Current-limiting DC circuit breaker and control method thereof

Abstract

The invention discloses a current limiting type direct current circuit breaker and a control method. The method comprises two or more than two current limiting modules which are connected in parallel; the current limiting module comprises a first diode, a second diode, a third diode, a fourth diode, a first insulated gate bipolar transistor, a second insulated gate bipolar transistor and a first inductor; the anode of the first diode is connected with the cathode of the third diode; the cathode of the second diode and the collector of the first insulated gate bipolar transistor are connected with the cathode of the first diode; the positive electrode of the fourth diode and the collector electrode of the second insulated gate bipolar transistor are connected with the positive electrode of the third diode; one end of the first inductor is connected with the cathode of the fourth diode; the emitter of the first insulated gate bipolar transistor is connected with the emitter of the second insulated gate bipolar transistor; the other end of the first inductor serves as the output end of the current limiting module. The circuit can be widely applied to the technical field of electronic circuits.

Description

Technical Field

[0001] The present application relates to the technical field of electronic circuits, and in particular to a current limiting DC circuit breaker and a control method thereof. Background Art

[0002] In the related art, the existing DC fault current limiter usually uses the characteristics of inductance passing low frequencies and blocking high frequencies to limit the fault current; however, it still has the following problems: increasing the current limiting inductance can enhance the current limiting effect, but during the current limiting process, the inductance will reach saturation as the fault current increases, thereby losing the current limiting ability; there is no natural zero crossing point in the DC power grid, and as the current limiting inductance value increases, the reactor volume will also increase, resulting in an increase in the volume and cost of the current limiter; the traditional DC solid-state current limiter has a large number of IGBTs, the required cost is high, and the economic benefit is low; the traditional circuit breaker still has a large current stress when cutting off the fault current, and the arrester input loss increases. Therefore, there are still technical problems that need to be solved in the related art. Summary of the invention

[0003] The purpose of this application is to solve one of the technical problems existing in the prior art to at least a certain extent.

[0004] To this end, an object of an embodiment of the present application is to provide a current limiting DC circuit breaker and a control method thereof. This solution can significantly reduce the number of IGBTs used while achieving circuit current limiting, reduce costs, and improve the economy and practicality of the circuit breaker.

[0005] In order to achieve the above technical objectives, the technical solution adopted by the embodiment of the present application includes: a current limiting DC circuit breaker, including: two or more current limiting modules connected in parallel; wherein each of the current limiting modules includes a first diode, a second diode, a third diode, a fourth diode, a first insulated gate bipolar transistor, a second insulated gate bipolar transistor and a first inductor; the positive electrode of the first diode and the negative electrode of the third diode are connected, and the positive electrode of the first diode serves as the input end of the current limiting module; the negative electrode of the second diode and the collector of the first insulated gate bipolar transistor are connected to the negative electrode of the first diode; The anode of the fourth diode and the collector of the second insulated gate bipolar transistor are connected to the anode of the third diode; the anode of the second diode and one end of the first inductor are connected to the cathode of the fourth diode; the emitter of the first insulated gate bipolar transistor is connected to the emitter of the second insulated gate bipolar transistor; the other end of the first inductor serves as the output end of the current limiting module; the gate of the first insulated gate bipolar transistor and the gate of the second insulated gate bipolar transistor are used to access the PWM signal; two or more of the output ends are connected in parallel; and two or more of the input ends are connected in parallel.

[0006] In addition, the current limiting DC circuit breaker described in the above embodiment of the present invention may also have the following additional technical features:

[0007] Furthermore, in an embodiment of the present application, the current limiting DC circuit breaker further includes a buffer circuit; one end of the buffer circuit is connected to the cathode of the first diode; and one end of the buffer circuit is connected to the anode of the third diode.

[0008] Furthermore, in an embodiment of the present application, the buffer circuit includes a first resistor and a first capacitor; one end of the first capacitor is connected to the positive electrode of the third diode; the negative electrode of the first diode is connected to one end of the first resistor; and the other end of the first capacitor is connected to the other end of the first resistor.

[0009] Furthermore, in an embodiment of the present application, the current limiting DC circuit breaker also includes a lightning arrester; one end of the lightning arrester is connected to the cathode of the first diode; and one end of the lightning arrester is connected to the anode of the third diode.

[0010] Furthermore, in the embodiment of the present application, both the first insulated gate bipolar transistor and the second insulated gate bipolar transistor are N-type insulated gate bipolar transistors.

[0011] Furthermore, in an embodiment of the present application, the current limiting DC circuit breaker further includes a transistor control module; the transistor control module is used to output a PWM signal to control the first insulated gate bipolar transistor and / or the second insulated gate bipolar transistor.

[0012] Furthermore, in an embodiment of the present application, the current limiting DC circuit breaker also includes a current detection module; the current detection module is connected to two or more current limiting modules connected in parallel; the current detection module is used to detect the node current flowing into the parallel node of two or more current limiting modules connected in parallel.

[0013] Furthermore, in the embodiment of the present application, the first diode, the second diode, the third diode and the fourth diode are all rectifier diodes.

