Conventional high-voltage direct-current transmission system control method for providing optimal transient voltage support

Abstract

The invention discloses a conventional high-voltage direct-current transmission system control method for providing optimal transient voltage support, belongs to the technical field of LCC-HVDC control, and is characterized in that a direct-current instruction is updated in real time by adopting a two-stage method based on a sending-end alternating-current system equivalent model, and the instruction can realize maximum voltage support. Meanwhile, in order to relieve the negative influence on the inverter side caused by the modification of the direct current, the turn-off angle instruction is modified in a coordinated manner on the inverter side, so that the alternating current voltage of the inverter side is maintained not to exceed the limit, and the risk of subsequent commutation failure is reduced. According to the method, the defect that effective voltage support cannot be provided under transient voltage disturbance in a conventional scheme is overcome, the severity of the transient voltage disturbance is suppressed by utilizing the regulation capability of the LCC-HVDC to the maximum extent, and the impact of the voltage disturbance on the wind turbine generator can be reduced; according to the invention, the coupling effect between the rectification side and the inversion side is considered, and serious side effects on the inversion side caused by voltage support provided at the rectification side can be avoided.

Description

Technical Field

[0001] The present invention belongs to the technical field of LCC-HVDC control, and in particular relates to a conventional high voltage direct current transmission system control method for providing optimal transient voltage support. Background Art

[0002] Conventional high-voltage direct current (LCC-HVDC) transmission systems have become one of the best choices for long-distance, large-capacity wind power transmission due to their advantages of low construction cost, low transmission loss, and long transmission distance. However, in such high-proportion wind power DC transmission systems, faults such as short circuits and line breaks in the nearby area, as well as DC blocking and commutation failures will cause various transient voltage disturbances at the transmission end, threatening the normal operation of wind turbines. In severe cases, it will cause the units to be disconnected from the grid, resulting in instability of the entire transmission-end power system.

[0003] LCC-HVDC has a huge transmission capacity of several gigawatts and has great regulation potential. In theory, it can provide support for suppressing transient voltage disturbances. However, since the LCC-HVDC converter valve is built based on a semi-controlled thyristor, it is impossible to achieve decoupling control of active power and reactive power. It is generally believed that its transient voltage control capability is limited and cannot actively provide millisecond-level transient voltage support. Some studies have improved the low-voltage current limiting control link (Voltage Dependent Current Order Limiter, VDCOL) of the DC control system, which can suppress the continuous "first low and then high" transient voltage disturbance caused by commutation failure. However, due to the difference in the formation mechanism, these schemes are not applicable under transient voltage disturbances caused by other faults. In addition, the existing schemes do not consider the coupling effect between the rectifier station and the inverter station, and do not explore how to maximize the control capability of LCC-HVDC. The control potential of the high-voltage direct current transmission system is not fully utilized. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the conventional high-voltage direct current transmission system control method for providing optimal transient voltage support provided by the present invention solves the problems that the traditional method cannot be used under various transient voltage disturbances, does not consider maximizing the voltage support capability of the high-voltage direct current, cannot fully utilize the regulation potential of the high-voltage direct current converter station, causes errors when a high proportion of wind power is connected, and does not consider the coupling effect of the high-voltage direct current rectifier station and the inverter station, resulting in the operation of the AC system on one side exceeding the normal operating range of the system.

[0005] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is: a conventional high-voltage direct current transmission system control method for providing optimal transient voltage support, including rectifier side control and inverter side control, wherein: For the rectifier side control, the rectifier side control is started based on the real-time detected AC bus voltage and DC current. When the rectifier side control is started, the system equivalent parameter estimation is introduced to recalculate the DC current command of the rectifier side, and the rectifier side control is performed based on it; For inverter side control, based on the impact of DC current command on the power transmission of the inverter station, the inverter side control is started according to the real-time detected AC bus voltage. When starting the inverter side control, the system equivalent parameter estimation is introduced to calculate the shutdown angle command, and the inverter side control is performed based on it.

