A hybrid dc circuit breaker and a control method thereof

Abstract

This invention discloses a hybrid DC circuit breaker and its control method, relating to the field of circuit breaker technology. The hybrid DC circuit breaker includes a main branch connected in series between the DC input and DC output terminals to carry normal operating current and fault current; a voltage injection circuit magnetically coupled to a transformer in the main branch to inject reverse voltage into the main branch during fault disconnection; an energy dissipation branch connected in parallel across the main branch to absorb and dissipate energy during fault disconnection; and a capacitor charging branch to charge the capacitor in the voltage injection circuit. This invention designs a reliable disconnection circuit, decoupling the disconnection process from the line inductance, enabling rapid provision of a zero-current disconnection window for the mechanical switch even under conditions of large line inductance. A single-coupling structure is proposed, reducing topology complexity and the number of components, thereby reducing cost, simplifying design, and improving reliability.

Description

Technical Field

[0001] This invention relates to the field of circuit breakers, and in particular to a hybrid DC circuit breaker and its control method. Background Technology

[0002] As a typical high-energy-consuming special equipment, elevators have significant energy waste during operation. Under conditions such as descent and braking, the potential and kinetic energy generated by the elevator are usually dissipated as heat through the braking resistor, which not only reduces energy utilization efficiency but may also affect the equipment's lifespan due to heat dissipation problems.

[0003] Among them, supercapacitor-based potential energy storage and feedback technology has become the mainstream technology path in the current elevator energy-saving field due to its advantages such as high energy density (suitable for elevators' short-term high-power charging and discharging needs), fast charging and discharging speed (responding to frequent elevator start-stop conditions), and long cycle life (suitable for long-term elevator operation scenarios). The core logic of this technology is: to connect a supercapacitor energy storage module to the elevator power supply system, and to realize the recovery and storage of redundant energy of the elevator (when going down) through a power converter, and to feed the stored energy back to the DC bus during the energy-demanding stages such as elevator start-up and going up, thereby reducing the elevator's dependence on grid energy consumption. Actual calculations show that it can achieve an energy consumption reduction of 15%-30%, with significant energy-saving effects and broad industrialization prospects.

[0004] However, the core energy interaction links of the aforementioned elevator energy storage and feedback system based on supercapacitors (supercapacitor charging and discharging control, energy transmission to the power grid / elevator load) rely on a low-voltage DC system (typical voltage level 240V-750V). There is a fundamental difference between DC and AC systems: AC systems naturally have periodic zero-crossing points in the current, which provides favorable conditions for interrupting fault currents (such as short circuits and overloads); but DC systems lack natural current zero-crossing points. Once a fault occurs, the fault current will rise rapidly at a microsecond rate (the peak value can reach 5-10 times the rated current) and always remain at a high amplitude.

[0005] For elevator applications, the hazards of DC system failures are even more pronounced: elevator shafts are compact, and core components (supercapacitor modules, power converters, and control units) are densely packed. If the fault current cannot be quickly interrupted, it may not only burn out the circuit breaker itself but also trigger an electric arc, leading to a chain reaction of failures such as supercapacitor explosions and converter damage, directly threatening elevator operational safety (e.g., entrapment, emergency stops). Therefore, reliable fault disconnection of the DC circuit has become a core bottleneck restricting the large-scale deployment of supercapacitor-based elevator energy feedback systems. Developing low-voltage DC circuit breakers (DCCBs) that can adapt to the characteristics of elevator DC circuits (low voltage, high current, space constraints, and high safety priority) is a key prerequisite for ensuring system safety and promoting the industrialization of the technology. It has now become a key research topic in the intersection of elevator energy conservation and power electronics.

[0006] Hybrid DC circuit breakers (HCBs) offer low conduction losses and moderate fault breaking speeds (in milliseconds), making them a highly competitive option in current development. When an HCB breaks a fault, the fault current first commutates from the main branch to the commutated branch, and is then broken by a solid-state switch. However, this process limits further increases in breaking speed, and after commutation, the fault current continues to rise through the commutated branch, potentially damaging the power supply, converter, and load. Series hybrid circuit breakers (SHCBs) based on variable voltage injection still face the following challenges:

[0007] 1. Complex topology: The above-mentioned series hybrid circuit breaker (SHCB) has a highly complex topology, requiring a large number of components, resulting in low reliability, high design difficulty and high cost, which limits its large-scale deployment.

