Power aircraft dc protection system based on superconducting circuit breaker and method of operation thereof

Abstract

The application discloses a power aircraft direct current protection system based on a superconducting circuit breaker and a working method thereof, and the system comprises a fault current limiting module and a fault current breaking module in series, wherein the fault current breaking module comprises a main direct current branch, a buffer branch, a commutation branch and a charging branch; the main direct current branch comprises a fast switch S1 and a circuit breaker CB in series; the buffer branch comprises a buffer resistor R1 and a buffer capacitor C1 in series; the commutation branch comprises a fast switch S2, a commutation inductor L and a commutation capacitor C in series; and the charging branch comprises a fast switch S3 and a charging resistor R C The fault current limiting module can not only suppress the fault current to a lower level, but also continuously consume the accumulated energy in the system due to the resistive characteristic of the superconducting tape, so that the fault can be quickly cleared, the efficiency of clearing the fault is improved, and the manufacturing cost of the protection part is reduced.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of electric power system protection of an airplane, in particular to a direct-current protection system of an electric airplane based on a superconducting circuit breaker and a working method thereof. BACKGROUND

[0002] To cope with the challenge of greenhouse gas emissions and alleviate the problem of global warming, the current trend of the aviation industry is to eliminate all forms of energy except electric energy in airplanes, so that more-electric airplanes and all-electric airplanes have become the current research focus. However, the huge power demand is too heavy for the traditional electric power system, and even cannot be carried out. The high-temperature superconducting electric system is considered as a reasonable new solution, adopts a direct-current power distribution architecture, and the entire system is in a superconducting state, so that the line resistance is approximately zero, and the loss of direct-current transmission in the transmission process is minimized. However, when the high-voltage direct current occurs a direct-current fault, the fault current sharply rising in a short time will seriously affect the normal operation of the entire electric power system, therefore, the development of the high-voltage direct-current transmission network needs the direct-current circuit breaker to have the ability of quickly identifying faults and breaking large currents, and mainly adapts to the actual needs of the superconducting electric airplane system, that is, high efficiency and small heat loss, otherwise it will aggravate the pressure of the refrigeration system of the entire electric power system. At present, the common circuit breakers for breaking direct-current faults in the market mainly include mechanical circuit breakers, hybrid circuit breakers and solid-state circuit breakers. However, in the background of the new type of airplane electric power system, the mechanical circuit breaker can break the large current fault, but the breaking time is long and an additional power supply auxiliary system is needed; the hybrid circuit breaker and the solid-state circuit breaker are composed of a large number of power electronic switches (mainly IGBT), which are high in cost, and there is a large power loss in the system operation, and because the power electronic period does not have the current limiting ability, the weakness of the overvoltage resistance of the power electronic period will cause equipment damage and aggravate the development of the accident when the system appears a serious accident. That is to say, the common protection scheme in the market is not suitable for our new type of airplane electric power system, and it has problems such as long breaking time, high cost and large loss which need to be improved.

[0003] The existing common direct-current fault protection scheme has the defects of long breaking time, many additional auxiliary branches and high cost for using the mechanical direct-current circuit breaker; for the hybrid circuit breaker or the solid-state circuit breaker, in the background of the superconducting electric power system, too many power electronic switches will cause a large heat loss, which causes an additional burden on the overall refrigeration system, and the cost is high, which is not the first choice for protecting the superconducting electric power system of the airplane. For different protection schemes, there are the defects of fast rising of fault current and large breaking of fault current. SUMMARY

[0004] In order to solve the problems existing in the prior art, the application provides a power aircraft DC protection system based on a superconducting circuit breaker and a working method thereof.

[0005] The power aircraft DC protection system based on the superconducting circuit breaker comprises a fault current limiting module and a fault current breaking module connected in series, the fault current breaking module comprises a main DC branch, a buffer branch, a commutation branch and a charging branch, the main DC branch comprises a fast switch S1 and a circuit breaker CB connected in series, the buffer branch comprises a buffer resistor R1 and a buffer capacitor C1 connected in series, the commutation branch comprises a fast switch S2, a commutation inductor L and a commutation capacitor C connected in series, and the charging branch comprises a fast switch S3 and a charging resistor R C The buffer branch and the commutation branch are connected in parallel at both ends of the circuit breaker CB, and the charging branch is grounded at one end close to the charging resistor R C , and the other end close to the fast switch S3 is connected between the fast switch S2 and the commutation inductor L.

[0006] Preferably, the fault current limiting module comprises superconducting tapes R S and shunt resistors R P .

[0007] Preferably, the circuit breaker CB is a mechanical circuit breaker.

[0008] The application further provides a working method of the power aircraft DC protection system based on the superconducting circuit breaker, comprising the following steps.

