KR102611989B1 - Converter having protection device for protecting power semiconductor - Google Patents

Abstract

The present invention relates to a converter, and more specifically, to a converter equipped with a power semiconductor device protection circuit.
The present invention is a converter having an AC input terminal connected to an AC power source (111, 112, 113), a DC output terminal that outputs DC power, and a plurality of power semiconductor elements, and when the DC output terminal is short-circuited, the power Disclosed is a converter that includes a protection circuit unit 300 that diverts a portion of the short-circuit current generated when the DC output terminal is short-circuited so that a current smaller than the rated current flows through the semiconductor device.

Description

Converter having protection device for protecting power semiconductor}

The present invention relates to a converter, and more specifically, to a converter equipped with a power semiconductor device protection circuit.

The HVDC (High Voltage Direct Current) system is a power system that converts alternating current power into direct current and transmits power efficiently and safely. There has been a lot of discussion about direct current and alternating current in power transmission for a long time, but until recently, it was easy to convert to an appropriate voltage size and it was relatively easy to protect the power system by blocking the fault current in the event of an accident, so the frequency of 50Hz or 60Hz was used. The exchange method with is mainly used.

However, recently, there is a limit distance for undergrounding (20-30 km) due to charging capacity, which is a technical limitation of the alternating current (HVAC) method, and problems such as harmfulness to the human body due to electromagnetic wave emissions and large-scale transmission tower problems due to high peak voltage have been highlighted. Interest in power transmission (HVDC) is increasing.

Compared to the existing HVAC method, the HVDC method has advantages such as long-distance large power transmission, loss reduction, power flow control, and improved system reliability by preventing failure propagation. In particular, long-distance underground transmission is possible without restrictions on the transmission distance (ultra-high-voltage, high-capacity (765kV) underground transmission network is possible), and flexible transmission line construction that mixes overhead and underground is possible.

Meanwhile, direct current transmission improves transmission efficiency by reducing alternating current losses, and enables system division, which improves system reliability through effects such as prevention of accident spread and suppression of short-circuit current. In addition, since the voltage and current are constant, there is theoretically no problem with the influence of electromagnetic fields, so it can be an alternative to resolving conflicts with local residents that arise during the construction of transmission lines, and can be used for capacity expansion in large urban centers. Since direct current has no frequency, it can solve the problem of linking heterogeneous frequency power grids, and it is predicted that the demand for HVDC systems will increase as a Supper-Grid means of linking power systems between countries.

In addition, in terms of facilities and costs, the initial investment cost of the high-voltage direct current (HVDC) transmission method is greater than that of the high-voltage alternating current transmission method, but research results show that it is economical in cases where submarine underground cables of more than 40 km are required and in the case of long-distance transmission of more than 400 km. . From an OHL (Over-Head Line) perspective, the direct current transmission method requires less space and is less expensive than the alternating current transmission method.

Meanwhile, HVDC systems can be largely divided into current type (Line Commutated Converter, LCC) HVDC and voltage type (Voltage Source Converter, VSC) HVDC depending on the power semiconductor device. The composition of current-type HVDC using the thyristor power semiconductor device, which has been developed and commercialized since 1970 as a first-generation power conversion device, consists of a converter, smoothing reactor, harmonic filter, electrode, DC line, AC circuit breaker, and reactive power source. It consists of a harmonic filter and a parallel capacitor or reactive power compensation facility to supply harmonics generated by the converter and reactive power absorbed. In addition, it consists of an electrode for grounding and an AC circuit breaker to distinguish between a healthy section and an accident section in the event of an AC accident.

On the other hand, a voltage-type HVDC system using IGBT (Insulated-Gate Bipolar Transistor), a second-generation semiconductor, consists of a converter station, transformer, AC filter, phase reactor, capacitor, DC breaker, and DC cable. Two converter stations consist of IGBT-based voltage converters. One converter station operates as a rectifier, and the other operates as an inverter. The two converter stations are connected by DC cables and can be controlled independently from each other.

Recently, due to the continuous increase in demand for HVDC, discussions on HVDC Grid configuration are actively underway, and the demand for voltage-type HVDC is increasing due to advantages such as installation area and voltage control.

