Inertia support method based on sub-module capacitance energy adjustment network construction control

Abstract

The invention discloses an inertia support method based on sub-module capacitance energy adjustment network construction control, and the method comprises the steps: obtaining the voltage and current of an MMC grid-connected point, and carrying out the decomposition of the voltage and current to obtain components; mMC direct-current voltage, current, a sub-module capacitor voltage average value and reactive power are obtained; obtaining an AC voltage and an angular frequency of an MMC grid-connected point; calculating the capacitance energy of the MMC sub-module, and calculating the phase of the MMC; calculating the voltage and current of the MMC grid connection point; the voltage of the MMC modulation voltage is calculated, and the voltage of the MMC modulation voltage in the static coordinate system is calculated; the DC internal potential of the MMC is calculated, and the bridge arm modulation voltage of the MMC is calculated; and calculating the number of sub-modules needing to be input by the MMC bridge arm, and generating a corresponding control pulse by using a nearest level approximation modulation theory to realize inertia support control of the MMC. The self-synchronization control without the phase-locked loop is realized by utilizing the capacitance energy of the sub-modules, and the inertia supporting capability of the MMC is improved by dynamically adjusting the input number of the sub-modules.

Description

Technical Field

[0001] This invention relates to the field of active support control technology for MMC converter stations, and more specifically, to an inertial support method based on submodule capacitor energy regulation network control. Background Technology

[0002] In the process of building a new power system, new energy sources are increasingly becoming an important part of the energy supply system. Flexible DC transmission technology based on modular multilevel converters (MMC) is currently the preferred solution for large-scale transmission of new energy. However, with the grid connection of a high proportion of new energy and a high proportion of power electronic equipment, the power grid faces problems such as reduced inertia, weakened damping, and insufficient support capacity. Converters using traditional grid-connected control are no longer sufficient to support the safe and stable operation of the new power system.

[0003] Network-based control is an effective way to address the lack of inertia in converters, achieving synchronization without the need for a phase-locked loop (PLL). Furthermore, modular multilevel converters (MMCs) contain numerous energy storage components, with energy primarily stored in capacitors as potential energy, becoming the main source of energy for inertia support. Therefore, it is urgent to develop the capacitor energy margin and control dimensions of MMCs to enhance the converter's inertia support capability. Summary of the Invention

[0004] The purpose of this invention is to overcome the defects and shortcomings of the prior art and provide an inertia support method based on submodule capacitor energy adjustment network control. This method utilizes the capacitor energy of the submodules to achieve phase-locked loop-free self-synchronization control and achieves the maximum utilization of capacitor energy margin by dynamically adjusting the number of submodules, thereby significantly improving the inertia support capability of the modular multilevel converter (MMC).

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] An inertia support method based on submodule capacitor energy regulation network control includes the following steps:

[0007] Obtain the voltage and current at the MMC grid connection point, and perform dq decomposition to obtain d-axis and q-axis components; obtain the actual and reference values ​​of the MMC DC voltage, DC current, average value of submodule capacitor voltage, and reactive power; obtain the actual and reference values ​​of the MMC grid connection point AC voltage and angular frequency.

[0008] Calculate the actual and reference values ​​of the capacitor energy of the MMC submodule; calculate the phase reference value of the MMC; calculate the d-axis and q-axis voltage reference values ​​and d-axis and q-axis current reference values ​​of the MMC grid connection point; calculate the d-axis and q-axis voltage reference values ​​of the MMC modulation voltage; calculate the voltage reference value of the MMC modulation voltage in the stationary coordinate system.

[0009] Calculate the reference value of the DC internal potential of the MMC and the reference value of the modulation voltage of the MMC bridge arm; calculate the number of submodules that need to be put into the MMC bridge arm; and use the nearest level approximation modulation theory to generate corresponding control pulses to realize the inertia support control of the MMC.

