Low-voltage side fault ride-through control method and system based on LLC direct-current transformer

Abstract

The invention provides a low-voltage side fault ride-through control method and system based on an LLC direct-current transformer, and the method comprises the steps: forcibly adjusting a phase shift angle to be an angle lower limit value when an inter-electrode short-circuit fault occurs at a low-voltage side; amplitude limiting is carried out on the output voltage of the LLC direct-current transformer by adopting frequency conversion control, and amplitude limiting is carried out on the output current of the LLC direct-current transformer by adopting phase shift control; after the inter-electrode short circuit fault is eliminated, smoothly adjusting the phase shift angle from the angle lower limit value to the angle upper limit value, so that the voltage of the low-voltage side is recovered, the LLC direct-current transformer is automatically restarted, and fault ride-through is completed; according to the method and the system, the fault current can be quickly suppressed by forcibly shifting the phase to the angle lower limit value, and then the fault current can be controlled within a required range through phase-shifting control; and meanwhile, the capacitor voltage of the LLC direct current transformer is prevented from greatly dropping through frequency conversion control, and the smooth adjustment of the phase shift angle can enable the equipment to be quickly restarted, so that fault ride-through is realized, and the operation stability of the power distribution network is ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of direct current power distribution, and in particular relates to a low-voltage side fault ride-through control method and system based on an LLC direct current transformer. Background Art

[0002] With the construction of new power systems and the rapid development of power electronics technology, DC distribution networks have gradually become a research hotspot for industry scholars. Compared with traditional AC distribution networks, DC distribution networks have the advantages of high transmission efficiency, low loss, and applicability to various power sources and loads. They can also effectively avoid voltage fluctuations and flickers, frequency offsets, harmonic pollution, and other problems, further improving power quality and grid reliability. As the core equipment of DC distribution networks, DC power electronic transformers can achieve voltage changes, energy exchange, and electrical isolation between medium and low voltage DC distribution networks and low voltage DC microgrids. They can be widely used in places such as high penetration of new energy, concentrated multiple loads, high-quality electricity demand areas, and hub substations.

[0003] The topological structures of DC transformers mainly include DC transformer circuits based on MMC (Modular Multilevel Converter) and ISOP (Input Series Output Parallel) topologies. Current research and applications are mainly focused on ISOP topologies. Among them, ISOP topological subunits can adopt DAB (Dual Active Bridge Converter) structures, CLLC (Capacitive-Inductive-Lossless-Inductive) resonant structures, LLC (LC Resonant) resonant structures, etc. Based on the simple design of the resonant branch, the natural soft switching characteristics and the bidirectional power flow characteristics, LLC resonant DC transformers are selected as the research object.

[0004] The fault types of DC system are mainly divided into inter-pole short circuit fault, single-pole ground fault and short line fault, among which inter-pole short circuit fault is the most serious fault and will cause serious damage to the DC power distribution system. Since the LLC topology structure is equipped with supporting capacitors on both the high and low voltage sides, when a short circuit fault occurs on the low voltage side of the DC transformer, the capacitor discharges rapidly and the fault current rises sharply. The existing topology scheme cannot effectively limit the fault current and cannot meet the requirements of the power distribution system to quickly and accurately locate the fault point. In addition, the capacitor voltage drops sharply and needs to be recharged to complete the restart after the fault is cleared, which endangers the safety of the equipment itself and the stable operation of the DC system.

[0005] Therefore, a DC transformer low-voltage side fault ride-through control method is needed to maintain the stable operation of the DC distribution network and improve the load power supply reliability. Summary of the invention

[0006] In order to overcome the above-mentioned deficiencies of the prior art, the present invention proposes a low-voltage side fault ride-through control method based on an LLC DC transformer, comprising:

[0007] Based on the acquired operation data of the LLC DC transformer, determining whether an inter-pole short circuit fault occurs on the low voltage side of the LLC DC transformer;

[0008] When an inter-pole short circuit fault occurs on the low-voltage side of the LLC DC transformer, the phase shift angle of the LLC DC transformer is forced to be adjusted to the lower limit of the angle, and based on the operating data at the time of the inter-pole short circuit fault, the output voltage of the LLC DC transformer is limited by frequency conversion control, and the output current of the LLC DC transformer is limited by phase shift control until the inter-pole short circuit fault is eliminated;

[0009] After the inter-pole short-circuit fault is eliminated, the phase shift angle is smoothly adjusted from the angle lower limit value to the angle upper limit value, so that the low-voltage side voltage is restored, the LLC DC transformer automatically restarts, and the fault ride-through is completed.

