Alternating current micro-grid construction inertia compensation control method

Abstract

The invention discloses an alternating-current micro-grid construction inertia compensation control method, which comprises the following steps of: according to nodes of an alternating-current micro-grid and a power interaction physical model of a distributed power supply, determining a coupling relationship between the distributed power supply and the alternating-current micro-grid, including a coupling relationship among a grid-following converter, a grid-construction converter and the alternating-current micro-grid; calculating an inertia time constant of an alternating current micro-grid node, determining an inertia output margin of the inertia time constant of the alternating current micro-grid node, and determining an inertia compensation range of the grid-forming converter; and calculating the actual output power of the distributed power supply input power distribution network based on the coupling relationship, taking the actual output power of the network construction type converter as the power feedback input of network construction control, and controlling the inertia power of the source side energy storage device to be output to the power grid based on the network following control strategy and the inertia compensation range of the network construction type converter. And reaching the boundary of the inertia compensation range. By coordinating the networking converter and the energy storage converter, the fluctuation can be efficiently stabilized, and the system stability is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of AC microgrid networking, and in particular to an AC microgrid networking inertia compensation control method. Background Art

[0002] The inertia of traditional AC microgrids is mainly provided by the rotor of synchronous generators. This characteristic enables AC microgrids to effectively resist changes in external conditions. However, as various new energy devices are continuously connected to AC microgrids, AC microgrids are gradually showing a trend of power electronics, resulting in a significant weakening of inertia characteristics. Therefore, improving the inertia characteristics of AC microgrids is of great significance for maintaining the stable operation of their systems.

[0003] In order to solve the problem of reducing the inertia of AC microgrids containing new energy equipment, a network control strategy that introduces virtual inertia can be adopted. However, since new energy itself cannot provide inertial energy, the realization of virtual inertia requires the introduction of energy storage devices in the source side equipment to realize the injection of inertial energy.

[0004] At present, AC microgrid grid control has been widely used in high-proportion new energy systems. This control method simulates the frequency and voltage regulation characteristics of synchronous generators, that is, frequency regulation is achieved through the differential flow of active power, and voltage stability is ensured through the differential flow of reactive power. This method is highly grid-friendly, but it also has two significant disadvantages: ① Small equivalent impedance: When there are grid-connected converters and other equipment at the public grid connection point or nearby nodes, the system is easily affected by coupling. ② The capacity of new energy equipment and energy storage equipment needs to match each other: The converter control speed of traditional energy storage equipment is not enough to quickly respond to the demand for inertial power.

[0005] Therefore, there is an urgent need to find an AC microgrid network control method that can efficiently and accurately respond to inertial power, so as to improve the inertial characteristics of the AC microgrid when a high proportion of new energy is connected, ensure its stable operation, and ensure that the AC microgrid can maintain good stability and response performance under various complex working conditions. Summary of the invention

[0006] The purpose of the present invention is to provide an AC microgrid inertia compensation control method to solve the shortcomings of traditional virtual inertia in high-penetration new energy and multi-node AC microgrids. The present invention can respond to energy storage scheduling and emit transient power to achieve inertia compensation. By coordinating various converters, it can ultimately effectively smooth fluctuations and improve system stability. It is suitable for complex microgrid environments with a high proportion of new energy access.

[0007] An AC microgrid inertia compensation control method comprises the following steps:

[0008] S1. According to different types of renewable energy grid-connected synchronization, determine the power interaction physical model of the nodes of the AC microgrid and the distributed power source; establish the coupling relationship between the distributed power source and the AC microgrid according to the power interaction physical model; among which different types of renewable energy grid-connected synchronization include grid-following type and grid-building type, and the coupling relationship includes the coupling relationship between the grid-following type converter, the grid-building type converter and the AC microgrid;

[0009] S2. Calculate the inertia time constant of the AC microgrid node; determine the inertia output margin of the inertia time constant of the AC microgrid node according to the capacity of the energy storage device on the source side of the AC microgrid; determine the inertia compensation range of the grid-type converter based on the AC microgrid topology and the inertia time constant of the AC microgrid node;

[0010] S3. Based on the coupling relationship, the actual output power of the distributed power supply input into the distribution network is calculated, and the actual output power of the grid-forming inverter is used as the power feedback input of the grid control. Based on the grid-following control strategy and the inertia compensation range of the grid-forming inverter, the inertial power of the source-side energy storage device is controlled to be output to the grid, and finally reach the boundary of the inertia compensation range.

