Multi-port mechanical direct-current circuit breaker integrated with power flow control function and control process

Abstract

The invention discloses a multi-port mechanical direct-current circuit breaker integrated with a power flow control function and a control flow, oscillation current limiting discharges based on a capacitor C1 and an inductor L1, and current opposite to a main path is formed along with gradual increase of the current, so that a zero crossing point of a main path switch at a fault position is disconnected; the mutual inductance reverse voltage is conducted after the zero crossing point of the fault main path is switched off, the discharge of the capacitor C2 generates the mutual inductance voltage to hinder the conduction of the thyristor T4, and the switching from the current conversion stage to the current limiting stage is achieved; the power flow control is based on a fault current elimination stage, each switch state of a power flow module in a normal operation state is kept unchanged, a non-fault line current flows to a fault side, and after a fault is eliminated, the fault side current is subjected to PI regulation to output different on-off signals of a switch tube in the power flow module, so that each main current reaches a stable current state of normal operation; the technical problems of quick fault current elimination in a short time, conversion at different stages during fault elimination and power flow control under fault elimination are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronics, and in particular relates to a multi-port mechanical DC circuit breaker with integrated power flow control function and a control process. Background Art

[0002] The rapid development of multi-terminal flexible DC transmission systems benefits from its advantages of reliable commutation and independent control of active and reactive power. However, as the number of ports and transmission lines increases, the problems that follow also gradually emerge. The natural distribution of power flow in the DC grid is mainly determined by the resistance of each line. It is possible that some lines are overloaded while other lines are lightly loaded, and the current margin of each transmission line is unevenly distributed. In mild cases, the line loss increases and the transmission efficiency of the DC grid decreases; in severe cases, the DC circuit breaker of the overloaded line malfunctions, and the failure to close the circuit breaker in time leads to a chain reaction of overload of other lines, destroying the safety and stability of the DC grid. Therefore, a DC power flow controller needs to be configured to ensure the reasonable distribution of power flows in each line and improve the integrity of the system. At present, there have been many studies on DC power flow controllers. The variable resistance power flow controller is not widely used in actual engineering applications because it will generate large losses in the system and only has one-way control power flow reduction. The capacitor-based line power exchange type structure is relatively simple, low cost, and good in all aspects. The double H-bridge power flow controller proposes a three-port DC circuit breaker with power flow control function. In this topology, the power flow controller is connected to the flow branches of the two output ports. Since the double H-bridge power flow control structure is the same as the power electronic auxiliary switch structure in the flow branch, the number of power electronic devices used is saved. However, this structure sets an independent disconnection branch for each output port, which is costly. The accurate disconnection of the mechanical circuit breaker in the elimination of fault current directly affects the stable operation of the power system. When a short circuit fault occurs on the DC side of the flexible DC grid, the fault current rises rapidly and has a large amplitude. If the fault cannot be quickly isolated, it will affect the normal operation of the entire power system. Compared with the mechanical type, the solid-state DC circuit breaker is mainly composed of power electronic devices. It is difficult to be widely promoted in practice due to its high cost and large conduction loss. In addition, the main branch of the hybrid circuit breaker is composed of a mechanical switch and a turnable power electronic switch in series, and the disconnection branch is composed of a large number of turnable power electronic switches in series and parallel. The energy absorption branch is the same as other circuit breakers, but the hybrid circuit breaker requires many components, complex control, and high cost, which still restricts its widespread promotion. Therefore, it is of great significance to study the similarities in the topological structures of the current limiter, the power flow controller and the DC circuit breaker, and to propose a composite multi-port DC circuit breaker with good current limiting effect, high reliability, strong economy and diverse functions.

[0003] In the prior art, the Chinese patent "Multi-port hybrid DC circuit breaker with flow control function and control method" with publication number CN202010387694.4 provides a multi-port hybrid DC circuit breaker with flow control function, which is characterized by comprising: a main disconnect switch and a flow control module; each line is connected to a common main disconnect switch through its corresponding diode branch, the main disconnect switch is connected to the DC bus, and the main disconnect switch is used for current disconnection between the DC bus and each line and isolation of the faulty line; at the same time, one of all the lines is connected to the DC bus through a fast mechanical switch and a load transfer switch connected in series, and the remaining lines are connected to the flow control module through their corresponding fast mechanical switches, and the flow control module is connected to the DC bus. connected to the DC bus; all lines are also connected in series with a residual current switch; a multi-port hybrid DC circuit breaker, by expanding the traditional double H-bridge line flow controller into a multi-H-bridge line flow controller and integrating it into the multi-port hybrid DC circuit breaker in the form of a module, when a short circuit fault occurs at any port, the working mode of the DC circuit breaker is controlled, and the multi-port hybrid DC circuit breaker quickly acts to clear and isolate the fault; the flow control module includes a discharge module for releasing the energy stored in the energy storage capacitor in the flow control module; although this technology can solve the problem of eliminating the fault current, the hybrid circuit breaker is used in the design of clearing and isolating the fault, which uses more components than the mechanical circuit breaker, and the control is more complicated and the cost is high.