[0010] Preferably, the operating data includes a low-voltage side output current and a low-voltage side output voltage;

[0011] The determining, based on the acquired operation data of the LLC DC transformer, whether an inter-pole short circuit fault occurs in the LLC DC transformer comprises:

[0012] When it is detected that the low-voltage side output current exceeds a preset fault current reference value, or the low-voltage side output voltage is lower than a preset fault voltage reference value, it is determined that an inter-pole short circuit fault occurs in the LLC DC transformer.

[0013] Preferably, the step of limiting the output voltage of the LLC DC transformer by using variable frequency control comprises:

[0014] Based on the low-voltage side output voltage in the operation data when there is an inter-pole short circuit fault, the difference between the fault voltage reference value and the low-voltage side output voltage is input into a variable frequency proportional integral controller;

[0015] Outputting the control frequency lower limit value of the LLC DC transformer through the variable frequency proportional integral controller;

[0016] The switching frequency of the LLC DC transformer is adjusted according to the lower limit of the control frequency to achieve amplitude limitation of the output voltage.

[0017] Preferably, the adopting phase shift control to limit the output current of the LLC DC transformer comprises:

[0018] Based on the low-voltage side output current in the operating data when there is an inter-pole short circuit fault, the difference between the fault current reference value and the low-voltage side output current is input into a phase-shifted proportional-integral controller;

[0019] Outputting the phase shift angle control value of the LLC DC transformer through the phase shift proportional integral controller;

[0020] The switching pulse of the LLC DC transformer is phase-shifted according to the phase-shift angle control value to achieve amplitude limitation of the output current.

[0021] Preferably, the lower limit value of the angle is 0°, and the upper limit value of the angle is 180°.

[0022] Preferably, the adjustment time for forcing the phase shift angle of the LLC DC transformer to be adjusted to the lower limit of the angle is less than 100 ms.

[0023] Preferably, it also includes:

[0024] If an inter-pole short circuit fault occurs on the high voltage side of the LLC DC transformer, the high voltage side uses the same frequency conversion control and phase shift control strategy as the low voltage side to complete the fault ride-through.

[0025] Based on the same inventive concept, the present invention also provides a low-voltage side fault ride-through control system based on an LLC DC transformer, comprising:

[0026] A judgment module, used for judging whether an inter-pole short circuit fault occurs on the low-voltage side of the LLC DC transformer based on the acquired operation data of the LLC DC transformer;

[0027] A ride-through control module, configured to force the phase shift angle of the LLC DC transformer to be adjusted to a lower limit value when an inter-pole short circuit fault occurs on the low-voltage side of the LLC DC transformer, and to limit the output voltage of the LLC DC transformer by frequency conversion control and limit the output current of the LLC DC transformer by phase shift control based on the operating data at the time of the inter-pole short circuit fault, until the inter-pole short circuit fault is eliminated;

[0028] The restart control module is used to smoothly adjust the phase shift angle from the lower limit value to the upper limit value after the inter-pole short circuit fault is eliminated, so that the low-voltage side voltage is restored, the LLC DC transformer is automatically restarted, and the fault ride-through is completed.

[0029] Preferably, the operating data includes a low-voltage side output current and a low-voltage side output voltage; and the judgment module is specifically used for:

[0030] When it is detected that the low-voltage side output current exceeds a preset fault current reference value, or the low-voltage side output voltage is lower than a preset fault voltage reference value, it is determined that an inter-pole short circuit fault occurs in the LLC DC transformer.

