A short arc type hybrid dc fault circuit breaker and a control method thereof

Abstract

The application relates to a short-arc type hybrid DC fault circuit breaker and a control method thereof. The circuit breaker disclosed by the patent does not use IGBT, fully plays the advantages of low thyristor cost, small conduction voltage drop, current zero natural turn-off and the like, realizes short-time arc breaking between fast mechanical switch (FMS) contacts, low-cost removal of fault current and adaptive reclosing after breaking, the main flow branch of the circuit breaker is only composed of FMS, power devices are not needed to be connected in series, power loss during normal operation of the system is reduced, and the capacitor in the additional oscillation circuit is pre-charged by the system, an additional pre-charging power supply is not needed, and the economy of the system is improved. The application has good use value and economic benefits in flexible DC power transmission and distribution and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of flexible DC power transmission and distribution network, in particular to a short arc type hybrid DC fault circuit breaker and a control method thereof. BACKGROUND

[0002] Since the 21st century, new power systems based on renewable energy have developed rapidly, and research on new switching electrical appliances has attracted widespread attention, especially research on DC circuit breakers has become a hot topic. At present, compared with AC power grids, DC power grids have a low damping characteristic, and if a short-circuit fault occurs in the system, the fault current rises very quickly, and the fault current on the DC side cannot naturally pass through zero, which increases the difficulty of fault isolation. Therefore, the development of DC circuit breakers with fast shutdown capability is the key to ensuring the stable operation of flexible DC power grids.

[0003] For the development of DC circuit breakers, it is mainly divided into mechanical DC circuit breakers, solid-state DC circuit breakers and hybrid DC circuit breakers. For the mechanical DC circuit breaker, the through-flow branch is only composed of a fast mechanical switch, and no power element is connected in series, so that the conduction loss is extremely low. However, the mechanical DC circuit breaker also has defects in commutation technology, such as long commutation time and difficulty in breaking small current; for the solid-state DC circuit breaker, it mainly relies on fully controlled power electronic devices to shut off the current, which can achieve fast shutdown and fast action, which is its obvious advantage, but because there are a large number of power electronic devices, the conduction loss is also extremely large, which is not ideal for the economy of the circuit breaker; for the hybrid DC circuit breaker, because the hybrid DC circuit breaker not only has the advantage of low conduction loss of the mechanical DC circuit breaker, but also has the advantage of fast shutdown of the solid-state DC circuit breaker, which makes the hybrid DC circuit breaker the most ideal DC circuit breaker in the flexible DC power transmission and distribution network, and becomes a hot topic of research at present.

[0004] Most existing hybrid DC circuit breakers use IGBT, which has high cost, and the service life of the fast mechanical switch is relatively short, so the present application proposes a short arc type hybrid DC fault circuit breaker and a control method thereof, which significantly reduces the cost while enhancing the operation reliability of the multi-terminal flexible DC power transmission and distribution network under fault. SUMMARY

[0005] The purpose of the present application is to provide a short arc type hybrid DC fault circuit breaker and a control method thereof.

[0006] To achieve the above purpose, the technical scheme of the present application is as follows:

[0007] A short arc type hybrid DC fault circuit breaker, comprising a main through-flow branch, a fault handling branch and a pre-charge branch; wherein,

[0008] The main through branch is only composed of a fast mechanical switch;

[0009] The fault handling branch is composed of branch 1, branch 2, branch 3, branch 4, branch 5, branch 6, branch 7, branch 8 and an oscillation circuit; branch 1 is composed of thyristor group T1 and thyristor group T2 in anti-parallel connection, branch 2 is composed of thyristor group T3 and thyristor group T4 in anti-parallel connection, branch 3 is composed of thyristor group T5, branch 4 is composed of thyristor group T6, branch 5 is composed of thyristor group T7, branch 6 is composed of thyristor group T8, branch 7 is composed of voltage dividing capacitor C2, branch 8 is composed of lightning arrester group MOA, and the oscillation circuit is composed of inductor L1 and capacitor C1 in series connection; branch 1 and branch 2 are connected in series and then connected in parallel at both ends of the fast mechanical switch, the cathodes of the thyristor groups in branch 3 and branch 4 are connected to each other and the anodes of each are connected in parallel at both ends of the fast mechanical switch, and the cathodes of the thyristor groups in branch 5 and branch 6 are connected to each other and the anodes of each are connected in parallel at both ends of the fast mechanical switch; one end of the oscillation circuit is connected to the connection point of branch 1 and branch 2, and the other end is connected to the connection point of branch 3 and branch 4; one end of branch 7 is connected to the connection point of branch 3 and branch 4, and the other end is connected to the connection point of branch 5 and branch 6; branch 8 is connected in parallel at both ends of the fast mechanical switch;

