A control system for enhancing the inertia support capability of a flexible DC transmission system

Abstract

The present invention relates to the technical field of flexible direct current transmission. In view of the problem that conventional grid-following flexible direct current transmission systems have poor frequency support capabilities for power systems, the present invention proposes a control system for enhancing the inertia support capability of flexible direct current transmission systems. A real-time linkage mechanism among the AC frequency, DC voltage, and grid voltage of the sending-end converter station is established, solving the frequency decoupling problem of the sending-end converter station and the receiving-end converter station under conventional grid-following control. The DC voltage signal of the flexible direct current transmission system is transmitted to the new energy power supply side, replacing the conventional method of using a phase-locked loop to observe the grid frequency, and using the DC voltage signal to adjust the output power of the new energy power supply to realize the frequency support function for the grid. Inertia support and frequency adjustment control are added to the new energy power supply, and the inertia support coefficient and frequency adjustment coefficient are adjusted in real time according to the DC voltage signal of the direct current transmission system, thereby enhancing the inertia support capability of the flexible direct current transmission system.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible direct current (DC) transmission technology, and in particular to a control system for enhancing the inertia support capability of a flexible DC transmission system. Background Art

[0002] Due to the randomness and volatility of wind and solar energy, the effective inertia of the power system will be reduced, resulting in significant frequency fluctuations. For long-distance transmission of electricity, the use of high-voltage direct current (HVDC) transmission is one of the effective solutions to the challenge of integrating renewable energy into the grid. Currently, HVDC transmission using conventional vector control strategies decouples the frequencies of the sending and receiving systems. This makes it difficult for HVDC to provide inertia support for the power system under active power disturbances, which is detrimental to the frequency stability of the power system.

[0003] Grid-based control is an effective method for addressing inertia losses in HVDC converter stations. Grid-based control directly controls the phase and amplitude of the converter output voltage, enabling autonomous grid synchronization without a phase-locked loop (PLL). Grid-based control allows converter stations to actively support the grid, exhibiting voltage source characteristics similar to those of synchronous generators, making it suitable for emerging power systems primarily powered by renewable energy.

[0004] Currently, power synchronization control, power reduction control, and virtual synchronous generator control can all be considered grid-based control. These grid-based control methods employ active power control at converter stations, which can lead to interactive instability issues on the DC side. Therefore, for HVDC transmission systems, it is necessary to develop a new grid-based control method that utilizes DC voltage control. Summary of the Invention

[0005] In order to address the problem of poor frequency support capability of the power system due to the frequency decoupling of the sending-end converter station and the receiving-end converter station in the conventional grid-following flexible direct current transmission system, the present invention proposes a control system for enhancing the inertia support capability of the flexible direct current transmission system, thereby effectively improving the frequency stability of the flexible direct current transmission system connected to the power grid.

[0006] In view of this, the first aspect of the present application provides a control system for enhancing the inertia support capability of a flexible direct current transmission system, the control system comprising: a new energy power source, a sending-end converter station, a receiving-end converter station, and a power grid, wherein the new energy power source is connected to the AC side of the sending-end converter station, the DC side of the sending-end converter station is connected to the DC side of the receiving-end converter station via a DC cable, and the AC side of the receiving-end converter station is connected to the power grid;

[0007] The control structure of the sending-end converter station includes: a dual-loop control structure consisting of an AC voltage control outer loop and an AC current control inner loop, and a frequency control loop is used to control the AC frequency of the sending-end converter station; in the frequency control loop of the sending-end converter station, the DC voltage u of the sending-end converter station is detected. dc , let u dc The per-unit value of the DC voltage is obtained by dividing the rated value of the DC voltage of the sending-end converter station by , The output after passing through an integrator with a gain of 100π is the phase θ s ;

[0008] Detect the three-phase voltage on the AC side of the sending-end converter station , three-phase current , The d-axis component of the AC voltage generated by the sending-end converter station is generated through the rotation coordinate transformation , q-axis component , The d-axis component of the AC current at the sending-end converter station is generated through the rotation coordinate transformation , q-axis component , where the phase for the rotational coordinate transformation is θ s .