[0031] Preferably, the crossing control module is specifically used for:

[0032] Based on the low-voltage side output voltage in the operation data when there is an inter-pole short circuit fault, the difference between the fault voltage reference value and the low-voltage side output voltage is input into a variable frequency proportional integral controller;

[0033] Outputting the control frequency lower limit value of the LLC DC transformer through the variable frequency proportional integral controller;

[0034] The switching frequency of the LLC DC transformer is adjusted according to the lower limit of the control frequency to achieve amplitude limitation of the output voltage.

[0035] Preferably, the crossing control module is specifically used for:

[0036] Based on the low-voltage side output current in the operating data when there is an inter-pole short circuit fault, the difference between the fault current reference value and the low-voltage side output current is input into a phase-shifted proportional-integral controller;

[0037] Outputting the phase shift angle control value of the LLC DC transformer through the phase shift proportional integral controller;

[0038] The switching pulse of the LLC DC transformer is phase-shifted according to the phase-shift angle control value to achieve amplitude limitation of the output current.

[0039] Preferably, the lower limit value of the angle is 0°, and the upper limit value of the angle is 180°.

[0040] Preferably, the adjustment time for forcing the phase shift angle of the LLC DC transformer to be adjusted to the lower limit of the angle is less than 100 ms.

[0041] Preferably, it also includes:

[0042] The high-voltage side control module is used to adopt the same frequency conversion control and phase shift control strategy as the low-voltage side to complete the fault ride-through of the high-voltage side when an inter-pole short circuit fault occurs on the high-voltage side of the LLC DC transformer.

[0043] Based on the same inventive concept, the present invention also provides a computer device, including: one or more processors;

[0044] A memory for storing one or more programs;

[0045] When the one or more programs are executed by the one or more processors, a low-voltage side fault ride-through control method based on an LLC DC transformer as described above is implemented.

[0046] Based on the same inventive concept, the present invention also provides a computer-readable storage medium on which a computer program is stored. When the computer program is executed, a low-voltage side fault ride-through control method based on an LLC DC transformer as described above is implemented.

[0047] Compared with the closest prior art, the present invention has the following beneficial effects:

[0048] The present invention provides a low-voltage side fault ride-through control method and system based on an LLC DC transformer, comprising: judging whether an inter-pole short circuit fault occurs on the low-voltage side of the LLC DC transformer based on the acquired operation data of the LLC DC transformer; when an inter-pole short circuit fault occurs on the low-voltage side of the LLC DC transformer, forcing the phase shift angle of the LLC DC transformer to be adjusted to a lower limit of the angle, and based on the operation data at the time of the inter-pole short circuit fault, using frequency conversion control to limit the output voltage of the LLC DC transformer, and using phase shift control to limit the output current of the LLC DC transformer, until The inter-pole short-circuit fault is eliminated; after the inter-pole short-circuit fault is eliminated, the phase shift angle is smoothly adjusted from the lower limit value of the angle to the upper limit value of the angle, so that the voltage on the low-voltage side is restored, and the LLC DC transformer is automatically restarted to complete the fault ride-through; this method and system can quickly suppress the fault current by forcing the phase shift to the lower limit value of the angle, and then the fault current can be controlled within the required range through phase shift control; at the same time, frequency conversion control is used to avoid a sharp drop in the capacitor voltage of the LLC DC transformer. After the fault is eliminated, the operation of smooth adjustment of the phase shift angle can realize rapid re-commissioning of the equipment, thereby realizing fault ride-through and ensuring the stability of the distribution network operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 A schematic flow chart of a low-voltage side fault ride-through control method based on an LLC DC transformer provided by the present invention;

[0050] Figure 2 A schematic diagram of the LLC DC transformer topology provided by the present invention;

[0051] Figure 3 The frequency conversion control block diagram provided by the present invention;

[0052] Figure 4 The phase shift control block diagram provided by the present invention;

[0053] Figure 5 A schematic diagram of the control pulse of the LLC DC transformer with variable frequency control provided by the present invention;

[0054] Figure 6 A schematic diagram of the control pulse of the phase-shift controlled LLC DC transformer provided by the present invention;

[0055] Figure 7 A low voltage side fault ride-through timing diagram provided by the present invention;

[0056] Figure 8 A schematic diagram of the structure of a low-voltage side fault ride-through control system based on an LLC DC transformer provided by the present invention;

[0057] Fig. 9 The present invention provides a schematic diagram of the structure of an electronic device. DETAILED DESCRIPTION

[0058] The specific implementation modes of the present invention are further described in detail below with reference to the accompanying drawings.