[0011] The grid-connected converter is implemented by creating a voltage difference to form a power flow, and the grid-connected converter controls the output active power P GFL and reactive power Q GFL It is expressed as:

[0012]

[0013] In the formula, u v and u g The distribution represents the instantaneous value of the output voltage of the common connection node between the grid-following converter and the AC microgrid; Y g Represents the complex equivalent admittance of the AC microgrid node connected to the grid-type converter; Re represents the real part of the complex number; Im represents the imaginary part of the complex number; the phase angle of the grid-type converter is synchronized with the grid, and the reactive power is absorbed by the line reactance.

[0014] The grid-connected converter realizes grid-connected synchronization by autonomously constructing voltage and phase difference to form the transmission of active power and reactive power. The grid-connected converter controls the output active power P GFM and reactive power Q GFM It is expressed as:

[0015]

[0016] Where θ is the grid electrical angle, θ* is the grid-connected converter output electrical angle, and arg represents the complex angle.

[0017] Among them, in step S1, the coupling relationship between the distributed power source and the AC microgrid is determined by establishing a coupling matrix between the grid-following converter and the grid-forming converter; n grid-following converters and m grid-forming converters are connected to have a coupling relationship, and the matrix form of complex power coupling is expressed as:

[0018]

[0019] In the formula, represents the power coupling matrix, represents the internal coupling matrix of the grid-following converter, Represents the internal coupling matrix of the grid-type converter; and Respectively represent the coupling matrices between the grid-type converter and the grid-forming converter;

[0020]

[0021]

[0022] Where P L Represents the active power transmitted between the grid-type converter, P M Represents the active power transmitted between grid-connected converters, P LM Represents the active power transmitted from the grid-following converter to the grid-forming converter, P ML represents the active power transmitted from the grid-connected converter to the grid-following converter, Q L Represents the reactive power transmitted between the grid-type converter, Q M Represents the reactive power transmitted between grid-connected converters, Q LM Represents the reactive power transmitted from the grid-following converter to the grid-connecting converter, Q ML represents the reactive power transmitted from the grid-forming converter to the following converter. The subscripts x and y represent the corresponding element numbers in the matrix, and j represents the imaginary unit.

[0023] Wherein, in step S2, the node inertia time constant of the AC microgrid is calculated using the following formula:

[0024]

[0025] In the formula, is the inertia time constant at sampling time t, T is the sampling time interval; is the instantaneous frequency calculated by the phase-locked loop of the grid node l at sampling time t, It is the instantaneous value of input active power calculated based on the grid node l voltage and input current at sampling time t.

[0026] Wherein, in step S2, the inertia output margin of the inertia time constant of the AC microgrid node is determined according to the capacity of the energy storage device on the source side of the AC microgrid, including:

[0027] The DC side response of the energy storage device on the source side is transformed into a first-order voltage dynamic equation:

[0028]

[0029] Where ΔP c represents the first-order dynamic voltage response, S ess,i , U dc,i and S ne,i They respectively represent the rated capacity of the energy storage station corresponding to the i-th grid-connected converter, the DC input voltage, and the rated capacity of the DC-coupled new energy equipment;

[0030] The equivalent capacitance of the energy storage device is introduced as an intermediate variable to calculate the output inertia of the grid-connected converter.

[0031]

[0032] In the formula, J i Represents the output inertia of the grid-type converter, U dc,ref is the reference value of the DC input voltage; ω ref Represents the rated frequency of the AC microgrid; ω v,i represents the grid-forming frequency of the ith grid-forming converter; when the new energy station and the energy storage device are installed, the inertia output margin that the grid-forming converter can provide is inferred through the output inertia calculation formula of the grid-forming converter.