[0009] Optionally, the AC voltage control outer loop includes a D-axis voltage control loop and a Q-axis voltage control loop, and the AC current control inner loop includes a D-axis current control loop and a Q-axis current control loop, the output of the D-axis voltage control loop serves as the input of the D-axis current control loop, and the output of the Q-axis voltage control loop serves as the input of the Q-axis current control loop;

[0010] In the AC voltage control outer loop, the D-axis component of the AC voltage reference value at the sending-end converter station and Entering the D-axis voltage control loop, the Q-axis component of the AC voltage reference value of the sending-end converter station and Enter the Q-axis voltage control loop; in the AC current control inner loop, the output of the D-axis voltage control loop is Entering the D-axis current control loop, the output of the Q-axis voltage control loop is Enter the Q-axis current control loop; the outputs of the D-axis current control loop and the Q-axis current control loop are transformed by rotating coordinates and pulse width modulation to generate trigger pulses for the sending-end converter station. The phase for the rotating coordinate transformation is θ s .

[0011] Optionally, the receiving-end converter station adopts the following control structure:

[0012] The receiving-end converter station adopts a three-loop control structure consisting of an outer loop for reactive power control, a middle loop for AC voltage control, and an inner loop for AC current control. In addition, a DC voltage control loop is used to control the DC voltage of the receiving-end converter station. In the DC voltage control loop of the receiving-end converter station, the DC voltage u is detected. dc , let u dc Divide by the reference value u of the DC voltage dcref , and then the output after passing through an integrator with a gain of 100π is the phase θ; detect the three-phase voltage on the AC side of the receiving converter station , three-phase current , The d-axis component of the AC voltage at the receiving converter station is generated through the rotation coordinate transformation , q-axis component , The d-axis component of the AC current at the receiving converter station is generated through the rotation coordinate transformation , q-axis component , where the phase used for the rotational coordinate transformation is θ.

[0013] Optionally, the AC voltage control middle loop includes a D-axis voltage control loop and a Q-axis voltage control loop, and the AC current control inner loop includes a D-axis current control loop and a Q-axis current control loop; the output of the D-axis voltage control loop serves as the input of the D-axis current control loop, and the output of the Q-axis voltage control loop serves as the input of the Q-axis current control loop;

[0014] In the reactive power control outer loop, the reference value of reactive power is and feedback value The difference enters the reactive power controller; in the AC voltage control loop, the output of the reactive power controller is Entering the D-axis voltage control loop, 0 and Enter the Q-axis voltage control loop; in the AC current control inner loop, the output of the D-axis voltage control loop is Entering the D-axis current control loop, the output of the Q-axis voltage control loop is Enter the Q-axis current control loop; the outputs of the D-axis current control loop and the Q-axis current control loop are transformed by rotating coordinates and pulse width modulated to generate trigger pulses for the receiving converter station, and the phase used for the rotating coordinate transformation is θ.

[0015] Optionally, the D-axis voltage control loop, the Q-axis voltage control loop, the D-axis current control loop, and the Q-axis current control loop in the sending-end converter station adopt proportional-integral regulators;

[0016] Optionally, the reactive power controller, the D-axis current control loop, and the Q-axis current control loop in the receiving-end converter station adopt proportional-integral regulators.

[0017] Optionally, the D-axis voltage control loop and the Q-axis voltage control loop in the receiving-end converter station adopt a regulator based on a first-order low-pass filter.

[0018] Optionally, the DC voltage u of the sending-end converter station dc Transmitted to the new energy power supply side, the new energy power supply adopts the following control structure for inertia support control:

[0019] DC voltage u at the sending-end converter station dc Divide by the rated value of the DC voltage at the sending-end converter station to get the per-unit value of the DC voltage , The output after entering the inertia support control module is P in ; The output after entering the frequency regulation control module is P dr , the active power setting value P of the new energy power supply to achieve maximum power tracking control mppt Overlay P in 、 P dr Generate the reference value P of the active power output of the new energy power supply mref ;

[0020] In the inertia support control module, After a gain of -K in The differential link, then multiply The latter is the output of the inertia support control module, where K in is the inertia support coefficient;

[0021] In the frequency adjustment control module, Subtract 1 to get the DC voltage deviation , After a gain of -K dr The proportional link is followed by the output of the frequency regulation control module, where K dr is the frequency regulation control coefficient.

[0022] Optionally, the inertia support coefficient K in according to Real-time adjustment, K in and The relationship between them is:

[0023] ;

[0024] Where H W is the inertia time constant of the new energy power source.

