Direct-current charging starting method and system of SLCC, computer device and medium

Abstract

The application relates to a direct-current charging starting method, system, computer equipment and medium of an SLCC. The direct-current charging starting method controls the direct-current bus voltage of the SLCC to rise to a preset target voltage through a voltage rising curve, so that the SVF is subjected to the charging starting of the direct-current side of the terminal LCC. In order to ensure that the bridge arm full-bridge sub-modules of the SVF are subjected to the charging of the direct-current side of the terminal LCC to the direct-current voltage level that can be unlocked and operated, the active voltage equalization charging control is used to meet the voltage equalization requirement of the three-phase bridge arm in the SVF, so that the SLCC direct-current system has the target of supporting the operation of an island power grid. Meanwhile, the charging needs of the SLCC direct-current transmission system starting and the SLCC re-put-in process after the SVF is withdrawn from the island power grid are met.

Description

Technical Field

[0001] This invention relates to the field of active charging technology for converters, specifically to a DC charging start-up method, system, computer equipment, and medium for SLCC. Background Technology

[0002] The Statcom and Line Commutation Converter (SLCC) technology connects a Static Var Filter (SVF) between a six-pulse (or twelve-pulse) Line Commutation Converter (LCC) and the converter transformer. The SVF replaces the AC filter / parallel capacitor bank in conventional DC transmission, compensating for the reactive power consumed by the LCC and the harmonic current generated by the LCC, saving converter station space and reducing converter transformer noise and losses. The SVF is connected to the converter transformer valve side via a reactor. The SVF topology is a three-phase star connection without grounding or a delta connection. Its converter chain consists of multiple links (sub-modules) connected in series. The sub-module structure is an H-shaped full-bridge structure, such as... Figure 1 As shown in the diagram.

[0003] When SLCC DC transmission systems are used in large-scale power transmission environments, they are often connected to a stable AC power grid. In this case, the SVF startup process can directly draw energy from the AC power grid via the converter transformer, and charge the full-bridge submodule capacitors of the three-phase bridge arms of the SVF through three-phase symmetrical AC power, enabling the SVF to have the ability to connect to the system and unlock compensation functions. However, when SLCC DC systems are used in islanded grid environments or weak AC power grids, there is no stable AC power grid before the SLCC starts up, so the SVF cannot be charged and started through three-phase symmetrical AC power.

[0004] The AC grid charging start-up technology for SVF is quite mature and widely used in the charging start-up process of high-voltage chain-type modular multilevel converters. However, there is still no detailed research on the starting process of SVF with charging energy provided by the DC side of LCC without the support of a stable AC grid. The lack of a mature DC charging start-up method has become a technical challenge that needs to be overcome for the application of SLCC DC systems in islanded grid environments. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention proposes a DC charging start-up method, system, computer equipment, and medium for SLCC.

[0006] The first invention provides a DC charging start-up method for SLCC, the method comprising: When the sending-end LCC converter valve and the receiving-end LCC converter valve in the SLCC are connected, the DC bus voltage of the SLCC is controlled to rise according to the voltage rise curve based on the DC bus voltage in the current cycle and the target voltage to be used in the current cycle. When the DC bus voltage rises, the power module capacitor of the SVF in the SLCC is uncontrolled charged based on the triggering cycle of the receiving end LCC converter valve. Based on the firing angle of the LCC converter valve at the sending end and the preset target voltage, the DC bus voltage is controlled within the preset voltage range, and the power module capacitor continues to be actively charged. Based on the current DC bus voltage and the preset module unlocking voltage, active voltage equalization charging control is performed on the power module capacitor to realize the DC charging start of the SLCC.

[0007] Optionally, the step of controlling the DC bus voltage of the SLCC to rise according to the voltage rise curve based on the DC bus voltage in the current cycle and the target voltage to be used in the current cycle includes: Based on the DC bus voltage and the target voltage to be used in the current cycle, the firing angle of the sending-end LCC converter valve is generated using a firing angle generation strategy. Based on the firing angle of the LCC converter valve at the sending end, the DC bus voltage of the SLCC is controlled to rise according to the voltage rise curve, so that the DC bus voltage of the SLCC reaches the preset target voltage.

[0008] Optionally, the voltage rise curve is generated in the following ways: The minimum value of the preset target voltage is obtained based on the lowest unlocking voltage of the power module in the SVF and the number of modules in each phase arm of the SVF. Based on the boosting capability of the LCC converter valve at the sending end and the power grid system conditions, the maximum value of the preset target voltage is obtained; Based on the minimum and maximum values ​​of the preset target voltage, select the preset target voltage corresponding to the DC bus voltage; The voltage rise curve is generated based on the preset target voltage and the rise parameters within a single cycle.

[0009] Optionally, the rise parameters include voltage difference and rise time; The step of generating the voltage rise curve based on the preset target voltage and the rise parameters within a single cycle includes: Based on the voltage requirement of the reverse cut-off of the switching tube in the receiving-end LCC converter valve, the voltage difference of the periodic decrease of the DC bus voltage is obtained. Based on the maximum inrush current allowed by the SVF during charging, the maximum rate of rise of the DC bus voltage during periodic increase is obtained. Based on the maximum rise rate, the maximum voltage difference and minimum rise time of the periodic rise are obtained; Based on the periodically decreasing voltage difference, the periodically increasing maximum voltage difference, the minimum rise time, and the preset target voltage, a preset DC bus voltage rise curve is obtained.

[0010] Optionally, the uncontrolled charging of the power module capacitor of the SVF in the SLCC based on the triggering cycle of the receiving-end LCC converter valve includes: Based on the control cycle of the trigger angle change in the sending-end LCC converter valve, the trigger cycle of the receiving-end LCC converter valve is obtained. Based on the triggering cycle of the receiving-end LCC converter valve, the timing sequence is controlled according to a preset cycle to control the conduction of two-phase bridge arms in different combinations of the receiving-end LCC converter valve, so that the two-phase bridge arms in different combinations of the receiving-end LCC converter valve and the two-phase bridge arms in the SVF form a charging circuit, and the power module capacitor of the SVF in the SLCC is uncontrolled charged through the charging circuit.

[0011] Optionally, controlling the DC bus voltage within a preset voltage range based on the firing angle of the sending-end LCC converter valve and a preset target voltage includes: When the DC bus voltage reaches the preset target voltage, the firing angle of the sending-end LCC converter valve is controlled based on the triggering period, so that the DC bus voltage fluctuates periodically within the preset voltage range.

