A mutual inductance current limiter for DC side short circuit fault protection and working method

Abstract

A mutual inductance current limiter for DC side short-circuit fault protection is composed of a fault current limiting branch module, an energy absorption branch module and a freewheeling branch module. Its working method includes four stages: normal operation, fault current suppression, fault current clearing and fault recovery. Compared with traditional series inductors, the present invention can automatically increase the equivalent inductance in the current rising stage to enhance the fault current suppression capability; automatically reduce the equivalent inductance in the current falling stage to increase the fault current attenuation speed; and also has a self-recovery function.

Description

[Technical field]

[0001] The invention relates to protection and fault processing of a DC line of a DC power transmission system with a short circuit fault, and in particular to a mutual inductance current limiter for DC side short circuit fault protection and a working method. [Background technology]

[0002] Unlike AC transmission lines, DC transmission lines do not have a natural zero-crossing point for current, and it is difficult to remove fault currents. Therefore, the protection and fault handling of DC lines have become one of the main factors restricting the further development of multi-terminal DC transmission. Traditional fault current limiters can suppress fault currents, but they all have significant defects. For example, current limiting reactors have the advantages of simple structure and easy and quick installation, but they will cause voltage drop and power loss on the AC side under normal system operation. At the same time, if the value of the series current limiting reactor is too large, it will reduce the response speed of the DC system, cause voltage oscillation, and reduce the stability of the system. The design of fault current limiters using new technologies such as superconducting materials and high-power semiconductor devices is also theoretically effective.

[0003] Superconducting fault current limiters are mainly divided into resistive fault current limiters and inductive fault current limiters. Due to their zero impedance characteristics under normal operating conditions, they can effectively suppress fault currents after a fault occurs, without any negative impact on the normal operation of the system. However, there are still problems in the rapid quenching, rapid recovery and installation of cryogenic liquid nitrogen devices of fault current limiters after faults, which need to be further solved. Fault current limiters based on high-power semiconductor devices can effectively suppress fault currents, such as series switch type fault current limiters, bridge type fault current limiters and resonant type fault current limiters. For power electronic fault current limiters, it is necessary to focus on power loss, voltage and current stress, cost, auxiliary circuits, control and timing under normal conditions. [Summary of the invention]

[0004] The purpose of the present invention is to provide a mutual inductance current limiter and a working method for DC side short-circuit fault protection, which can solve the problems existing in the existing fault current limiting methods in ensuring the reliability of system power supply and the technical difficulty of achieving fault current suppression. It is a fault current limiter with a simple structure and an easy working method. It can ensure the fault current suppression function while avoiding its influence on the normal operation of the system, so as to improve the reliability of the multi-terminal DC transmission system.

[0005] The technical solution of the present invention is a mutual inductance current limiter for DC side short-circuit fault protection, characterized in that it includes a fault current limiting branch module, an energy absorption branch module and a freewheeling branch module; wherein the freewheeling branch module is connected in parallel with the energy absorption module and in parallel with the fault current limiting branch module.

[0006] The fault current limiting branch module consists of a main reactor L M and auxiliary reactor L A The main reactor L M One end is connected to the DC power supply, and the other end is connected to the auxiliary reactor L A Connection: The auxiliary reactor L A The other end is connected to a DC circuit breaker DC-CB (DC Circuit Breaker) and is connected in parallel with the freewheeling branch module.

[0007] The main reactor L M and auxiliary reactor L A It is a coupled inductor, and mutual inductance M can be generated between the two.

[0008] The energy absorption branch module is composed of an energy dissipation resistor R and is connected in parallel with the freewheeling branch module.

[0009] The freewheeling branch module is composed of a freewheeling diode group and a fully controlled switch tube group connected in series; the negative terminal of the freewheeling diode group is connected to the main inductor L M and auxiliary reactor L A At the series connection point, its positive terminal is connected to the fully controlled switch tube group; one end of the fully controlled switch tube group is connected to the freewheeling diode group, and the other end is connected to the auxiliary inductor L of the fault current limiting branch module. A One end is connected; the fully controlled switch tube group and the energy absorption branch module are connected in parallel with each other.