[0004] Therefore, it is necessary to propose a multi-port mechanical DC circuit breaker and a control process with integrated power flow control function to solve the above problems. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a multi-port mechanical DC circuit breaker and a control process with integrated power flow control function, aiming to solve the technical problems of quickly eliminating fault current in a short time, conversion of different stages when clearing faults, and power flow control under fault elimination, realize the rapid elimination of short-circuit fault current, and the regulation of current of each line by the power flow module when the fault is eliminated, improve the stability of power system operation, and provide users with reliable power.

[0006] In order to solve the above technical problems, the technical scheme adopted by the present invention is: a multi-port mechanical DC circuit breaker with integrated flow control function, the oscillation current limiting is based on the discharge of capacitor C1 and inductor L1, as the current gradually increases, a current opposite to the main path is formed, so that the main path switch at the fault is disconnected at zero crossing; the mutual inductance reverse pressure is based on the mutual inductance being turned on after the fault main path is turned off at zero crossing, at this time, the discharge of capacitor C2 generates a mutual inductance voltage to hinder the thyristor T4 from turning on, so as to achieve the switching from the commutation stage to the current limiting stage; the flow control is based on the fault current elimination stage, keeping the states of each switch of the flow module unchanged under the normal operating state, at this time the non-fault line current flows to the fault side, resulting in a sharp increase in the fault current measurement; after the fault is eliminated, the fault side current is adjusted by PI to output different disconnection signals of the switch tubes Tia, Tib (i=2, 3...) in the flow module, so that each main current reaches a stable current state of normal operation, the specific technical scheme is: A multi-port mechanical DC circuit breaker with integrated power flow control function includes a current limiting branch, an MOV branch, a commutation branch and a power flow module. One end of port I1 is connected in series with a mechanical switch S1 and a power flow module, and the other end of the power flow module is connected to port I2 and port I3. The commutation branch includes a thyristor T1 connected to port I1, and one end of the thyristor T1 is connected in series with an inductor L1, a thyristor T2, and a thyristor T3 in sequence. 3、 The other end of capacitor C1, thyristor T4 and inductor L4 is connected to port 2 I2 through thyristor T9. 11 Connected to port three I3; a current limiting branch is set in parallel on the commutation branch, one end of the current limiting branch is connected to the circuit between the inductor L1 and the thyristor T3, and the other end is connected to the circuit between the inductor L4 and the thyristor T9; an MOV branch is set in parallel on the current limiting branch.

[0007] Preferably, the current limiting branch includes thyristors T connected in series in sequence. 13 , resistor R and inductor L2; a thyristor T is provided in the loop behind the inductor L2 14 , Thyristor T 14 The other end is connected in parallel to the circuit between the capacitor C1 and the thyristor T4 of the commutation branch.

[0008] Preferably, the MOV branch includes a first lightning arrester MOV1, one end of the MOV branch is connected in parallel to the circuit between the inductor L1 and the thyristor T3, and the other end of the MOV branch is connected in parallel to the circuit between the inductor L2 and the thyristor T9.

[0009] Preferably, thyristor T1, thyristor T3, thyristor T4, thyristor T9, thyristor T 13 and thyristor T 11 All from port 1 I1 to port 2 I2 or port 3 I3; thyristor T 14 From the commutation branch toward the current limiting branch.

[0010] Preferably, a branch of a thyristor T2 is provided between the first port I1 and the second port I2 , the other end of the branch is connected to the second port I2 through the thyristor T9 , and the thyristor T2 faces the first port I1 .

[0011] Preferably, the port 2 I2 and the port 3 I3 are connected to the thyristor T8 and the thyristor T 10 The two branches are connected in parallel between thyristor T1 and inductor L1; thyristor T8 and thyristor T 10 Towards port one I1.