[0010] Furthermore, by obtaining the average value of the capacitor voltage of the obtained MMC submodule, the capacitor energy of all submodules in the MMC is calculated, and the actual value W of the MMC submodule capacitor energy is obtained. C The calculation formula is as follows:

[0011] ;

[0012] Where N is the number of individual bridge arm submodules, C0 is the capacitance value of the MMC submodule, and U c This represents the average capacitor voltage of the MMC submodules;

[0013] Introducing angular frequency-capacitor energy droop control to automatically adjust the submodule capacitor energy reference value under different operating conditions. (MMC submodule capacitor energy reference value) The calculation formula is as follows:

[0014] ;

[0015] Among them, W C0 k is the reference value for the capacitor energy of the MMC submodule under steady state. dr ω is the angular frequency-submodule capacitor energy droop coefficient, where ω and ω0 are the actual and reference values ​​of the angular frequency at the MMC grid connection point, respectively.

[0016] Furthermore, the MMC angular frequency reference value is obtained through proportional control, and then the phase reference value is generated through integration. The calculation formula is as follows:

[0017] ;

[0018] Where s is the Laplace operator, k W This is the energy droop factor of the MMC submodule capacitor.

[0019] Furthermore, by utilizing the reactive power of the MMC, the voltage amplitude at the MMC grid connection point is actively controlled, and the d-axis voltage reference value at the MMC grid connection point is... and q-axis voltage reference value The calculation formula is as follows:

[0020] ;

[0021] Among them, U sm k is the reference value for the voltage amplitude at the MMC grid connection point. pq Q is a proportional parameter. * Q and Q represent the reference and actual values ​​of the reactive power of the MMC, respectively. The above formula controls the q-axis voltage reference value of the MMC grid connection point to zero so that the d-axis coincides with the grid voltage vector. At this time, the d-axis voltage amplitude of the MMC grid connection point is the voltage amplitude of the MMC grid connection point.

[0022] Furthermore, the d-axis current reference value at the MMC grid connection point and q-axis current reference value The calculation formula is as follows:

[0023] ;

[0024] Where, k pu and k iu These are the proportional and integral parameters of the voltage outer loop controller, respectively, where s is the Laplace operator, and u... sd and u sq These are the d-axis and q-axis components of the AC voltage at the MMC grid connection point in the dq rotating coordinate system, respectively.

[0025] Furthermore, the d-axis voltage reference value of the MMC modulation voltage. and q-axis voltage reference value The calculation formula is as follows:

[0026] ;

[0027] Where, k pi and k ii These are the proportional and integral parameters of the current inner loop controller, respectively; w is the actual value of the angular frequency at the MMC grid connection point; i vd and i vq The d-axis and q-axis components of the MMC grid-connected current are represented separately, with L being the MMC connection reactance. Dual-loop PID control allows for rapid current adjustment and limiting, preventing overcurrent in the MMC and thus avoiding equipment damage.

[0028] Furthermore, in order to generate the bridge arm modulation voltage reference value, it is necessary to transform the d-axis and q-axis voltage reference values ​​of the MMC modulation voltage to the abc stationary coordinate system. The a-axis voltage reference value of the MMC modulation voltage in the abc stationary coordinate system... b-axis voltage reference value and c-axis voltage reference value The calculation formula is as follows:

[0029] .

[0030] Furthermore, the DC current is controlled by adjusting the DC internal potential. The reference value E of the DC internal potential of the MMC is... dc The calculation formula is as follows:

[0031] ;

[0032] Where, k pidc and k iidc These are the proportional and integral parameters of the DC current inner loop controller, respectively, where s is the Laplace operator, and I... dc and These are the actual and reference values ​​of the MMC DC current, U. dc This represents the actual value of the MMC DC voltage. Through a DC dual closed-loop control circuit, decoupled control of the submodule capacitor energy and DC voltage can be achieved, avoiding the impact of submodule capacitor voltage fluctuations on the DC voltage.

[0033] Furthermore, the DC current reference value of MMC The calculation formula is as follows:

[0034] ;

[0035] Where, k pudc and k iudc These are the proportional and integral parameters of the DC voltage outer loop controller, respectively. This is a reference value for the MMC DC voltage. The DC voltage, based on the submodule capacitor energy regulation network control, can be controlled through the DC current control loop of the MMC converter station.