[0059] Embodiment 1:

[0060] The present invention provides a low-voltage side fault ride-through control method based on LLC DC transformer, such as Figure 1 As shown, including:

[0061] A1. Based on the acquired operation data of the LLC DC transformer, determine whether an inter-pole short circuit fault occurs on the low-voltage side of the LLC DC transformer;

[0062] A2. When an inter-pole short circuit fault occurs on the low-voltage side of the LLC DC transformer, the phase shift angle of the LLC DC transformer is forced to be adjusted to the lower limit of the angle, and based on the operating data at the time of the inter-pole short circuit fault, the output voltage of the LLC DC transformer is limited by frequency conversion control, and the output current of the LLC DC transformer is limited by phase shift control until the inter-pole short circuit fault is eliminated;

[0063] A3. After the inter-pole short-circuit fault is eliminated, the phase shift angle is smoothly adjusted from the lower limit value to the upper limit value, so that the voltage on the low-voltage side is restored, the LLC DC transformer automatically restarts, and the fault ride-through is completed.

[0064] Considering that when a short circuit fault occurs on the low-voltage side of the DC transformer, the existing topology scheme cannot effectively limit the fault current, and cannot maintain the fault current at 1.15-1.35pu for a period of time to meet the requirements of the distribution system to quickly and accurately locate the fault point, and the capacitor voltage drops sharply, and needs to be recharged after the fault is cleared to complete the restart. The present invention can quickly suppress the fault current by forcing the phase shift to the lower limit of the angle, and then the fault current can be controlled within the required range through phase shift control. Specifically, through the current limiting reactance and adjustment control strategy in the LLC DC transformer, the fault current can be effectively suppressed from rising, and the fault current can be maintained at 1.15-1.35pu, so as to achieve fault location; at the same time, the capacitor voltage of the LLC DC transformer is prevented from dropping sharply through frequency conversion control. After the fault is eliminated, the low-voltage side capacitor voltage can be quickly increased to a given value in combination with the smooth adjustment of the phase shift angle, so as to achieve rapid re-investment of the equipment, thereby achieving fault crossing and ensuring the stability of the distribution network operation.

[0065] The present invention is mainly based on LLC resonant transformer, that is, LLC DC transformer, whose topology is as follows Figure 2 As shown. The DC transformer consists of N subunits connected in series on the high-voltage side and in parallel on the low-voltage side. Each subunit contains an SC (Series Capacitor) module and an LLC module. Among them, the SC module consists of an IGBT half-bridge Q11 / Q12, and the LLC module consists of a high-voltage side full bridge S1~S4, an isolation transformer T, a low-voltage side full bridge S5~S8, a resonant capacitor Cr, a resonant inductor Lr, an excitation inductor Lm, and a support capacitor Cs / Cp. The high-voltage side terminal voltage u of the isolation transformer T k1 , low voltage side voltage u k2 A current limiting reactance L1 and L2 are respectively configured on the high voltage side and the low voltage side to suppress the current rising speed at the moment of the fault, which can effectively limit the fault current peak value, and realize fault location and fault crossing in conjunction with the control strategy provided by the present invention.

[0066] An inter-pole short circuit fault refers to a fault condition in which a low-impedance path is accidentally formed between two or more electrodes that should not be directly connected in an electrical device for some reason, resulting in an abnormal increase in current. When an inter-pole short circuit fault occurs on the low-voltage side of an LLC DC transformer, the current on the secondary side will rise sharply, which may exceed the design limit and damage the components in the converter, such as switching devices, inductors, capacitors, etc. Due to the surge in current, the components on the transformer and circuit board may heat up rapidly, causing thermal damage; at the same time, the output voltage will be reduced, and the normal operating voltage cannot be provided to the load.

