Resistance-capacitance type inductive hybrid direct current circuit breaker

Abstract

The invention relates to a resistance-capacitance type inductive hybrid direct current circuit breaker and a control method thereof. When overcurrent occurs in the system, the current transfer branch is input to realize reversing of fault current, a resistor in the current transfer branch shunts the fault current, the amplitude of the fault current and the voltage rise rate of a circuit breaker port are effectively inhibited, and it is ensured that the mechanical switch can reliably complete breaking. Capacitors in the current transfer branch and the breaking branch do not need additional pre-charging circuits, the overall size of the circuit breaker is reduced, only mechanical switch reactive power devices are connected in series in the through-flow branch, and the loss of normal work of a system is reduced; the breaking capacitor and the thyristor replace a traditional full-control device, so that the overall economical efficiency of the circuit breaker is greatly improved; and meanwhile, the reliability of the system is further improved by phase selection on-off and small current on-off of the circuit breaker.

Description

Technical Field

[0001] The present invention relates to the field of flexible direct current distribution networks, and in particular to a resistive-capacitive-inductive hybrid direct current circuit breaker and a control method thereof. Background Art

[0002] In the construction plan of DC power distribution system, the main difficulty lies in the design of protection scheme. Due to the low damping characteristics of DC system, fault current spreads rapidly in DC system. If it cannot be suppressed and removed in time, serious consequences can be caused within ms. Therefore, fault detection, location and isolation in DC system are the focus of DC distribution network research. The use of DC circuit breaker to complete the removal of fault current can meet the requirements of rapid disconnection and is currently the most effective protection scheme in DC power grid. Hybrid DC circuit breaker combines the advantages of mechanical circuit breaker and solid-state circuit breaker, and has great development potential and market value.

[0003] With the massive access of energy storage devices and DC loads in low-voltage distribution networks, the amplitude of fault current has increased significantly. In addition, the breaking capacity of existing traditional low-voltage DC circuit breakers is relatively small, only a few hundred A, which is difficult to meet the protection requirements of future DC distribution networks. At present, with the increase of DC power loads such as new energy electric vehicles, solar power generation, and distributed photovoltaic access in my country and the development of DC distribution systems, the construction of medium and low voltage DC distribution networks will become a future trend. Therefore, in the field of flexible DC distribution, it is of great theoretical and engineering significance to study hybrid DC circuit breakers with fast disconnection, reliability and economy. Summary of the invention

[0004] In order to improve the operational reliability of a DC power grid under a DC fault and reduce the requirement for the current breaking capacity of a DC circuit breaker, the present invention proposes a hybrid RC-inductive DC circuit breaker and a control method thereof, so as to timely limit the rising rate and amplitude of the fault current after a system fault. The proposed circuit breaker does not require a fully controlled device and eliminates a capacitor pre-charging circuit, thereby increasing the reliability and economy of the system.

[0005] The technical solution of the present invention is as follows:

[0006] 1. In the present invention, a RC-inductive hybrid DC circuit breaker is characterized in that the current-carrying branch is composed of a mechanical switch MS.

[0007] 2. In the present invention, a RC-inductive hybrid DC circuit breaker is characterized in that the current transfer branch includes thyristors T1 and T2 connected in series through anodes, thyristors T3 and T4 connected in series through cathodes, thyristors T7, capacitor C, inductor L, and diode D connected in series with resistor R through anodes. Thyristor T7 is connected in reverse parallel to both ends of thyristor T1, the cathode of diode D is connected to capacitor C, the other end of capacitor C is connected to resistor R and then connected to the cathode of thyristor T3, one end of inductor L is connected to the anode of thyristor T1, and the other end is connected to the cathode of diode D; the capacitance value of capacitor C and the inductance value of inductor L in the current transfer branch are determined by the optimization targets such as the desired oscillation frequency and commutation capability, and the resistance value of resistor R is determined by the desired voltage rise rate of capacitor C.

[0008] 3. In the present invention, a RC-inductive hybrid DC circuit breaker is characterized in that the disconnecting branch includes a disconnecting capacitor C B , thyristor T5 and thyristor T6 connected in series through the cathode, wherein thyristor T5 and thyristor T6 are connected to thyristor T3 and thyristor T4 through the anode respectively, disconnecting capacitor C B One end is connected to the cathode of thyristor T3, and the other end is connected to the cathode of thyristor T5; the disconnecting capacitor C B The capacitance value is determined by the desired switching time.