[0036] Furthermore, the reference value of the modulation voltage of the three-phase upper arm of the MMC. and lower arm modulation voltage reference value The calculation formula is as follows:

[0037] ;

[0038] In the formula, Let j be the reference value of the MMC modulated voltage in the abc stationary coordinate system, where j = a, b, c;

[0039] Through the above control, the sum of the voltages of the upper and lower arms of the MMC is a variable control quantity, increasing the control dimensions of the MMC.

[0040] The number of submodules N required for the MMC three-phase upper arm pj The number of submodules N that need to be invested in the lower bridge arm nj The calculation formula is as follows:

[0041] ;

[0042] Here, `round()` is the floor function. Based on the number of submodules engaged in the three-phase bridge arm of the MMC, the control pulses of each switching device in the MMC can be generated using the nearest-level approximation theory to achieve inertia support control of the MMC.

[0043] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0044] This invention utilizes the energy of submodule capacitors to achieve self-synchronization control without a phase-locked loop, thus realizing the network control objective. By introducing a DC internal potential and dynamically adjusting the number of submodules in operation, decoupling control of submodule capacitor energy and DC voltage is achieved, thereby widening the operating range of submodule capacitor voltage. Simultaneously, this invention employs angular frequency-capacitor energy droop control to adjust the reference value of submodule capacitor energy, maximizing the utilization of capacitor energy margin and improving the inertia support capability of the modular multilevel converter (MMC).

[0045] The control method proposed in this invention enables the Modular Multilevel Converter (MMC) to exhibit voltage source characteristics on both the DC and AC sides, making it suitable for DC voltage-controlled MMCs connected to weak power grids. Theoretical analysis and simulation examples verify that the control method of this invention can maintain reliable operation under conditions such as weak AC power grids and power fluctuations, and also verify the effect of the angular frequency-capacitor energy droop coefficient on improving the inertia support capability of the MMC. Attached Figure Description

[0046] Figure 1 This is a flowchart of the inertia support method based on submodule capacitor energy regulation network control according to the present invention.

[0047] Figure 2 This is a schematic diagram of the dynamic characteristics of a system using traditional submodule capacitor energy network control.

[0048] Figure 3 This is a schematic diagram of the dynamic characteristics of a system using the sub-module capacitor energy network control method described in this invention.

[0049] Figure 4 This is a schematic diagram of the system dynamic characteristics under different angular frequencies and submodule capacitor energy droop coefficients. Detailed Implementation

[0050] The inertia support method based on submodule capacitor energy regulation network control of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0051] Please see Figure 1This invention discloses an inertia support method based on submodule capacitor energy regulation network control, comprising the following steps:

[0052] S1: Obtain the voltage and current at the MMC grid connection point, and perform dq decomposition to obtain the d-axis and q-axis components; obtain the actual and reference values ​​of the MMC DC voltage, DC current, average value of the submodule capacitor voltage, and reactive power; obtain the actual and reference values ​​of the MMC grid connection point AC voltage and angular frequency.

[0053] S2: Calculate the actual and reference values ​​of the capacitor energy of the MMC submodule, and calculate the phase reference value of the MMC;

[0054] S3: Calculate the reference values ​​of d-axis and q-axis voltage and current at the MMC grid connection point;

[0055] S4: Calculate the d-axis and q-axis voltage reference values ​​of the MMC modulation voltage, and calculate the voltage reference value of the MMC modulation voltage in the stationary coordinate system;

[0056] S5: Calculate the reference value of the DC internal potential of the MMC and the reference value of the modulation voltage of the MMC bridge arm;

[0057] S6: Calculate the number of sub-modules that need to be put into the MMC bridge arm, and use the nearest level approximation modulation theory to generate corresponding control pulses to realize the inertia support control of MMC.

[0058] Step S1: Obtain the voltage and current at the MMC grid connection point, and perform dq decomposition to obtain d-axis and q-axis components; obtain the actual and reference values ​​of the MMC DC voltage, DC current, average value of the submodule capacitor voltage, and reactive power; obtain the actual and reference values ​​of the MMC grid connection point AC voltage and angular frequency.