[0033] Wherein, in step S2, determining the inertia compensation range of the grid-connected converter based on the AC microgrid topology and the inertia time constant of each AC microgrid node comprises the following steps:

[0034] The number of clusters k is determined according to the number of nodes K connected to the grid-forming converter;

[0035] Select all grid-type converters as initial clustering points, and according to the access nodes of distributed power sources and grid-type converters, merge the clustering points of grid-type converters connected to the same node according to the inertia output margin to obtain the final clustering point;

[0036] The output inertia margin of the grid-type converter is classified according to the cluster number k and the final clustering point, so as to characterize the inertia compensation range of the grid-type converter.

[0037] Among them, in step S3, the actual output power calculation expression of the distributed power supply input to the distribution network is as follows:

[0038]

[0039] Where P rea,L,m and Q rea,L,m They represent the actual values ​​of the power transmission of the grid-following converter and the grid-forming converter in the AC microgrid respectively, diag represents obtaining the main diagonal values ​​of the matrix and integrating them into a column vector, and n and m represent the maximum number of grid-following converters and grid-forming converters connected to the AC microgrid respectively.

[0040] In step S2, the grid-following control strategy is designed based on the basic equations of virtual synchronization technology, namely, the rotor swing equation and stator voltage equation of the synchronous generator, including:

[0041]

[0042] Where P ref,i , Q ref,i and ω ref Represents the reference value of active power, reactive power and frequency, U ref Represents the voltage level of the access distribution network; D p and D q represents the active power droop coefficient and reactive power droop coefficient of virtual synchronous control, J ne,i represents the virtual inertia constant, E v,i Represents virtual electromotive force.

[0043] In step S2, the inertial power output of the source-side energy storage device is controlled based on the following model:

[0044] P in,M,i =P ne,i +P ess,i +P ess,tre,i ;

[0045]

[0046] Where P in,M,i represents the input power of the i-th grid-connected converter, P ne,i represents the instantaneous active power of all renewable energy sources connected to the i-th GFM, P ess,i represents the static instantaneous active power of all energy storage devices connected to the i-th GFM network, P ess,tre,i Represents the inertial active power generated by the energy storage device connected to the GFM network, P ess,tre,i represents the inertial power response of the GFC following the grid (P ref,i -P rea,M,i ).

[0047] The present invention accurately describes the relationship between each converter and the AC microgrid by constructing a coupling matrix, and carefully depicts the inertial characteristics in the multi-node AC microgrid by characterizing the inertial time constant of the AC microgrid node. It can not only characterize the inertial power propagation range of each new energy node, but also significantly improve the response speed of the inertial power of the grid-forming converter. Finally, by coordinating the grid-forming converter and the energy storage converter, it can efficiently smooth out fluctuations and improve system stability. It is suitable for the current complex microgrid environment with a high proportion of new energy access. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a processing flow chart of the AC microgrid network inertia compensation control method according to an embodiment of the present invention.

[0049] Figure 2 It is a schematic diagram of the main circuit of the system and its network inertia compensation control applicable to the present invention.

[0050] Figure 3 It is an equivalent circuit model diagram of the new energy access to the AC microgrid node of the present invention. DETAILED DESCRIPTION

[0051] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0052] See also Figure 1 As shown, the processing flow of the AC microgrid network inertia compensation control method according to the embodiment of the present invention includes:

[0053] S1. According to different types of renewable energy grid-connected synchronization, determine the power interaction physical model of the nodes of the AC microgrid and the distributed power source; establish the coupling relationship between the distributed power source and the AC microgrid according to the power interaction physical model; among which different types of renewable energy grid-connected synchronization include grid-following type and grid-forming type, and the coupling relationship includes the coupling relationship between the grid-following type (GFL) converter, the grid-forming type (GFM) converter and the AC microgrid;

