Bidirectional controllable coupling inductor Z-source solid-state direct-current circuit breaker and application method thereof

Abstract

The invention discloses a bidirectional controllable coupling inductor Z-source solid-state direct-current circuit breaker and an application method thereof.The bidirectional controllable coupling inductor Z-source solid-state direct-current circuit breaker comprises a thyristor T3, the cathode of the thyristor T3 is sequentially connected with a capacitor C and a resistor R in series, the end, away from the capacitor, of the resistor R is grounded, the anode of the thyristor T3 is connected with one end of a main switch branch, and the main switch branch is connected with an energy absorption branch in parallel; the cathode of the thyristor T3 is connected with one end of a commutation branch, the other end of the commutation branch is connected with one end, close to the resistor R, of the capacitor C, and the commutation branch is coupled with the main switch branch; the anode of the thyristor T3 is connected with the anode of the direct-current power supply U0, and the other end of the main switch branch is connected with the anode of the load Us; or the anode of the thyristor T3 is connected with the anode of the load Us, the other end of the main switch branch is connected with the anode of the direct-current power supply U0, and the cathode of the load Us is connected with the cathode of the direct-current power supply U0. According to the invention, when the load is suddenly changed, turn-off can be accurately carried out, and small current can be actively turned off.

Description

Technical Field

[0001] The present invention belongs to the technical field of DC circuit breakers, and particularly relates to a bidirectional controllable coupled inductor Z-source solid-state DC circuit breaker, and also relates to an application method of the bidirectional controllable coupled inductor Z-source solid-state DC circuit breaker. Background Art

[0002] As it becomes increasingly difficult to integrate various large-scale photovoltaic power generations into the grid, new technologies must be adopted. At the same time, due to the low line impedance of the DC power transmission system, when a short-circuit fault occurs in the line, the fault current rises rapidly, with a high amplitude. It is required that the DC circuit breaker has a fast response speed and can interrupt large current and voltage amplitudes. Moreover, the DC system current has no natural zero-crossing point, and the system current rise rate is very high during a fault, seriously affecting the power supply continuity and reliability of sensitive loads. Therefore, short-circuit protection is very challenging. Solid-state DC circuit breakers have broad application prospects due to their advantages such as short fault current interruption time, no arc generation during the interruption process compared with mechanical switches, no risk of causing damage to other surrounding devices, and increased service life. Currently, in practical applications, solid-state DC circuit breakers are mainly used in the aerospace field with a DC voltage of 270V, and are rarely used in photovoltaic power generation and energy storage with a DC voltage of 1500V. Since mechanical circuit breakers commonly used in the photovoltaic and energy storage systems will generate arcs when interrupting fault currents, which will severely erode the contacts and shorten their service life, and the generated arcs may also pose a risk of damage to surrounding devices, so the use of solid-state DC circuit breakers in the photovoltaic and energy storage systems is also an option due to their own advantages. As a novel DC protection means, the Z-source solid-state DC circuit breaker uses thyristors as the main switches. Compared with fully controlled devices such as insulated gate bipolar transistors and metal-oxide semiconductor field effect transistors carried by traditional solid-state DC circuit breakers, thyristors have lower on-state losses, stronger voltage and current withstand capabilities, and lower costs. With the help of the LC oscillating impedance source network, autonomous commutation under fault transients can be achieved, and the main thyristor can be quickly turned off, effectively suppressing the short-circuit current peak and providing more effective protection. Currently, among many solutions, the Z-source solid-state DC circuit breaker has attracted much attention for its advantages such as simple structure, low cost, fast response, natural commutation, and no need for detection and control systems. However, traditional Z-source solid-state DC circuit breakers have problems such as misoperation during load mutation and inability to actively turn off small currents. Summary of the Invention

[0003] The purpose of the present invention is to provide a bidirectional controllable coupled inductor Z-source solid-state DC circuit breaker to solve the problems of misoperation caused by load mutation and inability to actively turn off small currents in traditional Z-source solid-state DC circuit breakers.

[0004] Another purpose of the present invention is to provide an application method of the bidirectional controllable coupled inductor Z-source solid-state DC circuit breaker.

