Multi-port direct-current circuit breaker with self-adaptive reclosing function and control method of multi-port direct-current circuit breaker

Abstract

The invention relates to the technical field of direct-current circuit breakers, and discloses a multi-port direct-current circuit breaker with a self-adaptive reclosing function and a control method of the multi-port direct-current circuit breaker. The multi-port direct-current circuit breaker comprises a thyristor Tmi and a diode Dmi which are reversely connected in parallel to form a through-current branch; the anode of the thyristor Tmi is connected with the cathode of the thyristor Ti, the cathode of the thyristor Tmi is connected with a direct-current bus, and i = 1, 2,..., n; the anodes of the thyristors Tp1 and Tp3 are connected with a direct current bus; the cathode of the thyristor Tp1 is grounded through a resistor R1; the cathode of the diode Dp is connected with the cathode of the thyristor Tp1, and the anode is grounded through a resistor R2; the anode of the thyristor Ti is respectively connected with the cathode of the thyristor Tp3, the inductor, the lightning arrester and the cathode of the thyristor Tp2; and the other end of the inductor is connected with the cathode of the thyristor Tp1 through the capacitor, the other end of the lightning arrester and the anode of the thyristor Tp2. The multi-port DC circuit breaker is simple in topology, high in utilization rate of power electronic devices, and low in operation complexity and cost.

Description

Technical Field

[0001] The present invention relates to the technical field of direct current circuit breakers, and in particular to a multi-port direct current circuit breaker with an adaptive reclosing function and a control method thereof. Background Art

[0002] In recent years, DC microgrids and DC distribution systems have developed rapidly. However, due to the low impedance of the DC grid, after a short-circuit fault occurs, the fault current will quickly rise to dozens of times the rated value, seriously threatening the safety of grid equipment. Therefore, the rapid clearance of DC faults is one of the main technical difficulties that currently hinder the development of DC systems. Compared with other protection schemes, configuring a DC circuit breaker can achieve fully selective DC fault protection and can have reclosing protection capabilities, which is an ideal choice for protecting DC grids.

[0003] Compared with fully controlled devices, thyristors have low cost, low conduction loss and strong current tolerance. Therefore, solid-state DC circuit breakers based on thyristor design have become an emerging research hotspot. Thyristor DC circuit breakers can be divided into two categories according to the breaking mode: passive scheme and active scheme. The passive scheme triggers the inductor voltage mutation by fault, and applies reverse voltage to the thyristor to achieve automatic shutdown, but it is prone to malfunction when the load is switched or the line power fluctuates. The active scheme triggers the flow thyristor to turn off by actively turning on the auxiliary thyristor, thereby improving the initiative and reliability. Whether it is a passive scheme or an active scheme, it usually cannot handle the capacitor energy problem well, and it is necessary to use an external power supply or circuit to complete the capacitor charging and discharging, and the operation complexity and cost are high. In addition, in order to ensure the reliable operation of the system, the DC circuit breaker is generally required to have a reclosing function, but most of the current schemes only consider the first fault current breaking process and do not have a reclosing protection function.

[0004] In addition, as the DC system gradually develops in the direction of multi-terminal, in order to meet the full selectivity of protection, DC circuit breakers need to be configured at both ends of each line, which greatly increases the number of DC circuit breakers used and has poor economic efficiency. Summary of the invention

[0005] In order to solve the above technical problems existing in the prior art, the present invention aims to provide a DC circuit breaker which has the advantages of low construction cost, active fault current interruption, fast interruption speed, and adaptive reclosing protection function, and can be applied to multi-terminal medium and low voltage DC systems.

[0006] Specifically, in a first aspect, the present invention provides a multi-port DC circuit breaker with an adaptive reclosing function, and the technical solution is as follows: Including the current branch i, thyristor T i and auxiliary circuits, i=1,2,...,n; The input end of the current branch i is connected to the thyristor T i The cathode of the output terminal is connected to the DC bus; Auxiliary circuits include: Thyristor p1 The anode of the diode D is connected to the DC bus, and the cathode is grounded through the resistor R1; p The cathode of the thyristor is connected to p1 The cathode of the thyristor is grounded through the resistor R2; p3 The anode is connected to the DC bus, and the cathode is connected to the thyristor T i anode of the thyristor T; one end of the capacitor C is connected to the thyristor T p1 The cathode of the other end is connected through the inductor L c Connect to thyristor T i anode of the arrester MOV; one end is connected to the thyristor T p1 The other end is connected to the cathode of the thyristor T i Anode of thyristor T p2 The anode of the thyristor is connected to p1 The cathode of the thyristor is connected to i anode.