Meanwhile, the converter used in the voltage-type HVDC system has an input terminal to which AC voltage is applied and an output terminal to output DC voltage.

However, if a DC short circuit occurs at the DC output terminal, overcurrent may flow and damage or destroy the power semiconductor device. To prevent this, the converter is equipped with a circuit breaker at the AC input terminal.

However, there is still a problem that it takes a certain amount of time to detect a DC short circuit and to operate the circuit breaker according to the short circuit detection, and that overcurrent may flow before the circuit breaker operates, damaging or destroying the power semiconductor device.

Accordingly, a method such as Patent Document 1 is proposed to solve the problem of damage or destruction to power semiconductor devices due to overcurrent flowing before the circuit breaker operates.

The DC short circuit protection method presented in Patent Document 1 is as follows.

As shown in Figure 1, when a DC short circuit occurs between + and - of the DC output terminals expressed as p and n in the voltage type converter, the reference numeral between the AC power system 7 and the power semiconductor device 12 As shown in Figure 10, a closed circuit is formed and the short-circuit current increases.

In FIG. 1, reference numerals 6a, 6b, and 6c indicate leakage impedance of a transformer (not shown) and the leakage impedance of the AC power system 7. Additionally, in FIG. 1, reference numerals 2a, 2b, and 2c indicate phase modules corresponding to each phase. In addition, reference numeral 3 in FIG. 1 indicates a contact point of the transformer and each phase module (2a, 2b, and 2c).

When the short-circuit current exceeds the preset rating of the power semiconductor switch, all controllable power semiconductor devices 12 are turned off. However, a short circuit continues to occur through the controllable power semiconductor device 12 and the diode 13 connected in anti-parallel, and the short circuit current continues to increase.

This phenomenon continues until the circuit breaker 8 performs a blocking operation. In general, the operating speed of the AC breaker 8 is slow at tens to hundreds of msec, and the short-circuit current increases faster than the operating speed of the breaker 8 by the circuit constant, so the diode 13 connected in anti-parallel is burned out. In general, since the controllable power semiconductor device 12 and the diode 13 connected in anti-parallel are manufactured as one package, both power semiconductor devices 12 and 13 are burned out.

In order to protect the diode (13) connected in anti-parallel until the circuit breaker (8) operates, the freewheeling diode (20) or thyristor (22) is connected in parallel to the lower switch of the submodule (15) so that the large current is DC. In the event of a short circuit, the power semiconductor devices 12 and 13 are protected by flowing through the diode 20 or thyristor 22.

Meanwhile, FIG. 3 is a diagram illustrating an example of each phase module 2a, 2b, and 2c in more detail, and the reactor 14 can be used not only for controlling circulating current but also for limiting short-circuit current.

And the reactor (9) installed at the DC output terminal can be used to limit short-circuit current, and the transformer leakage reactance components (6a, 6b and 6c) can also be used to limit short-circuit current.

However, the DC short circuit protection method shown in Patent Document 1 has the following disadvantages.

First, as shown in Figures 2 and 3, it has the disadvantage that it can only be applied to a half bridge submodule structure and cannot be applied to other voltage type converters.

Also, as shown in FIG. 3, when using the thyristor 22, a gate driving circuit is required, which has the disadvantage of requiring as many driving circuits as the number of thyristors 22.

Additionally, since a large reactor is used to limit the short-circuit current during a short-circuit, it has the disadvantage of causing loss due to the short-circuit reactor component during normal operation.

In order to solve the above problems, the purpose of the present invention is to provide a converter equipped with a power semiconductor device protection circuit that can protect the power semiconductor device from DC short circuit without power loss.

The present invention was created to achieve the object of the present invention as described above, and the present invention includes an AC input terminal connected to the AC power source (111, 112, 113), a DC output terminal that outputs DC power, and a plurality of devices. A converter including power semiconductor devices, wherein when the DC output terminal is short-circuited, a protection circuit unit 300 that diverts a portion of the short-circuit current generated when the DC output terminal is short-circuited so that a current smaller than the rated current flows through the power semiconductor device. Disclosed is a converter comprising:

The converter equipped with the power semiconductor device protection circuit according to the present invention includes a protection circuit unit that diverts part of the short-circuit current generated when the DC output terminal is short-circuited so that a current smaller than the rated current flows through the power semiconductor device when the DC output terminal is short-circuited. By including (300), there is an advantage in that the power semiconductor device can be protected from DC short circuit without power loss.