[0009] S1: in normal operation, the superconducting tapes R S conduct current, the circuit breaker CB is in a closed state, the fast switches S1 and S3 are closed, and the fast switch S2 is disconnected, at this time, the commutation capacitor C is in a charging state; when the commutation capacitor C is in the charging state, the voltage across the commutation capacitor C is:

[0010] U C =E

[0011] wherein U C is the voltage across the commutation capacitor C when the commutation capacitor C is in the charging state, and E is an equivalent voltage of the system;

[0012] S2: when a DC fault occurs, the superconducting tapes R S in the fault current limiting module lose superconductivity rapidly, respond and start to limit the current rise, and part of the system current flows to the shunt resistors RP The transfer; the dynamic impedance of the superconducting tape R is calculated by the following formula: S

[0013]

[0014] Wherein, R SC is the maximum resistance of the superconducting tape R S after complete quench, τ R is the time constant, t is the running time of the system, t0 is the moment when the critical current flows through the superconducting tape R S ;

[0015] S3: When the current level meets the breaking operation of the circuit breaker CB, the circuit breaker CB is tripped, and after reaching the safe opening distance, the fast switch S2 is closed, and the fast switch S3 is disconnected, the discharge of the commutation capacitor C generates a high-frequency reverse current, which is superimposed with the current flowing to the circuit breaker CB to make a zero point; the discharge current of the commutation branch is calculated by the following formula:

[0016]

[0017]

[0018] Wherein, U C is the voltage across the commutation capacitor C when it is in the charging state, R is the resistance of the commutation branch, and ω is the frequency;

[0019] S4: After the circuit breaker CB successfully shuts down, all the residual current is transferred to the commutation branch, and after the short-circuit current is limited to a safe range, the fast switch S1 is disconnected to cut off the residual current and clear the short-circuit fault.

[0020] Preferably, in step S3, the fault current limiting module cooperates with the fault current breaking module to consume residual energy and accelerate the isolation time of the fault.

[0021] Preferably, the specific process of the fault current limiting module cooperating with the fault current breaking module to absorb residual energy is as follows:

[0022] The superconducting tape R S quench presents resistance, which not only can suppress the rising rate and size of the fault current, but also can consume residual energy all the time, and the expression of the consumed energy is represented as:

[0023]

[0024] Wherein, R SC is the maximum resistance of the superconducting tape R S after complete quench, i f (t) is the fault current flowing through the superconducting tape in the fault current limiting module in the t5-t7 time period. ​

[0025] Compared with the prior art, the present application has the following advantages:

[0026] The present application comprises a fault current limiting module combined with a fault current breaking module. The fault current limiting module not only suppresses the fault current to a low level before the circuit breaker operates, but also continuously consumes the energy accumulated in the system due to the resistive characteristics of the superconducting tape, which can quickly clear the fault, improve the efficiency of clearing the fault, save the additional auxiliary power charging module and energy dissipation module, greatly reduce the manufacturing cost of the protection part, and at the same time, reduce the energy loss caused by power electronic devices, reduce the refrigeration burden of the entire superconducting power system, and improve the efficiency of the system. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0028] Figure 1 Structure diagram of the aircraft power system based on the superconducting circuit breaker;

[0029] Figure 2 The present application is a DC protection system circuit topology diagram.

[0030] Figure 3 The process diagram of energy consumption of MOV for current limiters with different quench resistance values. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0032] As shown in Figure 1 The structure diagram of the aircraft power system based on the superconducting circuit breaker, the battery is connected with the high-voltage bus, the generator set G is connected with the high-voltage bus through the AC-DC converter, the motor M is connected with the high-voltage bus through the inverter, the superconducting cable line, the fault current limiting module (SFCL) and the fault current breaking module (DCCB).

[0033] As shown in Figure 2As shown in the direct current protection system circuit topology diagram, the direct current protection system circuit topology diagram comprises a fault current limiting module and a fault current breaking module in series, the fault current limiting module comprises superconducting tapes R S , shunt resistors R P in parallel, the fault current breaking module comprises a main direct current branch, a buffer branch, a commutation branch and a charging branch, the main direct current branch comprises fast switches S1 and mechanical circuit breakers CB in series, the buffer branch comprises buffer resistors R1 and buffer capacitors C1 in series, and is used for limiting overvoltage caused by breaking of the mechanical circuit breakers CB. The commutation branch comprises fast switches S2, commutation inductors L and commutation capacitors C in series, and the charging branch comprises fast switches S3 and charging resistors R C in series. The buffer branch and the commutation branch are connected in parallel at both ends of the circuit breakers CB, and the charging branch is grounded at one end close to the charging resistors R C and connected between the fast switches S2 and the commutation inductors L at one end close to the fast switches S3. The fast switches S1, S2 and S3 are connected with a control device and controlled by the control device.