[0010] The freewheeling diode group is composed of at least two diodes with positive and negative electrodes connected in series end to end, and one end is connected to the main reactor L M and auxiliary reactor L A At the series connection point, the other end is connected to the fully controlled switch tube group, and the number of diodes is selected to ensure that the divided voltage of each diode does not exceed its rated voltage.

[0011] The fully controlled switch tube group is composed of no less than 2 GTO devices, which are connected in series through the anode and cathode in sequence, one end of which is connected to the freewheeling diode group, and the other end is connected to the auxiliary reactor L of the fault current limiting branch module. A One end is connected, and the number of GTOs should be selected to ensure that the divided voltage of each GTO does not exceed its rated voltage.

[0012] The DC circuit breaker DC-CB is composed of at least two IGBTs and diodes connected in parallel and connected in positive phase with each other, and two ends of the IGBT and diodes are connected in parallel with a variable resistor.

[0013] A working method of a mutual inductance current limiter for DC side short circuit fault protection comprises the following steps:

[0014] (1) Normal operation stage

[0015] Under normal operating conditions, the DC circuit breaker is in a closed state and the DC current i dc The main reactor L through the fault current limiting branch module M , auxiliary reactor L A and the DC circuit breaker flows to the load; since the line transmits a stable DC current, the main reactor L of the fault current limiting branch module M and auxiliary reactor L A The mutual inductance M between them is equivalent to 0; therefore, the mutual inductance current limiter is equivalent to a series reactance with slightly increased power loss during normal operation;

[0016] Main reactor L M Self-inductance voltage V M , auxiliary reactor L A Self-inductance voltage V A , the mutual inductance voltage V of the auxiliary reactor to the main reactor Mm And the mutual inductance voltage V of the main reactor to the auxiliary reactor Am Calculated by formula (1):

[0017]

[0018] : Among them, i LM is the current flowing through the main reactor L M The current, i AM is the current flowing through the auxiliary reactor L A The current;

[0019] (2) Fault current suppression stage

[0020] In the fault current suppression stage, the DC circuit breaker has not yet operated and is still in the closed state, wherein the IGBT of the DC circuit breaker DC-CB is in the on state; at this time, the DC current i dc The main reactor L through the fault current limiting branch module M , auxiliary reactor L A and the DC circuit breaker flows to the fault point; the current flowing through the mutual inductance current limiter can be expressed as formula (2)

[0021]

[0022] From formula (1), we can see that due to the DC current i dc is in the rising stage, so the main reactor self-inductance voltage V A , Auxiliary reactor self-inductance voltage V M , the mutual inductance voltage V of the auxiliary reactor to the main reactor Mm And the mutual inductance voltage V of the main reactor to the auxiliary reactor Am Both are positive values; main reactor LM and auxiliary reactor L A The mutual inductance between the two coupled inductors is in a magnetizing state, and its voltage is shown in formula (3):

[0023]

[0024] At this time, the voltage across the freewheeling diode group and the fully controlled switch tube group is -(V A +V Mm ), so the freewheeling diode group cannot conduct;

[0025] In the fault current suppression stage, the fault current continues to rise. Due to the main reactor L of the fault current limiting branch module M and auxiliary reactor L A The mutual inductance between them, at this time the mutual inductance current limiter additionally generates V Mm and V Am Two mutual inductance voltages, L A , L M The equivalent inductance L eq The voltage across the two ends is U Leq As shown in formula (4):

[0026]

[0027] Therefore, in the fault current suppression stage, the current rises and the mutual inductance current limiter is equivalent to an inductor L eq , as shown in formula (5):

[0028] L eq =L M +L A +2M (5)

[0029] Therefore, compared with the traditional series inductor, the current peak I peak There is a certain degree of reduction, which improves the fault current limiting capability;

