Method and system for detecting high-resistance short-circuit fault of hydrogen fuel cell ship direct-current power system

Abstract

The invention discloses a high-resistance short-circuit fault detection method and system for a hydrogen fuel cell ship direct-current power system, the hydrogen fuel cell ship direct-current power system is jointly connected into a radiation direct-current bus through a source side unit and a load unit, and the source side unit comprises a hydrogen fuel cell unit, a storage battery unit and a super capacitor unit. The storage battery unit and the super capacitor unit jointly form a hybrid energy storage unit. According to the invention, the current change rate is calculated by using the instantaneous change of the capacitance current at the direct-current side of each unit of the direct-current power system of the hydrogen fuel cell ship, and the calculated current change rate is compared with a set current change rate threshold value to judge whether a fault occurs in the ship, so that the high-resistance fault detection is completed. The method has an important engineering application prospect for developing a hydrogen fuel cell ship direct current power system relay protection method.

Description

Technical Field

[0001] The present invention relates to the fields of shipbuilding and marine engineering and new energy technology, and in particular to a method and system for detecting high-resistance short-circuit faults in a direct current power system of a hydrogen fuel cell ship. Background Art

[0002] Maritime transport plays a vital role in the transportation industry, yet the environmental pollution caused by ships is becoming increasingly serious. New energy sources are of great significance to the sustainable development of human society and the harmonious coexistence of man and nature. The green transformation of shipping is developing rapidly and rapidly. Hydrogen fuel cells, with their high conversion efficiency, high energy density, zero carbon emissions, low vibration and noise, and long life, are the optimal choice for ship electric propulsion systems. As fuel application technology matures and supporting infrastructure improves, their application will gradually expand. Hydrogen-powered ships are commonly used in lake, inland river, and offshore shipping scenarios, primarily including passenger ships, ferries, inland cargo ships, and tugboats. The development of large hydrogen-powered vessels, such as offshore engineering vessels, roll-on / roll-off vessels, and superyachts, is a current international trend. As the DC power systems of hydrogen fuel cell ships increase in range and duration, they are susceptible to unexpected interference and physical damage from factors such as wave impact and salt spray, making them highly susceptible to short-circuit failures. The drastic changes in electrical quantities caused by complex ship operation conditions are very similar to the characteristics of electrical quantity changes caused by high-resistance short-circuit faults. Therefore, it is very difficult to accurately detect high-resistance short-circuit faults in the DC power system of hydrogen fuel cell ships.

[0003] The 2023 "Guidelines for Inspection of Integrated DC Power Systems on Ships" clearly stipulates that when a short circuit occurs at the output of any power supply device (including the converter), separate short-circuit protection should be installed to limit the impact of the short circuit on the system or equipment. How to quickly and accurately detect high-resistance short-circuit faults in the DC power system of hydrogen fuel cell ships has become a key and urgent fundamental issue for the long-term stable operation of hydrogen fuel cell ship DC power systems.

[0004] Therefore, for the hydrogen fuel cell ship DC power system with complex operating conditions, in order to accurately detect the occurrence of high-resistance short-circuit faults and avoid the problem of false operation of protection, a high-resistance short-circuit fault detection method for hydrogen fuel cell ship DC power system is adopted. By collecting and analyzing the capacitor current on the DC output side of the hydrogen fuel cell ship DC power system, the maximum change of the capacitor current under normal operation and the minimum current at the time of fault are used to determine the fault threshold, which is used as the fault criterion to detect whether the fault occurs. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a method and system for detecting high-resistance short-circuit faults in the DC power system of a hydrogen fuel cell ship. The method can accurately detect high-resistance short-circuit faults when the DC power system of a hydrogen fuel cell ship operates under complex working conditions, thereby avoiding the problem of misjudgment of the protection method due to changes in electrical quantities caused by frequent power changes, and improving the reliability of the protection method. The detection method can not only accurately detect high-resistance short-circuit faults, but also detect low-resistance short-circuit faults, thereby improving the reliability and stability of the operation of the DC power system of a hydrogen fuel cell ship.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a method for detecting high-resistance short-circuit faults in a DC power system of a hydrogen fuel cell ship, comprising the following steps:

[0007] Step S1: sampling the electrical quantities of the hydrogen fuel cell ship DC power system, including the output current i of the bus side capacitor of each unit converter C1 、i C2 、…、i Cn , the inductor current of each unit i L1 、i L2 、…、i Ln ;

[0008] Step S2: Output current i to the bus side capacitor of each unit converter C1 、i C2 、…、i Cn Calculate and obtain the output current change rate of each unit bus side capacitor di C1 / dt、di C2 / dt,…,di Cn / dt;

[0009] Step S3: By analyzing the working conditions of the DC power system of the hydrogen fuel cell ship, the bus side capacitance current change rate under normal operation and the fault current change rate during high resistance short circuit fault are calculated, and the middle value of the two is taken to obtain the capacitance current change rate protection threshold (di C / dt) th ;

[0010] Step S4: Each unit compares the capacitance current change rate calculated by itself with the protection threshold value. If the calculated value is greater than the protection threshold value, it is determined that a fault has occurred in the system.