[0014] On the other hand, an embodiment of the present application further provides a current limiting DC circuit breaker control method, the method is used to control any of the current limiting DC circuit breaker described above, the method comprising:

[0015] When the number of the current limiting modules is 2n, and the current input to the current limiting type DC circuit breaker is greater than a preset threshold, the first insulated gate bipolar transistors of n current limiting modules are controlled to be turned on, and the first insulated gate bipolar transistors of n current limiting modules are controlled to be turned off, and the second insulated gate bipolar transistors of 2n current limiting modules are controlled to be turned off, so that the first diode, the first insulated gate bipolar transistor, the second insulated gate bipolar transistor and the fourth diode in the n current limiting modules form a current loop to reduce the current output by the current limiting type DC circuit breaker;

[0016] Alternatively, when the number of the current limiting modules is 2n and the current input to the current limiting type DC circuit breaker is greater than a preset threshold, the second insulated gate bipolar transistors of n of the current limiting modules are controlled to be turned on, and the second insulated gate bipolar transistors of n of the current limiting modules are controlled to be turned off, and the first insulated gate bipolar transistors of 2n of the current limiting modules are controlled to be turned off, so that the third diode, the first insulated gate bipolar transistor, the second insulated gate bipolar transistor and the second diode in the n current limiting modules form a current loop to reduce the current flowing out of the output of the current limiting type DC circuit breaker;

[0017] When the number of the current limiting modules is 2n+1 and the current input to the current limiting type DC circuit breaker is greater than a preset threshold, the first insulated gate bipolar transistors of the n+1 current limiting modules are controlled to be turned on, the first insulated gate bipolar transistors of the n current limiting modules are controlled to be turned off, and the second insulated gate bipolar transistors of the 2n+1 current limiting modules are controlled to be turned off, so that the first diode, the first insulated gate bipolar transistor, the second insulated gate bipolar transistor and the fourth diode in the n+1 current limiting modules form a current loop to reduce the current output by the current limiting type DC circuit breaker;

[0018] Alternatively, when the number of the current limiting modules is 2n+1 and the current input to the current limiting DC circuit breaker is greater than a preset threshold, the second insulated gate bipolar transistors of the n+1 current limiting modules are controlled to be turned on and the second insulated gate bipolar transistors of the n current limiting modules are controlled to be turned off, and the first insulated gate bipolar transistors of the 2n+1 current limiting modules are controlled to be turned off, so that the third diode, the first insulated gate bipolar transistor, the second insulated gate bipolar transistor and the second diode in the n+1 current limiting modules form a current loop to reduce the current output by the current limiting DC circuit breaker; wherein n is an integer greater than or equal to 1.

[0019] In addition, the present application also provides a power system, comprising the current limiting DC circuit breaker as described in any of the above items.

[0020] The advantages and benefits of the present application will be partially given in the following description, and partially become apparent from the following description, or be understood through the practice of the present application:

[0021] The present application can control the first insulated gate bipolar transistor and the second insulated gate bipolar transistor of each module to conduct alternately through PWM signals when a fault occurs in the circuit, thereby realizing the continuous current limiting capability of the current limiting DC circuit breaker. The present application uses four diode bridges to realize bidirectional conduction, which not only greatly reduces the number of insulated gate bipolar transistors used, but also realizes the bidirectional breaking function, reduces costs, and improves the economy and practicality of the circuit breaker. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a structural schematic diagram of a current limiting DC circuit breaker in a specific embodiment of the present invention;

[0023] Figure 2 It is a structural schematic diagram of a current limiting DC circuit breaker in another specific embodiment of the present invention;

[0024] Figure 3 A schematic diagram of the current direction when the system is operating normally in a specific embodiment of the present invention;

[0025] Figure 4 A schematic diagram of the current direction when the system fails to operate in a specific embodiment of the present invention;

[0026] Figure 5 A schematic diagram of the current direction when the system fails to operate in another specific embodiment of the present invention;

[0027] Figure 6 A schematic diagram of the current direction when the system fails to operate in another specific embodiment of the present invention;

[0028] Figure 7 A schematic diagram of the current direction when the system fault current is transferred in a specific embodiment of the present invention;

[0029] Figure 8 It is a schematic diagram of a circuit structure of energy consumption of a lightning arrester in a specific embodiment of the present invention;

[0030] Fig. 9 It is a circuit breaker overall control topology diagram in a specific embodiment of the present invention;

[0031] Fig.10 It is an equivalent circuit diagram of a circuit breaker topology in normal operation in a specific embodiment of the present invention;

[0032] Fig.11It is an equivalent circuit diagram of a circuit breaker topology fault detection stage in a specific embodiment of the present invention;

[0033] Fig.12 It is an equivalent circuit diagram of the circuit breaker topology commutation stage in a specific embodiment of the present invention;

[0034] Fig.13 A system short circuit fault simulation waveform diagram in a specific embodiment of the present invention;

[0035] Fig.14 A fault current peak value diagram under different parameters in a specific embodiment of the present invention;

[0036] Fig.15 A three-dimensional diagram of a fault under different parameters in a specific embodiment of the present invention;

[0037] Fig.16 A current collection flow chart in a specific embodiment of the present invention;

[0038] Fig.17 It is an overall flow chart of a control system in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0039] The embodiments of the present invention are described in detail below in conjunction with the accompanying drawings to illustrate the principles and processes of the current limiting DC circuit breaker and the control method in the embodiments of the present invention.