[0012] Preferably, the port 2 I2 is connected to a branch of a thyristor T7, and the other end of the branch is connected to a thyristor T5 through a thyristor T7. 14 In the branch, thyristor T7 is directed toward port I1.

[0013] Preferably, a grounding loop is connected between the thyristor T3 and the capacitor C1, and the grounding loop includes the thyristors T3 and the capacitor C1 connected in series. 12 and capacitor C2, the other end of which is grounded; a circuit formed by a thyristor T6 and an inductor L3 in series is connected in parallel at both ends of capacitor C2. 12 and thyristor T6 are both toward the ground terminal.

[0014] Preferably, the flow control module includes a fully controlled power electronic device, multiple anti-parallel diodes, a capacitor CF, a discharge resistor R1 and a second lightning arrester MOV2. The terminals of the upper bridge switch tube Sa and the lower bridge switch tube Sb are connected to the DC bus; the terminals of the remaining IGBT half-bridges are respectively connected in series with the fast mechanical switches S2 and S3 of each line; T2a and T2b are the upper and lower switch tubes of port two I2, and T3a and T3b are the upper and lower switch tubes of port three I3; D1a and D1b are anti-parallel diodes of port one I1, D2a and D2b are anti-parallel diodes of port two I2, and D3a and D3b are anti-parallel diodes of port three I3.

[0015] Preferably, the control method of the control process of the above-mentioned multi-port mechanical DC circuit breaker with integrated power flow control function is: When the line current changes in the power grid and power flow control is required, the power flow control module is activated when the system is stable. The difference between the state of each switch tube and the steady-state operation state is that the IGBT half-bridge in the module is no longer in the normally closed current-carrying state, but is regulated according to the current of each line, and the PWM signal is used to control the module. , The on-off of the capacitor makes the capacitor connected to the circuit in three different states: discharge, charge and bypass. In addition, the states of other switch tubes are consistent with the on or off state in the steady state. The specific control process is as follows: Under normal operating conditions, the current flows through the main path, during which the grid current flows to the capacitor and Precharge; if When a short circuit fault occurs at port 2 I2, the fault current will increase sharply in a short period of time. At this time, the circuit mathematical model is: ; In the formula, is the fault current; is the system voltage; is the equivalent resistance of the line; , They are line equivalent inductance and buffer inductance respectively; When a fault occurs, the circuit breaker does not detect the fault and does not take corresponding action. At this moment, the fault current value reaches the circuit breaker action value, the circuit breaker detects the fault, acts, turns on the commutation branch, and the current flows through the inductor and capacitor , and under its action, an oscillating current opposite to the main fault path is generated; The oscillation branch is put into use at all times, because the capacitor With initial voltage, it is an active oscillation; as the current increases, Always generate an oscillating current in the opposite direction to the main branch , the mathematical model of the unidirectional oscillation circuit is: ; in Indicates capacitance The voltage, is the inductance value, is the capacitance value; The parallel output current of the mechanical switch and the oscillation branch is: ; is the current value flowing through the mechanical switch, is the current value flowing through the oscillation branch; At this moment, the mechanical switch is turned off in the state of zero current, and the thyristor is turned on at this time. , due to the capacitance The discharge causes a larger voltage value to be generated on the secondary side. Time makes the thyristor It is shut down due to reverse pressure, and the commutation phase ends; Among them, the primary capacitance is , the primary inductance of the coupled reactor is , the secondary inductance is , mutual inductance is M, capacitance The precharge voltage is , the commutation side capacitance is , the current on the low voltage side of the circuit breaker is , the current on the commutation side is , then: ; ; exist Turn on the thyristor at all times Entering the current limiting stage, the inductor ,capacitance , and resistor R to limit the increase of fault current; When the voltage across the arrester reaches the operating voltage, the energy-consuming branch MOV is turned on to consume the remaining fault energy. At this moment, the output current of the circuit breaker is zero, and the fault current elimination action is completed.

[0016] The beneficial effects of the present invention are as follows: 1. The multi-port mechanical DC circuit breaker and control process with integrated power flow control function proposed in the present invention can reduce the operational instability of the power system under short-circuit fault conditions, quickly eliminate fault currents, ensure the quality of electric energy, and meet the power safety and needs of users. In addition, it can be in the main flow state when the system is in normal operation, and improve the power flow between different ports after the fault is eliminated; the control can adapt to the number of different ports and has good flexibility and reliability.