[0059] Specifically, the grid voltage and current at the grid connection point of the modular multilevel converter (MMC) are obtained, and the grid voltage and current at the grid connection point of the MMC are decomposed into dq components to obtain the d-axis and q-axis components of the voltage and current at the grid connection point of the MMC in the dq rotating coordinate system.

[0060] Obtain the actual values ​​of DC voltage, DC current, average submodule capacitor voltage, reactive power, and the AC voltage and angular frequency at the grid connection point of the modular multilevel converter (MMC). Obtain reference values ​​of DC voltage, DC current, average submodule capacitor voltage, reactive power, and the AC voltage and angular frequency at the grid connection point of the modular multilevel converter (MMC).

[0061] In step S2, the actual and reference values ​​of the capacitor energy of the modular multilevel converter (MMC) submodule are calculated.

[0062] Specifically, by obtaining the average capacitor voltage of the obtained MMC submodule, the capacitor energy of all submodules in the MMC is calculated, and the actual value W of the capacitor energy of the modular multilevel converter MMC submodule is obtained. C The calculation formula is as follows:

[0063] ;

[0064] Where N is the number of individual bridge arm submodules, C0 is the capacitance value of the modular multilevel converter (MMC) submodule, and U c This represents the average value of the capacitor voltage of the submodules in a modular multilevel converter (MMC).

[0065] Introducing angular frequency-capacitor energy droop control to automatically adjust the submodule capacitor energy reference value under different operating conditions; Modular Multilevel Converter (MMC) submodule capacitor energy reference value. The calculation formula is as follows:

[0066] ;

[0067] Among them, W C0 k is the reference value for the capacitor energy of the modular multilevel converter (MMC) submodule under steady-state conditions. dr ω is the angular frequency-submodule capacitor energy droop coefficient, and ω and ω0 are the actual and reference values ​​of the angular frequency at the grid connection point of the modular multilevel converter (MMC), respectively.

[0068] In step S2, the phase reference value of the modular multilevel converter (MMC) is calculated.

[0069] Specifically, the angular frequency reference value of the MMC is obtained through proportional control, and then the phase reference value is generated through integration. This provides the phase reference value for the modular multilevel converter (MMC). The calculation formula is as follows:

[0070] ;

[0071] Where s is the Laplace operator, k W The energy droop factor of the capacitor in the MMC submodule of the modular multilevel converter.

[0072] In step S3, the reference values ​​of the d-axis voltage and q-axis voltage at the grid connection point of the modular multilevel converter (MMC) are calculated.

[0073] Specifically, by utilizing the reactive power of the MMC, the voltage amplitude at the MMC grid connection point is actively controlled, and the d-axis voltage reference value at the MMC grid connection point of the modular multilevel converter is determined. and q-axis voltage reference value The calculation formula is as follows:

[0074] ;

[0075] Among them, U sm k is a reference value for the grid connection point voltage amplitude of the modular multilevel converter (MMC). pq Q is a proportional parameter. * Q and Q represent the reference and actual reactive power values ​​of the Modular Multilevel Converter (MMC), respectively. The above formula controls the q-axis voltage reference value at the MMC grid connection point to zero to achieve d-axis alignment with the grid voltage vector. At this time, the d-axis voltage amplitude at the MMC grid connection point is the voltage amplitude at the MMC grid connection point.

[0076] In step S3, the d-axis current reference value and q-axis current reference value of the modular multilevel converter (MMC) are calculated.

[0077] Specifically, the d-axis current reference value of the modular multilevel converter (MMC) and q-axis current reference value The calculation formula is as follows:

[0078] ;

[0079] Where, k pu and k iu These are the proportional and integral parameters of the voltage outer loop controller, u. sd and u sq These represent the d-axis and q-axis components of the AC voltage at the grid connection point of the modular multilevel converter (MMC) in the dq rotating coordinate system.

[0080] In step S4, the d-axis voltage reference value and q-axis voltage reference value of the modular multilevel converter (MMC) modulation voltage are calculated.