[0054] S2. Calculate the inertia time constant of the AC microgrid node; determine the inertia output margin of the inertia time constant of the AC microgrid node according to the capacity of the energy storage device on the source side of the AC microgrid; determine the inertia compensation range of the grid-type converter based on the AC microgrid topology and the inertia time constant of the AC microgrid node;

[0055] S3. Based on the coupling relationship, the actual output power of the distributed power supply input into the distribution network is calculated, and the actual output power of the grid-forming inverter is used as the power feedback input of the grid control. Based on the grid-following control strategy and the inertia compensation range of the grid-forming inverter, the inertial power of the source-side energy storage device is controlled to be output to the grid, and finally reach the boundary of the inertia compensation range.

[0056] The technology of the present invention, using the coupling matrix established by the converter type and its electrical distance, can effectively optimize the cooperative relationship between converters and improve the overall stability of the system. Secondly, through the characterization of the proposed multi-node AC microgrid inertia time constant, the inertial characteristics of each node can be accurately depicted, improving the system's perception and response capabilities to inertial characteristics. In addition, the technology that includes the energy storage converter's response to the inertia of the network control can more efficiently manage and dispatch the inertial power of new energy sources, ensuring that the inertial power propagation range of each node is clear, thereby significantly improving the response speed of the inertial power of the network-forming converter, and effectively enhancing the dynamic performance and stability of the microgrid.

[0057] In the embodiment of the present application, when establishing the coupling relationship between the distributed power source and the AC microgrid, firstly, according to different types of new energy grid synchronization, the power interaction model between the distributed power source and the AC microgrid node is determined, and then based on the power interaction model, the admittance matrix of the distributed power source is established to establish the coupling relationship between heterogeneous new energy sources. Among them, the larger the coupling admittance, the stronger the coupling between the two distributed power sources, and the closer the geographical distance.

[0058] Specifically, according to different types of renewable energy grid-connected synchronization, a power interaction model between distributed power sources and AC microgrid nodes is determined, including a power interaction model between a grid-following converter and a grid-building converter and AC microgrid nodes, wherein the grid-following converter realizes grid-connected synchronization by creating a voltage difference to form a power flow, and the grid-following grid-connected control outputs active power P GFL and reactive power Q GFL It is expressed as:

[0059]

[0060] In the formula, u v and u g The distribution represents the instantaneous value of the output voltage of the common connection node between the grid-following converter and the AC microgrid; Y g Represents the complex equivalent admittance of the AC microgrid node connected to the grid-type converter; Re represents the real part of the complex number; Im represents the imaginary part of the complex number; the phase angle of the grid-type converter is synchronized with the grid, and the reactive power is absorbed by the line reactance.

[0061] The grid-connected converter realizes grid-connected synchronization by autonomously constructing voltage and phase difference to form the transmission of active power and reactive power. The grid-connected converter controls the output active power P GFM and reactive power Q GFM It is expressed as:

[0062]

[0063] Where θ is the grid electrical angle, θ* is the grid-connected converter output electrical angle, and arg represents the complex angle.

[0064] Through the above, the power interaction model between the grid-following converter and the grid-building converter and the AC microgrid nodes is established, and the power interaction mechanism between the distributed power source and the AC microgrid nodes is determined.

[0065] Since there is a certain degree of power coupling between distributed power sources in the same AC microgrid according to the different line lengths, in the embodiment of the present application, in step S1, the coupling relationship between the distributed power source and the AC microgrid is determined according to the power interaction model. Specifically, the coupling relationship between the distributed power source and the AC microgrid is determined by establishing a coupling matrix between the grid-following converter and the grid-forming converter;

[0066] In reality, there may be multiple groups of grid-following converters and multiple groups of grid-forming converters connected to a substation or a node at the same time, which strengthens the coupling between converters. If there are n grid-following converters and m grid-forming converters connected, there is a strong coupling relationship that meets the requirements. The matrix form of complex power coupling is expressed as:

[0067]

