Current pre-limiting hybrid direct-current circuit breaker based on inductive coupling principle and control method
By using a pre-current limiting hybrid DC circuit breaker based on the principle of inductive coupling, and by combining current transfer and current limiting branches with control methods of capacitors and coupled inductors, the shortcomings of traditional DC circuit breakers in terms of fault current clearing speed and cost are solved, achieving rapid fault current clearing and reducing system cost.
Patent Information
- Application Number
- CN202511628391.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-07
- Publication Date
- 2026-02-10
AI Technical Summary
Existing DC circuit breakers are insufficient in terms of fault current clearing speed and cost. Traditional hybrid DC circuit breakers have high on-state losses and are expensive, making it difficult to meet the requirements of high performance and low cost.
A pre-current limiting hybrid DC circuit breaker based on the inductive coupling principle is adopted, including a main branch and an auxiliary branch. A bridge commutation branch composed of high-speed mechanical switches, IGBT valve groups, thyristors and diode valve groups is used to achieve rapid transfer and suppression of fault current through current transfer, current limiting, self-charging and energy dissipation branches, combined with the control methods of capacitor and coupled inductor.
It enables rapid fault current clearing, reduces system costs, decreases conduction losses and surge arrester energy dissipation, and improves the reliability and economy of fault clearing equipment.
Smart Images
Figure CN121507665A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of power electronics technology, specifically to a pre-current limiting hybrid DC circuit breaker and its control method based on the principle of inductive coupling. Background Technology
[0002] With the rapid development of power electronics technology, power electronic devices are increasingly used as converters in power systems. Flexible DC grids based on modular multilevel converters, in addition to facilitating the integration of distributed renewable energy sources, also offer significant advantages in high-capacity power transmission, ensuring power quality, and providing reactive power compensation for AC systems. Therefore, they have received widespread attention both domestically and internationally and have been applied in offshore and submarine power systems, railway transportation, distributed generation, and energy storage. However, how to handle short-circuit faults (including single-pole grounding and bipolar short circuits) in DC grids remains a major problem in current DC system applications. On the one hand, unlike AC grid faults, DC grid fault currents do not have a zero-crossing point, thus preventing the direct application of mature AC circuit breakers to DC faults. On the other hand, when a short-circuit fault occurs in a DC grid, the fault current rises rapidly. If the fault cannot be quickly cleared within a short time, it will affect the normal operation of the entire DC system, thus placing high demands on the fault clearing speed of DC fault clearing equipment.
[0003] Currently, there are three main methods for clearing short-circuit faults in DC power transmission and distribution systems: First, using fast disconnect switches in conjunction with AC circuit breakers to cut off the electrical connection between AC and DC systems, interrupting power transmission at the source. Second, using converters with automatic fault clearing capabilities to transfer and clear high-current short-circuit faults. Third, using DC circuit breakers to cut off DC fault current, isolate the fault point, and ensure the normal operation of non-faulty sections. DC circuit breakers are commonly used as DC fault clearing devices. Compared to the first two methods, DC circuit breakers, in coordination with the control and protection system, can quickly switch to a high-resistance state after a fault occurs, ensuring rapid isolation of the fault point before the converter station is locked out, without affecting the operation of non-faulty lines, and reducing additional equipment costs. Based on the above analysis, the independent design and development of a DC circuit breaker that combines environmental friendliness, reliability, and economy has significant theoretical and engineering practical value for the safety and operation and maintenance of DC power transmission and distribution systems.
[0004] With the development of DC circuit breakers, they can be mainly divided into three categories: mechanical DC circuit breakers, solid-state DC circuit breakers, and hybrid DC circuit breakers. Mechanical circuit breakers have advantages such as low on-state losses, stable operation, and simple control methods, but their current breaking time is relatively long, and they mainly rely on oscillation circuits to achieve current zero crossing, placing high demands on circuit parameters. Solid-state circuit breakers use all power electronic devices to achieve current switching, resulting in extremely fast breaking speeds and high reliability, but their on-state losses are relatively large during normal operation, and the large number of power electronic devices connected in series and parallel leads to excessive costs, limiting their practicality in high-voltage power grids. Hybrid circuit breakers combine the advantages of both mechanical and solid-state DC circuit breakers, meeting the need for rapid fault current interruption while achieving low on-state losses during normal operation, thus becoming the main research direction for DC circuit breakers. Although traditional hybrid DC circuit breakers combine the advantages of mechanical and solid-state DC circuit breakers, they still have disadvantages such as high on-state losses and high cost. Considering the future need to build multi-terminal DC power grids, researching high-performance, low-cost hybrid DC circuit breakers is of great significance for creating a safe, reliable, and economical smart grid.
[0005] Therefore, providing a pre-current limiting hybrid DC circuit breaker and its control method based on the principle of inductive coupling that can solve the above-mentioned technical problems is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention
[0006] The purpose of this invention is to provide a pre-current limiting hybrid DC circuit breaker and control method based on the principle of inductive coupling, so as to solve the problems mentioned in the background art.
[0007] To achieve the above objectives, the present invention provides the following technical solution: a pre-current limiting hybrid DC circuit breaker based on the principle of inductive coupling, comprising a main branch and an auxiliary branch connected in parallel;
[0008] The auxiliary branch includes a bridge commutation branch composed of thyristors and diode valve groups Q1, Q2, Q3, and Q4. The bridge commutation branch internally includes a current transfer branch, a bypass branch, a current limiting section, a self-charging section, and an energy dissipation branch. Both ends of capacitors C1 and C2 are equipped with energy dissipation branches composed of ordinary mechanical switches and resistors. The energy dissipation branches are used to discharge the corresponding capacitors after the circuit breaker operates.
[0009] The bypass branch, the current limiting section, and the self-charging section are connected in parallel and then connected in series with the energy-consuming branch to form a series unit. The series unit is connected in parallel with the current transfer branch, and the two ends of the current transfer branch and the series unit are respectively connected between the cathode connection points of the thyristor and diode valve group Q1 and diode valve group Q2, and the anode connection points of diode valve group Q3 and diode valve group Q4.
