Electric vehicle charging station fault ride-through control method, device and equipment considering reactive power support and charging power

Abstract

The invention relates to the field of power system fault ride-through, and particularly discloses an electric vehicle charging station fault ride-through control method, device and equipment considering reactive power support and charging power. The method comprises the steps that when it is detected that the alternating current bus voltage of the charging station drops below a preset voltage, the system calculates fault clearing time by comparing a voltage threshold value, compares the fault clearing time with main protection action time, and dynamically adjusts control strategies of a dual-active bridge converter and a voltage source converter of the charging station; therefore, direct-current voltage out-of-limit is prevented, battery charging safety is protected, stable operation and smooth recovery of the charging station in the fault period are finally ensured, and the fault ride-through process is completed.

Description

Technical Field

[0001] The present invention relates to the field of power system fault ride-through, and in particular to a fault ride-through control method, device and equipment for an electric vehicle charging station taking both reactive power support and charging power into consideration. Background Art

[0002] With the continuous growth of electric vehicle ownership, the use of power batteries as controllable loads or mobile energy storage to support the power grid has attracted much attention. Electric vehicle charging stations generally charge batteries through a two-stage grid-connected structure of a voltage source converter and a dual active bridge converter. In the event of a grid short-circuit fault, the charging station can output reactive power to support the grid voltage through the flexible control of the voltage source converter (VSC). However, after the grid fault, the input power of the charging station is reduced due to the voltage drop, and unbalanced power is generated on the DC side of the charging station, resulting in a drop in DC voltage. When the DC voltage drops to the limit value, the dual active bridge converter (DAB) is repeatedly unlocked in a short period of time, and the DC capacitor is repeatedly charged and discharged, which not only causes an impact on the charging system, but also multiple large changes in charging power may cause safety issues such as battery overcharging, overheating, and even explosion.

[0003] At present, when a power grid fails, electric vehicle charging stations are generally disconnected from the grid directly by triggering low voltage protection, and then reconnected to the grid after the voltage is restored. However, direct disconnection from the grid not only makes the charging station unable to provide support for the power grid, but also because the power grid failure lasts for a short time, the charging power of electric vehicles still drops and increases suddenly in a short period of time, affecting the life and safety of the power battery. At present, there is no relevant technology for charging station fault ride-through. There have been some studies on using electric vehicles to provide reactive power for the power grid. Researchers have demonstrated the feasibility of electric vehicles providing reactive support for the power grid from the perspective of hardware and control; researchers have analyzed the reactive compensation capacity of electric vehicles under charging mode through prototype testing; researchers have proposed a reactive power optimization method for electric vehicles that takes into account the interests of the power grid and the user side by establishing a reactive power optimization model. However, existing studies all start from the perspective of the operation benefits of the power grid or the user, and use voltage deviation, network loss and other targets for optimization and solution. The control response is at the minute or hour level, and the problem of reactive power support and DC voltage over-limit of charging stations under power grid failure is not considered.

[0004] The structure of an electric vehicle charging station is similar to that of a new energy source with an inverter interface. The fault ride-through of the new energy source with an inverter interface mainly avoids DC voltage over-limit by using additional energy storage devices, supercapacitors, load shedding, and adjusting the DC-side power to achieve power rebalancing, and then supports the power grid by controlling the output reactive power of the grid-connected converter. The construction cost and operation and maintenance costs of additional energy storage and supercapacitors are relatively high, which are not suitable for large-scale promotion in charging stations. The active power flow direction of the charging station is opposite to that of the new energy source, resulting in different DC voltage change directions of the two under grid faults. Load shedding does not help to prevent the DC voltage of the charging station from dropping below the lower limit. Adjusting the charging power on the DC side of the charging station can suppress the decrease of the DC voltage, but the change of the charging power may threaten the safety of electric vehicles. Especially due to the constraint of AC current limiting, the output reactive power of the voltage source converter often comes at the cost of reducing the active power, which may lead to a large change in the charging power. The fault ride-through of the charging station needs to consider both the decrease of the DC voltage, the change of the charging power, and the reactive power support. None of the existing new energy fault ride-through technologies can be directly applied to charging stations.

[0005] Therefore, how to achieve the fault ride-through of an electric vehicle charging station while taking into account reactive power support and charging power has become an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0006] Aiming at the deficiencies of the above-mentioned existing technologies, the present invention provides a fault ride-through control method, device, and equipment for an electric vehicle charging station that takes into account reactive power support and charging power, effectively solves the problem of safe ride-through of the charging station under faults, and provides a reference for the fault ride-through of charging stations with a large number of electric vehicles connected.

[0007] In the first aspect of the present invention, the following technical solution is adopted. A fault ride-through control method for an electric vehicle charging station that takes into account reactive power support and charging power is applied to an electric vehicle charging station. In the electric vehicle charging station, a dual-active full-bridge converter and a voltage source converter are used to achieve AC-DC conversion and charging control. The method includes the following steps:

[0008] S101: Real-time collect the AC bus voltage, active power, and reactive power of the electric vehicle charging station before and after the grid fault, and real-time detect whether the AC bus voltage of the charging station drops below a preset voltage. If so, implement S102;

[0009] S102: Compare whether the amplitude of the AC bus voltage of the charging station is greater than the voltage threshold value that causes the AC current of the charging station to be limited. If so, implement S103; if not, implement S104;

[0010] S103: The control of the dual-active full-bridge converter remains unchanged, and the voltage source converter adopts DC voltage and reactive power control. The reference value of the reactive power control is set to Q 1, until the AC bus voltage of the charging station is greater than the preset voltage, execute S109;

[0011] S104: Calculate the fault critical clearing time to avoid DC voltage over-limit of the charging station according to the AC bus voltage of the charging station;

[0012] S105: Compare the fault critical clearing time with the main protection operation time of the distribution network. If the fault critical clearing time is less than the main protection operation time, execute S106; otherwise, execute S107;

[0013] S106: The voltage source converter adopts DC voltage and reactive power control, the reactive power reference value is set to 0, and the phase shift ratio reference value of the dual active bridge converter is set to D f *, until the AC bus voltage of the charging station is greater than the preset voltage, execute S109;

[0014] S107: The voltage source converter adopts active power and reactive power control, and the active power and reactive power reference values are set to P 2 and Q 2 , the control of the dual active bridge converter remains unchanged until the main protection operation moment. Detect whether the AC bus voltage is greater than the preset voltage. If so, execute S109; if not, it indicates that the main protection refuses to operate, and execute S108;

[0015] S108: At the main protection operation moment, the voltage source converter switches to DC voltage and reactive power control, the reactive power reference value is set to 0, and the phase shift ratio of the dual active bridge converter is set to D f *;

[0016] S109: The voltage source converter adopts DC voltage and reactive power control, the reactive power reference value is set to 0, and the phase shift ratio of the dual active bridge converter is set to the reference value before the fault, and the fault ride-through of the charging station ends;

[0017] Among them, Q 1 is the reactive power under the maximum allowable AC current constraint of the voltage source converter corresponding to the active power of the charging station before the fault, and D f * is the phase shift ratio that makes the power transmitted by the dual active bridge converter just reach the maximum active power of the voltage source converter under the fault, and P 2 and Q 2 are the active power and reactive power at the intersection of the charging station power boundary with the maximum allowable AC current constraint and the charging station power boundary with the DC voltage constraint.