[0005] The technical solution adopted by the present invention is a bidirectional controllable coupled-inductor Z-source solid-state DC circuit breaker, which includes a thyristor T3. The cathode of the thyristor T3 is successively connected in series with a capacitor C and a resistor R. The end of the resistor R far from the capacitor is grounded. The anode of the thyristor T3 is connected to one end of the main switch branch. An energy absorption branch is connected in parallel with the main switch branch. The cathode of the thyristor T3 is connected to one end of the commutation branch. The other end of the commutation branch is connected to the end of the capacitor C close to the resistor R. The commutation branch and the main switch branch form a coupling; The anode of the thyristor T3 is connected to the positive pole of the DC power supply U0, and the other end of the main switch branch is connected to the positive pole of the load U s ; s The negative pole of the load U is connected to the negative pole of the DC power supply U0; Alternatively, the anode of the thyristor T3 is connected to the positive pole of the load U s ; the other end of the main switch branch is connected to the positive pole of the DC power supply U0, and the negative pole of the load U s is connected to the negative pole of the DC power supply U0. The features of the present invention also lie in: The main switch branch includes thyristors T1 and T2. The cathode of the thyristor T1 is connected to the same-name end of the inductor L1. The anode of the thyristor T2 is connected to the non-same-name end of the inductor L2. After the cathode of the thyristor T2 and the anode of the thyristor T1 are connected, they are then connected to the anode of the thyristor T3. The non-same-name end of the inductor L1 and the same-name end of the inductor L2 are connected and then connected to the positive pole of the load U s ; or, the non-same-name end of the inductor L1 and the same-name end of the inductor L2 are connected and then connected to the positive pole of the DC power supply U0.

[0006] The commutation branch includes a thyristor T4. The cathode of the thyristor T4 is connected to the same-name end of the inductor L3. The anode of the thyristor T4 is respectively connected to the cathode of the thyristor T3 and the cathode of the diode D. The non-same-name end of the inductor L3 is respectively connected to the anode of the diode D and the end of the capacitor C close to the resistor R. The inductor L3 forms a coupling with the inductor L1 and the inductor L2 respectively.

[0007] The coupling coefficients of the inductor L3 forming couplings with the inductor L1 and the inductor L2 respectively are both 0.98.

[0008] The coupling coefficient between the inductor L1 and the inductor L2 is 0.

[0009] The energy absorption branch is composed of a lightning arrester MOV, and the lightning arrester MOV is connected in parallel at both ends of the main switch branch.

[0010] Another technical solution adopted by the present invention is an application method of the bidirectional controllable coupled-inductor Z-source solid-state DC circuit breaker. Using the above-mentioned bidirectional controllable coupled-inductor Z-source solid-state DC circuit breaker, the specific steps are as follows: Normal current-carrying state: The current flows through the main switch branch, triggering thyristor T3, and the capacitor C is pre-charged; Short-circuit fault occurs: When the current rises and reaches the detection current threshold, thyristor T4 conducts, and the capacitor C discharges. The current flows through inductor L3. Under the action of magnetic induction, a coupled inductor will be formed in the main switch branch to induce an induced current in the direction opposite to the short-circuit current. When the magnitude of the induced current is equal to the short-circuit current, the thyristor turns off. When the voltage across the main switch branch is greater than the clamping voltage of arrester MOV, arrester MOV conducts, and the short-circuit current energy is dissipated by arrester MOV, realizing the interruption of the short-circuit fault current.

[0011] The features of the present invention also lie in: When the anode of thyristor T3 is connected to the positive pole of DC power supply U0, in the event of a short-circuit fault, the inductor that induces an induced current in the direction opposite to the short-circuit current is inductor L1, and the thyristor that turns off is thyristor T1; When the anode of thyristor T3 is connected to the positive pole of load U s in the event of a short-circuit fault, the inductor that induces an induced current in the direction opposite to the short-circuit current is inductor L2, and the thyristor that turns off is thyristor T2.

[0012] Active turn-off rated current: Control thyristor T4 to conduct, and the pre-charged capacitor C discharges. The current flows through the coupled inductor L L3. Under the action of magnetic induction, an induced current in the direction opposite to the rated current will be induced in the coupled inductor formed in the main switch branch. When the magnitude of the induced current is equal to the rated current, the thyristor in the main switch branch turns off. When the voltage across the main switch branch is greater than the clamping voltage of arrester MOV, arrester MOV conducts, and the current energy is dissipated by arrester MOV, realizing the interruption of small current.

[0013] When the anode of thyristor T3 is connected to the positive pole of DC power supply U0, the inductor that induces an induced current in the direction opposite to the short-circuit current is inductor L1, and the thyristor that turns off is thyristor T1; When the anode of thyristor T3 is connected to the positive pole of load U s in the event of a short-circuit fault, the inductor that induces an induced current in the direction opposite to the short-circuit current is inductor L2, and the thyristor that turns off is thyristor T2.