[0012] Optionally, the active voltage equalization charging control of the power module capacitor based on the current DC bus voltage and the preset module unlocking voltage includes: After the voltage of the power module capacitor is greater than or equal to the preset module unlocking voltage, based on the current DC bus voltage and the rated voltage of the sub-modules of the SVF, the minimum number of sub-modules put into each phase arm of the SVF and the maximum number of sub-modules removed from each phase arm are obtained. Based on the minimum number of submodules put into each phase arm and the maximum number of submodules removed from each phase arm, the number of submodules removed from each phase arm in a single triggering cycle is obtained. Based on the number of sub-modules removed, the capacitor of the power module is actively charged; During active charging, the power module capacitors are charged using voltage equalization control based on the voltages of all sub-modules in the SVF.

[0013] Optionally, the step of performing voltage equalization control charging on the power module capacitor based on the voltages of all sub-modules in the SVF includes: Sort the voltages of all submodules in the SVF to obtain the voltage sorting result; Based on the voltage sorting results, the minimum number of sub-modules connected to each phase arm, and the current direction of the cascaded sub-module valve string in the SVF, the power module capacitors are charged using voltage equalization control.

[0014] A second aspect of the present invention also provides a DC charging start-up system for SLCC, the system comprising: A voltage rise control unit is used to control the rise of the DC bus voltage of the SLCC according to the voltage rise curve when the sending-end LCC converter valve and the receiving-end LCC converter valve are connected. This control is based on the DC bus voltage in the current cycle and the target voltage to be used in the current cycle. A power module capacitor charging unit is used to perform uncontrolled charging of the power module capacitor of the SVF in the SLCC based on the triggering cycle of the receiving end LCC converter valve when the DC bus voltage rises. The DC bus voltage control unit is used to control the DC bus voltage within a preset voltage range based on the firing angle of the sending-end LCC converter valve and the preset target voltage, and to continue to actively charge the power module capacitor. The active voltage equalization charging control unit is used to perform active voltage equalization charging control on the power module capacitor based on the current DC bus voltage and the preset module unlocking voltage, so as to realize the DC charging start of the SLCC.

[0015] Optionally, the voltage rise control unit is specifically used for: Based on the DC bus voltage and the target voltage to be used in the current cycle, the firing angle of the sending-end LCC converter valve is generated using a firing angle generation strategy. Based on the firing angle of the LCC converter valve at the sending end, the DC bus voltage of the SLCC is controlled to rise according to the voltage rise curve, so that the DC bus voltage of the SLCC reaches the preset target voltage.

[0016] Optionally, the system further includes: a voltage rise curve generation unit; the voltage rise curve generation unit includes: The minimum value determination module is used to obtain the minimum value of the preset target voltage based on the lowest unlocking voltage of the power module in the SVF and the number of modules in each phase arm of the SVF. The maximum value determination module is used to obtain the maximum value of the preset target voltage based on the boosting capability of the sending-end LCC converter valve and the power grid system conditions. A preset target voltage determination module is used to select a preset target voltage corresponding to the DC bus voltage based on the minimum and maximum values ​​of the preset target voltage. The voltage rise curve generation module is used to generate the voltage rise curve based on the preset target voltage and the rise parameters within a single cycle.

[0017] Optionally, the rise parameters include voltage difference and rise time; The voltage rise curve generation module is specifically used for: Based on the voltage requirement of the reverse cut-off of the switching tube in the receiving-end LCC converter valve, the voltage difference of the periodic decrease of the DC bus voltage is obtained. Based on the maximum inrush current allowed by the SVF during charging, the maximum rate of rise of the DC bus voltage during periodic increase is obtained. Based on the maximum rise rate, the maximum voltage difference and minimum rise time of the periodic rise are obtained; Based on the periodically decreasing voltage difference, the periodically increasing maximum voltage difference, the minimum rise time, and the preset target voltage, a preset DC bus voltage rise curve is obtained.

[0018] Optionally, the power module capacitor charging unit is used for: Based on the control cycle of the trigger angle change in the sending-end LCC converter valve, the trigger cycle of the receiving-end LCC converter valve is obtained. Based on the triggering cycle of the receiving-end LCC converter valve, the timing sequence is controlled according to a preset cycle to control the conduction of two-phase bridge arms in different combinations of the receiving-end LCC converter valve, so that the two-phase bridge arms in different combinations of the receiving-end LCC converter valve and the two-phase bridge arms in the SVF form a charging circuit, and the power module capacitor of the SVF in the SLCC is uncontrolled charged through the charging circuit.

[0019] Optionally, the DC bus voltage control unit is specifically used for: When the DC bus voltage reaches the preset target voltage, the firing angle of the sending-end LCC converter valve is controlled based on the triggering period, so that the DC bus voltage fluctuates periodically within the preset voltage range.

[0020] Optionally, the active voltage equalization charging control unit includes: The submodule quantity parameter determination module is used to determine the minimum number of submodules to be engaged in each phase arm of the SVF and the maximum number of submodules to be disconnected in each phase arm of the SVF based on the current DC bus voltage and the rated voltage of the submodules of the SVF after the voltage of the power module capacitor is greater than or equal to the preset module unlocking voltage. The module for determining the number of submodules to be cut is used to determine the number of submodules to be cut in each phase arm within a single triggering cycle based on the minimum number of submodules to be put into each phase arm and the maximum number of submodules to be cut in each phase arm. An active charging module is used to actively charge the capacitor of the power module based on the number of cut sub-modules. The voltage equalization control charging module is used to perform voltage equalization control charging on the power module capacitor based on the voltage of all sub-modules in the SVF during active charging.

[0021] Optionally, the voltage equalization control charging module is specifically used for: Sort the voltages of all submodules in the SVF to obtain the voltage sorting result; Based on the voltage sorting results, the minimum number of sub-modules connected to each phase arm, and the current direction of the cascaded sub-module valve string in the SVF, the power module capacitors are charged using voltage equalization control.

[0022] A third aspect of the present invention also provides a computing device, comprising: one or more processors; A processor is used to execute one or more programs; When the one or more programs are executed by the one or more processors, a DC charging startup method for an SLCC as described above is implemented.