[0006] Furthermore, the rectifier side control method is specifically as follows: SA1. Real-time collection of DC system operating parameters and sending-end AC system parameters; SA2: For the AC bus voltage and DC current detected in real time in the acquisition parameters; When the AC bus voltage is within the preset range, no additional rectification side control is required and the system is in a normal rectification control state; When the AC bus voltage exceeds the maximum value of the preset interval, the system experiences a transient voltage rise, starts the rectifier side control, and enters step SA3; When the AC bus voltage is lower than the minimum value of the preset interval and the DC current is lower than the preset threshold, a transient voltage drop occurs in the system, the rectifier side control is started, and the process goes to step SA3; When the AC bus voltage is lower than the minimum value of the preset interval and the DC current is greater than or equal to the preset threshold, the system fails to commutate, starts the rectifier side control, and enters step SA3; SA3, based on the voltage and current measurement values ​​collected in real time and combined with the equivalent parameters of the wind farm during normal operation, the Thevenin equivalent parameters of the AC system are estimated; SA4. Calculate the optimal reactive power instruction on the rectifier side based on the estimated equivalent parameters and the measured active power; SA5. Recalculate the DC reference command on the rectifier side according to the optimal reactive power command, AC voltage and trigger angle; SA6. The rectifier side is controlled according to the recalculated DC reference instruction. During the control process, when the AC bus voltage and the DC current are both in the preset range and last for a preset time, it is determined that the rectifier side has resumed normal operation and the rectifier side control is exited.

[0007] Further, in step SA4, the optimal reactive power instruction is:

[0008] The upper limit of the optimal reactive power command for:

[0009] In the formula, represents the optimal reactive power, represents the Thevenin equivalent voltage, represents the equivalent reactance of the AC system at the sending end, Indicates the equivalent susceptance of the reactive power compensation device in the rectifier station. and Respectively represent the coefficients of active current and voltage first-order terms related and unrelated, and The coefficients that represent the reactive current and the voltage first-order term are related and unrelated, respectively. Indicates the active power consumed by the rectifier station.

[0010] Further, in step SA5, the DC reference instruction is:

[0011]

[0012] In the formula, represents the direct current, , , Indicates the number of six-pulse converters in a converter valve, represents the commutation reactance, Indicates the AC bus voltage on the rectifier side, represents the converter transformer ratio, Indicates the firing angle on the rectifier side.

[0013] Furthermore, the inverter side control method is: SB1, real-time collection of DC system operating parameters and receiving end AC system parameters; SB2. Determine whether the AC bus voltage detected in real time in the collected parameters is within a preset range; If yes, no additional inverter-side control is required, and the system is in normal inverter control state; If not, start the inverter side control and go to step SB3; SB3, collect the voltage and current of the AC system and estimate the Thevenin equivalent parameters of the receiving system; SB4. Calculate the reference reactive power command on the inverter side according to the estimated equivalent parameters and the measured active power; SB5. Calculate the shutdown angle as the inverter side shutdown angle instruction according to the reference reactive power instruction and the real-time detected AC voltage and DC current of the common connection point of the inverter side; SB6, control the inverter side according to the shutdown angle command, and detect whether commutation failure occurs during the control process; If yes, then increase the leading trigger angle and go to step SB7; If not, proceed to step SB7; SB7. When the AC bus voltage and DC current on the inverter side are both within the preset range and last for a preset period of time, it is determined that the inverter side has resumed normal operation and the inverter side control is exited; otherwise, return to step SB4.

[0014] Further, in step SB4, the reference reactive power instruction is:

[0015] In the formula, represents the reference reactive power, Indicates the equivalent susceptance of the reactive power compensation device in the inverter station. Indicates the AC bus voltage on the inverter side, represents the Thevenin equivalent reactance of the receiving-end AC system, Indicates the active power on the inverter side. Represents the Thevenin equivalent voltage.

[0016] Furthermore, in step SB5, the calculation formula of the cut-off angle is:

[0017] In the formula, represents the reference reactive power, represents the direct current, Indicates the AC bus voltage on the inverter side, Indicates the number of six-pulse converters in a converter valve, represents the inverter side converter transformer ratio, Indicates the measurement of the cut-off angle, Indicates the inverter side commutation reactance.

[0018] The beneficial effects of the present invention are: (1) The present invention proposes a control method for maximizing the transient voltage support capability of a conventional high-voltage direct current transmission system, which can provide optimal transient voltage support for the AC system under various types of transient voltage disturbances. Specifically, based on the equivalent model of the sending-end AC system, a two-stage method is used to update the DC current command in real time, which can achieve maximum voltage support. At the same time, in order to alleviate the negative impact of modifying the DC current on the inverter side, the shutdown angle command is coordinated and modified on the inverter side to maintain the AC voltage on the inverter side within the limit and reduce the risk of subsequent commutation failure.

