Short-circuit fault current limiting system and method for hydrogen fuel cell electric propulsion ship

Abstract

The invention discloses a short-circuit fault current limiting system and method for a hydrogen fuel cell electric propulsion ship, and the principle of the system is that the duty ratio of a bidirectional DC-DC power converter is controlled, the fault loop port characteristics are changed, and the current limiting control in a fault transient state is realized; in the steady state process after the fault occurs, the instantaneous current change rate is used as a criterion for mode switching to switch the control strategy to a constant current limiting control mode, and stable current output after the fault is achieved. According to the method, the cost of a direct-current circuit breaker is reduced, overload of power electronic devices is avoided, the problem that positioning is difficult after an electric propulsion ship breaks down is effectively solved, new fault features are constructed through switching of control strategies, and follow-up fault positioning is facilitated. The method has important engineering application prospects for developing a hydrogen fuel cell electric propulsion ship stable power supply technology.

Description

Technical Field

[0001] The present invention relates to the fields of ship and marine engineering and new energy technology, and in particular to a short-circuit fault current limiting system and method for a hydrogen fuel cell electric propulsion ship. Background Art

[0002] Marine transport plays an important role in the transportation industry, but the pollution caused by ships to the environment is becoming increasingly serious. New energy is of great significance to the sustainable development of human society and the harmonious coexistence of man and nature. The green transformation of ships is developing rapidly and changing with each passing day. Hydrogen fuel cells have become the best choice for ship electric propulsion systems with their high conversion efficiency, high energy density, zero carbon emissions, low vibration and noise, and long life. With the maturity of fuel application technology and the improvement of supporting facilities, its application scope will gradually expand. Hydrogen-powered ships are usually used in shipping scenarios such as lakes, inland rivers, and offshore, mainly including passenger ships, ferries, inland cargo ships, tugboats and other types. The development of large hydrogen-powered ships such as offshore engineering ships, offshore roll-on / roll-off ships, and super yachts is the current international trend. As the sailing distance and time of hydrogen fuel cell ships gradually increase, under the influence of many factors such as complex working conditions, wave impact and salt spray environment, the DC electric propulsion system will be accidentally interfered with and physically damaged, and short-circuit faults are very likely to occur. Due to the close layout of electrical components in the ship's electric propulsion system, overheating of electrical equipment caused by short-circuit faults may lead to destructive consequences, and even cause the paralysis of the entire ship's power system. Therefore, it is extremely important to study and realize accurate detection and rapid disconnection of its faults.

[0003] The "Guidelines for Inspection of Ship DC Integrated Power Systems 2023" clearly stipulates that the ship DC power distribution system can use air frame or molded case DC circuit breakers, solid-state switches, DC fuses and other protective electrical appliances, combined with protection strategy design, to achieve rapid disconnection and isolation of system short-circuit faults. However, due to the small capacity, short line and "low inertia" characteristics of the ship DC electric propulsion system, the fault current rises rapidly after the fault occurs and there is no natural zero crossing. The larger the fault current, the greater the requirements and burden on the circuit breaker. Therefore, after a short-circuit fault, the sudden change of current can be limited by adding a current limiting device, but this method increases the size and cost of the equipment. Based on the presence of a large number of power electronic devices in the ship DC electric propulsion system, it has good controllability. The impedance characteristics are mapped to the control of the corresponding interface converter by using its characteristics and the mathematical mapping method, so that it can suppress the transient output current when a fault occurs. At the same time, by controlling the steady-state current of the fault, the subsequent fault characteristics disappear due to the disconnection of the internal power switch of the converter, which is difficult to locate.

[0004] Therefore, in view of the small capacity, short lines and "low inertia" characteristics of hydrogen fuel cell electric propulsion ships, the instantaneous output current rises rapidly after a short-circuit fault occurs. An effective short-circuit fault current limiting method is adopted to reduce the instantaneous output current amplitude, which is of great significance to optimizing the stable operation of the entire ship's DC electric propulsion system. Summary of the invention

[0005] In view of this, the purpose of the present invention is to provide a short-circuit fault current limiting system and method for a hydrogen fuel cell electric propulsion ship, so as to limit the transient output current and steady-state fault current of the ship's DC electric propulsion system during a short-circuit fault, reduce the size of the hydrogen fuel cell electric propulsion ship and the requirements for circuit breakers, broaden the protection action time requirements, facilitate subsequent fault location, and improve its reliability and stability during operation.