[0014] The beneficial effects of the present invention are as follows: The two-way controllable coupled inductor Z-source solid-state DC circuit breaker of the present invention charges the capacitor through its own power supply without the need for an external auxiliary power supply. In the main switch branch, two non-coupled branches are used, and in each branch, the coupled inductor is connected to the thyristor and then paralleled to achieve bidirectional energy flow in the circuit. Combined with the three-winding inductor coupling, the controlled formation of the coupled inductor access can actively turn off the small current during stable operation, and can accurately turn off when the load changes; and when a short-circuit fault occurs, the access time of the controlled formation of the coupled inductor can be controlled to avoid voltage oscillation in the lower-level load and ensure the safety of the lower-level load; at the same time, the circuit breaker of the present invention realizes the common ground of the source and the load, and further improves the turn-off speed. It takes about 0.25 μs to turn off the small current and about 0.8 ms to turn off the short-circuit fault current. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 FIG. is a schematic topological structure diagram of the two-way controllable coupled inductor Z-source solid-state DC circuit breaker of the present invention when conducting forward; Figure 2 FIG. is a working principle diagram of the two-way controllable coupled inductor Z-source solid-state DC circuit breaker of the present invention for interrupting short-circuit current when conducting forward; Figure 3 FIG. is a simulation waveform of the thyristor T1 current when the load side of the two-way controllable coupled inductor Z-source solid-state DC circuit breaker of the present invention has a short-circuit fault when conducting forward; Figure 4 FIG. is a simulation waveform of the load current when the load side of the two-way controllable coupled inductor Z-source solid-state DC circuit breaker of the present invention has a short-circuit fault when conducting forward; Figure 5 FIG. is a simulation waveform of the thyristor T1 current when the two-way controllable coupled inductor Z-source solid-state DC circuit breaker of the present invention actively turns off a 2A small current when conducting forward; Figure 6 FIG. is a simulation waveform of the load current when the two-way controllable coupled inductor Z-source solid-state DC circuit breaker of the present invention actively turns off a 2A small current when conducting forward; Figure 7 FIG. is a schematic topological structure diagram of the two-way controllable coupled inductor Z-source solid-state DC circuit breaker of the present invention when conducting backward; Figure 8 FIG. is a simulation waveform of the thyristor T2 current when the load side of the two-way controllable coupled inductor Z-source solid-state DC circuit breaker of the present invention has a short-circuit fault when conducting backward; Figure 9 FIG. is a simulation waveform of the load current when the load side of the two-way controllable coupled inductor Z-source solid-state DC circuit breaker of the present invention has a short-circuit fault when conducting backward; Figure 10When reverse-conducting, it is the simulation waveform of the current of thyristor T2 when the bidirectional controllable coupled-inductor Z-source solid-state DC circuit breaker of the present invention actively shuts off a small current of 2A; Figure 11 When reverse-conducting, it is the simulation waveform of the load current when the bidirectional controllable coupled-inductor Z-source solid-state DC circuit breaker of the present invention actively shuts off a small current of 2A; Figure 12 It is the schematic diagram of the topological structure of the old-structured circuit breaker when forward-conducting; Figure 13 It is the comparison of the opening times of the circuit breaker of the present invention and the old-structured circuit breaker when breaking the same fault current; Figure 14 It is the comparison of the voltages that the thyristors need to withstand when the circuit breaker of the present invention and the old-structured circuit breaker break the same fault current.

[0016] In the figure, 1. Main switch branch, 2. Commutation branch, 3. Energy absorption branch, 4. Pre-charging branch. Specific embodiments

[0017] The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0018] Embodiment 1 The bidirectional controllable coupled-inductor Z-source solid-state DC circuit breaker of the present invention, as Figure 1 shown, is composed of a main switch branch 1, a commutation branch 2, an energy absorption branch 3 and a pre-charging branch 4. Specifically: The pre-charging branch 4 is composed of a thyristor T3, a capacitor C and a resistor R. The cathode of the thyristor T3 is connected in series with the capacitor C and the resistor R in sequence. The end of the resistor R far from the capacitor is grounded. The anode of the thyristor T3 is connected to one end of the main switch branch 1. An energy absorption branch 3 is connected in parallel with the main switch branch 1. The cathode of the thyristor T3 is connected to one end of the commutation branch 2. The other end of the commutation branch 2 is connected to the end of the capacitor C close to the resistor R. The commutation branch 2 and the main switch branch 1 form a coupling; the anode of the thyristor T3 is connected to the positive pole of the DC power supply U0. The other end of the main switch branch 1 is connected to the positive pole of the load U s The negative pole of the load U s is connected to the negative pole of the DC power supply U0. At this time, it is forward-conducting. The commutation branch 2 includes a thyristor T4. The cathode of the thyristor T4 is connected to the same-named end of the coupled inductor L3. The anode of the thyristor T4 is respectively connected to the cathode of the thyristor T3 and the cathode of the diode D. The non-same-named ends of the coupled inductor L3 are respectively connected to the anode of the diode D and the end of the capacitor C close to the resistor R.