[0040] Reference Figure 1 The present application provides a current limiting type DC circuit breaker. The current limiting type DC circuit breaker may include two or more current limiting modules connected in parallel. Each current limiting module may include a first diode D01, a second diode D02, a third diode D03, a fourth diode D04, a first insulated gate bipolar transistor T01, a second insulated gate bipolar transistor T02, and a first inductor. The anode of the first diode D01 and the cathode of the third diode D03 are connected, and the anode of the first diode D01 serves as the input end of the current limiting module. The cathode of the second diode D02 and the collector of the first insulated gate bipolar transistor T01 are connected to the cathode of the first diode D01. The anode of the fourth diode D04 and the collector of the second insulated gate bipolar transistor T02 are connected to the anode of the third diode D03. The anode of the second diode D02 and one end of the first inductor are connected to the cathode of the fourth diode D04. The emitter of the first insulated gate bipolar transistor T01 is connected to the emitter of the second insulated gate bipolar transistor T02. The other end of the first inductor serves as the output end of the current limiting module. The gate of the first insulated gate bipolar transistor T01 and the gate of the second insulated gate bipolar transistor T02 are used to access the PWM signal. Two or more output ends are connected in parallel. Two or more input ends are connected in parallel.

[0041] Furthermore, in the embodiment of the present application, the current limiting DC circuit breaker may further include a buffer circuit, one end of which is connected to the cathode of the first diode D01, and one end of which is connected to the anode of the third diode D03.

[0042] Further, refer to Figure 1 In the embodiment of the present application, the buffer circuit may include a first resistor R01 and a first capacitor C01. One end of the first capacitor C01 is connected to the anode of the third diode D03. The cathode of the first diode D01 is connected to one end of the first resistor R01. The other end of the first capacitor C01 is connected to the other end of the first resistor R01.

[0043] Further, refer to Figure 1 In the embodiment of the present application, the current limiting DC circuit breaker may further include a lightning arrester MOV1. One end of the lightning arrester MOV1 is connected to the cathode of the first diode D01. One end of the lightning arrester MOV1 is connected to the anode of the third diode D03.

[0044] Furthermore, in the embodiment of the present application, both the first insulated gate bipolar transistor T01 and the second insulated gate bipolar transistor T02 are N-type insulated gate bipolar transistors.

[0045] Furthermore, in the embodiment of the present application, the current limiting DC circuit breaker may further include a transistor control module. The transistor control module is used to output a PWM signal to control the first insulated gate bipolar transistor T01 and / or the second insulated gate bipolar transistor T02.

[0046] Furthermore, in the embodiment of the present application, the current limiting DC circuit breaker may further include a current detection module. The current detection module is connected to two or more current limiting modules connected in parallel. The current detection module is used to detect the node current flowing into the parallel node of the two or more current limiting modules connected in parallel.

[0047] Furthermore, in the embodiment of the present application, the first diode D01 , the second diode D02 , the third diode D03 , and the fourth diode D04 are all rectifier diodes.

[0048] On the other hand, the present application also provides a current limiting DC circuit breaker control method, which can be used to control the above current limiting DC circuit breaker. The method may include steps S101, S102, S103 or S104.

[0049] S101. When the number of current limiting modules is 2n and the current input to the current limiting DC circuit breaker is greater than a preset threshold value, the first insulated gate bipolar transistors of the n current limiting modules are controlled to be turned on, and the first insulated gate bipolar transistors of the n current limiting modules are controlled to be turned off, and the second insulated gate bipolar transistors of the 2n current limiting modules are controlled to be turned off, so that the first diode, the first insulated gate bipolar transistor, the second insulated gate bipolar transistor and the fourth diode in the n current limiting modules form a current loop to reduce the current output by the current limiting DC circuit breaker.

[0050] or,

[0051] S102. When the number of current limiting modules is 2n and the current input to the current limiting DC circuit breaker is greater than a preset threshold value, the second insulated gate bipolar transistors of the n current limiting modules are controlled to be turned on, and the second insulated gate bipolar transistors of the n current limiting modules are controlled to be turned off, and the first insulated gate bipolar transistors of the 2n current limiting modules are controlled to be turned off, so that the third diode, the first insulated gate bipolar transistor, the second insulated gate bipolar transistor and the second diode in the n current limiting modules form a current loop to reduce the current flowing out of the output of the current limiting DC circuit breaker.

[0052] S103. When the number of current limiting modules is 2n+1 and the current input to the current limiting DC circuit breaker is greater than a preset threshold value, the first insulated gate bipolar transistors of the n+1 current limiting modules are controlled to be turned on, the first insulated gate bipolar transistors of the n current limiting modules are controlled to be turned off, and the second insulated gate bipolar transistors of the 2n+1 current limiting modules are controlled to be turned off, so that the first diode, the first insulated gate bipolar transistor, the second insulated gate bipolar transistor and the fourth diode in the n+1 current limiting modules form a current loop to reduce the current output by the current limiting DC circuit breaker.