[0034] The working method of the direct current protection system of the superconducting circuit breaker-based electric aircraft, characterized in that the working method comprises the following steps:

[0035] S1: in normal operation, the superconducting tapes R S are in a superconducting state and flow through, and the resistance is 0, the shunt resistors R P are short-circuited, the circuit breakers CB are in a closed state, the fast switches S1 and S3 are closed, and the fast switch S2 is disconnected. At the same time, the current flows to the load, the system voltage charges the commutation capacitors C through the fast switch S3 and the charging resistors R C , and the commutation capacitors C are in a charging state. The voltage across the commutation capacitors C in the charging state is:

[0036] U C =E

[0037] wherein U C is the voltage across the commutation capacitors C in the charging state, and E is an equivalent voltage of the system.

[0038] S2: when a direct current fault occurs, the superconducting tapes R S in the fault current limiting module lose superconductivity quickly, respond and start to limit the current rise, so as to suppress the short-circuit current to a low level, thereby avoiding that the large fault current imposes a heavy burden on the power grid and the breaking performance of the subsequent circuit breakers. At the same time, part of the system current is diverted to the shunt resistors R P , thereby reducing the current passing pressure of the superconducting tapes and the refrigeration pressure of the system, so as to significantly improve the stability of the entire system. The dynamic impedance of the superconducting tapes R S is calculated by the following formula:

[0039]

[0040] wherein R SC is the superconducting tape R S , τ R is the time constant, t is the running time of the system, and t0 is the moment when the critical current flows through the superconducting tape R S ;

[0041] S3: When the current level meets the breaking operation of the circuit breaker CB, the circuit breaker CB is opened, and after reaching a safe distance, the fast switch S2 is closed, and the fast switch S3 is opened, the discharge current of the commutation branch is generated, and the high-frequency reverse current with periodic changes in size and direction is generated, which is superimposed with the current flowing to the circuit breaker CB to make a zero point; the discharge current of the commutation branch is calculated by the following formula:

[0042]

[0043]

[0044] wherein U C is the voltage across the commutation capacitor C when it is in the charging state, R is the resistance of the commutation branch, and ω is the frequency;

[0045] When the circuit breaker CB is opened, the current rate of change is large, which can cause overvoltage. When the threshold value of the buffer branch is reached, the buffer branch acts to suppress the overvoltage, thereby improving the reliability of the system.

[0046] The fault current limiting module cooperates with the fault current breaking module to consume the remaining energy and accelerate the isolation time of the fault;

[0047] The specific process of the fault current limiting module cooperating with the fault current breaking module to absorb residual energy is as follows:

[0048] The remaining energy in the entire fault process is mainly provided by the inductive energy storage elements in the line and the system power source (corresponding to the generator G and the battery in Figure 1 If the fault current breaking module follows the design of the traditional circuit, a lightning arrester MOV is connected in parallel across the circuit breaker CB, and the energy provided by the inductive energy storage elements can be calculated by the following formula:

[0049]

[0050] wherein E L is the energy stored by the equivalent inductance of the system, L is the equivalent inductance value of the system, and I f (t5) is the fault current value flowing through the inductive energy storage elements when the lightning arrester MOV starts to act.

[0051] The energy provided by the system power source can be calculated by the following formula:

[0052]

[0053] wherein t5-t7 represents the time period from the operation to the end of breaking of the lightning arrester MOV, i a (t) is the current flowing through the lightning arrester MOV.

[0054] In summary, in the absence of the fault current breaking module, the energy that needs to be consumed by the additional lightning arrester MOV can be calculated by the following formula:

[0055]

[0056] It can be obviously seen from the above formula that the greater the fault current, the longer the breaking time, the greater the system inductance, the more the residual energy, and the greater the burden of the circuit breaker breaking.

[0057] In combination with the fault current breaking module, the superconducting tape R S loses superconductivity and presents resistance, which not only can suppress the rising rate and size of the fault current, but also can consume the residual energy all the time. The expression of the consumed energy is represented as:

[0058]

[0059] wherein R SC is the maximum resistance value of the superconducting tape R S after complete loss of superconductivity, i f1 (t) is the fault current flowing through the superconducting tape in the fault current limiting module in the time period of t5-t7.

[0060] The energy Q' that needs to be consumed at this time can be calculated by the following formula:

[0061]

[0062] wherein I f1 (t5) is the fault current value flowing through the inductive energy storage element when the lightning arrester MOV starts to act in combination with the fault current limiting module, i a1 (t) is the current flowing through the lightning arrester MOV in combination with the fault current limiting module, i f1 (t) is the fault current flowing through the superconducting tape in the fault current limiting module in the time period of t5-t7.