[0019] The main switch branch 1 includes thyristors T1, T2, inductors L1 and L2. Inductors L1 and L2 are respectively coupled with inductor L3, and the coupling coefficient K is 0.98 for both. There is no coupling between inductors L1 and L2, that is, the coupling coefficient K is 0. The cathode of thyristor T1 is connected to the same-named end of inductor L1 that forms the coupling. The anode of thyristor T2 is connected to the non-same-named end of inductor L2 that forms the coupling. After the cathode of thyristor T2 is connected to the anode of thyristor T1 and then connected to the anode of thyristor T3, the non-same-named end of inductor L1 that forms the coupling is connected to the same-named end of inductor L2 that forms the coupling and then connected to the load U s is connected to the positive pole.

[0020] The energy absorption branch 3 consists of a lightning arrester MOV. The lightning arrester MOV is connected in parallel across the two ends of the main switch branch 1. When the voltage across the lightning arrester MOV reaches its clamping voltage, the lightning arrester MOV conducts and can quickly dissipate the system energy. The clamping voltage of the lightning arrester MOV is 1.2 times to 2 times the system voltage value.

[0021] Embodiment 2 The application method of the bidirectional controllable coupled inductor Z-source solid-state DC circuit breaker of the present invention uses the bidirectional controllable coupled inductor Z-source solid-state DC circuit breaker of Embodiment 1, which is in the forward conduction state. As Figure 2 shown, the specific steps are as follows: In the normal current-carrying state: The current flows through the main switch branch 1, and at the same time, thyristor T3 is triggered to pre-charge the capacitor C. The polarity of the capacitor C is positive on the left and negative on the right. The on-state loss of the system is the loss of the current in a single semiconductor device, which has a lower on-state loss compared with the current Z-source DC circuit breaker; at this time, there is no current flowing through the commutation branch, and the voltage across the lightning arrester MOV of the energy absorption branch is very low, and the lightning arrester MOV will not conduct; When a short-circuit fault occurs: Stage 1: The current in the main switch branch rises to the short-circuit current. Before the short-circuit current reaches the detection current threshold i th the load current i dc is: (1) In formula (1), i 0 is the initial value of the load current i dc U s is the voltage across the load, t is the time; Phase 2: When the short-circuit current reaches the detection current threshold, which is set to 10 times the rated current of the system, control the thyristor T4 to conduct, and the pre-charged capacitor C discharges. The current injects current into the same-named end of the coupled inductor L3 through the thyristor T4. Under the action of magnetic induction, an induced current opposite to the direction of the short-circuit current will be induced in the coupled inductor L1 in the main switch branch 1. When the magnitude of the induced current is equal to the short-circuit current, the thyristor T1 is turned off; According to Kirchhoff's voltage law (KVL), we have: (2) In Equation (2), u 1 is the voltage across the two ends of the coupled inductor L1, u T1 is the voltage across the two ends of the thyristor T1, u C is the voltage across the two ends of the capacitor C, u 2 is the voltage across the two ends of the coupled inductor L3, n is the turns ratio, k is the mutual inductance coefficient of the coupled inductor, u MOV is the voltage across the MOV; The voltage across the MOV u MOV is less than the clamping voltage of the MOV u clamp At this time, we can obtain: (3) In Equation (3), α is the ratio of U s to u clamp To turn off the thyristor T1, the thyristor T1 voltage u T1 should be less than 0; Phase 3: When the voltage across the main switch branch 1 is greater than the clamping voltage of the arrester MOV, the arrester MOV is turned on, and the current in the main switch branch 1 starts to transfer to the arrester MOV. The arrester MOV absorbs the energy of the short-circuit current and dissipates it as heat energy to achieve the interruption of the short-circuit fault current; After the thyristor T1 is turned off, the capacitor C continues to discharge. Ignoring the voltage drop and loss of the thyristor T4, the capacitor C and the coupled inductor L3 still form an LC oscillation circuit. According to Kirchhoff's voltage law (KVL), it can be deduced that: (4) From the structure, the voltage across the capacitor C u C and the current of the capacitor C i C The initial values of are US and - nki th , therefore, the solution of Equation (5): (5) When u MOV reaches u clamp the value of, that is u MOV = u clamp = α U S ; To ensure the turn - off of thyristor T1, during the turn - off period of thyristor T1 t q , u T1 should always be negative. Therefore, it can be obtained that: (6) According to Equation (6), the value of capacitor C can be obtained in relation to i th , n , k , L 3 and α; Selection of thyristors: The maximum current and voltage that a thyristor withstands during the short - circuit fault interruption process are the most important factors to prevent damage. In the main switch branch, the maximum current flowing through thyristor T1 and thyristor T2 should be greater than the set detection current threshold i th , in addition, the voltage to be withstood should be greater than the clamping voltage of MOV u clamp ; The maximum voltage and maximum current that thyristor T3 can withstand should be greater than U S and , thyristor T3 is used for charging capacitor C, and the maximum charging current i Dmax should be: (7) The maximum current flowing through thyristor T3 must be greater than i Dmax .