[0017] 2. This device can pre-charge the capacitor under normal operating conditions, avoiding the need to add a separate charging device and reducing costs; under fault conditions, the capacitor The discharge of the inductor causes an obstruction at the connection point between the inductor and the mutual inductance element. The voltage is turned on to realize the commutation shutdown and turn on the current limiting branch, which has both fault clearing and power flow control. It can ensure that the operating environment of the DC power grid can be better coped with at a lower investment cost, and the operating efficiency and system integrity can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A schematic diagram of a power flow module and a mechanical circuit breaker of the present invention; Figure 2 A schematic diagram of the flow of fault current in an embodiment of the present invention; Figure 3 Schematic diagram of oscillating current flow in an embodiment of the present invention; Figure 4 A schematic diagram of the flow of current-limiting current in an embodiment of the present invention; Figure 5A schematic diagram of energy consumption current flow in an embodiment of the present invention; Figure 6 This is a schematic diagram of a three-port power flow module control system in an embodiment of the present invention; Figure 7 A schematic diagram of a simulation connection in an embodiment of the present invention; Figure 8 A schematic diagram of the circuit breaker action timing during the simulation process in an embodiment of the present invention; Fig. 9 The simulation results in the embodiment of the present invention are Current diagram; Fig.10 The simulation results in the embodiment of the present invention are Current diagram; Fig.11 The simulation results in the embodiment of the present invention are Current diagram; Fig.12 The simulation results in the embodiment of the present invention are Current diagram; Fig.13 It is a schematic diagram of current change of line current under power flow control after the fault is eliminated in the simulation results in an embodiment of the present invention. DETAILED DESCRIPTION

[0019] Embodiment 1: like Figure 1 As shown, a multi-port mechanical DC circuit breaker with integrated power flow control function includes a current limiting branch, an MOV branch, a commutation branch and a power flow module. One end of the port I1 is connected in series with a mechanical switch S1 and a power flow module, and the other end of the power flow module is connected to the port I2 and the port I3; the commutation branch includes a thyristor T1 connected to the port I1, and one end of the thyristor T1 is connected in series with an inductor L1, a thyristor T2 and a thyristor T3 in sequence. 3、 The other end of capacitor C1, thyristor T4 and inductor L4 is connected to port 2 I2 through thyristor T9. 11 Connected to port three I3; a current limiting branch is set in parallel on the commutation branch, one end of the current limiting branch is connected to the circuit between the inductor L1 and the thyristor T3, and the other end is connected to the circuit between the inductor L4 and the thyristor T9; an MOV branch is set in parallel on the current limiting branch.

[0020] Preferably, the current limiting branch includes thyristors T connected in series in sequence. 13 , resistor R and inductor L2; a thyristor T is provided in the loop behind the inductor L2 14 , Thyristor T 14 The other end is connected in parallel to the circuit between the capacitor C1 and the thyristor T4 of the commutation branch.

[0021] Preferably, the MOV branch includes a first lightning arrester MOV1, one end of the MOV branch is connected in parallel to the circuit between the inductor L1 and the thyristor T3, and the other end of the MOV branch is connected in parallel to the circuit between the inductor L2 and the thyristor T9.

[0022] Preferably, thyristor T1, thyristor T3, thyristor T4, thyristor T9, thyristor T 13 and thyristor T 11 All from port 1 I1 to port 2 I2 or port 3 I3; thyristor T 14 From the commutation branch toward the current limiting branch.

[0023] Preferably, a branch of a thyristor T2 is provided between the first port I1 and the second port I2 , the other end of the branch is connected to the second port I2 through the thyristor T9 , and the thyristor T2 faces the first port I1 .

[0024] Preferably, the port 2 I2 and the port 3 I3 are connected to the thyristor T8 and the thyristor T 10 The two branches are connected in parallel between thyristor T1 and inductor L1; thyristor T8 and thyristor T 10 Towards port one I1.

[0025] Preferably, the port 2 I2 is connected to a branch of a thyristor T7, and the other end of the branch is connected to a thyristor T5 through a thyristor T7. 14 In the branch, thyristor T7 is directed toward port I1.

[0026] Preferably, a grounding loop is connected between the thyristor T3 and the capacitor C1, and the grounding loop includes the thyristors T3 and the capacitor C1 connected in series. 12 and capacitor C2, the other end of which is grounded; a circuit formed by a thyristor T6 and an inductor L3 in series is connected in parallel at both ends of capacitor C2. 12 and thyristor T6 are both toward the ground terminal.