[0010] The pre-charge branch is composed of thyristor T9 and current limiting resistor R1, the cathode of the thyristor in the pre-charge branch is connected to the ground through the current limiting resistor R1, and the anode of the thyristor is connected to the connection point of branch 5 and branch 6.

[0011] The inductance value of inductor L1 and the capacitance value of capacitor C1 in the oscillation branch are determined by the expected oscillation frequency optimization target. The number of thyristors in each group is determined by the voltage level on the source side and the capacitance voltage amplitude of capacitor C1 and voltage dividing capacitor C2. The rated voltage of lightning arrester group MOA is determined by the voltage on the source side, which is generally 1.5 times the voltage on the source side.

[0012] A control method of the short arc type hybrid DC fault circuit breaker includes the following processes:

[0013] Assuming that the system is in normal operation, the current flows from the left side to the right side of the short arc type hybrid DC fault circuit breaker, and a short circuit fault occurs on the right side of the short arc type hybrid DC fault circuit breaker, the left side is called the non-fault side or the source side, and the right side is called the fault side.

[0014] Phase 0 (t0-): the fast mechanical switch is in the open state, the trigger signal is applied to T1 and T9 and removed immediately after they are turned on, the non-fault side charges the capacitor C1 and the voltage dividing capacitor C2, when the sum of the voltages of the capacitor C1 and the voltage dividing capacitor C2 is equal to the voltage of the non-fault side, the pre-charge branch current is reduced to 0, and T1 and T9 complete natural turn-off;

[0015] Phase 1 (t0-t1): at t0, the fast mechanical switch is closed, and the system is put into work, and the current flows through the main flow branch in normal work;

[0016] Phase 2 (t1-t2): at t1, when the system detects that the main flow branch current is abnormal, the trigger signal is applied to the thyristor group T1, T3 and T5, among which T3 and T5 are triggered to turn on, and the trigger signal of T3 and T5 is removed immediately after they are turned on, and T1 cannot be turned on due to the pre-charge voltage of the capacitor C1, so the trigger signal of T1 is always given until it is turned on and then the trigger signal is removed; at the same time, the system starts to open the fast mechanical switch, and because there is an arc between the FMS contacts, an oscillation circuit is formed between L1, C1, T3, T5 and FMS, and the capacitor C1 and the inductor L1 in the oscillation circuit generate an oscillation current in the main flow branch, which is opposite to the direction of the main flow branch current in phase 1, and the current in the main flow branch will gradually decrease;

[0017] Phase 3 (t2-t3): at t2, the current in the main flow branch is reduced to zero, the FMS extinguishes the arc at the first current zero crossing and completes the breaking, at this time the abnormal current is diverted from the main flow branch to the fault handling branch, and the FMS contacts continue to operate until the safe opening distance is reached, and the capacitor C1 in the oscillation circuit is discharged through T3 and T5;

[0018] Phase 4 (t3-t4): at t3, the sum of the voltages of L1 and C1 is 0, and T1 begins to withstand the forward voltage and turns on, at this time, the system current is transferred from branch 3 to branch 1, and T5 is naturally turned off due to the current zero crossing;

[0019] Phase 5 (t4-t5): at t4, the system discriminates the abnormal current, if the system determines that the abnormal current is a non-fault current, it enters phase 6; if the system determines that the abnormal current is a fault current, it enters phase 7;

[0020] Phase 6 (t5-t6): at t5, the system judges that the abnormal current is non-fault current, the system closes the fast mechanical switch, and a trigger signal is applied to T7 and removed immediately after T7 is turned on, T1 is turned off due to the reverse voltage of C2, and C2 is discharged through T3, T7, L1 and C1, when the sum of the voltages of L1, C1 and C2 is equal to 0, the current is transferred to the main current branch again, the system resumes normal work, and then T1 and T9 are triggered and removed immediately after they are turned on to pre-charge C1 and C2;

