A thyristor type DC circuit breaker and a control method thereof

Abstract

This invention relates to the field of DC circuit breakers, and discloses a thyristor-type DC circuit breaker and its control method. The DC circuit breaker structure is a thyristor T... m1 Anode-connected thyristor T m2 The cathode forms the A terminal of the circuit breaker, T m1 Cathode connection T m2 The anode of the thyristor forms the B terminal of the circuit breaker; the thyristor T p1 anode, thyristor T p2 The cathode is connected to terminal A; T p1 Cathode connection T p2 After anode, it passes through resistor R in sequence. g Switch RCB g Grounding; T p1 Cathode connection T p2 After the anode, it also passes through inductor L p Capacitor C is connected to terminal B; one end of the surge arrester MOV is connected to terminal T. p1 The cathode is connected to the first terminal, and the other end is connected to the B terminal. This invention has a simple structure and significant cost advantages; under normal operating conditions, only a single thyristor is conducting, resulting in extremely low losses and extremely high circuit breaker efficiency. Combined with control methods, it can actively and reliably connect or disconnect bidirectional operating current or bidirectional fault current; it can also achieve fast reclosing functionality.

Description

Technical Field

[0001] This invention belongs to the field of DC circuit breakers, specifically relating to a thyristor-type DC circuit breaker and its control method. Background Technology

[0002] In recent years, with the continuous integration of renewable energy sources such as wind and solar power into the grid, DC system protection is crucial for the reliability and safety of power transmission, whether addressing temporary faults that are prone to occur in overhead lines during long-distance flexible DC transmission or meeting the isolation requirements of fault areas after a DC microgrid fault. Due to the advantages of voltage source converters based on fully controlled devices, such as low harmonic content, independent control of active and reactive power, and the ability to supply power to passive networks, various DC system scenarios, including electric aircraft and subway power supply, are moving towards the application of voltage source converters for power conversion and supply. However, voltage source converters have a large equivalent capacitance on the DC side. After a fault occurs on the DC side, the equivalent capacitance will dissipate energy through low-impedance lines and the fault point, causing the DC fault current to rise rapidly and continuously without crossing zero. The protection challenge of DC systems is becoming a bottleneck in the development of DC systems. Compared to blocking converter station opening faults, DC circuit breakers can selectively and quickly disconnect faulty lines to protect healthy lines, and are widely recognized in the industry as a protection solution with significant application value.

[0003] Solid-state circuit breakers offer rapid operation and effectively limit peak fault current, making them promising for applications in low- and medium-voltage DC scenarios. Thyristors, with their advantages of high surge current, low cost, high withstand voltage, and low conduction loss, have made thyristor-based solid-state DC circuit breakers a research hotspot in recent years. Thyristor-based solid-state circuit breakers can generally be categorized into passive and active types.

[0004] The working principle of passive schemes, represented by Z-source circuit breakers, is similar; they all use the fault itself as the triggering condition. After a fault occurs, the thyristors inside the DC circuit breaker automatically withstand a reverse recovery voltage and then turn off. To improve practicality, some researchers have proposed improved bidirectional passive schemes. However, existing bidirectional passive schemes have four universal problems: 1) High conduction losses: Since a circuit breaker is a long-term conductive device, the number and type of conductive switches are very important under normal conditions. Ideally, there should only be one set of parallel thyristors in the current-carrying branch; 2) Low controllability: These passive schemes are triggered after a fault, which means they cannot actively interrupt the normal operating current, i.e., they lack controllability; 3) Low reliability: During normal system operation, current fluctuations are inevitable, and drastic current fluctuations resemble fault conditions, which may lead to false triggering. In addition, passive schemes are designed according to ideal conditions, i.e., they do not consider line impedance and fault type, so passive schemes cannot guarantee reliable current interruption; 4) Lack of fast reclosing protection function: Many passive schemes proposed in the last decade only focus on the initial current interruption process. Because they cannot handle capacitor energy well, they do not have fast reclosing protection capability.