[0030] (3) Fault current clearing stage

[0031] During the fault current clearing stage, the DC circuit breaker is in the disconnected state, and the DC current i dc The main reactor L through the fault current limiting branch module M , auxiliary reactor L A and the arrester flows to the fault point. At this time, the main reactor current i LM , auxiliary reactor current i LA And the DC current i dc As shown in formula (6):

[0032]

[0033] From formula (1), we can see that the fully controlled switch tube group GTO device is turned on, and in the initial stage of fault current decay, V M and V Mm becomes negative, so the voltage across the freewheeling diode group is -(V A +V Mm ) becomes positive, the freewheeling diode group automatically turns on. At this time, the current i dc Flows through the diode group, the fully controlled switch tube group and the auxiliary reactor L A If the conduction loss of the diode group and the fully controlled switch tube group is ignored, combined with formula (4), it can be known that:

[0034]

[0035] Therefore, LA The rate of change can be expressed as

[0036]

[0037] Since V Mm <0, so

[0038]

[0039] This means that LA With -V Mm / L A As the main inductor increases, it can be seen from formula (4) that the mutual inductance voltage V Am Maintain a positive value, which is part of the reverse voltage of the fault circuit. Therefore, the auxiliary reactor L A The main reactor L M Absorb part of the energy; in addition, combining formula (1) and formula (6) can be obtained:

[0040]

[0041] Therefore, the equivalent inductance L of the mutual inductance current limiter in the current drop stage is eq for:

[0042]

[0043] Fault current limiting stage time T FCL It can be calculated as

[0044]

[0045] Among them, V arr is the arrester residual voltage of the DC circuit breaker, V dc is the DC voltage;

[0046] Since the equivalent inductance during the fault current clearing phase is smaller than the traditional series inductance, the current clearing time T of the mutual inductance current limiter is FCL The time required by traditional inductors is shorter than that required by traditional inductors, thereby improving the speed of fault current suppression; and, due to the main inductor L of the fault current limiting branch module M and auxiliary reactor L A The mutual inductance generated between them can absorb energy, and the freewheeling diode group and the fully controlled switch tube group can help increase the energy stored in the mutual inductance current limiter;

[0047] (4) Fault recovery phase

[0048] During the fault recovery phase, the DC current i dc The decay is 0, and the DC circuit breaker can be regarded as completely disconnected, achieving complete fault isolation, and shutting down the GTO device of the fully controlled switch tube group after a delay of a period of time; assuming that after disconnecting from the DC circuit breaker, the delay T recovery The GTO device is turned off in time, and the energy consumption resistor R of the energy absorption branch module is consumed and stored in the auxiliary reactor L A energy, so that the current of the energy absorption circuit is reduced to 0; T recovery Longer than T FCL ,satisfy

[0049] T recovery =k1T FCL (13)

[0050] Among them, k1 is the delay coefficient, k1>1;

[0051] The energy absorption branch module's energy dissipation resistor R is put into use, together with the freewheeling diode group, the fully controlled switch tube group and the auxiliary reactor L A The circuit is formed, consuming the energy stored in the auxiliary reactor; flowing through the auxiliary reactor L A The current gradually drops to 0, allowing the mutual inductance current limiter to return to normal and prepare for the next fault.

[0052] Advantages of the present invention: The equivalent inductance can be increased to L during the current rising stage. M +L A +2M, with the function of automatically limiting fault current; in the current limiting stage, the inductance is automatically reduced to L M -M 2 / L A , which helps to accelerate the decline of current. Therefore, the present invention has advantages in both the current rising stage and the current limiting stage, and no additional control is required during the DC fault interruption process. In addition, the present invention can also recover by itself and prepare for the next DC line fault.

Brief Description of the Drawings

[0053] Figure 1 The topological structure diagram of a mutual inductance current limiter for DC side short circuit fault protection according to the present invention.

[0054] FIG2 is a schematic diagram of a mutual inductance type current limiter operation scheme at different stages in a working method of a mutual inductance type current limiter for DC side short circuit fault protection according to the present invention (wherein, Figure 2-a It is the normal operation stage; Figure 2-b It is the fault current suppression stage; Figure 2-c It is the fault current clearing stage; Figure 2-d for the fault recovery phase). [Specific implementation method]

[0055] Embodiment: In order to enable those skilled in the art to better understand the present application, the present application will be further described in detail below in conjunction with the accompanying drawings.