[0025] Optionally, the frequency adjustment control coefficient Kdr according to Real-time adjustment, K dr and The relationship between them is:

[0026] .

[0027] It can be seen from the above technical solutions that the present invention has the following advantages:

[0028] 1) A real-time linkage mechanism among the AC frequency, DC voltage, and grid voltage at the sending-end converter station has been established, solving the frequency decoupling problem between the sending-end converter station and the receiving-end converter station under conventional grid-following control.

[0029] 2) The DC voltage signal of the flexible DC transmission system is transmitted to the renewable energy power source side, replacing the conventional method of using a phase-locked loop to observe the grid frequency. The DC voltage signal is used to adjust the output power of the renewable energy power source, thus realizing the frequency support function for the grid.

[0030] 3) Inertia support and frequency regulation control are added to the new energy power source, and the inertia support coefficient and frequency regulation coefficient are adjusted in real time according to the DC voltage signal of the DC transmission system, thereby enhancing the inertia support capability of the flexible DC transmission system. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0032] Figure 1 This is a block diagram of a control system for enhancing the inertia support capability of a flexible HVDC transmission system according to an embodiment of the present invention;

[0033] Figure 2 This is a block diagram of an inertia support and frequency regulation control system attached to a new energy power source according to an embodiment of the present invention;

[0034] Figure 3 This is a simulation waveform of a flexible DC transmission system when the load suddenly increases, a simulation embodiment of the present invention;

[0035] Figure 4 This is a simulation waveform of a flexible DC transmission system under wind speed fluctuations, a simulation embodiment of the present invention. DETAILED DESCRIPTION

[0036] In order to make the purpose, features, and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0037] See also Figure 1 A control system for enhancing the inertia support capability of a flexible direct current transmission system provided in an embodiment of the present invention includes: a new energy power source, a sending-end converter station, a receiving-end converter station, and a power grid, wherein the new energy power source is connected to the AC side of the sending-end converter station, the DC side of the sending-end converter station is connected to the DC side of the receiving-end converter station via a DC cable, and the AC side of the receiving-end converter station is connected to the power grid;

[0038] The control structure of the sending-end converter station includes:

[0039] The dual-loop control structure consists of an AC voltage control outer loop and an AC current control inner loop. In addition, a frequency control loop is used to control the AC frequency of the sending-end converter station. In the frequency control loop of the sending-end converter station, the DC voltage u dc , let u dc Divide by the rated value of the DC voltage at the sending end converter station to get the per unit value of the DC voltage , The output after passing through an integrator with a gain of 100π is the phase θ s ;

[0040] Detect the three-phase voltage on the AC side of the sending-end converter station , three-phase current , The d-axis component of the AC voltage generated by the sending-end converter station is generated through the rotation coordinate transformation , q-axis component , The d-axis component of the AC current at the sending-end converter station is generated through the rotation coordinate transformation , q-axis component , where the phase used for the rotational coordinate transformation is θ s .

[0041] In one embodiment, the AC voltage control outer loop includes a D-axis voltage control loop and a Q-axis voltage control loop, and the AC current control inner loop includes a D-axis current control loop and a Q-axis current control loop. The output of the D-axis voltage control loop serves as the input of the D-axis current control loop, and the output of the Q-axis voltage control loop serves as the input of the Q-axis current control loop.

[0042] In the AC voltage control outer loop, the D-axis component of the AC voltage reference value at the sending-end converter station and Entering the D-axis voltage control loop, the Q-axis component of the AC voltage reference value of the sending-end converter station and Enter the Q-axis voltage control loop; in the AC current control inner loop, the output of the D-axis voltage control loop is Entering the D-axis current control loop, the output of the Q-axis voltage control loop is Enter the Q-axis current control loop; the outputs of the D-axis current control loop and the Q-axis current control loop are transformed into the trigger pulse of the sending-end converter station after the rotation coordinate transformation and pulse width modulation. The phase for the rotation coordinate transformation is θ s .

[0043] In one embodiment, the receiving-end converter station adopts the following control structure:

[0044] The receiving-end converter station adopts a three-loop control structure consisting of an outer loop for reactive power control, a middle loop for AC voltage control, and an inner loop for AC current control. In addition, a DC voltage control loop is used to control the DC voltage of the receiving-end converter station. In the DC voltage control loop of the receiving-end converter station, the DC voltage u is detected. dc , let u dc Divide by the reference value u of the DC voltage dcref , and then the output after passing through an integrator with a gain of 100π is the phase θ; detect the three-phase voltage on the AC side of the receiving converter station , three-phase current , The d-axis component of the AC voltage at the receiving converter station is generated through the rotation coordinate transformation , q-axis component , The d-axis component of the AC current at the receiving converter station is generated through the rotation coordinate transformation , q-axis component , where the phase used for the rotational coordinate transformation is θ.