[0019] (2) The present invention provides an improved high-voltage direct current control strategy, which solves the problem that conventional solutions cannot provide effective voltage support under transient voltage disturbances, maximizes the use of LCC-HVDC regulation capabilities to suppress the severity of transient voltage disturbances, and can reduce the impact of voltage disturbances on wind turbines. In addition, the method of the present invention takes into account the coupling effect between the rectifier side and the inverter side, which can avoid providing voltage support on the rectifier side and causing serious side effects on the inverter side. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a flow chart of a conventional high voltage direct current transmission system control method for providing optimal transient voltage support in the present invention.

[0021] Figure 2 This is a structural diagram of a typical bipolar high-voltage direct current transmission system including a wind farm at the sending end in the present invention.

[0022] Figure 3 This is the equivalent circuit diagram of the wind power DC sending end system in the present invention.

[0023] Figure 4 This is a control block diagram of the rectifier side of the high voltage direct current transmission system in the present invention.

[0024] Figure 5 This is a control block diagram of the inverter side of the high voltage direct current transmission system in the present invention. DETAILED DESCRIPTION

[0025] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0026] One embodiment of the present invention provides a conventional high voltage direct current transmission system control method for optimal transient voltage support, such as Figure 1 As shown, it includes rectifier side control and inverter side control, where: For the rectifier side control, the rectifier side control is started based on the real-time detected AC bus voltage and DC current. When the rectifier side control is started, the system equivalent parameter estimation is introduced to recalculate the DC current command of the rectifier side, and the rectifier side control is performed based on it; For inverter side control, based on the impact of DC current command on the power transmission of the inverter station, the inverter side control is started according to the real-time detected AC bus voltage. When starting the inverter side control, the system equivalent parameter estimation is introduced to calculate the shutdown angle command, and the inverter side control is performed based on it.

[0027] The control method provided in the embodiment of the present invention is aimed at the conventional high-voltage direct current transmission system in the wind power direct current sending end system, and improves the control strategy of the high-voltage direct current rectifier side and the inverter side. The typical bipolar high-voltage direct current transmission system with a wind farm at the sending end is as follows: Figure 2 As shown, the simplified equivalent circuit of the corresponding sending-end system is as follows Figure 3 shown in Figure 3 In the example, the wind farm can be regarded as a current source. I wd + JI wq ,in I wd and I wq are active current and reactive current respectively. Since the electrical distance between the wind farm and the converter station is relatively short, the impedance of the interconnection line is R w + JXj w can be ignored; the AC system other than the wind farm is represented by the Thevenin equivalent, and the equivalent voltage is E sr , the equivalent impedance is R r + JXj r ; P r + Jb r represents the power provided by the AC system, P dr + Jb dr represents the power absorbed by the DC system, B c is the equivalent admittance of the reactive power compensation device in the converter station, U pr is the voltage at the common connection point.

[0028] In the embodiment of the present invention, Figure 4 As shown, the control method of the rectifier side is specifically as follows: SA1. Real-time collection of DC system operating parameters and sending-end AC system parameters; Specifically, the collected parameters include the trigger angle of the rectifier side of the DC system, DC current, etc., and the bus AC voltage, etc.; SA2: For the AC bus voltage and DC current detected in real time in the acquisition parameters; When the AC bus voltage is in a preset range, no additional rectification side control is required, and the system is in a normal rectification side control state; wherein no additional rectification side control is required means that the control method proposed by the present invention needs to be started according to subsequent steps, and the control method of the rectification side can be performed according to the normal rectification side control method; When the AC bus voltage exceeds the maximum value of the preset interval, the system experiences a transient voltage rise, starts the rectifier side control, and enters step SA3; When the AC bus voltage is lower than the minimum value of the preset interval and the DC current is lower than the preset threshold, a transient voltage drop occurs in the system, the rectifier side control is started, and the process goes to step SA3; When the AC bus voltage is lower than the minimum value of the preset interval and the DC current is greater than or equal to the preset threshold, the system fails to commutate, starts the rectifier side control, and enters step SA3; SA3, based on the voltage and current measurement values ​​collected in real time and combined with the equivalent parameters of the wind farm during normal operation, the Thevenin equivalent parameters of the AC system are estimated; SA4. Calculate the optimal reactive power instruction on the rectifier side based on the estimated equivalent parameters and the measured active power; SA5. Recalculate the DC reference command on the rectifier side according to the optimal reactive power command, AC voltage and trigger angle; SA6. The rectifier side is controlled according to the recalculated DC reference instruction. During the control process, when the AC bus voltage and the DC current are both in the preset range and last for a preset time, it is determined that the rectifier side has resumed normal operation and the rectifier side control is exited.

