Multi-port hybrid dc circuit breaker based on thyristors and control method

Abstract

The application provides a thyristor-based multi-port hybrid DC circuit breaker and a control method, comprising: a plurality of main branches and a shared branch; all the main branches are connected to the shared branch; the shared branch comprises a first thyristor branch, a power supply side circuit breaker unit and a fault side circuit breaker unit, the thyristor branch is used for bearing fault current in the process of breaking of a fast mechanical switch in the main branch; the fault side circuit breaker unit is composed of a first capacitor, a first discharge resistor and a first lightning arrester element in parallel connection; the power supply side circuit breaker unit is composed of a second thyristor branch, a current limiting resistor, a second capacitor, a second discharge resistor and a second lightning arrester, wherein the second capacitor, the second discharge resistor and the second lightning arrester are connected in parallel to form a second branch, the thyristor branch and the current limiting resistor are connected in series to form a first branch, and the first branch is connected in series to the second branch.

Description

Technical Field

[0001] This invention belongs to the field of DC-side fault isolation technology for flexible DC power grids, and particularly relates to a thyristor-based multi-port hybrid DC circuit breaker and its control method. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] Flexible DC transmission technology based on modular multilevel converters has demonstrated excellent performance in large-scale renewable energy grid integration, long-distance grid interconnection, and remote passive power supply. However, due to the low DC-side impedance of multi-terminal flexible DC grids, they are highly susceptible to DC-side short-circuit faults. When a short-circuit fault occurs on the DC side of a flexible DC grid, the fault current can rise to several times or even tens of times the rated current within milliseconds. Therefore, ultra-fast DC protection and DC circuit breakers are required to quickly isolate the fault.

[0004] Currently, DC circuit breakers are mainly classified into three types: solid-state DC circuit breakers, mechanical DC circuit breakers, and hybrid DC circuit breakers. Among them, hybrid DC circuit breakers have advantages such as low operating losses and fast operating speed, making them the preferred option for DC circuit breaker configuration in flexible DC power grids.

[0005] However, most existing hybrid DC circuit breakers are based on fully controlled power electronic switches (such as insulated-gate bipolar transistors), resulting in high manufacturing costs and large size and weight. Considering the huge demand for DC circuit breakers in flexible DC grids, the high cost of using hybrid DC circuit breakers would be unacceptable. Furthermore, the few thyristor-based hybrid DC circuit breakers that exist largely rely on external power to pre-charge the capacitor during operation to assist in turning off the thyristors, which increases both additional costs and maintenance workload.

[0006] Furthermore, since traditional two-port hybrid DC circuit breakers can only interrupt fault currents on the installed lines, the utilization rate of each hybrid DC circuit breaker is low from the perspective of the overall flexible DC grid, resulting in serious waste of hardware resources. Summary of the Invention

[0007] To overcome the shortcomings of the prior art, the present invention provides a thyristor-based multi-port hybrid DC circuit breaker, which reduces the topological complexity and maintenance workload of multi-port DC circuit breakers.

[0008] To achieve the above objectives, one or more embodiments of the present invention provide the following technical solutions: In the first aspect, a thyristor-based multi-port hybrid DC circuit breaker is disclosed, including: Several main and branch roads and shared branch roads; All main branch roads are connected to the common branch road; The common branch includes a first thyristor branch, a power supply side circuit breaker unit, and a fault side circuit breaker unit. The thyristor branch is used to carry the fault current during the fast mechanical switch opening process in the main branch. The fault-side circuit breaker unit consists of a first capacitor, a first discharge resistor, and a first surge arrester element connected in parallel. The power supply side circuit breaker unit consists of a second thyristor branch, a current-limiting resistor, a second capacitor, a second discharge resistor, and a second surge arrester. The second capacitor, the second discharge resistor, and the second surge arrester are connected in parallel to form a second branch. The thyristor branch and the current-limiting resistor are connected in series to form a first branch. The first branch is connected in series to the second branch.