[0022] Selection of coupling inductor and capacitor: When designing the coupling inductor, the maximum current and the inductance of the coil should be considered. According to Equation (1), the coupling inductor limits the rising rate of the fault current. The larger the inductance, the slower the rising rate of the fault current, and the larger the weight and volume of the coupling inductor. According to Equation (3), the turns ratio of the coupling inductor n should be greater than α / k; The relationship between C, L3 and n is shown in Equation (6).

[0023] As the voltage and current ratings increase, the size and cost of the coupled inductor also increase, while the mutual inductance coefficient of the coupled inductor k decreases; according to Equation (3), as k decreases, n must increase to ensure the normal operation of the arrester MOV; according to Equation (6), k the change in the value of affects the value of C, and as k decreases, the required value of C gradually increases. Therefore, a larger value of C can be adopted to compensate for k the decrease.

[0024] The definitions represented by the same letters used in the method formulas (1) to (7) of the present invention are the same.

[0025] Figure 3 is the simulation waveform of the current of thyristor T1 during a short-circuit fault on the load side when conducting forward at a DC voltage level of 1500V. When t = 0.3s, a short-circuit fault occurs on the load side, and the current rises rapidly. When the fault current detection threshold is reached, thyristor T4 is triggered, and the current of thyristor T1 starts to decrease. At t = 0.30047s, the current of thyristor T1 drops to 0.

[0026] Figure 4 is the simulation waveform of the load current during a short-circuit fault on the load side when conducting forward at a DC voltage level of 1500V. When a short-circuit fault occurs on the load side, the current rises rapidly. When the detection current threshold i th is reached, thyristor T4 is triggered, and the current of thyristor T1 starts to decrease. At this time, the energy absorption branch starts to work, and the load side current gradually drops to zero. The turn-off time is 0.8ms, ensuring the safety of the load side.

[0027] Embodiment 3 For the application method of the bidirectional controllable coupled inductor Z-source solid-state DC circuit breaker of the present invention, the bidirectional controllable coupled inductor Z-source solid-state DC circuit breaker of Embodiment 1 is adopted and is in the forward conduction state. The specific steps are as follows: In the normal current-carrying state: The current flows through the main switch branch 1, and at the same time, thyristor T3 is triggered to pre-charge the capacitor C; When actively turning off the rated current: Control the thyristor T4 to conduct, and the pre-charged capacitor C discharges. The current flows through the coupled inductor L3. Under the action of magnetic induction, an induced current opposite to the direction of the rated current will be induced in the coupled inductor L1 formed in the main switch branch 1. When the magnitude of the induced current is equal to the magnitude of the rated current, the thyristor T1 in the main switch branch 1 turns off. When the voltage across the main switch branch 1 is greater than the clamping voltage of the arrester MOV, the arrester MOV conducts, and the current energy is dissipated by the arrester MOV, completing the rated current turn-off and achieving the interruption of small current.

[0028] As Figure 5 and Figure 6 shown, when actively turning off a small current of 2A, when t = 0.3s, trigger the thyristor T4, and the current of the thyristor T1 starts to decrease. At t = 0.30000025s, the current of the thyristor T1 drops to zero. At the same time, the energy absorption branch starts to work, and the load-side current gradually drops to zero. The turn-off time is 0.25 μs.

[0029] Embodiment 4 The bidirectional controllable coupled inductor Z-source solid-state DC circuit breaker of the present invention, as Figure 7 shown, is composed of a main switch branch 1, a commutation branch 2, an energy absorption branch 3 and a pre-charging branch 4. Specifically: The pre-charging branch 4 is composed of a thyristor T3, a capacitor C and a resistor R. The cathode of the thyristor T3 is successively connected in series with the capacitor C and the resistor R. The end of the resistor R far from the capacitor is grounded. The anode of the thyristor T3 is connected to one end of the main switch branch 1. An energy absorption branch 3 is connected in parallel with the main switch branch 1. The cathode of the thyristor T3 is connected to one end of the commutation branch 2. The other end of the commutation branch 2 is connected to the end of the capacitor C close to the resistor R. The commutation branch 2 forms a coupling with the main switch branch 1; The anode of the thyristor T3 is connected to the positive pole of the load U s The positive pole of the main switch branch 1 is connected to the positive pole of the DC power supply U0, the negative pole of the load U s is connected to the negative pole of the DC power supply U0, and the negative pole of the load U s is connected to the negative pole of the DC power supply U0. At this time, it is reverse conduction. The commutation branch 2 includes a thyristor T4. The cathode of the thyristor T4 is connected to the same-named end of the coupled inductor L3. The anode of the thyristor T4 is respectively connected to the cathode of the thyristor T3 and the cathode of the diode D. The non-same-named end of the coupled inductor L3 is respectively connected to the anode of the diode D and the end of the capacitor C close to the resistor R.