[0008] 2. Unreliable breaking capacity: The aforementioned series hybrid circuit breaker (SHCB) is highly sensitive to line inductance in DC systems. Large line inductance slows the rate of decrease of fault current, delaying the time for the mechanical switch (MS) to create a zero-current breaking window, which may cause the MS to trip under large fault current, generating an arc. Summary of the Invention

[0009] Therefore, the technical problem to be solved by this invention is: the two core technical problems faced by existing series hybrid DC circuit breakers when applied to low-voltage DC systems such as elevator energy feedback:

[0010] 1. Complex topological structure:

[0011] The existing series hybrid circuit breaker (SHCB) topology is highly complex and requires a large number of components.

[0012] This results in low reliability, high design difficulty, and high manufacturing cost of circuit breakers, limiting their large-scale deployment and application.

[0013] 2. The segmentation is unreliable:

[0014] Existing solutions are highly sensitive to line inductance in DC systems.

[0015] When the line inductance is large, the rate of decrease of the fault current is slowed, which delays the time for the mechanical switch (MS) to create a "zero-current breaking window".

[0016] This causes the mechanical delay time of the mechanical switch to be shorter than the formation time of the zero current window, resulting in the mechanical switch disconnecting when the fault current is still very large, thus generating an electric arc and causing disconnection failure.

[0017] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a hybrid DC circuit breaker, characterized in that it includes: a main branch connected in series between a DC input terminal and a DC output terminal, the main branch being used to carry normal operating current and fault current; a voltage injection circuit, the voltage injection circuit being magnetically coupled to a transformer in the main branch, for injecting reverse voltage into the main branch during fault disconnection; an energy dissipation branch, the energy dissipation branch being connected in parallel across the two ends of the main branch, for absorbing and dissipating energy during fault disconnection; and a capacitor charging branch, the capacitor charging branch being used to charge the capacitor in the voltage injection circuit.

[0018] In a preferred embodiment of the hybrid DC circuit breaker of the present invention, the main branch includes an inductor, the secondary winding of the transformer, and a mechanical switch connected in series.

[0019] In a preferred embodiment of the hybrid DC circuit breaker of the present invention, the voltage injection circuit includes the capacitor, the first fully controlled switch, the second fully controlled switch, and the primary winding of the transformer; the capacitor, the first fully controlled switch, and the primary winding are connected in series to form a first discharge loop; the second fully controlled switch and the primary winding are connected in parallel to form a freewheeling loop.

[0020] As a preferred embodiment of the hybrid DC circuit breaker of the present invention, the energy-consuming branch includes a voltage clamping element, which includes, but is not limited to, a bidirectional transient voltage suppressor or a varistor.

[0021] In a preferred embodiment of the hybrid DC circuit breaker of the present invention, the capacitor charging branch includes a diode and a charging current-limiting resistor, and the capacitor charging branch is connected in parallel to the DC bus for automatically charging the capacitor after it discharges.

[0022] Another objective of this invention is to provide a control method for a hybrid DC circuit breaker, applied to the aforementioned hybrid DC circuit breaker. The method includes the following stages: Mode I: When the fault current of the main branch is detected to reach a preset breaking threshold, a disconnection command is sent to the mechanical switch, and the first fully controlled switch is simultaneously turned on. A reverse voltage is injected into the main branch through a voltage injection circuit, causing the fault current to rapidly decrease to near zero within the mechanical delay time of the mechanical switch; Mode II: After the fault current decreases to near zero, the first fully controlled switch is turned off and the second fully controlled switch is turned on for freewheeling. By alternately controlling the on / off states of the first and second fully controlled switches, the fault current is modulated to fluctuate within a hysteresis band centered on zero current, creating a continuous zero-current breaking window for the mechanical switch; Mode III: When the contacts of the mechanical switch begin to separate, the first fully controlled switch is turned on, and the voltage injection circuit is used to suppress the transient recovery voltage across the mechanical switch, assisting in the insulation recovery of the contact gap and achieving arc-free breaking.