[0053] or,

[0054] S104, when the number of current limiting modules is 2n+1, and the current input to the current limiting type DC circuit breaker is greater than a preset threshold, the second insulated gate bipolar transistors of the n+1 current limiting modules are controlled to be turned on, the second insulated gate bipolar transistors of the n current limiting modules are controlled to be turned off, and the first insulated gate bipolar transistors of the 2n+1 current limiting modules are controlled to be turned off, so that the third diode, the first insulated gate bipolar transistor, the second insulated gate bipolar transistor and the second diode in the n+1 current limiting modules form a current loop to reduce the current output by the current limiting type DC circuit breaker. Where n is an integer greater than or equal to 1.

[0055] The specific implementation principle of this application is described below with reference to the accompanying drawings:

[0056] In view of the problem that the traditional current-limiting DC circuit breaker does not have the current limiting function and the breaking current is large, this embodiment provides a current-limiting fast-response current-limiting DC circuit breaker. Through simulation verification, it is verified that the proposed circuit breaker has the advantages of suppressing the rise of fault current and preventing inductor saturation. By designing the control system, the circuit breaker can quickly detect the occurrence of faults, control the IGBT to alternately conduct, and achieve continuous current limiting capability. This topological circuit breaker structure uses a diode bridge to achieve bidirectional conduction, which not only greatly reduces the number of IGBTs used, but also can achieve a bidirectional breaking function, reduce costs, and improve the economy and practicality of this circuit breaker.

[0057] The circuit breaker of this embodiment is composed of three parallel branches, each of which includes two IGBTs connected in series, four rectifier diodes, a metal oxide surge arrester, a branch inductor, a snubber resistor and a snubber capacitor.

[0058] The working states of the circuit breaker in this embodiment are mainly divided into: normal operating state, fault current limiting state, continuous current limiting state and fault clearing state.

[0059] In terms of parameter design, this embodiment comprehensively considers various factors while ensuring that the current limiter has sufficient current limiting performance and shutoff capability. Through simulation analysis and parameter optimization design, it is ensured that the current limiter reduces loss, reduces cost, and reduces size while ensuring performance.

[0060] In terms of the entire power system design, this embodiment has a core processor in addition to the circuit breaker to achieve high-speed data acquisition and rapid fault response. The current flowing into the circuit breaker is monitored by the Hall current sensor. When it exceeds the set threshold, the current limiting mechanism is automatically triggered to accurately control the on and off of the IGBT.

[0061] Further, refer to Figure 2 as well as Fig. 9, the circuit breaker of this embodiment is composed of three parallel branches, each branch includes two IGBTs connected in series, four rectifier diodes, a metal oxide lightning arrester, a branch inductor, a buffer resistor, and a buffer capacitor. Specifically, the first branch includes two insulated gate bipolar transistors T1 and T2 connected in series, four rectifier diodes D1-D4, a metal oxide lightning arrester MOV1, a branch inductor L1, a buffer resistor R1, and a buffer capacitor C1. The second branch includes two insulated gate bipolar transistors T3 and T4 connected in series, four rectifier diodes D1-D4, a metal oxide lightning arrester MOV2, a branch inductor L2, a buffer resistor R2, and a buffer capacitor C2. The third branch includes two insulated gate bipolar transistors T5 and T6 connected in series, four rectifier diodes D1-D4, a metal oxide lightning arrester MOV3, a branch inductor L3, a buffer resistor R3, and a buffer capacitor C3. The diodes D1-D4 are connected in series and then in parallel to realize bidirectional rectification, R1-R3 are buffer resistors, C1-C3 are buffer capacitors, and MOV1-MOV3 are connected in parallel with buffer resistors R1-R3 and buffer capacitors C1-C3 as lightning arresters to form an energy-consuming branch. Since a large impulse voltage will be generated when the IGBT is turned off, in order to reduce the damage to the power electronic device, an energy-consuming branch is required to dissipate the energy stored in the inductor and absorb excess energy, thereby protecting the IGBT from being affected by excessive impulse voltage. The transistor control module of this embodiment uses DSPF28335 as a hardware control board. The current detection module uses a Hall current sensor to convert the current into a corresponding voltage value in proportion, collects the voltage analog quantity through the ADC acquisition I / O port, and compares the collected voltage with the set voltage threshold. When the collected voltage Vdc> the set voltage threshold Vset, the system determines that a fault has occurred and automatically and instantly transfers to the current limiting branch. It can be understood that the current detection module can also directly measure the current in the circuit. After obtaining the current or voltage comparison result, the transistor control module connected to the IGBT can change the duty cycle of the PWM signal to achieve the output of a complementary waveform, thereby controlling the on-time and off-time of the IGBT to be equal, thereby achieving continuous current limiting switching of each branch in the circuit.

[0062] Furthermore, the circuit breaker working states mainly include: normal operation state, fault current limiting state, fault continuous current limiting state and fault clearing state.

[0063] 1) Normal operation status

[0064] Reference Figure 3 When the power system is in normal operation, T1, T3 and T5 are all in the on state, and T2, T4 and T6 are in the off state. dc Generates a stable main circuit current i dcAt the same time, since the circuit structures of each branch are the same, the current of each branch is 1 / 3 of the main current.

