A thyristor-based bidirectional DC solid-state circuit breaker and its control method

Abstract

The present invention discloses a controllable bidirectional DC solid-state circuit breaker based on thyristors and its control method. The bidirectional DC solid-state circuit breaker is composed of a main branch, a commutation and capacitor charging branch, an energy absorption branch and a control unit. The present invention can realize the control of the commutation branch in combination with the control unit, and then utilize the induced current of the coupling inductor to interrupt and isolate the fault current. When the bidirectional DC solid-state circuit breaker is working normally, the main branch current only passes through one semiconductor device, with low on-state loss and controllable turn-off. The control algorithm of the present invention is simple, highly reliable, and has strong practicability, and can judge the short-circuit fault type during re-conduction.

Description

Technical Field

[0001] The invention belongs to the technical field of power electronics, and particularly relates to a bidirectional DC solid-state circuit breaker based on thyristors. Background Art

[0002] With the development of distributed power sources such as photovoltaic power generation and wind power generation, DC microgrids have received increasing attention as a more efficient access form. Compared with alternating current, direct current has better economy and a broader development prospect. Moreover, in terms of power transmission, DC transmission has the advantages of high efficiency and low loss. However, due to the lack of a natural zero-crossing point in direct current, how to effectively isolate faults in the DC grid restricts the development of direct current. Currently, DC circuit breakers are an effective method to solve this problem. However, traditional DC circuit breakers have problems such as long turn-off time, complex circuit structure, arc generation, low reliability, and low anti-interference ability. Solid-state circuit breakers based on solid-state power electronic devices have received increasing attention due to their advantages such as low loss, low cost, and simple structure.

[0003] The Z-source solid-state circuit breaker and its derivative topologies are a relatively common type of solid-state circuit breaker. The circuit structure is simple, and no additional fault detection and control circuits are required, and it can achieve the interruption and isolation of short-circuit faults. However, the performance of the Z-source solid-state circuit breaker is greatly affected by factors such as load and line impedance, which restricts its application in practice. In order to enhance the reliability of the circuit breaker and reduce the influence of circuit parameters on the performance of the circuit breaker, and at the same time to meet the requirements of the DC microgrid for bidirectional energy flow and bidirectional fault protection, Chinese Patent (202011145187.6) and Chinese Patent (201911098557.2) propose two types of bidirectional DC solid-state circuit breakers based on thyristors. These two bidirectional DC solid-state circuit breakers have the advantages of controllable turn-off, high reliability, and fast response speed. However, when the circuit is working normally, the current needs to pass through two semiconductor devices, and the on-state loss is relatively large. Summary of the Invention

[0004] In order to solve the deficiencies of the prior art, the invention proposes a verification and test method for the fault diagnosis and health management technology of contactors and relays. Using the verification and test method proposed by the invention, a series of PHM technology verification and test work for electromagnetic switch devices such as contactors and relays can be completed.

[0005] Aiming at the deficiencies of the current bidirectional DC solid-state circuit breaker, the invention proposes a bidirectional DC solid-state circuit breaker based on thyristors, which can achieve bidirectional energy flow and bidirectional interruption and isolation of faults. The bidirectional circuit breaker has the characteristics of controllability, high stability, fast response speed, and low on-state loss.

[0006] The described bidirectional DC solid-state circuit breaker based on thyristors has a topological structure composed of a main branch, a commutation and capacitor charging branch, an energy absorption branch, and a control unit, as shown in Figure 1 . The main branch is composed of a first thyristor (SCR1), a second thyristor (SCR2), and the primary coil of a coupling inductor (L w1 ). The commutation and capacitor charging branch is composed of a third thyristor (SCR3), a fourth thyristor (SCR4), a first capacitor (C1), a second capacitor (C2), the secondary coil of the coupling inductor (L w2 ), a first diode (D1), a second diode (D2), a first resistor (R1), and a second resistor (R2). The energy absorption branch is composed of a metal oxide varistor (MOV). The control unit is composed of a current sensor and a controller.