[0009] 4. In the present invention, a RC-inductive hybrid DC circuit breaker is characterized in that the energy consumption branch is composed of a lightning arrester MOV, wherein the MOV is connected in parallel at both ends of the current-carrying branch; the rated voltage of the MOV is determined by the source side voltage, and the transient voltage of the MOV is generally 1.6 times the source side voltage.

[0010] 5. In the present invention, a RC-type inductive hybrid DC circuit breaker is characterized in that the pre-charging branch is composed of a thyristor T9, an auxiliary resistor R A , mechanical switch S and pre-charge resistor R c The mechanical switch S is connected to the auxiliary resistor R A connected to the ground; the pre-charge resistor R c Connected in parallel with the mechanical switch S; auxiliary resistor R A One end is connected to the cathode of thyristor T9, and the other end is connected to the mechanical switch S; the anode of thyristor T9 is connected to the cathode of thyristor T5; the auxiliary resistor R A The resistance value is determined by the expected fault current amplitude under small current fault. c The resistor value is determined by the desired pre-charge current amplitude.

[0011] 6. In the present invention, a RC-inductive hybrid DC circuit breaker is characterized in that the auxiliary branch is composed of a thyristor T8, wherein an anode of the thyristor T8 is connected to a cathode of the thyristor T4, and the other end is connected to a cathode of the thyristor T9. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a topological diagram of a RC-inductive hybrid DC circuit breaker.

[0013] Figure 2 This is a schematic diagram of the current in each branch of the hybrid DC circuit breaker in normal breaking mode.

[0014] Figure 3 This is a schematic diagram of the current in each branch under the phase-selective breaking mode of the hybrid DC circuit breaker.

[0015] Figure 4 This is a schematic diagram of the current in each branch of the hybrid DC circuit breaker in the low current breaking mode.

[0016] Implementation

[0017] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0018] Figure 1 The invention discloses a topological schematic diagram of a RC-inductive hybrid DC circuit breaker, which includes a current-carrying branch, a current transfer branch, a disconnecting branch, an auxiliary branch, an energy-consuming branch and a pre-charging branch.

[0019] A control method for a RC-inductive hybrid DC circuit breaker includes the following process:

[0020] Assuming that the system is operating normally, the current flows from the left side to the right side of the DC circuit breaker, and the short circuit fault occurs at the right end of the DC circuit breaker. The left side of the DC circuit breaker is called the non-fault side or source side, and the right side is called the fault side. According to different fault conditions in the system, the three working modes of the circuit breaker are normal breaking mode, phase selection mode and low current mode.

[0021] (1) Normal breaking mode

[0022] Figure 2 It is a schematic diagram of the currents of each branch in a normal breaking mode of a resistive-capacitive-inductive hybrid DC circuit breaker proposed by the present invention.

[0023] Phase 1 (-t0): The mechanical switch MS is in the open circuit state, the mechanical switch S of the pre-charging branch is disconnected, and a trigger signal is applied to the thyristor T3 and the thyristor T9. The source side capacitor C BCharging, when the capacitor voltage is equal to the source side voltage, remove the applied trigger signal, the pre-charge branch current drops to zero, T3 and T9 are naturally turned off; then apply a trigger signal to thyristor T7 and thyristor T8, the source side charges capacitor C, when the capacitor voltage is equal to the source side voltage, remove the applied trigger signal, the pre-charge branch current drops to zero, T7 and T8 are naturally turned off, and then close the mechanical switch S;

[0024] Phase 2 (t0): Close the mechanical switch MS, and the current flows through the current branch when the system works normally;

[0025] Phase 3 (t0-t1): At time t1, when an abnormal current is detected in the circuit, a trip command is issued to the mechanical switch MS, and a trigger signal is applied to the thyristors T2 and T3 at the same time. The current transfer branch and the flow branch form a loop, and the capacitor C and inductor L in the current transfer branch generate a recoil current that is injected into the flow branch. When the current in the flow branch drops to zero, the mechanical switch MS is disconnected.

[0026] Phase 4 (t1-t2): At time t2, the system current is completely transferred from the current-carrying branch to the current-transferring branch, and the capacitor C continues to discharge. Since the diode D bears the negative voltage from the capacitor C, the resistor R will not be put into operation, and the system current reversely charges the capacitor C.

