A current-limiting hybrid dc circuit breaker based on coupled inductors

Abstract

The application provides a current-limiting hybrid DC circuit breaker based on coupled inductance, and relates to the field of power electronics. The circuit breaker is composed of a main branch and an auxiliary branch in parallel, the main branch is composed of a high-speed mechanical switch and an IGBT valve group, and the auxiliary branch is composed of a thyristor and a diode valve group to form a bridge circuit to realize bidirectional current breaking, and the bridge circuit is internally composed of a current-limiting breaking part and a self-charging part. The application realizes the suppression of fault current by using the thyristor and the capacitor to cooperate with each other to realize the fast switching of the primary winding of the coupled inductor, and can realize breaking after current limiting or resuming normal operation according to the fault detection result through the coupling effect of the coupled inductor. In addition, the application can also directly break small current without current limiting and complete capacitor self-charging by using a DC system. The application has obvious current-limiting effect, effectively reduces the number of IGBTs, reduces the control difficulty and cost, has reasonable design and high reliability, and has theoretical and significant engineering significance.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power electronics, and in particular to a current-limiting hybrid DC circuit breaker based on coupled inductors. BACKGROUND

[0002] High-voltage direct current (HVDC) transmission technology is a new generation of power transmission technology based on power electronic devices. It has been widely used in long-distance power transmission due to its irreplaceable advantages and is one of the important directions for the development and transformation of future power grids. However, the DC power grid has the characteristics of "low inertia and low impedance". When a short-circuit fault occurs on the DC side, the DC current rises rapidly. If the fault cannot be removed within a short time, it will affect the normal operation of the entire system. High-voltage direct current circuit breakers can remove short-circuit faults on the DC side and become a key device for building a reliable direct current transmission system. With the continuous increase of transmission distance, scale capacity and voltage level of the direct current power grid, the fault current rising rapidly puts higher requirements on the breaking capacity of the direct current circuit breaker. The lack of suitable high-voltage direct current circuit breakers has become one of the main limiting factors for the development of high-voltage direct current transmission technology.

[0003] Direct current circuit breakers can be divided into mechanical, solid-state and hybrid types. Mechanical circuit breakers have the advantages of small state loss and large load capacity, but the time to interrupt the current is too long. Solid-state circuit breakers can interrupt the current in a short time. However, due to the still high power consumption of solid-state circuit breakers under steady-state conditions, solid-state circuit breakers have not been widely used in high steady-state current applications. Hybrid circuit breakers can use a topology based on mechanical circuit breakers to handle steady-state currents connected to solid-state circuit breakers to perform current interruption, i.e., hybrid circuit breakers combine the economy of mechanical direct current circuit breakers and the reaction speed of solid-state direct current circuit breakers, have the advantages of low on-state loss, fast and controllable breaking, high reliability, etc., and have broad application prospects in direct current power grids.

[0004] Although great progress has been made in direct current circuit breaker technology in recent years, most of the research is still in some special small-capacity fields. The main problems are as follows: (1) It is difficult to quickly interrupt the direct current fault current. Since the impedance of the direct current system is small, when a short-circuit fault occurs, the short-circuit current will rise rapidly. For direct current circuit breakers, the existing power electronic devices have small capacity and cannot withstand rapid changes in voltage and current. (2) There are many series-connected power electronic devices. Hybrid circuit breakers can use fully controlled power electronic devices to interrupt the direct current circuit, but the voltage resistance of power electronic devices is limited, and the voltage sharing technology of fully controlled power electronic devices is difficult.

[0005] Therefore, it is an urgent problem for those skilled in the art to provide a current-limiting hybrid direct current circuit breaker based on coupled inductors that can solve the above technical problems. SUMMARY

[0006] Therefore, the technical problem to be solved by the present application is to overcome the shortcomings of the prior art, and to provide a current limiting type hybrid DC circuit breaker based on coupled inductance, which can solve the technical problems of high price, complex structure and low reliability of the current DC circuit breaker.