[0067] In this embodiment, the operation data includes the low-voltage side output current and the low-voltage side output voltage; when judging the inter-electrode short circuit fault in the above A1, it may include:

[0068] When it is detected that the output current on the low voltage side exceeds a preset fault current reference value, or the output voltage on the low voltage side is lower than a preset fault voltage reference value, it is determined that an inter-pole short circuit fault occurs in the LLC DC transformer.

[0069] In this embodiment, in order to prevent the capacitor voltage of the LLC DC transformer from dropping significantly, the output voltage of the LLC DC transformer is limited by frequency conversion control in A2, which may include:

[0070] Based on the low-voltage side output voltage in the operation data when the inter-pole short circuit fault occurs, the difference between the fault voltage reference value and the low-voltage side output voltage is input into the variable frequency proportional integral controller;

[0071] Output the control frequency lower limit value of LLC DC transformer through variable frequency proportional integral controller;

[0072] The switching frequency of the LLC DC transformer is adjusted according to the lower limit value of the control frequency to achieve the limitation of the output voltage.

[0073] In this embodiment, in order to effectively suppress the rise of the fault current and maintain the fault current at 1.15-1.35 pu, when the output current of the LLC DC transformer is limited by phase shift control in the above A2, it may include:

[0074] Based on the low-voltage side output current in the operating data during the inter-pole short-circuit fault, the difference between the fault current reference value and the low-voltage side output current is input into the phase-shift proportional-integral controller;

[0075] The phase shift angle control value of the LLC DC transformer is outputted through a phase shift proportional integral controller;

[0076] The switching pulses of the LLC DC transformer are phase-shifted according to the phase-shift angle control value to achieve output current limitation.

[0077] Specifically, the DC transformer LLC module is configured with both frequency conversion control and phase shift control, such as Figure 3 As shown, the variable frequency control takes the output voltage as the control target, the fault voltage reference value Vo_ref is subtracted from the actual output voltage Vo1, and the LLC control frequency F1_ref is generated by the PI proportional integral controller. By controlling this frequency, the output voltage and power control can be achieved;

[0078] Figure 4 A phase shift control is given with output current as the control target, 1.25pu as the given fault current reference value, the difference between the fault current reference value and the actual output current value Idc, and the high and low voltage side H-bridge phase shift angle θ, i.e. theta, is generated through the PI controller. By controlling this angle, the power transmission from the high voltage side to the low voltage side can be controlled.

[0079] When the system is operating normally, because the actual output current is less than the given fault current reference value, the phase shift control PI output θ is the upper limit value 180°, and the phase shift control output is at the upper limit value. At this time, the H-bridge IGBT switching frequency is adjusted by frequency conversion control to achieve the purpose of output voltage and power regulation. The switching frequency = 1 / Ts, Ts is the switching period, and its control pulse is as follows Figure 5 When an inter-pole short circuit fault occurs in the low-voltage DC bus, the output voltage Vo1 is less than the voltage set value, that is, the fault voltage reference value Vo_ref, and the frequency conversion control output is at the lower limit. At the same time, due to the rapid increase in the fault current, the PI output θ is quickly limited to the lower limit of 0°, which can quickly suppress the fault current. Subsequently, the PI regulator is used to limit the fault current limit within the required range. Its control pulse is as follows: Figure 6 shown.

[0080] In this embodiment, it also includes:

[0081] If an inter-pole short circuit fault occurs on the high-voltage side of the LLC DC transformer, the high-voltage side uses the same frequency conversion control and phase shift control strategy as the low-voltage side to complete the fault ride-through.

[0082] from Figure 5 and Figure 6 It can be seen from the control pulse diagram that the two control methods are compatible with each other for the high and low voltage side H-bridge (S1~S4) IGBT control, without the need for additional control strategy switching, thus shortening the fault current limiting delay.