[0018] In the second aspect of the present invention, the following technical solution is adopted. An electric vehicle charging station fault ride-through control device that takes into account reactive power support and charging power includes:

[0019] An acquisition module, which is used to collect the AC bus voltage, active power, and reactive power of the electric vehicle charging station before and after the grid fault;

[0020] A first comparison module, which is used to compare the AC bus voltage. If the AC bus voltage drops below a preset voltage, the second comparison module is called; The second comparison module is used to compare the amplitude of the AC bus voltage of the charging station with the voltage threshold value that limits the AC current of the charging station. If the amplitude of the AC bus voltage of the charging station is greater than the voltage threshold value that limits the AC current of the charging station, the first control module is called, otherwise the first calculation module is called;

[0021] The first control module keeps the control of the dual-active full-bridge converter unchanged. The voltage source converter adopts DC voltage and reactive power control, and the reference value of reactive power control is set to Q 1 , and then call the first comparison module and then call the fourth control module;

[0022] The first calculation module is used to calculate the fault critical clearing time to avoid the DC voltage of the charging station exceeding the limit. After the calculation is completed, the third comparison module is called;

[0023] The third comparison module is used to compare the fault critical clearing time with the main protection operation time of the distribution network. If the fault critical clearing time is less than the main protection operation time, the second control module is called; Otherwise, the third control module is called;

[0024] The second control module, the voltage source converter adopts DC voltage and reactive power control, the reference value of reactive power is set to 0, and the phase shift ratio reference value of the dual-active full-bridge converter is set to D f *, and then call the first comparison module and then call the fourth control module;

[0025] The third control module, the voltage source converter adopts active power and reactive power control, and the reference values of active power and reactive power are set to P 2 and Q 2 , the control of the dual-active full-bridge converter remains unchanged, and the fourth comparison module is called;

[0026] The fourth comparison module is used to compare whether the AC bus voltage at the main protection operation moment is less than the preset voltage. If it is less than the preset voltage, the second control module is called, otherwise the fourth control module is called;

[0027] The fourth control module, the voltage source converter adopts DC voltage and reactive power control, the reactive power reference value is set to 0, and the phase shift ratio of the dual-active full-bridge converter is set to the reference value before the fault;

[0028] Among them, Q 1 is the reactive power under the maximum allowable AC current constraint of the voltage source converter corresponding to the active power of the charging station before the fault, Df *For the phase shift ratio that enables the dual-active-bridge converter to transfer power exactly to the maximum active power of the voltage-source converter under a fault, P 2 and Q 2 are the active power and reactive power at the intersection of the charging station power boundary with the maximum allowable AC current constraint and the charging station power boundary with the DC voltage constraint.

[0029] In the third aspect of the present invention, the following technical solution is adopted. An electric vehicle fault ride-through control device that takes into account reactive power support and charging power includes a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor. When the processor executes the computer program, it implements the electric vehicle charging station fault ride-through control method that takes into account reactive power support and charging power as described in the first aspect of the present invention.

[0030] In view of the fact that under the existing technology, it is still difficult for a charging station to remain connected to the grid continuously during a fault while avoiding the impact of the fault on the power electronic devices and battery charging safety and providing reactive power support for the grid. The present invention discloses an electric vehicle charging station fault ride-through control method, device, and equipment that take into account reactive power support and charging power, and consider the impact of charging power and the DC voltage dropping below the lower limit on the charging station fault ride-through. Compared with the existing technology, the present invention has the following advantages:

[0031] 1. Existing technologies can use electric vehicles to provide reactive power support for the grid during normal operation, but mainly focus on the operating benefits of the grid or users. The adopted objectives and control response time scales do not meet the fast response requirements under grid faults; currently, there is no relevant technology specifically for the fault ride-through of charging stations under grid faults, and it is impossible to provide reactive power support as much as possible while ensuring the DC voltage safety and charging safety of the charging station.

[0032] 2. Existing fault ride-through technologies for inverter-interfaced new energy sources, such as using additional energy storage, supercapacitors, or load shedding, have problems such as high cost, complex operation and maintenance, or inapplicable principles, and cannot be applied to charging stations.

[0033] 3. The existing fault ride-through technologies for power electronic devices do not consider the balance among DC voltage reduction, charging power variation, and reactive power support, and cannot be directly applied to charging stations. It is impossible to provide maximum reactive power support while ensuring the charging safety of electric vehicles. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a flowchart of the electric vehicle charging station fault ride-through control method that takes into account reactive power support and charging power according to an embodiment of the present invention;

[0035] Figure 2Schematic diagram of the fault ride-through control device for an electric vehicle charging station that takes into account reactive power support and charging power according to an embodiment of the present invention;

[0036] Figure 3 Main circuit topology diagram of an electric vehicle charging station adopted in an embodiment of the present invention;

[0037] Figure 4 Schematic diagram of electrical quantities of Scheme 1 in an embodiment of the present invention;

[0038] Figure 5 Schematic diagram of electrical quantities of Scheme 2 in an embodiment of the present invention;

[0039] Figure 6 Schematic diagram of electrical quantities of Scheme 3 in an embodiment of the present invention;

[0040] Figure 7 Schematic diagram of electrical quantities of Scheme 4 in an embodiment of the present invention. Detailed implementation manners

[0041] To make the object, features, and advantages of the present invention more obvious and understandable, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the embodiments described below are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0042] The present invention will be further described in detail below with reference to the accompanying drawings.

