JPH0888982A - Overcurrent protecting device - Google Patents

Abstract

PURPOSE: To provide an overcurrent protecting device for a converter, which can obtain the secure overcurrent protection accurately all the time without the reduction in rated capacity of the converter, the provision of the large size for the device and the cost-up. CONSTITUTION: Current detectors 13a, 14a and 23 detect the output current of a voltage type converter 12. The current direction detectors 3a and the like detect the flowing direction of the output current of the voltage type converter 12. A current detector 22a judges the current value of the DC. An OR circuit 1 judges that which of the current detectors 13a, 14a, 23 and 22a is operated. AND circuits 2a-2f determine the sequence of the gate blocks of arms 19a-19f of the converter 12 based on the output of the OR circuit 1 and the outputs of the current direction detectors 3a and the like. These parts are provided. Then, the arm, wherein the DC in the arms on the positive electrode side and the negative electrode side of the arm pair in which the arm is shorted, is selected, and the gate blocking is performed in preference.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor power converter for converting DC power into AC power or AC power into DC power, and is particularly suitable for protection when an arm short circuit occurs in its main circuit. The present invention relates to an overcurrent protection device.

[0002]

2. Description of the Related Art Semiconductor power converters mainly include an inverse converter (inverter) for converting DC power into AC power and a forward converter (converter) for converting AC power into DC power. For example, in a reverse conversion device that uses a gate turn-off thyristor (GTO) that is a self-erasing element as a switching element that constitutes the main circuit of a converter and that converts DC power into three-phase AC power and outputs the three-phase AC power. An example is shown in FIG.

In FIG. 2, 10 is a DC power source, and 11
Is a smoothing capacitor, and 12 is a converter (main circuit), and the DC power of the DC power supply 10 is input to the smoothing capacitor 11 and the converter 12 via the breaker 16. In addition,
The converter in which the smoothing capacitor is provided on the DC side of the converter 12 as described above is called a voltage-type power converter.

The converter 12 is composed of six arms 19a to 19f each of which is composed of an antiparallel connection circuit of a GTO and a freewheel diode. Here, among these arms 19a to 19f, for example, a DC power source is used. 10+
The three arms 19a to 19c connected to the negative side are referred to as positive side arms, and the three arms 19d to 19f connected to the negative side are referred to as negative side arms, respectively.

Then, the converter 12 has these arms 1
By appropriately controlling ON / OFF of 9a to 19f, the DC power supplied from the DC power supply 10 via the smoothing capacitor 11 is converted into AC power. The AC power converted by the converter 12 is converted into an appropriate AC voltage value by the transformer 17 and supplied to an AC load 18 such as an induction motor.

By the way, in such a semiconductor power converter, if an overcurrent is generated in the converter 12, the switching element constituting the converter 12 may be destroyed.
It is customary to provide an overcurrent protection function, and various types of protection methods have been proposed, one of which is proposed in Japanese Patent Publication No. 4-63630. Therefore, regarding this conventional protection method,
Similarly, description will be made with reference to FIG.

As shown in FIG. 2, the converter 12 is provided with current transformers 13 and 14, which detect the AC output current, and current detectors 13a and 14a.
It is supplied to. On the other hand, on the DC side, a current transformer (DC current transformer) 15 for detecting the charging / discharging current of the smoothing capacitor 11 is provided, and the detection output is input to the current detector 15a.

Detection levels for detecting an overcurrent are set in the current detectors 13a to 15a, respectively, and when the current value detected by the current transformers 13 to 15 exceeds the above detection level. In addition, a predetermined detection signal is output. And these current detectors 13a-1
The output of 5a is supplied to the gate signal circuit 20, and if any one of the current detectors 13a to 15a has a signal exceeding the overcurrent detection level, the gate signal circuit 20 is detected. Is configured to directly output a gate block signal to the GTO of each arm 19a to 19f of the converter 12 and turn it off.

Therefore, in this case, first, in the case of an accident on the AC side of the converter 12, for example, a short circuit accident of the load 18 or an accident of the transformer 17, the current transformers 13 and 14 and the current detector 13 are first.
a, 14a can detect the overcurrent state of the converter 12, and as a result, the arms 19a to 1a of the converter 12 can be detected.
Gate 9f can be gated to protect converter 12 from overcurrent.

