CN112736879A

CN112736879A - Direct current fault rapid on-off circuit based on matching of current limiter and circuit breaker

Info

Publication number: CN112736879A
Application number: CN202011509071.6A
Authority: CN
Inventors: 唐诵; 陈敏; 贾冠龙; 张成浩; 朱冠南
Original assignee: Zhejiang University ZJU
Current assignee: Zhejiang University ZJU
Priority date: 2020-12-18
Filing date: 2020-12-18
Publication date: 2021-04-30
Anticipated expiration: 2040-12-18
Also published as: CN112736879B

Abstract

The invention relates to the field of power electronics, and aims to provide a direct-current fault rapid on-off circuit based on the matching of a current limiter and a circuit breaker. The fault current limiter and the direct current breaker are connected in series in a direct current circuit system; the fault current limiter is formed by connecting a main branch and an auxiliary branch in parallel; the second thyristor valve group and the third thyristor valve group are reversely connected in parallel in the main branch circuit and then are connected in series with the auxiliary capacitor, and then are connected in parallel with the current-limiting inductor and the fourth thyristor valve group to form the main branch circuit, and the direction of the fourth thyristor valve group is the same as the fault current direction; in the auxiliary branch, an ultra-fast mechanical switch and an auxiliary through-current switch are connected in series. The auxiliary through-flow switch is composed of IGBT valve groups connected in series. The invention provides extra back pressure for the switching-on and switching-off process by utilizing the auxiliary capacitor charged in the switching-on process of the fault current limiter. The inductor can limit the rise of fault current and realize the rapid transfer of inductor energy. The fault on-off speed is accelerated, the direct current fault protection time is effectively shortened, and the operation reliability of a power grid is improved.

Description

Direct current fault rapid on-off circuit based on matching of current limiter and circuit breaker

Technical Field

The invention belongs to the field of power electronics, and particularly relates to a fault current limiter and a direct-current fault rapid on-off circuit based on the matching of the current limiter and a circuit breaker.

Background

After flexible direct current transmission technology (VSC-HVDC) appeared, the construction of flexible direct current grids has gradually become a new development direction in the power industry. After research and development for more than 10 years, a Voltage Source Converter (VSC) has been widely used in occasions such as asynchronous grid interconnection, distributed energy access, island power supply and the like, and has become the foundation and core of a flexible direct-current grid technology. Nowadays, a Modular Multilevel Converter (MMC) is used in a plurality of flexible direct current power grid projects at home and abroad, and becomes the most valuable topology in the field.

In a flexible dc network consisting of MMC converter stations, how to cope with short-circuit faults occurring on the dc side (including monopolar grounding and bipolar short-circuit) is a major problem in the current applications: on one hand, the direct current power grid fault and the alternating current power grid fault are different, and the fault current does not have a zero crossing point, so that the alternating current circuit breaker with mature technology cannot be directly applied to the direct current fault; on the other hand, the rising speed of the fault current of the direct-current power grid is greatly higher than that of the alternating-current power grid, so that the requirement on the on-off capacity of the direct-current circuit breaker is high, in order to reduce the current on-off requirement on the direct-current circuit breaker, researchers provide various inductance type fault current limiter topologies, and after the fault occurs, the current limiting inductance is connected into a fault line in series, so that the rising rate of the fault current is restrained, and the on-off requirement of the direct-current circuit breaker is reduced.

However, the series connection of the current-limiting inductor into the line increases the system impedance, thereby slowing down the fault current cut-off speed, and may result in an excessively long fault protection time. Therefore, the research on the fault current quick cut-off circuit under the input of the fault current limiter has important significance for shortening the protection time of the high-voltage direct-current power grid and improving the operation reliability of the power grid.

Disclosure of Invention

The invention aims to solve the technical problem of overcoming the defects in the prior art and provides a direct current fault rapid on-off circuit based on the matching of a current limiter and a circuit breaker.

In order to solve the technical problem, the solution of the invention is as follows:

the fault current limiter for DC fault fast cut-off circuit consists of parallel main branch and parallel auxiliary branch; in the main branch circuit, the second thyristor valve group T2 and the third thyristor valve group T3 are reversely connected in parallel and then are connected in series with the auxiliary capacitor C, and then are connected in parallel with the current-limiting inductor L and the fourth thyristor valve group T4 to form the main branch circuit, and the direction of the fourth thyristor valve group T4 is the same as the fault current direction; in the auxiliary branch, an ultrafast mechanical switch UFD and an auxiliary through-flow switch LCS are connected in series.

In the invention, the auxiliary circulating switch LCS is composed of an IGBT valve bank T1 connected in series.