[0029] In this embodiment, in a specific example, in step SA2, the preset interval of the AC bus voltage is [0.9 pu, 1.1 pu], the preset threshold of the DC current is 1.0 pu, and when the AC bus voltage U pr When the AC bus voltage is in the range of [0.9 pu, 1.1 pu], the system is considered to be in a normal state and no additional measures are taken by the DC system. U pr When the voltage exceeds this range, the system is considered to have a fault, the enable signal Ctrl is set to 1, the high-voltage DC control system switches to the proposed rectifier side control process, and the fault mode is judged; when the measured AC bus voltage U pr Less than 0.9 pu and DC current I dc <1.0 pu, a voltage sag is considered to have occurred; when the AC bus voltage U pr Less than 0.9 pu and DC current I dc ≥1.0 pu, it is considered that commutation failure occurs; when the AC bus voltage U pr When it is higher than 1.1 pu, voltage swell is considered to have occurred.

[0030] In step SA3 of this embodiment, the equivalent parameters of the AC system are estimated based on the real-time collected AC system voltage and current. The wind farm equivalent is a controlled current source, as shown in formula (1), where K P1 , K P2 , K Q1 , K Q2 are all constant coefficients, which may be different during normal operation and fault ride-through. In this embodiment, only the wind farm equivalent parameters during normal operation are required, without considering the parameters of the fault ride-through state. K P1 , K Q1 , K Q2 Can be set to zero, so the difficulty of obtaining parameters is reduced. Thevenin equivalent parameters include equivalent voltage E sr and equivalent impedance R r + JXj r .

[0031] (1) In step SA4 of this embodiment, the optimal reactive power instruction is: (2) To ensure that the subsequent equations have solutions, the lower limit of the optimal reactive power command is set to Q dr,min =0, the upper limit is set Q critical , obtained by formula (3), formula (3) is the condition to ensure that the system power flow equation has a solution, corresponding to the static voltage stability limit. This equation is obtained by setting U pr =1 is solved. Due to the monotonic relationship between AC voltage and reactive power, the reactive power obtained can maximize the AC voltage support effect of high voltage DC, that is, maximize the voltage when the voltage is lower than 1.0 pu and minimize the voltage when the voltage is higher than 1.0 pu. Among them, the upper limit of the optimal reactive power instruction is for: (3) In the formula, represents the optimal reactive power, represents the Thevenin equivalent voltage, represents the equivalent reactance of the AC system at the sending end, Indicates the equivalent susceptance of the reactive power compensation device in the rectifier station. and respectively represent the coefficients related to and unrelated to the first-order term of the active current and voltage, and respectively represent the coefficients related to and unrelated to the first-order term of the reactive current and voltage, represents the active power consumed by the rectifier station.

[0032] In step SA5 of this embodiment, the DC reference instruction is: (4) wherein, , , and the other coefficients are:

[0033] In the formula, represents the DC current, , , represents the number of six-pulse converters in a commutation valve, represents the commutation reactance, represents the AC bus voltage on the rectifier side, represents the converter transformer ratio, represents the firing angle on the rectifier side.

[0034] The above equation is derived from the quasi-steady-state equation of LCC-HVDC. This formula only contains I dc one independent variable and can be solved analytically. To ensure the continuity of the DC current and not exceed the equipment's tolerance range, in this embodiment, the minimum value I dc,min of the DC current command is set to 0.2 p.u., and the maximum value I dc,max is set to 1.25 p.u.

[0035] In step SA6 of this embodiment, when the measured DC bus voltage U pr and the DC current satisfy 0.9 < U pr < 1.1 and 0.9 < I dc < 1.1 and last for 50 ms, it is considered that the system resumes normal operation, the proposed control method exits the operation, and the HVDC system switches to the conventional control.

[0036] In the embodiment of the present invention, due to the limitation of LCC-HVDC's own control, modifying the DC current on the rectifier side will inevitably affect the power transmission of the inverter station, resulting in AC voltage fluctuations at the receiving end. In the embodiment of the present invention, a control strategy without communication is designed to modify the cut-off angle of the inverter station according to local quantity measurement to maintain the AC voltage at the receiving end within a preset reasonable range.

