Fault isolation method and device for high-voltage direct-current line of electric vehicle

Abstract

The embodiment of the invention provides a fault isolation device for a high-voltage direct-current line of an electric vehicle. The high-voltage direct-current line comprises a voltage source, a line inductor, a load resistor and a fault isolation device, the fault isolation device comprises a first capacitor, a second capacitor, a first diode, a second diode, a first switch and a second switch. According to the fault isolation device, reverse voltage is generated in the RL circuit through the diode, part of fault energy is sent back to the direct-current power source, fault current can be rapidly attenuated till zero passage, the response speed of the fault isolation device of the electric vehicle is increased, and meanwhile the current absorption burden of the switch and the capacitor is reduced. In addition, the fault isolation device solves the voltage stress problem of a traditional circuit breaker. In addition, the fault isolation device does not need to use an inductor and does not need to use a capacitor with relatively large capacity, so that the cost, the size and the weight are further reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of fault isolation for electric vehicles, and particularly relates to an intelligent fault isolation method and device for high-voltage direct current lines of electric vehicles. Background Art

[0002] With the acceleration of the global energy transition, electric vehicles (EVs), as the core carriers of clean transportation, the safety and reliability of their high-voltage direct current (HVDC) systems have become the focus of industry attention. Modern electric vehicles generally adopt a high-voltage platform of 300 - 800V to improve energy efficiency. However, this design also brings severe fault protection challenges. When a short circuit occurs in the high-voltage line of an electric vehicle, the fault current can rise above 5kA within microseconds. Traditional fault protection devices, due to insufficient response speed, lead to arc combustion, device burnout, and even battery thermal runaway, seriously threatening the safety of occupants.

[0003] In the existing technology, the fault isolation technology of high-voltage DC lines for electric vehicles mainly relies on traditional circuit breakers, but these technologies have defects. For example, mechanical circuit breakers extinguish arcs by contact separation, and their breaking time is as long as 30-40ms, while the fault current rise rate of electric vehicles exceeds 10kA / ms, resulting in an arc energy density that is more than 100 times that of traditional low-voltage line systems. The problem of contact ablation is particularly prominent. According to tests, the contact resistance of traditional mechanical circuit breakers increases by 300% after 500 breaks, and the reliability decreases significantly. In addition, although solid-state circuit breakers (SSCBs) can achieve microsecond response, the conduction loss is as high as 0.5-1.0W / A, and the heat generation is serious under continuous high current scenarios. Actual measurements of a mainstream model show that the temperature of SSCB reaches 85°C under 400V / 100A conditions, and a complex heat dissipation system is required, resulting in a 40% increase in volume and weight. In addition, SSCBs rely on the trigger control of thyristors or IGBTs, and the cost is more than 5 times that of traditional mechanical circuit breakers, making it difficult to meet the needs of large-scale applications. In addition, hybrid circuit breakers combine mechanical and solid-state technologies to try to balance performance and cost, but there are still key defects. Traditional hybrid circuit breakers require additional series inductance to induce current oscillation, which leads to a serious increase in the size of the device, far exceeding the space limit of the vehicle. The energy absorption circuit relies on large-capacity capacitors. A 10kA hybrid circuit breaker needs to be equipped with a 2000μF capacitor, which weighs 3.5kg, significantly affecting the vehicle's energy efficiency. More seriously, the voltage stress problem has not been solved. The measured data shows that the capacitor voltage peak can reach 2.5 times the power supply voltage during fault disconnection, forcing the device withstand voltage level to be increased to more than 1.2kV, further increasing the cost. The special operating environment of electric vehicles further exacerbates the difficulty of protection. The on-board system needs to withstand extreme temperature changes from -40℃ to 85℃. The equivalent series resistance (ESR) of traditional capacitors increases by 50% at low temperatures, resulting in a 20% increase in disconnection time. Under vibration and impact environments, the contact alignment deviation of the mechanical switch exceeds 0.1mm, causing the probability of disconnection failure to increase. In addition, the upgrade of industry standards has also posed new challenges to fault protection technology. According to ISO 6469-3:2017, the high-voltage system of electric vehicles must complete fault isolation within 2ms, and the voltage spike during the disconnection process must not exceed 1.2 times the power supply voltage. In the existing technology, only solid-state circuit breakers can barely meet the time requirements, but the voltage spike problem cannot be solved.