[0045] In one embodiment, the AC voltage control middle loop includes a D-axis voltage control loop and a Q-axis voltage control loop, and the AC current control inner loop includes a D-axis current control loop and a Q-axis current control loop; the output of the D-axis voltage control loop serves as the input of the D-axis current control loop, and the output of the Q-axis voltage control loop serves as the input of the Q-axis current control loop;

[0046] In the reactive power control outer loop, the reference value of reactive power is and feedback value The difference enters the reactive power controller; in the AC voltage control loop, the output of the reactive power controller is Entering the D-axis voltage control loop, 0 and Enter the Q-axis voltage control loop; in the AC current control inner loop, the output of the D-axis voltage control loop is Entering the D-axis current control loop, the output of the Q-axis voltage control loop is Enter the Q-axis current control loop; the outputs of the D-axis current control loop and the Q-axis current control loop are transformed into a trigger pulse for the receiving converter station after rotating coordinate transformation and pulse width modulation. The phase used for rotating coordinate transformation is θ.

[0047] In one embodiment, the D-axis voltage control loop, Q-axis voltage control loop, D-axis current control loop, and Q-axis current control loop in the sending-end converter station employ proportional-integral regulators; the reactive power controller, D-axis current control loop, and Q-axis current control loop in the receiving-end converter station employ proportional-integral regulators. The D-axis voltage control loop and Q-axis voltage control loop in the receiving-end converter station employ regulators based on first-order low-pass filters.

[0048] In one embodiment, Figure 2 As shown, the DC voltage u dc Transmitted to the new energy power supply side, the new energy power supply adopts the following control structure for inertia support control:

[0049] DC voltage u at the sending-end converter station dc Divide by the rated value of the DC voltage at the sending-end converter station to get the per-unit value of the DC voltage , The output after entering the inertia support control module is P in ; The output after entering the frequency regulation control module is P dr , the active power setting value P of the new energy power supply to achieve maximum power tracking control mppt Overlay P in 、 P dr Generate the reference value P of the active power output of the new energy power supply mref ;

[0050] In the inertia support control module, After a gain of -K in The differential link, then multiply The latter is the output of the inertia support control module, where K in is the inertia support coefficient;

[0051] In the frequency regulation control module, Subtract 1 to get the DC voltage deviation , After a gain of -K drThe proportional link is followed by the output of the frequency regulation control module, where K dr is the frequency regulation control coefficient.

[0052] Among them, the inertia support coefficient K in according to Real-time adjustment, K in and The relationship between them is:

[0053] ;

[0054] Where H W is the inertia time constant of the new energy power source.

[0055] Among them, the frequency regulation control coefficient K dr according to Real-time adjustment, K dr and The relationship between them is:

[0056] .

[0057] Simulation Example 1:

[0058] like Figure 3 As shown in the figure, the simulation waveform of the flexible DC transmission system under load sudden increase is shown in the simulation embodiment of the present invention, where the grid short-circuit ratio is 2 and the wind speed is 9m / s. As the load increases and the grid frequency begins to decrease at 30 seconds, the per-unit value of the DC voltage at the receiving converter station changes with the per-unit value of the grid frequency, and the speed of the wind turbine ω t The power is reduced to release kinetic energy, and the output active power of the receiving converter station is increased to support the power grid. Figure 3 The simulation results in

[15] show that the proposed control system can enable the HVDC Flexible system to measure the grid frequency without using a phase-locked loop (PLL). The additional inertia support and frequency regulation control can enhance the HVDC Flexible system's support capability for the grid by releasing the kinetic energy stored in wind turbines.

[0059] Simulation Example 2:

[0060] like Figure 4As shown, a simulation waveform of a flexible DC transmission system under wind speed fluctuations, in a simulation embodiment of the present invention, is shown. The grid short-circuit ratio is 2, and the wind turbines use both maximum power point tracking (MPPT) control and the control strategy proposed in the present invention. When using maximum power point tracking control, the grid frequency fluctuates dramatically when the wind speed changes. When using the inertia support and frequency regulation control strategy proposed in the present invention, the frequency fluctuation in the grid is reduced, and the fluctuation in the active power output of the wind turbine is relatively low. It can be seen that the additional inertia support and frequency regulation control strategy proposed in the present invention can improve the flexible DC transmission system's ability to support the grid.