[0023] In a preferred embodiment of the control method for the hybrid DC circuit breaker of the present invention, in mode I, the capacitor of the voltage injection circuit discharges through the first full control switch and the primary winding, and an induced voltage is induced on the secondary winding. The amplitude of the induced voltage is greater than the clamping voltage of the energy-consuming branch.

[0024] In a preferred embodiment of the control method for the hybrid DC circuit breaker of the present invention, in Mode II, the upper and lower limits of the hysteresis band are set to near-zero current values ​​so that the mechanical switch opens at near-zero current.

[0025] In a preferred embodiment of the control method for the hybrid DC circuit breaker of the present invention, in mode III, the reverse voltage injected by the voltage injection circuit suppresses the voltage across the mechanical switch to a negative value or a low value close to zero.

[0026] As a preferred embodiment of the control method for the hybrid DC circuit breaker of the present invention, it further includes: Mode IV: After the mechanical switch is completely disconnected, the first full control switch and the second full control switch are turned off, so that the residual magnetic energy in the transformer is dissipated, and at the same time the capacitor is automatically charged from the DC bus through the capacitor charging branch to prepare for the next reclosing.

[0027] The beneficial effects of this invention are as follows: By designing a reliable breaking circuit, this invention decouples the breaking process from the line inductance, enabling a rapid zero-current breaking window for the mechanical switch even under conditions of large line inductance. The proposed single-coupling structure reduces topological complexity and the number of components, thereby lowering costs, simplifying design, and improving reliability. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings of the embodiments of the present invention will be briefly described below. Obviously, the drawings described below only relate to some embodiments of the present invention and are not intended to limit the present invention.

[0029] Figure 1 The topology diagram of the circuit breaker of the present invention is shown;

[0030] Figure 2 The diagram shows the current operation principle of the circuit breaker of the present invention in Mode I.

[0031] Figure 3 A timing diagram showing the breaking performance of the circuit breaker of the present invention is shown;

[0032] Figure 4 The diagram shows the current operation principle of the circuit breaker of the present invention in Mode II.

[0033] Figure 5 The diagram shows the current operation principle of the circuit breaker of the present invention in Mode III.

[0034] Figure 6 The diagram shows the current operation principle of the circuit breaker of the present invention in mode IV;

[0035] Figure 7 The key waveform diagram of the circuit breaker of the present invention is shown. Detailed Implementation

[0036] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0037] The terminology used in this invention is that which is currently widely used in the art in consideration of the function of the invention; however, these terms may vary according to the intent of those skilled in the art, precedent, or new technology in the art. Furthermore, specific terms may be chosen by the applicant, and in such cases, their detailed meanings will be described in the detailed description of the invention. Therefore, the terms used in this specification should not be construed as simple names, but rather based on their meanings and the overall description of the invention.

[0038] Example 1, referring to Figure 1 This embodiment provides a hybrid DC circuit breaker, including a main branch 1, a voltage injection circuit 2, an energy dissipation branch 3, and a capacitor charging branch 4.

[0039] Specifically, the main branch 1 includes an inductor 11, the secondary winding 12b of the transformer 12, and a mechanical switch 13 connected in series. The same-named end of the secondary winding 12b of the transformer 12 is connected to the inductor 11, and the other end is connected to the mechanical switch 13.

[0040] The voltage injection circuit 2 includes a capacitor 21, a first fully controlled switch 22, a second fully controlled switch 23, and the primary winding 12a of the transformer 12. In this embodiment, both the first fully controlled switch 22 and the second fully controlled switch 23 are N-channel enhancement-mode MOSFETs. The drain of the first fully controlled switch 22 is connected to the positive terminal of the capacitor 21, and its source is connected to the corresponding terminal of the primary winding 12a of the transformer 12. The negative terminal of the capacitor 21 is connected to the other end of the primary winding 12a of the transformer 12, forming a discharge loop. The drain of the second fully controlled switch 23 is connected to the corresponding terminal of the primary winding 12a of the transformer 12, and its source is connected to its other end, forming a freewheeling loop.