[0081] Specifically, the d-axis voltage reference value of the MMC modulation voltage of the modular multilevel converter. and q-axis voltage reference value The calculation formula is as follows:

[0082] ;

[0083] Where, k pi and k ii These are the proportional and integral parameters of the inner current loop controller, i. vd and i vq The d-axis and q-axis components of the grid-connected current of the modular multilevel converter (MMC) are respectively represented, where L is the connection reactance of the MMC. Dual-loop PID control allows for rapid current regulation and limiting, preventing overcurrent in the MMC and thus avoiding equipment damage.

[0084] In step S4, the reference values ​​of the modulated multilevel converter (MMC) voltage along the a-axis, b-axis, and c-axis in the abc stationary coordinate system are calculated.

[0085] Specifically, to generate the bridge arm modulation voltage reference value, it is necessary to transform the d-axis and q-axis voltage reference values ​​of the MMC modulation voltage to the abc stationary coordinate system. The a-axis voltage reference value of the modular multilevel converter MMC modulation voltage in the abc stationary coordinate system is then obtained. b-axis voltage reference value and c-axis voltage reference value The calculation formula is as follows:

[0086] .

[0087] In step S5, the reference value of the DC internal potential of the modular multilevel converter (MMC) is calculated.

[0088] Specifically, the DC current is controlled by adjusting the DC internal potential. The reference value E of the DC internal potential of the modular multilevel converter (MMC) is... dc The calculation formula is as follows:

[0089] ;

[0090] Where, k pidc and k iidc These are the proportional and integral parameters of the DC current inner loop controller, I. dc and These are the actual and reference values ​​of the DC current of the modular multilevel converter (MMC), U dc This represents the actual value of the MMC DC voltage. Through a DC dual closed-loop control circuit, decoupled control of the submodule capacitor energy and DC voltage can be achieved, avoiding the impact of submodule capacitor voltage fluctuations on the DC voltage.

[0091] Specifically, the DC current reference value of the modular multilevel converter (MMC) The calculation formula is as follows:

[0092] ;

[0093] Where, k pudc and k iudc These are the proportional and integral parameters of the DC voltage outer loop controller, U. dc and These are the actual and reference values ​​of the DC voltage of the Modular Multilevel Converter (MMC), respectively. The DC voltage, based on the submodule capacitor energy regulation network control, can be controlled through the DC current control loop of the MMC converter station.

[0094] In step S5, the reference values ​​for the modulation voltage of the upper and lower arms of the three-phase Modular Multilevel Converter (MMC) are calculated.

[0095] Specifically, the reference value of the three-phase upper arm modulation voltage of the modular multilevel converter (MMC) and lower arm modulation voltage reference value The calculation formula is as follows:

[0096] ;

[0097] In the formula, Let j be the reference value of the MMC modulated voltage in the abc stationary coordinate system, where j = a, b, c;

[0098] Through the above control, the sum of the voltages of the upper and lower arms of the MMC is a variable control quantity, increasing the control dimensions of the MMC.

[0099] In step S6, the number of submodules required for the upper and lower three-phase arms of the modular multilevel converter (MMC) is calculated. Using the nearest-level approximation modulation theory, corresponding control pulses are generated to achieve inertia support control of the MMC.

[0100] Specifically, the number N of submodules required for the three-phase upper arm of the Modular Multilevel Converter (MMC) is... pj The number of submodules N that need to be invested in the lower bridge arm nj The calculation formula is as follows:

[0101] ;

[0102] Wherein, round() is the floor function. Based on the number of submodules engaged in the three-phase bridge arm of the modular multilevel converter (MMC), the control pulses of each switching device in the MMC can be generated using the nearest level approximation theory, thereby realizing the inertia support control of the MMC.

[0103] Based on the inertia support method of submodule capacitor energy regulation grid control disclosed in this invention, simulation verification was performed using a single-pole 640kV test system, with the short-circuit ratio at the grid connection point of the modular multilevel converter (MMC) set to 1.5. It is assumed that the system has entered steady state at t=2s, and the receiving-end grid load decreases by 10% at t=3s. The dynamic characteristics of the systems using traditional submodule capacitor energy grid control and the decoupled submodule capacitor energy grid control involved in this invention are as follows: Figure 2 and Figure 3 As shown.