[0083] In this embodiment, the lower limit of the angle is 0° and the upper limit of the angle is 180°. When the fault disappears, there is no need to switch the device re-investment strategy. It is only necessary to control the phase shift angle θ to gradually increase from 0 to 180° to achieve output voltage reconstruction and device restart.

[0084] If the fault is a transient fault, after the fault disappears, the control strategy can achieve rapid recovery of the low-voltage side voltage and restart the equipment; if the fault is a permanent fault, after the fault is located, the equipment will be locked out. The control flow chart is as follows: Figure 7 As shown in the figure, the process of determining permanent fault is:

[0085] When the low-voltage side output current Io1 is detected, Figure 4 The Idc in the fault current exceeds the preset fault current reference value I1, or the low voltage side output voltage Vo1 is lower than the preset fault voltage reference value U1. Figure 3When Vo_ref in is reached, it is determined to be an inter-pole short circuit fault, and the above-mentioned fault ride-through control process is executed. After a delay of 100ms, it is determined whether the voltage on the low-voltage side is restored. If it is restored, that is, the output voltage Vo1 is greater than the normal voltage lower limit U2, normal frequency conversion control and phase shift control are performed. If it is not restored, the fault ride-through control process is continued with a delay of 100ms, and the judgment is repeated 3 times. If the voltage is still not restored after 3 delays, it is determined that the current fault is a permanent fault and the lock is executed.

[0086] In this embodiment, when the phase shift angle is smoothly adjusted from the lower limit value to the upper limit value in the above A3, it may specifically include:

[0087] Use a closed-loop control system, such as a PID (proportional-integral-derivative) controller or similar control algorithm, to gradually increase the phase shift angle. The controller adjusts the phase shift angle based on the difference between the actual value of the low-voltage side voltage and the target value.

[0088] Or set a slope to control the speed at which the phase shift angle increases. This ensures smooth adjustment of the phase shift angle and avoids sudden changes that may impact the system. The slope can be preset or dynamically adjusted based on the characteristics and requirements of the system.

[0089] A low-pass filter is applied to the control signal to remove any high frequency noise or jitter, ensuring smooth adjustment of the phase shift angle.

[0090] In this embodiment, the adjustment time for forcing the phase shift angle of the LLC DC transformer to be adjusted to the lower limit of the angle is less than 100 ms.

[0091] The present invention can use the current-limiting reactance to suppress the fault current rising rate when an inter-pole short-circuit fault occurs on the low-voltage side; at the same time, a low-voltage side fault ride-through control strategy is provided, which can not only realize fault ride-through, control the fault current within the required range, realize fault location, but also realize fault current limiting in other faults; finally, a low-voltage side transient fault re-throw strategy is provided, which can realize rapid re-throw of equipment after a fault.

[0092] Embodiment 2:

[0093] Based on the same inventive concept, the present invention also provides a low-voltage side fault ride-through control system based on LLC DC transformer, such as Figure 8 As shown, including:

[0094] A judgment module, used to judge whether an inter-pole short circuit fault occurs on the low-voltage side of the LLC DC transformer based on the acquired operation data of the LLC DC transformer;

[0095] A ride-through control module is used to force the phase shift angle of the LLC DC transformer to be adjusted to the lower limit value when an inter-pole short circuit fault occurs on the low-voltage side of the LLC DC transformer, and based on the operating data at the time of the inter-pole short circuit fault, use frequency conversion control to limit the output voltage of the LLC DC transformer and use phase shift control to limit the output current of the LLC DC transformer until the inter-pole short circuit fault is eliminated;

[0096] The restart control module is used to smoothly adjust the phase shift angle from the lower limit value to the upper limit value after the inter-pole short-circuit fault is eliminated, so that the voltage on the low-voltage side is restored, the LLC DC transformer is automatically restarted, and the fault ride-through is completed.

[0097] In this embodiment, the operation data includes the low-voltage side output current and the low-voltage side output voltage; the judgment module is specifically used for:

[0098] When it is detected that the output current on the low voltage side exceeds a preset fault current reference value, or the output voltage on the low voltage side is lower than a preset fault voltage reference value, it is determined that an inter-pole short circuit fault occurs in the LLC DC transformer.