[0009] As a further technical solution, the main branch route is composed of a load transfer switch (LCS) and a fast mechanical switch (UFD) connected in series.

[0010] Secondly, a fault isolation method for a thyristor-based multi-port hybrid DC circuit breaker is disclosed, including: Normal operating mode and DC fault isolation mode; In normal operating mode, the load transfer switch, fast mechanical switch and residual current switch of each port of the multi-port hybrid DC circuit breaker are all in the on or closed state, and the first thyristor branch and the second thyristor branch are both in the blocked state; the load current will only flow through the main branch of each port. The DC fault isolation mode includes a fault detection stage, a capacitor charging stage, a thyristor blocking stage, and a current dissipation stage, which are used to isolate faults in the DC lines connected to each port of the circuit breaker.

[0011] As a further technical solution, during the fault detection phase, fault current will be injected from the normal port into the faulty port. ， During this stage, the fault current will rise rapidly. The duration of this stage is mainly determined by the operating time of the DC line protection. After the DC line protection operates, the circuit breaker... t Upon receiving a trip signal, the fault current is interrupted.

[0012] As a further technical solution, during the capacitor charging phase, when the circuit breaker is... t Upon receiving a trip signal at moment 1, the first thyristor branch is turned on and the load transfer switch on the faulty port is blocked. Afterwards, the fault current will be transferred to the first thyristor branch, and the current flowing through the fast mechanical switch in the main branch where the fault is located will approach zero.

[0013] As a further technical solution, during the capacitor charging stage, the fault current path is: normal port P k -RCB k -UFD k -LCS k -T m - D 1-RCB1-Fault Port P 1- Fault point, k = 2,…, n ; The first capacitor in the fault-side circuit breaker unit is charged via the following path: normal port P k –RCB k –UFD k –LCS k – T m – C c – Grounding point, k = 2,…, n The voltage across the first capacitor is limited by the first surge arrester connected in parallel with it; Wherein, RCB stands for Residual Current Circuit Breaker, UFD for Fast Mechanical Circuit Breaker, and LCS for Load Transfer Switch. T m This is the first thyristor branch. D For diode branch, C c This is the first capacitor.

[0014] As a further technical solution, during the thyristor lockout phase, the fast mechanical switch of the main branch where the fault occurred... t At time 2, the tripping is completed, and the second thyristor branch in the power supply side circuit breaker unit is connected. At this time, the pre-charge first capacitor in the fault side circuit breaker unit will charge the second capacitor in the power supply side circuit breaker unit through the following path: C c - T m - T d - R d1 - C d .

[0015] As a further technical solution, during the thyristor lockout stage, in the first thyristor branch, the charging current of the second capacitor is opposite to the fault current. By controlling the resistance value of the current limiting resistor, the charging current is made greater than the fault current, thereby causing a reverse current to be generated in the first thyristor branch. The first thyristor branch is latched by maintaining the reverse current for a duration longer than the thyristor turn-off time, with the latch-up time set to [value missing]. t 3.

[0016] As a further technical solution, in the current dissipation stage, when... t At time 3, after the first thyristor branch is blocked, the fault circuit is disconnected at this time, and the healthy port cannot inject fault current into the fault point. The healthy port will continue to charge the second capacitor in the power supply side circuit breaker unit until the parallel second surge arrester is put into operation to dissipate current energy. The fault current in the fault-side circuit breaker unit will be dissipated by flowing through the first surge arrester in parallel. When the first capacitor in the fault-side circuit breaker unit discharges through the fault point, t After the voltage drops to zero at time 4, the residual current switch on the fault port is turned on to completely isolate the fault point.

[0017] As a further technical solution, after the circuit breaker's operation process ends and the second capacitor completes its discharge process through the second discharge resistor in parallel, the circuit breaker will be ready for the next fault.