[0004] In summary, the existing technologies cannot meet the stringent requirements of electric vehicles in terms of response speed, voltage stress control, etc. Therefore, the development of a fault isolation device with fast response, low voltage stress, compactness, lightness and high reliability has become the core bottleneck of the development of electric vehicle technology. Summary of the invention

[0005] A first aspect of the present invention provides a fault isolation device for a high voltage DC line of an electric vehicle, characterized in that:

[0006] The high-voltage DC line includes a voltage source Vs, a line inductor L, a load resistor R, and a fault isolation device; wherein, the fault isolation device includes a first capacitor C1, a second capacitor C2, a first diode D1, a second diode D2, a first switch SW1, and a second switch SW2; the positive pole of the voltage source Vs, the first switch SW1, the line inductor L, the load resistor R, the second switch SW2, and the negative pole of the voltage source are connected in series in sequence to form a main circuit. The first capacitor C1 is connected in parallel between the first switch SW1. The cathode of the first diode D1 is connected to the main circuit between the positive pole of the voltage source and the first switch SW1. The cathode of the second diode D2 is connected to the main circuit between the first switch SW1 and the line inductor L. The second capacitor C2 is connected in parallel between the second switch SW2. The anode of the second diode D2 is connected to the main circuit between the negative pole of the voltage source Vs and the second switch SW2. The anode of the first diode D1 is connected to the main circuit between the load resistor R and the second switch SW2.

[0007] As a further limitation of the present invention, it is characterized in that the fault isolation device further includes a surge arrester SPD1, and the surge arrester SPD1 is connected across the positive and negative poles of the voltage source Vs.

[0008] As a further limitation of the present invention, it is characterized in that the mechanical response time of the first switch SW1 is higher than that of the second switch SW2.

[0009] As a further limitation of the present invention, it is characterized in that the capacitance values of the first capacitor C1 and the second capacitor C2 are the same, and the models of the first diode D1 and the second diode D2 are the same.

[0010] As a further limitation of the present invention, it is characterized in that the capacitance value C of the first capacitor C1 and the second capacitor C2 is determined in the following manner: Use the voltage source Vs and the load resistor R to calculate the maximum fault current of the high-voltage DC line: I fault =V S / R, where I fault is the maximum fault current; Calculate the capacitance value C according to the maximum fault current: C = I fault / vr, where vr is the voltage change rate.

[0011] The second aspect of the present invention provides an intelligent fault isolation method for applying a fault isolation device of a high-voltage DC line for electric vehicles as described in claim 1, which is characterized by including the following steps:

[0012] S1: Set the mechanical response times of the first switch SW1 and the second switch SW2 respectively, where the mechanical response time of the first switch SW1 is higher than that of the second switch SW2; when the high-voltage DC line is in the normal mode, the first switch SW1 and the second switch SW2 are in the closed state.

[0013] S2: When a fault current occurs in the high-voltage DC line, the second switch SW2 disconnects first, and the line inductor L, the load resistor R, and the second capacitor C2 form an RLC oscillation circuit. The fault current decreases through the RLC oscillation circuit and charges the second capacitor C2 until the voltage of the second capacitor C2 exceeds the voltage of the voltage source Vs, and the first diode D1 conducts, entering step S3.

[0014] S3: After the first diode D1 conducts and before the first switch SW1 disconnects, the line inductor L, the load resistor R, and the first diode D1 form an RL circuit. The fault current continues to decrease through the RL circuit. After the first switch SW1 disconnects, enter step S4.

[0015] S4: After the first switch SW1 disconnects, the line inductor L, the load resistor R, the first diode D1, and the first capacitor C1 form an RLC oscillation circuit. The fault current continues to decrease through the RLC oscillation circuit and charges the first capacitor C1 until the voltage of the first capacitor C1 exceeds the voltage of the voltage source Vs, and the second diode D2 conducts, entering step S5.