[0104] Both of the above control strategies adjust the AC output frequency of the modular multilevel converter (MMC) by varying the energy of the submodule capacitors, enabling rapid tracking of grid frequency changes. Unlike traditional submodule capacitor energy grid control, decoupled submodule capacitor energy grid control achieves frequency response while dynamically adjusting the number of submodules in operation. This decouples the submodule capacitor energy and DC voltage, preventing the impact of submodule capacitor voltage fluctuations on the DC voltage.

[0105] Based on the inertia support method for grid control based on submodule capacitor energy regulation disclosed in this invention, simulation verification was performed using a single-pole 640kV test system. The modular multilevel converter (MMC) adopted the grid control based on submodule capacitor energy regulation involved in this invention, and the short-circuit ratio at the grid connection point was set to 1.5. Assuming that the system has entered steady state at t=2s, and the receiving-end grid load decreases by 10% at t=3s, the system dynamic characteristics under different angular frequencies and submodule capacitor energy droop coefficients are as follows: Figure 4 As shown.

[0106] As the angular frequency-submodule capacitor energy droop factor increases, the highest frequency gradually decreases. When the droop factor is 125, the highest frequency decreases from the initial 50.39Hz to 50.32Hz. Simulation results show that the change in submodule capacitor energy during transient processes is related to the magnitude of the droop factor. A larger angular frequency-submodule capacitor energy droop factor results in a larger change in submodule capacitor energy, allowing for fuller utilization of submodule capacitor energy and improving the inertia support capability of the modular multilevel converter (MMC).

[0107] In summary, this invention enables self-synchronization control without a phase-locked loop (PLL) by utilizing the energy of the submodule capacitors, thereby achieving the network control objective. By introducing a DC internal potential and dynamically adjusting the number of submodules in operation, decoupling control between the submodule capacitor energy and DC voltage is achieved, thus broadening the operating range of the submodule capacitor voltage. Simultaneously, this invention employs angular frequency-capacitor energy droop control to adjust the reference value of the submodule capacitor energy, maximizing the utilization of capacitor energy margin and enhancing the inertia support capability of the modular multilevel converter (MMC).

[0108] The control method proposed in this invention enables the Modular Multilevel Converter (MMC) to exhibit voltage source characteristics on both the DC and AC sides, making it suitable for DC voltage-controlled MMCs connected to weak power grids. Theoretical analysis and simulation examples verify that the control method of this invention can maintain reliable operation under conditions such as weak AC power grids and power fluctuations, and also verify the effect of the angular frequency-capacitor energy droop coefficient on improving the inertia support capability of the MMC.

[0109] The above description is a detailed description of the preferred embodiments of the present invention. However, the embodiments are not intended to limit the scope of the patent application of the present invention. All equivalent changes or modifications made under the technical spirit disclosed in the present invention should fall within the patent scope covered by the present invention.

Claims

1. An inertia support method based on submodule capacitor energy regulation network control, characterized in that, Includes the following steps: Obtain the voltage and current at the MMC grid connection point, and perform dq decomposition to obtain d-axis and q-axis components; obtain the actual and reference values ​​of the MMC DC voltage, DC current, average value of submodule capacitor voltage, and reactive power; obtain the actual and reference values ​​of the MMC grid connection point AC voltage and angular frequency. Calculate the actual and reference values ​​of the capacitor energy of the MMC submodule; calculate the phase reference value of the MMC; calculate the d-axis and q-axis voltage reference values ​​and d-axis and q-axis current reference values ​​of the MMC grid connection point. Calculate the d-axis and q-axis voltage reference values ​​of the MMC modulation voltage, and calculate the voltage reference value of the MMC modulation voltage in the stationary coordinate system; Calculate the reference value of the DC internal potential of the MMC and the reference value of the modulation voltage of the MMC bridge arm; The number of submodules required for the MMC bridge arm is calculated, and the corresponding control pulses are generated using the nearest level approximation modulation theory to achieve inertia support control of the MMC.