[0007] It is characterized in that: the first thyristor (SCR1) and the second thyristor (SCR2) are reversely connected in parallel to form a bidirectional current-carrying branch. The anode of the first thyristor (SCR1) is connected to the cathode of the second thyristor (SCR2), and the cathode of the first thyristor (SCR1) is connected to the anode of the second thyristor (SCR2). The cathode of the first thyristor (SCR1) is connected to the same-named terminal of the primary coil of the coupling inductor (L w1 ). The positive electrode of the first diode (D1) is connected to the anode of the first thyristor (SCR1), the negative electrode of the first diode (D1) is connected to the positive electrode of the first capacitor (C1), the negative electrode of the first capacitor (C1) is connected to one end of the first resistor (R1), and the other end of the first resistor (R1) is connected to the negative pole of the power supply. The positive electrode of the second diode (D2) is connected to the different-named terminal of the primary coil of the coupling inductor (L w1 ), the negative electrode of the second diode (D2) is connected to the positive electrode of the second capacitor (C2), the negative electrode of the second capacitor (C2) is connected to the same-named terminal of the secondary coil of the coupling inductor (L w2 ), the same-named terminal of the secondary coil of the coupling inductor (L w2 ) is connected to the cathode of the third thyristor (SCR3), the different-named terminal of the secondary coil of the coupling inductor (L w2 ) is connected to the negative electrode of the first capacitor (C1) and the cathode of the fourth thyristor (SCR4). The anode of the fourth thyristor (SCR4) is connected to the positive electrode of the second capacitor (C2). One end of the second resistor (R2) is connected to the negative electrode of the second capacitor (C2), and the other end is connected to the negative pole of the power supply. One end of the metal oxide varistor (MOV) is connected to the anode of the first thyristor (SCR1) and the positive electrode of the first diode (D1), and the other end of the metal oxide varistor (MOV) is connected to the primary coil of the coupling inductor (L w1)The opposite name terminals are connected to the positive electrode of the second diode (D2); the main circuit current flows through the current sensor, the output terminal of the current sensor is connected to the controller, and the output terminal of the controller is connected to the gates of the first (SCR1), second (SCR2), third (SCR3), and fourth thyristors (SCR4).

[0008] The thyristor-based bidirectional DC solid-state circuit breaker can achieve bidirectional energy flow and bidirectional interruption and isolation of short-circuit faults. The first thyristor (SCR1), the primary coil of the coupling inductor (L w1 ), and the current sensor constitute the main branch of the forward energy flow channel of the circuit breaker. The first diode (D1), the third thyristor (SCR3), the first capacitor (C1), the first resistor (R1), and the secondary coil of the coupling inductor (L w2 ) constitute the commutation and capacitor charging branch when the energy of the circuit breaker flows forward; the second thyristor (SCR2), the primary coil of the coupling inductor (L w1 ) constitute the main branch of the backward energy flow of the circuit breaker. The second diode (D2), the fourth thyristor (SCR4), the second capacitor (C2), the second resistor (R2), and the secondary coil of the coupling inductor (L w2 ) constitute the commutation and capacitor charging branch when the energy of the circuit breaker flows backward; the varistor (MOV) is the energy absorption circuit when the energy of the circuit breaker flows forward and backward; the current sensor and the controller are the control units when the energy of the circuit breaker flows forward and backward.

[0009] A control method for a thyristor-based controllable bidirectional DC solid-state circuit breaker is characterized in that it includes the following steps:

[0010] The output current is I O , and the reference current value is set to I ref1 , I ref2 , I ref1 <I ref2 , the difference between the output current and the reference current I ref1 is:

[0011] ΔI = I O - I ref1 (1)

[0012] When a fault occurs:

[0013] Step 1: When △I>0, start recording the sampled current data i k (k = 1, 2, 3... N), the number of samples is N, the sampling frequency is f, and then calculate the N data points collected and recorded to obtain the average sampled current I aver ,

[0014]

[0015] Step 2: If I aver >I ref2 , the controller sends a trigger signal to the gate of thyristor SCR3 to turn it on, so that capacitor C1, SCR3, and the secondary coil L of the coupling inductor w2 form a commutation circuit, thereby isolating the short-circuit fault.