[0010] Preferably, the main branch is composed of a high-speed mechanical switch UFD and an IGBT valve group LCS connected in series.
[0011] Preferably, the current transfer branch includes thyristor valve group T1 and thyristor valve group T2 connected in series; the anode of the thyristor valve group T1 is connected to the cathode connection point of diode valve group Q1 and diode valve group Q2 in the bridge commutation branch, and the cathode of the thyristor valve group T2 is connected to the anode connection point of diode valve group Q3 and diode valve group Q4 in the bridge commutation branch. The current transfer branch is used to provide a current transfer channel for the arc-free interruption of the main branch.
[0012] Preferably, the bypass branch includes a resistor R1 and a diode valve group D1 connected in series; the negative terminal of the diode valve group D1 is connected to the anode of the thyristor valve group T1 in the current transfer branch, and the other end of the resistor R1 is connected to the cathode of the thyristor valve group T1 in the current transfer branch.
[0013] Preferably, the current limiting section includes a coupling inductor L, a thyristor valve group T3, a thyristor valve group T5, and a capacitor C1; the primary winding inductance of the coupling inductor L is L1, the secondary winding inductance is L2, and the primary winding terminal 1' and the secondary winding terminal 2 are terminals of the same name; the primary winding of the coupling inductor L is connected in series with the thyristor valve group T3 and then in parallel across the two ends of the bypass branch, wherein the primary winding terminal 1 of the coupling inductor L is connected to the negative terminal of the diode valve group D1 in the bypass branch, and the cathode of the thyristor valve group T3 is connected to the other end of the resistor R1 in the bypass branch; the secondary winding of the coupling inductor L is connected in series with the thyristor valve group T5 and then in parallel across the two ends of the capacitor C1, wherein one end of the capacitor C1 is connected to the secondary winding terminal 2' of the coupling inductor L, and the other end is connected to the anode of the thyristor valve group T5.
[0014] Preferably, the self-charging section includes thyristor valve group T6, thyristor valve group T7, thyristor valve group T8, diode valve group D2, and resistor R2; the anode of thyristor valve group T6 is connected to the cathode connection point of diode valve group Q1 and diode valve group Q2 in the bridge commutation branch, and the cathode is connected to the anode of thyristor valve group T5 in the current limiting section, for providing a charging path for capacitor C1; diode valve group D2 is connected in antiparallel across Q4 in the bridge commutation branch, and thyristor valve group T8 is connected in antiparallel across thyristor valve group T4 in the energy dissipation branch, the two working together to provide a charging path for capacitor C2; thyristor valve group T7 and resistor R2 are connected in series and then grounded, wherein the anode of thyristor valve group T7 is connected between capacitor C1 and terminal 2' of the secondary winding of coupling inductor L, and the other end of resistor R2 is grounded, for limiting the charging current.
[0015] Preferably, the energy dissipation branch includes a thyristor valve group T4, a capacitor C2, and a metal oxide surge arrester (MOA); the capacitor C2 is connected in series with the thyristor valve group T4 and then in parallel with the surge arrester MOA, wherein the capacitor C2 is connected to the anode of the thyristor valve group T4; the energy dissipation branch is connected in parallel across the two ends of the thyristor valve group T2 in the current transfer branch, wherein the cathode of the thyristor valve group T2 is connected to the cathode of the thyristor valve group T4, and the anode of the thyristor valve group T2 is connected to the capacitor C2, and the energy dissipation branch is used to cut off the fault current.
[0016] Preferably, a control method for a pre-current limiting hybrid DC circuit breaker based on the inductive coupling principle includes capacitor charging and discharging control and circuit breaker tripping control. The capacitor charging and discharging control includes a capacitor charging stage before circuit breaker operation and a capacitor discharging stage after circuit breaker operation. The control steps for the capacitor charging stage are as follows:
[0017] S11: When the DC system is working normally, the high-speed mechanical switch UFD and IGBT valve group LCS are turned on to allow current to flow from the main branch.
[0018] S12: Triggers the conduction of thyristor valve group T7 and thyristor valve group T8. Diode valve group D2 is positively charged and conducts. The DC system charges capacitor C2 through this path. Resistor R2 limits the charging current. After capacitor C2 is fully charged, the thyristor turns off naturally.
[0019] S13: Trigger the conduction of thyristor valve group T6, thyristor valve group T7 and bridge commutation branch valve group Q1. The DC system charges capacitor C1 through this path. After capacitor C1 is fully charged, the thyristor turns off naturally, and the charging stage ends.
[0020] The control steps for the capacitor discharge stage are as follows:
[0021] S21: After the circuit breaker completes the current interruption, it closes the ordinary mechanical switch in the energy discharge branch of capacitors C1 and C2.
[0022] S22: The energy stored in the capacitor is dissipated through the resistor in the energy dissipation branch until the energy is completely consumed.
[0023] Preferably, the circuit breaker tripping control includes a current-limiting phase, post-current-limiting tripping, post-current-limiting recovery, and low-current tripping; the control steps of the current-limiting phase are as follows:
[0024] S31: After capacitors C1 and C2 have finished charging, if the DC system detects an overcurrent, it triggers the conduction valve group Q1, conduction valve group Q4, and thyristor valve group T1 and thyristor valve group T2, and then turns off the IGBT valve group LCS to transfer the overcurrent to the auxiliary branch. During this process, the system current continues to rise.
[0025] S32: After the current transfer is completed, control the high-speed mechanical switch UFD to start disconnecting, with a disconnection time of about 2ms;
[0026] S33: After the UFD is completely disconnected, the thyristor valve group T3 and thyristor valve group T5 are triggered to turn on. The capacitor C1 discharges through the secondary winding 2-2' of the coupling inductor L. The pulse current flowing into the secondary winding terminal 2 causes the primary winding terminal 1' to flow out an induced pulse current in the opposite direction to the fault current through coupling, forcing the current in the branch where the thyristor valve group T1 is located to decrease.
