A seamless switching method and device for network construction type and network following type control of MMC-HVDC converter station

Abstract

A seamless switching method and device for network-oriented MMC-HVDC converter station construction and network following control, relates to the field of power system control technology, without changing the inner loop current control, by constructing a unified outer loop reference current and initializing the setting of phase angle and voltage amplitude, the continuity of output voltage power angle and amplitude in the control mode switching process is ensured. The technology can quickly respond to changes in grid conditions, avoiding system disturbance and instability caused by mode switching. Simulation results show that this technology effectively reduces the impact of control switching on the system, significantly improves the stability and reliability of the system, and is suitable for flexible HVDC transmission systems under various grid conditions, especially in weak grid access and frequency support scenarios.

Description

Technical Field

[0001] This invention relates to the field of power system control technology, specifically to a method and apparatus for seamless switching between grid-based and grid-connected control for MMC-HVDC converter stations. Background Technology

[0002] Modular multilevel converter (MMC) high-voltage direct current (HVDC) systems are widely used in power grids, especially in the context of rapid development of new energy sources, where they can effectively connect large-scale renewable energy. With their flexibility and efficiency, MMC-HVDC systems have become an ideal choice for connecting weak grids.

[0003] With the increasing proportion of renewable energy integration, the grid inertia decreases, necessitating the use of Virtual Synchronous Generator (VSG) control technology to provide inertia support for the grid and simulate the characteristics of synchronous generators. MMC-HVDC converter stations typically need to switch between grid-connected and grid-integrated control to cope with different grid conditions. Grid-connected control is suitable for weak grids, providing voltage and frequency support; grid-integrated control is suitable for strong grids, controlling system current. However, current research on seamless switching technology between these two control modes is limited. Existing research mostly focuses on grid-connected and off-grid mode switching, with insufficient research on grid-connected and grid-integrated switching. Ensuring voltage and power stability during switching is a key research focus. Summary of the Invention

[0004] To overcome the shortcomings of the above technologies, this invention provides a method and apparatus for seamless switching between grid-type and grid-following control of MMC-HVDC converter stations, which can quickly respond to changes in grid conditions and avoid system disturbances and instabilities caused by mode switching.

[0005] The technical solution adopted by this invention to overcome its technical problems is:

[0006] A seamless switching method for grid-based and grid-connected control of MMC-HVDC converter stations includes:

[0007] S1. Run the MMC-HVDC system, analyze the current operating status of the MMC-HVDC system and the power grid conditions, and obtain raw power grid data;

[0008] S2. Provide virtual inertia to the MMC-HVDC system;

[0009] S3. Construct expressions for active power and frequency;

[0010] S4. Construct a reference value for active power after frequency modulation with droop control added based on the expressions for active power and frequency;

[0011] S5. The active power controller output phase angle θ is obtained based on the active power reference value;

[0012] S6. Calculate the voltage and reactive power regulation component ΔU based on voltage and reactive power droop control. q and voltage regulation component ΔU based on voltage control v ;

[0013] S7. Utilizing the voltage and reactive power-based droop control of the voltage reactive power regulation component ΔU q and voltage regulation component ΔU based on voltage control v The output voltage amplitude U of the reactive power controller is calculated. m ;

[0014] S8. Based on the output phase angle θ of the active power controller and the output voltage amplitude U of the reactive power controller. m Obtain the reference current of the grid-type MMC-HVDC converter station and the d-axis reference current i of the track-type MMC-HVDC converter station. d,ref and q-axis reference current i q,ref ;

[0015] S9. When the MMC-HVDC converter station switches from grid-based control to grid-following control, the active power controller output phase angle θ and reactive power controller output voltage amplitude U of the current grid-based control are used. m As the initial values ​​for grid-following control, when the MMC-HVDC converter station switches from grid-following control to grid-forming control, the current grid-following control PLL phase angle and the measured grid-side voltage amplitude are used as the initial values ​​for grid-forming control. The d-axis reference current i of the grid-following MMC-HVDC converter station is then controlled via a PI controller and a feedforward decoupling circuit. d,ref and q-axis reference current i q,ref The input is fed into the inner loop current controller.