[0011] In a preferred embodiment, in step S2, the capacitance current change rate di C / dt is determined by formula (1), where the sampling time t sample Take one tenth of the control step size:

[0012]

[0013] In formula (1), i c is the capacitor current, t0 is the time when the fault occurs, t1 is the sampling time interval after the fault occurs, t sample In a preferred embodiment, in step S3, the selection of the capacitance current change rate threshold should satisfy formula (2):

[0014]

[0015] In formula (2), k α is the fault current change rate starting coefficient, (di C / dt) max is the maximum normal operating capacitance current change rate, (di C / dt) th Set the threshold value for the capacitance current change rate, (di C / dt) max is the minimum fault capacitor current change rate. In a preferred embodiment, the bus side capacitor current change rate under normal operating conditions is obtained by formula (3):

[0016]

[0017] In formula (3), I L is the inductor current, ΔI L is the inductor current ripple, and Δt is the sampling time.

[0018] In a preferred embodiment, the rate of change of the capacitor current under a high-resistance short-circuit fault is obtained by formula (4):

[0019]

[0020] In formula (4), i f is the fault current, U c is the capacitor voltage, L is the inductance in the fault circuit, and R is the resistance in the fault circuit.

[0021] In a preferred embodiment, the fault current change rate starting coefficient k α To leave a certain margin with the normal operating state to avoid false protection operation, select 1.1~1.2.

[0022] In a preferred embodiment, the fault current under high-resistance short-circuit fault is obtained by formula (5):

[0023]

[0024] In formula 5, σ is the attenuation coefficient, β is the phase relationship between the voltage and current in the circuit, ω0 is the natural angular frequency of the circuit, i bus Output current for the source side unit.

[0025] In a preferred embodiment, in step S4, each unit protection module operates independently, and when it is detected that the rate of change of its own capacitance current exceeds a threshold, it is determined that a fault has occurred in the system. The fault judgment criterion should satisfy formula (6):

[0026]

[0027] The present invention also provides a high-resistance short-circuit fault detection system for a hydrogen fuel cell ship DC power system, and operates a high-resistance short-circuit fault detection method for a hydrogen fuel cell ship DC power system; the hydrogen fuel cell ship DC power system is connected to a radial DC bus by a source side unit and a load unit, the source side unit includes a hydrogen fuel cell unit, a battery unit and a supercapacitor unit, and the battery unit and the supercapacitor unit together constitute a hybrid energy storage unit; the hybrid energy storage unit is connected to the bus through a bidirectional DC-DC power converter and uses a voltage-current dual-loop control, and the hydrogen fuel cell unit is isolated and stepped A high-voltage full-bridge converter is connected to the bus and uses current loop constant power control; the load unit mainly includes an electric propulsion load and a DC load, and the electric propulsion load is connected to the bus via a DC / AC power converter; the DC load is connected to the bus via a DC / DC power converter; the hydrogen fuel cell unit, battery unit, supercapacitor unit, electric propulsion load and DC load are all connected to the bus through a circuit breaker; a high-resistance short-circuit fault occurs in the line connecting the source side unit or the load unit to the bus; high-resistance short-circuit fault detection is performed by collecting the DC side capacitor current of the source side unit and the load unit.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) The cost of relay protection is reduced. Compared with adding protection equipment to the ship's DC electric propulsion system, the present invention does not require additional devices and controllers. The data sampled by the current sensors on each source side unit and the load side are calculated as the fault detection criterion, and the data is processed by the corresponding converter controller. Compared with other fault detection methods, there is no need to add additional sensors and controllers, and no communication is required, which greatly reduces the cost of relay protection, realizes control and protection coordination, and improves the reliability of relay protection.

[0030] (2) It is not affected by the drastic fluctuations in electrical quantities caused by the complex working conditions of the ship, and prevents the circuit breaker from malfunctioning. The present invention distinguishes between the changes in electrical quantities caused by working condition changes and the changes in electrical quantities caused by faults, and finds that when the output current is the same, the capacitive current accounts for a higher proportion of the output current when a short-circuit fault occurs. Therefore, the present invention uses the capacitive current change rate (diC / dt)th as the fault judgment criterion. By adjusting the threshold, the selected threshold can exceed the maximum normal operating range, avoiding the protection malfunction caused by the drastic fluctuations in electrical quantities caused by working condition changes, and improving the reliability of the protection.