[0016] When the circuit breaker re-conducts:

[0017] Set the minimum time interval from the circuit breaker turning off to re-conducting as T0, and the time required for capacitor charging as T1. Then the time interval from the circuit breaker turning off to re-conducting should be greater than the charging time of capacitor C1, that is, T0 > T1.

[0018] When operating in the reverse direction, if I aver >I ref2 , the controller sends a trigger signal to the gate of thyristor SCR4 to turn it on, so that capacitor C2, SCR4, and the secondary coil L of the coupling inductor w2 form a commutation circuit, thereby isolating the short-circuit fault.

[0019] When the circuit breaker re-conducts:

[0020] Set the minimum time interval from the circuit breaker turning off to re-conducting as T0, and the time required for capacitor charging as T1. Then the time interval from the circuit breaker turning off to re-conducting should be greater than the charging time of capacitor C2, that is, T0 > T1.

[0021] Step 3: After the circuit breaker is turned off for T0 time due to a short-circuit fault, the controller sends a trigger signal to the gate of thyristor SCR1 to turn on the circuit breaker, and repeats Step 1 and Step 2. If the circuit breaker is turned off again, it is judged as a permanent fault, and the circuit breaker is not re-conducted until the fault is completely cleared.

[0022] When operating in the reverse direction, after the circuit breaker is turned off for T0 time due to a short-circuit fault, the controller sends a trigger signal to the gate of thyristor SCR2 to turn on the circuit breaker, and repeats Step 1 and Step 2. If the circuit breaker is turned off again, it is judged as a permanent fault, and the circuit breaker is not re-conducted until the fault is completely cleared.

[0023] The present invention can achieve the following beneficial effects:

[0024] 1) When the two-way circuit breaker is working normally, the current only flows through one thyristor, greatly reducing the on-state loss of the system;

[0025] 2) The two-way circuit breaker uses a controller to detect current, enhancing the controllability of the circuit breaker, improving its reliability, and reducing the possibility of false triggering of the circuit breaker;

[0026] 3) The two-way circuit breaker can achieve pre-charging of the commutation branch capacitor to protect the circuit when the circuit is powered on;

[0027] 4) The two-way circuit breaker is equipped with current detection and a controller, enabling it to perform switching functions;

[0028] 5) When cutting off the fault current, it will not feedback a large current to the power supply end;

[0029] 6) When re-conducting the circuit breaker, it can judge the type of short-circuit fault. Description of the Drawings

[0030] One or more embodiments are exemplarily illustrated by corresponding drawings. These exemplary illustrations and the drawings do not constitute limitations on the embodiments. Elements with the same reference numerals in the drawings are shown as similar elements. The drawings do not constitute a scale limitation, and among them:

[0031] Figure 1 is the circuit topology diagram of the present invention;

[0032] Figure 2 is the working timing diagram of the present invention when a load short-circuit fault occurs;

[0033] Figure 3 is the control method flowchart for fault isolation;

[0034] Figure 4 is the control method flowchart for judging the fault type during re-conduction;

[0035] Figure 5 is the working timing diagram of the present invention when used as a switch;

[0036] Figure 6 is the waveform diagram of the output current, the current of the first thyristor, and the voltage of the first capacitor during simulation of a load short-circuit fault;

[0037] Figure 7 is the waveform diagram of the load voltage and the load current during simulation of load power-off. Detailed Embodiments

[0038] In order to make the objectives, technical solutions and advantages of the present application more clearly understood, the present application will be described and explained below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments provided in the present application without creative efforts fall within the scope of protection of the present application.

[0039] Obviously, the accompanying drawings in the following description are only some examples or embodiments of the present application. For those of ordinary skill in the art, the present application can also be applied to other similar scenarios based on these drawings without creative efforts. In addition, it can also be understood that although the efforts made in this development process may be complex and lengthy, for those of ordinary skill in the art related to the content disclosed in the present application, some design, manufacturing or production changes based on the technical content disclosed in the present application are only conventional technical means and should not be understood as the content disclosed in the present application being insufficient.