[0016] Furthermore, the virtual inertia in step S2 is based on the mechanical and electromagnetic characteristic equations of virtual synchronous machine control.

[0017] Furthermore, the mechanical and electromagnetic characteristic equations based on virtual synchronous machine control are as follows:

[0018] In the formula T m T is the mechanical torque. e Let ω be the electromagnetic torque, D be the damping coefficient, ω be the angular frequency of the synchronizer, ω0 be the rated angular frequency of the system, J be the moment of inertia, and θ be the mechanical angle of the synchronizer.

[0019] Furthermore, the expressions for power and frequency in step S3 are as follows: In the formula P m For the input power of the synchronous machine, Pe This is the output power of the synchronous machine.

[0020] Furthermore, through formula P m ′=P ref +k ω The active power reference value P after frequency modulation is obtained by calculating (ω0-ω). m ′, where P ref Input power P of the synchronous machine m In the VSG controller, k is equivalent to a reference value of active power. ω This is the frequency gain coefficient.

[0021] Furthermore, step S5 includes the following steps:

[0022] S5-1. The active power reference value P m Introducing this into frequency droop control, we obtain the following equation:

[0023]

[0024] S5-2. Input the equation into the PI controller to obtain the active power controller output phase angle θ.

[0025] Furthermore, step S6 includes the following steps:

[0026] S6-1. Using the formula ΔU q =k q (Q ref -Q) The voltage and reactive power regulation component ΔU based on voltage and reactive power droop control is calculated. q In the formula, k q Q is the reactive power regulation coefficient. ref Q is the MMC reactive power reference value, and Q is the MMC measured value.

[0027] S6-2. Using the formula ΔU v =k v (Q acref -U ac The voltage regulation component ΔU based on voltage control is calculated. v In the formula, k v Q is the voltage regulation gain coefficient. acref U represents the change in the AC side voltage reference value. ac This is the measured value of the AC side voltage.

[0028] Furthermore, in step S7, formula U m =U n +ΔU q +ΔU v The output voltage amplitude U of the reactive power controller is calculated. m In the formula, Un This is the reference voltage.

[0029] Furthermore, step S8 includes the following steps:

[0030] S8-1. When the control mode of the MMC-HVDC converter station is grid-type, the output phase angle θ of the active power controller and the output voltage amplitude U of the reactive power controller are... m The reference voltage is obtained using a sine function, and then input into two PI controllers to generate a reference current in the dq coordinate system.

[0031] S8-2. When the control mode of the MMC-HVDC converter station is grid-following, the formula is used... The d-axis reference current i of the grid-connected MMC-HVDC converter station is calculated. d,ref In the formula V d The voltage dq-axis component is obtained by transforming the measured actual three-phase voltage Vabc of the power grid through an abc transformation. q The voltage dq-axis component is obtained by dq transformation of the measured actual three-phase voltage Vabc of the power grid; S8-3. When the control mode of the MMC-HVDC converter station is grid-following, the formula is used to obtain the voltage dq-axis component. The q-axis reference current i of the grid-connected MMC-HVDC converter station is calculated. q,ref .

[0032] On the other hand, the present invention also relates to a seamless switching device for grid-based and grid-connected control of MMC-HVDC converter stations, comprising: a processor, a communication interface, a memory, and a communication bus, wherein the processor, the communication interface, and the memory communicate with each other through the communication bus; wherein:

[0033] The memory is used to store computer programs;

[0034] The processor is configured to execute by running programs stored in the memory:

[0035] Run the MMC-HVDC system, analyze its current operating status and grid conditions, and obtain raw grid data.