[0068] In the formula, represents the power coupling matrix, represents the internal coupling matrix of the grid-following converter, Represents the internal coupling matrix of the grid-type converter; and Respectively represent the coupling matrices between the grid-type converter and the grid-forming converter;

[0069]

[0070] Where P L Represents the active power transmitted between the grid-type converter, P M Represents the active power transmitted between grid-connected converters, P LM Represents the active power transmitted from the grid-following converter to the grid-forming converter, P MLrepresents the active power transmitted from the grid-connected converter to the grid-following converter, Q L Represents the reactive power transmitted between the grid-type converter, Q M Represents the reactive power transmitted between grid-connected converters, Q LM Represents the reactive power transmitted from the grid-following converter to the grid-connecting converter, Q ML represents the reactive power transmitted from the grid-forming converter to the following converter. The subscripts x and y represent the corresponding element numbers in the matrix, and j represents the imaginary unit.

[0071] By establishing the above matrix, the establishment of the coupling matrix between the grid-following converter and the grid-building converter is completed, and the coupling relationship between the distributed power source and the AC microgrid is determined.

[0072] Since the traditional power system contains synchronous generators, it can provide inertia for the distribution network. However, the access of distributed power sources makes inertia analysis difficult. Therefore, it is necessary to calculate the inertia time constant of each node based on the data collected from the distribution network. h Expressed as:

[0073]

[0074] Therefore, in the embodiment of the present application, in step S2, the node inertia time constant of the AC microgrid is calculated using the following formula, that is, it is obtained based on two-point sampling calculation:

[0075]

[0076] In the formula, is the inertia time constant at sampling time t, T is the sampling time interval; is the instantaneous frequency calculated by the phase-locked loop of the grid node l at sampling time t, It is the instantaneous value of input active power calculated based on the grid node l voltage and input current at sampling time t.

[0077] In the embodiment of the present application, in step S2, the inertia output margin of the inertia time constant of the AC microgrid node is determined according to the capacity of the battery / supercapacitor energy storage device on the source side of the AC microgrid, including the following processing steps:

[0078] The DC side response of the energy storage device on the source side is transformed into a first-order voltage dynamic equation:

[0079]

[0080] Where ΔP c represents the first-order dynamic voltage response, S ess,i , U dc,i and Sne,i They respectively represent the rated capacity of the energy storage station corresponding to the i-th grid-connected converter, the DC input voltage, and the rated capacity of the DC-coupled new energy equipment;

[0081] The equivalent capacitance of the energy storage device is introduced as an intermediate variable to calculate the output inertia of the grid-connected converter.

[0082]

[0083] In the formula, J i Represents the output inertia of the grid-type converter, U dc,ref is the reference value of the DC input voltage; ω ref Represents the rated frequency of the AC microgrid; ω v,i represents the grid-forming frequency of the i-th grid-forming converter;

[0084] If the selected energy storage capacity is too small, the virtual inertia adjustment range will be limited. However, if the selected energy storage capacity is too large, the floor space will be increased. When the new energy station and energy storage devices are installed, the inertia output margin that the grid-type converter can provide can be inferred through the output inertia calculation formula of the grid-type converter.

[0085] In the embodiment of the present application, in step S2, determining the inertia compensation range of the grid-connected converter based on the AC microgrid topology and the inertia time constant of each AC microgrid node includes the following steps:

[0086] Firstly, the number of clusters k is determined according to the number of nodes K connected to the grid-forming converter;

[0087] Secondly, all grid-type converters are selected as initial clustering points. According to the access nodes of distributed power sources and grid-type converters, the grid-type converters connected to the same node are merged according to the inertia output margin to obtain the final clustering point.

[0088] Finally, the output inertia margin of the grid-type converter is classified according to the clustering number k and the final clustering point, the inertia compensation range of the grid-type converter is characterized, and the inertia compensation range of the grid-type converter is obtained.