[0061] In summary, the present invention proposes a control system for enhancing the inertia support capability of a flexible direct current transmission system. This system establishes a real-time linkage mechanism among the AC frequency, DC voltage, and grid voltage of a sending-end converter station, thereby solving the frequency decoupling problem of the sending-end converter station and the receiving-end converter station under conventional grid-following control. The DC voltage signal of the flexible direct current transmission system is transmitted to the renewable energy power supply side, replacing the conventional method of using a phase-locked loop to observe the grid frequency. The DC voltage signal is used to adjust the output power of the renewable energy power supply, thereby realizing the frequency support function for the grid. Inertia support and frequency adjustment control are added to the renewable energy power supply, and the inertia support coefficient and frequency adjustment coefficient are adjusted in real time according to the DC voltage signal of the DC transmission system, thereby enhancing the inertia support capability of the flexible direct current transmission system.

[0062] In the several embodiments provided by the present invention, it should be understood that the disclosed systems, devices, and methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, the division of units is merely a logical function division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the mutual coupling or direct coupling or communication connection shown or discussed can be through some interface, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0063] Units described as separate components may or may not be physically separate, and components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of these units may be selected to achieve the purpose of this embodiment according to actual needs.

[0064] In addition, the functional units in the various embodiments of the present invention may be integrated into a single processing unit, each unit may exist physically separately, or two or more units may be integrated into a single unit. The aforementioned integrated units may be implemented in the form of hardware or software functional units.

[0065] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the portion that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for causing a computer device (which can be a personal computer, server, or network device, etc.) to execute all or part of the steps of the various embodiments of the method of the present invention. The aforementioned storage medium includes various media that can store program code, such as USB flash drives, mobile hard drives, read-only memories (ROMs), random access memories (RAMs), magnetic disks, or optical disks.

[0066] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A control system for enhancing the inertia support capability of a flexible direct current transmission system, characterized in that: The control system includes: a new energy power source, a sending-end converter station, a receiving-end converter station, and a power grid, wherein the new energy power source is connected to the AC side of the sending-end converter station, the DC side of the sending-end converter station is connected to the DC side of the receiving-end converter station via a DC cable, and the AC side of the receiving-end converter station is connected to the power grid; The control structure of the sending-end converter station includes: a dual-loop control structure consisting of an AC voltage control outer loop and an AC current control inner loop, and a frequency control loop is used to control the AC frequency of the sending-end converter station; in the frequency control loop of the sending-end converter station, the DC voltage u of the sending-end converter station is detected. dc , let u dc The per-unit value of the DC voltage is obtained by dividing the rated value of the DC voltage of the sending-end converter station by , The output after passing through an integrator with a gain of 100π is the phase θ s ; Detect the three-phase voltage on the AC side of the sending-end converter station , three-phase current , The d-axis component of the AC voltage at the sending-end converter station is generated by rotating coordinate transformation , q-axis component , The d-axis component of the AC current at the sending-end converter station is generated through the rotation coordinate transformation , q-axis component , where the phase for the rotational coordinate transformation is θ s； Among them, the DC voltage u of the sending-end converter station dc Transmitted to the new energy power supply side, the new energy power supply adopts the following control structure for inertia support control: DC voltage u at the sending-end converter station dc Divide by the rated value of the DC voltage at the sending-end converter station to get the per-unit value of the DC voltage , The output after entering the inertia support control module is ; The output after entering the frequency regulation control module is , the active power setting value P of the new energy power supply to achieve maximum power tracking control mppt Overlay 、 Generate the reference value P of the active power output of the new energy power supply mref ; In the inertia support control module, After a gain of -K in The differential link, then multiply The latter is the output of the inertia support control module, where K in is the inertia support coefficient; In the frequency adjustment control module, Subtract 1 to get the DC voltage deviation , After a gain of -K dr The proportional link is followed by the output of the frequency regulation control module, where K dr is the frequency regulation control coefficient.