[0027] Preferably, the flow control module includes a fully controlled power electronic device, multiple anti-parallel diodes, a capacitor CF, a discharge resistor R1 and a second lightning arrester MOV2. The terminals of the upper bridge switch tube Sa and the lower bridge switch tube Sb are connected to the DC bus; the terminals of the remaining IGBT half-bridges are respectively connected in series with the fast mechanical switches S2 and S3 of each line; T2a and T2b are the upper and lower switch tubes of port two I2, and T3a and T3b are the upper and lower switch tubes of port three I3; D1a and D1b are anti-parallel diodes of port one I1, D2a and D2b are anti-parallel diodes of port two I2, and D3a and D3b are anti-parallel diodes of port three I3.

[0028] Embodiment 2: A control method for a control process of a multi-port mechanical DC circuit breaker with integrated power flow control function is as follows: When the line current changes in the power grid and power flow control is required, the power flow control module is activated when the system is stable. The difference between the state of each switch tube and the steady-state operation state is that the IGBT half-bridge in the module is no longer in the normally closed current-carrying state, but is regulated according to the current of each line, and the PWM signal is used to control the module. , The on-off of the capacitor makes the capacitor connected to the circuit in three different states: discharge, charge and bypass. In addition, the states of other switch tubes are consistent with the on or off state in the steady state. The specific control process is as follows: Under normal operating conditions, the current flows through the main path, during which the grid current flows to the capacitor and Precharge; if When a short circuit occurs at port 2 I2, the fault current will increase sharply in a short period of time. Figure 2 As shown, the circuit mathematical model is: ; In the formula, is the fault current; is the system voltage; is the equivalent resistance of the line; , They are line equivalent inductance and buffer inductance respectively; When a fault occurs, the circuit breaker does not detect the fault and does not take corresponding action. At this moment, the fault current value reaches the circuit breaker action value, the circuit breaker detects the fault, acts, turns on the commutation branch, and the current flows through the inductor and capacitor , and under its action, an oscillating current opposite to the main fault path is generated, and the current flows in the direction of Figure 3 As shown; The oscillation branch is put into use at all times, because the capacitor With initial voltage, it is an active oscillation; as the current increases, Always generate an oscillating current in the opposite direction to the main branch , the mathematical model of the unidirectional oscillation circuit is: ; in Indicates capacitance The voltage, is the inductance value, is the capacitance value; The parallel output current of the mechanical switch and the oscillation branch is: ; is the current value flowing through the mechanical switch, is the current value flowing through the oscillation branch; At this moment, the mechanical switch is turned off in the state of zero current, and the thyristor is turned on at this time. , due to the capacitance The discharge causes a larger voltage value to be generated on the secondary side. Time makes the thyristor It is shut down due to reverse pressure, and the commutation phase ends; Among them, the primary capacitance is , the primary inductance of the coupled reactor is , the secondary inductance is , mutual inductance is M, capacitance The precharge voltage is , the commutation side capacitance is , the current on the low voltage side of the circuit breaker is , the current on the commutation side is , then: ; ; exist Turn on the thyristor at all times Entering the current limiting stage, such as Figure 4 As shown, in the inductor ,capacitance , and resistor R to limit the increase of fault current; When the voltage at both ends of the arrester reaches the operating voltage, the energy consumption branch MOV is turned on to consume the remaining fault energy. Figure 5 As shown; At this moment, the output current of the circuit breaker is zero, and the fault current elimination action is completed.

[0029] Embodiment three: In this embodiment, a simulation circuit with a DC side of 500kv is built in Matlab / Simulink. Taking a three-port control system as an example, when a line short circuit fault occurs on the load side of port 2 I2, the fault current at the fault location increases, and the fault current is transferred to the circuit breaker to be eliminated; the port current after the fault is eliminated is used as the input of the power flow control signal, and after PI regulation and limit regulation, a control signal is generated under comparison with the triangular wave. The square wave signal driven by the The drive control signal and system parameter settings of the platform simulation are shown in Table 1 below: Table 1: Main parameters of the simulation system:

[0030] like Figure 6The control system theory of the power flow module is shown. Figure 7 The structural diagram of the circuit breaker connected to the simulation system; setting the capacitance of the switch tube under different breaking signal control Voltage conditions: Solution 1: When the input switch tube , switch tube and When the parallel diode is turned on, the current flows through , , ,capacitance , we know that the capacitance The discharge current is output from port 2 I2.