2. The inertia support method based on submodule capacitor energy regulation network control according to claim 1, characterized in that, By obtaining the average capacitor voltage of the MMC submodule, the capacitor energy of all submodules in the MMC is calculated, and the actual value W of the MMC submodule capacitor energy is obtained. C The calculation formula is as follows: ； Where N is the number of individual bridge arm submodules, C0 is the capacitance value of the MMC submodule, and U c This represents the average capacitor voltage of the MMC submodules; Introducing angular frequency-capacitor energy droop control to automatically adjust the submodule capacitor energy reference value under different operating conditions. (MMC submodule capacitor energy reference value) The calculation formula is as follows: ； Among them, W C0 k is the reference value for the capacitor energy of the MMC submodule under steady state. dr ω is the angular frequency-submodule capacitor energy droop coefficient, where ω and ω0 are the actual and reference values ​​of the angular frequency at the MMC grid connection point, respectively.

3. The inertia support method based on submodule capacitor energy regulation network control according to claim 2, characterized in that, The MMC angular frequency reference value is obtained through proportional control, and then the phase reference value is generated through integration. The calculation formula is as follows: ； Where s is the Laplace operator, k W This is the energy droop factor of the MMC submodule capacitor.

4. The inertia support method based on submodule capacitor energy regulation network control according to claim 1, characterized in that, Utilizing the reactive power of the MMC, the voltage amplitude at the MMC grid connection point is actively controlled, and the d-axis voltage reference value at the MMC grid connection point is determined. and q-axis voltage reference value The calculation formula is as follows: ； Among them, U sm k is the reference value for the voltage amplitude at the MMC grid connection point. pq Q is a proportional parameter. * Q and Q represent the reference and actual values ​​of MMC reactive power, respectively.

5. The inertia support method based on submodule capacitor energy regulation network control according to claim 4, characterized in that, Reference value of d-axis current at MMC grid connection point and q-axis current reference value The calculation formula is as follows: ； Where, k pu and k iu These are the proportional and integral parameters of the voltage outer loop controller, respectively, where s is the Laplace operator, and u... sd and u sq These are the d-axis and q-axis components of the AC voltage at the MMC grid connection point in the dq rotating coordinate system, respectively.

6. The inertia support method based on submodule capacitor energy regulation network control according to claim 5, characterized in that, d-axis voltage reference value of MMC modulation voltage and q-axis voltage reference value The calculation formula is as follows: ； Where, k pi and k ii These are the proportional and integral parameters of the current inner loop controller, respectively; w is the actual value of the angular frequency at the MMC grid connection point; i vd and i vq The d-axis and q-axis components of the MMC grid connection current are given respectively, and L is the MMC connection reactance value.

7. The inertia support method based on submodule capacitor energy regulation network control according to claim 6, characterized in that, To generate bridge arm modulation voltage reference values, the d-axis and q-axis voltage reference values ​​of the MMC modulation voltage need to be transformed to the abc stationary coordinate system. The a-axis voltage reference value of the MMC modulation voltage in the abc stationary coordinate system is... b-axis voltage reference value and c-axis voltage reference value The calculation formula is as follows: 。 8. The inertia support method based on submodule capacitor energy regulation network control according to claim 1, characterized in that, The DC current is controlled by adjusting the DC internal potential. The reference value of the DC internal potential E of the MMC is... dc The calculation formula is as follows: ； Where, k pidc and k iidc These are the proportional and integral parameters of the DC current inner loop controller, respectively, where s is the Laplace operator, and I... dc and These are the actual and reference values ​​of the MMC DC current, U. dc This is the actual value of the MMC DC voltage.

9. The inertia support method based on submodule capacitor energy regulation network control according to claim 8, characterized in that, DC current reference value of MMC The calculation formula is as follows: ； Where, k pudc and k iudc These are the proportional and integral parameters of the DC voltage outer loop controller, respectively. This is a reference value for the DC voltage of the MMC.

10. The inertia support method based on submodule capacitor energy regulation network control according to claim 8, characterized in that, MMC three-phase upper arm modulation voltage reference value and lower arm modulation voltage reference value The calculation formula is as follows: ； In the formula, Let j be the reference value of the MMC modulated voltage in the abc stationary coordinate system, where j = a, b, c; The number of submodules N required for the MMC three-phase upper arm pj The number of submodules N that need to be invested in the lower bridge arm nj The calculation formula is as follows: ； Here, round() is the rounding function.

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