[0041] Energy dissipation branch 3 is connected in parallel to both ends of the main branch 1. In this embodiment, energy dissipation branch 3 is composed of a bidirectional transient voltage suppressor (TVS) or a varistor MOV, used to absorb and dissipate energy during fault disconnection.

[0042] The capacitor charging branch 4 includes a diode 41 and a charging current-limiting resistor 42. The capacitor charging branch 4 is connected in parallel to the DC bus and is used to automatically charge the capacitor 21 after it has discharged. The two ends of the capacitor 21 are respectively connected to the diode 41 and the charging current-limiting resistor 42.

[0043] Example 2, refer to Figure 1 This embodiment provides a control method for a hybrid DC circuit breaker, applied to the aforementioned hybrid DC circuit breaker, which mainly has four control modes, specifically:

[0044] (1) Mode I (rapid decrease in fault current):

[0045] exist t At time 1, the fault current i 1 rises to the segmentation threshold i F The control system sends a disconnect command to mechanical switch 13. However, due to mechanical delay... t D At this time, mechanical switch 13 is still in the closed state.

[0046] At the same time, the first full control switch 22 is turned on, triggering the voltage injection circuit 2.

[0047] The capacitor 21 discharges through the following circuit: capacitor 21 (positive terminal) — first fully controlled switch 22 — primary winding 12a — capacitor 21 (negative terminal), as follows: Figure 2 As shown. The voltage across the primary winding 12a is V 1. An induced voltage exceeding the DC system voltage is induced on the secondary winding 12b. V 2 (Ignoring the voltage drop of the switching transistor, when the first full control switch 22 is turned on,) VC = V 1, n V C = V 2， V C (This refers to the voltage across capacitor 21). According to Kirchhoff's voltage law, the following formula can be obtained:

[0048] (1)

[0049] in, i 1 represents the fault current, which is the current flowing through mechanical switch 13. V in and V out These are the input and output voltages of the circuit breaker, respectively. V TVS This is the voltage across the TVS. During Mode I, the slope of the fault current decrease can be expressed as:

[0050] (2)

[0051] According to the above formula, when condition n is satisfied... V C > V TVS At that time, fault current i 1. The fault current can be quickly reduced to zero. The fault current clearing time depends on the turns ratio n and the voltage across capacitor 21. V C and transient voltage suppressor diode (TVS) voltage V TVS The fault current clearing time can be expressed as:

[0052] (3)

[0053] The fault current can be controlled by properly designing the above parameters. i The decreasing slope of 1 can reduce the fault current. i 1. The clearing time is reduced to a few microseconds.

[0054] like Figure 3 As shown, the prerequisite for normal tripping of a series-type hybrid DC circuit breaker (SHCB) is the fault current clearing time. t F That is, the time required to form a zero-current window is shorter than the mechanical delay experienced when mechanical switch 13 is opened. t D This allows the mechanical switch 13 to open within the zero-current breaking window, achieving arc-free breaking.

[0055] Traditional SHCBs may face the risk of tripping faults. This is because they achieve fault current interruption by adjusting the voltage across the line's parasitic inductance. Therefore, the breaking speed is highly sensitive to the line's parasitic inductance, and the slope of the fault current decreases significantly as the line's parasitic inductance increases. When the line's parasitic inductance is large, the process of the fault current dropping to zero and creating a zero-current breaking window will be significantly delayed. The mechanical switch is very likely to open before the fault current drops to zero and a zero-current breaking window is created, leading to arcing.

[0056] The fault current breaking and zero-current window formation time of the SHCB of this invention are not affected by the line inductance, and it has reliable breaking characteristics. The SHCB of this invention decouples the energy dissipation process of the line inductance from the formation process of the zero-current breaking window in the main branch 1 through a robust breaking loop. The energy on the line inductance will be dissipated through the energy-dissipating branch 3 and will not participate in the formation of the zero-current breaking window. According to formulas (2) and (3), when the parasitic inductance of the line is large, the TVS on the energy-dissipating branch 3 will operate at the clamping voltage. V clamp When operating in clamping mode, its clamping voltage remains essentially constant.