Next, an arm short circuit accident in the converter 12,
In the event of an arm short circuit, for example, when the arms 19a and 19d are simultaneously fired, the smoothing capacitor 1
Since the discharge current from No. 1 becomes excessive, the current transformer 15 and the current detector 15a can detect the overcurrent state of the converter 12, and the detection signal by this can detect the converter 12
By outputting a gate block signal to each of the arms 19a to 19f, the converter 12 is protected from overcurrent.

In the configuration of FIG. 2, as can be seen from the above description, when an arm short-circuit accident occurs, the short-circuit current flowing through the short-circuited arm depends on the discharge current of the smoothing capacitor 11 and the AC circuit. There is a short circuit current supplied from the side.

However, in the converter for supplying electric power to the load as shown in FIG. 2, the impedance on the AC side is usually high, and the value of the short-circuit current from the AC side is generated even if an arm short circuit occurs. The rate of increase of the short circuit current is smaller than that of the discharge current from the smoothing capacitor 11.

Therefore, as in this prior art, the method of detecting the overcurrent by the value of the charging / discharging current of the smoothing capacitor 11 and gate-blocking the switching elements of the arms 19a to 19f is sufficient to prevent the converter 12 from overdriving. It was able to protect from electric current.

[0014]

The above-mentioned prior art does not consider the case of a system configuration in which the converter is connected to the power system for operation, and a sufficient protection function cannot be obtained. There was a problem.

That is, in a system in which the converter is operating in conjunction with the power system, when an arm short circuit occurs in the converter, the short circuit current from the AC side becomes large, and when the overcurrent is detected, the short circuit current is already generated. In some cases, a current exceeding the self-interruption ability is flowing in the arm. Therefore, if the gate is blocked at this point, the switching element will be destroyed and the protection function cannot be obtained.

More specifically, for example, as shown in FIG. 3, the converter 12 is connected to the power system 21,
It is assumed that electric power is exchanged between the converter 12 and the electric power system 21.

Now, the arm 19a of the converter 12 will now be described.
And 19d are fired at the same time, causing an arm short circuit. First, the ignition state and the direction of the alternating current of each arm before the short circuit between the arms 19a and 19d occurs are shown in FIG.
It was assumed that That is, 19a, 19b, 19f
It is assumed that the AC currents iu to iw are in the direction of the arrow shown in the figure with the arms of No. 1 being on, the arms of 19c, 19d and 19e being off.

Next, in this state, if the arm 19d erroneously ignites for some reason, the state of the current in each part immediately after the erroneous ignition will be the state shown in FIG. 4 (b). Since the arms 19a and 19d are short-circuited, the short-circuit current is from the smoothing capacitor 11 is generated by the arms 1a and 19d.
It flows to 9a and 19d.

On the other hand, at the same time, the path of the alternating current iu also changes, and the short circuit current (iw + is) flows through the arm 19d.

At this time, in the case of the prior art shown in FIG. 2, since the impedance on the AC side is large as described above, the current increase rate of the short-circuit current from the AC side is small, and the short-circuit current flowing through the arm 19d is small. Since most of the current is determined by the value of the short-circuit current is from the smoothing capacitor 11, the value of this current is is detected by the current transformer 15 and gate-blocked to perform the overcurrent protection as described above. be able to.

On the other hand, as shown in FIG.
In many cases, the impedance of the current system 21 is small when it is connected to the circuit 1, and the current increase rate of the AC short-circuit current iu is much larger than that in the case of FIG.

Therefore, the short-circuit current flowing in the arm 19d
The value of (is + iw) may be much larger than the short circuit current is from the smoothing capacitor 11, and as a result, the protection function cannot be obtained as described above.

In order to avoid this, a method of lowering the overcurrent detection level of the current detector for cooperation, or a method of individually installing the current detector for each arm can be considered.

However, in the former method, it is necessary to consider the maximum value of the short-circuit current from the AC side and set the level of the overcurrent detector lower by that amount, which is equivalent to the output of the converter. Since it will be used after reducing it, there is a problem that the output of the converter cannot be used effectively, while the latter method increases the number of current transformers and current detectors necessary for current detection. However, there is a problem that the converter becomes large and the cost increases.

The object of the present invention is to reduce the rated capacity of the converter, increase the size of the device, and increase the cost.
It is an object of the present invention to provide an overcurrent protection device for a converter that always provides accurate and reliable overcurrent protection.