[0036] Provide virtual inertia to the MMC-HVDC system;

[0037] Construct expressions for active power and frequency;

[0038] Construct a reference value for active power after frequency modulation with droop control incorporating active power and frequency based on expressions for active power and frequency.

[0039] The active power reference value is used to obtain the active power controller output phase angle θ;

[0040] Calculate the voltage and reactive power droop control component ΔU based on voltage and reactive power. q and voltage regulation component ΔU based on voltage control v ;

[0041] Voltage reactive power regulation component ΔU based on voltage and reactive power droop control q and voltage regulation component ΔU based on voltage control v The output voltage amplitude U of the reactive power controller is calculated. m ;

[0042] Based on the output phase angle θ of the active power controller and the output voltage amplitude U of the reactive power controller m Obtain the reference current of the grid-type MMC-HVDC converter station and the d-axis reference current i of the track-type MMC-HVDC converter station. d,ref and q-axis reference current i q,ref ;

[0043] When the MMC-HVDC converter station switches from grid-based control to grid-following control, it uses the active power controller output phase angle θ and reactive power controller output voltage amplitude U of the current grid-based control. m As the initial values ​​for grid-following control, when the MMC-HVDC converter station switches from grid-following control to grid-forming control, the current grid-following control PLL phase angle and the measured grid-side voltage amplitude are used as the initial values ​​for grid-forming control. The d-axis reference current i of the grid-following MMC-HVDC converter station is then controlled via a PI controller and a feedforward decoupling circuit. d,ref and q-axis reference current i q,ref The input is fed into the inner loop current controller.

[0044] The beneficial effects of this invention are: without changing the inner loop current control, by constructing a unified initialization setting for the outer loop reference current, phase angle, and voltage amplitude, the continuity of the output voltage's power angle and amplitude during control mode switching is ensured. This technology can quickly respond to changes in grid conditions, avoiding system disturbances and instability caused by mode switching. Simulation results show that this technology effectively reduces the impact of control switching on the system, significantly improves system stability and reliability, and is suitable for flexible DC transmission systems under various grid conditions, especially showing significant advantages in scenarios with weak grid access and frequency support. Detailed Implementation

[0045] The present invention will be further described below.

[0046] Example 1

[0047] A seamless switching method for grid-based and grid-connected control of MMC-HVDC converter stations includes:

[0048] S1. Run the MMC-HVDC system, analyze the current operating status of the MMC-HVDC system and the power grid conditions, and obtain the original power grid data.

[0049] S2. Provide virtual inertia to the MMC-HVDC system. The control principle of a virtual synchronous machine is adopted, using the mechanical and electromagnetic characteristic equations of the synchronous machine as its control model.

[0050] S3. Construct expressions for active power and frequency.

[0051] S4. Construct a reference value for active power after frequency modulation with droop control added based on the expressions for active power and frequency.

[0052] S5. The active power controller output phase angle θ is obtained based on the active power reference value.

[0053] S6. Calculate the voltage and reactive power regulation component ΔU based on voltage and reactive power droop control. q and voltage regulation component ΔU based on voltage control v .

[0054] S7. Utilizing the voltage and reactive power-based droop control of the voltage reactive power regulation component ΔU q and voltage regulation component ΔU based on voltage control v The output voltage amplitude U of the reactive power controller is calculated. m .

[0055] S8. Based on the output phase angle θ of the active power controller and the output voltage amplitude U of the reactive power controller. m Obtain the reference current of the grid-type MMC-HVDC converter station and the d-axis reference current i of the track-type MMC-HVDC converter station. d,ref and q-axis reference current i q,ref .