[0037] Specifically, in the embodiment of the present invention, Figure 5 As shown, the inverter side control method is: SB1, real-time collection of DC system operating parameters and receiving end AC system parameters; Specifically, the collected parameters include the inverter-side shut-off angle and DC current of the DC system, as well as the inverter-side commutation bus AC voltage; SB2. Determine whether the AC bus voltage detected in real time in the collected parameters is within a preset range; If yes, no additional inverter side control is required, and the system is in a normal inverter control state; similarly, no additional inverter side control is required here means that the control method proposed by the present invention needs to be started according to the subsequent steps, and the control method can be performed according to the normal inverter side control method; If not, start the inverter side control and go to step SB3; Specifically, the preset interval of the AC bus voltage is [0.9 pu, 1.1 pu]. When it is within this interval, the system is considered to be in a normal state. When it exceeds the preset interval, step SB3 is entered to start the inverter side coordinated control; SB3, collect the voltage and current of the AC system and estimate the equivalent parameters of the AC system and the Thevenin equivalent parameters of the receiving end system; Specifically, the equivalent parameters of the AC system are estimated based on the AC system voltage and current collected in the embodiment. For the receiving end system, due to the low proportion of wind power, the Thevenin equivalent can be directly used, and the parameters are the equivalent voltage E si and equivalent impedance R si + JXj si , its online estimation method is the same as that on the rectifier side; SB4. Calculate the reference reactive power command on the inverter side according to the estimated equivalent parameters and the measured active power; SB5. Calculate the shutdown angle as the inverter side shutdown angle instruction according to the reference reactive power instruction and the real-time detected AC voltage and DC current of the common connection point of the inverter side; SB6, control the inverter side according to the shutdown angle command, and detect whether commutation failure occurs during the control process; If yes, then increase the leading trigger angle and go to step SB7; If not, proceed to step SB7; SB7. When the AC bus voltage and DC current on the inverter side are both within the preset range and last for a preset period of time, it is determined that the inverter side has resumed normal operation and the inverter side control is exited; otherwise, return to step SB4.

[0038] In step SB4 of this embodiment, the reference reactive power instruction is: (5) In the formula, represents the reference reactive power, Indicates the equivalent susceptance of the reactive power compensation device in the inverter station. Indicates the AC bus voltage on the inverter side, represents the Thevenin equivalent reactance of the receiving-end AC system, Indicates the active power on the inverter side. Represents the Thevenin equivalent voltage.

[0039] Specifically, when the AC bus voltage U pi When the upper limit of 1.1 pu is exceeded, substitute U pi =1.1 pu, solve the above formula to get the reference reactive DC; when the AC bus voltage U pi When it is below the lower limit of 0.9 pu, substitute U pi =0.9 pu. The calculated work-free voltage maintains the inverter-side AC voltage within the preset upper or lower limit of the interval.

[0040] In step SB5 of this embodiment, according to the reference reactive power instruction and the measured U pi and I dc , the calculation formula of the cut-off angle is: (6) In the formula, represents the reference reactive power, represents the direct current, Indicates the AC bus voltage on the inverter side, Indicates the number of six-pulse converters in a converter valve, represents the inverter side converter transformer ratio, Indicates the measurement of the cut-off angle, Indicates the inverter side commutation reactance.

[0041] In step SB6 of this embodiment, when a commutation failure is detected, the leading firing angle is increased to reduce the risk of subsequent commutation failure. β, increase Δ β is 10°.

[0042] The present invention uses specific embodiments to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present invention.

[0043] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the principles of the present invention, and should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific variations and combinations that do not deviate from the essence of the present invention based on the technical revelations disclosed by the present invention, and these variations and combinations are still within the protection scope of the present invention.

Claims

1. A conventional high voltage direct current transmission system control method for providing optimal transient voltage support, characterized in that: It includes rectifier side control and inverter side control, where: For the rectifier side control, the rectifier side control is started based on the real-time detected AC bus voltage and DC current. When the rectifier side control is started, the system equivalent parameter estimation is introduced to recalculate the DC current command of the rectifier side, and the rectifier side control is performed based on it; For inverter side control, based on the impact of DC current command on the power transmission of the inverter station, the inverter side control is started according to the real-time detected AC bus voltage. When starting the inverter side control, the system equivalent parameter estimation is introduced to calculate the shutdown angle command, and the inverter side control is performed based on it.