[0016] S5: The first diode D1 and the second diode D2 conduct simultaneously, form a reverse RL circuit with the line inductor L and the load resistor R, and reverse charge the voltage source Vs. The fault current continues to decrease through the reverse RL circuit until the fault current becomes zero, entering step S6.

[0017] S6: The remaining energy of the first capacitor C1 and the second capacitor C2 is dissipated through the load resistor R, and the voltages of the first capacitor C1 and the second capacitor C2 are stabilized at Vs / 2, completing the isolation of the fault current this time.

[0018] The present invention can at least achieve the following beneficial effects: By generating a reverse voltage in the RL circuit through a redirecting diode, part of the fault energy is sent back to the DC power supply, which can quickly attenuate the fault current until it crosses zero, improving the response speed of the electric vehicle fault isolation device and reducing the current absorption burden on the switches and capacitors. Moreover, the fault isolation device of the present invention limits the voltage borne by the mechanical switch and the parallel capacitor to the voltage of the voltage source, solving the voltage stress problem of the traditional circuit breaker. In addition, the fault isolation device of the present invention does not require the use of inductors or large-capacity capacitors, further reducing the cost, size, and weight. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present invention or the prior art, the following briefly introduces the drawings required for the description of the embodiments or the prior art; obviously, the following described drawings are some embodiments of the present invention, and those of ordinary skill in the art can also obtain other drawings based on these drawings without creative efforts.

[0020] Figure 1 is a fault isolation device for a high-voltage DC line for electric vehicles provided by an embodiment of the present invention.

[0021] Figure 2 is the working principle diagram (corresponding to step S1) of a fault isolation device for a high-voltage DC line for electric vehicles provided by an embodiment of the present invention.

[0022] Figure 3 is the working principle diagram (corresponding to step S2) of a fault isolation device for a high-voltage DC line for electric vehicles provided by an embodiment of the present invention.

[0023] Figure 4 is the working principle diagram (corresponding to step S3) of a fault isolation device for a high-voltage DC line for electric vehicles provided by an embodiment of the present invention.

[0024] Figure 5 is the working principle diagram (corresponding to step S4) of a fault isolation device for a high-voltage DC line for electric vehicles provided by an embodiment of the present invention.

[0025] Figure 6 is the working principle diagram (corresponding to step S5) of a fault isolation device for a high-voltage DC line for electric vehicles provided by an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The present application will be described based on embodiments, but the present application is not limited to these embodiments. In the following detailed description of the present application, some specific details are described in detail. Those skilled in the art can fully understand the present application without the description of these details. In order to avoid obscuring the essence of the present application, well-known methods, processes, procedures, components, and circuits are not described in detail.

[0027] In addition, those of ordinary skill in the art should understand that the accompanying drawings provided herein are for illustrative purposes only and are not necessarily drawn to scale.

[0028] Unless the context clearly requires otherwise, the words "including", "comprising", and the like throughout the application should be construed in an inclusive sense rather than an exclusive or exhaustive sense; that is, the meaning of "including but not limited to".

[0029] In the description of the present application, it should be understood that the terms "first", "second", etc. are used only for descriptive purposes and cannot be construed as indicating or implying relative importance. In addition, in the description of the present application, unless otherwise specified, the meaning of "plurality" is two or more.

[0030] Embodiment 1:

[0031] The first aspect of the present invention provides a fault isolation device for a high-voltage DC line for an electric vehicle, characterized in that:

[0032] The high-voltage DC line includes a voltage source Vs, a line inductor L, a load resistor R, and a fault isolation device; wherein, the fault isolation device includes a first capacitor C1, a second capacitor C2, a first diode D1, a second diode D2, a first switch SW1, and a second switch SW2; the positive electrode of the voltage source Vs, the first switch SW1, the line inductor L, the load resistor R, the second switch SW2, and the negative electrode of the voltage source are connected in series in sequence to form a main circuit, the first capacitor C1 is connected in parallel between the first switch SW1, the cathode of the first diode D1 is connected to the main circuit between the positive electrode of the voltage source and the first switch SW1, the cathode of the second diode D2 is connected to the main circuit between the first switch SW1 and the line inductor L, the second capacitor C2 is connected in parallel between the second switch SW2, the anode of the second diode D2 is connected to the main circuit between the negative electrode of the voltage source Vs and the second switch SW2, and the anode of the first diode D1 is connected to the main circuit between the load resistor R and the second switch SW2.