[0057] (4)

[0058] Therefore, it can be seen from the above formula that when the line parasitic inductance is large, the fault current clearing time, i.e., the time for the zero current window to be generated, is only affected by the internal inductance L of the loop, and is independent of the line parasitic inductance. The ultrafast breaking performance of the SHCB of this invention is basically unaffected by the line inductance, achieving robust breaking.

[0059] (2) Mode II (Zero Current Modulation Stage):

[0060] The hybrid circuit breaker of this invention operates in both Mode I and Mode II, such as... Figure 4 As shown, t At time 2, the fault current i 1 From i F When the voltage drops to the lower limit of the current hysteresis loop, the first fully controlled switch 22 turns off, the voltage injection circuit 2 stops working, the first fully controlled switch 23 turns on, and the pulse current... i 2. Freewheeling is achieved via the second full-control switch 23. In Mode II, the fault current... i 1. It rises naturally from the lower limit of the hysteresis loop. When i When the hysteresis limit is reached, the first full control switch 22 is turned on again, and Mode II ends. Mode II fault current. i The slope is:

[0061] (5)

[0062] existt 2- t During phase 3, the circuit breaker rapidly switches between Mode I and Mode II to achieve hysteresis control based on zero current, thereby controlling the fault current. i 1. Modulation to near-zero ripple. This modulation creates a zero-current breaking window for mechanical switch 13, enabling arc-free breaking at any time within the window, thus solving the problem faced by other circuit breakers that rely on a single current zero-crossing point. Furthermore, voltage injection circuit 2 operates in an intermittent mode, conducting in mode I and turning off in mode II.

[0063] It should be noted that the control scheme uses the fault current of main branch 1. i The controller uses hysteresis control as its core to achieve rapid and reliable switching of the circuit breaker between three operating modes. The controller measures the fault current of the main branch in real time. i 1. When i 1. Reaching the segmentation threshold i F When the mechanical switch 13 is triggered to disconnect, the voltage injection circuit 2 (first full control switch 22 is turned on) is simultaneously triggered, entering mode I. The voltage injection circuit 2 injects reverse voltage into the main branch 1 to reduce the fault current. i 1 drops rapidly to near zero within microseconds;

[0064] when i 1≤ i low When the hysteresis lower limit is reached, switch to mode II. Voltage injection circuit 2 is disconnected (first full control switch 22 is turned off, second full control switch 23 is turned on). The excitation current is maintained by the freewheeling circuit, allowing the fault current to continue. i 1. It rises again within the hysteresis interval.

[0065] Fault current in main branch 1 i 1. The current ripple amplitude within the hysteresis band, based on zero current, continuously varies, thus creating a continuous zero-current breaking window for the mechanical switch 13. Typically, the current ripple amplitude within the hysteresis band is set to be less than 10% of the fault current amplitude to achieve a smaller breaking current. The parameter setting of the hysteresis band needs to comprehensively consider the current sampling frequency and the control frequency. The smaller the hysteresis band, the closer the fault current ripple is to zero, achieving better arc-free breaking performance, but placing higher demands on current measurement accuracy and sampling frequency. To ensure robustness, the current measurement and sampling frequencies should be much higher than the hysteresis frequency, and the bandwidth and accuracy should meet the requirements. di / dt The response requirements.

[0066] (3) Mode III (Voltage Suppression Stage):

[0067] like Figure 5 As shown, tAt time 4, the contacts of mechanical switch 13 begin to separate. At this point, the contact gap is small, and the insulation recovery is insufficient to withstand high voltage. Therefore, the first full-control switch 22 turns on, and the voltage injection circuit 2 injects voltage into the main branch 1 again, suppressing the voltage across mechanical switch 13. Through proper design, the voltage across mechanical switch 13 can be reduced to a sufficiently small negative value. This process helps restore the insulation of the contact gap of mechanical switch 13 and suppresses arcing. When the contact gap of mechanical switch 13 is sufficient to withstand the system voltage, the first full-control switch 22 turns off.

[0068] (4) Mode IV (Energy Dissipation and Automatic Recharging Phase) t > t 5)

[0069] like Figure 6 As shown, during this stage, the pulse current i 2. The current flows through the freewheeling circuit: primary winding 12a—second fully controlled switch 23—primary winding 12a and gradually dissipates. Simultaneously, capacitor 21 begins charging, preparing for reclosing. Because the discharge of capacitor 21 is very small and the charging process is short, rapid reclosing is ensured.