[0005] Besides these passive solutions, scholars from various countries have also proposed a variety of active solutions. The key difference between active and passive solutions is that they actively control the auxiliary thyristor to turn off the thyristor in the current-carrying branch through an external sensing circuit, thus possessing the potential to interrupt operating current. However, none of these solutions effectively address the other three issues besides controllability. Summary of the Invention

[0006] To address the shortcomings of the existing technology, this invention provides a thyristor-type DC circuit breaker and its control method. This invention is an active solution that utilizes its internal circuit structure and control method for active control, addressing the common problems in existing technologies such as high conduction losses, low controllability, low reliability, and lack of fast reclosing protection.

[0007] The technical solution for achieving the objective of this invention is as follows:

[0008] A thyristor-type DC circuit breaker, thyristor T m1 Anode-connected thyristor T m2 The cathode forms the A terminal of the circuit breaker, T m1 Cathode connection T m2 The anode forms the B terminal of the circuit breaker; the thyristor T p1 anode, thyristor T p2 The cathode is connected to terminal A; T p1 Cathode connection T p2 After anode, it passes through resistor R in sequence. gSwitch RCB g Grounding; T p1 Cathode connection T p2 After the anode, it also passes through inductor L p Capacitor C is connected to terminal B; one end of the surge arrester MOV is connected to terminal T. p1 The cathode is connected to the B terminal.

[0009] Based on the above control method for thyristor-type DC circuit breakers, the state of the DC circuit breaker is T. m1 or T m2 On, RCB g The circuit is closed, and capacitor C is fully charged; when an active disconnect signal is received, the current I flowing from terminal A to terminal B is measured. m If the current I m If the value is greater than 0, then T is turned on. p1 And disconnect RCB g If the current I m If the value is less than 0, then T is turned on. p1 And disconnect RCB g After waiting for half an LC resonant cycle, T is turned on. p2 .

[0010] Based on the above control method for thyristor-type DC circuit breakers, the state of the DC circuit breaker is T. m1 or T m2 On, RCB g The process of closing the circuit and fully charging capacitor C includes the following steps:

[0011] S1: Measure the current I flowing from terminal A to terminal B. m ;if I m The absolute value is greater than the current threshold I f0 Then judge I again m If the value is positive, proceed to S2; if it is negative, proceed to S3.

[0012] S2: Conducting T p1 And disconnect RCB g ; Wait until all thyristors and RCBs g Both are disconnected, while T is simultaneously connected. m1 and T p2 At time t f1 Inside, measure I m ;if I m The absolute value is greater than or equal to I f0 Then the thyristor T is turned on. p1 Otherwise, T is simultaneously turned on. m1 and T m2 And close RCB g .

[0013] S3: Conducting T p1And disconnect RCB g After half an LC resonant cycle, T is turned on. p2 ; Wait until all thyristors and RCBs g Both are disconnected, and T is connected. m2 At time t f2 Inside, measure I m ;if I m The absolute value is greater than or equal to I f0 Then the thyristor T is turned on. p1 The thyristor T turns on after half an LC resonant cycle. p2 Otherwise, T is simultaneously turned on. m1 and T m2 And close RCB g .

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] 1. This invention utilizes semi-controlled power electronic devices, such as thyristors, to design DC circuit breakers, requiring only two sets of parallel thyristors, resulting in extremely low circuit breaker costs.

[0016] 2. Only one pair of parallel thyristors is needed in the current-carrying branch, that is, the conducting device is only a single thyristor under normal operating conditions, the conduction loss is extremely low, and the circuit breaker efficiency is extremely high.

[0017] 3. No external power supply is required to charge the capacitor during the current interruption and reclosing processes, further reducing cost and design complexity.

[0018] 4. The DC circuit breaker of the present invention can actively and reliably open or close bidirectional operating current or bidirectional fault current, ensuring system safety.