[0021] Phase 7 (t5-t6): at t5, the system judges that the abnormal current is fault current, a trigger signal is applied to T7 and removed immediately after T7 is turned on, T1 is turned off due to the reverse voltage of C2, and the system and C2 are discharged through T3, T7, L1 and C1 to the fault point; C1 and C2 are reverse charged, when the sum of the voltages of L1, C1 and C2 is equal to the operating voltage of the MOA, the MOA is put into operation to dissipate the system energy, and when the energy is completely dissipated, the fault is isolated, at this time, T1 and T9 are triggered and removed immediately after they are turned on to pre-charge C1 and C2;

[0022] Phase 8 (t6-t7): at t6, C1 and C2 are pre-charged, after a period of deionization, T1 and T3 are triggered, then the system current is identified and judged, if the fault does not exist, the operation of phase 6 is performed once; if the fault still exists, the operation of phase 7 is performed once;

[0023] Thus, one cycle is completed.

[0024] t0 is the time when the system is pre-charged before t0, t0 is the time when the fast mechanical switch FMS is turned on, t1 is the time when the system detects the abnormal circuit current, t2 is the time when the fault current commutation is completed, t3 is the time when the current in the circuit is transferred from the oscillation branch, t4 is the time when the system identifies the abnormal current, t5 is the time when the system judges the abnormal current, and t6 is the time when the reclosing is to be performed.

[0025] Compared with the prior art, the present application has the following advantages:

[0026] The short-arc hybrid DC fault circuit breaker of the application does not have a current limiting part, completely eliminates IGBT and is realized based on thyristors only, fully gives play to the advantages of low cost, small conduction voltage drop and natural zero-crossing turn-off of the thyristors, realizes short-time arc interruption between contacts of a fast mechanical switch (FMS), low-cost clearing of fault current and adaptive reclosing after interruption, while ensuring system reliability, reduces cost and improves economy of the system.

[0027] In the control method of the application, the C1 voltage is reduced by reverse charging during oscillation, and the current is transferred to the T1, T3 and FMS circuit during the T1 conduction moment, thereby improving the service life of the fast mechanical switch, realizing short-arc and complete current transfer to the T1 and T3 during turn-off.

[0028] In the application, the branch 7 composed of a new voltage dividing capacitor is introduced, and when the system judges abnormal current, the thyristor group T1 is turned off by the reverse voltage of the voltage dividing capacitor C2, and then the circuit is discharged to realize current transfer and fault isolation.

[0029] Meanwhile, the fault handling branch in the application realizes turn-off of the FMS in the main flow branch by using the LC oscillation branch, thereby transferring the current to the fault handling branch and increasing the reliability of the system. In addition, the pre-charging branch composed of the thyristor T9 and the current limiting resistor R1 pre-charges the capacitor, thereby eliminating an additional power supply and a complex pre-charging branch, optimizing the system, and for the capacitor C1 in the oscillation branch, the pre-charging voltage of the capacitor C1 can be adjusted by changing the C2, thereby increasing the reliability of the system.

[0030] In the control method of the application, when overcurrent occurs in the circuit, whether a fault occurs is detected according to fault detection to decide whether to resume normal operation or cut off the fault line (i.e. whether to select phase 6 or phase 7), thereby reducing the misoperation of the system and increasing the reliability of the system. The application has good use value and economic benefits in the field of DC power transmission and distribution. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The application is a short-arc hybrid DC fault circuit breaker, and the topological diagram is shown in the figure. DETAILED DESCRIPTION

[0032] The application is described in detail below with reference to the drawings, but this is not intended to limit the protection scope of the application.

[0033] Figure 1 The application is a short-arc hybrid DC fault circuit breaker, and the topological diagram is shown in the figure.