[0023] A third aspect of the present invention also provides a computer-readable storage medium having a computer program stored thereon, wherein when the computer program is executed, it implements a DC charging start-up method for an SLCC as described above.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a DC charging startup method, system, computer equipment, and medium for SLCC. The DC charging startup method controls the DC bus voltage of the SLCC to rise to a preset target voltage through a voltage rise curve, which enables the SVF receiver-end LCC DC side to start charging. To ensure that the SVF bridge arm submodules are charged to the receiver-end LCC DC side to a DC voltage level that allows for unlocking and operation, active voltage equalization charging control is used to meet the phase-to-phase voltage balance requirements of the SVF three-phase bridge arm, enabling the SLCC DC system to support the operation of an islanded power grid. At the same time, it meets the charging needs of the SLCC DC transmission system startup and the SLCC reconnection process after the SVF is removed in the islanded power grid. Attached Figure Description

[0025] Figure 1 A flowchart of a DC charging start-up method for SLCC provided by the present invention; Figure 2A schematic diagram of the voltage rise parameter within a single cycle, provided by the present invention; Figure 3 A schematic diagram of an SLCC system topology provided by the present invention; Figure 4 A schematic diagram of a voltage rise curve provided by the present invention; Figure 5 A schematic diagram illustrating the periodic fluctuation of DC bus voltage provided by the present invention; Figure 6 This invention provides a schematic diagram of a charging circuit formed by LCC valve phase sequence switching; Figure 7 This invention provides a schematic diagram of a charging circuit formed by LCC valve phase sequence switching; Figure 8 This invention provides a schematic diagram of a charging circuit formed by LCC valve phase sequence switching; Figure 9 A schematic diagram of voltage and current during the DC charging startup process of an SVF via an LCC, provided by an embodiment of the present invention; Figure 10 A block diagram of a DC charging start-up system for SLCC provided by the present invention; Figure 11 A schematic diagram of a control system for starting an SVF via LCC DC charging, provided by the present invention; Figure 12 A block diagram of a computer device provided by the present invention. Detailed Implementation

[0026] Example 1: Figure 1 A flowchart of a DC charging start-up method for SLCC provided by the present invention is shown below. Figure 1 As shown, the method may include the following steps 101 to 104: In step 101, when the sending-end LCC converter valve and the receiving-end LCC converter valve in the SLCC are connected, the DC bus voltage of the SLCC is controlled to rise according to the voltage rise curve based on the DC bus voltage in the current cycle and the target voltage to be used in the current cycle.

[0027] In step 102, when the DC bus voltage rises, the power module capacitor of the SVF in the SLCC is uncontrolled charged based on the triggering cycle of the receiving-end LCC converter valve.

[0028] In step 103, based on the firing angle of the LCC converter valve at the sending end and the preset target voltage, the DC bus voltage is controlled within the preset voltage range, and the power module capacitor continues to be actively charged.

[0029] In step 104, based on the current DC bus voltage and the preset module unlocking voltage, active voltage equalization charging control is performed on the power module capacitor to realize the DC charging start of the SLCC.

[0030] The voltage rise curve can be divided into a rising phase and a steady phase. Based on the triggering cycle of the receiving-end LCC converter valve, the rising phase of the voltage rise curve can be further divided into multiple periodic rising phases, with the triggering cycle as the time unit. Figure 2 As shown, each rising phase of the cycle includes a periodically rising voltage difference, a rising time, and a periodically falling voltage difference. The periodically falling voltage difference can be understood as the decrease in DC bus voltage that causes the receiving-end LCC converter valve to shut off naturally within a single cycle. The periodically rising voltage difference can be understood as the increase in DC bus voltage within a single cycle. During the rising process, the receiving-end LCC converter valve is triggered to close. The periodically rising voltage difference is greater than the periodically falling voltage difference. The rising time can be understood as the time it takes for the DC bus voltage to rise from its minimum value to its maximum value (i.e., the target voltage to be used in the current cycle) within a single cycle. When the DC bus voltage reaches the preset target voltage, the voltage rise curve enters the stable stage. By controlling the firing angle of the sending-end LCC converter valve to maintain a periodic change, the voltage difference in rise and voltage difference in a single cycle are equal, thus controlling the DC bus voltage within the preset voltage range. During this period, according to the preset periodic control sequence, the closing of two-phase bridge arm valves in different combinations of the receiving-end LCC converter valve and the periodic conduction of two-phase bridge arms in different combinations of the SVF are controlled respectively, so as to perform uncontrolled charging or active charging of the power module capacitors of the SVF.

[0031] It should be noted that when the SLCC DC system is applied to islanded power grids and large-scale renewable energy island transmission systems, the charging and startup process of the SVF differs from the conventional three-phase symmetrical AC charging and startup process. It requires charging and startup via the LCC DC side. To ensure that the SVF bridge arm submodules are charged to the unlockable DC voltage level via the LCC DC side and to meet the phase-to-phase voltage balance requirements of the SVF three-phase bridge arm, so that the SLCC DC system can support the operation of islanded power grids, a startup method for SVF charging via the LCC DC side is proposed. The entire process is stable and reliable, and can meet the charging needs of the SLCC DC transmission system startup and the re-engagement process after the SVF is removed in the islanded power grid.

[0032] SLCC system topology as follows Figure 3As shown, the SLCC DC transmission system includes the sending-end LCC rectifier converter valve (i.e., the sending-end LCC converter valve), the sending-end pole line circuit breaker Q11, the receiving-end pole line circuit breaker Q12, the receiving-end LCC inverter converter valve (i.e., the receiving-end LCC converter valve), and the receiving-end LCC parallel SVF converter valve, which are in the conventional DC transmission system. The AC side of the sending-end LCC rectifier converter valve can be connected to the external power grid. The DC side of the sending-end LCC rectifier converter valve can be connected to the DC side of the receiving-end LCC inverter converter valve through the sending-end pole line circuit breaker Q11 and the receiving-end pole line circuit breaker Q12. The AC side of the receiving-end LCC inverter converter valve can be connected to the SVF converter valve and the external three-phase AC power grid. The topology of the SVF converter valve can be a three-phase star connection without grounding or a delta connection.

[0033] The SVF converter valve can include three bridge arms, each of which can be formed by multiple sub-modules connected in series. These sub-modules can be H-shaped full-bridge sub-modules, and the switching transistors constituting the H-shaped full-bridge sub-modules can be fully controlled power electronic devices such as IGBTs (Insulated-Gate Bipolar Transistors). Both the sending-end LCC rectifier converter valve and the receiving-end LCC inverter converter valve include six or twelve bridge arms, each of which can be formed by switching transistors connected in series. These switching transistors can be semi-controlled power electronic devices such as thyristors. Figure 3 In a six-pulse LCC converter valve, T1, T2, T3, T4, T5, and T6 can be switching transistors, and Udc can be the DC bus voltage.