[0031] Solution 2: When the input switch is in the locked state, the switch and When the parallel diode is turned on, the current flows through , , ,capacitance , we know that the capacitance Charging outflow port three I3.

[0032] Solution 3: When the input switch is in the locked state, the switch When on, current flows , , , then the capacitor Charging outflow port 2 I2.

[0033] Solution 4: When the input switch tube On, switch tube When on, current flows , , , then the capacitor The discharge current is output from port three I3.

[0034] The current flowing through the mechanical switch, the commutation current, the current limiting current, the arrester current and the current of each main path under the action of the power flow module are analyzed.

[0035] The fault occurrence time of the simulation design is 1.0 second. After 0.55ms, the circuit breaker detects the fault occurrence, at which time the circuit breaker starts to operate, and after 5.2ms, the fault current becomes 0.

[0036] like Figure 8The figure shows the timing diagram of circuit breaker action. A short circuit fault occurs at t0. At t1, the commutation branch is turned on and the oscillation circuit is put into operation. At t2, the mechanical switch S2 is turned off at zero current. At t3, the thyristor T4 is turned off by the reverse voltage and the current limiting branch is turned on. At t4, the arrester action voltage is reached and the residual current is consumed. At t5, the output fault current value is zero and the fault current is eliminated. At t6, the flow control module is activated and the flow is adjusted. At t7, the current in the main path returns to normal.

[0037] The simulation is carried out under the numerical conditions in Table 1. The current flowing through the main path; is the current flowing through the commutation branch; is the current flowing through the current limiting branch; is the current flowing through the arrester MOV; The current is Fig. 9 As shown, Current as Fig.10 As shown, Current as Fig.11 As shown, Current as Fig.12 As shown in the figure, after the fault is eliminated, the current change of the line current under power flow control is as follows Fig.13 shown.

Claims

1. A multi-port mechanical DC circuit breaker with integrated power flow control function, characterized in that: The circuit comprises a current limiting branch, an MOV branch, a commutation branch and a power flow module. One end of the port I1 is connected in series with a mechanical switch S1 and a power flow module, and the other end of the power flow module is connected to the port I2 and the port I3. The commutation branch comprises a thyristor T1 connected to the port I1, and one end of the thyristor T1 is connected in series with an inductor L1, a thyristor T2 and a thyristor T3. 3、 The other end of capacitor C1, thyristor T4 and inductor L4 is connected to port 2 I2 through thyristor T9. 11 Connected to port three I3; a current limiting branch is set in parallel on the commutation branch, one end of the current limiting branch is connected to the circuit between the inductor L1 and the thyristor T3, and the other end is connected to the circuit between the inductor L4 and the thyristor T9; an MOV branch is set in parallel on the current limiting branch.

2. A multi-port mechanical DC circuit breaker with integrated power flow control function according to claim 1, characterized in that: The current limiting branch includes thyristors T connected in series. 13 , resistor R and inductor L2; a thyristor T is provided in the loop behind the inductor L2 14 , Thyristor T 14 The other end is connected in parallel to the circuit between the capacitor C1 and the thyristor T4 of the commutation branch.

3. The multi-port mechanical DC circuit breaker with integrated power flow control function according to claim 2, characterized in that: The MOV branch includes a first lightning arrester MOV1, one end of the MOV branch is connected in parallel to the circuit between the inductor L1 and the thyristor T3, and the other end of the MOV branch is connected in parallel to the circuit between the inductor L2 and the thyristor T9.

4. The multi-port mechanical DC circuit breaker with integrated power flow control function according to claim 3, characterized in that: Thyristor T1, Thyristor T3, Thyristor T4, Thyristor T9, Thyristor T 13 and thyristor T 11 All from port 1 I1 to port 2 I2 or port 3 I3; thyristor T 14 From the commutation branch toward the current limiting branch.

5. The multi-port mechanical DC circuit breaker with integrated power flow control function according to claim 1, characterized in that: A branch of a thyristor T2 is provided between the first port I1 and the second port I2 , and the other end of the branch is connected to the second port I2 through the thyristor T9 , and the thyristor T2 faces the first port I1 .