The invention further provides a direct current fault rapid on-off circuit based on the matching of the current limiter and the circuit breaker, and the fault current limiter and the direct current circuit breaker are connected in series in a direct current circuit system.

In the invention, the direct current circuit system comprises a direct current voltage source and uses an equivalent inductance L_dcAnd an equivalent resistance R_dcAnd is connected in series to form a single-ended direct current equivalent circuit system.

In the invention, the direct current breaker is a hybrid direct current breaker which is put into based on MOA, or a hybrid direct current breaker which uses an auxiliary capacitor to put into a current-limiting inductor.

Description of the inventive principles:

the fault current limiter used in the invention is an inductive current limiter and comprises an auxiliary capacitor and other switching devices for assisting the input of the current limiting inductor. By placing a current limiter in series with a circuit breaker in the fault line, fault current interruption is achieved by means of a series MOV into the fault line. Besides the reverse voltage provided by the direct current breaker, the current limiter can also provide partial reverse voltage, so that the fault breaking speed is accelerated.

Therefore, in the equivalent circuit of the current limiting process, the auxiliary capacitor is connected in parallel with the current limiting inductor, and with the input of the current limiting inductor, the voltage of the auxiliary capacitor continuously rises until the current of the auxiliary capacitor is zero, the branch circuit where the capacitor is located is turned off, and the fault current is completely transferred to the branch circuit where the current limiting inductor is located. In the fault breaking stage, the direct current breaker connects the MOV into the fault line in series, at the moment, the equivalent circuit of the fault current limiter is that an auxiliary capacitor is connected with an inductor in parallel, and the initial voltage direction of the capacitor is the same as the counter voltage direction provided by the MOV. After the current of the fault line is completely cut off, the capacitor and the inductor in the fault current limiter are kept in parallel connection, the energy stored by the inductor is transferred to the capacitor until the current of the loop crosses zero, the loop is cut off by the semiconductor switching device, and the cut-off process is completely finished.

Compared with the prior art, the invention has the beneficial effects that:

the invention provides extra back pressure for the switching-on and switching-off process by utilizing the auxiliary capacitor charged in the switching-on process of the fault current limiter. The inductor can limit the rise of fault current and realize the rapid transfer of inductor energy. Therefore, the fault on-off speed is accelerated, the direct current fault protection time can be effectively shortened, and the operation reliability of a power grid system is improved.

Drawings

Fig. 1 illustrates an ABB hybrid circuit breaker topology used in the present method example;

FIG. 2 is a circuit diagram of a single-ended DC system used in an example of the present method;

FIG. 3 is a single-ended DC system equivalent circuit during the process of the method;

fig. 4 is a comparison of fault current waveforms for the present method versus other methods.

Detailed Description

An embodiment of the present invention will be described with reference to the accompanying drawings. It should be noted that the method is applicable to all the hybrid dc circuit breakers based on the MOA input and the hybrid dc circuit breakers using the auxiliary capacitor input current limiting inductor, and the embodiments are described herein for better utilizing and implementing the present invention by those skilled in the art, and the scope of the present invention is not limited to the examples.

Fig. 1 shows a hybrid dc circuit breaker product sold by ABB corporation, which is formed by connecting an auxiliary branch and a main branch in parallel, wherein the auxiliary branch is formed by connecting an ultra fast mechanical switch ufd (ultra fast disconnect) and an auxiliary current switch lcs (load communication switch) in series, and the main branch is formed by connecting an IGBT valve bank T2 in parallel with a metal oxide arrester MOA. The basic working principle of the product is as follows: when the circuit works normally, current flows through the auxiliary branch circuit; when a fault occurs, the T2 valve bank is turned on, the LCS is turned off, and fault current is transferred from the auxiliary branch to the main branch. And after the current of the auxiliary branch passes zero, switching on and switching off the UFD. After about 2ms, the UFD reaches the rated opening distance, at which time the T2 valve set is turned off, i.e., the MOA is put into the fault line. The nonlinear current-voltage characteristic of the MOA enables the MOA to present back pressure in a line, and therefore fault current is cut off.