[0027] S34: After the current in the branch where the thyristor valve group T1 is located crosses zero and is turned off, the primary winding of the coupling inductor L is put into current limiting; as the discharge current of capacitor C1 decays, an induced pulse current flows out of terminal 1 of the coupling inductor L in the opposite direction to the fault current, further suppressing the fault current until capacitor C1 is completely discharged and the current limiting stage ends.
[0028] The control steps for disconnection after current limiting are as follows:
[0029] S41: After the primary winding of the coupling inductor L is fully engaged in current limiting, if the fault detection confirms that the system needs to cut off the fault current, the thyristor valve group T4 will be triggered to turn on.
[0030] S42: The discharge of capacitor C2 causes thyristor valve group T2 to be shut off under reverse pressure, and the fault current is transferred to the branch where capacitor C2 is located.
[0031] S43: After capacitor C2 is discharged, the system reverse charges it. As the reverse voltage across capacitor C2 increases, diode valve group D1 is forward-biased and conducts, the bypass branch is activated and consumes the energy stored in the coupling inductor until the energy is consumed.
[0032] S44: When capacitor C2 is charged to the operating voltage of surge arrester MOA, MOA is engaged to absorb energy in the fault line until the fault current decays to zero. The current in the primary winding of coupling inductor L and the branch where thyristor valve group T3, diode valve group Q1, and diode valve group Q4 are located crosses zero and is turned off. The current limiting and disconnection process ends.
[0033] The control steps for recovery after current limiting are as follows:
[0034] S51: After the primary winding of the coupling inductor L is fully engaged in current limiting, if the fault detection confirms that there is no fault in the line and operation needs to be restored, close the high-speed mechanical switch UFD.
[0035] S52: After the UFD is fully closed, it triggers the conduction of the IGBT valve group LCS and the thyristor valve group T4;
[0036] S53: The discharge of capacitor C2 causes the thyristor valve group T2 to be turned off by reverse voltage, and the current is transferred to the branch where capacitor C2 is located.
[0037] S54: After capacitor C2 is fully discharged, the system reverse-charges it, diode valve group D1 is turned on, and the bypass branch consumes the energy of the coupling inductor.
[0038] S55: After the grid current is transferred from the auxiliary branch back to the main branch and the main branch current is restored to the normal operating current, the current in the branch where the primary winding of the coupling inductor L and the thyristor valve group T3, diode valve group Q1 and diode valve group Q4 are located is turned off at zero, and the current limiting and recovery process ends.
[0039] The control steps for the small current interruption are as follows:
[0040] S61: If a small current needs to be interrupted, trigger the conduction of diode valve group Q1, diode valve group Q4 and thyristor valve group T1 and thyristor valve group T2, turn off IGBT valve group LCS, transfer the current to the auxiliary branch, and then control UFD to start interruption. The interruption time is about 2ms.
[0041] S62: After the UFD is completely disconnected, the thyristor valve group T4 is triggered to turn on, and the capacitor C2 discharges, causing the thyristor valve group T2 to be turned off by reverse pressure.
[0042] S63: After capacitor C2 is fully discharged, it begins to charge in reverse. When the charge reaches the operating voltage of the surge arrester MOA, MOA engages to absorb energy from the line.
[0043] S64: The small current disconnection process ends after the residual energy of the line is consumed by the MOA.
[0044] Beneficial effects:
[0045] (1) The main branch of the hybrid DC circuit breaker of the present invention is composed of a high-speed mechanical switch and an IGBT valve group connected in series, which has low on-state loss; the auxiliary branch is composed of a bridge commutation branch consisting of thyristors and diode valve groups to achieve bidirectional current interruption, and is composed of a current transfer branch, a bypass branch, a current limiting part, a self-charging part and an energy consumption branch. It can use the DC grid to realize capacitor self-charging and ensure normal operation in the next operation.
[0046] (2) When an overcurrent occurs in the power grid, the hybrid DC circuit breaker described in this invention can use IGBTs and thyristors to transfer the fault current to the auxiliary branch. Subsequently, based on the characteristics of the coupled inductor, the overcurrent is rapidly suppressed through the cooperation of the thyristor, capacitor, and coupled inductor. Furthermore, based on the fault detection results, the metal oxide arrester (MOA) can be activated through the cooperation of the thyristor and capacitor to achieve current limiting and then disconnect the faulty line or restore normal operation of the line. The auxiliary branch of this invention uses semi-controlled thyristors in cooperation with capacitors and coupled inductors to completely replace fully controlled IGBTs, effectively reducing system costs. It can also quickly activate the coupled inductor to effectively suppress overcurrent, reduce breaking current, reduce arrester energy dissipation, and accelerate the speed of disconnecting the faulty line.
[0047] The above description is merely an overview of the technical solutions of the embodiments of this application. In order to better understand the technical means of the embodiments of this application and to implement them in accordance with the contents of the specification, and to make the above and other objects, features and advantages of the embodiments of this application more apparent and understandable, specific implementation methods of this application are described below. Attached Figure Description
[0048] Figure 1 This is a schematic diagram of the pre-current limiting hybrid DC circuit breaker topology based on the inductive coupling principle of the present invention;
[0049] Figure 2 This is a schematic diagram of the operation process of the hybrid DC circuit breaker of the present invention at each time point in three modes;
[0050] Figure 3 This is a schematic diagram of the charging stage of the hybrid DC circuit breaker of the present invention;
[0051] Figure 4 This is a schematic diagram of the current limiting stage of the hybrid DC circuit breaker of the present invention;
[0052] Figure 5 This is a schematic diagram of the current-limiting and disconnection stage of the hybrid DC circuit breaker of the present invention;
[0053] Figure 6 This is a schematic diagram of the recovery phase after current limiting in the hybrid DC circuit breaker of the present invention;
[0054] Figure 7 This is a schematic diagram of the low-current breaking stage of the hybrid DC circuit breaker of the present invention;
[0055] Figure 8 This is a schematic diagram of the equivalent circuit of the DC side of the MMC converter station with a circuit breaker installed and a bipolar short-circuit fault occurring.