[0007] Preferably, the flow branch i comprises: Diode D mi The anode of the thyristor is connected to i The cathode of the thyristor is connected to the DC bus; mi With diode D mi Reverse parallel.

[0008] In a second aspect, the present invention further provides a control method for the multi-port DC circuit breaker with adaptive reclosing function, comprising the following steps: Step S1: Connect the flow branches 1 to n in sequence to the DC line L1 to the DC line L n , turn on thyristor T m1 To thyristor T mn ; Step S2: Turn on the thyristor T p3 , capacitor C is charged; when the voltage across capacitor C reaches the bus voltage V bus When the thyristor T p3 Natural shut-off; Step S3: Measure the DC line L j The current I fj ; where j=1,2,...,n; Step S4: If the current is greater than the current threshold I setj , then go to step S5, otherwise return to step S3; Step S5: Turn on the thyristor Tp1 and thyristor T j , so that the capacitor C and inductor L c Generate resonant current; When the resonant current is greater than the current I fj When the thyristor T mj Shut down; When the polarity of capacitor C is reversed and charged to the action voltage of the arrester MOV, the arrester MOV starts to dissipate energy; the thyristor T p1 and thyristor T j The current flowing through it gradually decreases until it is naturally shut down.

[0009] Furthermore, after step S5, the following steps are further included: Step S6: Turn on the thyristor T p2 , so that the polarity of capacitor C is reversed for the second time and restored to the initial state; Step S7: Turn on the thyristor T j , measure the discharge current I of capacitor C at the input end of the current branch i C and discharge duration d C ; Capacitor C discharges and thyristor T j Natural shut-off; Step S8: If I max <I r_m , and d C >d r , it is determined that a transient fault has occurred and the thyristor T is turned on. mj , complete reclosing, restore DC line L j Power supply; where I max is the discharge current I C The peak value, I r_m is the preset current value, d r The preset duration; Otherwise, it is determined that a permanent fault has occurred and the operation ends.

[0010] It can be seen that in the technical solution provided by the present invention, the multi-port DC circuit breaker with adaptive reclosing function does not contain fully controlled devices, and multiple current-carrying branches are connected to the auxiliary circuit through a DC bus, which improves the utilization rate of electrical devices, reduces the complexity and overall volume of the topological structure, and makes the cost lower; in addition, the capacitor C can realize charging and discharging operations without an external charging power supply, which can reduce the cost and operation complexity. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a circuit topology diagram of a multi-port DC circuit breaker with an adaptive reclosing function in the present invention.

[0012] Figure 2It is a control strategy diagram of the multi-port DC circuit breaker with adaptive reclosing function in the present invention under fault current breaking condition.

[0013] Figure 3 This is a control strategy diagram of the multi-port DC circuit breaker with adaptive reclosing function in the present invention under the adaptive reclosing working condition. DETAILED DESCRIPTION

[0014] Hereinafter, the technical solution proposed by the present invention will be further elaborated in combination with embodiments and drawings.

[0015] Embodiment 1: like Figure 1 As shown, a multi-port DC circuit breaker with an adaptive reclosing function provided in this embodiment includes a main current-carrying branch part, a thyristor part for line selection, and a shared auxiliary circuit part; The main current branch part includes n current branches, and the input end of each current branch i is connected to the thyristor T i The cathode of the output terminal is connected to the DC bus BUS, i=1,2, ...,n; The thyristor part includes n thyristors T i , its cathode is connected to port P i , the anode is connected to the thyristor T p3 The cathode; The shared auxiliary circuit part includes thyristor T p1 , Thyristor T p2 , Thyristor T p3 、Diode D p , resistor R1, resistor R2, capacitor C, inductor L c and arrester MOV.

[0016] Thyristor p3 The anode is connected to the DC bus, and the cathode is connected to the thyristor T i Anode; thyristor T p1 The anode of the thyristor is connected to p3 The anode of the diode D p The cathode of the thyristor is connected to p1 The cathode of the capacitor C is connected to the anode of the thyristor T through the resistor R2. p1 cathode, and the other end through the inductor L c Connect thyristor T p3 Cathode; one end of the arrester is connected to the thyristor T p1 The cathode of the thyristor is connected to the other end. p3 Cathode; Thyristor T p2 Anode connection thyristor T p1 The cathode of the thyristor T is connected to the cathode of the thyristor Tp3 The cathode of; thyristor T p3 The cathode of is connected to thyristor T i The anode of.