[0070] Furthermore, when the contacts of mechanical switch 13 separate, the circuit breaker of the present invention should be in the zero-current modulation stage. Therefore, the fault current clearing time... t F It should be significantly shorter than the mechanical delay time of mechanical switch 13. t D In addition, the fault current clearing time t F It must also be less than the maximum disconnection time specified by the DC system. T r It satisfies the following relationship:

[0071] (6)

[0072] in V Clamp This is the clamping voltage of the TVS. t D The mechanical delay is for mechanical switch 13. The parameters of its TVS and internal inductance L can be determined using the relationships described above. Furthermore, the capacity of the TVS needs to be considered based on the remaining energy in the line inductance. It should be noted that, ideally, L is an independent element in the circuit breaker, but in practical designs, the effect of the transformer leakage inductance on inductance L, and the resulting reduction in the turns ratio n, must be considered.

[0073] Furthermore, the main considerations in transformer design are n , i 2max andL 11 The principle is to ensure a short fault current clearing time. t F Small primary current peak i 2max and acceptable sizes, i 2max It can be obtained through the following formula:

[0074] (7)

[0075] in:

[0076] (8)

[0077] Based on the above formula, we can obtain i 2max , n and L 11 The relationship between them. It is necessary to ensure... n It should be within a reasonable range. Otherwise, it could lead to longer disconnection times or larger transformer sizes. L 11 The selection follows the same principles. Therefore, careful consideration is needed to balance these factors. Furthermore, to ensure low conduction losses in the main branch, the number of turns on the normal conducting side (i.e., the secondary side) of the transformer should be minimized. This constraint also limits the turns ratio. n He Yuanbian felt L 11 The increase in [something]. To prevent transformer saturation caused by pulse current at a limited number of turns (such as nanocrystalline alloys and silicon steel).

[0078] Furthermore, according to the law of conservation of energy, the capacitor 21 in the circuit breaker voltage injection circuit 2... t 1 and t The energy at time 5 satisfies the following equation:

[0079] (9)

[0080] in V C and V Cmin They are t 1 and t The voltage across capacitor 21 at time 5. t 1- t At 5 o'clock, it should meet the following requirements. nV Cmin > V TVS .

[0081] In summary, the beneficial effects of the present invention are as follows:

[0082] 1. The prerequisite for the normal operation of a series hybrid circuit breaker is the fault current clearing time. t F That is, the zero-current window formation time is shorter than the mechanical delay time when mechanical switch 13 is turned off. t D Traditional series hybrid circuit breakers (SHCBs) may face the risk of breaking failure because large line inductance can cause them to break. t F Extended to more than tD ( This causes the mechanical switch to trip even when the fault current is still high.

[0083] This invention's series hybrid circuit breaker isolates the line inductance through a reliable breaking circuit, ensuring that the fault current clearing time remains essentially stable. When the line inductance Ls is large, the fault current clearing time of the circuit breaker is limited by the reliable breaking circuit. Therefore, as long as it is ensured This allows for reliable disconnection. t F It depends only on the internal inductance L of the circuit and is independent of the line inductance Ls, thus achieving effective isolation of the line inductance.

[0084] 2. Since circuit breakers will be widely deployed in DC systems, manufacturing cost is also a key consideration. The series hybrid circuit breaker of this invention adopts a single-coupled structure, containing only one fully controlled device, one freewheeling diode, one capacitor, and one transformer, eliminating the need for additional transformers, capacitors, and power devices. Furthermore, the economic advantages of the proposed circuit breaker are also reflected in a significant reduction in design complexity.

[0085] Finally, it should be noted that the methods and devices described in detail above are merely embodiments, and those skilled in the art can modify these embodiments in different ways as long as they do not depart from the scope of the present invention.