[0033] As a further limitation of the present invention, it is characterized in that the fault isolation device further includes a surge arrester SPD1, and the surge arrester SPD1 is connected across the positive and negative poles of the voltage source Vs.

[0034] As a further limitation of the present invention, it is characterized in that the mechanical response time of the first switch SW1 is higher than that of the second switch SW2.

[0035] As a further limitation of the present invention, it is characterized in that the capacitance values of the first capacitor C1 and the second capacitor C2 are the same, and the models of the first diode D1 and the second diode D2 are the same.

[0036] As a further limitation of the present invention, it is characterized in that the capacitance value C of the first capacitor C1 and the second capacitor C2 is determined as follows: Use the voltage source Vs and the load resistor R to calculate the maximum fault current of the high-voltage DC line: I fault =V S / R, where I fault is the maximum fault current; Calculate the capacitance value C according to the maximum fault current: C = I fault / vr, where vr is the voltage change rate.

[0037] Embodiment 2:

[0038] The second aspect of the present invention provides an intelligent fault isolation method for applying a fault isolation device for a high-voltage DC line for electric vehicles as described in claim 1, which is characterized by including the following steps:

[0039] S1: Set the mechanical response times of the first switch SW1 and the second switch SW2 respectively, wherein the mechanical response time of the first switch SW1 is higher than that of the second switch SW2; When the high-voltage DC line is in the normal mode, the first switch SW1 and the second switch SW2 are in the closed state;

[0040] S2: When a fault current occurs in the high-voltage DC line, the second switch SW2 disconnects first, and the line inductor L, the load resistor R, and the second capacitor C2 form an RLC oscillation circuit. The fault current decreases through the RLC oscillation circuit and charges the second capacitor C2 until the voltage of the second capacitor C2 exceeds the voltage of the voltage source Vs, and the first diode D1 conducts, entering step S3;

[0041] S3: After the first diode D1 is turned on and before the first switch SW1 is turned off, the line inductor L, the load resistor R, and the first diode D1 form an RL circuit, and the fault current continues to decrease through the RL circuit. After the first switch SW1 is turned off, step S4 is entered;

[0042] S4: After the first switch SW1 is turned off, the line inductor L, the load resistor R, the first diode D1, and the first capacitor C1 form an RLC oscillation circuit, and the fault current continues to decrease through the RLC oscillation circuit and charges the first capacitor C1 until the voltage of the first capacitor C1 exceeds the voltage of the voltage source Vs, and the second diode D2 is turned on, and step S5 is entered;

[0043] S5: The first diode D1 and the second diode D2 are turned on simultaneously, form a reverse RL circuit with the line inductor L and the load resistor R, and reverse charge the voltage source Vs. The fault current continues to decrease through the reverse RL circuit until the fault current crosses zero, and step S6 is entered;

[0044] S6: The remaining energy of the first capacitor C1 and the second capacitor C2 is dissipated through the load resistor R, and the voltages of the first capacitor C1 and the second capacitor C2 are stabilized at Vs / 2, completing the isolation of the fault current this time.

[0045] The following combines the attached Figure 1 —6 to elaborate on Embodiment 1 and Embodiment 2 in detail.

[0046] As Figure 1 shown, the embodiment of the present invention provides a fault isolation device for a high-voltage DC line for electric vehicles, as Figure 1 shown by the dashed box in. The fault isolation device of the present invention adopts a series combination of two switches, and the switches are equipped with parallel capacitors and redirection diodes. Therefore, the voltages across the switches and their associated capacitors will not exceed the voltage of the DC power supply, and the rated voltages of the switches and capacitors are kept at a low level. In addition, when used near the power supply, part of the fault energy will be sent back to the DC power supply, thus reducing the absorption burden on the switches and capacitors. The following combines Figure 2 —6 to elaborate on the working principle of the fault isolation device proposed by the present invention, where Figures 3 - 6 the white arrow in is the current direction.