[0018] The above one or more technical solutions have the following beneficial effects: This invention proposes a thyristor-based multi-port hybrid DC circuit breaker, which can quickly isolate short-circuit faults at any port. The main current-breaking component of the multi-port hybrid DC circuit breaker, the main disconnector, is based on thyristors, which are lower in cost and have higher current-carrying capacity. However, the thyristor needs to withstand reverse voltage and have zero current to turn off. Therefore, the turn-off of the first thyristor branch relies on the capacitor in the fault-side circuit breaker unit discharging to the capacitor in the power-side circuit breaker unit, causing the current in the first thyristor branch to be less than zero.

[0019] The multi-port hybrid DC circuit breaker in this invention does not require an additional pre-charging device to pre-charge the capacitor, thereby saving device costs and reducing the topological complexity and maintenance workload of the multi-port DC circuit breaker.

[0020] The technical solution of this invention does not require pre-charging, thus avoiding the expense of an additional charging power supply required for pre-charging, and also avoiding the workload of inspecting and maintaining the charging power supply.

[0021] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0022] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0023] Figure 1 This is a schematic diagram of the topology of a thyristor-based multi-port hybrid DC circuit breaker according to an embodiment of the present invention; Figure 2 For the fault detection stage of the embodiments of the present invention ( t 0< t < t 1); Figure 3 For the capacitor charging stage of the embodiment of the present invention ( t 1< t < t 2); Figure 4 This is the thyristor lockout stage in an embodiment of the present invention. t 2< t < t 3); Figure 5 For the current dissipation stage of the embodiment of the present invention ( t 3< t < t 4); Figure 6 A simulation model of a three-terminal flexible DC power grid; Figure 7 The simulation waveforms for the fault isolation process are shown in Figure (a), which shows the port current. i p1 , i p2 and i p3 (b) Current i Tm , i c and i Td (c) Surge arrester A c , A d Voltage across terminals. (d) Thyristor T m , T d Voltage at both ends u Tm , u Td . Detailed Implementation

[0024] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0025] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations of the present invention.

[0026] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0027] Example 1 This embodiment discloses a thyristor-based multi-port hybrid DC circuit breaker (T-MHCB), with the basic topology as follows: Figure 1 As shown, this DC circuit breaker can replace n A typical two-port hybrid DC circuit breaker (T-MHCB). Each port of the T-MHCB is equipped with one main branch, one diode branch, and one residual current circuit breaker (RCB). The main branch consists of a load transfer switch (LCS) and a fast mechanical switch (UFD) connected in series. In addition, the T-MHCB is also equipped with three branches shared by all ports, namely thyristor branches. T m Power supply side circuit breaker unit (SBU) and fault side circuit breaker unit (FBU).

[0028] Thyristor branch T m Used to carry fault current during the UFD tripping process. The FBU consists of three parallel elements, including a capacitor. C c Discharge resistor R c and surge arresters A c .

[0029] SBU consists of a thyristor branch T d Current limiting resistor R d1 ,capacitance C d Discharge resistor R d2 and surge arresters A d Among them, capacitor C d Discharge resistor R d2 and surge arresters A d Parallel connection. Due to the key components of T-MHCB ( Tm Since the T-MHCB (SBU and FBU) does not contain fully controlled power electronic devices and is shared by all ports, the total investment is significantly lower than that of traditional hybrid DC circuit breakers. Although there are existing designs for two-port DC circuit breakers, they cannot meet the needs of multi-port DC circuit breakers.

[0030] Example 2 The purpose of this embodiment is to provide a fault isolation method for a thyristor-based multi-port hybrid DC circuit breaker, including: Step (1) Normal operation: When the T-MHCB is working normally, the LCS, UFD and RCB of each port are in the on or closed state, while the thyristor T m , T d All are in a locked state. At this time, the load current will only flow through the main branch of each port, so no additional power loss will occur.