[0056] like Figure 1 As shown, a mutual inductance current limiter for DC side short-circuit fault protection is characterized in that it includes a fault current limiting branch module, an energy absorption branch module and a freewheeling branch module; wherein the freewheeling branch module is connected in parallel with the energy absorption module and in parallel with the fault current limiting branch module.

[0057] The fault current limiting branch module consists of a main reactor L M and auxiliary reactor L A The main reactor L M One end is connected to the DC power supply, and the other end is connected to the auxiliary reactor L A Connection: The auxiliary reactor L A The other end is connected to the DC circuit breaker DC-CB and is connected in parallel with the freewheeling branch module.

[0058] The main reactor L M and auxiliary reactor L A It is a coupled inductor, and mutual inductance M can be generated between the two.

[0059] The energy absorption branch module is composed of an energy dissipation resistor R and is connected in parallel with the freewheeling branch module.

[0060] The freewheeling branch module is composed of a freewheeling diode group and a fully controlled switch tube group connected in series; the negative terminal of the freewheeling diode group is connected to the main inductor L M and auxiliary reactor L A At the series connection point, its positive terminal is connected to the fully controlled switch tube group; one end of the fully controlled switch tube group is connected to the freewheeling diode group, and the other end is connected to the auxiliary inductor L of the fault current limiting branch module. A One end is connected; the fully controlled switch tube group and the energy absorption branch module are connected in parallel with each other.

[0061] The freewheeling diode group is composed of at least two diodes with positive and negative electrodes connected in series end to end, and one end is connected to the main reactor L M and auxiliary reactor L A At the series connection point, the other end is connected to the fully controlled switch tube group, and the number of diodes is selected to ensure that the divided voltage of each diode does not exceed its rated voltage.

[0062] The fully controlled switch tube group is composed of no less than 2 GTO devices, which are connected in series through the anode and cathode in sequence, one end of which is connected to the freewheeling diode group, and the other end is connected to the auxiliary reactor L of the fault current limiting branch module. A One end is connected, and the number of GTOs should be selected to ensure that the divided voltage of each GTO does not exceed its rated voltage.

[0063] The DC circuit breaker DC-CB is composed of at least two IGBTs and diodes connected in parallel and connected in positive phase with each other, and two ends of the IGBT and diodes are connected in parallel with a variable resistor.

[0064] The specific steps include:

[0065] Step 1: Operation plan during normal operation

[0066] As shown in Figure 2(a), under normal operation, the DC circuit breaker is in a closed state. dc Through the main reactor L M , auxiliary reactor L A and DC circuit breaker to the load. Since the line transmits a stable DC current, the mutual inductance M between the main and auxiliary reactors can be equivalent to 0. Therefore, the mutual inductance current limiter can be equivalent to a series reactor with slightly increased power loss during normal operation. V M , V A , V Mm and V Am They are the main reactor self-inductance voltage, the auxiliary reactor self-inductance voltage, the auxiliary reactor to the main reactor mutual inductance voltage and the main reactor to the auxiliary reactor mutual inductance voltage. These four voltages can be calculated by the following formula

[0067]

[0068] Among them, i LM is the current flowing through the main reactor, i AM is the current flowing through the auxiliary reactor.

[0069] Step 2: Operational scheme for fault current suppression stage

[0070] As shown in Figure 2(b), in the fault current suppression stage, the DC circuit breaker has not yet operated and the IGBT in it is also in the on state. dcThrough the main reactor L M , auxiliary reactor L A The current flowing through the mutual inductance current limiter can be expressed as

[0071]

[0072] From (1), we can see that due to i dc is in the rising stage, so the main reactor self-inductance voltage V A , Auxiliary reactor self-inductance voltage V M , the mutual inductance voltage V of the auxiliary reactor to the main reactor Mm And the mutual inductance voltage V of the main reactor to the auxiliary reactor Am The mutual inductance between the two coupled inductors is in a magnetizing state, and the voltage can be expressed as

[0073]

[0074] The voltage across the anti-parallel diode D and GTO is -(V A +V Mm ), so D cannot conduct.