Claims

1. A hybrid DC circuit breaker, characterized by include: A main branch (1) connected in series between the DC input terminal and the DC output terminal is used to carry normal operating current and fault current; A voltage injection circuit (2) is magnetically coupled to a transformer (12) in the main branch (1) and is used to inject reverse voltage into the main branch (1) when a fault is disconnected. Energy-consuming branch (3), which is connected in parallel to both ends of the main branch (1), is used to absorb and dissipate energy during fault disconnection; A capacitor charging branch (4) is used to charge the capacitor (21) in the voltage injection circuit (2); The energy-consuming branch (3) includes a voltage clamping element, which includes a bidirectional transient voltage suppressor or a varistor; The energy-consuming branch (3) is triggered to conduct when the voltage injection circuit (2) injects reverse voltage into the main branch (1), and together with the main branch (1) forms a robust breaking loop, so that the rapid decrease of the fault current of the main branch is limited by the internal parameters of the local loop, thereby avoiding the delay of the construction process of the zero current breaking window by the external large line inductance, ensuring that the mechanical switch can enter the near-zero current breaking state within its mechanical delay time and avoid arcing. 2.The hybrid DC circuit breaker according to claim 1, characterized in that: The main branch (1) includes an inductor (11), the secondary winding (12b) of the transformer (12) and a mechanical switch (13) connected in series. 3.The hybrid DC circuit breaker according to claim 2, characterized in that: The voltage injection circuit (2) includes the capacitor (21), the first full control switch (22), the second full control switch (23) and the primary winding (12a) of the transformer (12). The capacitor (21), the first fully controlled switch (22), and the primary winding (12a) are connected in series to form the first discharge loop; The second fully controlled switch (23) is connected in parallel with the primary winding (12a) to form a freewheeling loop. 4.The hybrid DC circuit breaker according to claim 3, characterized in that: The capacitor charging branch (4) includes a diode (41) and a charging current limiting resistor (42). The capacitor charging branch (4) is connected in parallel to the DC bus and is used to automatically charge the capacitor (21) after it discharges.

5. A control method of a hybrid DC circuit breaker, characterized by: The method, applied to the hybrid DC circuit breaker as described in any one of claims 1 to 4, includes the following stages: Mode I: When the fault current of the main branch (1) is detected to reach the preset breaking threshold, a disconnection command is sent to the mechanical switch (13), and the first full control switch (22) is turned on at the same time. A reverse voltage is injected into the main branch (1) through the voltage injection circuit (2), so that the fault current drops rapidly to near zero within the mechanical delay time of the mechanical switch (13). Mode II: After the fault current drops to near zero, the first full control switch (22) is turned off and the second full control switch (23) is turned on for freewheeling; by alternately controlling the on and off of the first full control switch (22) and the second full control switch (23), the fault current is modulated to fluctuate within the hysteresis band centered on zero current, creating a continuous zero current breaking window for the mechanical switch (13); Mode III: When the contacts of the mechanical switch (13) begin to separate, the first full control switch (22) is turned on, and the transient recovery voltage at both ends of the mechanical switch (13) is suppressed by the voltage injection circuit (2) to assist the insulation recovery of the contact gap and achieve arc-free disconnection. 6.The control method of the hybrid DC circuit breaker of claim 5, characterized in that: In the mode I, the capacitor (21) of the voltage injection circuit (2) discharges through the first full control switch (22) and the primary winding (12a), and induces an induced voltage on the secondary winding (12b). The amplitude of the induced voltage is greater than the clamping voltage of the energy dissipation branch (3). 7.The control method of the hybrid DC circuit breaker of claim 6, characterized in that: In Mode II, the upper and lower limits of the hysteresis band are set to near-zero current values ​​so that the mechanical switch (13) is disconnected at near-zero current. 8.The control method of the hybrid DC circuit breaker of claim 7, characterized in that: In Mode III, the reverse voltage injected by the voltage injection circuit (2) suppresses the voltage across the mechanical switch (13) to a negative value or a low value close to zero. 9.The control method of the hybrid DC circuit breaker of claim 8, characterized in that: It also includes, Mode IV: After the mechanical switch (13) is completely disconnected, the first full control switch (22) and the second full control switch (23) are turned off, so that the residual magnetic energy in the transformer (12) is dissipated. At the same time, the capacitor (21) is automatically charged from the DC bus through the capacitor charging branch (4) to prepare for the next reclosing.

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