[0034] The above Figure 1 Possible implementations of step 101 shown may include the following steps 1011 to 1012: In step 1011, based on the DC bus voltage and the target voltage to be used in the current cycle, the firing angle of the sending-end LCC converter valve is generated using a firing angle generation strategy.

[0035] In step 1012, based on the firing angle of the LCC converter valve at the sending end, the DC bus voltage of the SLCC is controlled to rise according to the voltage rise curve, so that the DC bus voltage of the SLCC reaches the preset target voltage.

[0036] It should be noted that by collecting the DC bus voltage and the target voltage to be used in the current cycle, the firing angle of the sending-end LCC converter valve is adjusted using the feedback control strategy in the firing angle generation strategy. Thus, by generating the firing angle of the sending-end LCC converter valve, the DC bus voltage can be made to rise along the rising trajectory given by the voltage rise curve, and finally the DC bus voltage will rise to the preset target voltage.

[0037] The generation of the voltage rise curve in step 1012 above may include the following steps S1 to S2: In step S1, the minimum value of the preset target voltage is obtained based on the lowest unlocking voltage of the power module in the SVF and the number of modules in each phase arm of the SVF.

[0038] In step S2, the maximum value of the preset target voltage is obtained based on the boosting capability of the sending-end LCC converter valve and the power grid system conditions.

[0039] In step S3, based on the minimum and maximum values ​​of the preset target voltage, the preset target voltage corresponding to the DC bus voltage is selected.

[0040] In step S4, the voltage rise curve is generated based on the preset target voltage and the rise parameter within a single cycle.

[0041] The rise parameters include voltage difference and rise time.

[0042] It should be noted that the rise parameters corresponding to each rise stage in the voltage rise curve are fixed. As long as the rise parameters within one cycle are determined, the voltage rise curve can be generated by setting the target voltage and the rise parameters.

[0043] Possible implementations of step S4 above may include the following steps S41 to S44: In step S41, the voltage difference of the DC bus voltage that periodically decreases is obtained based on the voltage requirement of the reverse cut-off of the switching tube in the receiving-end LCC converter valve.

[0044] In step S42, the maximum rate of increase of the DC bus voltage during the periodic rise is obtained based on the maximum inrush current allowed by the SVF during the charging process.

[0045] In step S43, based on the maximum rise rate, the maximum voltage difference and minimum rise time of the periodic rise are obtained.

[0046] In step S44, a preset DC bus voltage rise curve is obtained based on the periodically decreasing voltage difference, the periodically increasing maximum voltage difference, the minimum rise time, and the preset target voltage.

[0047] The above Figure 1 Possible implementations of step 102 shown may include the following steps 1021 to 1022: In step 1021, the triggering period of the receiving-end LCC converter valve is obtained based on the control cycle of the triggering angle change in the sending-end LCC converter valve.

[0048] In step 1022, based on the triggering cycle of the receiving-end LCC converter valve, the two-phase bridge arms of different combinations in the receiving-end LCC converter valve are controlled to conduct according to the preset cycle control sequence, so that the two-phase bridge arms of different combinations in the receiving-end LCC converter valve and the two-phase bridge arms in the SVF form a charging circuit, and the power module capacitor of the SVF in the SLCC is uncontrolled charged through the charging circuit.

[0049] The above Figure 1 A possible implementation of step 103 shown may include: when the DC bus voltage reaches a preset target voltage, controlling the firing angle of the sending-end LCC converter valve based on the triggering period, so that the DC bus voltage fluctuates periodically within the preset voltage range.

[0050] The above Figure 1 Possible implementations of step 104 shown may include the following steps 1041 to 1044: In step 1041, after the voltage of the power module capacitor is greater than or equal to the preset module unlocking voltage, based on the current DC bus voltage and the rated voltage of the sub-modules of the SVF, the minimum number of sub-modules put into each phase arm of the SVF and the maximum number of sub-modules removed from each phase arm are obtained.

[0051] In step 1042, the number of submodules removed from each phase arm in a single triggering cycle is obtained based on the minimum number of submodules put into operation per phase arm and the maximum number of submodules removed per phase arm.

[0052] In step 1043, the power module capacitor is actively charged based on the number of sub-modules removed.

[0053] In step 1044, during the active charging process, the power module capacitor is charged using voltage equalization control based on the voltages of all sub-modules in the SVF.

[0054] Possible implementations of step 1044 above may include: sorting the voltages of all submodules in the SVF to obtain a voltage sorting result; and performing voltage equalization control charging on the power module capacitor based on the voltage sorting result, the minimum number of submodules connected to each phase arm, and the current direction of the cascaded submodule valve string in the SVF.

[0055] Furthermore, in the above Figure 1 After step 104 shown, the method may further include: when the voltage of the power module capacitor is greater than or equal to the preset module rated voltage and the SLCC polarity control is enabled, generating an unlock command to control the SVF compensation function to unlock, so that the SFV enters normal operation mode.

[0056] There is no mature DC charging start-up method for SLCC in the existing technology. For example, the flexible DC converter valve charging method and control system with application number 202010652717.X describes in detail the uncontrolled and controlled charging control methods of the full-half hybrid modular multilevel converter valve, so that the voltage of all full-half bridge sub-modules in the converter valve can reach the charging set value, with small imbalance, effectively solving the charging problem when the hybrid flexible DC converter valve is put into operation online. However, the charging process of this patent needs to rely on the AC power grid and focuses on the control method of sub-module voltage balancing during the charging process, without mentioning how to draw energy from the DC side to start up the process and control method.

[0057] The patent application number 202310434698.7 describes a startup test method, system, and electronic equipment for a high-voltage direct-connected energy storage system. This patent solves the SVG startup logic problem of a 35kV high-voltage direct-connected energy storage system. The first preset method described in this patent provides a detailed design of the startup charging steps for the SVG mode of the chain-type high-voltage energy storage converter, specifies the composition of the charging circuit, and completes the charging and unlocking process of the DC capacitor of the power unit. However, the charging circuit described in this patent also relies on the AC power grid for power supply and does not describe a method for starting the converter of the direct-connected energy storage when there is no stable AC power grid.