[0006] To achieve the above-mentioned purpose, the present invention adopts the following technical scheme: a short-circuit fault limiting system for a hydrogen fuel cell electric propulsion ship, wherein the hydrogen fuel cell power is connected to a ship power supply unit and a ship load that cooperates with the ship power supply via a DC bus: the ship power supply unit includes a hydrogen fuel cell unit, a battery unit and a supercapacitor unit, wherein the battery unit and the supercapacitor unit together constitute an energy storage system.

[0007] In a preferred embodiment, the hydrogen fuel cell electric propulsion ship comprises a proton exchange membrane fuel cell power generation unit (1), a battery unit (2), a super capacitor unit (3), a ship DC electric propulsion unit (4), a load unit (5), and a resistor unit (6); the proton exchange membrane fuel cell power generation unit (1) is connected to a DC bus through the output side of an isolated boost full-bridge converter; the battery unit (2) and the super capacitor unit (3) are connected to the DC bus through the output side of a bidirectional DC-DC power converter, wherein the bidirectional DC-DC power converter uses a voltage-current dual-loop control; the input side of the ship DC electric propulsion unit (4) is connected to a DC bus (7); the input side of the load unit (5) is connected to the DC bus (7); and the resistor load unit (6) is connected to the DC bus (7).

[0008] In a preferred embodiment, the system is composed of unit 1, unit 2...unit n; the unit n is a proton exchange membrane fuel cell power generation unit, a battery unit, a supercapacitor unit, a ship DC electric propulsion unit or a load unit; the units n are interconnected through a bus to form a radial unipolar DC electric propulsion system; the unit n is connected to the radial DC bus through two circuit breakers.

[0009] The present invention also provides a short-circuit fault current limiting method for a hydrogen fuel cell electric propulsion ship, using the above-mentioned short-circuit fault current limiting system for a hydrogen fuel cell electric propulsion ship, comprising the following steps:

[0010] Step S1: Sampling various electrical quantities of the ship, including the instantaneous output current of the bidirectional DC-DC power converter; the inductor current i L ; Power supply unit input voltage and u i ; Bus side output voltage u o ; Generate a PWM wave, a control signal of the switch tube, based on the output voltage on the bus side;

[0011] Step S2: Add an adaptive virtual impedance link in the control of the bidirectional DC-DC power converter, and its virtual impedance coefficient k v Determined by the current fault state, the more serious the fault, the larger the virtual impedance coefficient;

[0012] Step S3: Inductor current reference i ref With the inductor current feedback i L The inductor current deviation value Δi is obtained by subtracting, and its value is sent to the current controller G i (s), pulse width modulation is performed as a modulation wave, and the high-frequency chopping signal generated controls the on-off state of the power switch Q1 in the bidirectional DC-DC power converter, and the on-off state of the power switch Q2 is a PWM wave complementary to the Q1 drive signal;

[0013] Step S4: By sampling the instantaneous output current i of the bidirectional DC-DC power converter o , use the first-order differential to find the instantaneous output current change rate di o / dt, determine whether its value is greater than the threshold current change rate di o / dt th ;

[0014] Step S5: When the instantaneous output current change rate di o / dt is greater than the threshold current change rate di o / dt th When , the control mode is switched to the constant current limiting control mode. At this time, the current controller outputs a modulation wave for pulse width modulation. The generated high-frequency chopping signal controls the on-off state of the power switch Q1 in the bidirectional DC-DC power converter. The on-off state of the power switch Q2 is a PWM wave with a phase difference of 180° with the Q1 drive signal. The bidirectional DC-DC power converter drive signal is switched to phase shift control.

[0015] In a preferred embodiment, in step 2, the virtual current limiting impedance R V With the output current i o Multiplication produces voltage negative feedback ΔU V, the voltage generated by negative feedback and ΔU V with U ref The voltage deviation value ΔU obtained by the difference is summed to obtain the actual voltage loop reference value, and its value is sent to the capacitor voltage PI controller G composed of proportional and integral links. v (s), G v The output of (s) is the inductor current reference i of the bidirectional DC-DC power converter ref .

[0016] In a preferred embodiment, the virtual impedance coefficient k in step S2 is v Determined by the current fault state, that is, the virtual impedance number k v Determined by formula (1);

[0017]

[0018] In a preferred embodiment, in step S4, the threshold current change rate is used as a criterion for determining a switching control strategy of the bidirectional DC-DC power converter.