[0017] Among them, the resistance value of resistor R1 is much larger than that of resistor R2, at least R1 > 100R2.

[0018] The current-carrying branch i includes a thyristor T mi And a diode D mi Connected in reverse parallel. Diode D mi The anode of is connected to the cathode of thyristor T i The cathode of which is connected to the DC bus.

[0019] A control method for a multi-port DC circuit breaker with an adaptive reclosing function provided in this embodiment includes three working conditions: normal operation, fault current interruption, and adaptive reclosing.

[0020] Under the normal operation condition, all thyristors in the main current-carrying branch are turned on. At this time, the load current only flows through each current-carrying branch, and the power loss is very low. Among them, the input port P of the current-carrying branch j j Is connected to the DC line L j ; Turn on the thyristor T in the shared auxiliary circuit part p3 , Then the capacitor C is charged through the thyristor T p3 , Inductor L c , Capacitor C and resistor R1 to the ground circuit, so that the voltage across the capacitor C is charged to the bus voltage V bus , Then the thyristor T p3 Naturally turns off. Among them, j = 1, 2,..., n.

[0021] As Figure 2 Shown, under the fault current interruption condition, the control method of the multi-port DC circuit breaker with an adaptive reclosing function includes the following stages: t0 < t < t1: Fault detection stage. At t = t0, a ground short-circuit fault occurs on the DC line L j Connected to the port P j On, the fault current flows through the thyristor T mj To the faulty cable, when the current I fj Is greater than the current threshold I setj , The line protection device detects a short-circuit fault on the DC line L j And commands the DC circuit breaker to start current interruption.

[0022] t1 < t < t2: Current transfer stage. At t = t1, turn on the thyristor T p1 And thyristor T j Simultaneously, so that the capacitor C and the inductor Lc A resonant current is generated, and the resonant current gradually increases. When the resonant current is greater than the fault current flowing through the thyristor T mj , the current flowing through the thyristor T mj drops to 0, and the thyristor T mj reversely withstands the conduction voltage drop of the diode D mj and is reliably turned off. Thereafter, the fault current is transferred to the branch formed by the thyristor T p1 , capacitor C, inductor L c , thyristor T j and the fault grounding point. After about half a resonant period of the LC resonance occurs, the polarity of the capacitor C is reversed and it is reversely charged.

[0023] t2 < t < t3: Fault isolation stage. When t = t2, the voltage of the capacitor C reaches the operating voltage of the arrester MOV, and the arrester MOV starts to dissipate the energy of the system, and the fault current gradually drops to 0; when t = t3, the current flowing through the thyristor T p1 and thyristor T j is less than its holding current, and the thyristor T p1 and thyristor T j are naturally turned off, and the multi-port DC circuit breaker completes the fault current interruption process.

[0024] As Figure 3 shown, in the case of adaptive reclosing, the control method of the multi-port DC circuit breaker with adaptive reclosing function includes the following stages: t3 < t < t4: Capacitor voltage recovery stage. When t = t3, the fault isolation is completed, and the conducting thyristor T p2 is turned on. At this time, the capacitor C and inductor L c will generate a resonant current in the opposite direction to the initial direction, and the capacitor C completes the polarity reversal and returns to the initial state.

[0025] t4 < t < t5: Fault type judgment stage. When t = t4, the thyristor T j connected to the faulty line L j is turned on. Since the resistance R1 is much larger than R2 and can be regarded as an open circuit, the capacitor C will discharge through the path formed by the resistance R2, diode D p , capacitor C, inductor L c , thyristor T j and line L j . The peak current and discharge time of the capacitor C discharge at the detection port P j (i.e., the input end of the current-carrying branch j) are detected to determine the fault type. When the peak current is less than the preset value I r_m , and the discharge time is greater than d rWhen it is, it indicates that the fault is a transient fault; conversely, the fault is a permanent fault. After the capacitor discharges, the thyristor T j naturally turns off.

[0026] t5 < t < t6: Reclosing stage. At t = t5, the fault judgment is completed. If the judgment result is a transient fault, then turn on the thyristor T mj , and the line L j restores power supply; if the judgment result is a permanent fault, then end the operation to avoid the secondary current impact caused by the circuit breaker reclosing on a permanent fault.

[0027] In the technical solution provided in this embodiment, the capacitor C is charged to the bus voltage V p3 through the thyristor T c , inductor L bus , capacitor C and resistor R1 grounded circuit, which is simple to operate and does not require an external charging power supply.

[0028] In addition, it is necessary to ensure that the LC resonance current is greater than the line L j and the duration of the fault current is longer than the reverse recovery time of the thyristor T mj to ensure that the thyristor T mj turns off.