[0065] When the ADC of the power system collects the main current i dc set When the IGBT drive module is in normal working state, the on-resistance of each branch IGBT is the same, and the current through the inductor is a constant value. At this time, the inductor is equivalent to the wire. Therefore, the DC power supply U dc The generated line current flows through the diodes into T1, T3, and T5, and the branch currents are equal. Figure 3 As shown, the current paths from left to right are D1-T1-D4, D1-T3-D4, and D1-T5-D4. The current-limiting inductor does not affect the normal power flow of the system. Therefore, the current flowing through each branch IGBT is:

[0066]

[0067] 2) Fault current limiting state

[0068] When the system detects a short circuit fault, the line current surges rapidly. The DSP collects the line current through the ADC sampling module, and the Hall current sensor proportionally converts it into a corresponding voltage value, which also surges rapidly. dc When the current rises to the threshold value within the short-circuit time, the current-limiting inductor is immediately put into use. At this time, the PWM outputs a complementary waveform to achieve alternating conduction control of the IGBTs in each branch.

[0069] When a ground short circuit occurs in the power system, the current flowing through the Hall current sensor of the automatic current limiting module changes, and the voltage V collected by DSPF28335 changes. i It also increases. Since each parallel branch is connected in series with a current-limiting inductor, the rapid increase of the short-circuit current can be effectively suppressed. At the same time, each parallel branch has a shunting effect, which can reduce the current stress when the IGBT is turned off, effectively improve the safety of each device in the power system, improve the working stability of the device, and reduce damage to the device. When the short-circuit current exceeds the threshold, T1 is immediately given a shutdown pulse, and T3 and T5 are given a turn-on pulse. The branch current on iL1 is cut off, and L2 and L3 are instantly put into the current-limiting state. At this time, the equivalent inductance (Leq) of the line is:

[0070]

[0071]

[0072] From the above formula, we can see that as the current limiting inductance increases, the current limiting inductance's ability to suppress short-circuit current surges improves. At this time, the direction of the fault current flow is as follows: Figure 4 ​As shown, the current flows in the circuit breaker through D1-T3-D4 and D1-T5-D4. The current limiting inductor is charged in the positive direction, which can limit the rapid rise of the fault current to a certain extent. At the same time, the buffer capacitor and buffer resistor connected in parallel with the IGBT on branch 1 are put into use. At this time, a directional voltage is generated when the capacitor is charged, which can limit the growth of the short-circuit current to a certain extent.

[0073] When the above current limiting process lasts for T / 2 cycles, the transistor control module controls two PWM waveforms to output low-level signals to turn off T3 and T5 immediately, and one PWM waveform outputs high-level signals to trigger T1 to turn on. The current limiting process enters state 2. The direction of the fault current flow is as above. Figure 5 As shown, in the circuit breaker, the current passes through D1-T1-D4, and the current limiting inductor L1 is instantly put into the current limiting state. Since T3 and T5 are in parallel, the current on each branch is relatively small, which can effectively reduce the loss of the device and increase the branch breaking current. In this process, the line inductance is L1, and the system equivalent inductance changes from parallel to series. The increase in inductance value can further effectively suppress the increase of fault current.

[0074] 3) Continuous current limiting state

[0075] Reference Figure 6 When a short circuit occurs in the system, the current limiting inductors of each branch are put into use instantaneously, with T as the cycle. The first T / 2 time is state one, at which time the PWM output is high to control T3 and T5 to turn on, and the PWM output is low to control T1 to turn off. The DC current flows in the directions of D1-T3-D4 and D1-T5-D4. The second state is state two, in which the PWM output is high to turn on T1, and the PWM output is low to turn off T3 and T5, and the DC current flows in the direction of D1-T1-D4. After the fault occurs, the two different states repeat the above process with T as the cycle, and the current flow direction of each branch changes continuously. By taking advantage of the characteristic that the inductor current cannot change suddenly, the DC current flowing through the line branch is converted into a high-frequency AC current, so that the fault current rise speed is reduced, effectively suppressing the current surge and preventing the purpose of inductor saturation.

[0076] In the above continuous current limiting process, DSP controls the PWM function module to output complementary waveforms, and controls the IGBT drive power module to realize the alternating conduction state of T1, T3, and T5 during the fault period, and the conduction time is half a cycle respectively. At the same time, the counter starts counting. During the continuous current limiting time, the ADC continuously collects the line voltage and detects the line current in real time to ensure that the current limiting drive circuit continues to work and continue to provide drive voltage for the IGB T.

[0077] 4) Fault clearing status

[0078] Reference Figure 7 as well as Figure 8 When the fault current is continuously limited to a low level for a period of time, the fault current is almost zero, and the current split in each branch is small. The PWM waveform gives each IGBT a shutdown signal, and T1, T3, and T5 cooperate with the main circuit breaker to produce a shutdown action. Figure 7 As shown in Figure 1, when the IGBT is turned off, the capacitor C starts to charge and absorbs the energy released in the inductor, thereby reducing the voltage stress on the IGBT. The resistor R is used to consume the energy stored in the capacitor C and prevent the capacitor from overcharging. Figure 8 As shown, when the capacitor is charged to a voltage that exceeds the action voltage of the arrester, the arrester begins to conduct, absorbing and dissipating the overvoltage energy. This can effectively limit the system voltage within the allowable range and prevent equipment from being damaged by overvoltage. When the energy generated by the short-circuit fault in the circuit breaker is completely consumed, the system detects the closing signal of the current-limiting DC circuit breaker, and T1, T3, and T5 are turned on again, and the current-limiting circuit breaker is put back into normal use. Different from the circuit breakers mentioned in other documents, the current-limiting circuit breaker mentioned in this patent can achieve safe and low-loss interruption of larger currents.