[0089] In the embodiment of the present application, in step S3, in order to enable the system to respond to the inertia power of the grid-forming converter and emit power to achieve inertia compensation, it is necessary to calculate the actual output power of the distributed power supply input to the distribution network, and then use the virtual synchronization principle to design the grid-forming converter control on the source side (the DC side composed of the distributed power supply and the energy storage), while considering the change of the active power reference value, the output power result and the inertia compensation range obtained by clustering, and control the inertia power output of the source-measured energy storage device; wherein, the actual output power of the distributed power supply input to the distribution network can be shown according to the coupling matrix in step S1, and the actual work of all GFLs and GFMs is calculated, and the calculation expression is as follows:

[0090]

[0091] Where P rea,L,m and Q rea,L,m They represent the actual values ​​of the power transmission of the grid-following converter and the grid-forming converter in the AC microgrid respectively, diag represents obtaining the main diagonal values ​​of the matrix and integrating them into a column vector, and n and m represent the maximum number of grid-following converters and grid-forming converters connected to the AC microgrid respectively.

[0092] In the embodiment of the present application, in step S2, the grid-following control strategy is designed according to the basic equations of the virtual synchronization technology, namely, the rotor swing equation and the stator voltage equation of the synchronous generator, to perform GFC virtual synchronization control, including:

[0093]

[0094] Where P ref,i , Q ref,i and ω ref Represents the reference value of active power, reactive power and frequency, U ref Represents the voltage level of the access distribution network; D p and D q represents the active power droop coefficient and reactive power droop coefficient of virtual synchronous control, J ne,i represents the virtual inertia constant, E v,i Represents virtual electromotive force.

[0095] In the embodiment of the present application, in step S2, the inertial power output of the source-side energy storage device is controlled, and the output is controlled based on the following model:

[0096] P in,M,i =P ne,i +P ess,i +P ess,tre,i ;

[0097]

[0098] Where P in,M,i represents the input power of the i-th grid-connected converter, P ne,i represents the instantaneous active power of all renewable energy sources connected to the i-th GFM, P ess,i represents the static instantaneous active power of all energy storage devices connected to the i-th GFM network, P ess,tre,i Represents the inertial active power generated by the energy storage device connected to the GFM network, P ess,tre,i represents the inertial power response of the GFC following the grid (P ref,i -P rea,M,i ).

[0099] The AC microgrid network compensation control method of the embodiment of the present invention is used in a specific application, such as Figure 1 The proposed circuit collects the three-phase voltage U at the output side of the grid-type converter abc 、Current I abc After the data is obtained, the power calculation and decoupling are performed, and the inertia time constant is collected. The power calculation and decoupling results P / Q (actual value of the transmission power of the grid-following converter and the grid-forming converter) and the inertia time constant J are calculated and decoupled. n Input into the designed grid-type control main loop, and output the first modulation wave to the first PWM generation module through the grid-type control main loop to generate the first PWM wave to control the grid-type converter to work; at the same time, the grid-type control main loop outputs a control signal to the energy storage converter control module, so that the energy storage converter control module outputs the second modulation wave, controls, to the second PWM generation module, generates the second PWM wave, controls the energy storage converter to work, and finally realizes the coordination of the grid-type converter and the energy storage converter, achieving efficient smoothing of fluctuations and improving system stability. Among them, the input of the energy storage converter is P ne,i , the output is P in,M,i .

[0100] Specifically, Figure 2 In the circuit structure shown, the energy storage converter includes a single bridge arm circuit formed by two switch tubes connected in series and an energy storage device. The energy storage device is a battery system energy storage device, one end of which is grounded and the other end is connected to the single bridge arm circuit. The grid-type converter is a three-bridge arm parallel circuit formed by six switch tubes connected in series in pairs and then in parallel. The three bridge arms are respectively connected to the grid connection point, and each bridge arm is connected to a resistor Y g , the other ends of the three resistors are connected. Figure 3 GFM1, GFM2, GFMm, GFL1, and GFLn shown in the figure refer to a grid-forming converter and a grid-following converter, respectively.