[0030] The main switch branch 1 includes thyristors T1, T2, inductors L1 and L2. Inductors L1 and L2 are respectively coupled with inductor L3, and the coupling coefficient K is 0.98 for both. There is no coupling between inductors L1 and L2, that is, the coupling coefficient K is 0. The cathode of thyristor T1 is connected to the same-named end of inductor L1 that forms the coupling. The anode of thyristor T2 is connected to the non-same-named end of inductor L2 that forms the coupling. After the cathode of thyristor T2 is connected to the anode of thyristor T1 and then connected to the anode of thyristor T3, the non-same-named end of inductor L1 that forms the coupling is connected to the same-named end of inductor L2 that forms the coupling and then connected to the load U s The positive pole of is connected.

[0031] The energy absorption branch 3 consists of a lightning arrester MOV. The lightning arrester MOV is connected in parallel across the two ends of the main switch branch 1. When the voltage across the lightning arrester MOV reaches its clamping voltage, the lightning arrester MOV conducts, and the system energy can be quickly dissipated. The clamping voltage of the lightning arrester MOV is 1.2 times to 2 times the system voltage value.

[0032] Embodiment 5 The application method of the bidirectional controllable coupled inductor Z-source solid-state DC circuit breaker of the present invention uses the bidirectional controllable coupled inductor Z-source solid-state DC circuit breaker of Embodiment 4 and is reverse-conducting. The specific steps are as follows: In the normal current-carrying state: The current flows through the main switch branch 1, and at the same time, thyristor T3 is triggered to pre-charge the capacitor C. The polarity of the capacitor C is positive on the left and negative on the right. The conduction loss of the system is the loss of the current in a single semiconductor device, which has a lower conduction loss compared with the current Z-source DC circuit breaker; at this time, there is no current flowing through the commutation branch, and the voltage across the lightning arrester MOV of the energy absorption branch is very low, and the lightning arrester MOV will not conduct; When a short-circuit fault occurs: Stage 1: The current in the main switch branch rises to the short-circuit current; Stage 2: When the short-circuit current reaches the detection current threshold, the detection current threshold is set to 10 times the system rated current, control thyristor T4 to conduct, and the pre-charged capacitor C discharges. The current injects current into the same-named end of inductor L3 that forms the coupling through thyristor T4. Under the action of magnetic induction, an induced current opposite to the direction of the short-circuit current will be induced in inductor L2 that forms the coupling in the main switch branch 1. When the magnitude of the induced current is equal to the short-circuit current, thyristor T2 turns off; Stage 3: When the voltage across the two ends of the main switch branch 1 is greater than the clamping voltage of the lightning arrester MOV, the lightning arrester MOV is conducted, and the current in the main switch branch 1 starts to transfer to the lightning arrester MOV. The lightning arrester MOV absorbs the energy of the short-circuit current and dissipates it as heat energy, realizing the interruption of the short-circuit fault current.

[0033] The principle of the switch for the short-circuit fault current in this embodiment is the same as that of Embodiment 2.

[0034] Figure 8 For the simulation waveform of the current of thyristor T2 under a DC voltage level of 1500V during reverse conduction when there is a short - circuit fault on the load side. When t = 0.3s, a short - circuit fault occurs on the load side, and the current rises rapidly. When the detected current threshold is reached, thyristor T4 is triggered, and the current of thyristor T2 starts to decrease. At t = 0.30047s, the current of thyristor T2 drops to zero.

[0035] Figure 9 For the simulation waveform of the load current under a DC voltage level of 1500V during reverse conduction when there is a short - circuit fault on the load side. When a short - circuit fault occurs on the load side, the current rises rapidly. When the detected current threshold is reached, thyristor T4 is triggered, and the current of thyristor T2 starts to decrease. At this time, the energy absorption branch starts to work, and the load - side current gradually drops to zero. The turn - off time is 0.8ms, ensuring the safety of the load side.