[0058] A startup method for an offshore wind power DC transmission system, application number 202110752626.8, solves the reliability and stability issues of the startup process of the overall system where offshore wind power is transmitted to the onshore AC power grid via DC submarine cable. In the first step of the patent, the offshore flexible DC converter valve is charged via the DC side of the onshore converter station, which is similar to the process of SVF being charged via LCC DC voltage. However, the flexible DC converter valve is an MMC topology structure with a DC port, which can successfully charge the power module capacitor voltage to the rated voltage via DC voltage to unlock the control function of the offshore flexible DC converter valve. In contrast, the chain SVF topology has no DC port, which is very different from the patent. Therefore, the method of starting the offshore flexible DC valve via DC charging cannot be directly adopted.

[0059] To ensure stable and reliable startup and operation of SLCC in islanded power grids, this invention provides a startup method for SVF in an SLCC DC system via LCC DC charging, based on the aforementioned SLCC DC transmission system. The specific charging startup method includes: Closed circuit breaker Q11 , Q12 Based on the DC bus voltage and target voltage in the current cycle, a firing angle generation strategy is used to control the firing angle of the LCC converter valve at the sending end, gradually raising the DC bus voltage to the preset target voltage according to the preset voltage rise curve. U dc .

[0060] During the DC bus voltage rise process, the control end LCC converter valve turns on the corresponding thyristor in turn, and forms a charging path in turn with the two-phase bridge arms with different combinations of SVF connected in parallel on the inverter side of the control end LCC converter valve.

[0061] Through the charging circuit, the capacitors of the two-phase bridge arm power modules with different SVF combinations are charged uncontrolled in turn until the voltage of each bridge arm module reaches the preset unlocking voltage. U dc_c1 .

[0062] Once the DC bus voltage reaches the preset voltage, the firing angle of the LCC converter valve at the sending end is controlled to stabilize the DC bus voltage at the preset target voltage according to the preset voltage curve. U dc Nearby; at the same time, keep the receiving end LCC converter valve in turn conducting the corresponding position thyristor to ensure that the charging circuit of each two phases of the three-phase bridge arm is conducted in turn.

[0063] The SVF power module is unlocked and enters the active charging process. Active voltage equalization control is activated, and the charging circuit charges each pair of SVF bridge arms alternately until the SVF power module voltage reaches the preset rated voltage. U dc_cN .

[0064] Once the SVF bridge arm module voltage reaches the rated voltage, the SVF completes the DC charging startup process via LCC and waits for the function unlock command to enter normal operation mode.

[0065] The first step mentioned above includes: based on the minimum unlock voltage of the SVF module. U dc_thr Determine the minimum preset target voltage for the DC bus based on the number N of single-phase bridge arm modules. Based on the LCC boost capacity at the sending end and the grid system conditions, determine the maximum preset target voltage U of the DC bus. dc_max Select the preset target voltage to which the DC bus voltage needs to be raised. ,and Considering that the receiving-end LCC needs to alternately turn on the thyristors to form a charging circuit, the voltage difference Δ of the periodic decrease in DC bus voltage is determined based on the voltage requirement for the reverse cut-off of the thyristors of the receiving-end LCC converter valve. U dc_down According to the maximum allowable inrush current during SVF charging. I charge_max Determine the maximum rate of rise of the DC bus voltage during periodic increases. k rate_max Determine the preset DC bus voltage rise curve (with Figure 4(For example); gradually change the firing angle of the LCC converter valve at the sending end to control the DC bus voltage to rise periodically to the preset target voltage according to the preset voltage rise curve. U dc The periodically rising voltage difference Δ U dc_up1 and rise time t up_1 It is necessary to ensure that the DC voltage rise rate within the cycle is not greater than k rate_max The number of periodic rises during the DC voltage rise process must be a multiple of 3 to ensure that the voltage at the valve terminals of the three-phase bridge arms is balanced after the uncontrolled charging of the SVF is completed.

[0066] The second step mentioned above includes: determining the triggering period T of the receiving-end LCC based on the control cycle of the LCC firing angle change at the sending end; coordinating with the periodic rise of the DC bus voltage, triggering the receiving-end LCC thyristors T1 / T4, T3 / T6, and T2 / T5 to conduct in pairs at period T, forming a charging circuit as follows: Figure 6 , 7 As shown in Figure 8; when the DC bus voltage decreases periodically by Δ... U dc_down When the thyristors T1 / T4, T3 / T6, and T2 / T5 are turned off in reverse, they will automatically be turned off.

[0067] The third step mentioned above includes: Within each cycle T, when the receiving-end LCC thyristors T1 / T4, T3 / T6, and T2 / T5 are turned on, the A / B, B / C, and C / A phase sub-modules of each pair of SVF bridge arms take turns performing uncontrolled charging; when the thyristors T1 / T4, T3 / T6, and T2 / T5 are automatically reverse-biased and turned off, the uncontrolled charging of the SVF bridge arm modules in this cycle ends; when the DC voltage rise ends, the voltage of each bridge arm module is not less than the preset unlocking voltage (i.e., the preset module unlocking voltage). U dc_c1 .

[0068] The fourth step mentioned above includes: controlling the firing angle of the LCC converter valve at the sending end to cause the DC bus voltage to fluctuate periodically, such as... Figure 5 As shown, the fluctuation period is T, and the peak value of the DC bus voltage fluctuation is... U dc The periodically increasing voltage difference Δ U dc_up2 =Δ U dc_down Rise time t up_2 The DC voltage rise rate within the cycle must not exceed k. rate_maxDuring the DC voltage fluctuation, the number of periodic rises must be a multiple of 3 to ensure that the three-phase bridge arm valve terminal voltages are balanced after the SVF controllable charging is completed. During the periodic fluctuation of the DC bus voltage, the receiving end LCC continuously triggers the corresponding group of thyristors to turn on and off in turn according to the method described in step 2, forming an active charging circuit for the SVF bridge arm.

[0069] The fifth step above includes: based on the DC bus voltage U dc Rated voltage of SVF bridge arm submodule U dc_cN Calculate the minimum number of submodules M that can be engaged per phase of the SVF, and determine the maximum number of submodules NM that can be disconnected per phase; disconnect P submodules per phase within each cycle T, and continue charging 2*(NP) submodules to ensure that the charging current during the active charging process of the SVF does not exceed I charge_max After sorting the voltage sampling values ​​of all submodules in each phase of the SVF, and combining the current direction of the cascaded submodule valve series and the number M of submodules put into operation, the removed submodules and put-in submodules are rotated within each bridge arm to determine the specific M submodules to be put into operation. Based on the determined specific M submodules to be put into operation, a submodule modulation signal is generated to complete the voltage equalization process of the modules within the active charging bridge arm.