In particular, the converter equipped with the power semiconductor device protection circuit according to the present invention is configured to allow current to flow only during a DC short circuit, compared to the protection method presented in Patent Document 1, where current flows even during normal operation and power loss occurs. There is an advantage in that it can be minimized.

Specifically, in the prior art of Patent Document 1, the protection circuit in the submodule is located on the phase or valve as shown in Figures 1 to 3, and current flows in the reactor that limits the short-circuit current even under normal conditions, whereas in the case of the present invention, in the event of a short-circuit, the current flows. Current flows only through

Therefore, in the prior art of Patent Document 1, current flows in a reactor that limits short-circuit current even under normal conditions, whereas in the present invention, current flows only during a short-circuit, thereby reducing reactive power loss.

In addition, the prior art in Patent Document 1 requires a gate driving circuit for each submodule, but the present invention can reduce the driving circuit by using a thyristor with a large capacity.

Meanwhile, the voltage rating can be selected according to the AC voltage applied to the actual thyristor applied according to the present invention.

1 is a conceptual diagram showing an example of the prior art.
FIG. 2 is a circuit diagram showing an example of a phase module in the circuit diagram of FIG. 1.
FIG. 3 is a conceptual diagram showing a so-called MMC module in which a plurality of submodules are installed in series as an example of a phase module in the circuit diagram of FIG. 1.
FIG. 4 is an equivalent circuit diagram showing submodules constituting the phase module shown in FIG. 3 in which a diode is connected in parallel with a freewheeling diode.
FIG. 5 is an equivalent circuit diagram showing submodules constituting the phase module shown in FIG. 3 in which a thyristor is connected in parallel with a freewheeling diode.
6A to 6G are conceptual diagrams showing embodiments of a converter equipped with a power semiconductor device protection circuit according to the present invention.
FIGS. 7A to 7D are conceptual diagrams showing definitions of symbols shown in FIGS. 6A to 6G.
FIGS. 8A and 8B are conceptual diagrams showing examples of submodules SM1 to SM N shown in FIG. 7A.
FIG. 9 is a conceptual diagram showing definitions of the symbols shown in FIGS. 8A and 8B.
FIG. 10 is a conceptual diagram showing the flow of current in the circuit diagram shown in FIG. 6A.

Hereinafter, a converter equipped with a power semiconductor device protection circuit according to the present invention will be described with reference to the attached drawings.

The converter equipped with the power semiconductor device protection circuit according to the present invention, as shown in FIGS. 6A to 10, has an AC input terminal connected to the AC power source (111, 112, 113), and a DC output terminal that outputs DC power. and a converter including a plurality of power semiconductor elements, a protection circuit unit (300) that diverts a portion of the short-circuit current generated when the DC output terminal is short-circuited so that a current smaller than the rated current flows through the power semiconductor device when the DC output terminal is short-circuited. ) is characterized in that it includes.

A converter equipped with a power semiconductor device protection circuit according to the present invention can be applied to a voltage type converter in which IGBT, IGCT, GTO, etc. can be used.

The protection circuit unit 300 bypasses part of the short-circuit current generated when the DC output terminal is short-circuited so that a current smaller than the rated current (red line in FIG. 10) flows to the power semiconductor device when the DC output terminal is short-circuited (FIG. 10). (blue line), various embodiments are possible as shown in FIGS. 6A to 6F depending on the circuit configuration of the converter.

As an example, the protection circuit unit 300 may be controlled by a control unit and one or more thyristors having a preset impedance value may be used.

In particular, the protection circuit unit 300 preferably has a plurality of thyristors installed in series, and depending on the circuit configuration, as shown in FIG. 10, a pair of thyristor groups connected in parallel in the forward and reverse directions is one. It may consist of the above.

Meanwhile, the present invention is to prevent the power semiconductor elements constituting the converter from being damaged due to the short-circuit current that increases before the circuit breaker (131, 132, 133) operates when a short circuit occurs at both DC ends of the voltage-type converter. A protection circuit consisting of a thyristor is used as shown in FIGS. 6A to 6G.