[0019] In a preferred embodiment, the threshold current change rate di in step S5 is o / dt th , its instantaneous output current i o The value is obtained from the equivalent circuit at the moment of fault. At this time, the bidirectional DC-DC power converter is equivalent to a series RLC circuit of the output capacitor C and the line impedance Z. The instantaneous output current i o Determined by formula (2);

[0020]

[0021] In a preferred embodiment, in the phase shift control strategy in step S5, the duty cycle D of the driving signal of the power switch Q1 is less than 50%.

[0022] In a preferred embodiment, the phase shift control strategy in step S5 is to connect an RC absorption circuit in parallel on both sides of the power switch, wherein the capacitance and resistance values ​​are determined by equations (3) and (4);

[0023]

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The investment cost is low. Compared with adding current limiting equipment in the ship DC electric propulsion system, the present invention utilizes the existing power electronic devices in the system, maps the impedance characteristics to the corresponding interface converter control through the mathematical mapping method, and realizes the limitation of the fault transient output current. Compared with other current limiting schemes, there is no need to specially add current dissipation branches, which reduces the complexity of the topological structure, reduces the floor space in the small-volume ship DC power system, and reduces the investment cost.

[0026] The invention can actively limit the current and realize DC side fault ride-through. o / dth is used as the control strategy switching criterion. The control strategy is actively switched in the early stage of fault development to limit the steady-state output current when a fault occurs. Compared with the passive fault current limiting strategy, it takes effect faster and can effectively suppress the size of the fault steady-state output current when facing a high-resistance fault. During the process, there is no need to lock the converter or cut off the source side. After the fault is cleared, the control strategy is switched to the normal working mode to quickly restore the DC bus voltage and achieve fault ride-through.

[0027] It is convenient for subsequent fault location and accurate fault removal. The present invention does not need to lock the converter or cut off the source side during the fault. Compared with other fault current limiting methods, the present invention still outputs a stable and controllable fault current when a fault occurs. Based on this fault current, it is beneficial for subsequent fault location and fault removal.

[0028] The present invention is designed for hydrogen fuel cell electric propulsion ships with small capacity, short lines and "low inertia" characteristics. Based on the idea of ​​control and protection coordination, current limiting control is performed when a short circuit fault occurs in the ship's DC electric propulsion system. It can effectively reduce the system volume, reduce the system's requirements for circuit breakers and the hardware cost required for the protection circuit, broaden the protection time of the protection method, facilitate subsequent fault location and accurate isolation, and at the same time improve the stability and reliability of the ship's electric propulsion system with hydrogen fuel cells as the main propulsion energy source, providing a technical basis for hydrogen fuel cells to replace diesel engines. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a structural diagram of a hydrogen fuel cell electric propulsion ship according to a preferred embodiment of the present invention;

[0030] Figure 2 This is a control strategy diagram of a short-circuit fault current limiting method for a hydrogen fuel cell electric propulsion ship according to a preferred embodiment of the present invention;

[0031] Figure 3 This is a control principle diagram of a short-circuit fault transient current limiting method for a hydrogen fuel cell electric propulsion ship according to a preferred embodiment of the present invention;

[0032] Figure 4is a circuit diagram of a bidirectional DC-DC power converter according to a preferred embodiment of the present invention;

[0033] Figure 5 It is a short-circuit fault equivalent model diagram of a bidirectional DC-DC power converter in a preferred embodiment of the present invention;

[0034] Figure 6 is a fault current simulation waveform diagram of a preferred embodiment of the present invention;

[0035] Figure 7 This is a fault current simulation waveform diagram after adding adaptive virtual impedance in a preferred embodiment of the present invention;

[0036] Figure 8 It is a fault current simulation waveform diagram after switching the current limiting strategy of the preferred embodiment of the present invention. DETAILED DESCRIPTION

[0037] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0038] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0039] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application; as used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or their combinations.