[0056] S9. When the MMC-HVDC converter station switches from grid-based control to grid-following control, the active power controller output phase angle θ and reactive power controller output voltage amplitude U of the current grid-based control are used. m As the initial values ​​for grid-following control, when the MMC-HVDC converter station switches from grid-following control to grid-forming control, the current grid-following control PLL phase angle and the measured grid-side voltage amplitude are used as the initial values ​​for grid-forming control. The d-axis reference current i of the grid-following MMC-HVDC converter station is then controlled via a PI controller and a feedforward decoupling circuit. d,ref and q-axis reference current i q,ref The input is fed into the inner loop current controller.

[0057] During the control mode switching period, the inner loop current control remains unchanged, and the new reference value is gradually applied to smoothly transition to the target control mode. When switching from grid-type control to follow-grid control, the phase angle generated by the grid-type control is used as the initial value for the follow-grid control, the reference value of PQ remains unchanged, and the reference current i... d,ref and reference current i q,ref The switch is determined by grid-following control. When switching from grid-following control to grid-forming control, the active power controller outputs a phase angle θ as the initial value of the grid-forming control phase angle. Simultaneously, the grid-side voltage amplitude measured by the grid-following control is used as the reference value for the grid-forming control voltage amplitude, with the reference current i... d,ref and reference current i q,ref Switching to a grid-based control to determine the reference current i d,ref and reference current i q,ref The input is fed into the inner current loop controller, allowing the same current control loop to be applied to two different control modes. Finally, the MMC's internal controller calculates the MMC's voltage modulation signal, and the PWM determines the switching signal throughout the switching process. The power angle and amplitude of the output voltage are monitored to ensure continuity and avoid abrupt changes. After a successful switch, the system status continues to be monitored in real time to ensure stable operation in the new mode.

[0058] In this embodiment, the virtual inertia in step S2 is the mechanical characteristic equation and electromagnetic characteristic equation based on virtual synchronous machine control.

[0059] In this embodiment, the mechanical and electromagnetic characteristic equations based on virtual synchronous machine control are as follows:

[0060] In the formula T m T is the mechanical torque. e Let J be the electromagnetic torque, D be the damping coefficient, ω be the angular frequency of the synchronizer, ω0 be the rated angular frequency of the system, J be the moment of inertia, and θ be the mechanical angle of the synchronizer. The moment of inertia J and the damping coefficient D are adjustable control parameters. Adjusting the moment of inertia J adjusts the system's inertia, while adjusting the damping coefficient D adjusts the system's damping, improving robustness.

[0061] In this embodiment, the expressions for power and frequency in step S3 are as follows: In the formula P m For the input power of the synchronous machine, P e This represents the output power of the synchronous machine. The VSG simulates the rotor motion equations of the synchronous machine, giving it virtual inertia and damping characteristics.

[0062] The expressions for active power and frequency are as follows: The rotor motion equations of the described synchronous machine give the VSG virtual inertia and damping characteristics. By incorporating droop control of active power and frequency, a reference value for the active power after frequency modulation can be obtained. Therefore, in this embodiment, the active power reference value is obtained through formula P. m ′=P ref +k ω The active power reference value P after frequency modulation is obtained by calculating (ω0-ω). m ′, where P ref Input power P of the synchronous machine m In the VSG controller, k is equivalent to a reference value of active power. ω This is the frequency gain coefficient. When the AC system experiences frequency deviation, the active power reference value P after frequency modulation is adjusted. m This can change the system's active power output, thereby adjusting the system's frequency and providing a stable frequency for subsequent seamless switching.

[0063] In this embodiment, step S5 includes the following steps:

[0064] S5-1. The active power reference value P m Introducing this into frequency droop control, we obtain the following equation:

[0065]

[0066] S5-2. Input the equation into the PI controller to obtain the active power controller output phase angle θ.

[0067] In this embodiment, step S6 includes the following steps:

[0068] S6-1. To achieve voltage regulation similar to a synchronous machine, the simulated VSG uses a voltage-reactive power control loop to simulate the excitation system of a synchronous machine. The voltage and reactive power of the system are controlled by controlling the output voltage of the MMC, using the formula ΔU... q =k q (Q ref -Q) The voltage and reactive power regulation component ΔU based on voltage and reactive power droop control is calculated. q In the formula, k q Q is the reactive power regulation coefficient. ref Q is the MMC reactive power reference value, and Q is the measured MMC value.