[0027] Phase 5 (t2-t3): At t3, the voltage of capacitor C decreases to zero, diode D no longer bears negative pressure, and resistor R is put into operation and connected in parallel at both ends of the circuit where capacitor C is located to jointly limit the rise of fault current;

[0028] Phase 6 (t3-t4): At t4, the mechanical switch MS of the current-carrying branch reaches the rated opening distance, and a trigger signal is applied to the thyristor T5, disconnecting the capacitor C B It starts to discharge, and the thyristor T3 is subjected to the negative pressure from the disconnecting capacitor;

[0029] Phase 7 (t4-t5): At t5, the current in the branch where the thyristor T3 is located drops to zero, the thyristor T3 is naturally turned off, and the system current is transferred to the disconnecting branch and the current transfer branch, and the disconnecting capacitor C B Carry out reverse charging;

[0030] Phase 8 (t5-t6): At t6, the voltage across the circuit breaker reaches the MOV action voltage, and the fault current is transferred to the energy consumption branch. Because the MOV's own volt-ampere characteristic will present a large reverse voltage in the fault line, the fault current is cut off; at the same time, the energy stored in the capacitor C begins to be discharged through the resistor R;

[0031] Phase 9 (t6-t7): At t7, the fault current has been reduced to zero, the circuit breaker has completed the isolation of the fault point, and the energy of the capacitors in each branch of the circuit breaker has been discharged. The mechanical switch S of the pre-charge branch is disconnected, and a trigger signal is applied to the thyristor T3 and the thyristor T9. The source side capacitor C B Charging, when the capacitor voltage is equal to the source side voltage, remove the applied trigger signal, the pre-charge branch current drops to zero, T3 and T9 are naturally turned off; then apply a trigger signal to thyristor T7 and thyristor T8, the source side charges capacitor C, when the capacitor voltage is equal to the source side voltage, remove the applied trigger signal, the pre-charge branch current drops to zero, T7 and T8 are naturally turned off, and then close the mechanical switch S;

[0032] At this point, the circuit breaker completes the action process in normal breaking mode.

[0033] (2) Phase selection mode

[0034] Figure 3 It is a schematic diagram of the currents of each branch in a phase selection mode of a resistive-capacitive-inductive hybrid DC circuit breaker proposed by the present invention.

[0035] The phase selection mode has the same operation process as the normal breaking mode in the time period from t0 to t3, which will not be repeated here. Having a long fault judgment time is one of the main advantages of the circuit breaker. The phase selection mode prolongs the fault judgment time and improves the reliability of the system. At t3, the mechanical switch MS of the current branch reaches the rated opening distance, and the system continues to identify the fault. At the same time, the circuit breaker can limit the fault current within a certain range, effectively suppressing the rise of the fault current. At t4, it is determined that a fault has occurred in the system, and a trigger signal is applied to the thyristor T5 to disconnect the capacitor C B The thyristor T3 starts to discharge, and it is subjected to the negative pressure from the disconnecting capacitor. The subsequent operation process is the same as that of stage 7 to stage 9. If it is determined that there is no fault in the system, it is necessary to exit the phase selection mode, close the mechanical switch MS of the current branch, and enter stage 10.

[0036] Phase 10 (t5-t8): At t8, the system current is completely transferred to the current-carrying branch, thyristors T2 and T3 are naturally turned off, and the energy stored in capacitor C begins to be discharged through resistor R;

[0037] Phase 11 (t8-t9): At t9, the energy of the capacitors in each branch of the circuit breaker is discharged, the mechanical switch S of the pre-charge branch is disconnected, and a trigger signal is applied to the thyristor T3 and the thyristor T9, and the source side capacitor C BCharging, when the capacitor voltage is equal to the source side voltage, remove the applied trigger signal, the pre-charge branch current drops to zero, T3 and T9 are naturally turned off; then apply a trigger signal to thyristor T7 and thyristor T8, the source side charges capacitor C, when the capacitor voltage is equal to the source side voltage, remove the applied trigger signal, the pre-charge branch current drops to zero, T7 and T8 are naturally turned off, and then close the mechanical switch S;

[0038] At this point, the circuit breaker completes the action process in the phase selection mode.

[0039] (3) Low current mode

[0040] Figure 3 It is a schematic diagram of the currents of each branch in a small current mode of a resistive-capacitive-inductive hybrid DC circuit breaker proposed by the present invention.