2. The control system for enhancing the inertia support capability of a flexible HVDC transmission system according to claim 1, characterized in that: The AC voltage control outer loop contains a D-axis voltage control loop and a Q-axis voltage control loop, and the AC current control inner loop contains a D-axis current control loop and a Q-axis current control loop. The output of the D-axis voltage control loop serves as the input of the D-axis current control loop, and the output of the Q-axis voltage control loop serves as the input of the Q-axis current control loop. In the AC voltage control outer loop, the D-axis component of the AC voltage reference value at the sending-end converter station and Entering the D-axis voltage control loop, the Q-axis component of the AC voltage reference value of the sending-end converter station and Enter the Q-axis voltage control loop; in the AC current control inner loop, the output of the D-axis voltage control loop is Entering the D-axis current control loop, the output of the Q-axis voltage control loop is Enter the Q-axis current control loop; the outputs of the D-axis current control loop and the Q-axis current control loop are transformed by rotating coordinates and pulse width modulation to generate trigger pulses for the sending-end converter station. The phase for the rotating coordinate transformation is θ s .

3. The control system for enhancing the inertia support capability of a flexible HVDC transmission system according to claim 1, characterized in that: The receiving-end converter station adopts the following control structure: The receiving-end converter station adopts a three-loop control structure consisting of an outer loop for reactive power control, a middle loop for AC voltage control, and an inner loop for AC current control. In addition, a DC voltage control loop is used to control the DC voltage of the receiving-end converter station. In the DC voltage control loop of the receiving-end converter station, the DC voltage u is detected. dc , let u dc Divide by the reference value u of the DC voltage dcref , and then the output after passing through an integrator with a gain of 100π is the phase θ; detect the three-phase voltage on the AC side of the receiving converter station , three-phase current , The d-axis component of the AC voltage at the receiving converter station is generated through the rotation coordinate transformation , q-axis component , The d-axis component of the AC current at the receiving converter station is generated through the rotation coordinate transformation , q-axis component , where the phase used for the rotational coordinate transformation is θ.

4. The control system for enhancing the inertia support capability of a flexible HVDC transmission system according to claim 3, characterized in that: The AC voltage control middle loop includes a D-axis voltage control loop and a Q-axis voltage control loop, and the AC current control inner loop includes a D-axis current control loop and a Q-axis current control loop; the output of the D-axis voltage control loop serves as the input of the D-axis current control loop, and the output of the Q-axis voltage control loop serves as the input of the Q-axis current control loop; In the reactive power control outer loop, the reference value of reactive power is and feedback value The difference enters the reactive power controller; in the AC voltage control loop, the output of the reactive power controller is Entering the D-axis voltage control loop, 0 and Enter the Q-axis voltage control loop; in the AC current control inner loop, the output of the D-axis voltage control loop is Entering the D-axis current control loop, the output of the Q-axis voltage control loop is Enter the Q-axis current control loop; the outputs of the D-axis current control loop and the Q-axis current control loop are transformed by rotating coordinates and pulse width modulated to generate trigger pulses for the receiving converter station, and the phase used for the rotating coordinate transformation is θ.

5. The control system for enhancing the inertia support capability of a flexible HVDC transmission system according to any one of claims 1 to 4, characterized in that: The D-axis voltage control loop, the Q-axis voltage control loop, the D-axis current control loop, and the Q-axis current control loop in the sending-end converter station adopt proportional-integral regulators.

6. The control system for enhancing the inertia support capability of a flexible HVDC transmission system according to any one of claims 1 to 4, characterized in that: The reactive power controller, the D-axis current control loop and the Q-axis current control loop in the receiving-end converter station adopt proportional-integral regulators.

7. The control system for enhancing the inertia support capability of a flexible HVDC transmission system according to any one of claims 1 to 4, characterized in that: The D-axis voltage control loop and the Q-axis voltage control loop in the receiving-end converter station adopt a regulator based on a first-order low-pass filter.

8. The control system for enhancing the inertia support capability of a flexible HVDC transmission system according to claim 1, characterized in that: The inertia support coefficient K in according to Real-time adjustment, K in and The relationship between them is: ； Where H W is the inertia time constant of the new energy power source.

9. The control system for enhancing the inertia support capability of a flexible HVDC transmission system according to claim 1, characterized in that: The frequency adjustment control coefficient K dr according to Real-time adjustment, K dr and The relationship between them is: ； Where H W is the inertia time constant of the new energy power source.

Images