[0079] 5) Equivalent circuit diagram during normal operation

[0080] When the circuit breaker is in normal operation, its equivalent circuit diagram and current direction are as follows Fig.10 As shown, at this time, the IGBT valve groups of each branch in the circuit breaker are all in the on state. Under normal operation of the DC system, since the currents of each branch are constant, the inductor has a very small effect on the current. The DC resistance of the inductor is ignored and the inductor is regarded as a conductor. In the circuit: idc is the main current, iL1, iL2, iL3 are the currents of each branch respectively, R load is the load resistance. dc is the DC power supply voltage, R1, R2, R3 are the IGBT on-resistances, R line is the line resistance, and Reqs is the equivalent resistance of each branch.

[0081] The red line represents the main current. At this time, the three-element method is used to analyze the main current. The initial current value is zero, and the steady-state value can be expressed as:

[0082]

[0083] R eqs =R1 / / R2 / / R3=R1 / 3

[0084]

[0085] Substituting in, the line current is:

[0086]

[0087] in, Time constant, L is the equivalent inductance of the line, and t0 is the time point when a short circuit fault occurs in the system.

[0088] 6) Equivalent circuit diagram of fault detection stage

[0089] When a ground fault occurs in the line, it takes time for the DSP to detect the fault and control the IGBT to start operating. At this time, the fault current increases rapidly. At the beginning of the fault, the IGBT is still in the on state. Taking t0 as the initial moment of the fault, the fault detection time is analyzed. The equivalent circuit diagram is as follows Fig.11 shown.

[0090] The structures of each branch of the system are the same, and the loop expression of the system equivalent circuit can be expressed as:

[0091]

[0092] Performing Laplace transformation on the above formula gives:

[0093]

[0094] Therefore, the line current time domain expression during the fault detection period is obtained as follows:

[0095]

[0096] Among them, the short-circuit resistance is zero, Time constant:

[0097] When a line fault occurs, the DSP immediately outputs a PWM complementary waveform to control the IGBT to conduct alternately, so that the fault current can be continuously switched in different branches. The current-limiting inductor uses the characteristics of passing low frequencies and blocking high frequencies to quickly limit the fault current to a certain range. The following is an analysis of the changes in the short-circuit current in the first T / 2 of a commutation cycle.

[0098] 0-T / 2 cycle: At this time, T1 receives the shutdown signal, and T3 and T5 pulses trigger the turn-on signal. The specific equivalent circuit diagram is as follows Fig.12 As shown in the figure, in the first half of the commutation cycle, when T1 is turned off, a spike impulse voltage will be generated. The voltage is related to the current in the current limiting inductor and the current change rate. Since the generation of impulse voltage may cause the diodes D1 and D4 to be turned off, the current on the inductor L1 is zero at this time. When the transient impulse voltage gradually decreases to less than the power supply voltage U dc When , D1 and D4 are turned on, the buffer capacitor and buffer resistor in parallel with the IGBT branch are put into use, the inductor releases energy through the resistor R to limit the current change rate, and the capacitor is charged during the voltage spike to reduce the size of the IGBT repetitive peak voltage.

[0099] According to the loop current method, when T1 is turned off during the fault period, the relationship between the capacitor charging stage is expressed as follows:

[0100] i dcf =i dcf1 +i dcf2

[0101]

[0102] L r =L2 / / L3 Req_s=R2 / / R3

[0103] Among them, R _eqs is the equivalent resistance of the parallel branches 2 and 3, L r is the equivalent inductance, U cs_eq Buffer voltage across the capacitor. Since the line resistance is approximately zero, ignore the line resistance and perform Laplace transform on the above equation:

[0104]

[0105] I dcf (s)=I dcf1 (s)+I dcf2 (s)

[0106] Among them I l0 is the initial current when the current-limiting inductor of a branch is commutated, I dcf0 It is the initial current when the current-limiting inductor of branch 2 is commutated.

[0107] T / 2-T cycle: T1 is on, T3 and T5 are off, and the analysis is similar to the above.

[0108] Furthermore, in order to verify the fast fault current suppression capability of the current-limiting DC solid-state current limiter proposed in the present invention, the main circuit and control generation are first designed, and a simulation model is installed through Matlab / Simulink to ensure that the current limiting performance purpose is met. The specific simulation parameters are shown in Table I. The proposed system is assumed to have a short-circuit fault at 0.02s. Fig.13 It can be seen that the proposed circuit breaker has the ability to quickly suppress the rise of fault current and prevent inductor saturation.

[0109]

[0110]

[0111] Table I.

[0112] From the above equivalent circuit theory analysis, it can be seen that when the IGBT is alternately turned on and enters the current limiting process, the fault current idc repetitive current limiting peak value is mainly related to the switching frequency (f) and the current limiting inductance value (L). By reasonably designing the switching frequency and inductance value, the current limiting effect can be improved and the system's ability to suppress fault current can be optimized.