[0043] Please refer to Figure 1 , as Figure 1 shown, a flowchart of a fault ride-through control method for an electric vehicle charging station that takes into account reactive power support and charging power provided by an embodiment of the present invention is applied to an electric vehicle charging station. The electric vehicle charging station at least includes a dual-active full-bridge converter and a voltage source converter, and includes the following steps:

[0044] S101: Real-time collect the AC bus voltage, active power, and reactive power of the charging station, and real-time detect whether the AC bus voltage of the charging station drops below a preset voltage. If so, implement S102;

[0045] S102: Compare whether the amplitude of the AC bus voltage of the charging station is greater than the voltage threshold value that limits the AC current of the charging station. If so, implement S103; if not, implement S104;

[0046] S103: Keep the control of the dual-active full-bridge converter of the charging station unchanged, and the voltage source converter adopts DC voltage and reactive power control. The reference value of the reactive power control is set to Q1 , until the AC bus voltage of the charging station is greater than the preset voltage, execute S109;

[0047] S104: Calculate the fault critical clearing time to avoid DC voltage over-limit of the charging station according to the AC bus voltage of the charging station;

[0048] S105: Compare the fault critical clearing time with the main protection operation time of the distribution network. If the fault critical clearing time is less than the main protection operation time, then execute S106; otherwise, execute S107;

[0049] S106: The voltage source converter adopts DC voltage and reactive power control, the reactive power reference value is set to 0, and the phase shift ratio reference value of the dual-active full-bridge converter is set to D f *, until the AC bus voltage of the charging station is greater than the preset voltage, execute S109;

[0050] S107: The voltage source converter adopts active power and reactive power control, the active power and reactive power reference values are set to P 2 and Q 2 , the control of the dual-active full-bridge converter remains unchanged until the main protection operation moment. Detect whether the AC bus voltage is greater than the preset voltage. If so, execute S109; if not, it indicates that the main protection refuses to operate, and execute S108;

[0051] S108: At the main protection operation moment, the voltage source converter of the charging station switches to DC voltage and reactive power control, the reactive power reference value is set to 0, and the phase shift ratio of the dual-active full-bridge converter is set to D f *;

[0052] Among them, the main protection operation moment refers to the time point or time range of the entire process from the occurrence of a fault to the completion of fault clearing (such as tripping) by the configured main protection device when a power equipment (such as the voltage source converter of the charging station, the dual-active full-bridge converter, etc.) fails.

[0053] S109: The voltage source converter of the charging station adopts DC voltage and reactive power control, the reactive power reference value is set to 0, the phase shift ratio of the dual-active full-bridge converter is set to the reference value before the fault, and the fault ride-through of the charging station ends.

[0054] Specifically, in step S101, some electrical parameter measuring instruments such as power analyzers and power quality analyzers can be used to measure the voltage, current, active power, reactive power and other parameters of the AC bus of the charging station in real time; for example, a resistive voltage divider or an isolated voltage sensor is used to collect the DC bus voltage of the DAB, and the specific limitations in this field are not made here.

[0055] In the embodiment of the present invention, in step S101, the preset voltage may be 0.95 p.u. times the rated voltage. Such a preset voltage can intuitively reflect the voltage deviation situation. For example, if the rated voltage of the bus of a charging station is 110 kV, 0.95 p.u. times the rated voltage is 110×0.95 = 104.5 kV. If the actual bus voltage is close to this value, it indicates that the AC bus voltage of the charging station has decreased to a certain extent but is still within an acceptable range; if the deviation is large, step S102 needs to be implemented to ensure the normal operation of the equipment.

[0056] Specifically, in step S102, the voltage threshold value for limiting the AC current of the charging station is the minimum AC bus voltage that can restore the active power of the charging station to the value before the fault, which is determined by the active power of the charging station before the fault and the maximum allowable AC current of the voltage source converter. Its calculation method includes:

[0057] Calculate the maximum AC current value that the voltage source converter can withstand according to the product of the maximum allowable AC current coefficient of the voltage source converter and the rated AC current of the voltage source converter.

[0058] Calculate the voltage threshold value for limiting the AC current of the charging station according to the ratio of the active power of the charging station before the fault to the maximum AC current value that the voltage source converter can withstand.

[0059] In some embodiments, the voltage threshold value for limiting the AC current of the charging station is calculated by the following formula:

[0060]

[0061] where P 0 is the active power of the charging station before the fault; K I is the maximum allowable AC current coefficient of the voltage source converter; I N is the rated AC current of the voltage source converter.

[0062] The embodiment of the present invention takes into account the maximum allowable AC current limit, prevents the AC current of the charging station from exceeding the tolerance of the converter in case of a fault, prolongs the service life of the power electronic equipment, and reduces the maintenance cost. By the ratio of the active power of the charging station before the fault to the maximum AC current value that the voltage source converter can withstand, the voltage threshold value can be reasonably set to ensure that the charging station can restore to the active power level before the fault after the fault.

[0063] Specifically, in step S103, the reactive power reference value Q 1 of the voltage source converter is the reactive power under the constraint of the maximum allowable AC current of the voltage source converter corresponding to the active power of the charging station before the fault. Its calculation method includes:

[0064] The maximum instantaneous apparent power that the voltage source converter is allowed to output at the moment of fault is calculated according to the product of the AC bus voltage amplitude at the moment of fault, the maximum allowable AC current coefficient of the voltage source converter, and the rated AC current of the voltage source converter;

[0065] The reactive power under the maximum allowable AC current constraint of the voltage source converter corresponding to the active power of the charging station before the fault is calculated according to the square root of the difference between the square of the maximum instantaneous apparent power that the voltage source converter is allowed to output at the moment of fault and the square of the active power of the charging station before the fault.

[0066] In some embodiments, the reactive power under the maximum allowable AC current constraint of the voltage source converter corresponding to the active power of the charging station before the fault is calculated by the following formula:

[0067]

[0068] In the formula, (U f K I I N ) is used to represent the maximum instantaneous apparent power that the voltage source converter is allowed to output at the moment of fault, and U f is the AC bus voltage amplitude at the moment of fault.

[0069] In the embodiments of the present invention, considering the maximum allowable AC current limit, preventing the AC current of the charging station from exceeding the tolerance of the converter in case of a fault, and by reasonably setting the reactive power reference value, it is ensured that the charging station can recover to the active power level before the fault after the fault.

[0070] Specifically, in step S104, the fault critical clearing time to avoid the DC voltage of the charging station exceeding the limit is the fault duration when the power boundary of the charging station with the maximum allowable AC current constraint is tangent to the power boundary of the charging station with the DC voltage constraint, which is determined by the DC voltage reference value, the DC voltage critical value, the DC capacitor, the AC bus voltage amplitude at the moment of fault, the power transmitted by the dual-active full-bridge converter under the fault, and the maximum allowable AC current of the voltage source converter. Its calculation method includes:

[0071] According to the DC voltage reference value, the critical voltage for the dual-active full-bridge converter to lock, and the bus capacitor of the charging station, the energy difference released when the bus capacitor of the charging station discharges from the DC voltage reference value to the critical voltage for the dual-active full-bridge converter to lock is calculated;

[0072] According to the AC bus voltage amplitude at the moment of fault, the maximum allowable AC current coefficient of the voltage source converter, the square of the rated AC current of the voltage source converter, and the total power transmitted by the dual-active full-bridge converters in the charging station under the fault, the power output by the charging station with the maximum current is calculated;

[0073] The fault critical clearing time to avoid DC voltage over-limit of the charging station is calculated according to the ratio of the energy difference released when the bus capacitor of the charging station discharges from the DC voltage reference value to the critical voltage at which the dual-active-bridge converter locks up to the power output by the charging station at the maximum current.