[0034] The main flow branch is only composed of a fast mechanical switch;

[0035] The fault processing branch is composed of branch 1, branch 2, branch 3, branch 4, branch 5, branch 6, branch 7, branch 8 and an oscillation circuit; branch 1 is composed of thyristor group T1 and thyristor group T2 in anti-parallel connection, branch 2 is composed of thyristor group T3 and thyristor group T4 in anti-parallel connection, branch 3 is composed of thyristor group T5, branch 4 is composed of thyristor group T6, branch 5 is composed of thyristor group T7, branch 6 is composed of thyristor group T8, branch 7 is composed of voltage dividing capacitor C2, branch 8 is composed of lightning arrester group MOA, and the oscillation circuit is composed of inductor L1 and capacitor C1 in series connection; branch 1 and branch 2 are connected in series and then connected in parallel at both ends of the fast mechanical switch, the cathodes of the thyristor groups in branch 3 and branch 4 are connected to each other and the anodes of each are connected in parallel at both ends of the fast mechanical switch, and the cathodes of the thyristor groups in branch 5 and branch 6 are connected to each other and the anodes of each are connected in parallel at both ends of the fast mechanical switch; one end of the oscillation circuit is connected to the connection point of branch 1 and branch 2, and the other end is connected to the connection point of branch 3 and branch 4; one end of branch 7 is connected to the connection point of branch 3 and branch 4, and the other end is connected to the connection point of branch 5 and branch 6; branch 8 is connected in parallel at both ends of the fast mechanical switch;

[0036] The pre-charge branch is composed of thyristor T9 and current limiting resistor R1, the cathode of the thyristor in the pre-charge branch is connected to the ground through the current limiting resistor R1, and the anode of the thyristor is connected to the connection point of branch 5 and branch 6.

[0037] The inductance value of inductor L1 and the capacitance value of capacitor C1 in the oscillation branch are determined by the expected oscillation frequency optimization target. The number of thyristors in each group is determined by the source side voltage level and the capacitance voltage amplitude of capacitor C1 and capacitor C2. The rated voltage of lightning arrester MOA is determined by the source side voltage, which is generally 1.5 times the source side voltage.

[0038] A control method of a short arc type hybrid DC fault circuit breaker includes the following processes:

[0039] Assuming that the system is in normal operation, the current flows from the left side to the right side of the short arc type hybrid DC fault circuit breaker, and a short circuit fault occurs at the right side of the short arc type hybrid DC fault circuit breaker. The left side is called the non-fault side or the source side, and the right side is called the fault side.

[0040] Stage 0 (t0-): The fast mechanical switch is in the off state, a trigger signal is applied to T1 and T9, and the trigger signal is removed immediately after T1 and T9 are turned on. The non-fault side charges capacitor C1 and voltage dividing capacitor C2. When the sum of the voltages of capacitor C1 and voltage dividing capacitor C2 is equal to the voltage of the non-fault side, the pre-charge branch current decreases to 0, and T1 and T9 complete natural turn-off.

[0041] Phase 1 (t0-t1): At t0, the fast mechanical switch is closed, and the system is put into operation. When the system is in normal operation, the current flows through the main flow branch;

[0042] Phase 2 (t1-t2): At t1, when the system detects that the current in the main flow branch is abnormal, trigger signals are applied to thyristors T1, T3 and T5. T3 and T5 are triggered to be turned on, and immediately after being turned on, the trigger signals of T3 and T5 are removed. At this time, T1 is always given a trigger signal until it is turned on, and then the trigger signal is removed. At the same time, the system starts to open the fast mechanical switch. Because there is an electric arc between the FMS contacts, an oscillation circuit is formed between L1, C1, T3, T5 and FMS. The capacitor C1 and the inductor L1 in the oscillation circuit generate an oscillation current in the main flow branch, which is opposite to the current direction in phase 1. The current in the main flow branch will gradually decrease.

[0043] Phase 3 (t2-t3): At t2, the current in the main flow branch decreases to zero, and the FMS extinguishes the arc at the first current zero crossing and completes the breaking. At this time, the abnormal current is diverted from the main flow branch to the fault handling branch, and the FMS contacts continue to operate until the safe opening distance is reached. The capacitor C1 in the oscillation circuit is discharged through T3 and T5.

[0044] Phase 4 (t3-t4): At t3, the sum of the voltages of L1 and C1 is 0, and T1 begins to withstand the forward voltage and is turned on. At this time, the system current is transferred from branch 3 to branch 1, and T5 is naturally turned off due to the current zero crossing.

[0045] Phase 5 (t4-t5): At t4, the system discriminates the abnormal current. If the system determines that the abnormal current is a non-fault current, it enters phase 6. If the system determines that the abnormal current is a fault current, it enters phase 7.