[0031] (3) The high-resistance short-circuit fault detection method of the present invention can also detect low-resistance short-circuit faults by relying on the natural response current of the capacitor caused by the fault. The smaller the fault resistance, the greater the rate of change of the capacitor current. Therefore, high-resistance and low-resistance short-circuit faults can be detected at the same time, reducing the complexity of the fault protection method.

[0032] (4) It has high reliability and can avoid noise interference caused by sampling. After sampling the capacitor current, the low-pass filter added in the program is used to filter out the noise, and then its rate of change is calculated. The calculated value eliminates the influence of high-frequency noise, making fault detection more reliable and accurate.

[0033] (5) The present invention detects faults by detecting changes in capacitor current in real time, which can greatly improve the fault detection speed. The fault detection time is only tens of microseconds, effectively suppressing the amplitude of the fault current.

[0034] (6) The present invention is designed for a hydrogen fuel cell ship DC power system with small capacity, short lines and "low inertia" characteristics, which avoids the impact on protection judgment when the ship is operating under complex working conditions, improves the stability and reliability of the ship's electric propulsion system with hydrogen fuel cells as the main propulsion energy, and provides a technical basis for hydrogen fuel cells to replace diesel engines as the main power source. It is of great significance to promote my country's early realization of the "dual carbon" goal. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A structural diagram of a hydrogen fuel cell ship DC power system according to a preferred embodiment of the present invention;

[0036] Figure 2 This is a working principle diagram of a method for detecting high-resistance short-circuit faults in a DC power system of a hydrogen fuel cell ship according to a preferred embodiment of the present invention;

[0037] Figure 3 This is an equivalent circuit diagram of each unit when a high-resistance short-circuit fault occurs in the hydrogen fuel cell ship DC power system of the preferred embodiment of the present invention;

[0038] Figure 4The following are simulation waveforms of the capacitor current change rate when a high-resistance short-circuit fault occurs under no-load conditions and when switching from no-load to full-load conditions in a preferred embodiment of the present invention; wherein (a) is the capacitor current change rate when a 5Ω fault occurs, and (b) is the capacitor current change rate when load switching occurs.

[0039] Figure 5 This is a simulation waveform of the capacitor current change rate diagram when a high-resistance short-circuit fault occurs under half-load conditions and when switching from half-load to full-load under a preferred embodiment of the present invention; where (a) is the capacitor current change rate when a 5Ω fault occurs, and (b) is the capacitor current change rate when the load is switched. DETAILED DESCRIPTION

[0040] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0041] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present application belongs.

[0042] 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, and 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.

[0043] like Figure 1 As shown, the hydrogen fuel cell ship DC power system is connected to the radial DC bus by a source side unit and a load unit. The source side unit includes a hydrogen fuel cell unit, a battery unit and a super capacitor unit. The battery unit and the super capacitor unit together constitute a hybrid energy storage unit; the hybrid energy storage unit is connected to the bus through a bidirectional DC-DC power converter and uses a voltage-current dual-loop control, and the hydrogen fuel cell unit is connected to the bus through an isolated boost full-bridge converter and uses a current loop constant power control; the load unit mainly includes an electric propulsion load and a DC load, and the electric propulsion load is connected to the bus through a DC / AC power converter; the DC load is connected to the bus through a DC / DC power converter; the hydrogen fuel cell unit, battery unit, super capacitor unit, electric propulsion load and DC load are all connected to the bus through a circuit breaker; a high-resistance short-circuit fault occurs on the line connecting the source side unit or the load unit to the bus; a high-resistance short-circuit fault is detected by collecting the DC side capacitor current of the source side unit and the load unit.