[0113] Reference Fig.15 , at the same switching frequency, increasing the current limiting inductance value, the repetitive current limiting peak value gradually decreases; after the inductance value is 1mh, the change rate of the fault current repetitive peak value gradually slows down. Under the same inductance, as the switching frequency increases, the repetitive current peak value tends to decrease, and the current limiting effect is better. However, when the current limiting inductance value is small, the current limiting peak value is large and the current limiting effect is poor. When the IGBT switching frequency is small, it will cause a large current limiting peak value. When the IGBT switching frequency is large, the number of device commutations increases and the breaking loss increases. For the inductance value, increasing the inductance value will increase the cost of the current limiter. Therefore, the current limiting inductance value only needs to meet the maximum value of the fault current is less than the current limiting peak value given by the system. From the perspective of system safety and stability, the steady-state current limiting peak value is set to 1.5 times the steady-state value.

[0114] Furthermore, the process of the system controlling the circuit breaker includes: the current acquisition module continuously acquires the circuit breaker line current value and compares the acquired current value with the designed threshold value. The current limiter is in normal operation most of the time, ready to enter the fault current limiting state at any time. When the system is in normal state, the DSP controls the PWM output of three high-level drives to turn on the circuit breakers T1, T3, and T5. When the system detects a fault, the line current rises rapidly. When it reaches the threshold set by the program, the processor acts and immediately controls the current limiter to enter the fault current limiting state module. At this time, T1 is alternately turned on with T3 and T5 to achieve continuous current conversion in each branch. The use of current limiting inductors effectively suppresses the rise of fault current and prevents the inductance saturation of each parallel branch. After a period of time, at the point where the fault current is close to zero, the IGBTs of each parallel branch cooperate with the ABB circuit breaker to clear the fault. The energy stored in the inductor is consumed by the RC buffer branch and the lightning arrester to reduce the impact of the peak impact voltage when the IGBT is turned off.

[0115] Further, refer to Fig.16 The transistor control module of this embodiment uses TMS320F28335 as a processor. TMS320C2000 series DSP has the characteristics of microcontroller and high performance. The chip running memory can reach 68KB, the main frequency reaches 150MHz, the core instruction execution cycle is as short as 6.67ns, and it can respond to interrupts quickly. DSPF28335 has powerful control and signal processing capabilities and can implement complex control algorithms. The development board integrates Flash memory, fast AD converter, enhanced CAN module, PWM module and other peripherals.

[0116] The ADC sampling module integrated inside the DSPF28335 can only process 0-3.3V voltage signals. The AD conversion module has 16 sampling channels, which can realize 16-channel analog input through cascading. The ADC conversion clock frequency can be configured to a maximum of 25MHz, the sampling bandwidth is a maximum of 12.5MHz, and the fastest conversion time is 80ns. The current detection module of this embodiment collects current signals through the Erhu current sensor, converts them into proportional voltage signals through IC induction, and then outputs the voltage to the AD sampling channel. The conversion result is transmitted to the host computer through the analog-to-digital conversion unit for fault identification.

[0117] Further, refer to Fig.17 , the current detection module of this embodiment continuously collects the current value of the circuit breaker line and compares the collected current value with the designed threshold value. The current limiter is in normal operation most of the time, ready to enter the fault current limiting state at any time. When the power system is in normal state, the transistor control module (DSP) controls the PWM output of three high-level drives to turn on the circuit breakers T1, T3, and T5. When the system detects a fault, the line current rises rapidly. When it reaches the threshold set by the program, the processor acts and immediately controls the current limiter to enter the fault current limiting state module. At this time, T1 is alternately turned on with T3 and T5 to achieve continuous current commutation of each branch. The use of current limiting inductors effectively suppresses the rise of fault current and prevents the inductance saturation of each parallel branch. After a period of time, at the point where the fault current is close to zero, the IGBTs of each parallel branch cooperate with the circuit breaker to clear the fault. The stored energy in the inductor is consumed by the RC buffer branch and the lightning arrester to reduce the impact of the peak impact voltage when the IGBT is turned off.

[0118] In addition, the present application also provides a power system, comprising the current limiting DC circuit breaker as described in any of the above items.

[0119] The contents of the above-mentioned current limiting DC circuit breaker embodiment are all applicable to the present power system embodiment. The functions specifically implemented by the present power system embodiment are the same as those of the above-mentioned current limiting DC circuit breaker embodiment, and the beneficial effects achieved are also the same as those achieved by the above-mentioned current limiting DC circuit breaker embodiment.

[0120] In the above description of this specification, the description with reference to the terms "one embodiment / example", "another embodiment / example" or "certain embodiments / examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0121] Although the embodiments of the present application have been shown and described, those skilled in the art will appreciate that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present application, and that the scope of the present application is defined by the claims and their equivalents.

[0122] The above is a specific description of the preferred implementation of the present application, but the present application is not limited to the described embodiments. Technical personnel familiar with the field may make various equivalent modifications or substitutions without violating the spirit of the present application. These equivalent modifications or substitutions are all included in the scope defined by the claims of the present application.