FIG. 2 is a circuit diagram of a single-ended DC system using an exemplary method using a DC voltage source and an equivalent inductance L_dcAnd an equivalent resistance R_dcThe single-ended direct current equivalent system is shown, and a fault current limiter and a direct current breaker are connected in series in a line. The hybrid inductive fault current limiter topology shown in fig. 2 is also composed of an auxiliary branch and a main branch connected in parallel. The structure of the auxiliary branch is similar to that of fig. 1, and is not described herein again. The main branch of the fault current limiter is composed of a current-limiting inductor L, an auxiliary capacitor C and a thyristor valve group T2-T4, and the capacitor C is precharged. When a fault occurs, firstly, a T4 valve group is switched on, an LCS is switched off, fault current is transferred to a main branch, and after the current of an auxiliary branch crosses zero, the UFD is switched on. After about 2ms, the UFD reaches the nominal open distance, which turns on to the T2 valve bank, providing a back pressure to T4 for a period of time through the T2 valve bank due to the pre-charge of capacitor C, and removing the T4 turn on signal. After the T4 valve bank is closed, the auxiliary capacitor and the current-limiting inductor are equivalently connected in parallel and then connected in series into a fault line. The inductor current rises smoothly and the capacitor forward voltage also rises continuously. When the capacitor current passes through zero, the forward voltage reaches the peak value, at the moment, the T2 valve group conducting signal is removed, the T2 valve group is naturally turned off, the current-limiting inductor is considered to be completely put into a line, the fault current starts to be inhibited from rising, and the auxiliary capacitor C is positively charged to a high voltage peak value.

As shown in fig. 3, when the dc circuit breaker is put into the MOA, the thyristor valve block T3 is turned on, so that the capacitor and the inductor are equivalent to be connected in parallel and then connected in series to the fault line. Because the capacitor is positively charged in the current limiting process, the back voltage in the same direction as the voltage of the direct current breaker is presented in a fault line at the moment, so that the reduction speed of the fault current is accelerated, and the fault clearing speed is finally accelerated.

Except for the quick on-off circuit, after the fault current limiter is completely put into a line, the current main on-off circuit is a direct current breaker to be directly switched off, or a current limiting inductor is temporarily bypassed by the current limiter and is switched off by the direct current breaker. The invention carries out simulation comparison on the fault current waveforms under the three open-close circuits without using the fault current limiter and after using the fault current limiter. Four curves 1-4 in fig. 4 represent fault current waveforms under four working conditions, where curve 1 is a curve that is opened and closed only by using a dc circuit breaker, curve 2 is a curve that is opened and closed by using a dc circuit breaker after a current limiting inductor is retained in a fault loop after a fault current limiter is limited, curve 3 is a curve that is opened and closed by using a dc circuit breaker after a current limiting inductor is bypassed, and curve 4 is a curve that is opened and closed by using a current limiter and a dc circuit breaker after a current limiting is limited by a fault current limiter. It can be seen from the figure that the fault open current can be reduced from 14.3kA to 6.9kA based on the use of a fault current limiter. When a direct current breaker is used for directly breaking a fault line after the current limiter is put into use, the fault breaking time is 4ms, when the current limiter is used for bypassing and then breaking, the fault breaking time is 2ms, and the breaking time of the method is 1 ms. The comparison shows that the method can greatly accelerate the fault on-off speed under the condition that the fault current limiter is put into use, thereby shortening the protection time and improving the operation reliability of the system.

Generally, the novel fault on-off circuit based on the matching of the current limiter and the circuit breaker can greatly accelerate the fault on-off speed under the condition that the current limiting inductor is put into a line, thereby shortening the fault protection time and improving the operation reliability of a system.

Claims

1. A fault current limiter for a direct current fault quick cut-off circuit is characterized by being formed by connecting a main branch and an auxiliary branch in parallel; wherein the content of the first and second substances,

in the main branch, the second thyristor valve group T2 and the third thyristor valve group T3 are reversely connected in parallel and then are connected in series with the auxiliary capacitor C, and then are connected in parallel with the current-limiting inductor L and the fourth thyristor valve group T4 to form a main branch, and the direction of the fourth thyristor valve group T4 is the same as the fault current direction;

in the auxiliary branch, the ultrafast mechanical switch UFD is connected in series with the auxiliary through-flow switch LCS.

2. A fault current limiter according to claim 1, characterized in that the auxiliary current passing switch LCS is constituted by a series IGBT valve bank T1.

3. A dc fault fast open/close circuit based on the cooperation of a current limiter and a circuit breaker, characterized in that the fault current limiter and the dc circuit breaker of claim 1 are connected in series in a dc circuit system.

4. The dc fault fast disconnect circuit of claim 3, wherein the dc circuitry comprises a dc voltage source and has an equivalent inductance L_dcAnd an equivalent resistance R_dcAnd is connected in series to form a single-ended direct current equivalent circuit system.

5. The direct current fault fast open circuit of claim 3, characterized in that the direct current breaker is a hybrid direct current breaker based on MOA investment or a hybrid direct current breaker using auxiliary capacitance investment current limiting inductance.