[0019] 5. Based on the traditional approach of using a resonant circuit to turn off the thyristor in the current-carrying branch, this invention utilizes the moment when the current-carrying branch switch is turned on during reclosing to further restore the capacitor polarity using a resonant circuit, thereby meeting the requirements for fast reclosing protection. Attached Figure Description

[0020] Figure 1 This is a circuit diagram of a thyristor-type DC circuit breaker proposed in this invention.

[0021] Figure 2 This is a flowchart of a control method for a thyristor-type DC circuit breaker proposed in this invention. Detailed Implementation

[0022] The specific embodiments of the present invention will be described in further detail below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0023] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0024] like Figure 1 The diagram shows a thyristor-type DC circuit breaker, which includes a current-carrying branch, a parallel branch, and a charging branch.

[0025] The current-carrying branch includes a pair of thyristors T. m1 and T m2 ; Thyristor T m1 anode and thyristor T m2 The cathode connection forms the A terminal of the circuit breaker; thyristor T m1 Cathode and thyristor T m2 The anode connection forms the B terminal of the circuit breaker.

[0026] The parallel branch includes a pair of thyristors T p1 and T p2 Inductor L p Capacitor C and surge arrester MOV. Thyristor T p1 anode, thyristor T p2 Cathode connected to terminal A; thyristor T p1 Cathode connected thyristor T p2 After anode, through inductor L p The capacitor C is connected to terminal B; one end of the surge arrester MOV is connected to the cathode of Tp1, and the other end is connected to terminal B.

[0027] The charging branch includes a resistor R. g and switch RCB g The resistor R g One end is connected to thyristor T p1 The cathode, the other end is connected to the switch RCB g Grounding.

[0028] The DC circuit breaker in this example is based on a semi-controlled power electronic device, the thyristor, and as... Figure 1 As shown, only two pairs of parallel thyristors are needed, resulting in low investment in the circuit breaker.

[0029] The DC circuit breaker solution in this example does not require an external charging power supply, such as... Figure 1 As shown, costs and design complexity are reduced.

[0030] In this example, the surge arrester MOV is connected in parallel across the LC resonant circuit and has two functions: first, to clamp the voltage, thereby protecting the power electronic devices; second, to dissipate the energy of the DC system.

[0031] In this example, the resistor R g For a large resistance, the time constant R should be... g The C value is controlled within a reasonable range, generally within a few minutes, to ensure that the charging speed is not slow while avoiding the introduction of new short-circuit faults when the thyristors in the parallel branch are turned on.

[0032] In this example, the thyristors in the parallel branch only need to carry current during the current interruption process, and the thyristors have strong surge current tolerance. In high current operating scenarios, the number of thyristors in the parallel branch can be reasonably designed, thereby further reducing costs.

[0033] like Figure 2 As shown, this invention proposes a control method with fast reclosing protection function based on the above-mentioned thyristor-type DC circuit breaker. The initial state of the DC circuit breaker is that all thyristors and switches RCB are in the state of... g All connections are disconnected. The control scheme will be further illustrated below through embodiments under different conditions.

[0034] The initial state of the above thyristor-type DC circuit breaker is all thyristors and switches RCB. g All connections are disconnected. The complete control process includes the following steps:

[0035] S1: When DC current needs to be applied, thyristor T is simultaneously turned on. m1 and thyristor T m2 And close RCB g Due to the difference in potential between terminals A and B, T m1 and T m2 Ultimately, only one path will be conductive. Capacitor C passes through the resistance R of the charging branch. g Fully charge and enter S2.