[0044] Furthermore, in this embodiment, a method for detecting high-resistance short-circuit faults in a DC power system of a hydrogen fuel cell ship is provided, and its working principle is as follows: Figure 2 As shown, the instantaneous change in the current of each unit capacitor is detected and the current change rate is calculated. The calculated current change rate is compared with the set current change rate threshold to determine whether a fault has occurred in the ship. Follow the steps below to implement:

[0045] Step S1: Sampling the electrical quantities of the hydrogen fuel cell ship DC power system, including the bus side capacitor output current i of each unit converter C1 、i C2 、…、i Cn , the inductor current of each unit i L1 、i L2 、…、i Ln ;

[0046] Step S2: Sample electrical quantity i C1 、i C2 、…、i Cn Calculate and get the output current change rate of each unit bus side capacitor di C1 / dt、di C2 / dt,…,di Cn / dt;

[0047] Step S3: By analyzing the working conditions of the DC power system of the hydrogen fuel cell ship, the busbar side capacitance current change rate under normal operation and the fault current change rate during high resistance short circuit fault are calculated, and the middle value between the two can be used to obtain the capacitance current change rate protection threshold (di C / dt) th ;

[0048] Step S4: Each unit compares the capacitance current change rate calculated by itself with the protection threshold. If the calculated value is greater than the protection threshold, it is determined that a fault has occurred in the system.

[0049] Furthermore, in this embodiment, the capacitance current change rate di in step S2 is C / dt is determined by formula (1), where the sampling time t sample Take one tenth of the control step size:

[0050]

[0051] In formula 1, i c is the capacitor current, t0 is the time when the fault occurs, t1 is the sampling time interval after the fault occurs, t sample is the sampling time.

[0052] Furthermore, in this embodiment, the selection of the capacitance current change rate threshold in step S3 should satisfy Formula 2:

[0053]

[0054] In formula 2, k α is the fault current change rate starting coefficient, (di C / dt) max is the maximum normal operating capacitance current change rate, (di C / dt) th Set the threshold value for the capacitance current change rate, (di C / dt) max is the minimum fault capacitance current change rate.

[0055] Furthermore, in this embodiment, the bus-side capacitance current change rate under normal operating conditions needs to be obtained in Formula 2, which can be obtained by Formula 3:

[0056]

[0057] In formula 3, I L is the inductor current, ΔI L is the inductor current ripple, and Δt is the sampling time.

[0058] Furthermore, in this embodiment, the bus-side capacitance current change rate under a high-resistance short-circuit fault needs to be obtained in Formula 2, which can be obtained by Formula 4:

[0059]

[0060] In formula 4, i f is the fault current, U c is the capacitor voltage, L is the inductance in the fault circuit, and R is the resistance in the fault circuit.

[0061] Furthermore, in this embodiment, the fault current change rate starting coefficient k in formula 2 is α To leave a certain margin with the normal operating state to avoid false protection operation, select 1.1~1.2.

[0062] Furthermore, in this embodiment, the fault current under high-resistance short-circuit fault needs to be obtained in Formula 4. The equivalent circuit diagram under high-resistance short-circuit fault is as follows: Figure 3 As shown, the fault current under high-resistance short-circuit fault can be obtained as shown in Equation 5:

[0063]

[0064] In formula 5 i busFurther, in this embodiment, in step S4, each unit protection module operates independently, and when it is detected that the rate of change of its own capacitance current exceeds the threshold, it is determined that a fault has occurred in the system, and the fault judgment criterion should satisfy Formula 6:

[0065]

[0066] 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 and effects do not exceed the scope of the technical solution of the present invention, shall fall within the scope of protection of the present invention.

[0067] In order to verify the effectiveness of the high-resistance short-circuit fault detection method for hydrogen fuel cell ship DC power system proposed in this invention, a simulation experiment was carried out. The simulation model was built based on MATLAB / Simulink. Figure 4-5 The reliability of the fault detection method of the present invention is compared, and it is found that the fault can be accurately detected in various situations. Figure 4 The effectiveness of fault detection in the case of high-resistance short-circuit faults and no-load to full-load switching of the DC power system of hydrogen fuel cell ships was demonstrated. Figure 5 The effectiveness of fault detection when a high-resistance short-circuit fault occurs in the half-load condition of the DC power system of a hydrogen fuel cell ship and when switching from half-load to full-load occurs is demonstrated. Figure 4 and Figure 5 It can be seen from the comparison that the fault detection method proposed in the present invention can well distinguish between operating condition changes and high-resistance short-circuit faults; using the fault detection method proposed in the present invention, when the ship is operating in a complex situation with changing operating conditions, it can also accurately detect short-circuit faults occurring in the system, thereby enhancing the reliability of the protection of the hydrogen fuel cell ship's DC power system, effectively limiting the amplitude and rising speed of the fault current, making the fault current output in a steady state, reducing the complexity of the fault protection method, and ensuring the long-term stable operation of the hydrogen fuel cell ship's DC power system.