[0069] S6-2. Using the formula ΔU v =k v (Q acref -U ac The voltage regulation component ΔU based on voltage control is calculated. v In the formula, k v Q is the voltage regulation gain coefficient. acrefU represents the change in the AC side voltage reference value. ac This is the measured value of the AC side voltage.

[0070] In this embodiment, in step S7, formula U m =U n +ΔU q +ΔU v The output voltage amplitude U of the reactive power controller is calculated. m In the formula, U n It serves as the reference voltage for VSG control and the basis for generating the seamless switching reference current.

[0071] In this embodiment, step S8 includes the following steps:

[0072] S8-1. When the control mode of the MMC-HVDC converter station is grid-type, the output phase angle θ of the active power controller and the output voltage amplitude U of the reactive power controller are... m The reference voltage is obtained using a sine function, and then input into two PI controllers to generate a reference current in the dq coordinate system.

[0073] S8-2. When the control mode of the MMC-HVDC converter station is grid-following, the formula is used... The d-axis reference current i of the grid-connected MMC-HVDC converter station is calculated. d,ref In the formula V d The voltage dq-axis component is obtained by transforming the measured actual three-phase voltage Vabc of the power grid through an abc transformation. q The measured actual three-phase voltage Vabc of the power grid is obtained by dq transformation of the voltage dq axis component. S8-3. When the control mode of the MMC-HVDC converter station is grid-following, the formula is used to obtain the voltage dq axis component. The q-axis reference current i of the grid-connected MMC-HVDC converter station is calculated. q,ref .

[0074] By designing a unified outer-loop reference current for both grid-based and grid-following control modes, the continuity of the power angle and amplitude of the converter station's output voltage during switching processes is ensured. The current control mode (grid-based or grid-following) and its corresponding output state (phase angle and voltage amplitude) of the converter station are determined. Then, the initial current reference value for the target control mode to which the converter station is about to switch is calculated.

[0075] Example 2

[0076] A seamless switching device for grid-based and grid-connected control of MMC-HVDC converter stations includes: a processor, a communication interface, a memory, and a communication bus, wherein the processor, the communication interface, and the memory communicate with each other via the communication bus; wherein:

[0077] The memory is used to store computer programs;

[0078] The processor is configured to execute by running programs stored in the memory:

[0079] Run the MMC-HVDC system, analyze its current operating status and grid conditions, and obtain raw grid data.

[0080] Provide virtual inertia to the MMC-HVDC system.

[0081] Construct expressions for active power and frequency.

[0082] Based on the expressions for active power and frequency, construct the frequency-modulated active power reference value with droop control incorporating active power and frequency.

[0083] The active power reference value is used to obtain the active power controller output phase angle θ.

[0084] Calculate the voltage and reactive power droop control component ΔU based on voltage and reactive power. q and voltage regulation component ΔU based on voltage control v .

[0085] Voltage reactive power regulation component ΔU based on voltage and reactive power droop control q and voltage regulation component ΔU based on voltage control v The output voltage amplitude U of the reactive power controller is calculated. m .

[0086] Based on the output phase angle θ of the active power controller and the output voltage amplitude U of the reactive power controller m Obtain the reference current of the grid-type MMC-HVDC converter station and the d-axis reference current i of the track-type MMC-HVDC converter station. d,ref and q-axis reference current i q,ref .