[0036] S2: Under normal operating conditions, if no active disconnect signal is received, proceed to S3. If an active disconnect signal is received, measure the current I flowing from A to B. m If the current I m Greater than 0, thyristor T is turned on. p1 And disconnect RCB g When the current in the parallel branch is greater than I m At that time, thyristor T m1 When the capacitor is turned off due to residual voltage, capacitor C reverse-charges. When the DC circuit breaker voltage reaches the MOV operating voltage of the surge arrester, the MOV starts to dissipate system energy, ultimately energizing all thyristors and RCBs. g Both are disconnected; if the current Im Less than 0, conduction T p1 And disconnect RCB g After waiting for half an LC resonant cycle, the capacitor polarity reverses, turning on the thyristor T. p2 When the current in the parallel branch is greater than I m At that time, thyristor T m1 When the capacitor is turned off due to residual voltage, capacitor C is forward charged. When the DC circuit breaker voltage reaches the MOV operating voltage of the surge arrester, the MOV starts to dissipate system energy, ultimately energizing all thyristors and RCBs. g All circuits are disconnected. The active shutdown circuit process is now complete.

[0037] S3: Measure the current I flowing from terminal A to terminal B. m Determine I m Is it equal to 0? If I m Equals 0, and T is turned on at the same time. m1 and T m2 Due to the difference in potential between terminals A and B, T m1 and T m2 Ultimately, only one path will be open. Enter S4.

[0038] S4: Preset a current threshold I f0 and I m The absolute value of I f0 For comparison, if I m The absolute value is less than I f0 If I m The absolute value is greater than or equal to I f0 This indicates a possible fault. The current I... m Compare with 0; if the current I m If the current is greater than 0, the fault is determined to be on side B, and S5 is entered; if the current I m If the value is less than 0, it is determined that the possible fault occurs on side A, and the process proceeds to S6.

[0039] S5: Conducting T p1 And disconnect RCB g When the current in the parallel branch is greater than I m At that time, thyristor T m1 When the residual voltage of the capacitor is turned off, capacitor C is reverse-charged. When the DC circuit breaker voltage reaches the operating voltage of the surge arrester MOV, the surge arrester MOV starts to dissipate system energy. After the DC circuit breaker enters the initial state, the reclosing process begins, and T is simultaneously turned on. m1 and T p2 Set a detection time threshold t f1 , in t f1 Inside, measure I m and with I f0 Make a comparison; if Im The absolute value is greater than or equal to I f0 If the fault is determined to be permanent, turn on thyristor T. p1 Thyristor T that shuts off the current-carrying branch m1 To achieve fast reclosing protection function; if I m The absolute value is less than I f0 If the fault is determined to be temporary and the system has returned to normal, return to S1 to allow it to re-enter normal operating conditions.

[0040] S6: Conducting T p1 And disconnect RCB g After waiting for half an LC resonant cycle, the capacitor polarity reverses, and conduction begins (T). p2 When the current in the parallel branch is greater than I m At that time, thyristor T m1 When the residual voltage of the capacitor is turned off, capacitor C is forward charged. When the DC circuit breaker voltage reaches the operating voltage of the surge arrester MOV, the surge arrester MOV starts to dissipate system energy. After the DC circuit breaker enters the initial state, the reclosing process begins, and T is turned on. m2 Set a detection time threshold t f2 , in t f2 Inside, measure I m and with I f0 Make a comparison; if I m The absolute value is greater than or equal to I f0 If the fault is determined to be permanent, turn on thyristor T. p1 After half an LC resonant cycle, the thyristor T is turned on. p2 Thyristor T that shuts off the current-carrying branch m2 To achieve fast reclosing protection function; if I m Absolute value to less than I f0 If the fault is determined to be temporary and the system has returned to normal, return to S1 to allow it to re-enter normal operating conditions.