[0031] Step (2) DC fault isolation steps: When a DC fault occurs, the operation of the T-MHCB can be divided into four stages: fault detection stage, capacitor charging stage, thyristor latch-up stage, and current dissipation stage. For ease of analysis of the T-MHCB's operating principle, we assume... t Connect to port at time 0 P A short circuit fault occurred in the DC line of circuit 1. F .

[0032] (2-1) Fault Detection Phase When the fault F After it occurs, the fault current will flow from the normal port. P 2~ P n Inject fault port P 1, such as Figure 2 As shown. During this stage, the fault current will rise rapidly. The duration of this stage is mainly determined by the operating time of the DC line protection, typically several milliseconds.

[0033] The DC line is equipped with line protection to determine if a fault has occurred. Upon fault detection, a trip signal is sent to the DC circuit breaker. After the DC line protection operates, the T-MHCB... t Upon receiving a trip signal from the line protection system, the fault current is interrupted.

[0034] (2-2) Capacitor charging stage: When T-MHCB is t Upon receiving the trip signal at time 1, the thyristor branch is activated. T mAnd the LCS (LCS1) on the faulty port is blocked. Afterwards, the fault current will be transferred to the thyristor branch. T m The current flowing through UFD1 will be close to zero. Because UFDs are specifically designed for fast operation, their current breaking capacity is relatively poor. Their advantage is a short tripping time, typically only 2ms, much shorter than conventional mechanical switches. Due to the blocking of the fault port LCS, UFD1 can trip under near-zero current conditions, such as... Figure 3 As shown. The operating time of a UFD is typically considered to be 2 milliseconds. The fault current path during this phase is: normal port... P k ( k =2,…, n -RCB k -UFD k -LCS k -T m - D 1-RCB1-Fault Port P 1. Fault point. Additionally, the capacitors in the FBU. C c It will also be charged via the following path: [Unclear - possibly a port name] P k ( k = 2,…, n –RCB k –UFD k –LCS k – T m – C c – Grounding point. Capacitor. C c The voltage at both ends is affected by its parallel surge arrester. A c Restrictions.

[0035] The charging stage described above is due to the following: when the thyristor branch Tm is turned on, the fault-side circuit breaker unit FBU can be regarded as being directly connected to the DC bus. Since the DC bus potential is close to the system rated voltage at this time, and the other end of the FBU is directly grounded, the capacitor in the FBU will be charged at this time.

[0036] As the capacitor voltage in the FBU gradually increases during the charging process, it is eventually clamped to the residual voltage of the parallel surge arrester.

[0037] (2-3) Thyristor lockout stage: Assume UFD1 is in t At time 2, the tripping is completed, and the thyristor branch in the SBU is turned on. T d At this time, the pre-charge capacitor in the FBUC c The capacitors in the SBU will be accessed via the following path. C d Charge: C c - T m - T d - R d1 - C d ,like Figure 4 As shown. In the thyristor branch T m In the middle, capacitor C d The charging current is opposite to the fault current. Therefore, by controlling the current-limiting resistor... R d1 The resistance value can cause the charging current to exceed the fault current, thereby causing the thyristor branch to... T m A reverse current is generated in the thyristor. By maintaining the reverse current for a duration longer than the thyristor turn-off time, the thyristor branch can be controlled. T m Locking. Assume the locking time is... t 3.

[0038] This stage achieves the integration of the thyristor branch. T The m is turned off, thus isolating the power supply from the fault point.

[0039] (2-4) Current dissipation stage: when t 3-time thyristor branch T m After the blockade, since the fault circuit is now open, the healthy port cannot inject fault current into the fault point. At this time, the healthy port will continue to supply current to the capacitor in the SBU. C d Charge until the parallel surge arrester A d The input begins to dissipate electrical energy, such as... Figure 5 As shown. Furthermore, the fault current in the FBU will flow through the parallel surge arrester. A c And dissipated. When the capacitor in the FBU... C c After the fault point is discharged, t After the voltage drops to zero at time 4, open the fault port. P RCB1 on capacitor 1 completely isolates the fault point. At this point, the T-MHCB's operation ends. (Capacitor) C d Through parallel resistors Rd2 After the discharge process is complete, the T-MHCB will be ready for the next fault.