[0040] like Figure 1-8As shown, the hydrogen fuel cell ship electric propulsion system adopts a radial unipolar DC power supply structure, including a proton exchange membrane fuel cell power generation unit 1, a battery unit 2, a super capacitor 3, a ship DC power propulsion unit 4, a DC / AC load unit 5 and a resistive load 6. The proton exchange membrane fuel cell power generation unit 1 is composed of a proton exchange membrane fuel cell 11 and a single-phase full-bridge boost power converter 12 in cascade, and the output side of the single-phase full-bridge boost power converter 12 is connected to the DC bus 7; the battery unit 2 is composed of a battery 21 and a bidirectional DC-DC power converter 22 in cascade, and the output side 22 of the bidirectional DC-DC power converter is connected to the bus 7; the super capacitor unit 3 is composed of a super capacitor 31 and a bidirectional DC-DC power converter 32 in cascade, and the output side 32 of the bidirectional DC-DC power converter is connected to the bus 7; the ship DC propulsion power unit 4 includes a bidirectional inverter 43, a permanent magnet synchronous motor 42 and a propeller 41, a bidirectional inverter 43 is cascaded with the permanent magnet synchronous motor 42, the mechanical shaft of the permanent magnet synchronous motor 42 is directly connected to the shaft of the propeller 41, and the input side of the bidirectional inverter 43 is connected to the DC bus 7; the constant power load unit 5 is composed of two forms: the first form is composed of a DC power converter 52 and a DC load 51 cascaded, and the second form is composed of an inverter 54 and an AC load 53 cascaded, and both forms of constant power load units 5 are connected to the DC bus 7 through the input side of the power converter; the resistive load unit 6 is directly connected to the DC bus 7 as a resistive load.

[0041] A short-circuit fault current limiting method for a hydrogen fuel cell electric propulsion ship, the control block diagram of which is as follows Figure 2 As shown, the control of the bidirectional DC-DC power converter in the ship DC microgrid is realized, characterized in that the hydrogen fuel cell electric propulsion ship includes a ship power supply and a ship load that cooperates with the ship power supply via a DC bus: the ship power supply unit includes a hydrogen fuel cell unit, a battery unit and a super capacitor unit, wherein the battery unit and the super capacitor unit together constitute an energy storage system, and when the fault current limiting method is not added, a short circuit fault current occurs in the system as shown in FIG. Figure 6 As shown; follow the steps below to implement:

[0042] Step S1: Sampling various electrical quantities of the new energy ship, including the instantaneous output current of the bidirectional DC-DC power converter; the inductor current i L ; Power supply unit input voltage and u i ; Bus side output voltage u o The control signal PWM wave of the switch tube is generated based on the output voltage on the bus side.

[0043] Step S2: Add an adaptive virtual impedance link to the control of the bidirectional DC-DC power converter. Figure 3 As shown, its virtual impedance coefficient kv Determined by the current fault state, the more serious the fault, the larger the virtual impedance coefficient. Virtual current limiting impedance R V With the output current i o Multiplication produces voltage negative feedback ΔU V , the voltage generated by negative feedback and ΔU V with U ref The voltage deviation value ΔU obtained by the difference is summed to obtain the actual voltage loop reference value, and its value is sent to the capacitor voltage PI controller G composed of proportional and integral links. v (s), G v The output of (s) is the bidirectional DC-DC power converter inductor current reference iref. In order to compare the fault current optimization effect before and after adding the adaptive virtual impedance link, the system short-circuit fault current is as follows Figure 7 As shown, after adopting the method of the present invention, the peak value of the fault current drops from 1400A to 950A, and the fault current drops by about 32%.

[0044] Step S3: Inductor current reference i ref With the inductor current feedback i L The inductor current deviation value Δi is obtained by subtracting, and its value is sent to the current controller G i (s) is used as a modulation wave for pulse width modulation, and the generated high-frequency chopping signal controls Figure 4 The on-off state of the power switch Q1 in the bidirectional DC-DC power converter and the on-off state of the power switch Q2 are PWM waves complementary to the Q1 drive signal, thus achieving the current limiting effect under the fault transient state.

[0045] Step S4: By sampling the instantaneous output current i of the bidirectional DC-DC power converter o , use the first-order differential to find the instantaneous output current change rate di o / dt, determine whether its value is greater than the threshold current change rate di o / dt th The threshold current change rate is a criterion for determining the switching control strategy of the bidirectional DC-DC power converter.