[0047] Step S1 (as Figure 2 shown): In this process, both mechanical switches are closed, and the current flows through switch SW1, the power line, the load resistor, and switch SW2. There is no charge in the capacitor, and the diode is in the OFF state.

[0048] Step S2 (as shown in Figure 3 Figure): The trip signal is sent to two switches. However, due to their inherent different mechanical characteristics, they do not open simultaneously. The second switch SW2 will open first due to its smaller mechanical response time, and start to generate an increasing voltage across its contacts. Subsequently, the current is redirected through the capacitor C2. The voltage across the breaker contacts is established due to the rapid increase in path impedance and the initiation of the arc. However, a properly sized parallel capacitor C2 can prevent a significant arc (i.e., no visible arc and no distorted breaker current), and thus complete the current redirection with a minimum arc. The fault current continues to flow through SW1 and C2. In the RLC circuit, including the load resistance, line inductance, and C2, until the voltage across C2 exceeds the source voltage. At this time, the diode D1 conducts. The established RLC circuit generates an underdamped oscillation in the current, causing the current to decay rapidly.

[0049] Step S3 (as shown in Figure 4 Figure): Since SW1 is still closed, the fault current continues to flow through the diode D1, forming an RL circuit.

[0050] Step S4 (as shown in Figure 5 Figure): After opening the switch SW1, the capacitor C1 starts to redirect the current. Therefore, in the current RLC circuit, including the resistor, inductor, and C1 (and D1), the voltage across C1 increases until the voltage across C1 exceeds the source voltage. At this time, the diode D2 conducts.

[0051] Step S5 (as shown in Figure 6 Figure): Since SW1 is now open, the fault current continues to flow through D2 and D1, forming an RL circuit, causing the resistive element to consume the inductive energy. The reverse DC voltage across the RL circuit helps the rapid current decay and zero crossing. In this case, the time constant related to the current decay is the same as the time constant of the original current rise. During this process, some of the energy related to the interrupted current is fed back to the voltage source.

[0052] Step S6: Once the current crosses zero and reverses direction, D1 and D2 turn off. The RLC circuit composed of the capacitors C1 and C2, line inductance, resistor, and DC power supply causes the voltages across C1 and C2 to decay to half of the DC power supply. Since the energy stored in the capacitors is very small, the oscillating current in this state is very small.

[0053] As described above, the fault isolation device proposed by the present invention has several advantages. The redirection diode generates a reverse voltage in the RL circuit, resulting in a rapid decay and current zero-crossing. In contrast, the hybrid circuit breaker requires a solid-state switch to introduce a delay to allow the mechanical switch to separate, which significantly increases the fault current. Regardless of the capacitor size, the fault isolation device of the present invention limits the voltage borne by the mechanical switch and the shunt capacitor to the voltage of the voltage source, which has a significant advantage compared to a circuit breaker where the shunt capacitor voltage is much higher than the source voltage. Therefore, a smaller shunt capacitor value can be applied to the fault isolation device of the present invention, resulting in a reduced overall size. Finally, part of the fault energy is returned to the DC power supply, increasing the current decay rate of the fault isolation device and also reducing the burden of dissipating fault energy on the absorption and release circuits.

[0054] The total current interruption time can be calculated according to the different processes described above. Since each process has a different equivalent circuit, the times of all corresponding processes need to be added together to obtain the total interruption time. Step S1 includes the fault load current I1 = I fault . Steps S2 - S5 cover the time from the start of interruption to current zero-crossing, as follows:

[0055] Step S2 (from t1 to t2, where t1 is the end time of step S1 and t2 is the end time of step S2, and t 21 is the duration of step S2) (corresponds to Figure 3 )

[0056] Due to the asynchronous operation of the mechanical switch, SW2 opens first, forcing the current to flow through the shunt capacitor C2 branch. This process starts when the current passes through C2. Ideally, the current would be immediately rerouted through the shunt capacitor C2, and the initial voltage V C2 (0) = 0. The breaker contact opening time Ts affects the initial voltage V C2 (0), which is the time between when the switch contacts start to move and the current flowing through the switch reaches zero; that is, the commutation is complete. During the switch operation, the capacitor current changes from zero to the fault current I1 = I fault almost linearly, and V C2 (00 can be approximated as: where Ts is the switch operation time. Additionally, when using an appropriate capacitor (sufficiently large), Ts can be neglected (i.e., Ts ≈ 0), so V C2 (0) ≈ 0.