[0074] In some embodiments, the fault critical clearing time to avoid DC voltage over-limit of the charging station is calculated by the following formula:

[0075]

[0076] In the formula, C is the bus capacitor of the charging station; is the DC voltage reference value; U dc,th is the critical voltage at which the dual-active-bridge converter locks up, generally taking 0.5 p.u. rated voltage; P s,f is the total transmission power of the dual-active-bridge converters in the charging station under the fault, which characterizes the battery charging power in the charging station.

[0077] In specific implementation, in step S106, the phase-shift ratio D f * of the dual-active-bridge converter is the phase-shift ratio that makes the transmission power of the dual-active-bridge converter just reach the maximum active power of the voltage-source converter under the fault. Its calculation method includes:

[0078] Calculate the transmission power of the dual-active-bridge converter according to the energy storage inductor of the dual-active-bridge converter, the switching frequency of the dual-active-bridge converter, and the turns ratio of the high-voltage side and the low-voltage side coils of the dual-active-bridge converter;

[0079] Calculate the maximum active power of the voltage-source converter according to the ohmic internal resistance of the electric vehicle battery, the constant voltage of the battery, the battery polarization voltage constant, the battery capacity, the amplitude of the voltage drop in the exponential region of the battery typical discharge curve and the reciprocal of the time constant, the state of charge of the battery, and the number of electric vehicles in the charging station when the fault occurs;

[0080] Based on the transmission power of the dual-active-bridge converter and the maximum active power of the voltage-source converter, solve the equations simultaneously to obtain the phase-shift ratio that makes the transmission power of the dual-active-bridge converter just reach the maximum active power of the voltage-source converter under the fault.

[0081] In some embodiments, the phase-shift ratio that makes the transmission power of the dual-active-bridge converter just reach the maximum active power of the voltage-source converter under the fault is calculated by the following formula:

[0082]

[0083] In the formula, a 1 is the first parameter, a 2 is the second parameter, a3 is the third parameter; is the DC voltage reference value.

[0084] In specific implementation, the first, second, and third parameters are calculated from the charging station parameters:

[0085]

[0086] In the formula, L r is the energy storage inductor of the dual-active full-bridge converter; f s is the switching frequency of the dual-active full-bridge converter; n is the turns ratio of the high-voltage side to the low-voltage side coils of the dual-active full-bridge converter; R ba is the ohmic internal resistance of the electric vehicle battery; E 0 is the constant voltage of the battery; K is the battery polarization voltage constant; Q c is the battery capacity; A ba , B ba are respectively the amplitude of the voltage drop in the exponential region of the typical discharge curve of the battery and the reciprocal of the time constant; soc is the state of charge of the battery; N is the number of electric vehicles in the charging station when the fault occurs.

[0087] In specific implementation, in step S107, the reference values of the active power and reactive power of the voltage source converter P 2 and Q 2 are the active power and reactive power at the intersection of the charging station power boundary with the maximum allowable AC current constraint and the charging station power boundary with the DC voltage constraint, and their calculation methods include:

[0088] Calculate the active power at the intersection of the charging station power boundary with the maximum allowable AC current constraint and the charging station power boundary with the DC voltage constraint according to the pre-fault active power of the charging station, the DC voltage reference value, the critical voltage for the dual-active full-bridge converter to lock, the charging station bus capacitance, and the main protection operation time;

[0089] Calculate the reactive power at the intersection of the charging station power boundary with the maximum allowable AC current constraint and the charging station power boundary with the DC voltage constraint according to the amplitude of the AC bus voltage at the moment of the fault, the maximum allowable AC current coefficient of the voltage source converter, the square of the rated AC current of the voltage source converter, and the arithmetic square root of the square of the active power at the intersection of the charging station power boundary with the maximum allowable AC current constraint and the charging station power boundary with the DC voltage constraint.

[0090] In some embodiments, the calculation formulas for the reference values of the active power and reactive power of the voltage source converter P 2 and Q 2 which are the active power and reactive power at the intersection of the charging station power boundary with the maximum allowable AC current constraint and the charging station power boundary with the DC voltage constraint are as follows:

[0091]

[0092] Among them, P 2 is the active power at the intersection of the charging station power boundary of the maximum allowable alternating current constraint and the charging station power boundary of the direct current voltage constraint, and Q 2 is the reactive power at the intersection of the charging station power boundary of the maximum allowable alternating current constraint and the charging station power boundary of the direct current voltage constraint; P 0 is the active power of the charging station before the fault; C is the capacitance of the charging station bus; is the reference value of the direct current voltage; U dc,th is the critical voltage for the double active bridge converter to lock; t 1 is the main protection action time; U f is the amplitude of the alternating current bus voltage at the moment of the fault; K I is the maximum allowable alternating current coefficient of the voltage source converter; I N is the rated alternating current of the voltage source converter.

[0093] In the embodiment of the present invention, when determining P 2 and Q 2 considering the maximum allowable alternating current and direct current voltage constraints can avoid damage to the equipment due to overcurrent or overvoltage, extend the service life of the equipment, and reduce the maintenance cost; by reasonably determining the reference values of P 2 and Q 2 to ensure that the charging station can not only meet the constraints of alternating current and direct current voltage during operation, but also stably output the required active and reactive power to maintain its normal charging service function.