2. The conventional high voltage direct current transmission system control method for providing optimal transient voltage support according to claim 1, characterized in that: The method for controlling the rectifier side is specifically as follows: SA1. Real-time collection of DC system operating parameters and sending-end AC system parameters; SA2: For the AC bus voltage and DC current detected in real time in the acquisition parameters; When the AC bus voltage is within the preset range, no additional rectification side control is required and the system is in a normal rectification control state; When the AC bus voltage exceeds the maximum value of the preset interval, the system experiences a transient voltage rise, starts the rectifier side control, and enters step SA3; When the AC bus voltage is lower than the minimum value of the preset interval and the DC current is lower than the preset threshold, a transient voltage drop occurs in the system, the rectifier side control is started, and the process goes to step SA3; When the AC bus voltage is lower than the minimum value of the preset interval and the DC current is greater than or equal to the preset threshold, the system fails to commutate, starts the rectifier side control, and enters step SA3; SA3, based on the voltage and current measurement values ​​collected in real time and combined with the equivalent parameters of the wind farm during normal operation, the Thevenin equivalent parameters of the AC system are estimated; SA4. Calculate the optimal reactive power instruction on the rectifier side based on the estimated equivalent parameters and the measured active power; SA5. Recalculate the DC reference command on the rectifier side according to the optimal reactive power command, AC voltage and trigger angle; SA6. The rectifier side is controlled according to the recalculated DC reference instruction. During the control process, when the AC bus voltage and the DC current are both in the preset range and last for a preset time, it is determined that the rectifier side has resumed normal operation and the rectifier side control is exited.

3. The conventional high voltage direct current transmission system control method for providing optimal transient voltage support according to claim 2, characterized in that: In step SA4, the optimal reactive power instruction is: The upper limit of the optimal reactive power command for: In the formula, represents the optimal reactive power, represents the Thevenin equivalent voltage, represents the equivalent reactance of the AC system at the sending end, Indicates the equivalent susceptance of the reactive power compensation device in the rectifier station. and Respectively represent the coefficients of active current and voltage first-order terms related and unrelated, and The coefficients that represent the reactive current and the voltage first-order term are related and unrelated, respectively. Indicates the active power consumed by the rectifier station.

4. The conventional high voltage direct current transmission system control method for providing optimal transient voltage support according to claim 2, characterized in that: In step SA5, the DC reference instruction is: In the formula, represents the direct current, , , Indicates the number of six-pulse converters in a converter valve, represents the commutation reactance, Indicates the AC bus voltage on the rectifier side, represents the converter transformer ratio, Indicates the firing angle on the rectifier side.

5. The conventional high voltage direct current transmission system control method for providing optimal transient voltage support according to claim 1, characterized in that: The inverter side control method is: SB1, real-time collection of DC system operating parameters and receiving end AC system parameters; SB2. Determine whether the AC bus voltage detected in real time in the collected parameters is within a preset range; If yes, no additional inverter-side control is required, and the system is in normal inverter control state; If not, start the inverter side control and go to step SB3; SB3, collect the voltage and current of the AC system and estimate the Thevenin equivalent parameters of the receiving system; SB4. Calculate the reference reactive power command on the inverter side according to the estimated equivalent parameters and the measured active power; SB5. Calculate the shutdown angle as the inverter side shutdown angle instruction according to the reference reactive power instruction and the real-time detected AC voltage and DC current of the common connection point of the inverter side; SB6, control the inverter side according to the shutdown angle command, and detect whether commutation failure occurs during the control process; If yes, then increase the leading trigger angle and go to step SB7; If not, proceed to step SB7; SB7. When the AC bus voltage and DC current on the inverter side are both within the preset range and last for a preset period of time, it is determined that the inverter side has resumed normal operation and the inverter side control is exited; otherwise, return to step SB4.

6. The conventional high voltage direct current transmission system control method for providing optimal transient voltage support according to claim 5, characterized in that: In step SB4, the reference reactive power instruction is: In the formula, represents the reference reactive power, Indicates the equivalent susceptance of the reactive power compensation device in the inverter station. Indicates the AC bus voltage on the inverter side, represents the Thevenin equivalent reactance of the receiving-end AC system, Indicates the active power on the inverter side. Represents the Thevenin equivalent voltage.

7. The conventional high voltage direct current transmission system control method for providing optimal transient voltage support according to claim 5, characterized in that: In step SB5, the calculation formula of the cut-off angle is: In the formula, represents the reference reactive power, represents the direct current, Indicates the AC bus voltage on the inverter side, Indicates the number of six-pulse converters in a converter valve, represents the inverter side converter transformer ratio, Indicates the measurement of the cut-off angle, Indicates the inverter side commutation reactance.

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