[0029] The conduction voltage drop of the diode D mj ensures the smooth progress of the reverse recovery process of the thyristor and avoids the overvoltage problem during the reverse recovery process. The grounding resistor R1 should have a large resistance value to ensure that the auxiliary thyristor T p1 can be reliably turned off. The grounding resistor R2 should have a small resistance value to ensure that the peak current and discharge duration of the capacitor discharge during the adaptive reclosing stage meet the detection requirements of the line protection device.

[0030] In summary, in the technical solution provided by the present invention, the multi-port DC circuit breaker with an adaptive reclosing function does not contain fully controlled devices, and multiple current-carrying branches are all connected to the auxiliary circuit through the DC bus, improving the utilization rate of power electronic devices, reducing the complexity of the topological structure and the overall volume, and making the cost lower; in addition, the capacitor C can be charged without the help of an external charging power supply, which can reduce the operation complexity and cost.

[0031] Furthermore, the present invention uses an LC resonance circuit to reverse the polarity of the capacitor, which can solve the problem of energy recovery of the capacitor after the circuit breaker interrupts the fault current; it can also perform fault type judgment and reclosing operation only through the capacitor and circuit inside the circuit breaker, avoiding the secondary current impact caused by blind reclosing in the case of permanent faults; in addition, the adaptive reclosing function is realized without external equipment, which can further reduce the operation complexity and cost.

Claims

1. A multi-port DC circuit breaker with adaptive reclosing function, characterized in that: Including the current branch i, thyristor T i and auxiliary circuits, i=1,2,...,n; The input end of the current branch i is connected to the thyristor T i The cathode of the output terminal is connected to the DC bus; Auxiliary circuits include: Thyristor p1 The anode of the diode D is connected to the DC bus, and the cathode is grounded through the resistor R1; p The cathode of the thyristor is connected to p1 The cathode of the thyristor is grounded through the resistor R2; p3 The anode is connected to the DC bus, and the cathode is connected to the thyristor T i anode of the thyristor T; one end of the capacitor C is connected to the thyristor T p1 The cathode of the other end is connected through the inductor L c Connect to thyristor T i anode of the arrester MOV; one end is connected to the thyristor T p1 The other end is connected to the cathode of the thyristor T i Anode of thyristor T p2 The anode of the thyristor is connected to p1 The cathode of the thyristor is connected to i anode.

2. The multi-port DC circuit breaker with adaptive reclosing function according to claim 1, characterized in that: The through-flow branch i comprises: Diode D mi The anode of the thyristor is connected to i The cathode of the thyristor is connected to the DC bus; mi With diode D mi Reverse parallel.

3. A control method for a multi-port DC circuit breaker with adaptive reclosing function as claimed in claim 2, characterized in that: The following steps are involved: Step S1: Connect the flow branches 1 to n in sequence to the DC line L1 to the DC line L n , turn on thyristor T m1 To thyristor T mn ; Step S2: Turn on the thyristor T p3 , capacitor C is charged; when the voltage across capacitor C reaches the bus voltage V bus When the thyristor T p3 Natural shut-off; Step S3: Measure the DC line L j The current I fj ; where j=1,2,...,n; Step S4: If the current is greater than the current threshold I setj , then go to step S5, otherwise return to step S3; Step S5: Turn on the thyristor T p1 and thyristor T j , so that the capacitor C and inductor L c Generate resonant current; When the resonant current is greater than the current I fj When the thyristor T mj Shut down; When the polarity of capacitor C is reversed and charged to the action voltage of the arrester MOV, the arrester MOV starts to dissipate energy; the thyristor T p1 and thyristor T j The current flowing through it gradually decreases until it is naturally shut down.

4. A control method for a multi-port DC circuit breaker with adaptive reclosing function as claimed in claim 3, characterized in that: After step S5, the following steps are also included: Step S6: Turn on the thyristor T p2 , so that the polarity of capacitor C is reversed for the second time and restored to the initial state; Step S7: Turn on the thyristor T j , measure the discharge current I of capacitor C at the input end of the current branch i C and discharge duration d C ; Capacitor C discharges and thyristor T j Natural shut-off; Step S8: If I max <I r_m , and d C >d r , it is determined that a transient fault has occurred and the thyristor T is turned on. mj , complete reclosing, restore DC line L j Power supply; where I max is the discharge current I C The peak value, I r_m is the preset current value, d r The preset duration; Otherwise, it is determined that a permanent fault has occurred and the operation ends.

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