[0007] In the present application, a current limiting type hybrid DC circuit breaker based on coupled inductance is composed of a main branch and an auxiliary branch in parallel, wherein the auxiliary branch is composed of a bridge circuit composed of valve groups Q1, Q2, Q3 and Q4, the valve groups Q1, Q2, Q3 and Q4 are each composed of a plurality of thyristors and diodes connected in the same direction in series, the bridge circuit is internally composed of a current limiting breaking part and a self-charging part, one end of the current limiting breaking part and the self-charging part connected in parallel is connected to the common connection point of the valve groups Q1 and Q2, and the other end of the current limiting breaking part and the self-charging part connected in parallel is connected to the common connection point of the valve groups Q3 and Q4.

[0008] In the present application, the current limiting type hybrid DC circuit breaker based on coupled inductance is characterized in that the main branch is composed of a high-speed mechanical switch UFD and an IGBT valve group LCS; the IGBT valve group LCS is composed of a plurality of IGBT units connected in series, and each IGBT unit includes two IGBT modules connected in reverse.

[0009] In the present application, the current limiting type hybrid DC circuit breaker based on coupled inductance is characterized in that the current limiting breaking part in the auxiliary branch includes a coupled inductor L, auxiliary capacitors C1 and C2, thyristor valve groups T1, T2, T4 and T5, a diode valve group D1, and metal oxide arresters MOA1 and MOA2; the coupled inductor L is composed of a primary winding L1 and a secondary winding L2, and the terminal 1 of the primary winding L1 of the coupled inductor is connected to the terminal 2 of the secondary winding L2 of the coupled inductor; the thyristor valve group T1 and the metal oxide arrester MOA1 are connected in parallel, and are connected in parallel with the capacitor C1 and the thyristor valve group T2 in a series branch; the primary winding L1 of the coupled inductor and the thyristor valve group T4 are connected in series, and are connected in parallel with the capacitor C1 and the thyristor valve group T2 in a series branch, the metal oxide arrester MOA2 and the diode valve group D1 are connected in reverse parallel across the terminals of the primary winding L1 of the coupled inductor; the secondary winding L2 of the coupled inductor and the thyristor valve group T5 are connected in series, and the capacitor C2 is connected in parallel with the series branch of the secondary winding L2 of the coupled inductor and the thyristor valve group T5; the common connection point of the positive polarity terminal of the capacitor C2 and the secondary winding L2 of the coupled inductor is connected to the positive polarity terminal of the capacitor C3 of the self-charging part, and the common connection point of the negative polarity terminal of the capacitor Cx and the thyristor valve group T5 is connected to the thyristor valve group T6 of the self-charging part.

[0010] In the application, the self-charging part in the auxiliary branch comprises a capacitor C3, a thyristor valve group T3, T6, T7, T8, a resistor R and a grounding terminal; the thyristor valve group T3 is connected in antiparallel across the thyristor valve group T2 of the current-limiting breaking part; the thyristor valve group T8 is connected in antiparallel across the valve group Q4 of the bridge circuit; the capacitor C3, the thyristor valve group T7 and the resistor R are connected in series and grounded, and the other end of the capacitor C3 is connected with the positive polarity end of the capacitor C2 of the current-limiting breaking part; one end of the thyristor valve group T6 is connected with the common connection point of the thyristor valve group T5 and the capacitor C2 of the current-limiting breaking part, and the other end of the thyristor valve group T6 is connected with the common connection point of the thyristor valve group T7 and the resistor R.

[0011] Compared with the prior art, the application has the following beneficial effects:

[0012] 1. The main branch of the hybrid DC circuit breaker of the application is composed of a high-speed mechanical switch and an IGBT valve group, and has a small on-state loss; the auxiliary branch uses a semi-controlled device thyristor to replace a fully-controlled device IGBT, thereby reducing the control difficulty and system cost, and the design is reasonable, the cost is low, and the reliability is high.

[0013] 2. When overcurrent occurs in the power grid, the application can realize the transfer of fault current by using the cooperation of IGBT and thyristor, and then can realize the rapid switching of the primary winding of the coupling inductor by using the cooperation of thyristor and capacitor, so as to effectively suppress the fault current, and according to the fault detection result, the thyristor can cooperate with the secondary winding of the coupling inductor and the pre-charging capacitor to inject a counter-current pulse by the coupling effect of the coupling inductor and cooperate with the metal oxide surge arrester MOA to force the fault current to pass zero, so as to realize the removal of the fault line or the resumption of normal operation after current limiting, improve the breaking speed under the premise of not using IGBT, reduce the breaking current and the energy dissipation of MOA, and speed up the removal speed of the fault line.