[0075] In the fault current suppression stage, the fault current continues to rise, and the mutual inductance current limiter generates additional V due to the mutual inductance effect. Mm and V Am Two mutually inducted voltages.

[0076]

[0077] The equivalent inductance L of the mutual inductance current limiter in the current rising stage eq for

[0078] L eq =L M +L A +2M (5)

[0079] Therefore, compared with the traditional series inductor, the peak current I peak It is reduced to a certain extent and the fault current limiting capability is enhanced.

[0080] Step 3: Operational plan for the fault current clearing phase

[0081] As shown in Figure 2(c), during the fault current clearing stage, the DC circuit breaker is in the breaking stage, and the current flows to the fault point through the arrester. The current flowing through the mutual inductance current limiter can be expressed as

[0082]

[0083] From (1), we can see that the GTO is turned on and in the initial stage of fault current decay, V M and V Mm becomes negative. Therefore, the voltage across diode D is -(V A +V Mm ) becomes positive, D automatically turns on. The current flows through the diode D, GTO and auxiliary reactor L A .

[0084] If the conduction loss of D and GTO is ignored, combined with formula (4-1), we can get

[0085]

[0086] Therefore, LA The rate of change can be expressed as

[0087]

[0088] Since V Mm <0, so

[0089]

[0090] This means that LA With -V Mm / L A As it rises, it rises. From (4-1), we can see that V Am remains positive and is part of the reverse voltage of the fault circuit. Therefore, the auxiliary reactor can absorb part of the energy through the main reactor. In addition, combining (1) and (6), it can be obtained that

[0091]

[0092] Therefore, the equivalent inductance L of the mutual inductance current limiter in the current drop stage is eq for

[0093]

[0094] Fault current limiting stage time T FCL It can be calculated as

[0095]

[0096] Among them, V arr is the arrester residual voltage of the DC circuit breaker, V dc is a DC voltage.

[0097] Since the equivalent inductance of the fault current limiting stage is smaller than the traditional series inductance, the current clearing time T of the mutual inductance current limiter is FCL Less time than traditional inductors.

[0098] In summary, in the fault current clearing stage, the equivalent inductance of the proposed mutual inductance current limiter is lower than that of the traditional series inductance, which can improve the fault current suppression speed. From the perspective of energy transfer, the energy stored in the auxiliary reactor increases because the mutual inductance absorbs energy and continues to flow through the diode and the fully controlled switch tube.

[0099] Step 4: Operation plan for the fault recovery phase

[0100] As shown in Figure 2(d), the DC current i dc The decay is 0, and the DC circuit breaker can be regarded as completely disconnected, achieving complete fault isolation. Assume that after the DC circuit breaker is disconnected, the delay T recovery The time to turn off the GTO, the resistor R consumes the energy stored in the auxiliary reactor L A energy, so that the current of the energy absorption circuit is reduced to 0. recovery Longer than T FCL ,satisfy

[0101] T recovery =k1T FCL (13)

[0102] Among them, k1 is the delay coefficient, k1>1.

[0103] The resistor R in the energy absorption circuit is put into use, together with D, GTO and auxiliary reactor L A A loop is formed, consuming the energy stored in the auxiliary reactor. The current flowing through the auxiliary reactor gradually drops to 0, which means that the mutual inductance current limiter has returned to normal and is ready for the next fault. Due to the delay time T of the fault recovery phase of the mutual inductance current limiter recovery Longer than T FCL , that is, the GTO disconnection moment is after the moment when the fault current decays to 0, so it will not affect the fault clearing process.

