Control system for enhancing inertia supporting capability of flexible direct-current power transmission system

Abstract

The invention relates to the technical field of flexible direct-current power transmission, and provides a control system for enhancing the inertia supporting capacity of a flexible direct-current power transmission system in order to solve the problem that a conventional grid-following type flexible direct-current power transmission system is poor in power system frequency supporting capacity. A real-time linkage mechanism among the alternating-current frequency, the direct-current voltage and the power grid voltage of the sending-end converter station is established, and the frequency decoupling problem of the sending-end converter station and the receiving-end converter station under conventional network following type control is solved. A direct-current voltage signal of the flexible direct-current power transmission system is transmitted to a new energy power supply side, a conventional method for observing the frequency of a power grid by using a phase-locked loop is replaced, the output power of the new energy power supply is adjusted by using the direct-current voltage signal, and a frequency supporting function for the power grid is realized. Inertia support and frequency adjustment control are added on a new energy power supply, and an inertia support coefficient and a frequency adjustment coefficient are adjusted in real time according to a direct current voltage signal of the direct current power transmission system, so that the inertia support capability of the flexible direct current power transmission system is enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible direct current power transmission, and in particular to a control system for enhancing the inertia support capability of a flexible direct current power 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 electric energy, the use of high-voltage direct current transmission is one of the effective solutions to the problem of renewable energy grid connection. At present, the high-voltage direct current transmission using conventional vector control strategy will decouple the frequency of the sending and receiving systems. When the active power disturbance occurs in the power grid, high-voltage direct current transmission is difficult to provide inertial support for the power system, which is not conducive to the frequency stability of the power system.

[0003] Grid-type control is an effective method to solve the inertia loss of converter stations in high-voltage direct current transmission systems. Grid-type control directly controls the phase and amplitude of the converter output voltage and has the function of autonomously synchronizing the power grid without a phase-locked loop. The converter station with grid-type control can actively support the power grid and exhibits external characteristics of a voltage source similar to that of a synchronous generator, which is suitable for new power systems based on renewable energy.

[0004] At present, power synchronization control, power reduction control and virtual synchronous generator control can all be regarded as grid-type control. Under these grid-type controls, the converter station adopts the active power control mode and faces some interactive instability problems on the DC side. Therefore, it is necessary to develop a new grid-type control method using the DC voltage control mode for HVDC transmission systems. Summary of the invention

[0005] In view of the frequency decoupling of the sending-end converter station and the receiving-end converter station in the conventional grid-following flexible DC transmission system, and the poor frequency supporting capability of the power system, the present invention proposes a control system for enhancing the inertia supporting capability of the flexible DC transmission system, thereby effectively improving the frequency stability of the flexible DC 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 through 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 Divide by the rated value of the DC voltage of the sending-end converter station to obtain the per unit value of the DC voltage , The output after passing through an integrator with a gain of 100π is 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 by rotating coordinate transformation , q-axis component , where the phase for the rotational coordinate transformation is θ s .

[0009] Optionally, the AC voltage control outer loop contains a D-axis voltage control loop and a Q-axis voltage control loop, 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;

[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 of reactive power control outer loop, AC voltage control middle loop, and AC current control inner loop. 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 by rotating coordinate transformation , q-axis component , The d-axis component of the AC current at the receiving converter station is generated by rotating coordinate transformation , q-axis component , where the phase used for the rotational coordinate transformation is θ.

[0013] Optionally, the AC voltage control middle 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;

[0014] In the reactive power control outer loop, the reference value of reactive power is With 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 modulation 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 converter station to get the per unit value of the DC voltage , The output after entering the inertial 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 part, then multiply The latter is the output of the inertial 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 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] In the formula, 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 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;

[0029] 2) The DC voltage signal of the flexible DC 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 to achieve 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 capacity 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 drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. 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 creative labor.