[0070] The sixth step mentioned above includes: real-time sampling of the voltage of all SVF submodules. U dc_c Determine that all voltages are not less than U dc_cN Then, a signal indicating that SVF charging is complete and the function is ready to be unlocked is sent to the LCC polar controller.

[0071] For example, step 1 specifically includes: Taking a certain SLCC DC project as an example, on the DC side, the LCC rectifier valve is controlled by the sending end to gradually increase the DC voltage at the receiving end to 180kV. The DC voltage increases stepwise in stages with a 2.2s cycle, increasing by 2.4kV per cycle, and reaches 180kV after 75 cycles (165s). During the increase, within the 2.2s cycle, the DC voltage increases at a slope of 72kV / s from 0-100ms, remains constant from 100-200ms, and decreases by 4.8kV at 200ms, maintaining this voltage until 2.2s. The single-cycle waveform is as follows: Figure 2 As shown, the waveform during the DC voltage rise process is as follows: Figure 4 .

[0072] Step 2 specifically includes: Taking a certain three-cycle rotation as an example: From 34.1 to 34.2 seconds, transistors T1 and T4 are triggered to conduct, causing the DC side voltage to rise to 38.4 kV and remain there for 0.1 seconds. During this time, transistors T1 and T4 conduct, forming a charging circuit with the AB phase bridge arm of the SVF. Figure 6 As shown; from 34.3 to 35.8 seconds, the DC side voltage drops to 33.6 kV, causing the sum of the voltages of the AB phase bridge arm submodules of the SVF to exceed the DC side voltage, and transistors T1 and T4 are turned off due to reverse voltage.

[0073] From 36.3 to 36.4 seconds, transistors T3 and T6 are triggered, causing the DC side voltage to rise to 40.8 kV and remain there for 0.1 seconds. At this time, transistors T3 and T6 conduct, forming a charging circuit with the BC phase bridge arm of the SVF. Figure 7 As shown; 36.5-38s, with the DC side voltage dropping to 36kV, the sum of the voltages of the BC phase bridge arm submodules of the SVF is greater than the DC side voltage, and transistors T3 and T6 are turned off due to reverse voltage.

[0074] From 38.5 to 38.6 seconds, transistors T5 and T2 are triggered, causing the DC side voltage to rise to 43.2 kV and remain there for 0.1 seconds. At this time, transistors T5 and T2 conduct, forming a charging circuit with the CA phase bridge arm of the SVF. Figure 8 As shown; 38.7-40.2s, with the DC side voltage dropping to 38.4kV, the sum of the voltages of the CA phase bridge arm submodules of the SVF is greater than the DC side voltage, causing transistors T5 and T2 to be turned off due to reverse voltage.

[0075] Step 3 specifically includes: In a complete LCC three-phase switching cycle described in step 2, there are three uncontrolled charging processes for paired SVF bridge arm submodules. Each phase switching increases the DC voltage by ΔUdc (2.4kV) compared to the previous phase. After 33 phase sequence switchings, with the DC voltage rising to 79.2kV over 72.6s, the uncontrolled charging of the SVF allows the submodule voltage to reach above 500V, enabling the module to autonomously switch off under valve control. The phase sequence continues to switch, for a total of 75 switchings, with the DC voltage rising to and holding at 180kV over 165s. The SVF submodule voltage reaches above 1.2kV, completing the uncontrolled charging and meeting the conditions for controlled charging.

[0076] Step 4 specifically includes: The DC voltage remained between 175.2kV and 180kV with a period of 2.3 seconds after 165s, and the waveform during this period was as follows. Figure 5 As shown, the LCC continues to maintain phase sequence rotation as described in step 2, forming a charging circuit with the two phase arms of the corresponding SVF.

[0077] Step 5 specifically includes: After 165 seconds, the controlled charging process begins. The SVF gradually disconnects some of the sub-modules with the highest voltage to raise their voltage to the rated operating voltage. Simultaneously, during this process, an active voltage equalization strategy is implemented based on the module voltage ranking to ensure that the voltage deviation of each sub-module remains within a set range, thus enabling the converter valve to transition from the charging state to the normal unlocked standby state. Throughout the entire charging process, the charging inrush current is less than 130A. Figure 9 As shown.

[0078] Compared with existing technologies, this invention closes the DC bus circuit breaker and alternately conducts the corresponding thyristors of the receiving-end LCC converter valve, forming a charging circuit with the SVF converter valve of the SLCC. By controlling the sending-end LCC converter valve to gradually increase the DC bus voltage, the SVF converter valve of the converter station is gradually charged uncontrolledly and actively. After the SVF converter valve of the converter station is fully charged, it can provide grid voltage support for isolated power grids and large-scale renewable energy island transmission systems, making the startup of isolated power grids feasible. This invention provides a feasible solution for the startup of isolated renewable energy transmission systems via SLCC and the re-entry of SLCCs after their removal from isolated power grids. Furthermore, the startup method of this invention can also be applied to normal startup conditions of SLCC DC transmission systems. Verification during implementation shows that the startup method of SVF charging via the DC side of this invention is stable and reliable, without system overvoltage or overcurrent faults, and has wide applicability.

[0079] Example 2: Figure 10 The present invention provides a frame for a DC charging start-up system for SLCC, such as... Figure 10 As shown, the system may include: A voltage rise control unit is used to control the rise of the DC bus voltage of the SLCC according to the voltage rise curve when the sending-end LCC converter valve and the receiving-end LCC converter valve are connected. This control is based on the DC bus voltage in the current cycle and the target voltage to be used in the current cycle. A power module capacitor charging unit is used to perform uncontrolled charging of the power module capacitor of the SVF in the SLCC based on the triggering cycle of the receiving end LCC converter valve when the DC bus voltage rises. The DC bus voltage control unit is used to control the DC bus voltage within a preset voltage range based on the firing angle of the sending-end LCC converter valve and the preset target voltage, and to continue to actively charge the power module capacitor. The active voltage equalization charging control unit is used to perform active voltage equalization charging control on the power module capacitor based on the current DC bus voltage and the preset module unlocking voltage, so as to realize the DC charging start of the SLCC.