[0041] When the power grid is grounded or the line is under maintenance, the current that needs to be disconnected is very small, which can easily cause the mechanical switch MS to fail to disconnect. For this reason, an auxiliary branch is introduced when disconnecting small currents, and the disconnecting current flowing through the mechanical switch MS is increased so that it can successfully complete the disconnection. The time period from t0 to t1 in the small current mode is the same as the action process of the normal disconnection mode. At t1, when an abnormal current is detected in the circuit and it is judged to be a small current fault, a disconnection command is issued to the mechanical switch MS, and a trigger signal is applied to thyristors T4 and T8 at the same time. The auxiliary branch further increases the fault current; at t2, a trigger signal is applied to thyristors T2 and T5 to disconnect the capacitor C in the branch. B , the capacitor C and inductor L in the current transfer branch generate a kickback current that is injected into the current-carrying branch, and the thyristor T4 is subjected to the current from the capacitor C B Negative pressure automatically shuts down. When the current in the flow branch drops to zero, the mechanical switch MS completes the disconnection, and the fault current continues to flow to the capacitor C B and reversely charge the capacitor C; the subsequent action process is the same as that of stage 8 to stage 9;

[0042] At this point, the circuit breaker completes the action process in the low current mode.

[0043] Any matters not described in the present invention are applicable to the prior art.

Claims

1. A RC-inductive hybrid DC circuit breaker, characterized in that: It consists of a current-passing branch, a current transfer branch, a disconnecting branch, an auxiliary branch, an energy-consuming branch and a pre-charging branch.

2. A RC-inductive hybrid DC circuit breaker according to claim 1, characterized in that: The through-current branch is composed of a mechanical switch MS.

3. The RC-inductive hybrid DC circuit breaker according to claim 1, characterized in that: The current transfer branch includes thyristors T1 and T2 connected in series through anodes, thyristors T3 and T4 connected in series through cathodes, thyristor T7, capacitor C, inductor L, and diode D connected in series with resistor R through anodes. Thyristor T7 is connected in reverse parallel to both ends of thyristor T1, the cathode of diode D is connected to capacitor C, the other end of capacitor C is connected to resistor R and then connected to the cathode of thyristor T3, one end of inductor L is connected to the anode of thyristor T1, and the other end is connected to the cathode of diode D; the capacitance value of capacitor C and the inductance value of inductor L in the current transfer branch are determined by optimization targets such as desired oscillation frequency and commutation capability, and the resistance value of resistor R is determined by the desired voltage rise rate of capacitor C.

4. The RC-inductive hybrid DC circuit breaker according to claim 1, characterized in that: The disconnecting branch includes a disconnecting capacitor C B , thyristor T5 and thyristor T6 connected in series through the cathode, wherein thyristor T5 and thyristor T6 are connected to thyristor T3 and thyristor T4 through the anode respectively, disconnecting capacitor C B One end is connected to the cathode of thyristor T3, and the other end is connected to the cathode of thyristor T5; the disconnecting capacitor C B The capacitance value is determined by the desired switching time.

5. The RC-inductive hybrid DC circuit breaker according to claim 1, characterized in that: The energy consumption branch is composed of a lightning arrester MOV, wherein the MOV is connected in parallel at both ends of the current-carrying branch; the rated voltage of the MOV is determined by the source side voltage, and the transient voltage of the MOV is generally 1.6 times the source side voltage.

6. The RC-inductive hybrid DC circuit breaker according to claim 1, characterized in that: The pre-charging branch is composed of thyristor T9, auxiliary resistor R A , mechanical switch S and pre-charge resistor R c The mechanical switch S is connected to the auxiliary resistor R A connected to the ground; the pre-charge resistor R c Connected in parallel with the mechanical switch S; auxiliary resistor R A One end is connected to the cathode of thyristor T9, and the other end is connected to the mechanical switch S; the anode of thyristor T9 is connected to the cathode of thyristor T5; the auxiliary resistor R A The resistance value is determined by the expected fault current amplitude under small current fault. c The resistor value is determined by the desired pre-charge current amplitude.

7. The RC-inductive hybrid DC circuit breaker according to claim 1, characterized in that: The auxiliary branch is composed of a thyristor T8 , wherein an anode of the thyristor T8 is connected to a cathode of the thyristor T4 , and the other end of the thyristor T8 is connected to a cathode of the thyristor T9 .

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