[0026]

The above object is to provide a plurality of arm pairs, each of which is composed of a series circuit of a switching element forming a positive electrode side arm and a switching element forming a negative electrode side arm, between DC terminals. In the voltage type power converter in which the connection point between the positive electrode side arm and the negative electrode side arm of the pair is connected to the AC terminal, the flow direction of the current flowing between the connection point and the AC terminal of the arm pair in which the arm short circuit occurs,
Detecting at the time when the arm short circuit occurs, depending on the detection result, select the arm of which the circulating current is small among the positive electrode side and the negative electrode side of the arm pair in which the arm short circuit has occurred, This is achieved by preferentially gate blocking.

[0027]

The short-circuit current flowing in each arm of the arm pair in which the arm short circuit occurs is the sum of the DC current flowing from the positive electrode to the negative electrode of the DC circuit and the AC current flowing between the connection point of the arm pair and the AC terminal. . Then, at this time, the flow direction of the direct current does not change, but the flow direction of the alternating current is reversed every half cycle of the output frequency, so that only one of the positive arm and the negative arm is provided for each half cycle. Flowing.

Therefore, by knowing the direction in which the AC current flows when the arm short circuit occurs, it is possible to know which one of the positive arm and the negative arm of the arm pair is the one through which only the DC short current flows. Therefore, the arm can be preferentially gate-blocked, and as a result, a larger short-circuit current can be interrupted so far, and the converter can be provided with a larger overcurrent withstanding capacity than ever before.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The overcurrent protection device according to the present invention will be described in detail below with reference to the illustrated embodiments. FIG. 1 shows an embodiment of the present invention. In FIG. 1, those having the same numbers as those in the prior art described in FIGS. 2 and 3 have the same functions.

The converter 12 comprises three positive side arms 19a to 19c connected to the + side of the DC power source 10 and three negative side arms 19d to 19f connected to the-side. However, here, each positive arm 19
The series circuit of a to 19c and the negative arm 19d to 19f is called an arm pair, and the connection points of these arm pairs are A, B, and C.
And these are connected to the three-phase AC output terminals U, V, W.

The output current of the converter 12 is the current transformers 13 and 14
The current detection values i _U and i _W thus detected are input to the current detectors 13a and 14a, respectively, and also to the adder 24, where they are vector-wise added and the output current of the converter 12 is detected. The detected value i _V of the remaining one-phase current is calculated and input to the current detector 23. on the other hand,
The current on the DC side of the converter 12 is detected by a current transformer (DC current transformer) 22, and the current detection value i _D is also detected by the current detector 22.
Input to a.

Current detectors 13a, 14a, 23 and 22
A predetermined predetermined overcurrent detection level is set in a, so that no signal is output when the input detected current value is less than or equal to this level value, but the detected current value is When it becomes equal to or higher than this level value, the overcurrent detection signal i is generated immediately, and this overcurrent detection signal i is input to the OR circuit 1. Therefore, from this OR circuit 1, the current detectors 13a, 14a, 23
When the overcurrent detection signal i is output from any one of the output terminals 22a and 22a, the signal is output with the output logic "1".

Next, the two-phase current detection values i _U and i _W detected by the current transformers 13 and 14 and the remaining one-phase current detection value i _V calculated by the adder 24 are Current direction detector 3
It is also input to a to 3c.

These current direction detectors 3a to 3c detect the flow direction of the AC current between the connection points A, B and C of each arm pair of the converter 12 and the AC output terminals U, V and W. Then, it functions to generate a signal at either the (+) output or the (-) output, and when an alternating current is flowing from the converter 12 to the transformer 17, that is, in each arm pair. When flowing from the connection points A, B, C toward the AC output terminals U, V, W, a signal is generated at the (+) output, and conversely, the AC current flows from the transformer 17 to the converter 12. When the current is flowing, that is, when the current is flowing from the AC output terminals U, V, W toward the connection points A, B, C of each arm pair, a signal is generated at the (-) output. ing.

The overcurrent detection signal from the OR circuit 1 and the output signals of the current direction detectors 3a to 3c are input to the six AND circuits 2a to 2f, respectively, as shown in the figure, and these AND times 2a are inputted. To 2f, the output signal of the OR circuit 1 and the output signals of the current direction detectors 3a to 3c are respectively AN.
D is configured to be taken.

The outputs of the AND circuits 2a to 2f are input to the corresponding six OR circuits 4a to 4f, and via the OR circuits 4a to 4f, the GTOs of the corresponding arms are respectively supplied as shown in the drawing. A gate block signal is supplied.

Therefore, if the output signals of the current direction detectors 3a to 3c are output from the (-) output at the time when the overcurrent detection signal is output from the OR circuit 1, at this time, the corresponding arm is A signal for gate-blocking the pair of positive-side arms is output from the OR circuits 4a, 4c, and 4e.