[0080] Optionally, the voltage rise control unit is specifically used for: Based on the DC bus voltage and the target voltage to be used in the current cycle, the firing angle of the sending-end LCC converter valve is generated using a firing angle generation strategy. Based on the firing angle of the LCC converter valve at the sending end, the DC bus voltage of the SLCC is controlled to rise according to the voltage rise curve, so that the DC bus voltage of the SLCC reaches the preset target voltage.

[0081] Optionally, the system further includes: a voltage rise curve generation unit; the voltage rise curve generation unit includes: The minimum value determination module is used to obtain the minimum value of the preset target voltage based on the lowest unlocking voltage of the power module in the SVF and the number of modules in each phase arm of the SVF. The maximum value determination module is used to obtain the maximum value of the preset target voltage based on the boosting capability of the sending-end LCC converter valve and the power grid system conditions. A preset target voltage determination module is used to select a preset target voltage corresponding to the DC bus voltage based on the minimum and maximum values ​​of the preset target voltage. The voltage rise curve generation module is used to generate the voltage rise curve based on the preset target voltage and the rise parameters within a single cycle.

[0082] Optionally, the rise parameters include voltage difference and rise time; The voltage rise curve generation module is specifically used for: Based on the voltage requirement of the reverse cut-off of the switching tube in the receiving-end LCC converter valve, the voltage difference of the periodic decrease of the DC bus voltage is obtained. Based on the maximum inrush current allowed by the SVF during charging, the maximum rate of rise of the DC bus voltage during periodic increase is obtained. Based on the maximum rise rate, the maximum voltage difference and minimum rise time of the periodic rise are obtained; Based on the periodically decreasing voltage difference, the periodically increasing maximum voltage difference, the minimum rise time, and the preset target voltage, a preset DC bus voltage rise curve is obtained.

[0083] Optionally, the power module capacitor charging unit is used for: Based on the control cycle of the trigger angle change in the sending-end LCC converter valve, the trigger cycle of the receiving-end LCC converter valve is obtained. Based on the triggering cycle of the receiving-end LCC converter valve, the timing sequence is controlled according to a preset cycle to control the conduction of two-phase bridge arms in different combinations of the receiving-end LCC converter valve, so that the two-phase bridge arms in different combinations of the receiving-end LCC converter valve and the two-phase bridge arms in the SVF form a charging circuit, and the power module capacitor of the SVF in the SLCC is uncontrolled charged through the charging circuit.

[0084] Optionally, the DC bus voltage control unit is specifically used for: When the DC bus voltage reaches the preset target voltage, the firing angle of the sending-end LCC converter valve is controlled based on the triggering period, so that the DC bus voltage fluctuates periodically within the preset voltage range.

[0085] Optionally, the active voltage equalization charging control unit includes: The submodule quantity parameter determination module is used to determine the minimum number of submodules to be engaged in each phase arm of the SVF and the maximum number of submodules to be disconnected in each phase arm of the SVF based on the current DC bus voltage and the rated voltage of the submodules of the SVF after the voltage of the power module capacitor is greater than or equal to the preset module unlocking voltage. The module for determining the number of submodules to be cut is used to determine the number of submodules to be cut in each phase arm within a single triggering cycle based on the minimum number of submodules to be put into each phase arm and the maximum number of submodules to be cut in each phase arm. An active charging module is used to actively charge the capacitor of the power module based on the number of cut sub-modules. The voltage equalization control charging module is used to perform voltage equalization control charging on the power module capacitor based on the voltage of all sub-modules in the SVF during active charging.

[0086] Optionally, the voltage equalization control charging module is specifically used for: Sort the voltages of all submodules in the SVF to obtain the voltage sorting result; Based on the voltage sorting results, the minimum number of sub-modules connected to each phase arm, and the current direction of the cascaded sub-module valve string in the SVF, the power module capacitors are charged using voltage equalization control.

[0087] SVF start-up control system via LCC DC charging, such as Figure 11 As shown, the control system includes: The uncontrolled charging control module is used to close circuit breakers Q11 and Q12 to perform uncontrolled charging of the SVF until the voltage of all sub-modules in the SVF converter valve reaches the preset unlocking voltage U. dc_c1 .

[0088] The sending-end LCC boost module is used to generate the thyristor firing angle of the sending-end LCC converter valve during uncontrolled charging, and control the DC bus voltage to gradually and periodically rise to the preset target voltage according to the preset voltage rise curve.

[0089] The sending-end LCC voltage regulator module is used to generate the thyristor firing angle of the sending-end LCC converter valve during active charging, and control the DC bus voltage to fluctuate periodically near the preset target voltage according to the preset voltage fluctuation curve.

[0090] The receiving-end LCC converter valve conduction module is used to periodically generate thyristor trigger signals to control the receiving-end LCC thyristors T1 / T4, T3 / T6, and T2 / T5 to periodically conduct in pairs. The SVF active charging module generates modulation signals for the sub-modules during active charging, switches the charging and discharging states of the sub-modules, and ultimately ensures that the voltage of all SVF sub-modules reaches the preset rated voltage U. dc_cN Furthermore, the module voltages are basically the same.

[0091] The voltage monitoring module is used to acquire the voltage of each submodule in real time.

[0092] Example 3: Based on the same inventive concept, the present invention also provides a computer device, such as... Figure 12 As shown, the computer device includes a processor and a memory. The memory stores a computer program, which includes program instructions. The processor executes the program instructions stored in the computer storage medium. The processor may be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing and control core of the terminal, and is suitable for implementing one or more instructions. Specifically, it is suitable for loading and executing one or more instructions in the computer storage medium to implement the corresponding method flow or corresponding function, so as to implement the steps of the DC charging start-up method of an SLCC in the above embodiment.

[0093] Example 4: Based on the same inventive concept, this invention also provides a storage medium, specifically a computer-readable storage medium (Memory), which is a memory device in a computer device used to store programs and data. It is understood that the computer-readable storage medium here can include both the built-in storage medium in the computer device and extended storage media supported by the computer device. The computer-readable storage medium provides storage space that stores the terminal's operating system. Furthermore, this storage space also stores one or more instructions suitable for loading and execution by a processor. These instructions can be one or more computer programs (including program code). It should be noted that the computer-readable storage medium here can be high-speed RAM or non-volatile memory, such as at least one disk storage device. The processor can load and execute one or more instructions stored in the computer-readable storage medium to implement the steps of the DC charging startup method for an SLCC in the above embodiments.

[0094] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied 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.

[0095] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0096] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxesFigure 1 The function specified in one or more boxes.