[0056] Figure 9 This is a schematic diagram of the current in each branch and a timing diagram of the operation of the hybrid DC circuit breaker of the present invention during the current limiting and breaking process. Detailed Implementation
[0057] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0058] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings.
[0059] Please see Figures 1-9 This invention discloses a pre-current limiting hybrid DC circuit breaker based on the principle of inductive coupling, comprising a main branch and an auxiliary branch connected in parallel. The main branch is composed of a high-speed mechanical switch UFD and an IGBT valve group LCS connected in series.
[0060] The auxiliary branch includes a bridge commutation branch composed of thyristors and diode valve groups Q1, Q2, Q3, and Q4. The bridge commutation branch internally includes a current transfer branch, a bypass branch, a current limiting section, a self-charging section, and an energy dissipation branch. Both ends of capacitors C1 and C2 are equipped with energy dissipation branches composed of ordinary mechanical switches and resistors. The energy dissipation branches are used to discharge the corresponding capacitors after the circuit breaker operates.
[0061] The bypass branch, the current limiting section, and the self-charging section are connected in parallel and then connected in series with the energy-consuming branch to form a series unit. The series unit is connected in parallel with the current transfer branch, and the two ends of the current transfer branch and the series unit are respectively connected between the cathode connection points of the thyristor and diode valve group Q1 and diode valve group Q2, and the anode connection points of diode valve group Q3 and diode valve group Q4.
[0062] In this invention, the current transfer branch includes a series-connected thyristor valve group T1 and a thyristor valve group T2; the anode of the thyristor valve group T1 is connected to the cathode connection point of the diode valve group Q1 and the diode valve group Q2 in the bridge commutation branch, and the cathode of the thyristor valve group T2 is connected to the anode connection point of the diode valve group Q3 and the diode valve group Q4 in the bridge commutation branch. The current transfer branch is used to provide a current transfer channel for the arc-free interruption of the main branch.
[0063] In this invention, the bypass branch includes a resistor R1 and a diode valve group D1 connected in series; the negative terminal of the diode valve group D1 is connected to the anode of the thyristor valve group T1 in the current transfer branch, and the other end of the resistor R1 is connected to the cathode of the thyristor valve group T1 in the current transfer branch.
[0064] In this invention, the current limiting section includes a coupling inductor L, a thyristor valve group T3, a thyristor valve group T5, and a capacitor C1. The primary winding inductance of the coupling inductor L is L1, and the secondary winding inductance is L2, with the primary winding terminal 1' and the secondary winding terminal 2 being terminals of the same name. The primary winding of the coupling inductor L is connected in series with the thyristor valve group T3 and then in parallel across the bypass branch. Terminal 1 of the primary winding of the coupling inductor L is connected to the negative terminal of the diode valve group D1 in the bypass branch, and the cathode of the thyristor valve group T3 is connected to the other end of the resistor R1 in the bypass branch. The secondary winding of the coupling inductor L is connected in series with the thyristor valve group T5 and then in parallel across the capacitor C1. One end of the capacitor C1 is connected to terminal 2' of the secondary winding of the coupling inductor L, and the other end is connected to the anode of the thyristor valve group T5.
[0065] In this invention, the self-charging section includes thyristor valve group T6, thyristor valve group T7, thyristor valve group T8, diode valve group D2, and resistor R2. The anode of thyristor valve group T6 is connected to the cathode connection point of diode valve group Q1 and diode valve group Q2 in the bridge commutation branch, and the cathode is connected to the anode of thyristor valve group T5 in the current limiting section, providing a charging path for capacitor C1. Diode valve group D2 is connected in antiparallel across Q4 in the bridge commutation branch, and thyristor valve group T8 is connected in antiparallel across thyristor valve group T4 in the energy dissipation branch, both working together to provide a charging path for capacitor C2. Thyristor valve group T7 and resistor R2 are connected in series and then grounded, wherein the anode of thyristor valve group T7 is connected between capacitor C1 and terminal 2' of the secondary winding of coupling inductor L, and the other end of resistor R2 is grounded, used to limit the charging current.
[0066] In this invention, the energy-dissipating branch includes a thyristor valve group T4, a capacitor C2, and a metal oxide surge arrester (MOA). The capacitor C2 is connected in series with the thyristor valve group T4 and then in parallel with the surge arrester MOA, wherein the capacitor C2 is connected to the anode of the thyristor valve group T4. The energy-dissipating branch is connected in parallel across the two ends of the thyristor valve group T2 in the current transfer branch, wherein the cathode of the thyristor valve group T2 is connected to the cathode of the thyristor valve group T4, and the anode of the thyristor valve group T2 is connected to the capacitor C2. The energy-dissipating branch is used to cut off fault current.
[0067] This invention also discloses a control method for a pre-current limiting hybrid DC circuit breaker based on the principle of inductive coupling, including capacitor charging and discharging control and circuit breaker tripping control. The capacitor charging and discharging control includes a capacitor charging stage before circuit breaker operation and a capacitor discharging stage after circuit breaker operation. The control steps for the capacitor charging stage are as follows:
[0068] S11: When the DC system is working normally, the high-speed mechanical switch UFD and IGBT valve group LCS are turned on to allow current to flow from the main branch.
[0069] S12: Triggers the conduction of thyristor valve group T7 and thyristor valve group T8. Diode valve group D2 is positively charged and conducts. The DC system charges capacitor C2 through this path. Resistor R2 limits the charging current. After capacitor C2 is fully charged, the thyristor turns off naturally.