[0094] Please refer to Figure 2 , Figure 2 which is a schematic structural diagram of a fault ride-through control device for an electric vehicle charging station that takes into account reactive power support and charging power, including:

[0095] An acquisition module, configured to collect the alternating current bus voltage, active power, and reactive power of the electric vehicle charging station before and after the grid fault;

[0096] A first comparison module, configured to compare the alternating current bus voltage. If the alternating current bus voltage drops below a preset voltage, the second comparison module is called; the second comparison module is configured to compare the amplitude of the alternating current bus voltage of the charging station with the voltage threshold value that limits the alternating current of the charging station. If the amplitude of the alternating current bus voltage of the charging station is greater than the voltage threshold value that limits the alternating current of the charging station, the first control module is called, otherwise the first calculation module is called;

[0097] The first control module keeps the control of the double active bridge converter unchanged, and the voltage source converter adopts direct current voltage and reactive power control, and the reference value of the reactive power control is set to Q 1, and call the first comparison module and then call the fourth control module;

[0098] The first calculation module is used to calculate the fault critical clearing time to avoid the DC voltage of the charging station exceeding the limit. After the calculation is completed, call the third comparison module;

[0099] The third comparison module is used to compare the fault critical clearing time with the operating time of the main protection of the distribution network. If the fault critical clearing time is less than the operating time of the main protection, call the second control module; otherwise, call the third control module;

[0100] The second control module, the voltage source converter adopts DC voltage and reactive power control, the reactive power reference value is set to 0, and the phase shift ratio reference value of the dual active bridge converter is set to D f *, and call the first comparison module and then call the fourth control module;

[0101] The third control module, the voltage source converter adopts active power and reactive power control, and the active power and reactive power reference values are set to P 2 and Q 2 , the control of the dual active bridge converter remains unchanged, and call the fourth comparison module;

[0102] The fourth comparison module is used to compare whether the AC bus voltage at the main protection operating moment is less than the preset voltage. If it is less than the preset voltage, call the second control module; otherwise, call the fourth control module;

[0103] The fourth control module, the voltage source converter adopts DC voltage and reactive power control, the reactive power reference value is set to 0, and the phase shift ratio of the dual active bridge converter is set to the reference value before the fault;

[0104] Among them, Q 1 is the reactive power under the maximum allowable AC current constraint of the voltage source converter corresponding to the active power of the charging station before the fault, and D f * is the phase shift ratio that makes the power transmitted by the dual active bridge converter just reach the maximum active power of the voltage source converter under the fault, and P 2 and Q 2 are the active power and reactive power at the intersection of the charging station power boundary with the maximum allowable AC current constraint and the charging station power boundary with the DC voltage constraint.

[0105] Through the combination of the acquisition module, multiple comparison modules, and multiple control modules in the embodiments of the present invention, the balance among DC voltage reduction, charging power variation, and reactive power support is fully considered, and it can be directly applied to electric vehicle charging stations, providing reactive support to the maximum extent while ensuring the charging safety of electric vehicles.

[0106] In an embodiment of the present invention, the electric vehicle fault ride-through control device that takes into account reactive power support and charging power includes a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor. When the processor executes the computer program, it implements the electric vehicle charging station fault ride-through control method that takes into account reactive power support and charging power as described in the present invention.

[0107] In some embodiments, the memory may include non-permanent memory in a computer-readable medium, in the form of random access memory (RAM) and / or non-volatile memory, such as read-only memory (ROM) or flash RAM. The memory is an example of a computer-readable medium.

[0108] In an embodiment of the present invention, this embodiment establishes Figure 3 the simulation model shown in MATLA / Simulink to verify the correctness and effectiveness of the theoretical analysis and the solution of the present invention. There are a total of 4 electric vehicles in the charging station. The charging station is connected to the distribution network through a 0.380 / 10 kV transformer. The DC rated voltage is 800 V, and the outer-loop control parameters of the voltage source converter are k p = 1, k i = 50. The parameters of the dual-active full-bridge converter are k vp = 0.0005, k vi = 20, L r is 20e-6 H, f s = 10000 Hz, n = 800 / 420. The voltage reference value of each electric vehicle battery pack under constant voltage charging is 415 V, and under constant current charging is 380 A. The maximum allowable coefficient of the alternating current of the voltage source converter is 1.2, and the rated current is 1440 A. The blocking voltage of the dual-active full-bridge converter is 0.55 p.u. The operation time of the main protection of the distribution network is 0.4 s, and the operation time of the backup protection is 1 s. Under normal operation, 2 electric vehicles are under constant current charging, 2 electric vehicles are under constant voltage charging, the transmission power of the dual-active full-bridge converter is 1.0 p.u., and the reactive power of the voltage source converter is 0 p.u. Three comparison groups are set up to verify the control method proposed in this paper: Method 1 is that the voltage source converter adopts DC voltage control and constant reactive power control, and the dual-active full-bridge converter maintains the constant current / constant voltage control before the fault; Method 2 refers to the requirements of new energy fault ride-through, controls the reactive power of the voltage source converter according to the degree of voltage drop, and the reactive power reference value is 1.5(0.9 - U f )I N , and the active power reference value is the smaller of the maximum instantaneous apparent power allowed to be output by the voltage source converter at the moment of the fault and the active power before the fault; Method 3 is the method of the present invention.

[0109] Embodiment Scheme 1 of the present invention: When the current of the voltage source converter is not limited

[0110] Suppose a three-phase short-circuit fault occurs in the distribution network at 0.3 s. After the fault, the AC bus voltage is as shown in Figure 4 (a). The AC bus voltage of the charging station drops to 0.85 p.u. According to the calculation method of the voltage threshold value for limiting the AC current of the charging station, the AC bus voltage threshold value at which the voltage source converter can restore the active power before the fault is 0.83 p.u. After the fault, the AC bus voltage of the charging station is greater than the threshold voltage, and the current of the voltage source converter is not limited. The reference values of active and reactive power of Method 2 are 1.01 p.u. and 0.064 p.u. respectively; the reference value of reactive power of Method 3 is 0.65 p.u. It can be obtained by simulation that the AC bus voltage, DC voltage, active and reactive power of the voltage source converter, and the power transmitted by the dual-active active bridge converter under the three methods are as shown in Figure 4 shown in.

[0111] As shown in Figure 4 (b) and Figure 4 (c), since the AC current is not limited, the active power of the voltage source converter can be restored to the power before the fault under the three methods. Therefore, the change range of the DC voltage is small and does not exceed the limit. However, there are obvious differences in the reactive power provided by the charging station under the three methods. As shown in Figure 4 (d), Method 1 maintains the control strategy of normal operation, and the charging station does not emit reactive power; under Method 2, since the AC bus voltage drops not deeply, the charging station only emits 0.064 p.u. of reactive power, and the reactive power capacity of the charging station is not fully utilized; under Method 3, the charging station emits a maximum of 0.65 p.u. of reactive power. Method 3 accurately depicts the power feasible region of the charging station, so the reactive power capacity is fully utilized. As shown in Figure 4 (a), during the fault, the AC bus voltage under Method 3 rises from 0.85 p.u. to 0.875 p.u., while the AC bus voltages of Method 1 and 2 are maintained near 0.85 p.u. As shown in Figure 4 (e), the power transmitted by the dual-active active bridge converter under the three methods is basically the same. The improvement of the control of the voltage source converter by Method 3 does not affect the charging of electric vehicles during the fault. When the voltage drop is small, the present invention can better support the AC bus voltage while avoiding the DC voltage exceeding the limit and the change of the charging power.