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

[0033] Figure 2 This is an embodiment of the present invention - an additional inertia support and frequency regulation control block diagram on a new energy power source;

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

[0035] Figure 4 This is a simulation waveform of a flexible DC power transmission system when wind speed fluctuates, 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 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 comprises: 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 through 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 of the sending-end converter station is detected. 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 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 by rotating 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, 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 by rotating coordinates and pulse width modulation to generate trigger pulses for the sending-end converter station. The phase used for rotating 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 of reactive power control outer loop, AC voltage control middle loop, and AC current control inner loop. 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 by rotating coordinate transformation , q-axis component , The d-axis component of the AC current at the receiving converter station is generated by rotating 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 With 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 modulation to generate trigger pulses for the receiving converter station, and 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 adopt proportional-integral regulators; the reactive power controller, D-axis current control loop, and Q-axis current control loop in the receiving-end converter station adopt proportional-integral regulators. The D-axis voltage control loop and Q-axis voltage control loop in the receiving-end converter station adopt regulators based on first-order low-pass filters.

[0048] In one embodiment, Figure 2 As shown, 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:

[0049] DC voltage u at the sending end converter station dc Divide by the rated value of the DC voltage at the sending converter station to get the per unit value of the DC voltage , The output after entering the inertial 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 inertial support control module, After a gain of -K in The differential part, then multiply The latter is the output of the inertial 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 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] In the formula, 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 when the load suddenly increases in a 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 end converter station changes with the per-unit value of the grid frequency, and the speed ω of the wind turbine set t The voltage 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 show that the proposed control system can enable the flexible DC transmission system to measure the grid frequency without using a phase-locked loop, and the additional inertial support and frequency regulation control can enhance the support capacity of the flexible DC transmission system to the grid by releasing the kinetic energy stored in the wind turbines.

[0059] Simulation Example 2:

[0060] like Figure 4As shown, a simulation waveform of a flexible DC power transmission system when the wind speed fluctuates is shown in a simulation embodiment of the present invention, wherein the short-circuit ratio of the power grid is 2, and the wind turbines respectively adopt the maximum power point tracking (MPPT) control and the control strategy proposed in the present invention. When the maximum power point tracking control is adopted, the frequency of the power grid will fluctuate violently when the wind speed changes; when the inertia support and frequency regulation control strategy proposed in the present invention is used, the frequency fluctuation degree in the power grid is reduced, and the active power output of the wind turbine set fluctuates less. It can be seen that the additional inertia support and frequency regulation control strategy proposed in the present invention can improve the support capacity of the flexible DC power transmission system for the power grid.

[0061] In summary, the present invention proposes a control system for enhancing the inertia support capability of a flexible direct current transmission system, establishes a real-time linkage mechanism among the AC frequency, DC voltage, and grid voltage of a sending-end converter station, and solves the frequency decoupling problem of a sending-end converter station and a receiving-end converter station under conventional grid-following control; transmits the DC voltage signal of the flexible direct current transmission system to the new energy power supply side, replacing the conventional method of using a phase-locked loop to observe the grid frequency, and uses the DC voltage signal to adjust the output power of the new energy power supply to realize the frequency support function for the grid; adds inertia support and frequency adjustment control to the new energy power supply, and adjusts the inertia support coefficient and the frequency adjustment coefficient 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.

[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 only schematic, for example, the division of units is only a logical function division, and there may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or units, which can be electrical, mechanical or other forms.

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

[0064] In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0065] If the integrated unit is implemented in the form of 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, in essence, or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, server, or network device, etc.) to perform all or part of the steps of the methods of each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, etc. Various media that can store program codes.

[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 the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. 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 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 through 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 Divide by the rated value of the DC voltage of the sending-end converter station to obtain the per unit value of the DC voltage , The output after passing through an integrator with a gain of 100π is 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 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 by rotating coordinate transformation , q-axis component , where the phase for the rotational coordinate transformation is θ s .

2. The control system for enhancing the inertia support capability of a flexible DC 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, 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 DC 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 of reactive power control outer loop, AC voltage control middle loop, and AC current control inner loop. 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 by rotating coordinate transformation , q-axis component , The d-axis component of the AC current at the receiving converter station is generated by rotating 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 DC 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 With 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 modulation 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 DC power 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 DC power 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 DC power 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 DC transmission system according to claim 1, characterized in that: 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 converter station to get the per unit value of the DC voltage , The output after entering the inertial 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 ; In the inertia support control module, After a gain of -K in The differential part, then multiply The latter is the output of the inertial 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 the output of the frequency regulation control module, where K dr is the frequency regulation control coefficient.

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

10. The control system for enhancing the inertia support capability of a flexible DC transmission system according to claim 8, characterized in that: The frequency regulation control coefficient K dr according to Real-time adjustment, K dr and The relationship between them is: 。

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