Claims

1. A mutual inductance current limiter for DC side short circuit fault protection, characterized in that It includes a fault current limiting branch module, an energy absorption branch module and a freewheeling branch module; wherein the freewheeling branch module is connected in parallel with the energy absorption module and in parallel with the fault current limiting branch module; the fault current limiting branch module is composed of a main reactor L M and auxiliary reactor L A The main reactor L M One end is connected to the DC power supply, and the other end is connected to the auxiliary reactor L A Connection: The auxiliary reactor L A The other end is connected to the DC circuit breaker DC-CB and is connected in parallel with the freewheeling branch module; the energy absorption branch module is composed of an energy dissipation resistor R and is connected in parallel with the freewheeling branch module; the freewheeling branch module is composed of a freewheeling diode group and a fully controlled switch tube group connected in series; the negative terminal of the freewheeling diode group is connected to the main inductor L M and auxiliary reactor L A At the series connection point, its positive terminal is connected to the fully controlled switch tube group; one end of the fully controlled switch tube group is connected to the freewheeling diode group, and the other end is connected to the auxiliary inductor L of the fault current limiting branch module. A One end is connected; the fully controlled switch tube group and the energy absorption branch module are connected in parallel with each other.

2. A mutual inductance current limiter for DC side short circuit fault protection according to claim 1, characterized in that The main reactor L M and auxiliary reactor L A It is a coupled inductor, and mutual inductance M can be generated between the two.

3. A mutual inductance current limiter for DC side short circuit fault protection according to claim 1, characterized in that The freewheeling diode group is composed of at least two diodes with positive and negative electrodes connected in series end to end, and one end is connected to the main reactor L M and auxiliary reactor L A At the series connection point, the other end is connected to the fully controlled switch tube group, and the number of diodes is selected to ensure that the divided voltage of each diode does not exceed its rated voltage.

4. A mutual inductance current limiter for DC side short circuit fault protection according to claim 1, characterized in that The fully controlled switch tube group is composed of no less than 2 GTO devices, which are connected in series through the anode and cathode in sequence, one end of which is connected to the freewheeling diode group, and the other end is connected to the auxiliary reactor L of the fault current limiting branch module. A One end is connected, and the number of GTOs should be selected to ensure that the divided voltage of each GTO does not exceed its rated voltage.

5. A mutual inductance current limiter for DC side short circuit fault protection according to claim 1, characterized in that The DC circuit breaker DC-CB is composed of at least two IGBTs and diodes connected in parallel and connected in positive phase with each other, and two ends of the IGBT and diodes are connected in parallel with a variable resistor.