[0099] In this embodiment, the crossing control module is specifically used for:

[0100] Based on the low-voltage side output voltage in the operation data when the inter-pole short circuit fault occurs, the difference between the fault voltage reference value and the low-voltage side output voltage is input into the variable frequency proportional integral controller;

[0101] Output the control frequency lower limit value of LLC DC transformer through variable frequency proportional integral controller;

[0102] The switching frequency of the LLC DC transformer is adjusted according to the lower limit value of the control frequency to achieve the limitation of the output voltage.

[0103] In this embodiment, the crossing control module is specifically used for:

[0104] Based on the low-voltage side output current in the operating data during the inter-pole short-circuit fault, the difference between the fault current reference value and the low-voltage side output current is input into the phase-shift proportional-integral controller;

[0105] The phase shift angle control value of the LLC DC transformer is outputted through a phase shift proportional integral controller;

[0106] The switching pulses of the LLC DC transformer are phase-shifted according to the phase-shift angle control value to achieve output current limitation.

[0107] In this embodiment, the lower limit of the angle is 0°, and the upper limit of the angle is 180°.

[0108] In this embodiment, the adjustment time for forcing the phase shift angle of the LLC DC transformer to be adjusted to the lower limit of the angle is less than 100 ms.

[0109] In this embodiment, it also includes:

[0110] The high-voltage side control module is used to complete the fault ride-through on the high-voltage side by adopting the same frequency conversion control and phase shift control strategy as the low-voltage side when an inter-pole short circuit fault occurs on the high-voltage side of the LLC DC transformer.

[0111] Example 3

[0112] like Fig. 9 As shown, the present invention also provides an electronic device, which may be a computer device, a single-chip device, an intelligent mobile device, etc. The electronic device in this embodiment may include a processor, a memory, a transceiver component, etc. The memory, the processor, and the transceiver component are connected via a bus; the memory may be used to store an execution program, and an exemplary execution program may include instructions; the processor is used to execute the instructions stored in the memory. The memory may also be used to store data, which may be called and / or modified when the instructions are executed.

[0113] The processor may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc. It is the computing core and control core of the terminal, which is suitable for implementing one or more instructions, specifically suitable for loading and executing one or more instructions in a storage medium to implement corresponding method processes or corresponding functions, so as to implement the steps of a low-voltage side fault ride-through control method based on an LLC DC transformer in the above-mentioned embodiment.

[0114] Example 4

[0115] Based on the same inventive concept, the present invention also provides a readable storage medium, specifically an electronic device readable storage medium (Memory), which is a memory device in an electronic device for storing programs and data. It can be understood that the storage medium here can include both built-in storage media in electronic devices and, of course, extended storage media supported by electronic devices. The storage medium provides a storage space, which stores the operating system of the terminal. In addition, one or more instructions suitable for being loaded and executed by a processor are also stored in the storage space, and these instructions can be one or more execution programs (including program codes). It should be noted that the storage medium here can be a high-speed RAM memory or a non-volatile memory, such as at least one disk memory. The processor loads and executes one or more instructions stored in the storage medium, which can implement the steps of a low-voltage side fault ride-through control method based on an LLC DC transformer in the above embodiment.

[0116] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0117] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0118] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1A function specified in one or more boxes.

[0119] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0120] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit its protection scope. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that after reading the present invention, those skilled in the art can still make various changes, modifications or equivalent substitutions to the specific implementation methods of the application, but these changes, modifications or equivalent substitutions are all within the protection scope of the claims of the present invention.

Claims

1. A low-voltage side fault ride-through control method based on LLC DC transformer, characterized in that: include: Based on the acquired operation data of the LLC DC transformer, determining whether an inter-pole short circuit fault occurs on the low voltage side of the LLC DC transformer; When an inter-pole short circuit fault occurs on the low-voltage side of the LLC DC transformer, the phase shift angle of the LLC DC transformer is forced to be adjusted to the lower limit of the angle, and based on the operating data at the time of the inter-pole short circuit fault, the output voltage of the LLC DC transformer is limited by frequency conversion control, and the output current of the LLC DC transformer is limited by phase shift control until the inter-pole short circuit fault is eliminated; After the inter-pole short-circuit fault is eliminated, the phase shift angle is smoothly adjusted from the angle lower limit value to the angle upper limit value, so that the low-voltage side voltage is restored, the LLC DC transformer automatically restarts, and the fault ride-through is completed.

