596 results about "Admittance" patented technology

Power flow in a power distribution system is controlled using control commands generated based on values of system parameters. In this regard, generation prediction data, load prediction data, and real-time device status of equipment are utilized to generate scheduling data for power generation and power consumption and a network topology of the system is also obtained. The values of the system parameters are generated as an outcome of an unbalanced load flow analysis of the power distribution system using the scheduling data and the network topology. The unbalanced load flow analysis utilizes a compact multi-bus based nodal admittance model to represent relationships between nodal injected currents and nodal voltages at a plurality of non-overlapped phases of buses for a section formed by zero impedance branch connected with impedance branches in the power distribution system.

The present invention provides a method and system of self-adaptive setting of closed-loop parameters for suppressing PV coupling harmonics, comprising: acquiring node voltages and node currents of PV grid-connected inverters; constructing harmonic coupling admittance matrix according to the node voltages and node currents; calculating an amplitude of each element in the constructed harmonic coupling admittance matrix; screening contribution sources of coupling harmonics according to the calculated amplitude of the each element; evaluating quantitatively harmonic admittance of the PV grid-connected inverter according to screened contribution sources; and, carrying out optimization iteration for double-closed-loop PI control parameters of inverter with objective of minimizing the coupling harmonics of the PV grid-connected inverter according to results of the quantitative evaluation of the harmonic admittance, to complete self-adaptive setting of closed-loop parameters for suppressing PV coupling harmonics.

The invention discloses a power grid strength evaluation method and device, equipment, a medium and a product, and relates to the field of power system dynamic stability, and the method comprises the steps: building admittance and impedance models of all power supplies and network elements of a system in the impedance modeling process of the power system; the admittance and impedance model comprises a power supply admittance matrix, a power supply impedance matrix, a network node admittance matrix and a network node impedance matrix of all power supplies; based on the admittance and impedance model, establishing a whole-system closed-loop admittance matrix according to a closed-loop feedback relation between equivalent voltage disturbance and equivalent current disturbance of all buses; based on the closed-loop feedback relationship, defining a source network voltage interaction stability boundary representing the power grid strength according to the sensitivity of the system characteristic value to a source network voltage transfer function; and positioning a power grid strength weak area according to the source network voltage interaction stability boundary, and improving the power grid strength. According to the method, the oscillation risk caused by interaction of the control loops in the converter can be described.

The invention provides a fault ride-through control method and system for a network-forming converter, and relates to the technical field of power electronics. The fault ride-through control method of the network construction type converter comprises the following steps: determining a real-time virtual impedance value corresponding to a control loop based on a virtual admittance control module; in response to the fact that the real-time virtual impedance value is larger than or equal to the reference virtual impedance value of the control loop, transient current output by the network-building type converter is adjusted based on first-stage current limiting, and steady-state current output by the network-building type converter is adjusted based on second-stage current limiting; calculating an active power proportionality coefficient based on the real-time parameter and the reference parameter; calculating a target active power reference value according to the active power proportionality coefficient and the reference active power reference value; and executing power control based on the target active power reference value, and adjusting the output voltage of the network-forming converter. According to the method, when the power grid breaks down, the grid-forming type converter can have the functions of current limiting and transient synchronization stability improving at the same time.

The invention discloses a GaN totem-pole bridgeless PFC converter harmonic suppression method based on adaptive virtual admittance, and belongs to the technical field of converter control. The invention aims to solve the problem that LC resonance in a GaN totem-pole bridgeless PFC converter in a wide load range causes power grid voltage distortion to be converted into grid-side current harmonics. Comprising the following steps: decoupling a virtual admittance vector in a polar coordinate system, and optimizing under different load working conditions to obtain an optimal virtual admittance set; the system delay influence is compensated to ensure the robustness of the proposed method under different operation conditions; and a load power adaptive virtual admittance mechanism is constructed based on a segmented cubic Hermite interpolation method, so that suppression of network-side specific current harmonics in a wide load range is realized. The self-adaptive suppression method is used for self-adaptive suppression of the grid-side current harmonics of the GaN totem-pole bridgeless PFC converter.

A method and system for evaluating strength of a voltage source converter (VSC)-penetrated power grid based on voltage stiffness are provided. First data corresponding to a to-be-analyzed power grid is acquired in real time, and processed to generate a first admittance matrix corresponding to the to-be-analyzed power grid. The first admittance matrix is processed to generate device impedance data of each VSC and a second admittance matrix corresponding to the to-be-analyzed power grid. Rows and columns where a grid-forming VSC node and a rated alternating-current (AC) bus voltage grid-following VSC node are located are removed from the second admittance matrix to generate a third admittance matrix, which is processed to generate second data and third data corresponding to the VSC node. Strength evaluation data corresponding to the to-be-analyzed power grid is generated based on the third data in combination with the second data.