[0046] Phase 6 (t5-t6): At t5, the system determines that the abnormal current is a non-fault current. The system closes the fast mechanical switch, applies a trigger signal to T7, and immediately removes the trigger signal after T7 is turned on. Because C2 has a pre-charge voltage, thyristor T1 withstands the reverse voltage and is turned off. At this time, C2 is discharged through T3, T7, L1 and C1. When the sum of the voltages of L1, C1 and C2 is equal to 0, the current is transferred to the main flow branch again, and the system returns to normal operation. Then T1 and T9 are triggered and immediately removed after being turned on, and C1 and C2 are pre-charged.

[0047] Stage 7 (t5-t6): at t5, the system judges that the abnormal current is a fault current, a trigger signal is applied to T7 and removed immediately after T7 is turned on, T1 is turned off due to the pre-charge voltage of C2 and the reverse voltage of T1, the system and C2 are discharged to the fault point through T3, T7, L1 and C1, the system reversely charges C1 and C2, when the sum of the voltages of L1, C1 and C2 is equal to the operating voltage of MOA, MOA is put into operation to dissipate the system energy, when the energy is completely dissipated, the fault is isolated, at this time, T1 and T9 are triggered and the trigger signal is removed immediately after T1 and T9 are turned on, C1 and C2 are pre-charged;

[0048] Stage 8 (t6-t7): at t6, C1 and C2 are pre-charged, after a period of deionization, T1 and T3 are triggered, then the system current is identified and judged, if the fault does not exist, stage 6 is executed once, if the fault still exists, stage 7 is executed once;

[0049] Thus, one cycle is completed.

[0050] The pre-charge branch of the application does not need a switch device, does not need to introduce an additional power supply, the circuit breaker itself can charge the capacitor, avoids the introduction of an additional DC power supply and a complex pre-charge circuit, significantly reduces the cost and further improves the economy.

[0051] The unmentioned parts of the application are applicable to the prior art.

Claims

1. A short arc type hybrid DC fault circuit breaker, comprising a main flow branch, a fault handling branch and a pre-charge branch; characterized in that, the main flow branch is only composed of a fast mechanical switch; the fault handling branch is composed of branch 1, branch 2, branch 3, branch 4, branch 5, branch 6, branch 7, branch 8 and an oscillation circuit; branch 1 is composed of thyristor group T1 and thyristor group T2 in anti-parallel connection, branch 2 is composed of thyristor group T3 and thyristor group T4 in anti-parallel connection, branch 3 is composed of thyristor group T5, branch 4 is composed of thyristor group T6, branch 5 is composed of thyristor group T7, branch 6 is composed of thyristor group T8, branch 7 is composed of voltage dividing capacitor C2, branch 8 is composed of lightning arrester group MOA, and the oscillation circuit is composed of inductor L1 and capacitor C1 in series connection; branch 1 and branch 2 are connected in series and then connected in parallel at both ends of the fast mechanical switch, the cathodes of the thyristor groups in branch 3 and branch 4 are connected to each other and the anodes of each are connected in parallel at both ends of the fast mechanical switch, and the cathodes of the thyristor groups in branch 5 and branch 6 are connected to each other and the anodes of each are connected in parallel at both ends of the fast mechanical switch; one end of the oscillation circuit is connected to the connection point of branch 1 and branch 2, and the other end is connected to the connection point of branch 3 and branch 4; one end of branch 7 is connected to the connection point of branch 3 and branch 4, and the other end is connected to the connection point of branch 5 and branch 6; branch 8 is connected in parallel at both ends of the fast mechanical switch FMS; the pre-charge branch is composed of thyristor T9 and current limiting resistor R1, the cathode of the thyristor in the pre-charge branch is connected to the ground through the current limiting resistor R1, and the anode of the thyristor is connected to the connection point of branch 5 and branch 6.

2. The hybrid short arcing DC fault circuit breaker according to claim 1, characterized in that The inductance value of inductor L1 and the capacitance value of capacitor C1 in the oscillation circuit are determined by the expected oscillation frequency optimization target; the number of thyristors in each group is determined by the source side voltage level, the capacitance voltage amplitude of capacitor C1 and voltage dividing capacitor C2; the rated voltage of lightning arrester group MOA is determined by the source side voltage, which is 1.5 times the source side voltage.