6. A working method of a mutual inductance current limiter for DC side short circuit fault protection, comprising the following steps: (1) Normal operation stage Under normal operating conditions, the DC circuit breaker is in a closed state and the DC current i dc The main reactor L through the fault current limiting branch module M , auxiliary reactor L A and the DC circuit breaker flows to the load; since the line transmits a stable DC current, the main reactor L of the fault current limiting branch module M and auxiliary reactor L A The mutual inductance M between them is equivalent to 0; therefore, the mutual inductance current limiter is equivalent to a series reactance with slightly increased power loss during normal operation; Main reactor L M Self-inductance voltage V M , auxiliary reactor L A Self-inductance voltage V A , the mutual inductance voltage V of the auxiliary reactor to the main reactor Mm And the mutual inductance voltage V of the main reactor to the auxiliary reactor Am Calculated by formula (1): Among them, i LM is the current flowing through the main reactor L M The current, i AM is the current flowing through the auxiliary reactor L A The current; (2) Fault current suppression stage In the fault current suppression stage, the DC circuit breaker has not yet operated and is still in the closed state, wherein the IGBT of the DC circuit breaker DC-CB is in the on state; at this time, the DC current i dc The main reactor L through the fault current limiting branch module M , auxiliary reactor L A and the DC circuit breaker flows to the fault point; the current flowing through the mutual inductance current limiter is expressed as formula (2) From formula (1), we can see that due to the DC current i dc is in the rising stage, so the main reactor self-inductance voltage V A , Auxiliary reactor self-inductance voltage V M , the mutual inductance voltage V of the auxiliary reactor to the main reactor Mm And the mutual inductance voltage V of the main reactor to the auxiliary reactor Am Both are positive values; main reactor L M and auxiliary reactor L A The mutual inductance between the two coupled inductors is in a magnetizing state, and its voltage is shown in formula (3): At this time, the voltage across the freewheeling diode group and the fully controlled switch tube group is -(V A +V Mm ), so the freewheeling diode group cannot conduct; In the fault current suppression stage, the fault current continues to rise. Due to the main reactor L of the fault current limiting branch module M and auxiliary reactor L A The mutual inductance between them, at this time the mutual inductance current limiter additionally generates V Mm and V Am Two mutual inductance voltages, L A , L M The equivalent inductance L eq The voltage across the two ends is U Leq As shown in formula (4): Therefore, in the fault current suppression stage, the current rises and the mutual inductance current limiter is equivalent to an inductor L eq , as shown in formula (5): L eq =L M +L A +2M (5) Therefore, compared with the traditional series inductor, the current peak value L peak There is a certain degree of reduction, which improves the fault current limiting capability; (3) Fault current clearing stage During the fault current clearing stage, the DC circuit breaker is in the disconnected state, and the DC current i dc The main reactor L through the fault current limiting branch module M , auxiliary reactor L A and the arrester flows to the fault point. At this time, the main reactor current i LM , auxiliary reactor current i LA And the DC current i dc As shown in formula (6): From formula (1), we can see that the fully controlled switch tube group GTO device is turned on, and in the initial stage of fault current decay, V M and V Mm becomes negative, so the voltage across the freewheeling diode group is -(V A +V Mm ) becomes positive, the freewheeling diode group automatically turns on. At this time, the current i dc Flows through the diode group, the fully controlled switch tube group and the auxiliary reactor L A If the conduction loss of the diode group and the fully controlled switch tube group is ignored, combined with formula (4), it can be known that: Therefore, LA The rate of change is expressed as Since V Mm <0, so This means that LA With -V Mm / L A As the main inductor increases, it can be seen from formula (4) that the mutual inductance voltage V Am Maintain a positive value, which is part of the reverse voltage of the fault circuit. Therefore, the auxiliary reactor L A Through the main reactor L M Absorb part of the energy; In addition, combining formula (1) and formula (6) yields the following two Therefore, the equivalent inductance L of the mutual inductance current limiter in the current drop stage is eq for: Fault current limiting stage time T FCL Calculated as Among them, V arr is the arrester residual voltage of the DC circuit breaker, V dc is the DC voltage; Since the equivalent inductance during the fault current clearing phase is smaller than the traditional series inductance, the current clearing time T of the mutual inductance current limiter is FCL The time required by traditional inductors is shorter than that required by traditional inductors, thereby improving the speed of fault current suppression; and, due to the main inductor L of the fault current limiting branch module M and auxiliary reactor L A The mutual inductance generated between them can absorb energy, and the freewheeling diode group and the fully controlled switch tube group can help increase the energy stored in the mutual inductance current limiter; (4) Fault recovery phase During the fault recovery phase, the DC current i dc The decay is 0, the DC circuit breaker is considered to be completely disconnected, the fault is completely isolated, and the GTO device of the fully controlled switch tube group is turned off after a delay of a period of time; Assuming that after the DC circuit breaker is disconnected, the delay T recovery The GTO device is turned off in time, and the energy consumption resistor R of the energy absorption branch module is consumed and stored in the auxiliary reactor L A energy, so that the current of the energy absorption circuit is reduced to 0; T recovery Longer than T FCL ,satisfy T recovery =k1T FCL (13) Wherein, k1 is the delay coefficient, k1>1; The energy absorption branch module's energy dissipation resistor R is put into use, together with the freewheeling diode group, the fully controlled switch tube group and the auxiliary reactor L A The circuit is formed, consuming the energy stored in the auxiliary reactor; flowing through the auxiliary reactor L A The current gradually drops to 0, allowing the mutual inductance current limiter to return to normal and prepare for the next fault.

Images