[0014] 3. The application can also directly perform small-current breaking without current limiting, and can also use the DC system to complete capacitor self-charging to ensure the normal operation of the next operation. BRIEF DESCRIPTION OF DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope, and other related drawings can also be obtained by those skilled in the art without creative labor on the premise of not paying creative labor.

[0016] Figure 1is a topology diagram of a current-limiting hybrid DC circuit breaker based on coupled inductance;

[0017] Figure 2 is a schematic diagram of a DC circuit breaker energy release branch;

[0018] Figure 3 is a schematic diagram of the action process of three modes of the DC circuit breaker represented by a time axis;

[0019] Figure 4 is an equivalent circuit schematic diagram of a DC side of an MMC converter station equipped with a circuit breaker and a bipolar short circuit fault;

[0020] Figure 5 is a negative DC circuit breaker topology schematic diagram;

[0021] Figure 6 is a working timing diagram of the current-limiting breaking process of the DC circuit breaker topology;

[0022] Figure 7 is a working timing diagram of the current-limiting recovery process of the DC circuit breaker topology;

[0023] Figure 8 is a working timing diagram of the small current breaking process of the DC circuit breaker topology. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0025] Figure 1 is a topology diagram of a current-limiting hybrid DC circuit breaker based on coupled inductance, wherein the capacitors C1, C2 and C3 are both connected in parallel with the energy release branch as shown in Figure 2 . For ease of illustration, the action process at each time is as shown in Figure 3 . Considering that the DC system has positive and negative poles, the current-limiting breaking and current-limiting recovery processes of the hybrid DC circuit breaker topology installed in the positive pole ( Figure 1 ) will be described below taking the bipolar short circuit fault as an example. The actual installation mode of the DC circuit breaker in the system and the equivalent circuit after the fault are as shown in Figure 4 . The parameter design of the LC buffer current-limiting loop can be completed according to the equivalent circuit. Considering that the negative pole current direction of the DC system is opposite, since the self-charging needs to be completed by the DC system, the circuit breaker topology installed in the negative pole needs to be adjusted locally, as shown in Figure 5 . The action process of the negative pole circuit breaker topology is as shown in Figure 1The action process of the topologies shown in Figs. 1 and 2 is basically the same, and will not be described separately. In addition, Figure 1 and Figure 5 The positive direction of the capacitors C1, C2, and C3 marked in the figures is the positive direction of the pre-charge voltage.

[0026] Since the present application is a bidirectional hybrid DC circuit breaker, the current direction is taken as from left to right for description. Figure 1 The action process of the topologies shown in Figs. 1 and 2 is basically the same, and will not be described separately. In addition,

[0027] Embodiment 1: When a large overcurrent occurs in the system under certain conditions, but it is not determined whether to break immediately, the current limiting can be first put into operation, and then it is decided whether to break or restore the current. The working timing diagram of the current limiting breaking and current limiting recovery process in this embodiment is shown in Fig. 3. Figure 6 and Figure 7

[0028] (1) Self-charging process:

[0029] When the DC power grid is normally working, the UFD and the LCS are turned on, and the current flows through the main branch. The self-charging process is as follows:

[0030] Stage 1: At t=t0, the thyristor valve groups T3, T7, and T8 are triggered to be turned on, so that the DC system charges the capacitor C1, C3 is used to divide the voltage for C1, and the resistor R is used to limit the charging current. As the voltages of C1 and C3 gradually rise, the current flowing through the capacitors gradually decreases, until t=t1', the current decays to 0, and the charging of C1 is completed, and the thyristors are naturally turned off. Similarly, at t=t1', Q2 and T6 are triggered to be turned on, so that the system charges the capacitor C2, until t=t1, the self-charging stage is completed, and the thyristors are naturally turned off.

[0031] (2) Current limiting process:

[0032] When the DC system detects an overcurrent at t=t2, the current limiting breaking part needs to be put into operation to suppress the fault current. The specific action process is as follows:

[0033] Stage 2: After the self-charging process is completed, at t=t2, the thyristor valve groups Q1, Q4, and T1 are triggered to be turned on to form a current path. Then the LCS is turned off, and the overcurrent of the power grid is transferred to the auxiliary branch, during which the power grid current continues to rise. After the power grid current is transferred, the UFD starts to break, and the breaking of the UFD is completed in about 2 ms.