[0101] The grid-building control method of the embodiment of the present invention can accurately describe the relationship between each converter by constructing a coupling matrix, and can carefully depict the inertia characteristics in a multi-node AC microgrid through a new inertia time constant characterization method; it can characterize the inertia power propagation range of each new energy node, significantly improve the response speed of the inertia power of the grid-building converter, and by coordinating the grid-building converter and the energy storage converter, it can efficiently smooth out fluctuations and improve system stability, and is suitable for the current complex microgrid environment with a high proportion of new energy access.

[0102] The basic principles and main features of the present invention and the advantages of the present invention are shown and described above. It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention.

[0103] Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is therefore intended that all changes falling within the meaning and range of equivalent elements of the claims are included in the present invention.

[0104] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. An AC microgrid inertia compensation control method, characterized in that: Includes steps: S1. According to different types of renewable energy grid-connected synchronization, determine the power interaction physical model of the nodes of the AC microgrid and the distributed power source; establish the coupling relationship between the distributed power source and the AC microgrid according to the power interaction physical model; among which different types of renewable energy grid-connected synchronization include grid-following type and grid-building type, and the coupling relationship includes the coupling relationship between the grid-following type converter, the grid-building type converter and the AC microgrid; S2. Calculate the inertia time constant of the AC microgrid node; determine the inertia output margin of the inertia time constant of the AC microgrid node according to the capacity of the energy storage device on the source side of the AC microgrid; determine the inertia compensation range of the grid-type converter based on the AC microgrid topology and the inertia time constant of the AC microgrid node; S3. Based on the coupling relationship, the actual output power of the distributed power supply input into the distribution network is calculated, and the actual output power of the grid-forming inverter is used as the power feedback input of the grid control. Based on the grid-following control strategy and the inertia compensation range of the grid-forming inverter, the inertial power of the source-side energy storage device is controlled to be output to the grid, and finally reach the boundary of the inertia compensation range.

2. According to claim 1, the AC microgrid inertia compensation control method is characterized in that: The grid-connected converter realizes grid-connected synchronization by creating a voltage difference to form power flow. The grid-connected converter controls the output active power P GFL and reactive power Q GFL It is expressed as: In the formula, u v and u g The distribution represents the instantaneous value of the output voltage of the common connection node between the grid-following converter and the AC microgrid; Y g Represents the complex equivalent admittance of the AC microgrid node connected to the grid-type converter; Re represents the real part of the complex number; Im represents the imaginary part of the complex number; the phase angle of the grid-type converter is synchronized with the grid, and the reactive power is absorbed by the line reactance.

3. The AC microgrid inertia compensation control method according to claim 2 is characterized in that: The grid-connected converter achieves grid-connected synchronization by autonomously constructing voltage and phase difference to form the transmission of active power and reactive power. The grid-connected converter controls the output active power P GFM and reactive power Q GFM It is expressed as: Where θ is the grid electrical angle, θ* is the grid-connected converter output electrical angle, and arg represents the complex angle.

4. The AC microgrid inertia compensation control method according to claim 3 is characterized in that: In step S1, the coupling relationship between the distributed power source and the AC microgrid is determined by establishing a coupling matrix between the grid-following converter and the grid-forming converter; n grid-following converters and m grid-forming converters are connected to have a coupling relationship, and the matrix form of complex power coupling is expressed as: In the formula, represents the power coupling matrix, represents the internal coupling matrix of the grid-following converter, Represents the internal coupling matrix of the grid-type converter; and Respectively represent the coupling matrices between the grid-type converter and the grid-forming converter; Where P L Represents the active power transmitted between the grid-type converter, P M Represents the active power transmitted between grid-connected converters, P LM Represents the active power transmitted from the grid-following converter to the grid-forming converter, P ML represents the active power transmitted from the grid-connected converter to the grid-following converter, Q L Represents the reactive power transmitted between the grid-type converter, Q M Represents the reactive power transmitted between grid-connected converters, Q LM Represents the reactive power transmitted from the grid-following converter to the grid-connecting converter, Q ML represents the reactive power transmitted from the grid-forming converter to the following converter. The subscripts x and y represent the corresponding element numbers in the matrix, and j represents the imaginary unit.