[0087] When the MMC-HVDC converter station switches from grid-based control to grid-following control, it uses the active power controller output phase angle θ and reactive power controller output voltage amplitude U of the current grid-based control. m As the initial values ​​for grid-following control, when the MMC-HVDC converter station switches from grid-following control to grid-forming control, the current grid-following control PLL phase angle and the measured grid-side voltage amplitude are used as the initial values ​​for grid-forming control. The d-axis reference current i of the grid-following MMC-HVDC converter station is then controlled via a PI controller and a feedforward decoupling circuit. d,ref and q-axis reference current i q,ref The input is fed into the inner loop current controller.

[0088] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A seamless switching method for grid-based and grid-following control of MMC-HVDC converter stations, characterized in that, include: S1. Run the MMC-HVDC system, analyze the current operating status of the MMC-HVDC system and the power grid conditions, and obtain raw power grid data; S2. Provide virtual inertia to the MMC-HVDC system; S3. Construct expressions for active power and frequency; S4. Construct a reference value for active power after frequency modulation with droop control added based on the expressions for active power and frequency; S5. The active power controller output phase angle θ is obtained based on the active power reference value; S6. Calculate the voltage and reactive power regulation component ΔU based on voltage and reactive power droop control. q and voltage regulation component ΔU based on voltage control v ; S7. Utilizing the voltage and reactive power-based droop control of the voltage reactive power regulation component ΔU q and voltage regulation component ΔU based on voltage control v The output voltage amplitude U of the reactive power controller is calculated. m ; S8. Based on the output phase angle θ of the active power controller and the output voltage amplitude U of the reactive power controller. m Obtain the reference current of the grid-type MMC-HVDC converter station and the d-axis reference current i of the track-type MMC-HVDC converter station. d,ref and q-axis reference current i q,ref ; S9. When the MMC-HVDC converter station switches from grid-based control to grid-following control, the active power controller output phase angle θ and reactive power controller output voltage amplitude U of the current grid-based control are used. m As the initial values ​​for grid-following control, when the MMC-HVDC converter station switches from grid-following control to grid-forming control, the current grid-following control PLL phase angle and the measured grid-side voltage amplitude are used as the initial values ​​for grid-forming control. The d-axis reference current i of the grid-following MMC-HVDC converter station is then controlled via a PI controller and a feedforward decoupling circuit. d,ref and q-axis reference current i q,ref The input is fed into the inner loop current controller.

2. The seamless switching method for grid-type and grid-following control of MMC-HVDC converter stations according to claim 1, characterized in that: The virtual inertia in step S2 is based on the mechanical and electromagnetic characteristic equations of virtual synchronous machine control.

3. The seamless switching method for grid-type and grid-following control of MMC-HVDC converter stations according to claim 2, characterized in that: The mechanical and electromagnetic characteristic equations based on virtual synchronous machine control are as follows: In the formula T m T is the mechanical torque. e Let ω be the electromagnetic torque, D be the damping coefficient, ω be the angular frequency of the synchronizer, ω0 be the rated angular frequency of the system, J be the moment of inertia, and θ be the mechanical angle of the synchronizer.

4. The seamless switching method for grid-type and grid-following control of MMC-HVDC converter stations according to claim 3, characterized in that: The expressions for power and frequency in step S3 are as follows: In the formula P m For the input power of the synchronous machine, P e This is the output power of the synchronous machine.

5. The seamless switching method for grid-type and grid-following control of MMC-HVDC converter stations according to claim 4, characterized in that: Through formula P m ′=P ref +k ω The active power reference value P after frequency modulation is obtained by calculating (ω0-ω). m ′, where P ref Input power P of the synchronous machine m In the VSG controller, k is equivalent to a reference value of active power. ω This is the frequency gain coefficient.

6. The seamless switching method for grid-type and grid-following control of MMC-HVDC converter stations according to claim 5, characterized in that, Step S5 includes the following steps: S5-1. The active power reference value P m Introducing this into frequency droop control, we obtain the following equation: S5-2. Input the equation into the PI controller to obtain the active power controller output phase angle θ.