[0041] Example 1:

[0042] When normal operation is required, thyristor T is simultaneously turned on. m1 and thyristor T m2 And close RCB g The capacitor C passes through the resistor R in the charging branch. g Fully charged. Upon receiving an active disconnect signal, measure the current I flowing from A to B. m If the current I m Greater than 0, thyristor T is turned on. p1 And disconnect RCB g When the current in the parallel branch is greater than I m At that time, thyristor T m1When the capacitor is turned off due to residual voltage, capacitor C reverse-charges. When the DC circuit breaker voltage reaches the MOV operating voltage of the surge arrester, the MOV starts to dissipate system energy, ultimately energizing all thyristors and RCBs. g Both are disconnected; if the current I m Less than 0, conduction T p1 And disconnect RCB g After waiting for half an LC resonant cycle, the capacitor polarity reverses, turning on the thyristor T. p2 When the current in the parallel branch is greater than I m At that time, thyristor T m1 When the capacitor is turned off due to residual voltage, capacitor C is forward charged. When the DC circuit breaker voltage reaches the MOV operating voltage of the surge arrester, the MOV starts to dissipate system energy, ultimately energizing all thyristors and RCBs. g All circuits are disconnected. The active control shutdown of the DC circuit breaker has ended.

[0043] Example 2:

[0044] When normal operation is required, thyristor T is simultaneously turned on. m1 and thyristor T m2 And close RCB g The capacitor C passes through the resistor R in the charging branch. g Fully charged. When the circuit current reverses, it may cause the normally conducting thyristor T to... m1 or thyristor T m2 Natural shutdown, measure the current I flowing from terminal A to terminal B. m , if I m Equals 0, and T is turned on at the same time. m1 and T m2 To ensure the circuit continues to operate normally.

[0045] Example 3:

[0046] When normal operation is required, thyristor T is simultaneously turned on. m1 and thyristor T m2 And close RCB g The capacitor C passes through the resistor R in the charging branch. g Fully charged. To monitor for potential circuit faults, measure the current I flowing from terminal A to terminal B. m A preset current threshold I is set. f0 and I m The absolute value of I f0 For comparison, if I m The absolute value is less than I f0 This is considered normal. If I... m The absolute value is greater than or equal to I f0 Then the current I m Compare with 0; if the current Im If the current I is greater than 0, the fault is determined to occur on side B. m If the value is less than 0, the fault is determined to occur on side A.

[0047] When the fault occurs on side B, conduction T is activated. p1 And disconnect RCB g When the current in the parallel branch is greater than I m At that time, thyristor T m1 When the residual voltage of the capacitor is turned off, capacitor C is reverse-charged. When the DC circuit breaker voltage reaches the operating voltage of the surge arrester MOV, the surge arrester MOV starts to dissipate system energy. Once the DC circuit breaker enters its initial state, the reclosing process begins, and T is simultaneously turned on. m1 and T p2 Set a detection time threshold t f1 , in t f1 Inside, measure I m and with I f0 Make a comparison; if I m The absolute value is greater than or equal to I f0 The fault was determined to be permanent, and the thyristor T was turned on. p1 Thyristor T that shuts off the current-carrying branch m1 To achieve fast reclosing protection function; if I m The absolute value is less than I f0 The malfunction was determined to be temporary, and the system will continue to operate normally.

[0048] When the fault occurs on side A, conduction T is activated. p1 And disconnect RCB g After waiting for half an LC resonant cycle, the capacitor polarity reverses, and conduction begins (T). p2 When the current in the parallel branch is greater than I m At that time, thyristor T m1 When the residual voltage of the capacitor is turned off, capacitor C is forward charged. When the DC circuit breaker voltage reaches the operating voltage of the surge arrester MOV, the surge arrester MOV starts to dissipate system energy. After the DC circuit breaker enters the initial state, the reclosing process begins, and T is turned on. m2 Set a detection time threshold t f2 , in t f2 Inside, measure I m and with I f0 Make a comparison; if I m The absolute value is greater than or equal to I f0 The fault was determined to be permanent, and the thyristor T was turned on. p1 After half an LC resonant cycle, the thyristor T is turned on. p2 Thyristor T that shuts off the current-carrying branch m2 To achieve fast reclosing protection function; if I m Absolute value to less than If0 The malfunction was determined to be temporary, and the system will continue to operate normally.