[0040] Referring to "embodiment" in the present application means that the specific features, structures or characteristics described in combination with the embodiment can be included in at least one embodiment of the present application. The appearance of this phrase at various positions in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those of ordinary skill in the art explicitly and implicitly understand that the embodiments described in the present application can be combined with other embodiments without conflict.

[0041] Unless otherwise defined, the technical terms or scientific terms involved in the present application should be understood as the ordinary meaning understood by those with ordinary skills in the technical field to which the present application belongs. The similar terms such as "a", "an", "one kind", "the" involved in the present application do not indicate a quantity limitation and can represent a single or plural number. The terms "including", "comprising", "having" and any variations thereof involved in the present application are intended to cover non-exclusive inclusion; for example, a process, method, system, product or device including a series of steps or modules (units) is not limited to the listed steps or units, but may further include unlisted steps or units, or may further include other steps or units inherent to these processes, methods, products or devices.

[0042] The technical solutions of the present invention will be described in detail below with reference to the accompanying drawings.

[0043] The bidirectional DC solid-state circuit breaker based on thyristor disclosed in the present invention is as Figure 1As shown, its topological structure consists of a main branch, a commutation and capacitor charging branch, an energy absorption branch, and a control unit. The main branch consists of a first thyristor (SCR1), a second thyristor (SCR2), and the primary coil of a coupled inductor (L w1 ) The commutation and capacitor charging branch consists of a third thyristor (SCR3), a fourth thyristor (SCR4), a first capacitor (C1), a second capacitor (C2), the secondary coil of a coupled inductor (L w2 ), a first diode (D1), a second diode (D2), a first resistor (R1), and a second resistor (R2). The energy absorption branch consists of a metal oxide varistor (MOV). The control unit consists of a current sensor and a controller.

[0044] The following describes the specific working principle of the thyristor-based controllable bidirectional DC solid-state circuit breaker and its control method proposed by the present invention:

[0045] When the energy of the circuit breaker flows forward, the first thyristor (SCR1), the primary coil of the coupled inductor (L w1 ), and the current sensor constitute the main branch of the forward energy flow channel of the circuit breaker. The first diode (D1), the third thyristor (SCR3), the first capacitor (C1), the first resistor (R1), and the secondary coil of the coupled inductor (L w2 ) constitute the commutation and capacitor charging branch when the energy of the circuit breaker flows forward. The metal oxide varistor (MOV) is the energy absorption branch, and the current sensor and the controller are the control unit. At this time, the first thyristor (SCR1) is in the conduction state, and the power supply charges the first capacitor (C1) through the first diode (D1) so that its voltage is equal to the power supply voltage.

[0046] As shown in Figure 2 and Figure 3 , the circuit breaker isolates the short-circuit fault. When a short-circuit fault occurs at the load at time t0, the output current I O shows an upward trend. When the difference ΔI between the output current I O and the reference current I ref1 is greater than 0, the current is recorded and sampled, and its average value I aver is calculated. At time t1, when I aver is greater than I ref2 , the controller sends a trigger signal to the gate of the third thyristor (SCR3) and makes it conduct. At this time, the first capacitor (C1), the third thyristor (SCR3), and the secondary coil of the coupled inductor (L w2 ) form a path, and the first capacitor (C1) discharges. The instantaneous large current passes through the third thyristor (SCR3) and flows through the secondary coil of the coupled inductor (L w2 ). At this time, in the primary coil of the coupled inductor (L w1) A reverse induced current will be generated at , reducing the current flowing through the first thyristor to 0 at t3. At this time, the first thyristor (SCR1) turns off and the fault is removed. After that, the varistor (MOV) absorbs the energy stored in the coupled inductor, and the power supply charges the first capacitor (C1) again through the first diode (D1), making its voltage equal to the power supply voltage to prepare for the next turn-off.