[0036] Embodiment 6 The application method of the bidirectional controllable coupled - inductor Z - source solid - state DC circuit breaker of the present invention uses the bidirectional controllable coupled - inductor Z - source solid - state DC circuit breaker of Embodiment 4 for reverse conduction. The specific steps are as follows: In the normal current - flowing state: The current flows through the main switch branch 1, and at the same time, thyristor T3 is triggered to pre - charge the capacitor C; When actively turning off the rated current: Control thyristor T4 to conduct, and the pre - charged capacitor C discharges. The current flows through the coupled inductor L3. Under the action of magnetic induction, an induced current opposite to the direction of the rated current will be induced in the coupled inductor L2 in the main switch branch 1. When the magnitude of the induced current is equal to the magnitude of the rated current, the thyristor T2 in the main switch branch 1 turns off. When the voltage across the main switch branch 1 is greater than the clamping voltage of the arrester MOV, the arrester MOV conducts, and the current energy is dissipated by the arrester MOV, completing the turn - off of the rated current and realizing the interruption of small current.

[0037] As Figure 10 and Figure 11 shown, when actively turning off a small current of 2A, when t = 0.3s, thyristor T4 is triggered, and the current of thyristor T1 starts to decrease. At t = 0.30000025s, the current of thyristor T2 drops to zero. At the same time, the energy absorption branch starts to work, and the load - side current gradually drops to zero. The turn - off time is 0.25μs.

[0038] The structure of the old - type circuit breaker is as Figure 12As shown, it includes thyristor SCR1. The anode of thyristor SCR1 is respectively connected to the positive pole of DC power supply U0 and the cathode of diode D2. The anode of diode D2 is connected to the anode of diode D1. The cathode of diode D1 is respectively connected to the anode of thyristor SCR2 and the positive pole of load U S The cathode of thyristor SCR1 is respectively connected to the homonymous end of coupled inductor L 11 formed, the cathode of diode D3, and the cathode of thyristor SCR2 to form the non - homonymous end of coupled inductor L 11 which is connected to the homonymous end of coupled inductor L 12 formed. The non - homonymous end of coupled inductor L 12 is respectively connected to the anode of diode D2 and one end of resistor R d One end of resistor R d is connected to the anode of diode D4. The cathode of diode D4 is connected to the homonymous end of coupled inductor L 12 formed. The anode of diode D3 is connected to one end of resistor R. The other end of resistor R is respectively connected to the non - homonymous end of coupled inductor L 11 formed and one end of capacitor C. The other end of capacitor C is respectively connected to the negative pole of DC power supply U0 and the negative pole of load U S

[0039] As Figure 13 shown, when the circuit breaker of the present invention and the circuit breaker with the old structure break the same - sized fault current, the time required for the circuit breaker with the old structure to break the fault current is 1.25 ms, while the time required for the circuit breaker of the present invention to break the fault current is 0.87 ms, which is a 30.4% reduction compared to the breaking time of the circuit breaker with the old structure.

[0040] As Figure 14 shown, when the circuit breaker of the present invention and the circuit breaker with the old structure break the same - sized fault current, the maximum surge voltage borne by the thyristor when the circuit breaker with the old structure breaks the fault current is 67 V, while the maximum surge voltage borne by the thyristor when the circuit breaker of the present invention breaks the fault current is 57 V, which is a 15.9% reduction compared to the maximum surge voltage borne by the thyristor of the circuit breaker with the old structure.

[0041] ​For the bidirectional controllable coupled inductor Z-source solid-state DC circuit breaker of the present invention, due to the presence of diode D in the commutation branch 2, the current initially flowing through capacitor C starts to flow through diode D instead. Due to the forward bias voltage of diode D, the voltage of capacitor C becomes zero. Since the voltage of capacitor C does not become negative voltage, a DC capacitor can be used, which is smaller in volume and more economical than an AC capacitor under the same voltage; the main switch branch 1 is composed of two uncoupled branches, that is, thyristor T1 and inductor L1 form one branch, and thyristor T2 and inductor L2 form another branch. Moreover, the structure in which the coupled inductor and the thyristor are connected in parallel after being connected in each branch realizes the bidirectional flow in the circuit.

Claims

1. A bidirectional controllable coupled inductor Z-source solid-state DC circuit breaker, characterized in that: The invention comprises a thyristor T3, wherein the cathode of the thyristor T3 is connected in series with a capacitor C and a resistor R in sequence, the end of the resistor R away from the capacitor is grounded, the anode of the thyristor T3 is connected to one end of a main switch branch (1), the main switch branch (1) is connected in parallel with an energy absorption branch (3), the cathode of the thyristor T3 is connected to one end of a commutation branch (2), the other end of the commutation branch (2) is connected to one end of the capacitor C close to the resistor R, and the commutation branch (2) is coupled with the main switch branch (1); The anode of thyristor T3 is connected to the positive electrode of DC power supply U0, and the other end of the main switch branch (1) is connected to the load U s The positive connection of the load U s The negative electrode of is connected to the negative electrode of the DC power supply U0; Alternatively, the anode of thyristor T3 and the load U s The other end of the main switch branch (1) is connected to the positive electrode of the DC power supply U0, and the load U s The negative pole of is connected to the negative pole of the DC power supply U0.