[0046] Step S5: When the instantaneous output current change rate di o / dt is greater than the threshold current change rate di o / dt thWhen the control mode is switched to the constant current limiting control mode, the current controller outputs a modulation wave for pulse width modulation, and the generated high-frequency chopping signal controls the on-off state of the power switch Q1 in the bidirectional DC-DC power converter. The on-off state of the power switch Q2 is a PWM wave with a phase difference of 180° with the Q1 drive signal, and the bidirectional DC-DC power converter drive signal is switched to phase shift control. In order to compare the fault current changes before and after the current limiting control mode, the system fault current is as follows Figure 8 shown.

[0047] The virtual impedance coefficient k in step S2 v Determined by the current fault state, that is, the virtual impedance number k v Determined by formula (1).

[0048]

[0049] In step S5, the threshold current change rate di o / dt th , its instantaneous output current i o Value by Figure 5 The equivalent circuit at the moment of fault is obtained. At this time, the bidirectional DC-DC power converter is equivalent to a series RLC circuit of the output capacitor C and the line impedance Z. The instantaneous output current i is obtained. o Determined by formula (2).

[0050]

[0051] From formula 1, it can be obtained that the instantaneous output current of a short-circuit fault of a hydrogen fuel cell electric propulsion ship is related to the equivalent inductance of the fault discharge circuit. Therefore, the virtual impedance control strategy is used to increase the inductance value in the fault circuit to:

[0052] L′=L+L v (3)

[0053] The phase shift control strategy in step S5 is to prevent the inductor in the bidirectional DC-DC converter from being charged to a saturation state, so the duty cycle D of the driving signal of the power switch Q1 is less than 50%.

[0054] In the phase shift control strategy in step S5, in order to avoid the reverse electromotive force generated by the power switches Q1 and Q2 not being turned on and damaging the internal devices, an RC absorption circuit is connected in parallel on both sides of the power switch, wherein the capacitance and resistance values ​​are determined by equations (4) and (5).

[0055]

[0056] The hydrogen fuel cell electric propulsion ship can be composed of unit 1, unit 2, unit 3...unit n; the units can be proton exchange membrane fuel cell power generation units, battery units, supercapacitor units, ship DC electric propulsion units, load units; the units are interconnected through a bus to form a radial unipolar DC electric propulsion system; each unit is connected to the radial DC bus through two circuit breakers.

[0057] The above are preferred embodiments of the present invention. Any changes made according to the technical solution of the present invention, as long as the resulting functions do not exceed the scope of the technical solution of the present invention, belong to the protection scope of the present invention.

[0058] In order to verify the effectiveness of the short-circuit fault current limiting method for hydrogen fuel cell electric propulsion ships proposed in this invention, a simulation experiment was carried out. The simulation model was built based on MATLAB / Simulink. Figures 6 to 8 The fault current changes before and after the current limiting method is added in the present invention are compared. Figure 6 and Figure 7 It can be seen from the comparison that after using adaptive virtual impedance, the fault current peak value decreased by about 32%; Figure 8 The difference in fault current between the present invention and the method without current limiting is compared. After using the current limiting method proposed in the present invention, the amplitude and rising speed of the fault current are effectively limited, so that the fault current is output in a steady state, the system requirements and cost requirements for circuit breakers are reduced, the protection time of the protection method is widened, and subsequent fault location and accurate isolation are facilitated.

Claims

1. A short-circuit fault current limiting system for a hydrogen fuel cell electric propulsion ship, characterized in that: The hydrogen fuel cell power is connected to the ship power supply unit and the ship load that cooperates with the ship power supply via a DC bus: the ship power supply unit includes a hydrogen fuel cell unit, a battery unit and a super capacitor unit, wherein the battery unit and the super capacitor unit together constitute an energy storage system.

2. A short-circuit fault current limiting system for a hydrogen fuel cell electric propulsion ship according to claim 1, characterized in that: The hydrogen fuel cell electric propulsion ship comprises a proton exchange membrane fuel cell power generation unit (1), a battery unit (2), a super capacitor unit (3), a ship DC electric propulsion unit (4), a load unit (5), and a resistor unit (6); the proton exchange membrane fuel cell power generation unit (1) is connected to a DC bus through the output side of an isolated boost full-bridge converter; the battery unit (2) and the super capacitor unit (3) are connected to the DC bus through the output side of a bidirectional DC-DC power converter, wherein the bidirectional DC-DC power converter uses a voltage-current dual-loop control; the input side of the ship DC electric propulsion unit (4) is connected to a DC bus (7); the input side of the load unit (5) is connected to the DC bus (7); and the resistor load unit (6) is connected to the DC bus (7).