[0047] As Figure 4 shown, after the circuit breaker is turned off for T0 time due to a short-circuit fault, the controller sends a trigger signal to the gate of thyristor SCR1 to turn on the circuit breaker, and then performs the Figure 2 and Figure 3 fault detection and isolation steps shown in . If the circuit breaker is turned off again, it is judged as a permanent fault, and the circuit breaker is not turned on again until the fault is completely cleared.

[0048] As Figure 5 shown, this circuit breaker is used as a switch to cut off the power supply to the load. Before time t0, the circuit operates normally. At time t0, the controller sends a trigger signal to the gate of the third thyristor (SCR3) to turn it on. Similarly, at this time, the first capacitor (C1), the third thyristor (SCR3), and the secondary coil of the coupled inductor (L w2 ) form a path, and the first capacitor (C1) discharges. The instantaneous large current flows through the third thyristor (SCR3) and through the secondary coil of the coupled inductor (L w2 ). At this time, a reverse induced current will be generated at the primary coil of the coupled inductor (L w1 ), causing the first thyristor (SCR1) to turn off, and the load voltage and load current to decrease to 0.

[0049] A simulation experiment was carried out in the Saber simulation software for the example to verify the thyristor-based controllable bidirectional DC solid-state circuit breaker proposed in the present invention. Here, the forward flow of the circuit breaker energy is taken as an example for explanation. The simulation power supply voltage is 270V, the load is 10Ω, the first and second capacitors are 100uF, the first and second resistors are 40Ω, and the inductance values of the primary and secondary coils of the coupled inductor are 900uH and 100uH respectively.

[0050] Example 1: Simulation of a load short-circuit fault

[0051] The simulation waveform is as Figure 6 shown. It is set that a short-circuit fault occurs at t = 0.5ms. At this time, the system output current and the current flowing through the first thyristor (SCR1) increase. When the current sensor recognizes that the output current meets the fault protection condition, the controller outputs a control signal to turn on the third thyristor (SCR3). At this time, the first capacitor discharges (C1), releasing an instantaneous large current and flowing through the secondary coil of the coupled inductor (L w2), a large reverse current is induced at the primary coil (L w1 ) to turn off the first thyristor (SCR1), ultimately achieving short - circuit fault isolation.

[0052] Example 2: Simulation of load disconnection

[0053] The simulation waveform diagram is as shown in Figure 7 . It is set that at t = 0.5 ms, a control signal is output from the controller to the gate of the third thyristor (SCR3) to turn it on. At this time, the first capacitor (C1) discharges, releasing an instantaneous large current that flows through the secondary coil of the coupled inductor (L w2 ), and a large reverse current is induced at the primary coil of the coupled inductor (L w1 ) to turn off the first thyristor (SCR1), ultimately achieving load power - off.