[0034] Stage 3: After the UFD is completely disconnected at t=t3, the thyristor valve group T2 is triggered to be turned on. The discharge of the capacitor C1 will cause the T1 valve group to bear a reverse voltage for a period of time and be turned off. At t=t4, the discharge of C1 is completed, at which time the thyristor valve group T4 is triggered to be turned on, C1 starts to be reversely charged and is connected in parallel with the primary winding L1 of the coupling inductor L, and L1 starts to put into current limiting. ​

[0035] Phase 4: At t=t5, the forward voltage of Cl rises to the peak value, the current of the branch where T2 is located is zero and naturally turns off, and the primary winding of L is fully put into current limiting.

[0036] (3) Breaking or recovery process after current limiting:

[0037] 1) Breaking after current limiting

[0038] At t=t6, the fault detection is completed, and if it is confirmed that the system has a fault and needs to cut off the fault current, the specific action process is as follows:

[0039] Phase 5: At t=t6, T5 is triggered to turn on, and capacitor C2 is discharged through the secondary winding 2-2' of coupling inductor L. At this time, the voltage on both sides of the primary winding 1-1' of L makes MOA1 enter the fault line to absorb energy, and the pulse current entering terminal 2 of coupling inductor L makes terminal 1 flow out the induced pulse current in the opposite direction of the fault current.

[0040] Phase 6: At t=t7, the induced current pulse forces the current i L1 of the branch where L1 and T4 are located to zero and turn off. At t=t8, MOA1 makes the fault current decay to zero, and the fault breaking is completed.

[0041] Phase 7: At t=t9, the pulse current i L2 of terminal 2 of coupling inductor L reaches the peak value and decreases, terminal 1' flows out the induced pulse current due to the coupling effect, the energy induced by the primary winding of coupling inductor L is consumed by MOA2, at t=t 10 , C2 is reversely charged to the peak value, the current i L2 of the secondary winding of L is zero, and then at t=t 11 , the energy of the primary winding of coupling inductor L is consumed to zero by MOA2. At this time, the breaking process after current limiting is completed.

[0042] 2) Recovery after current limiting

[0043] At t=t6, the fault detection is completed, and if it is confirmed that there is no fault in the line, the circuit breaker needs to be restored from the current limiting state to the normal state, and the specific action process is as follows:

[0044] Phase 5: At t=t6, UFD is closed.

[0045] Phase 6: At t=t7, after UFD is completely closed, LCS and thyristor valve group T5 are triggered to turn on, and the grid current is transferred back to the main branch from the auxiliary branch, and at t=t8, the main branch current is restored to the normal working current.

[0046] The action process of stage 7 is the same as the current-limiting and breaking process, and details are not repeated here. Thus far, the current-limiting and recovery process is completed.

[0047] (4) Energy dissipation process:

[0048] As shown in the figure, the energy dissipation branch is connected in parallel between C1 and C3 in the DC circuit breaker topology of the application. Figure 2 When t=t 12 , the switches of the three capacitor energy dissipation branches are closed, and the energy in C1 to C3 is dissipated through the energy dissipation resistor in the energy dissipation branch. When t=t 13 , the energy dissipation is completed, and the circuit breaker waits for the next action command.

[0049] Embodiment 2: When small current breaking is required in some cases, such as line maintenance, current limiting is not required. The working timing diagram of the small current breaking process in this embodiment is shown in the figure. Figure 8

[0050] (1) Self-charging process:

[0051] The self-charging action process of the capacitor in stage 1 in the small current breaking case is the same as the self-charging process in Embodiment 1, and details are not repeated here.

[0052] (2) Small current breaking process:

[0053] Stage 2: Under normal circumstances, the grid current flows through the UFD and the LCS.

[0054] Stage 3: When t=t2, small current breaking is required, Q1, Q4 and T1 valve group are triggered to conduct, and the LCS is turned off, so that the current is transferred to the auxiliary branch. After the current transfer is completed, the UFD starts to break.

[0055] Stage 4: When t=t3, the UFD breaking is completed, the thyristor valve group T2 is triggered to conduct, and the capacitor C1 discharges to make the T1 valve group bear a reverse voltage for a period of time and turn off. Then, C1 discharges and starts to reverse charge.