Claims

1. A method for detecting high-resistance short-circuit faults in a hydrogen fuel cell ship DC power system, characterized in that The steps include: Step S1: Sampling the electrical quantities of the hydrogen fuel cell ship DC power system, including the output current i of the bus side capacitor of each unit converter C1 、i C2 、…、i Cn , the inductor current of each unit i L1 、i L2 、…、i Ln ; Step S2: Output current i to the bus side capacitor of each unit converter C1 、i C2 、…、i Cn Calculate and obtain the output current change rate of each unit bus side capacitor di C1 / dt、di C2 / dt,…,di Cn / dt; Step S3: By analyzing the working conditions of the DC power system of the hydrogen fuel cell ship, the bus side capacitance current change rate under normal operation and the fault current change rate during high resistance short circuit fault are calculated, and the middle value of the two is taken to obtain the capacitance current change rate protection threshold (di C / dt) th ; Step S4: Each unit compares the capacitance current change rate calculated by itself with the protection threshold value. If the calculated value is greater than the protection threshold value, it is determined that a fault has occurred in the system.

2. A method for detecting high-resistance short-circuit faults in a hydrogen fuel cell ship DC power system according to claim 1, characterized in that: In step S2, the capacitance current change rate di C / dt is determined by formula (1), where the sampling time t sample Take one tenth of the control step size: In formula 1, i c is the capacitor current, t0 is the time when the fault occurs, t1 is the time interval after the fault occurs, t sample is the sampling time.

3. The method for detecting high-resistance short-circuit faults in a hydrogen fuel cell ship DC power system according to claim 1, characterized in that: In step S3, the selection of the capacitance current change rate threshold should satisfy formula (2): In formula (2), k α is the fault current change rate starting coefficient, (di C / dt) max is the maximum normal operating capacitance current change rate, (di C / dt) th Set the threshold value for the capacitance current change rate, (di C / dt) max is the minimum fault capacitance current change rate.

4. A method for detecting high-resistance short-circuit faults in a hydrogen fuel cell ship DC power system according to claim 3, characterized in that: Under normal operating conditions, the bus side capacitance current change rate is obtained by formula (3): In formula (3), I L is the inductor current, ΔI L is the inductor current ripple, and Δt is the sampling time.

5. A method for detecting high-resistance short-circuit faults in a hydrogen fuel cell ship DC power system according to claim 3, characterized in that: The capacitance current change rate under high resistance short circuit fault is obtained by formula (4): In formula (4), i f is the fault current, U c is the capacitor voltage, L is the inductance in the fault circuit, and R is the resistance in the fault circuit.

6. A method for detecting high-resistance short-circuit faults in a hydrogen fuel cell ship DC power system according to claim 3, characterized in that Fault current change rate starting coefficient k α To leave a certain margin with the normal operating state to avoid false protection operation, select 1.1~1.

2.

7. A method for detecting high-resistance short-circuit faults in a hydrogen fuel cell ship DC power system according to claim 5, characterized in that: The fault current under high-resistance short-circuit fault is obtained by formula (5): In formula (5), σ is the attenuation coefficient, β is the phase relationship between the voltage and current in the circuit, ω0 is the natural angular frequency of the circuit, i bus Output current for the source side unit.

8. The method for detecting high-resistance short-circuit faults in a hydrogen fuel cell ship DC power system according to claim 1, characterized in that: In step S4, each unit protection module operates independently. When it is detected that the rate of change of its own capacitance current exceeds a threshold, it is determined that a fault occurs in the system. The fault judgment criterion should satisfy formula (6):

9. A high-resistance short-circuit fault detection system for a hydrogen fuel cell ship DC power system, characterized in that: A method for detecting a high-resistance short-circuit fault in a hydrogen fuel cell ship DC power system according to any one of claims 1 to 8 is implemented; the hydrogen fuel cell ship DC power system is connected to a radial DC bus by a source-side unit and a load unit, the source-side unit includes a hydrogen fuel cell unit, a battery unit, and a supercapacitor unit, and the battery unit and the supercapacitor unit together constitute a hybrid energy storage unit; the hybrid energy storage unit is connected to the bus through a bidirectional DC-DC power converter and uses a voltage-current dual-loop control, the hydrogen fuel cell unit is connected to the bus through an isolated boost full-bridge converter, and uses a current loop constant power control; the load unit mainly includes an electric propulsion load and a DC load, the electric propulsion load is connected to the bus through a DC / AC power converter; the DC load is connected to the bus through a DC / DC power converter; the hydrogen fuel cell unit, battery unit, supercapacitor unit, electric propulsion load, and DC load are all connected to the bus through a circuit breaker; the high-resistance short-circuit fault occurs on the line connecting the source-side unit or the load unit to the bus; high-resistance short-circuit fault detection is performed by collecting the DC side capacitor current of the source-side unit and the load unit.

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