6. The multi-port mechanical DC circuit breaker with integrated power flow control function according to claim 1, characterized in that: Port 2 I2 and port 3 I3 are connected to thyristor T8 and thyristor T 10 The two branches are connected in parallel between thyristor T1 and inductor L1; thyristor T8 and thyristor T 10 Towards port one I1.

7. The multi-port mechanical DC circuit breaker with integrated power flow control function according to claim 1, characterized in that: Port 2 I2 is connected to a branch with thyristor T7, and the other end of the branch is connected to thyristor T5 through thyristor T 14 In the branch, thyristor T7 is directed toward port I1.

8. The multi-port mechanical DC circuit breaker with integrated power flow control function according to claim 1, characterized in that: A ground loop is connected between the thyristor T3 and the capacitor C1. The ground loop includes the thyristor T3 connected in series. 12 and capacitor C2, the other end of which is grounded; a circuit formed by a thyristor T6 and an inductor L3 in series is connected in parallel at both ends of capacitor C2. 12 and thyristor T6 are both toward the ground terminal.

9. The multi-port mechanical DC circuit breaker with integrated power flow control function according to claim 1, characterized in that: The power flow control module includes fully controlled power electronic devices, multiple anti-parallel diodes, capacitor CF, discharge resistor R1 and second lightning arrester MOV2. The terminals of the upper bridge switch tube Sa and the lower bridge switch tube Sb are connected to the DC bus; the terminals of the remaining IGBT half-bridges are respectively connected in series with the fast mechanical switches S2 and S3 of each line; T2a and T2b are the upper and lower switch tubes of port two I2, and T3a and T3b are the upper and lower switch tubes of port three I3; D1a and D1b are anti-parallel diodes of port one I1, D2a and D2b are anti-parallel diodes of port two I2, and D3a and D3b are anti-parallel diodes of port three I3.

10. The control process of a multi-port mechanical DC circuit breaker with integrated power flow control function according to any one of claims 1 to 9, characterized in that: The control method is: When the line current changes in the power grid and power flow control is required, the power flow control module is activated when the system is stable. The difference between the state of each switch tube and the steady-state operation state is that the IGBT half-bridge in the module is no longer in the normally closed current-carrying state, but is regulated according to the current of each line, and the PWM signal is used to control the module. , The on-off of the capacitor makes the capacitor connected to the circuit in three different states: discharge, charge and bypass. In addition, the states of other switch tubes are consistent with the on or off state in the steady state. The specific control process is as follows: Under normal operating conditions, the current flows through the main path, during which the grid current flows to the capacitor and Precharge; if When a short circuit fault occurs at port 2 I2, the fault current will increase sharply in a short period of time. At this time, the circuit mathematical model is: ； In the formula, is the fault current; is the system voltage; is the equivalent resistance of the line; , They are line equivalent inductance and buffer inductance respectively; When a fault occurs, the circuit breaker does not detect the fault and does not take corresponding action. At this moment, the fault current value reaches the circuit breaker action value, the circuit breaker detects the fault, acts, turns on the commutation branch, and the current flows through the inductor and capacitor , and under its action, an oscillating current opposite to the main fault path is generated; The oscillation branch is put into use at all times, because the capacitor With initial voltage, it is an active oscillation; as the current increases, Always generate an oscillating current in the opposite direction to the main branch , the mathematical model of the unidirectional oscillation circuit is: ； in Indicates capacitance The voltage, is the inductance value, is the capacitance value; The parallel output current of the mechanical switch and the oscillation branch is: ； is the current value flowing through the mechanical switch, is the current value flowing through the oscillation branch; At this moment, the mechanical switch is turned off in the state of zero current, and the thyristor is turned on at this time. , due to the capacitance The discharge causes a larger voltage value to be generated on the secondary side. Time makes the thyristor It is shut down due to reverse pressure, and the commutation phase ends; Among them, the primary capacitance is , the primary inductance of the coupled reactor is , the secondary inductance is , mutual inductance is M, capacitance The precharge voltage is , the commutation side capacitance is , the current on the low voltage side of the circuit breaker is , the current on the commutation side is , then: ； ； exist Turn on the thyristor at all times Entering the current limiting stage, the inductor ,capacitance , and resistor R to limit the increase of fault current; When the voltage across the arrester reaches the operating voltage, the energy-consuming branch MOV is turned on to consume the remaining fault energy. At this moment, the output current of the circuit breaker is zero, and the fault current elimination action is completed.

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