[0049] In this example, system energy refers to the energy of the entire DC system in which the circuit breaker operates. The system energy is absorbed and the circuit breaker itself is protected by the surge arrester MOV, resulting in good protection.

[0050] In Example 3, when dealing with a fault occurring on side A, the capacitor polarity needs to be reversed in advance. However, the capacitor polarity reversal requires half an LC resonance cycle. During this period, the current continues to rise. Therefore, the requirements for dealing with a fault occurring on side A are higher than those for dealing with a fault occurring on side B.

[0051] In this example, it is necessary to ensure that all thyristors withstand reverse voltage for a period of time longer than their required reverse recovery time, thereby ensuring that each thyristor can be reliably turned off.

[0052] This example is for medium and low voltage DC power grids. Figure 1 DC circuit breakers utilize Figure 2 The control method shown can reliably and proactively interrupt bidirectional operating current and fault current.

[0053] In this example, when handling a fault on side B, after the reclosing process is initiated, the sum of the time required for the capacitor polarity to reverse and the reverse recovery time of the thyristors in the parallel branch should be shorter than the time required for the circuit breaker to reoperate, in order to ensure the reliability of the reclosing protection.

Claims

1. A thyristor-type DC circuit breaker, characterized in that, Thyristor T m1 Anode-connected thyristor T m2 The cathode forms the A terminal of the circuit breaker, and the thyristor T... m1 Cathode connected thyristor T m2 The anode forms the B terminal of the circuit breaker; the thyristor T p1 anode and thyristor T p2 The cathode is connected to terminal A; thyristor T p1 Cathode connected thyristor T p2 After anode, it passes through resistor R in sequence. g and switch RCB g Grounding; Thyristor T p1 Cathode connected thyristor T p2 After the anode, it also passes through inductor L p The capacitor C is connected to terminal B; one end of the surge arrester MOV is connected to the thyristor T. p1 The cathode is connected to terminal B at one end; the inductor L p It is connected in series with capacitor C.

2. A control method for a thyristor-type DC circuit breaker as described in claim 1, characterized in that, The state of the DC circuit breaker is thyristor T. m1 or T m2 On, and RCB g The circuit is closed, and capacitor C is fully charged; When an active disconnect signal is received, the current I flowing from terminal A to terminal B is measured. m If the current I m If the value is greater than 0, then the thyristor T is turned on. p1 And disconnect RCB g If the current I m If the value is less than 0, then the thyristor T is turned on. p1 And disconnect RCB g After waiting for half an LC resonant cycle, the thyristor T is turned on. p2 .

3. A control method for a thyristor-type DC circuit breaker as described in claim 1, characterized in that, The state of the DC circuit breaker is thyristor T. m1 or T m2 On, RCB g The circuit is closed, and capacitor C is fully charged; include The following steps: S1: Measure the current I flowing from terminal A to terminal B. m ;if I m The absolute value is greater than the current threshold I f0 Then judge I again m If the value is positive, proceed to S2; if it is negative, proceed to S3. S2: Thyristor T is turned on p1 And disconnect RCB g ; Wait until all thyristors and RCBs g Both are disconnected, while thyristor T is turned on. m1 and T p2 At time t f1 Inside, measure I m ;if I m The absolute value is greater than or equal to I f0 Then the thyristor T is turned on. p1 Otherwise, thyristor T will be turned on simultaneously. m1 and T m2 And close RCB g ; S3: Thyristor T is in operation p1 And disconnect RCB g After half an LC resonant cycle, the thyristor T is turned on. p2 ; Wait until all thyristors and RCBs g All are disconnected, and thyristor T is turned on. m2 At time t f2 Inside, measure I m ;if I m The absolute value is greater than or equal to I f0 Then the thyristor T is turned on. p1 The thyristor T turns on after half an LC resonant cycle. p2 Otherwise, thyristor T will be turned on simultaneously. m1 and T m2 And close RCB g .

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