5. The AC microgrid inertia compensation control method according to claim 4 is characterized in that: In step S2, the node inertia time constant of the AC microgrid is calculated using the following formula: In the formula, is the inertia time constant at sampling time t, T is the sampling time interval; is the instantaneous frequency calculated by the phase-locked loop of the grid node l at sampling time t, It is the instantaneous value of input active power calculated based on the grid node l voltage and input current at sampling time t.

6. The AC microgrid inertia compensation control method according to claim 5 is characterized in that: In step S2, the inertia output margin of the inertia time constant of the AC microgrid node is determined according to the capacity of the energy storage device on the source side of the AC microgrid, including: The DC side response of the energy storage device on the source side is transformed into a first-order voltage dynamic equation: In the formula, ΔP c represents the first-order dynamic voltage response, S ess,i , U dc,i and S ne,i They respectively represent the rated capacity of the energy storage station corresponding to the i-th grid-connected converter, the DC input voltage, and the rated capacity of the DC-coupled new energy equipment; The equivalent capacitance of the energy storage device is introduced as an intermediate variable to calculate the output inertia of the grid-connected converter. In the formula, J i Represents the output inertia of the grid-type converter, U dc,ref is the reference value of the DC input voltage; ω ref Represents the rated frequency of the AC microgrid; ω v,i represents the grid-forming frequency of the ith grid-forming converter; when the new energy station and the energy storage device are installed, the inertia output margin that the grid-forming converter can provide is inferred through the output inertia calculation formula of the grid-forming converter.

7. The AC microgrid inertia compensation control method according to claim 6 is characterized in that: In step S2, the inertia compensation range of the grid-connected converter is determined based on the AC microgrid topology and the inertia time constant of each AC microgrid node, including the steps of: The number of clusters k is determined according to the number of nodes K connected to the grid-forming converter; Select all grid-type converters as initial clustering points, and according to the access nodes of distributed power sources and grid-type converters, merge the clustering points of grid-type converters connected to the same node according to the inertia output margin to obtain the final clustering point; The output inertia margin of the grid-type converter is classified according to the cluster number k and the final clustering point, so as to characterize the inertia compensation range of the grid-type converter.

8. The AC microgrid inertia compensation control method according to claim 7 is characterized in that: In step S3, the actual output power calculation expression of the distributed power supply input into the distribution network is as follows: Where P rea,L,m and Q rea,L,m They represent the actual values ​​of the power transmission of the grid-following converter and the grid-forming converter in the AC microgrid respectively, diag represents the acquisition of the main diagonal values ​​of the matrix and integration into a column vector, and n and m represent the maximum number of grid-following converters and grid-forming converters connected to the AC microgrid respectively.

9. The AC microgrid inertia compensation control method according to claim 8 is characterized in that: In step S2, the grid-following control strategy is designed based on the basic equations of virtual synchronization technology, namely, the rotor swing equation and stator voltage equation of the synchronous generator, including: Where P ref,i , Q ref,i and ω ref Represents the reference value of active power, reactive power and frequency, U ref Represents the voltage level of the access distribution network; D p and D q represents the active power droop coefficient and reactive power droop coefficient of virtual synchronous control, J ne,i represents the virtual inertia constant, E v,i Represents virtual electromotive force.

10. The AC microgrid inertia compensation control method according to claim 9, characterized in that: In step S2, the inertial power output of the source-side energy storage device is controlled based on the following model: P in,M,i =P ne,i +P ess,i +P ess,tre,i ; Where P in,M,i represents the input power of the i-th grid-connected converter, P ne,i represents the instantaneous active power of all renewable energy sources connected to the i-th GFM, P ess,i represents the static instantaneous active power of all energy storage devices connected to the i-th GFM network, P ess,tre,i Represents the inertial active power generated by the energy storage device connected to the GFM network, P ess,tre,i represents the inertial power response of the GFC following the grid (P ref,i -P rea,M,i ).

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