[0112] Embodiment Scheme 2 of the present invention: The fault limit cut-off time is greater than the main protection action time and the main protection operates correctly

[0113] After the fault, the AC bus voltage of the charging station drops to 0.7 p.u., as shown in Figure 5(a). The AC bus voltage is less than the threshold voltage, and the current of the voltage source converter is limited. The active and reactive power reference values of the voltage source converter in Method 2 are 0.81 p.u. and 0.21 p.u. respectively. According to the calculation method of the fault critical clearing time, the fault calculation time is 132 ms, which is greater than the main protection operation time. According to P 2 and Q 2 , the active and reactive power reference values of the voltage source converter in Method 3 are 0.72 p.u. and 0.43 p.u. respectively. The AC bus voltage, DC voltage, active and reactive power of the voltage source converter, and the power transmitted by the dual active bridge converter under the three methods are as Figure 5 shown.

[0114] As Figure 5 (b) shows, the DC voltages under the three methods do not exceed the limit. The DC voltage in Method 3 drops to 0.55 p.u., just reaching the locking value of the dual active bridge converter, which also verifies the correctness of the power feasible region of the charging station. As Figure 5 (c) and 5(d) show, under Method 1, the active power during the fault is 0.84 p.u. To restore the active power, the d-axis current of Method 1 is the limited current of the voltage source converter, so the output reactive power is 0. Method 2 gives priority to reactive power control and outputs 0.21 p.u. of reactive power according to the drop of the AC bus voltage. Therefore, the active power of the voltage source converter is less than that of Method 1. The reactive power output by Method 3 is 0.43 p.u., which is greatly improved compared with Methods 1 and 2. Although the active power of the voltage source converter is the least under Method 3, as Figure 5 (b) and Figure 5 (d) show, because the safety margin of the DC voltage of the charging station during the main protection operation time is accurately characterized, the DC voltage does not exceed the limit and provides a larger reactive power. As Figure 5 (a) shows, under Method 3, the AC bus voltage rises from 0.7 p.u. to 0.74 p.u. during the fault, and the AC bus voltages of Method 2 and Method 1 are maintained at 0.71 p.u. and 0.70 p.u. respectively. As Figure 5 (e) shows, the influence of the DC voltage drop on the power transmitted by the dual active bridge converter under the three methods is very small, and it basically maintains the power transmitted before the fault. The improvement of the control of the voltage source converter in Method 3 does not affect the charging of electric vehicles during the fault. The method proposed in this paper can better support the AC bus voltage while avoiding the DC voltage exceeding the limit and the change of the charging power.

[0115] Embodiment Scheme 3 of the present invention: The fault critical clearing time is greater than the main protection operation and the main protection refuses to operate

[0116] The fault conditions remain unchanged, as Figure 4As shown in (a), after the fault, the AC bus voltage of the charging station drops to 0.7 p.u. However, the main protection fails to operate, and the fault is removed by the backup protection. The control reference values of Method 1 and Method 2 are the same as those in Case 2, and the control reference value of Method 3 before the main protection operation time is also the same as that in Case 2. When Method 3 detects that the fault has not been removed at 0.4 s, it resumes the DC voltage control of the voltage source converter, and at the same time adjusts the phase shift ratio control reference value of the dual-active full-bridge converter to 0.0669. The DC voltage of the charging station, the AC bus voltage, the active and reactive powers of the voltage source converter, and the transmission power of the dual-active full-bridge converter are as shown in Figure 6 shown.

[0117] As Figure 6 shown in (b), the DC voltages under Method 1 and Method 2 drop to the locking value of the dual-active full-bridge converter at 0.43 s and 0.41 s respectively, and then the capacitor charges and discharges repeatedly, and the DC voltage oscillates continuously. Under Method 3, at 0.4 s, the active power of the voltage source converter and the transmission power of the dual-active full-bridge converter are balanced again, and the DC voltage just reaches the locking value of the dual-active full-bridge converter. Subsequently, the DC voltage of Method 3 gradually recovers to the reference value, avoiding the locking of the dual-active full-bridge converter, as shown in Figure 6 (b). Figure 6 In (c) and Figure 6 (d), since the d-axis current is the limited value current of the voltage source converter, during the fault, the active power of the voltage source converter of Method 1 is the largest, reaching 0.84 p.u., but the output reactive power is 0. The active power of the voltage source converter of Method 2 is 0.81 p.u., which is smaller than that of Method 1, and the output reactive power is 0.21 p.u. Before the main protection fails to operate, Method 3 provides more reactive power than Method 1 and Method 2, and the output reactive power is 0.43 p.u.; the active power of Method 3 is 0.72 p.u., which is slightly smaller than that of Method 1 and Method 2, but at this time the transmission power of the dual-active full-bridge converter is close to that of Method 1 and Method 2, and both maintain the power level before the fault, as shown in Figure 6 (e). After the main protection fails to operate, the transmission power of the dual-active full-bridge converter under Method 3 decreases slightly, becoming about 0.84 p.u., but for Method 1 and Method 2, due to the repeated unlocking and locking of the dual-active full-bridge converter, the transmission power decreases sharply and oscillates continuously near 0, seriously threatening the safety of electric vehicles. The present invention can better support the AC bus voltage while avoiding DC voltage over-limit and charging power change before the main protection fails to operate, and even if the main protection fails to operate, it can avoid DC voltage over-limit and large-scale change of charging power.

[0118] Embodiment 4 of the present invention: The fault limit removal time is less than the main protection operation time

[0119] After the distribution network fails, the AC bus voltage of the charging station drops to 0.65 p.u., as Figure 7 (b) shows. The reference values of the active and reactive powers of the voltage source converter in Method 2 are 0.74 p.u. and 0.24 p.u. respectively. The AC bus voltage of the charging station after the fault is less than the threshold voltage. According to the calculation method of the fault critical clearing time, the fault critical clearing time is obtained as 73 ms, which is less than the main protection operation time. According to the calculation method of the phase shift ratio reference value, the phase shift ratio reference value of the dual active bridge converter in Method 3 is 0.0669, and the reference value of the reactive power of the voltage source converter is 0. The electrical quantities of the charging station are as Figure 7 shown.