[0057] By applying Kirchhoff's voltage law (KVL) to the current path, we can obtain:

[0058]

[0059] Among them, I2 is the current in step S2. For the underdamped response, the condition is: C2 ≤ L / R 2 . Therefore, the solution of the above equation is:

[0060]

[0061] where α = R / 2L, the initial condition I2(0) = I fault and V C2 (0) = 0 are used for calculating and k1, and we get: At the end of step S2, the capacitor voltage V C2 (t2) = V S . Since the natural frequency is relatively high, the exponential term of I2 can be ignored and approximated as: where β = arctan(ω d / α). Therefore,

[0062] At the end of step S2, the current can be calculated as: This will be used as the initial condition for step S3. For most mechanical switches, in order to limit the voltage rate of change (vr) to not exceed 80 V / μs to avoid significant arcing, the selection of the capacitor size C needs to satisfy: I fault / 80e6 ≤ C.

[0063] Step S3 (t2 - t3, t3 is the end time of step S3, t 32 is the duration of step S3) (corresponding to Figure 4 )

[0064] During this period, the capacitor C2 stops conducting, while the switch SW1 still conducts due to the delayed operation. During this process, the energy stored in the series inductor discharges in the formed RL circuit. According to Figure 4 , the KVL equation can be written as: I3R + LdI3 / dt = 0, where I3 is the current in step S3, and the solution is: where I2(t 21 ) is the initial condition of step S2. The time t 32 is the response time of the switch SW1 and can be obtained from the circuit breaker specifications.

[0065] Step S4 (t3 - t4, t4 is the end time of step S4, t 43 is the duration of step S4) (corresponding to Figure 5 )

[0066] At the end of step S3, SW1 is turned on, and the current is directed to the parallel capacitor C1 and flows through the load RL path, D1, and C1, as Figure 5 shown. Similar to step S2, this forms a series RLC circuit, and applying KVL gives:

[0067]

[0068] where I4 is the current in step S4 and can be expressed as: where α = R / 2L, The initial conditions I3(t 32 ) and V C1 (0) = 0 are used to calculate and k2, resulting in: Similar to step S2, the capacitor voltage can be expressed as: where β = arctan(ω d / α),. Therefore,

[0069] At the end of step S4, the current can be calculated as: This will be used as the initial condition for step S5.

[0070] Step S5 (from t4 to t5, where t5 is the end time of step S5 and t 54 is the duration of step S5) (corresponding to Figure 5 )

[0071] During this process, capacitor C1 stops conducting, and the current flows through the voltage source, D2, the RL branch, and D1, as Figure 5 shown. Applying KVL gives: I5R + LdI5 / dt = -V s , where I5 is the current in step S5. Solving gives: where I 43 is the initial current calculated in step S4. At t = t 54 , the current goes to zero; therefore,

[0072] The total current zero-crossing time is then: t total = t 21 + t 32 + t 43 + t 54 .

[0073] Typically, a smaller line inductance results in a higher fault current, and a larger capacitor is required to carry the current to meet the required time. As the breaker location moves farther from the fault point, the fault current decreases, and the required capacitor size also decreases. Therefore, based on the breaker location, the maximum fault current needs to be calculated first, and using Ifault = C * vr to select the capacitor size, where vr is the rate of change of voltage across the breaker contacts (i.e., the capacitor). For a typical fast breaker, the rate of change of voltage vr < 80 V / μs.

[0074] Although the preferred embodiments of the present invention have been described, additional changes and modifications can be made to these embodiments by those skilled in the art once they learn the basic inventive concept. Therefore, the appended claims are intended to be construed to include the preferred embodiments as well as all changes and modifications that fall within the scope of the present invention.