[0070] S13: Trigger the conduction of thyristor valve group T6, thyristor valve group T7 and bridge commutation branch valve group Q1. The DC system charges capacitor C1 through this path. After capacitor C1 is fully charged, the thyristor turns off naturally, and the charging stage ends.
[0071] The control steps for the capacitor discharge stage are as follows:
[0072] S21: After the circuit breaker completes the current interruption, it closes the ordinary mechanical switch in the energy discharge branch between capacitors C1 and C2.
[0073] S22: The energy stored in the capacitor is dissipated through the resistor in the energy dissipation branch until the energy is completely consumed.
[0074] Circuit breaker tripping control includes a current-limiting phase, post-current-limiting tripping, post-current-limiting recovery, and low-current tripping; the control steps for the current-limiting phase are as follows:
[0075] S31: After capacitors C1 and C2 have finished charging, if the DC system detects an overcurrent, it triggers the conduction valve group Q1, conduction valve group Q4, and thyristor valve group T1 and thyristor valve group T2, and then turns off the IGBT valve group LCS to transfer the overcurrent to the auxiliary branch. During this process, the system current continues to rise.
[0076] S32: After the current transfer is completed, control the high-speed mechanical switch UFD to start disconnecting, with a disconnection time of about 2ms;
[0077] S33: After the UFD is completely disconnected, the thyristor valve group T3 and thyristor valve group T5 are triggered to turn on. The capacitor C1 discharges through the secondary winding 2-2' of the coupling inductor L. The pulse current flowing into the secondary winding terminal 2 causes the primary winding terminal 1' to flow out an induced pulse current in the opposite direction to the fault current through coupling, forcing the current in the branch where the thyristor valve group T1 is located to decrease.
[0078] S34: After the current in the branch where the thyristor valve group T1 is located crosses zero and is turned off, the primary winding of the coupling inductor L is put into current limiting; as the discharge current of capacitor C1 decays, an induced pulse current flows out of terminal 1 of the coupling inductor L in the opposite direction to the fault current, further suppressing the fault current until capacitor C1 is completely discharged and the current limiting stage ends.
[0079] The control steps for disconnection after current limiting are as follows:
[0080] S41: After the primary winding of the coupling inductor L is fully engaged in current limiting, if the fault detection confirms that the system needs to cut off the fault current, the thyristor valve group T4 will be triggered to turn on.
[0081] S42: The discharge of capacitor C2 causes thyristor valve group T2 to be shut off under reverse pressure, and the fault current is transferred to the branch where capacitor C2 is located.
[0082] S43: After capacitor C2 is discharged, the system reverse charges it. As the reverse voltage across capacitor C2 increases, diode valve group D1 is forward-biased and conducts, the bypass branch is activated and consumes the energy stored in the coupling inductor until the energy is consumed.
[0083] S44: When capacitor C2 is charged to the operating voltage of surge arrester MOA, MOA is engaged to absorb energy in the fault line until the fault current decays to zero. The current in the primary winding of coupling inductor L and the branch where thyristor valve group T3, diode valve group Q1, and diode valve group Q4 are located crosses zero and is turned off. The current limiting and disconnection process ends.
[0084] The control steps for recovery after current limiting are as follows:
[0085] S51: After the primary winding of the coupling inductor L is fully engaged in current limiting, if the fault detection confirms that there is no fault in the line and operation needs to be restored, close the high-speed mechanical switch UFD.
[0086] S52: After the UFD is fully closed, it triggers the conduction of the IGBT valve group LCS and the thyristor valve group T4;
[0087] S53: The discharge of capacitor C2 causes the thyristor valve group T2 to be turned off by reverse voltage, and the current is transferred to the branch where capacitor C2 is located.
[0088] S54: After capacitor C2 is fully discharged, the system reverse-charges it, diode valve group D1 is turned on, and the bypass branch consumes the energy of the coupling inductor.
[0089] S55: After the grid current is transferred from the auxiliary branch back to the main branch and the main branch current is restored to the normal operating current, the current in the branch where the primary winding of the coupling inductor L and the thyristor valve group T3, diode valve group Q1 and diode valve group Q4 are located is turned off at zero, and the current limiting and recovery process ends.
[0090] The control steps for the small current interruption are as follows:
[0091] S61: If a small current needs to be interrupted, trigger the conduction of diode valve group Q1, diode valve group Q4 and thyristor valve group T1 and thyristor valve group T2, turn off IGBT valve group LCS, transfer the current to the auxiliary branch, and then control UFD to start interruption. The interruption time is about 2ms.
[0092] S62: After the UFD is completely disconnected, the thyristor valve group T4 is triggered to turn on, and the capacitor C2 discharges, causing the thyristor valve group T2 to be turned off by reverse pressure.
[0093] S63: After capacitor C2 is fully discharged, it begins to charge in reverse. When the charge reaches the operating voltage of the surge arrester MOA, MOA engages to absorb energy from the line.
[0094] S64: The small current disconnection process ends after the residual energy of the line is consumed by the MOA.
[0095] Since this invention is a bidirectional hybrid DC circuit breaker, the current direction will be described from left to right. For ease of explanation, the operation process at each moment is as follows: Figure 2 As shown. Figure 1 The operation process of the topology shown is as follows:
[0096] (1) When a large overcurrent occurs in the system under certain circumstances, but it is uncertain whether to disconnect immediately, current limiting can be put in place first, and then it can be decided whether to disconnect or restore the current.
[0097] During the capacitor charging phase (t0→t1'): For example... Figure 3 As shown, when the DC system is operating normally, the UFD and LCS are turned on, and the current flows from the main branch. At t = t0, the thyristor valve group T7 and the thyristor valve group T8 are triggered to turn on, and the diode valve group D2 is turned on under positive voltage, so that the DC system charges the capacitor C2. The resistor R2 is used to limit the charging current. After C2 is fully charged, the thyristor turns off naturally. Then at t = t1, the thyristor valve group T6 and the thyristor valve group T7 are triggered to turn on, as well as the valve group Q1 of the commutation branch, so that the DC system charges the capacitor C1. This continues until at t = t1', when the capacitor C1 is fully charged, the thyristor turns off naturally, and the charging phase is complete.