2. The bidirectional controllable coupled inductor Z-source solid-state DC circuit breaker according to claim 1, characterized in that: The main switch branch (1) comprises a thyristor T1 and a thyristor T2, wherein the cathode of the thyristor T1 is connected to the same-name end of the inductor L1, the anode of the thyristor T2 is connected to the non-same-name end of the inductor L2, the cathode of the thyristor T2 is connected to the anode of the thyristor T1 and then to the anode of the thyristor T3, the non-same-name end of the inductor L1 is connected to the same-name end of the inductor L2 and then to the load U s Alternatively, the non-identical end of the inductor L1 is connected to the identical end of the inductor L2 and then connected to the positive electrode of the DC power supply U0.

3. The bidirectional controllable coupled inductor Z-source solid-state DC circuit breaker according to claim 2, characterized in that: The commutation branch (2) comprises a thyristor T4, the cathode of the thyristor T4 is connected to the same-name end of the inductor L3, the anode of the thyristor T4 is respectively connected to the cathode of the thyristor T3 and the cathode of the diode D, the non-same-name end of the inductor L3 is respectively connected to the anode of the diode D and one end of the capacitor C close to the resistor R, and the inductor L3 is respectively coupled with the inductor L1 and the inductor L2.

4. The bidirectional controllable coupled inductor Z-source solid-state DC circuit breaker according to claim 3, characterized in that: The coupling coefficients of the inductor L3, the inductor L1 and the inductor L2 are both 0.

98.

5. The bidirectional controllable coupled inductor Z-source solid-state DC circuit breaker according to claim 4, characterized in that: The coupling coefficient between the inductor L1 and the inductor L2 is 0.

6. The bidirectional controllable coupled inductor Z-source solid-state DC circuit breaker according to claim 5, characterized in that: The energy absorption branch (3) is composed of a lightning arrester MOV, and the lightning arrester MOV is connected in parallel to both ends of the main switch branch (1).

7. The application method of the bidirectional controllable coupled inductor Z source solid-state DC circuit breaker is characterized in that: The bidirectional controllable coupled inductor Z-source solid-state DC circuit breaker according to claim 6 is adopted, and the specific steps are as follows: Normal flow state: Current flows through the main switch branch (1), triggering thyristor T3 and capacitor C Perform pre-charging; Short circuit fault occurs: When the current rises and reaches the detection current threshold, the thyristor T4 is turned on and the capacitor C The discharge current flows through the inductor L3. Under the action of magnetic induction, the coupled inductor in the main switch branch (1) induces an induced current in the opposite direction to the short-circuit current. When the induced current is equal to the short-circuit current, the thyristor is turned off. When the voltage across the main switch branch (1) is greater than the arrester MOV clamping voltage, the arrester MOV is turned on, and the short-circuit current energy is dissipated by the arrester MOV, thereby realizing the interruption of the short-circuit fault current.

8. The application method of the bidirectional controllable coupled inductor Z-source solid-state DC circuit breaker according to claim 7 is characterized in that: When the anode of the thyristor T3 is connected to the positive electrode of the DC power supply U0, when a short circuit fault occurs, the inductor L1 senses the induced current in the opposite direction to the short circuit current, and the thyristor that is turned off is the thyristor T1; When the anode of thyristor T3 is connected to the load U s When the positive pole of is connected, when a short circuit fault occurs, the inductor L2 senses the induced current in the opposite direction to the short circuit current, and the thyristor that is turned off is the thyristor T2.

9. The application method of the bidirectional controllable coupled inductor Z-source solid-state DC circuit breaker according to claim 7 is characterized in that: Active shutdown rated current: Control thyristor T4 to conduct, pre-charge the capacitor C Discharge is performed, and the current flows through the inductor that forms the coupling L 3. Under the action of magnetic induction, an induced current in the opposite direction to the rated current will be induced in the coupled inductor of the main switch branch (1). When the induced current is equal to the rated current, the thyristor of the main switch branch (1) is turned off. When the voltage across the main switch branch (1) is greater than the arrester MOV clamping voltage, the arrester MOV is turned on, and the current energy is dissipated by the arrester MOV, thereby realizing the interruption of a small current.

10. The application method of the bidirectional controllable coupled inductor Z-source solid-state DC circuit breaker according to claim 9 is characterized in that: When the anode of the thyristor T3 is connected to the positive electrode of the DC power supply U0, the inductor L1 senses the induced current in the opposite direction to the short-circuit current, and the thyristor that is turned off is the thyristor T1; When the anode of thyristor T3 is connected to the load U s When the positive pole is connected, the inductor L2 senses the induced current in the opposite direction to the short-circuit current, and the thyristor that is turned off is the thyristor T2.

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