As shown in Figure 10, when a short circuit occurs, a red closed circuit is generated, and when the short circuit current is detected and the thyristor is turned on, a blue closed circuit is generated. Considering the impedance of the two circuits, the red circuit is limited to within the rated current, and other currents flow through the blue closed circuit to protect the voltage converter.

Meanwhile, the protection circuit proposed according to the present invention can be used not only in the MMC structure but also in other voltage type converters.

Hereinafter, various embodiments according to the circuit configuration of the converter and the combination of the protection circuit unit 300 will be illustrated.

Figure 6a is a circuit diagram according to the first embodiment of the present invention and shows an example applied to MMC for HVDC.

Figure 6b is a circuit diagram according to the second embodiment of the present invention and shows an example applied to MMC for HVDC.

Figure 6c is a circuit diagram according to the third embodiment of the present invention and shows an example applied to MMC for HVDC.

Figure 6d is a circuit diagram according to the fourth embodiment of the present invention and shows an example applied to MMC for HVDC.

Figure 6e is a circuit diagram according to the fifth embodiment of the present invention and shows an example applied to MMC for HVDC.

Figure 6f is a circuit diagram according to the sixth embodiment of the present invention, applied to a two-level voltage type converter, and shows an example in which a protection circuit is connected between a pair of power semiconductor devices.

Figure 6g is a circuit diagram according to the seventh embodiment of the present invention and shows an example applied to the 3-level case of diode clamped MMC.

Meanwhile, FIG. 7A is a circuit diagram showing examples of the portion indicated by 710 among the symbols shown in FIGS. 6A to 6E.

FIG. 7B is a circuit diagram of the rectangle indicated in black among the symbols shown in FIGS. 6A to 6G. For reference, Figure 7b shows a coil and a line as an equivalent circuit.

7C and 7D show examples of the protection circuit unit 300 according to the present invention as shown in FIGS. 6A to 6G, and various embodiments are possible depending on the connection position with other circuits and the structure of other circuits. Meanwhile, in FIGS. 6B and 6D, the portion of the protection circuit unit 300 that is not connected to other circuits refers to ground.

FIG. 9 is a conceptual diagram showing the definitions of the symbols shown in FIGS. 8A and 8B, and is an equivalent circuit of a line made of a coil and a resistance.

Since the above is only a description of some of the preferred embodiments that can be implemented by the present invention, as is well known, the scope of the present invention should not be construed as limited to the above embodiments, and the scope of the present invention described above Both the technical idea and the technical idea underlying it will be said to be included in the scope of the present invention.

Claims (7)

A converter having an AC input terminal connected to the AC power source (111, 112, 113), a DC output terminal that outputs DC power, and a plurality of power semiconductor elements,
It includes a protection circuit unit 300 that diverts a portion of the short-circuit current generated when the DC output terminal is short-circuited so that a current smaller than the rated current flows to the power semiconductor device when the DC output terminal is short-circuited,
The converter including the plurality of power semiconductor elements is a voltage type converter,
The AC power (111, 112, 113) is a three-phase AC power,
The AC input terminal is provided in three pieces corresponding to each phase of the AC power source (111, 112, 113),
The converter is each connected to the three AC input terminals and includes a plurality of submodules connected in series to three legs consisting of an upper arm and a lower arm,
The protection circuit unit 300 includes a plurality of thyristors connected to the three legs to form a closed circuit that does not pass through the plurality of submodules when the DC output terminal is short-circuited,
The protection circuit unit 300,
The thyristors connected to each of the three legs are connected to each other electrically to form a closed circuit that does not pass through a plurality of submodules when the DC output terminal is short-circuited,
A control unit that detects the short-circuit current and turns on the thyristor to allow a portion of the short-circuit current to flow along a closed circuit passing through the thyristor, thereby limiting the current passing through the power semiconductor elements to within the rated current when the DC output terminal is short-circuited. A converter comprising: delete In claim 1,
The protection circuit unit 300 is a converter characterized in that it includes one or more thyristors having a preset impedance value. In claim 1,
The protection circuit unit 300 is a converter characterized in that it includes one or more pairs of thyristor groups connected in parallel in forward and reverse directions. delete delete delete

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