2. The method according to claim 1, characterized in that The operation data includes the low-voltage side output current and the low-voltage side output voltage; The determining, based on the acquired operation data of the LLC DC transformer, whether an inter-pole short circuit fault occurs in the LLC DC transformer comprises: When it is detected that the low-voltage side output current exceeds a preset fault current reference value, or the low-voltage side output voltage is lower than a preset fault voltage reference value, it is determined that an inter-pole short circuit fault occurs in the LLC DC transformer.

3. The method according to claim 2, characterized in that The method of limiting the output voltage of the LLC DC transformer by using frequency conversion control includes: Based on the low-voltage side output voltage in the operation data when there is an inter-pole short circuit fault, the difference between the fault voltage reference value and the low-voltage side output voltage is input into a variable frequency proportional integral controller; Outputting the control frequency lower limit value of the LLC DC transformer through the variable frequency proportional integral controller; The switching frequency of the LLC DC transformer is adjusted according to the lower limit of the control frequency to achieve amplitude limitation of the output voltage.

4. The method according to claim 2 or 3, characterized in that The method of limiting the output current of the LLC DC transformer by using phase shift control includes: Based on the low-voltage side output current in the operating data when there is an inter-pole short circuit fault, the difference between the fault current reference value and the low-voltage side output current is input into a phase-shifted proportional-integral controller; Outputting the phase shift angle control value of the LLC DC transformer through the phase shift proportional integral controller; The switching pulse of the LLC DC transformer is phase-shifted according to the phase-shift angle control value to achieve amplitude limitation of the output current.

5. The method according to any one of claims 1 to 3, characterized in that: The lower limit value of the angle is 0°, and the upper limit value of the angle is 180°.

6. The method according to any one of claims 1 to 3, characterized in that: The adjustment time for forcing the phase shift angle of the LLC DC transformer to be adjusted to the lower limit of the angle is less than 100 ms.

7. The method according to any one of claims 1 to 3, characterized in that: Also includes: If an inter-pole short circuit fault occurs on the high voltage side of the LLC DC transformer, the high voltage side uses the same frequency conversion control and phase shift control strategy as the low voltage side to complete the fault ride-through.

8. A low voltage side fault ride-through control system based on LLC DC transformer, characterized in that: include: A judgment module, used for judging whether an inter-pole short circuit fault occurs on the low-voltage side of the LLC DC transformer based on the acquired operation data of the LLC DC transformer; A ride-through control module, configured to force the phase shift angle of the LLC DC transformer to be adjusted to a lower limit value when an inter-pole short circuit fault occurs on the low-voltage side of the LLC DC transformer, and to limit the output voltage of the LLC DC transformer by frequency conversion control and limit the output current of the LLC DC transformer by phase shift control based on the operating data at the time of the inter-pole short circuit fault, until the inter-pole short circuit fault is eliminated; The restart control module is used to smoothly adjust the phase shift angle from the lower limit value to the upper limit value after the inter-pole short circuit fault is eliminated, so that the low-voltage side voltage is restored, the LLC DC transformer is automatically restarted, and the fault ride-through is completed.

9. An electronic device, characterized in that: include: at least one processor and memory; The memory and the processor are connected via a bus; The memory is used to store one or more programs; When the one or more programs are executed by the at least one processor, a low-voltage side fault ride-through control method based on an LLC DC transformer as described in any one of claims 1 to 7 is implemented.

10. A readable storage medium, characterized in that: An execution program is stored thereon, and when the execution program is executed, a low-voltage side fault ride-through control method based on an LLC DC transformer as described in any one of claims 1 to 7 is implemented.

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