Next, when the (+) output signal is output from the current direction detectors 3a to 3c at the time when the overcurrent detection signal is output from the OR circuit 1, the negative arm of the corresponding arm pair. Signal for gate blocking OR
The signals are output from the circuits 4b, 4d, 4f.

Therefore, according to this embodiment, when an arm short circuit occurs, the current is cut off from the arm having the smaller short-circuit current flowing out of the positive arm and the negative arm of the arm pair. As a result, it becomes unnecessary to consider the maximum value of the AC side short-circuit current, and the overcurrent withstand capability of the converter can be sufficiently increased. The operation will be described below.

As described above, this embodiment is characterized in that the arm to be gate-blocked in each arm pair is selected by the output of the OR circuit 1 and the output signals of the current direction detectors 3a to 3c. However, for this purpose, it is necessary to understand what the short-circuit current that flows when the arm is short-circuited.

First, for simplification of description, the switching element (GTO) forming the arm of the converter 12 is replaced with a switch contact and displayed as shown in FIG.
Here, the ON state of each switch represents that the arm is in the ignition state, and the OFF state represents the non-ignition state.

Then, based on FIG. 5, the states of the short-circuit currents when the short-circuiting of each arm occurs for the combinations of the ignition state of the arms of the converter 12 and the flowing direction of the alternating current will be described below. explain. First, in the converter of FIG.
Although there are quite a lot of combinations of the ignition state of each arm and the alternating current direction, the basic operation pattern can be classified into 16 patterns as shown in FIG. Even when the ignition state of the arm in FIG. 5 is different from the pattern in FIG. 6, by rereading the phase current,
The fault current flow route when the arm is short-circuited is equivalent to the pattern of FIG. 6, so it is sufficient to study each mode of FIG.

Next, in each of the modes shown in FIG. 6, the arm which should be in the non-firing state is ignited by erroneous firing or due to a failure, and when an arm short circuit occurs, a failure which flows to the failure arm occurs. FIG. 7 shows the current value.

As is clear from FIG. 7,
When an arm short circuit occurs due to false ignition or a device failure, the smoothing capacitor 11 is attached to the shorted arm.
In some cases, the short-circuit current is from the AC side and the short-circuit current from the AC side may be superposed, and in some cases, the short-circuit current is the same, and therefore it is not uniform.

However, looking at the relationship between the direction in which the AC current flows when the arm short circuit occurs and the arm short circuit current, the AC current corresponds to the phase in the direction flowing out of the converter 12. Negative side arm of arm pair
It can be seen that the short circuit current of (19d, 19e, 19f) is always smaller than that of the positive arm (19a, 19b, 19c).

Further, the positive arm (19) of the arm pair corresponding to the phase in which the alternating current of the converter is flowing into the converter (19)
It can be seen that the short circuit current of (a, 19b, 19c) is always smaller than that of the negative arm (19d, 19e, 19f).

This is because, when an alternating current is flowing from the converter 12 to the transformer 17, this current acts so as to cancel the short-circuit current of the negative arm and the direction of the alternating current is changed. This is because in the opposite case, the alternating current operates so as to cancel the short circuit current of the positive arm.

From the result of FIG. 7, the direction of the alternating current at the time when any one of the current detectors 13a, 14a, 22a and 23 detects the overcurrent and the direction of the alternating current is explained above. In this way, if the arm with the smaller short-circuit current is selected and the gate is blocked preferentially from this one, the breaking current of the arm is almost the same value as the DC short-circuit current is.

In the worst condition that the short circuit current of the arm does not fall below the value of the DC short circuit current is (No. in FIG. 6).
7, No. 9, No. 10, No. 14 to No. 16)
As the value of the alternating current superposed on the value of the direct-current short-circuit current is, it is only necessary to consider the minimum value of the three-phase currents.

Therefore, according to this embodiment, it is not necessary to consider the maximum value of the alternating current as the set value of the home current detection level of the current detectors 13a, 14a, 22a, 23, unlike the prior art. As a result, the overcurrent withstand capability of the converter can be increased.

As described above, if the current is cut off by one of the arms of the arm pair, the short-circuited state has already been avoided, and the current cutoff for the remaining arms is as follows. No particular urgency is required.

Therefore, in this embodiment, the delay circuit 5 is provided as shown in FIG. 1 so that the remaining arms are gate-blocked. This point will be described below. That is, when a signal is output from any one of the AND circuits 2a to 2f, the delay circuit 5 is delayed by a certain time from this signal and OR circuits 4a to 4f.
Are supplied to all the arms, and thereby all the arms are made to output the gate block signal.