3. A short-circuit fault current limiting system for a hydrogen fuel cell electric propulsion ship according to claim 1 or 2, characterized in that: The system is composed of unit 1, unit 2...unit n; the unit n is a proton exchange membrane fuel cell power generation unit, a battery unit, a supercapacitor unit, a ship DC electric propulsion unit or a load unit; the units n are interconnected through a bus to form a radial unipolar DC electric propulsion system; the unit n is connected to the radial DC bus through two circuit breakers.

4. A short-circuit fault current limiting method for a hydrogen fuel cell electric propulsion ship, characterized in that: The short-circuit fault current limiting system for a hydrogen fuel cell electric propulsion ship according to claim 3 comprises the following steps: Step S1: Sampling various electrical quantities of the ship, including the instantaneous output current of the bidirectional DC-DC power converter; the inductor current i L ; Power supply unit input voltage and u i ; Bus side output voltage u o ; Generate a PWM wave, a control signal of the switch tube, based on the output voltage on the bus side; Step S2: Add an adaptive virtual impedance link in the control of the bidirectional DC-DC power converter, and its virtual impedance coefficient k v Determined by the current fault state, the more serious the fault, the larger the virtual impedance coefficient; Step S3: Inductor current reference i ref With the inductor current feedback i L The inductor current deviation value Δi is obtained by subtracting, and its value is sent to the current controller G i (s), pulse width modulation is performed as a modulation wave, and the high-frequency chopping signal generated controls the on-off state of the power switch Q1 in the bidirectional DC-DC power converter, and the on-off state of the power switch Q2 is a PWM wave complementary to the Q1 drive signal; Step S4: By sampling the instantaneous output current i of the bidirectional DC-DC power converter o , use the first-order differential to find the instantaneous output current change rate di o / dt, determine whether its value is greater than the threshold current change rate di o / dt th ; Step S5: When the instantaneous output current change rate di o / dt is greater than the threshold current change rate di o / dt th When , the control mode is switched to the constant current limiting control mode. At this time, the current controller outputs a modulation wave for pulse width modulation. The generated high-frequency chopping signal controls the on-off state of the power switch Q1 in the bidirectional DC-DC power converter. The on-off state of the power switch Q2 is a PWM wave with a phase difference of 180° with the Q1 drive signal. The bidirectional DC-DC power converter drive signal is switched to phase shift control.

5. A short-circuit fault current limiting method for a hydrogen fuel cell electric propulsion ship according to claim 4, characterized in that: In step 2, the virtual current limiting impedance R V With the output current i o Multiplication produces voltage negative feedback ΔU V , the voltage generated by negative feedback and ΔU V with U ref The voltage deviation value ΔU obtained by the difference is summed to obtain the actual voltage loop reference value, and its value is sent to the capacitor voltage PI controller G composed of proportional and integral links. v (s), G v The output of (s) is the inductor current reference i of the bidirectional DC-DC power converter ref .

6. A short-circuit fault current limiting method for a hydrogen fuel cell electric propulsion ship according to claim 5, characterized in that: The virtual impedance coefficient k in step S2 v Determined by the current fault state, that is, the virtual impedance number k v Determined by formula (1); 7. A short-circuit fault current limiting method for a hydrogen fuel cell electric propulsion ship according to claim 4, characterized in that: In step S4, the threshold current change rate is used as a criterion for determining a switching control strategy of the bidirectional DC-DC power converter.

8. A short-circuit fault current limiting method for a hydrogen fuel cell electric propulsion ship according to claim 4, characterized in that: In step S5, the threshold current change rate di o / dt th , its instantaneous output current i o The value is obtained from the equivalent circuit at the moment of fault. At this time, the bidirectional DC-DC power converter is equivalent to a series RLC circuit of the output capacitor C and the line impedance Z. The instantaneous output current i o Determined by formula (2); 9. A short-circuit fault current limiting method for a hydrogen fuel cell electric propulsion ship according to claim 4, characterized in that: In the phase shift control strategy in step S5, the duty cycle D of the driving signal of the power switch Q1 is less than 50%.

10. A short-circuit fault current limiting method for a hydrogen fuel cell electric propulsion ship according to claim 4, characterized in that: In the phase shift control strategy in step S5, an RC absorption circuit is connected in parallel on both sides of the power switch, wherein the capacitance and resistance values ​​are determined by equations (3) and (4);

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