[0063] Compared with the previous absence of the fault current breaking module, due to the suppression effect of the superconducting tape R S , I f1 (t5), i a1 (t) and i f1 (t) are all less than the corresponding I f (t5), i a(t) is much smaller, so it can be inferred that this time has not required additional energy branch.

[0064] S4: After the circuit breaker CB is successfully closed, the remaining current is all transferred to the converter branch. Since the fault current limiting module has the function of consuming residual energy, the current decays rapidly, and after the short-circuit current is limited to a safe range, the fast switch S1 is disconnected, cutting off the remaining current and clearing the short-circuit fault. At this time, the energy dissipation branch required by the traditional circuit breaker can be avoided, significantly reducing the manufacturing cost.

[0065] Referring to Figure 1 , when the DC bus voltage is selected as 4kV and the transmission line rated current is 1kA, the existing technology of parallel energy dissipation branch at both ends of the circuit breaker and the DC protection system of the present application are simulated in Simulink for the entire breaking process. Figure 3 For the process diagram of MOV dissipating residual energy when selecting different fault current limiting modules with different superconducting resistance values, it can be clearly seen that the greater the resistance value of the fault current limiting module, the less the residual energy remaining in the system, and the lower the role of the MOV. This is true for all voltage level circuit breakers. For the field of new electric aircraft, the additional energy dissipation branch can be eliminated.

Claims

1. A DC protection system for electric aircraft based on a superconducting circuit breaker, characterized in that, It includes a fault current limiting module and a fault current interrupting module connected in series. The fault current interrupting module includes a main DC branch, a buffer branch, a commutation branch, and a charging branch. The main DC branch includes a fast switch S1 and a circuit breaker CB connected in series. The buffer branch includes a buffer resistor R1 and a buffer capacitor C1 connected in series. The commutation branch includes a fast switch S2, a commutation inductor L, and a commutation capacitor C connected in series. The charging branch includes a fast switch S3 and a charging resistor R... C The buffer branch and the converter branch are both connected in parallel across the circuit breaker CB, and the charging branch is close to the charging resistor R. C One end of the circuit is grounded, and the end closest to the fast switch S3 is connected between the fast switch S2 and the commutation inductor L. The operating method of a DC protection system for electric aircraft based on superconducting circuit breakers includes the following steps: S1: During normal operation, the superconducting tape R S With current flowing, circuit breaker CB is in the closed state, fast switches S1 and S3 are both closed, and fast switch S2 is open. At this time, the commutator capacitor C is in the charging state; the voltage across the commutator capacitor C when it is in the charging state is: in, V is the voltage across the commutation capacitor C when it is in a charging state, and E is the system equivalent voltage. S2: When a DC circuit fault occurs, the superconducting tape R of the fault current limiting module S It quickly loses quench, responds and begins to limit the current rise, while some system current flows to the shunt resistor R. P Transfer; calculate the superconducting tape R using the following formula. S Dynamic impedance: Among them, R SC For superconducting tape R S The maximum resistance after complete loss of overload. Let t be the time constant, t be the system running time, and t0 be the critical current flowing through the superconducting tape R. S The moment; S3: When the current level meets the requirements for the circuit breaker CB to trip, the circuit breaker CB trips. After reaching the safe opening distance, the fast switch S2 closes, and at the same time, the fast switch S3 opens. The converter capacitor C discharges, generating a high-frequency reverse current, which is superimposed on the current flowing to the circuit breaker CB to create a zero-crossing point. The discharge current of the converter branch is calculated using the following formula: Among them, U C ω represents the voltage across the commutation capacitor C when it is charging, R is the resistance of the commutation branch, and ω is the frequency. The fault current limiting module, in conjunction with the fault current interrupting module, consumes the remaining energy, accelerating the fault isolation time. The specific process by which the fault current limiting module and the fault current interrupting module absorb residual energy is as follows: Superconducting tape R S The quench exhibits resistive properties, which not only suppress the rise rate and magnitude of the fault current, but also continuously consume remaining energy. The expression for its energy consumption is as follows: Among them, R SC For superconducting tape R S The maximum resistance after complete quench, i f (t) represents the fault current flowing through the superconducting tape in the fault current limiting module during the time period t5-t7; S4: After the circuit breaker CB is successfully turned off, all the remaining current is transferred to the converter branch. After the short-circuit current is limited to a safe range, the fast switch S1 is opened to cut off the remaining current and clear the short-circuit fault.

2. The DC protection system for electric aircraft based on a superconducting circuit breaker according to claim 1, characterized in that, The fault current limiting module includes parallel superconducting tape R S Shunt resistor R P .

3. The DC protection system for electric aircraft based on a superconducting circuit breaker according to claim 1, characterized in that, Circuit breaker CB is a mechanical circuit breaker.

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