3. The control method of the short arcing hybrid DC fault circuit breaker according to claim 1, characterized in that, The method comprises the following processes: Assuming that the system is in normal operation, the current flows from the left side to the right side of the short arc type hybrid DC fault circuit breaker, and the short circuit fault occurs at the right side of the short arc type hybrid DC fault circuit breaker, the left side is called the non-fault side or the source side, and the right side is called the fault side; Stage 0: the fast mechanical switch is in the off state, a trigger signal is applied to T1 and T9 and removed immediately after they are turned on, the non-fault side charges capacitor C1 and voltage dividing capacitor C2, and when the sum of the voltages of capacitor C1 and voltage dividing capacitor C2 is equal to the voltage of the non-fault side, the pre-charge branch current decreases to 0, and T1 and T9 complete natural turn-off; Stage 1: at time t0, the fast mechanical switch is closed, the system is put into operation, and the current flows through the main flow branch in normal operation; Phase 2: At time t1, when the system detects that the main current branch current is abnormal, trigger signals are applied to thyristor groups T1, T3 and T5, wherein T3 and T5 are triggered to be turned on, and immediately after being turned on, the trigger signals of T3 and T5 are removed. Because of the pre-charge voltage of capacitor C1, T1 bears a reverse voltage and thus is not turned on. At this time, the trigger signal is always applied to T1 until it is turned on and then the trigger signal is removed. Meanwhile, the system starts to open the fast mechanical switch. Because of the existence of electric arc between the contacts of FMS, an oscillation circuit is formed among L1, C1, T3, T5 and FMS. Capacitor C1 and inductor L1 in the oscillation circuit generate an oscillation current in the main current branch, which is opposite to the direction of the main current branch current in phase 1, and the current in the main current branch is gradually reduced. Phase 3: At time t2, the current in the main current branch is reduced to zero, and FMS extinguishes the arc at the first current zero-crossing point and completes the breaking. At this time, the abnormal current is diverted from the main current branch to the fault handling branch, and the contacts of FMS continue to operate until a safe opening distance is reached. Capacitor C1 in the oscillation circuit is discharged through T3 and T5. Phase 4: At time t3, the sum of the voltages of L1 and C1 is 0, and T1 is turned on. At this time, the system current is transferred from branch 3 to branch 1, and T5 is naturally turned off due to the current zero-crossing. Phase 5: At time t4, the system discriminates the abnormal current. If the system determines that the abnormal current is a non-fault current, phase 6 is entered. If the system determines that the abnormal current is a fault current, phase 7 is entered. Phase 6: At time t5, the system determines that the abnormal current is a non-fault current. The system closes the fast mechanical switch, applies a trigger signal to T7, and immediately removes the trigger signal after T7 is turned on. Because of the pre-charge voltage of C2, thyristor T1 bears a reverse voltage and is turned off. At this time, C2 is discharged through T3, T7, L1 and C1. When the sum of the voltages of L1, C1 and C2 is equal to 0, the current is transferred to the main current branch again, the system returns to normal operation, and then T1 and T9 are triggered and the trigger signals are removed immediately after they are turned on to pre-charge C1 and C2. Phase 7: At time t5, the system determines that the abnormal current is a fault current. A trigger signal is applied to T7, and the trigger signal is removed immediately after T7 is turned on. Because of the pre-charge voltage of C2, the thyristor group T1 bears a reverse voltage and is turned off. The system and capacitor C2 are discharged through T3, T7, L1 and C1 to the fault point. The system reversely charges C1 and C2. When the sum of the voltages of L1, C1 and C2 is equal to the operating voltage of the arrester group MOA, MOA is put into operation to dissipate the system energy. When the energy is completely dissipated, the isolation of the fault is completed. At this time, thyristors T1 and T9 are triggered and the trigger signals are removed immediately after they are turned on to pre-charge C1 and C2. Phase 8: At time t6, capacitors C1 and C2 are pre-charged. After a period of de-ionization, the thyristor group T1 and T3 are triggered, and then the system current is identified and judged. If the fault does not exist, phase 6 is executed once. If the fault still exists, phase 7 is executed once. A cycle of action is thus completed.

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