[0054] As described above, only the preferred specific embodiments of the present invention are provided, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A thyristor-based controllable bidirectional DC solid-state circuit breaker, characterized in that: It consists of a main branch, a commutation and capacitor charging branch, an energy absorption branch and a control unit; The main branch circuit consists of a first thyristor SCR1, a second thyristor SCR2, and the primary coil L of a coupling inductor w1 ; The commutation and capacitor charging branch is composed of a third thyristor SCR3, a fourth thyristor SCR4, a first capacitor C1, a second capacitor C2, the secondary coil L of a coupling inductor w2 , a first diode D1, a second diode D2, a first resistor R1 and a second resistor R2; The energy absorption branch consists of a varistor MOV; The control unit consists of a current sensor and a controller; Among them, the first thyristor SCR1 and the second thyristor SCR2 are reversely connected in parallel to form a bidirectional current flow branch; The anode of the first thyristor SCR1 is connected to the cathode of the second thyristor SCR2, the cathode of the first thyristor SCR1 is connected to the anode of the second thyristor SCR2, and the cathode of the first thyristor SCR1 is connected to the w1 homonymous end of the primary coil L of the coupled inductor; The positive electrode of the first diode D1 is connected to the anode of the first thyristor SCR1, the negative electrode of the first diode D1 is connected to the positive electrode of the first capacitor C1, the negative electrode of the first capacitor C1 is connected to one end of the first resistor R1, the other end of the first resistor R1 is connected to the negative electrode of the power supply, the positive electrode of the second diode D2 is connected to the w1 opposite-named terminal of the coupled inductor primary coil L, the negative electrode of the second diode D2 is connected to the positive electrode of the second capacitor C2, the negative electrode of the second capacitor C2 is connected to the w2 same-named terminal of the coupled inductor secondary coil L, the w2 same-named terminal of the coupled inductor secondary coil L is connected to the cathode of the third thyristor SCR3, the w2 opposite-named terminal of the coupled inductor secondary coil L is connected to the negative electrode of the first capacitor C1 and the cathode of the fourth thyristor SCR4, the anode of the fourth thyristor SCR4 is connected to the positive electrode of the second capacitor C2; One end of the second resistor R2 is connected to the negative electrode of the second capacitor C2, and the other end is connected to the negative electrode of the power supply; one end of the varistor MOV is connected to the anode of the first thyristor SCR1 and the positive electrode of the first diode D1, and the other end of the varistor MOV is connected to the primary coil L of the coupled inductor w1 the different-named terminal and the positive electrode of the second diode D2; the main branch current flows through the current sensor, the output end of the current sensor is connected to the controller, and the output end of the controller is connected to the gates of the first SCR1, the second SCR2, the third SCR3, and the fourth thyristor SCR4.

2. The controllable bidirectional DC solid-state circuit breaker based on thyristor according to claim 1, wherein: The first thyristor SCR1 and the primary coil L of the coupled inductor w1 , together with the current sensor, form the main branch of the forward flow channel of the circuit breaker's energy. The first diode D1, the third thyristor SCR3, the first capacitor C1, the first resistor R1 and the secondary coil L of the coupled inductor w2 form the commutation and capacitor charging branch when the energy of the circuit breaker flows forward; The second thyristor SCR2 and the primary coil L of the coupled inductor w1 form the main branch of the backward flow of the circuit breaker's energy. The second diode D2, the fourth thyristor SCR4, the second capacitor C2, the second resistor R2 and the secondary coil L of the coupled inductor w2 form the commutation and capacitor charging branch when the energy of the circuit breaker flows backward; The varistor MOV is the energy absorption circuit for the forward and backward flows of the circuit breaker's energy; The current sensor and the controller are the control units for the forward and backward flows of the circuit breaker's energy.

3. A control method for a thyristor-based controllable bidirectional DC solid-state circuit breaker according to any one of claims 1-2, characterized in that: It includes the following steps: The output current is I O , set the reference current value to I ref1 、I ref2 , I ref1 < I ref2 , the difference between the output current and the reference current I ref1 is: When a fault occurs: Step 1: Start recording the sampled current data i when △I > 0 k , where k = 1, 2, 3... N, the number of samples is N, and the sampling frequency is f. Then, calculate the N data points collected and recorded to obtain the average sampled current I aver , Step 2: If I aver > I ref2 , the controller sends a trigger signal to the gate of thyristor SCR3 to turn it on, so that the capacitor C1, SCR3, and the secondary coil L of the coupling inductor w2 form a commutation circuit, thereby isolating the short-circuit fault; When the circuit breaker re-conducts: Set the minimum time interval from the circuit breaker turning off to the circuit breaker re-conducting as T0, and the time required for capacitor charging as T1. Then the time interval from the circuit breaker turning off to the circuit breaker re-conducting should be greater than the charging time of capacitor C1, that is, T0 > T1; Step 3: After the circuit breaker is turned off for T0 time due to a short-circuit fault, the controller sends a trigger signal to the gate of thyristor SCR1 to turn on the circuit breaker, and repeat Step 1 and Step 2. If the circuit breaker is turned off again, it is judged as a permanent fault, and the circuit breaker is not re-conducted until the fault is completely cleared.

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