Claims

1. A current limiting DC circuit breaker, characterized in that: include: Two or more current limiting modules connected in parallel; wherein each current limiting module comprises a first diode, a second diode, a third diode, a fourth diode, a first insulated gate bipolar transistor, a second insulated gate bipolar transistor and a first inductor; The anode of the first diode and the cathode of the third diode are connected, and the anode of the first diode serves as the input end of the current limiting module; the cathode of the second diode and the collector of the first insulated gate bipolar transistor are connected to the cathode of the first diode; the anode of the fourth diode and the collector of the second insulated gate bipolar transistor are connected to the anode of the third diode; the anode of the second diode and one end of the first inductor are connected to the cathode of the fourth diode; the emitter of the first insulated gate bipolar transistor is connected to the emitter of the second insulated gate bipolar transistor; the other end of the first inductor serves as the output end of the current limiting module; the gate of the first insulated gate bipolar transistor and the gate of the second insulated gate bipolar transistor are used to access the PWM signal; two or more of the output ends are connected in parallel; and two or more of the input ends are connected in parallel.

2. The current limiting DC circuit breaker according to claim 1, characterized in that: The current limiting DC circuit breaker further includes a buffer circuit; one end of the buffer circuit is connected to the cathode of the first diode; one end of the buffer circuit is connected to the anode of the third diode.

3. The current limiting DC circuit breaker according to claim 2, characterized in that: The buffer circuit includes a first resistor and a first capacitor; one end of the first capacitor is connected to the positive electrode of the third diode; the negative electrode of the first diode is connected to one end of the first resistor; and the other end of the first capacitor is connected to the other end of the first resistor.

4. The current limiting DC circuit breaker according to claim 1, characterized in that: The current limiting DC circuit breaker further includes a lightning arrester; one end of the lightning arrester is connected to the cathode of the first diode; one end of the lightning arrester is connected to the anode of the third diode.

5. The current limiting DC circuit breaker according to claim 1, characterized in that: The first insulated gate bipolar transistor and the second insulated gate bipolar transistor are both N-type insulated gate bipolar transistors.

6. The current limiting DC circuit breaker according to claim 1, characterized in that: The current limiting DC circuit breaker further includes a transistor control module; the transistor control module is used to output a PWM signal to control the first insulated gate bipolar transistor and / or the second insulated gate bipolar transistor.

7. The current limiting DC circuit breaker according to claim 1, characterized in that: The current limiting DC circuit breaker also includes a current detection module; the current detection module is connected to two or more current limiting modules connected in parallel; the current detection module is used to detect the node current flowing into the parallel node of the two or more current limiting modules connected in parallel.

8. The current limiting DC circuit breaker according to claim 1, characterized in that: The first diode, the second diode, the third diode and the fourth diode are all rectifier diodes.

9. A current limiting DC circuit breaker control method, characterized in that: A method for controlling a current limiting DC circuit breaker according to any one of claims 1 to 8, comprising: When the number of the current limiting modules is 2n, and the current input to the current limiting type DC circuit breaker is greater than a preset threshold, the first insulated gate bipolar transistors of n current limiting modules are controlled to be turned on, and the first insulated gate bipolar transistors of n current limiting modules are controlled to be turned off, and the second insulated gate bipolar transistors of 2n current limiting modules are controlled to be turned off, so that the first diode, the first insulated gate bipolar transistor, the second insulated gate bipolar transistor and the fourth diode in the n current limiting modules form a current loop to reduce the current output by the current limiting type DC circuit breaker; Alternatively, when the number of the current limiting modules is 2n and the current input to the current limiting type DC circuit breaker is greater than a preset threshold, the second insulated gate bipolar transistors of n of the current limiting modules are controlled to be turned on, and the second insulated gate bipolar transistors of n of the current limiting modules are controlled to be turned off, and the first insulated gate bipolar transistors of 2n of the current limiting modules are controlled to be turned off, so that the third diode, the first insulated gate bipolar transistor, the second insulated gate bipolar transistor and the second diode in the n current limiting modules form a current loop to reduce the current flowing out of the output of the current limiting type DC circuit breaker; When the number of the current limiting modules is 2n+1 and the current input to the current limiting type DC circuit breaker is greater than a preset threshold, the first insulated gate bipolar transistors of the n+1 current limiting modules are controlled to be turned on, the first insulated gate bipolar transistors of the n current limiting modules are controlled to be turned off, and the second insulated gate bipolar transistors of the 2n+1 current limiting modules are controlled to be turned off, so that the first diode, the first insulated gate bipolar transistor, the second insulated gate bipolar transistor and the fourth diode in the n+1 current limiting modules form a current loop to reduce the current output by the current limiting type DC circuit breaker; Alternatively, when the number of the current limiting modules is 2n+1 and the current input to the current limiting DC circuit breaker is greater than a preset threshold, the second insulated gate bipolar transistors of the n+1 current limiting modules are controlled to be turned on and the second insulated gate bipolar transistors of the n current limiting modules are controlled to be turned off, and the first insulated gate bipolar transistors of the 2n+1 current limiting modules are controlled to be turned off, so that the third diode, the first insulated gate bipolar transistor, the second insulated gate bipolar transistor and the second diode in the n+1 current limiting modules form a current loop to reduce the current output by the current limiting DC circuit breaker; wherein n is an integer greater than or equal to 1.

10. A power system, characterized in that: It comprises a current limiting DC circuit breaker as described in any one of claims 1 to 8.

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