[0120] Since the AC bus voltage of the charging station drops significantly, as Figure 7 (a) shows. The constant voltage control of Method 1 cannot restore the active power of the voltage source converter. At 0.37 s, the DC voltage drops to the locking value of the dual active bridge converter, as Figure 7 (b) and 7(c) show. The reactive power output under Method 2 is 0.24 p.u., as Figure 7 (d) shows. In order to provide more reactive power, Method 2 makes the active power of the voltage source converter smaller during the fault, reaching 0.74 p.u. Therefore, at 0.35 s, the DC voltage of Method 2 drops to the locking value of the dual active bridge converter faster than Method 1. Under Method 3, due to the reduction of the output power of the voltage source converter at the moment of the fault, the DC voltage drops. As the transmission power of the dual active bridge converter decreases, the DC voltage quickly recovers. The DC voltage does not exceed the limit and the change range is also small. As Figure 7 (c) shows, the active powers of the voltage source converters of the three methods are close. However, as Figure 7 (e) shows, due to the DC voltage locking, the transmission powers of the dual active bridge converters of Method 1 and Method 2 drop sharply to nearly 0 and oscillate continuously, seriously affecting the safety of the electric vehicle charging circuit and the battery pack. Method 3 reduces the transmission power of the dual active bridge converter, but the maximum change amount is only 0.22 p.u. The present invention minimizes the change of the charging power while avoiding the over-limit of the DC voltage.

[0121] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit. Although the present invention has been described by referring to the preferred embodiments of the present invention, those of ordinary skill in the art should understand that various changes can be made in form and details without departing from the spirit and scope of the present invention defined by the appended claims.

Claims

1. A fault ride-through control method for an electric vehicle charging station taking into account both reactive power support and charging power, characterized in that: Applied to an electric vehicle charging station, the electric vehicle charging station adopts a dual active bridge converter and a voltage source converter to realize AC / DC conversion and charging control, and the method comprises the following steps: S101: Real-time collection of AC bus voltage, active and reactive power of the electric vehicle charging station before and after the power grid fault, and real-time detection of whether the AC bus voltage of the charging station drops below a preset voltage. If so, implementation of S102; S102: Compare whether the voltage amplitude of the AC busbar of the charging station is greater than the voltage threshold value that causes the AC current of the charging station to be limited. If so, implement S103; if not, implement S104; S103: The control of the dual active bridge converter remains unchanged, the voltage source converter adopts DC voltage and reactive power control, and the reactive power control reference value is set to Q1, until the AC bus voltage of the charging station is greater than the preset voltage, and S109 is implemented; S104: Calculating a fault limit clearing time to avoid a DC voltage exceeding a limit at the charging station according to the AC bus voltage of the charging station; S105: Compare the fault limit removal time with the main protection action time of the distribution network. If the fault limit removal time is less than the main protection action time, implement S106; otherwise, implement S107; S106: The voltage source converter adopts DC voltage and reactive power control, the reactive power reference value is set to 0, and the shift phase reference value of the dual active bridge converter is set to D f *, until the AC bus voltage of the charging station is greater than the preset voltage, implement S109; S107: The voltage source converter adopts active power and reactive power control, and the active power and reactive power reference values ​​are set to P2 and Q2. The dual-active active bridge converter control remains unchanged until the main protection is activated. It is detected whether the AC bus voltage is greater than the preset voltage. If so, S109 is implemented; if not, it indicates that the main protection refuses to operate, and S108 is implemented; S108: At the main protection action moment, the voltage source converter switches to DC voltage and reactive power control, the reactive power reference value is set to 0, and the dual active active bridge converter shift phase is set to D f *; S109: The voltage source converter adopts DC voltage and reactive power control, the reactive reference value is set to 0, the shift phase of the dual active bridge converter is set to the reference value before the fault, and the charging station fault ride-through ends; Where Q1 is the reactive power of the voltage source converter under the maximum allowable AC current constraint corresponding to the active power of the charging station before the fault, D f *In order to make the dual active bridge converter transfer power just reach the maximum active power shift of the voltage source converter under fault conditions, P2 and Q2 are the active power and reactive power at the intersection of the charging station power boundary constrained by the maximum allowable AC current and the charging station power boundary constrained by the DC voltage.

2. The fault ride-through control method for electric vehicle charging stations taking into account both reactive power support and charging power according to claim 1, characterized in that: In S102, the calculation method of the voltage threshold value AC bus that causes the AC current of the charging station to be limited includes: The maximum AC current value that the voltage source converter can withstand is calculated based on the product of the maximum allowable AC current coefficient of the voltage source converter and the rated AC current of the voltage source converter. According to the ratio of the active power of the charging station before the fault to the maximum AC current value that the voltage source converter can withstand, the voltage threshold value that causes the AC current of the charging station to be limited is calculated.

3. The fault ride-through control method for electric vehicle charging station taking into account both reactive power support and charging power according to claim 1, characterized in that: In S103, the calculation method of the reactive power under the maximum allowable AC current constraint of the voltage source converter corresponding to the active power of the charging station before the fault includes: The maximum instantaneous apparent power allowed to be output by the voltage source converter at the instant of the fault is calculated according to the product of the AC bus voltage amplitude at the instant of the fault, the maximum allowable AC current coefficient of the voltage source converter and the rated AC current of the voltage source converter; According to the square root of the difference between the square of the maximum instantaneous apparent power allowed to be output by the voltage source converter at the moment of fault and the square of the active power of the charging station before the fault, the reactive power under the maximum allowable AC current constraint of the voltage source converter corresponding to the active power of the charging station before the fault is calculated.

4. The electric vehicle charging station fault ride-through control method taking into account both reactive power support and charging power according to claim 1, characterized in that: In S104, the calculation method of the fault limit clearing time to avoid the DC voltage of the charging station exceeding the limit includes: According to the DC voltage reference value, the critical voltage of the dual active bridge converter locking, and the bus capacitance of the charging station, the energy difference released by the bus capacitance of the charging station from the DC voltage reference value to the critical voltage of the dual active bridge converter locking is calculated; The power output of the charging station at the maximum current is calculated based on the AC bus voltage amplitude at the moment of the fault, the maximum allowable AC current coefficient of the voltage source converter, the square of the rated AC current of the voltage source converter, and the total transmission power of the dual-active active bridge converter in the charging station under the fault; The fault limit clearing time for avoiding the DC voltage of the charging station from exceeding the limit is calculated based on the ratio of the energy difference released when the bus capacitor of the charging station is discharged from the DC voltage reference value to the critical voltage of the dual-active active bridge converter locking and the power output of the charging station at the maximum current.