[0040] Although the thyristor branch T After the m-blocking is completed, the power supply and the fault point are separated, but there is still fault current in the system. The remaining fault current energy needs to be dissipated so that the system can return to normal operation.

[0041] Simulation verification Simulation model A three-terminal asymmetric unipolar model was established in PSCAD / EMTDC software to verify the effectiveness of the proposed T-MHCB. Its topology is as follows: Figure 6 As shown in Table 1, the main parameters of the simulation model are listed. The operating times of the UFD and RCB are 2 milliseconds and 30 milliseconds, respectively. The line protection operating time is 3 milliseconds. A typical hybrid DC circuit breaker is configured at the MMC outlet to isolate line faults on the power supply side.

[0042] Table 1. Main parameters of the simulation model of the three-terminal flexible DC power grid

[0043] Simulation results: At 2.0 s, Figure 6 The simulation model shown assumes a short-circuit fault with a fault resistance of 0.01 Ω. F The T-MHCB received a trip signal at 2.003 seconds and began to isolate the faulty port. P 1. Simulation results of the T-MHCB fault isolation process are as follows: Figure 7 As shown.

[0044] Depend on Figure 7 (a) It can be seen that when a short-circuit fault occurs in a DC line, the fault current flows from the healthy port. P 2. P 3. Injection fault point. At 2.003 s, the thyristor branch is turned on. T m And LCS1 is blocked. The fault current will be forced to flow into the thyristor branch. T m And the capacitors in the FBU C c Charging, as shown in Figure 7(b). At this time, the capacitor... C c The voltage will rise rapidly and clamp onto the surge arrester. A c At the residual voltage, such as Figure 7 As shown in (d). After UFD1 trips at 2.005 s, the thyristor branch in the SBU is turned on. Td Subsequently, the reverse current (with an amplitude exceeding the fault current) flows into the thyristor branch. T m The superposition of fault currents makes the total current flowing into the thyristor negative, thereby blocking the thyristor branch. T m When the thyristor branch T m After latch-up, the fault point will be isolated from the power supply. Capacitors in the FBU. C c The capacitor discharges to the fault point and completes the discharge process in 2.011 seconds. C d Continue charging from the healthy port until its voltage reaches that of the surge arrester. A d The residual voltage.

[0045] During the entire operation of the T-MHCB, the thyristor T m and T d The maximum withstand voltages are 950 kV and 500 kV respectively, surge arresters A c , A d The energy dissipated was 0.06 MJ and 6.05 MJ, respectively.

[0046] The control method for implementing a thyristor-based multi-port hybrid DC circuit breaker includes: The DC line protection system determines a fault within the DC line's fault zone and sends a trip signal to the DC circuit breaker. Upon receiving the trip signal, the DC circuit breaker will control the operation of its internal components according to the operating procedures set within the circuit breaker controller.

