination circuit and lowers a protection level of an overcurrent protection circuit that protects the power conversion device from an overcurrent according to the number of parallel faults of the semiconductor device. A power conversion device, characterized in that the output current of the power conversion device is reduced in accordance with the number of faulty parallel connections and the overcurrent protection level is also reduced. 2. A power converter in which each arm comprises at least a plurality of semiconductor elements connected in parallel,
An element failure discriminating circuit for discriminating the number of faulty parallels of the semiconductor element, and a current detection value change responsive to the element faulty discriminating circuit to increase the detection value of the output current of the power converter according to the number of faulty parallels of the semiconductor element An overcurrent protection circuit for protecting the power converter from an overcurrent while providing an output of the current detection value changing circuit as a current feedback signal to a constant current control circuit for controlling an output current of the power converter. Also, the power conversion device is characterized in that the output current of the power conversion device is reduced and the overcurrent protection level is also reduced according to the number of faulty parallels of the semiconductor element. 3. A power converter in which each arm comprises at least a plurality of semiconductor elements connected in parallel,
An element failure discriminating circuit for discriminating the number of faulty parallels of the semiconductor element, and a current detection value change responsive to the element faulty discriminating circuit to increase the detection value of the output current of the power converter according to the number of faulty parallels of the semiconductor element A circuit, and an overcurrent level changing circuit that responds to the element failure determination circuit and reduces a protection level of an overcurrent protection circuit that protects the power converter from an overcurrent according to the number of faulty parallels of the semiconductor element. The output of the current detection value changing circuit is given as a current feedback signal to a constant current control circuit that controls the output current of the power conversion device, and the output current of the power conversion device is reduced according to the number of faulty parallels of the semiconductor elements. A power conversion device characterized by lowering the overcurrent protection level. 4. The device according to claim 1, wherein the element failure determination circuit stops the operation of the power conversion device when the limit of the number of faulty parallels of the semiconductor element is determined. The power converter according to claim 1.