5. The electric vehicle charging station fault ride-through control method taking into account both reactive power support and charging power according to claim 1, characterized in that: In S106, the calculation method of the shift phase ratio that makes the transmission power of the dual active bridge converter just reach the maximum active power of the voltage source converter under fault includes: According to the energy storage inductance of the dual active bridge converter, the switching frequency of the dual active bridge converter, and the ratio of the turns of the high-voltage side and the low-voltage side coils of the dual active bridge converter, the transmission power of the dual active bridge converter is calculated; The maximum active power of the voltage source converter is calculated based on the ohmic internal resistance of the electric vehicle battery, the constant voltage of the battery, the polarization voltage constant of the battery, the battery capacity, the amplitude of the voltage drop in the exponential region of the typical discharge curve of the battery and the inverse of the time constant, the battery charge state, and the number of electric vehicles in the charging station when the fault occurs; According to the transmission power of the dual-active active bridge converter and the maximum active power of the voltage source converter, the shift ratio that makes the transmission power of the dual-active active bridge converter just reach the maximum active power of the voltage source converter under fault is obtained by simultaneous solution.

6. The electric vehicle charging station fault ride-through control method taking into account both reactive power support and charging power according to claim 5, characterized in that: In S106, the calculation formula for the shift ratio that enables the dual active bridge converter to transmit power just reaching the maximum active power of the voltage source converter under fault conditions is expressed as: In the formula, In order to make the dual active bridge converter transmission power just reach the shift ratio of the maximum active power of the voltage source converter under fault, a1 is the first parameter, a2 is the second parameter, and a3 is the third parameter; is the DC voltage reference value; L r It is the energy storage inductor of the dual active bridge converter; is the switching frequency of the dual active bridge converter; n is the ratio of the number of turns of the high voltage side and the low voltage side coil of the dual active bridge converter; R ba is the ohmic internal resistance of the electric vehicle battery; E0 is the constant voltage of the battery; K is the polarization voltage constant of the battery; Q c is the battery capacity; A ba , B ba are the amplitude of the voltage drop in the exponential region of the typical discharge curve of the battery and the inverse of the time constant; soc i is the battery charge state of the i-th electric vehicle; N is the number of electric vehicles in the charging station when the fault occurs.

7. The fault ride-through control method for electric vehicle charging stations taking into account both reactive power support and charging power according to claim 1, characterized in that: In S107, the calculation method of the active power and reactive power at the intersection of the charging station power boundary constrained by the maximum allowed AC current and the charging station power boundary constrained by the DC voltage includes: According to the active power of the charging station before the fault, the DC voltage reference value, the critical voltage of the dual-active active bridge converter lockout, the bus capacitance of the charging station, and the main protection action time, the active power at the intersection of the charging station power boundary constrained by the maximum allowable AC current and the charging station power boundary constrained by the DC voltage is calculated; The reactive power at the intersection of the charging station power boundary constrained by the maximum allowable AC current and the charging station power boundary constrained by the DC voltage is calculated based on the AC bus voltage amplitude at the moment of fault, the maximum allowable AC current coefficient of the voltage source converter, the square of the rated AC current of the voltage source converter, and the arithmetic root of the square of the active power at the intersection of the charging station power boundary constrained by the maximum allowable AC current and the charging station power boundary constrained by the DC voltage.

8. The electric vehicle charging station fault ride-through control method taking into account both reactive power support and charging power according to claim 7, characterized in that: In S107, the calculation formula for active power and reactive power at the intersection of the charging station power boundary constrained by the maximum allowed AC current and the charging station power boundary constrained by the DC voltage is: Wherein, P2 is the active power at the intersection of the power boundary of the charging station constrained by the maximum allowed AC current and the power boundary of the charging station constrained by the DC voltage, Q2 is the reactive power at the intersection of the power boundary of the charging station constrained by the maximum allowed AC current and the power boundary of the charging station constrained by the DC voltage; P0 is the active power of the charging station before the fault; C is the bus capacitance of the charging station; is the DC voltage reference value; U dc,th is the critical voltage of the dual active bridge converter lockout; t1 is the main protection action time; U f K is the AC bus voltage amplitude at the moment of fault; I is the maximum allowable AC current coefficient of the voltage source converter; I N is the rated AC current of the voltage source converter.

9. A fault ride-through control device for an electric vehicle charging station that takes into account both reactive power support and charging power, characterized in that: include: Acquisition module, used to collect the AC bus voltage, active and reactive power of the electric vehicle charging station before and after the power grid fault; The first comparison module is used to compare the AC bus voltage. If the AC bus voltage drops below a preset voltage, the second comparison module is called. The second comparison module is used to compare the AC bus voltage amplitude of the charging station with the voltage threshold value that causes the AC current of the charging station to be limited. If the AC bus voltage amplitude of the charging station is greater than the voltage threshold value that causes the AC current of the charging station to be limited, the first control module is called, otherwise the first calculation module is called. In the first control module, the control of the dual active bridge converter remains unchanged, the voltage source converter adopts DC voltage and reactive power control, the reactive power control reference value is set to Q1, and the first comparison module is called and then the fourth control module is called; The first calculation module is used to calculate the fault limit removal time to avoid the DC voltage of the charging station exceeding the limit, and the third comparison module is called after the calculation is completed; A third comparison module is used to compare the fault limit removal time with the main protection action time of the distribution network, and if the fault limit removal time is less than the main protection action time, the second control module is called; Otherwise, calling the third control module; In the second control module, the voltage source converter adopts DC voltage and reactive power control, the reactive power reference value is set to 0, and the shift phase reference value of the dual active active bridge converter is set to D f *, and then call the fourth control module after calling the first comparison module; The third control module, the voltage source converter adopts active power and reactive power control, the active power and reactive power reference values ​​are set to P2 and Q2, the dual active active bridge converter control remains unchanged, and the fourth comparison module is called; The fourth comparison module is used to compare whether the AC bus voltage is less than the preset voltage at the time of the main protection action. If it is less than the preset voltage, the second control module is called, otherwise the fourth control module is called; The fourth control module, the voltage source converter adopts DC voltage and reactive power control, the reactive reference value is set to 0, and the shift phase of the dual active bridge converter is set to the reference value before the fault; Where Q1 is the reactive power of the voltage source converter under the maximum allowable AC current constraint corresponding to the active power of the charging station before the fault, D f *In order to make the dual active bridge converter transfer power just reach the maximum active power shift of the voltage source converter under fault conditions, P2 and Q2 are the active power and reactive power at the intersection of the charging station power boundary constrained by the maximum allowable AC current and the charging station power boundary constrained by the DC voltage.

10. An electric vehicle fault ride-through control device that takes into account both reactive power support and charging power, characterized in that: The invention comprises a processor, a memory and a computer program stored in the memory and configured to be executed by the processor. When executing the computer program, the processor implements the fault ride-through control method for an electric vehicle charging station taking into account both reactive support and charging power as described in any one of claims 1 to 8.

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