[0098] Rate limiting phase (t2→t5): such as Figure 4As shown, after capacitors C1 and C2 complete their charging process, when the DC system detects an overcurrent, at time t=t2, diode valve groups Q1 and Q4, as well as thyristor valve groups T1 and T2, are triggered to conduct, and then the LCS is turned off, transferring the overcurrent to the auxiliary branch. During this period, the system current continues to rise. After the current transfer is complete, the UFD begins to disconnect, with a disconnection time of approximately 2ms. At time t=t3, when the UFD is completely disconnected, thyristor valve groups T3 and T5 are triggered to conduct, and capacitor C1 discharges through the secondary winding 2-2' of the coupling inductor L, entering... The pulse current at terminal 2 of the secondary winding of the coupling inductor L causes an induced pulse current to flow out of terminal 1' in the opposite direction to the system fault current through coupling, forcing the current in the branch where valve group T1 is located to decrease. At t = t4, the current in the branch where valve group T1 is located crosses zero and is turned off, and the primary winding of L is engaged in current limiting. As the discharge current of capacitor C1 begins to decay, due to the characteristics of coupling, an induced pulse current will flow out of terminal 1 of the coupling inductor L in the opposite direction to the system fault current, further suppressing the system fault current. At t = t5, capacitor C1 discharges completely, the coupling effect ends, and the current limiting stage is completed.
[0099] After current limiting, the interruption phase (t5→t9): such as Figure 5 As shown, after the primary winding of the coupling inductor L is fully engaged in current limiting, when the system completes fault detection, if a fault is confirmed in the system, the fault current needs to be cut off. At t=t6, the thyristor valve group T4 is triggered to conduct. The discharge of capacitor C2 will cause the thyristor valve group T2 to be subjected to reverse voltage and turn off, and the fault current will be transferred to the branch where capacitor C2 is located. After capacitor C2 is fully discharged, the system begins to reverse charge. As the reverse voltage across capacitor C2 gradually increases, at t=t7, the diode valve group D1 is subjected to forward voltage and conducts. The bypass branch is engaged and consumes the energy stored in the coupling inductor until the energy stored in the coupling inductor is consumed at t=t7'. When capacitor C2 is charged to the operating voltage of the surge arrester MOA at t=t8, the surge arrester MOA is engaged and the fault line absorbs energy until the fault current decays to zero at t=t9. The current in the primary winding of the coupling inductor L and the branches where the thyristor valve group T3, diode valve group Q1, and diode valve group Q4 are located cross zero and are turned off. The current limiting and disconnection process is completed.
[0100] Recovery phase after rate limiting (t5→t9): such as Figure 6As shown, after the primary winding of the coupling inductor L is fully engaged in current limiting, when the system completes fault detection, if it is confirmed that no fault has occurred in the line and normal line operation needs to be restored, the UFD is closed first. After the UFD is fully closed at t = t6, the LCS and thyristor valve group T4 are triggered to conduct. The discharge of capacitor C2 will cause the thyristor valve group T2 to be reverse-voltaged and shut off, and the fault current will be transferred to the branch where capacitor C2 is located. After capacitor C2 has finished discharging, the system begins reverse charging. As the reverse voltage across capacitor C2 gradually increases, at t = t6... At time 7, diode valve group D1 is forward-biased and conducts, the bypass branch is engaged and consumes the energy stored in the coupling inductor until time t = t7', when the energy stored in the coupling inductor is consumed. When time t = t8, during the charging process of capacitor C2, the grid current is transferred back from the auxiliary branch to the main branch until time t = t9, when the main branch current recovers to the normal operating current. The current in the primary winding of coupling inductor L and the branches containing thyristor valve group T3, diode valve group Q1, and diode valve group Q4 are turned off at zero, and the current limiting and recovery process is completed.
[0101] capacitor discharge stage (t9→t) 11 ): After the circuit breaker has completely interrupted the current, when t = t 10 The ordinary mechanical switch in the energy dissipation branch of capacitors C1 and C2 is closed and turned on at all times, and the energy in capacitors C1 and C2 is dissipated through the energy-dissipating resistor in the energy dissipation branch. t = t 11 Once the energy release is complete, the circuit breaker awaits the next action command.
[0102] (2) When it is necessary to interrupt a small current (without current limiting) in certain situations, such as line maintenance, current limiting is not required.
[0103] The capacitor charging stage (t0→t1'): The self-charging process of the capacitor under the small current interruption is the same as the self-charging process under the overcurrent limiting condition (1), and will not be repeated here.
[0104] Small current breaking stage (t2→t5): such as Figure 7 As shown, at t=t2, diode valve group Q1, diode valve group Q4, thyristor valve group T1, and thyristor valve group T2 are triggered to conduct, and then the LCS is turned off. After the current is transferred to the auxiliary branch, the UFD starts to disconnect, and the disconnection time is about 2ms. At t=t3, after the UFD is completely disconnected, the thyristor valve group T4 is triggered to conduct. The discharge of capacitor C2 will cause the thyristor valve group T2 to be subjected to reverse voltage and turn off. Then, after the discharge of capacitor C2 is completed, it starts to charge in reverse. When t=t4, capacitor C2 is charged to the operating voltage of the surge arrester MOA, and the MOA is connected to the line. When t=t5, after the residual energy of the line is consumed by the MOA, the small current disconnection is completed.
[0105] Capacitor discharge stage (t5→t7): After the circuit breaker has completely interrupted the current, at t=t6, the ordinary mechanical switch in the energy discharge branch across capacitor C2 is closed to conduct, and the energy in capacitor C2 is dissipated through the energy-dissipating resistor in the energy discharge branch. Energy discharge is completed at t=t7, and the circuit breaker awaits the next operating command.