7. The seamless switching method for grid-type and grid-following control of MMC-HVDC converter stations according to claim 1, characterized in that, Step S6 includes the following steps: S6-1. Using the formula ΔU q =k q (Q ref -Q) The voltage and reactive power regulation component ΔU based on voltage and reactive power droop control is calculated. q In the formula, k q Q is the reactive power regulation coefficient. ref Q is the MMC reactive power reference value, and Q is the MMC measured value. S6-2. Using the formula ΔU v =k v (Q acref -U ac The voltage regulation component ΔU based on voltage control is calculated. v In the formula, k v Q is the voltage regulation gain coefficient. acref U represents the change in the AC side voltage reference value. ac This is the measured value of the AC side voltage.

8. The seamless switching method for grid-type and grid-following control of MMC-HVDC converter stations according to claim 7, characterized in that: In step S7, formula U m =U n +ΔU q +ΔU v The output voltage amplitude U of the reactive power controller is calculated. m In the formula, U n This is the reference voltage.

9. The seamless switching method for grid-type and grid-following control of MMC-HVDC converter stations according to claim 7, characterized in that, Step S8 includes the following steps: S8-1. When the control mode of the MMC-HVDC converter station is grid-type, the output phase angle θ of the active power controller and the output voltage amplitude U of the reactive power controller are... m The reference voltage is obtained using a sine function, and then input into two PI controllers to generate a reference current in the dq coordinate system. S8-2. When the control mode of the MMC-HVDC converter station is grid-following, the formula is used... The d-axis reference current i of the grid-connected MMC-HVDC converter station is calculated. d,ref In the formula V d The voltage dq-axis component is obtained by transforming the measured actual three-phase voltage Vabc of the power grid through an abc transformation. q The voltage dq-axis component is obtained by dq transformation of the measured actual three-phase voltage Vabc of the power grid; S8-3. When the control mode of the MMC-HVDC converter station is grid-following, the formula is used to obtain the voltage dq-axis component. The q-axis reference current i of the grid-connected MMC-HVDC converter station is calculated. q,ref .

10. A seamless switching device for grid-based and grid-following control of MMC-HVDC converter stations, characterized in that, include: The system comprises a processor, a communication interface, a memory, and a communication bus, wherein the processor, the communication interface, and the memory communicate with each other via the communication bus; wherein: The memory is used to store computer programs; The processor is configured to execute by running programs stored in the memory: Run the MMC-HVDC system, analyze its current operating status and grid conditions, and obtain raw grid data. Provide virtual inertia to the MMC-HVDC system; Construct expressions for active power and frequency; Construct a reference value for active power after frequency modulation with droop control incorporating active power and frequency based on expressions for active power and frequency. The active power reference value is used to obtain the active power controller output phase angle θ; Calculate the voltage and reactive power droop control component ΔU based on voltage and reactive power. q and voltage regulation component ΔU based on voltage control v ; Voltage reactive power regulation component ΔU based on voltage and reactive power droop control q and voltage regulation component ΔU based on voltage control v The output voltage amplitude U of the reactive power controller is calculated. m ; Based on the output phase angle θ of the active power controller and the output voltage amplitude U of the reactive power controller m Obtain the reference current of the grid-type MMC-HVDC converter station and the d-axis reference current i of the track-type MMC-HVDC converter station. d,ref and q-axis reference current i q,ref ; When the MMC-HVDC converter station switches from grid-based control to grid-following control, it uses the active power controller output phase angle θ and reactive power controller output voltage amplitude U of the current grid-based control. m As the initial values ​​for grid-following control, when the MMC-HVDC converter station switches from grid-following control to grid-forming control, the current grid-following control PLL phase angle and the measured grid-side voltage amplitude are used as the initial values ​​for grid-forming control. The d-axis reference current i of the grid-following MMC-HVDC converter station is then controlled via a PI controller and a feedforward decoupling circuit. d,ref and q-axis reference current i q,ref The input is fed into the inner loop current controller.

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