[0047] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A fault isolation method for a thyristor-based multi-port hybrid DC circuit breaker, characterized in that, include: Normal operating mode and DC fault isolation mode; In normal operating mode, the load transfer switch, fast mechanical switch and residual current switch of each port of the multi-port hybrid DC circuit breaker are all in the on or closed state, and the first thyristor branch and the second thyristor branch are both in the blocked state; the load current will only flow through the main branch of each port. In DC fault isolation mode, there are fault detection stage, capacitor charging stage, thyristor blocking stage and current dissipation stage, which are used to isolate faults in the DC lines connected to each port of the circuit breaker. During the fault detection phase, fault current will be injected from the normal port into the faulty port. ， During this stage, the fault current will rise rapidly. The duration of this stage is mainly determined by the operating time of the DC line protection. After the DC line protection operates, the circuit breaker... t Upon receiving a trip signal, the fault current is interrupted. During the capacitor charging phase, when the circuit breaker is... t Upon receiving a trip signal at moment 1, the first thyristor branch is turned on and the load transfer switch on the faulty port is blocked. Afterwards, the fault current will be transferred to the first thyristor branch, and the current flowing through the fast mechanical switch of the main branch where the fault is located will be close to zero. During the capacitor charging phase, the fault current path is: normal port. P k -RCB k -UFD k -LCS k -T m - D 1-RCB1-Fault Port P 1- Fault point, k = 2,…, n ; The first capacitor in the fault-side circuit breaker unit is charged via the following path: healthy port P k –RCB k –UFD k –LCS k – T m – C c – Grounding point, k = 2,…, n The voltage across the first capacitor is limited by the first surge arrester connected in parallel with it; In this context, RCB stands for Residual Current Circuit Breaker, UFD stands for Fast Mechanical Circuit Breaker, and LCS stands for Load Transfer Switch. T m This is the first thyristor branch. D For diode branch, C c This is the first capacitor; During the thyristor lockout phase, the fast mechanical switch of the main branch where the fault occurred... t At time 2, the tripping is completed, and the second thyristor branch in the power supply side circuit breaker unit is connected. At this time, the pre-charge first capacitor in the fault side circuit breaker unit will charge the second capacitor in the power supply side circuit breaker unit through the following path: C c - T m - T d - R d1 - C d ; During the thyristor lockout phase, in the first thyristor branch, the charging current of the second capacitor is opposite to the fault current. By controlling the resistance value of the current limiting resistor, the charging current is made greater than the fault current, thereby causing a reverse current to be generated in the first thyristor branch. The first thyristor branch is latched by maintaining the reverse current for a duration longer than the thyristor turn-off time, with the latch-up time set to [value missing]. t 3.

2. The fault isolation method for a thyristor-based multi-port hybrid DC circuit breaker as described in claim 1, characterized in that, During the current dissipation stage, when t At time 3, after the first thyristor branch is blocked, the fault circuit is disconnected at this time, and the healthy port cannot inject fault current into the fault point. The healthy port will continue to charge the second capacitor in the power supply side circuit breaker unit until the parallel second surge arrester is put into operation to dissipate current energy. The fault current in the fault-side circuit breaker unit will be dissipated by flowing through the first surge arrester in parallel. When the first capacitor in the fault-side circuit breaker unit discharges through the fault point, t After the voltage drops to zero at time 4, the residual current switch on the fault port is turned on to completely isolate the fault point.

3. The fault isolation method for a thyristor-based multi-port hybrid DC circuit breaker as described in claim 1, characterized in that, After the circuit breaker's operation is complete and the second capacitor completes its discharge process through the second discharge resistor in parallel, the circuit breaker will be ready for the next fault.

4. The fault isolation method for a thyristor-based multi-port hybrid DC circuit breaker as described in claim 1, characterized in that, The DC circuit breaker includes: Several main and branch roads and shared branch roads; All main branch roads are connected to the common branch road; The common branch includes a first thyristor branch, a power supply side circuit breaker unit, and a fault side circuit breaker unit. The thyristor branch is used to carry the fault current during the fast mechanical switch opening process in the main branch. The fault-side circuit breaker unit consists of a first capacitor, a first discharge resistor, and a first surge arrester element connected in parallel. The power supply side circuit breaker unit consists of a second thyristor branch, a current-limiting resistor, a second capacitor, a second discharge resistor, and a second surge arrester. The second capacitor, the second discharge resistor, and the second surge arrester are connected in parallel to form a second branch. The thyristor branch and the current-limiting resistor are connected in series to form a first branch. The first branch is connected in series to the second branch.

5. The fault isolation method for a thyristor-based multi-port hybrid DC circuit breaker as described in claim 4, characterized in that, The main branch of the DC circuit breaker consists of a load transfer switch (LCS) and a fast mechanical switch (UFD) connected in series.

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