[0106] Taking the most severe bipolar fault as an example, this paper explains the current-limiting and breaking process of a hybrid DC circuit breaker topology installed on the positive pole. The actual installation method of the DC circuit breaker in the system and the equivalent circuit after the fault are as follows: Figure 8 As shown, the parameter design of each branch of the hybrid DC circuit breaker of this invention can be completed based on this equivalent circuit. Figure 9 The schematic diagrams of the current in each branch and the timing diagram of the current limiting and breaking process of the hybrid DC circuit breaker of this invention show that when a bipolar short-circuit fault occurs, the novel hybrid DC circuit breaker proposed in this invention can effectively suppress the fault current and reduce the breaking current. The fault current clearing time and the energy dissipation completion time of the bypass branch can be flexibly selected according to parameters such as resistors and surge arresters as needed.
[0107] In summary, this invention effectively reduces costs by replacing IGBTs with the cooperation of thyristors and capacitors; it utilizes the characteristics of coupled inductors to achieve rapid overcurrent suppression; and based on fault detection results, it determines whether to disconnect the line or restore operation after current limiting. This invention also possesses low-current breaking capability without current limiting, enabling flexible response to various abnormal conditions in DC systems, and is rationally designed and highly reliable.
[0108] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.
Claims
1. A pre-current limiting hybrid DC circuit breaker based on the principle of inductive coupling, characterized in that: This includes main branches and auxiliary branches connected in parallel; The auxiliary branch includes a bridge commutation branch composed of thyristors and diode valve groups Q1, Q2, Q3, and Q4. The bridge commutation branch internally includes a current transfer branch, a bypass branch, a current limiting section, a self-charging section, and an energy dissipation branch. Both ends of capacitors C1 and C2 are equipped with energy dissipation branches composed of ordinary mechanical switches and resistors. The energy dissipation branches are used to discharge the corresponding capacitors after the circuit breaker operates. The bypass branch, the current limiting section, and the self-charging section are connected in parallel and then connected in series with the energy-consuming branch to form a series unit. The series unit is connected in parallel with the current transfer branch, and the two ends of the current transfer branch and the series unit are respectively connected between the cathode connection points of the thyristor and diode valve group Q1 and diode valve group Q2, and the anode connection points of diode valve group Q3 and diode valve group Q4.
2. The pre-current limiting hybrid DC circuit breaker based on inductive coupling principle according to claim 1, characterized in that: The main branch circuit consists of a high-speed mechanical switch UFD and an IGBT valve group LCS connected in series.
3. The pre-current limiting hybrid DC circuit breaker based on inductive coupling principle according to claim 1, characterized in that: The current transfer branch includes thyristor valve group T1 and thyristor valve group T2 connected in series; the anode of the thyristor valve group T1 is connected to the cathode connection point of diode valve group Q1 and diode valve group Q2 in the bridge commutation branch, and the cathode of the thyristor valve group T2 is connected to the anode connection point of diode valve group Q3 and diode valve group Q4 in the bridge commutation branch. The current transfer branch is used to provide a current transfer channel for the arc-free interruption of the main branch.
4. The pre-current limiting hybrid DC circuit breaker based on inductive coupling principle according to claim 1, characterized in that: The bypass branch includes a resistor R1 and a diode valve group D1 connected in series; the negative terminal of the diode valve group D1 is connected to the anode of the thyristor valve group T1 in the current transfer branch, and the other end of the resistor R1 is connected to the cathode of the thyristor valve group T1 in the current transfer branch.
5. The pre-current limiting hybrid DC circuit breaker based on inductive coupling principle according to claim 1, characterized in that: The current limiting section includes a coupling inductor L, a thyristor valve group T3, a thyristor valve group T5, and a capacitor C1. The primary winding inductance of the coupling inductor L is L1, and the secondary winding inductance is L2, with the primary winding terminal 1' and the secondary winding terminal 2 being terminals of the same name. The primary winding of the coupling inductor L is connected in series with the thyristor valve group T3 and then in parallel across the bypass branch. Terminal 1 of the primary winding of the coupling inductor L is connected to the negative terminal of the diode valve group D1 in the bypass branch, and the cathode of the thyristor valve group T3 is connected to the other end of the resistor R1 in the bypass branch. The secondary winding of the coupling inductor L is connected in series with the thyristor valve group T5 and then in parallel across the capacitor C1. One end of the capacitor C1 is connected to terminal 2' of the secondary winding of the coupling inductor L, and the other end is connected to the anode of the thyristor valve group T5.
6. The pre-current limiting hybrid DC circuit breaker based on inductive coupling principle according to claim 1, characterized in that: The self-charging section includes thyristor valve group T6, thyristor valve group T7, thyristor valve group T8, diode valve group D2, and resistor R2. The anode of thyristor valve group T6 is connected to the cathode of diode valve group Q1 and diode valve group Q2 in the bridge commutation branch, and the cathode is connected to the anode of thyristor valve group T5 in the current limiting section, providing a charging path for capacitor C1. Diode valve group D2 is connected in antiparallel across Q4 in the bridge commutation branch, and thyristor valve group T8 is connected in antiparallel across thyristor valve group T4 in the energy dissipation branch, working together to provide a charging path for capacitor C2. Thyristor valve group T7 and resistor R2 are connected in series and then grounded, wherein the anode of thyristor valve group T7 is connected between capacitor C1 and terminal 2' of the secondary winding of coupling inductor L, and the other end of resistor R2 is grounded, used to limit the charging current.
7. The pre-current limiting hybrid DC circuit breaker based on inductive coupling principle according to claim 1, characterized in that: The energy dissipation branch includes a thyristor valve group T4, a capacitor C2, and a metal oxide surge arrester MOA. The capacitor C2 is connected in series with the thyristor valve group T4 and then in parallel with the surge arrester MOA, wherein the capacitor C2 is connected to the anode of the thyristor valve group T4. The energy dissipation branch is connected in parallel across the two ends of the thyristor valve group T2 in the current transfer branch, wherein the cathode of the thyristor valve group T2 is connected to the cathode of the thyristor valve group T4, and the anode of the thyristor valve group T2 is connected to the capacitor C2. The energy dissipation branch is used to cut off the fault current.