[0075] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A fault isolation device for a high-voltage DC line for electric vehicles, characterized in that: The high-voltage DC line includes a voltage source Vs, a line inductor L, a load resistor R, and a fault isolation device; wherein, the fault isolation device includes a first capacitor C1, a second capacitor C2, a first diode D1, a second diode D2, a first switch SW1, and a second switch SW2; the positive pole of the voltage source Vs, the first switch SW1, the line inductor L, the load resistor R, the second switch SW2, and the negative pole of the voltage source are connected in series in sequence to form a main circuit, the first capacitor C1 is connected in parallel between the first switch SW1, the cathode of the first diode D1 is connected to the main circuit between the positive pole of the voltage source and the first switch SW1, the cathode of the second diode D2 is connected to the main circuit between the first switch SW1 and the line inductor L, the second capacitor C2 is connected in parallel between the second switch SW2, the anode of the second diode D2 is connected to the main circuit between the negative pole of the voltage source Vs and the second switch SW2, and the anode of the first diode D1 is connected to the main circuit between the load resistor R and the second switch SW2.

2. The fault isolation device for a high-voltage DC line for an electric vehicle according to claim 1, characterized in that, The fault isolation device further includes a surge arrester SPD1, and the surge arrester SPD1 is connected across the positive and negative poles of the voltage source Vs.

3. The fault isolation device for a high-voltage DC line for electric vehicles according to claim 1, characterized in that, The mechanical response time of the first switch SW1 is higher than that of the second switch SW2.

4. The fault isolation device for a high-voltage DC line for electric vehicles according to claim 1, characterized in that, The capacitance values of the first capacitor C1 and the second capacitor C2 are the same, and the models of the first diode D1 and the second diode D2 are the same.

5. The fault isolation device for a high-voltage DC line for electric vehicles according to claim 4, characterized in that, The capacitance values C of the first capacitor C1 and the second capacitor C2 are determined as follows: Use the voltage source Vs and the load resistor R to calculate the maximum fault current of the high-voltage DC line: I fault = V S / R, where I fault is the maximum fault current; Calculate the capacitance value C based on the maximum fault current: C = I fault / vr, where vr is the voltage change rate.

6. An intelligent fault isolation method for a fault isolation device of a high-voltage DC line for electric vehicles as described in claim 1, characterized in that, It includes the following steps: S1: Set the mechanical response times of the first switch SW1 and the second switch SW2 respectively, wherein the mechanical response time of the first switch SW1 is higher than that of the second switch SW2; when the high-voltage DC line is in the normal mode, the first switch SW1 and the second switch SW2 are in the closed state; S2: When a fault current occurs in the high-voltage DC line, the second switch SW2 disconnects first, and the line inductor L, the load resistor R, and the second capacitor C2 form an RLC oscillation circuit, and the fault current decreases through the RLC oscillation circuit and charges the second capacitor C2 until the voltage of the second capacitor C2 exceeds the voltage of the voltage source Vs, and the first diode D1 conducts, and enters step S3; S3: After the first diode D1 conducts and before the first switch SW1 disconnects, the line inductor L, the load resistor R, and the first diode D1 form an RL circuit, and the fault current continues to decrease through the RL circuit. After the first switch SW1 disconnects, it enters step S4; S4: After the first switch SW1 is turned off, the line inductor L, the load resistor R, the first diode D1, and the first capacitor C1 form an RLC oscillation circuit. The fault current continues to decrease through the RLC oscillation circuit and charges the first capacitor C1 until the voltage of the first capacitor C1 exceeds the voltage of the voltage source Vs, and then the second diode D2 conducts, entering step S5; S5: The first diode D1 and the second diode D2 conduct simultaneously, forming a reverse RL circuit with the line inductor L and the load resistor R, and reverse charging the voltage source Vs. The fault current continues to decrease through the reverse RL circuit until the fault current becomes zero, entering step S6; S6: The remaining energy of the first capacitor C1 and the second capacitor C2 is dissipated through the load resistor R, and the voltages of the first capacitor C1 and the second capacitor C2 are stabilized at Vs / 2, completing the isolation of the fault current this time.

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