[0097] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0098] The above are merely embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of the claims of the present invention pending approval.

Claims

1. A DC charging start-up method for SLCC, characterized in that, The method includes: When the sending-end LCC converter valve and the receiving-end LCC converter valve in the SLCC are connected, the DC bus voltage of the SLCC is controlled to rise according to the voltage rise curve based on the DC bus voltage in the current cycle and the target voltage to be used in the current cycle. When the DC bus voltage rises, the power module capacitor of the SVF in the SLCC is uncontrolled charged based on the triggering cycle of the receiving end LCC converter valve. Based on the firing angle of the LCC converter valve at the sending end and the preset target voltage, the DC bus voltage is controlled within the preset voltage range, and the power module capacitor continues to be actively charged. Based on the current DC bus voltage and the preset module unlocking voltage, active voltage equalization charging control is performed on the power module capacitor to realize the DC charging start of the SLCC.

2. The method according to claim 1, characterized in that, The step of controlling the DC bus voltage of the SLCC to rise according to the voltage rise curve, based on the DC bus voltage and the target voltage to be used in the current cycle, includes: Based on the DC bus voltage and the target voltage to be used in the current cycle, the firing angle of the sending-end LCC converter valve is generated using a firing angle generation strategy. Based on the firing angle of the LCC converter valve at the sending end, the DC bus voltage of the SLCC is controlled to rise according to the voltage rise curve, so that the DC bus voltage of the SLCC reaches the preset target voltage.

3. The method according to claim 2, characterized in that, The voltage rise curve is generated in the following ways: The minimum value of the preset target voltage is obtained based on the lowest unlocking voltage of the power module in the SVF and the number of modules in each phase arm of the SVF. Based on the boosting capability of the LCC converter valve at the sending end and the power grid system conditions, the maximum value of the preset target voltage is obtained; Based on the minimum and maximum values ​​of the preset target voltage, select the preset target voltage corresponding to the DC bus voltage; The voltage rise curve is generated based on the preset target voltage and the rise parameters within a single cycle.

4. The method according to claim 3, characterized in that, The rise parameters include voltage difference and rise time; The step of generating the voltage rise curve based on the preset target voltage and the rise parameters within a single cycle includes: Based on the voltage requirement of the reverse cut-off of the switching tube in the receiving-end LCC converter valve, the voltage difference of the periodic decrease of the DC bus voltage is obtained. Based on the maximum inrush current allowed by the SVF during charging, the maximum rate of rise of the DC bus voltage during periodic increase is obtained. Based on the maximum rise rate, the maximum voltage difference and minimum rise time of the periodic rise are obtained; Based on the periodically decreasing voltage difference, the periodically increasing maximum voltage difference, the minimum rise time, and the preset target voltage, a preset DC bus voltage rise curve is obtained.

5. The method according to claim 1, characterized in that, The uncontrolled charging of the power module capacitor of the SVF in the SLCC based on the triggering cycle of the receiving-end LCC converter valve includes: Based on the control cycle of the trigger angle change in the sending-end LCC converter valve, the trigger cycle of the receiving-end LCC converter valve is obtained. Based on the triggering cycle of the receiving-end LCC converter valve, the timing sequence is controlled according to a preset cycle to control the conduction of two-phase bridge arms in different combinations of the receiving-end LCC converter valve, so that the two-phase bridge arms in different combinations of the receiving-end LCC converter valve and the two-phase bridge arms in the SVF form a charging circuit, and the power module capacitor of the SVF in the SLCC is uncontrolled charged through the charging circuit.

6. The method according to claim 1, characterized in that, The step of controlling the DC bus voltage within a preset voltage range based on the firing angle of the sending-end LCC converter valve and the preset target voltage includes: When the DC bus voltage reaches the preset target voltage, the firing angle of the sending-end LCC converter valve is controlled based on the firing angle of the sending-end LCC converter valve, so that the DC bus voltage fluctuates periodically within the preset voltage range.

7. The method according to any one of claims 1-6, characterized in that, The active voltage equalization charging control of the power module capacitor based on the current DC bus voltage and the preset module unlocking voltage includes: After the voltage of the power module capacitor is greater than or equal to the preset module unlocking voltage, based on the current DC bus voltage and the rated voltage of the sub-modules of the SVF, the minimum number of sub-modules put into each phase arm of the SVF and the maximum number of sub-modules removed from each phase arm are obtained. Based on the minimum number of submodules put into each phase arm and the maximum number of submodules removed from each phase arm, the number of submodules removed from each phase arm in a single triggering cycle is obtained. Based on the number of sub-modules removed, the capacitor of the power module is actively charged; During active charging, the power module capacitors are charged using voltage equalization control based on the voltages of all sub-modules in the SVF.

8. The method according to claim 7, characterized in that, The step of performing voltage equalization control charging on the power module capacitor based on the voltages of all sub-modules in the SVF includes: Sort the voltages of all submodules in the SVF to obtain the voltage sorting result; Based on the voltage sorting results, the minimum number of sub-modules connected to each phase arm, and the current direction of the cascaded sub-module valve string in the SVF, the power module capacitors are charged using voltage equalization control.

9. A DC charging start-up system for SLCC, characterized in that, The system includes: A voltage rise control unit is used to control the rise of the DC bus voltage of the SLCC according to the voltage rise curve when the sending-end LCC converter valve and the receiving-end LCC converter valve are connected. This control is based on the DC bus voltage in the current cycle and the target voltage to be used in the current cycle. A power module capacitor charging unit is used to perform uncontrolled charging of the power module capacitor of the SVF in the SLCC based on the triggering cycle of the receiving end LCC converter valve when the DC bus voltage rises. The DC bus voltage control unit is used to control the DC bus voltage within a preset voltage range based on the firing angle of the sending-end LCC converter valve and the preset target voltage, and to continue to actively charge the power module capacitor. The active voltage equalization charging control unit is used to perform active voltage equalization charging control on the power module capacitor based on the current DC bus voltage and the preset module unlocking voltage, so as to realize the DC charging start of the SLCC.

10. A computer device, characterized in that, include: One or more processors; The processor is used to store one or more programs; When the one or more programs are executed by the one or more processors, a DC charging start-up method for an SLCC as described in any one of claims 1 to 8 is implemented.

11. A computer-readable storage medium, characterized in that, It contains a computer program, which, when executed, implements a DC charging start-up method for an SLCC as described in any one of claims 1 to 8.

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