8. A control method for a pre-current limiting hybrid DC circuit breaker based on the principle of inductive coupling, characterized in that, This includes capacitor charging and discharging control and circuit breaker tripping control. The capacitor charging and discharging control includes a capacitor charging phase before the circuit breaker trips and a capacitor discharging phase after the circuit breaker trips. The control steps for the capacitor charging phase are as follows: S11: When the DC system is working normally, the high-speed mechanical switch UFD and IGBT valve group LCS are turned on to allow current to flow from the main branch. S12: Triggers the conduction of thyristor valve group T7 and thyristor valve group T8. Diode valve group D2 is positively charged and conducts. The DC system charges capacitor C2 through this path. Resistor R2 limits the charging current. After capacitor C2 is fully charged, the thyristor turns off naturally. S13: Trigger the conduction of thyristor valve group T6, thyristor valve group T7 and bridge commutation branch valve group Q1. The DC system charges capacitor C1 through this path. After capacitor C1 is fully charged, the thyristor turns off naturally, and the charging stage ends. The control steps for the capacitor discharge stage are as follows: S21: After the circuit breaker completes the current interruption, it closes the ordinary mechanical switch in the energy discharge branch between capacitors C1 and C2. S22: The energy stored in the capacitor is dissipated through the resistor in the energy dissipation branch until the energy is completely consumed.
9. The control method for a pre-current limiting hybrid DC circuit breaker based on inductive coupling principle according to claim 8, characterized in that, The circuit breaker tripping control includes a current-limiting phase, post-current-limiting tripping, post-current-limiting recovery, and low-current tripping; the control steps for the current-limiting phase are as follows: S31: After capacitors C1 and C2 have finished charging, if the DC system detects an overcurrent, it triggers the conduction valve group Q1, conduction valve group Q4, and thyristor valve group T1 and thyristor valve group T2, and then turns off the IGBT valve group LCS to transfer the overcurrent to the auxiliary branch. During this process, the system current continues to rise. S32: After the current transfer is completed, control the high-speed mechanical switch UFD to start disconnecting, with a disconnection time of about 2ms; S33: After the UFD is completely disconnected, the thyristor valve group T3 and thyristor valve group T5 are triggered to turn on. The capacitor C1 discharges through the secondary winding 2-2' of the coupling inductor L. The pulse current flowing into the secondary winding terminal 2 causes the primary winding terminal 1' to flow out an induced pulse current in the opposite direction to the fault current through coupling, forcing the current in the branch where the thyristor valve group T1 is located to decrease. S34: After the current in the branch where the thyristor valve group T1 is located crosses zero and is turned off, the primary winding of the coupling inductor L is put into current limiting mode. As the discharge current of capacitor C1 decays, an induced pulse current flows out of terminal 1 of the coupling inductor L in the opposite direction to the fault current, further suppressing the fault current until capacitor C1 is fully discharged, and the current limiting stage ends. The control steps for disconnection after current limiting are as follows: S41: After the primary winding of the coupling inductor L is fully engaged in current limiting, if the fault detection confirms that the system needs to cut off the fault current, the thyristor valve group T4 will be triggered to turn on. S42: The discharge of capacitor C2 causes thyristor valve group T2 to be shut off under reverse pressure, and the fault current is transferred to the branch where capacitor C2 is located. S43: After capacitor C2 is discharged, the system reverse charges it. As the reverse voltage across capacitor C2 increases, diode valve group D1 is forward-biased and conducts, the bypass branch is activated and consumes the energy stored in the coupling inductor until the energy is consumed. S44: When capacitor C2 is charged to the operating voltage of surge arrester MOA, MOA is engaged to absorb energy in the fault line until the fault current decays to zero. The current in the primary winding of coupling inductor L and the branch where thyristor valve group T3, diode valve group Q1, and diode valve group Q4 are located crosses zero and is turned off. The current limiting and disconnection process ends. The control steps for recovery after current limiting are as follows: S51: After the primary winding of the coupling inductor L is fully engaged in current limiting, if the fault detection confirms that there is no fault in the line and operation needs to be restored, close the high-speed mechanical switch UFD. S52: After the UFD is fully closed, it triggers the conduction of the IGBT valve group LCS and the thyristor valve group T4; S53: The discharge of capacitor C2 causes the thyristor valve group T2 to be turned off by reverse voltage, and the current is transferred to the branch where capacitor C2 is located. S54: After capacitor C2 is fully discharged, the system reverse-charges it, diode valve group D1 is turned on, and the bypass branch consumes the energy of the coupling inductor. S55: After the grid current is transferred from the auxiliary branch back to the main branch and the main branch current is restored to the normal operating current, the current in the branch where the primary winding of the coupling inductor L and the thyristor valve group T3, diode valve group Q1 and diode valve group Q4 are located is turned off at zero, and the current limiting and recovery process ends. The control steps for the small current interruption are as follows: S61: If a small current needs to be interrupted, trigger the conduction of diode valve group Q1, diode valve group Q4 and thyristor valve group T1 and thyristor valve group T2, turn off IGBT valve group LCS, transfer the current to the auxiliary branch, and then control UFD to start interruption. The interruption time is about 2ms. S62: After the UFD is completely disconnected, the thyristor valve group T4 is triggered to turn on, and the capacitor C2 discharges, causing the thyristor valve group T2 to be turned off by reverse pressure. S63: After capacitor C2 is fully discharged, it begins to charge in reverse. When the charge reaches the operating voltage of the surge arrester MOA, MOA engages to absorb energy from the line. S64: The small current disconnection process ends after the residual energy of the line is consumed by the MOA.