[0056] Stage 5: When t=t4, C1 is charged to the MOA1 action voltage, and the MOA1 is put into the line. When t=t5, the residual energy in the line is consumed by the MOA1, and the small current breaking is completed.

[0057] (3) Energy dissipation process:

[0058] As shown in the figure, the energy dissipation branch is connected in parallel between C1 and C3 in the DC circuit breaker topology of the application. Figure 2 When t=t6, the switches of the energy dissipation branches of C1 and C3 are closed, and the energy in C1 and C3 is dissipated through the energy dissipation resistor in the energy dissipation branch. When t=t7, the energy dissipation is completed, and the circuit breaker waits for the next action command. ​

[0059] Overall, the current-limiting hybrid DC circuit breaker based on coupled inductance proposed in the application can suppress the rising rate of the fault current due to the current-limiting effect of the coupled inductor, reduce the actual breaking current of the circuit breaker, accelerate the breaking speed, save the cost, and improve the performance of the hybrid DC circuit breaker.

[0060] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical range disclosed in the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A current-limiting hybrid DC circuit breaker based on coupled inductance, characterized by, The auxiliary branch is composed of a bridge circuit composed of valve groups Q1, Q2, Q3 and Q4, wherein each of the valve groups Q1, Q2, Q3 and Q4 is composed of several thyristors and diodes connected in the same direction in series, and the bridge circuit is internally composed of a current-limiting breaking part and a self-charging part, one end of which is connected to the common connection point of the valve groups Q1 and Q2, and the other end of which is connected to the common connection point of the valve groups Q3 and Q4; The current-limiting breaking part comprises a coupling inductor L, auxiliary capacitors C1 and C2, thyristor valve groups T1, T2, T4 and T5, a diode valve group D1, and metal oxide arresters MOA1 and MOA2; the coupling inductor L is composed of a primary winding L1 and a secondary winding L2, and the terminal 1 of the coupling inductor primary winding L1 is connected to the terminal 2 of the coupling inductor secondary winding L2; the thyristor valve group T1 is connected in parallel with the metal oxide arrester MOA1, and is connected in parallel with the capacitor C1 and the thyristor valve group T2 in series; the coupling inductor primary winding L1 is connected in series with the thyristor valve group T4, and the series connection of the coupling inductor primary winding L1 and the thyristor valve group T4 is connected in parallel with the series connection of the capacitor C1 and the thyristor valve group T2; the metal oxide arrester MOA2 and the diode valve group D1 are connected in series and are connected in anti-parallel to the two terminals of the coupling inductor primary winding L1; the coupling inductor secondary winding L2 is connected in series with the thyristor valve group T5, and the capacitor C2 is connected in parallel with the series connection of the coupling inductor secondary winding L2 and the thyristor valve group T5; the common connection point of the positive polarity terminal of the capacitor C2 and the coupling inductor secondary winding L2 is connected to the positive polarity terminal of the capacitor C3 of the self-charging part, and the common connection point of the negative polarity terminal of the capacitor C2 and the thyristor valve group T5 is connected to the thyristor valve group T6 of the self-charging part; The self-charging part in the auxiliary branch comprises a capacitor C3, thyristor valve groups T3, T6, T7, T8, a resistor R and a grounding terminal; the thyristor valve group T3 is connected in anti-parallel to the two terminals of the thyristor valve group T2 of the current-limiting breaking part; the thyristor valve group T8 is connected in anti-parallel to the two terminals of the valve group Q4 of the bridge circuit; the capacitor C3, the thyristor valve group T7 and the resistor R are connected in series in order and are grounded, and the other terminal of the capacitor C3 is connected to the positive polarity terminal of the capacitor C2 of the current-limiting breaking part; one terminal of the thyristor valve group T6 is connected to the common connection point of the thyristor valve group T5 and the capacitor C2 of the current-limiting breaking part, and the other terminal of the thyristor valve group T6 is connected to the common connection point of the thyristor valve group T7 and the resistor R.

2. The current-limiting hybrid DC circuit breaker based on coupled inductances according to claim 1, characterized in that, The main branch is composed of a high-speed mechanical switch UFD and an IGBT valve group LCS; the IGBT valve group LCS is composed of several IGBT units connected in series, and each IGBT unit comprises two IGBT modules connected in reverse series.

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