Therefore, if the delay time of the delay circuit 5 is set to a value required for each arm to interrupt the current, the current direction detectors 3a to 3c and the AND circuit 2 are first gate-blocked. After the other arm cuts off the current, the gate block signals of the remaining arms are output, and the converter 12 can be stopped without any problem even if a short circuit occurs.

FIG. 1 shows another embodiment of the present invention.
4 will be described. In the embodiment of FIG. 14, the converter 12
In order to detect the current on the DC side of, the charging / discharging current of the smoothing capacitor 11 is detected by the current detector 15 as in the prior art described with reference to FIG. Same as the embodiment.

As is clear from the circuit configuration, the converter 12
When a short circuit occurs in the arm of the above, the short-circuit current from the DC side is the sum of the current supplied from the DC power supply 10 and the discharge current supplied from the smoothing capacitor 11, so that the short-circuit from the DC side at this time occurs. As a method of detecting the current,
As in the embodiment of FIG. 1, the method of detecting by the current transformer 22 is the most accurate detection method.

However, the DC power supply 10 is often made by rectifying an AC power supply, and in this case, the output impedance is considerably large. In addition, in many cases, it is installed away from the converter 12, and at this time, the impedance due to the wiring becomes considerably large. Therefore, most of the DC short circuit current at the time of arm short circuit is due to the discharge current from the smoothing capacitor 11. Therefore, the short-circuit current from the DC side is often substantially equivalent to the discharge current from the smoothing capacitor 11. Therefore, according to the embodiment of FIG. 14 as well, it is possible to detect the overcurrent on the DC side with sufficient accuracy, and the same effect as that of the embodiment of FIG. 1 can be obtained.

[0057]

According to the present invention, the overcurrent at the time of arm short circuit of the converter is surely cut off within the current cutoff capacity of the switching element without increasing the number of detectors for overcurrent detection. Therefore, it is possible to sufficiently prevent the breakdown of the switching element due to overcurrent at low cost.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an overcurrent protection device according to the present invention.

FIG. 2 is a block diagram showing an example of a conventional technique of an overcurrent protection device.

FIG. 3 is a block diagram showing another example of the conventional art of the overcurrent protection device.

FIG. 4 is an explanatory diagram of arm short circuit.

FIG. 5 is an explanatory view showing ON / OFF states of arms of the converter with switches.

FIG. 6 is a mode diagram of a short circuit pattern for explaining the operation of one embodiment of the present invention.

FIG. 7 is a mode diagram of a short circuit pattern for explaining the operation of the embodiment of the present invention.

FIG. 8 is a mode diagram of a short circuit pattern for explaining the operation of the embodiment of the present invention.

FIG. 9 is a mode diagram of a short circuit pattern for explaining the operation of the embodiment of the present invention.

FIG. 10 is an explanatory diagram of a current value in each short circuit pattern mode.

FIG. 11 is an explanatory diagram of a current value in each short circuit pattern mode.

FIG. 12 is an explanatory diagram of a current value in each short circuit pattern mode.

FIG. 13 is an explanatory diagram of a current value in each short circuit pattern mode.

FIG. 14 is a block diagram showing another embodiment of the overcurrent protection device according to the present invention.

[Explanation of symbols]

 10 DC power supply 11 Smoothing capacitor 12 Converter 13, 14, 22 Current transformer 16 Circuit breaker 17 Transformer 19a-19f Arm 21 Power system 24 Adder 22a, 13a, 14a, 23 Current detector 1 OR circuit (OR Logic circuit) 3a, 3b, 3c Current direction detector 2a to 2f AND circuit (AND logic circuit) 5 Delay circuit 4a to 4f OR circuit (OR logic circuit)

Claims (1)

[Claims] 1. A plurality of arm pairs made up of a series circuit of a switching element forming a positive side arm and a switching element forming a negative side arm are provided between DC terminals, and the positive side arm and the negative side of each arm pair are provided. In the voltage-type power converter in which the connection point of the arm is connected to the AC terminal, the current direction detection means for detecting the flow direction of the current flowing between the connection point and the AC terminal, and at the time when the arm short circuit occurs, Depending on the detection result of the current direction detecting means, among the arms on the positive electrode side and the negative electrode side,
An overcurrent protection device characterized in that arithmetic means for selecting one of the arms having a smaller flowing current is provided, and the arm selected by the arithmetic means is preferentially gate-blocked.