The invention relates to the technical field of cable line power distribution network harmonic resonance treatment, in particular to a global and local cooperative partition cooperative resonance suppression method and device. The method comprises the steps of determining a harmonic conductance sensitivity index of each node in a power distribution network according to a target power distribution network admittance matrix parameter, and performing node region division; performing modal analysis on the admittance matrix parameters to obtain modal impedance and participation factors; determining a global optimal virtual admittance instruction value according to the modal impedance, the participation factor and the voltage distortion rate; according to the global optimal virtual admittance instruction value and the voltage distortion rate, determining a regional optimal virtual admittance instruction value in the region; and determining a harmonic compensation current value according to the regional optimal virtual admittance instruction value and the harmonic voltage. According to the method, harmonic suppression is realized for the whole power distribution network by adopting a partition and cooperation mode, and meanwhile, for background harmonic injection change, external interference such as resonance center offset and the like can be effectively overcome, so that the optimal harmonic suppression effect is realized.

The invention provides an industrial park complex frequency domain admittance matrix modeling method based on a vector fitting technology. The method comprises the following steps that S101, real-time amplitude-frequency and phase-frequency characteristic curves of all new energy units in an industrial park grid-connected operation state are measured in a grid-connected point disturbance mode; s102, obtaining the number of peak values of the new energy unit, determining the order of the complex frequency domain impedance of the new energy unit, and then determining the order of vector fitting; s103, using a vector fitting technology to identify the complex frequency domain impedance model of each new energy unit segment by segment to obtain segment accurate parameter representation of the complex frequency domain impedance model; and S104, establishing a complex frequency domain admittance matrix of the industrial park based on the complex frequency domain impedance model of each new energy unit in combination with line topology information and line parameters in the industrial park. According to the method, the problems of'grey box 'and'black box' of the converter caused by manufacturer confidentiality are effectively solved, and a specific and accurate converter complex frequency domain admittance model is obtained to analyze the grid-connected stability of the converter.

The invention discloses a harmonic oscillation suppression method and system for a hydrogen energy grid-connected converter. A corresponding remolding transfer function Gig (s) is added in a forward channel of a d-axis current controller; constructing a power transmission relation between an alternating current system and a direct current system based on the direct current side small signal model and the alternating current side power small signal model of the hydrogen energy inverter; inputting a small signal transfer function model of a voltage outer loop and a current inner loop obtained by controlling the hydrogen energy grid-connected inverter into a power transmission relation of an alternating current system and a direct current system to obtain a small signal control model of the hydrogen energy grid-connected inverter in a dq coordinate system; and determining an equivalent output admittance model of the hydrogen energy inverter based on the remolded transfer function Gig (s) and the small signal control model, obtaining a minimum return rate matrix representing the stability of the hydrogen energy grid-connected inverter through the power grid impedance and the output admittance of the hydrogen energy inverter, and determining the stability of the grid-connected converter system based on the characteristic value of the minimum return rate matrix. And suppression of harmonic oscillation is realized.

The invention relates to the technical field of AC / DC module control, and discloses an intelligent control method and system for multi-mode switching of an AC / DC module. According to the method, a dynamic topology mapping model is constructed according to an impedance spectrum matrix, and a physical connection relation is converted into a node admittance relation network; generating an energy distribution state sequence based on the power fluctuation vector, and analyzing migration constraint conditions among different operation modes by adopting an association rule mining algorithm; when an operation mode switching instruction is detected, activating a node admittance relation network in the dynamic topology mapping model, and inputting a current energy distribution state sequence to an association rule mining algorithm; according to a real-time matching result of the node admittance relation network and the migration constraint condition, generating a switching control instruction containing an impedance adjustment gradient and a power distribution weight; and the power semiconductor execution unit transmits the switching control instruction to the AC / DC module. According to the method, multi-mode intelligent switching control of the alternating-current and direct-current module can be realized.

A global optimization method for the quality of electric energy of a micro-grid. The method comprises: on the basis of an equivalent virtual impedance of an inverter of each node in a micro-grid and a local load of each node, establishing a node admittance matrix for the micro-grid (S1); on the basis of a weight value assigned to each node in the micro-grid and a voltage distortion rate of each node, constructing an objective function for the micro-grid (S2); on the basis of the node admittance matrix and the remaining capacity of the inverter of each node, constructing a constraint condition for harmonic modulation of each node in the micro-grid (S3); and in response to the constraint conditions being met, analyzing an optimal solution to the objective function, and on the basis of the optimal solution, adjusting the equivalent virtual impedance on each node (S4).

The invention discloses a power distribution network single-phase earth fault positioning method and system based on zero-sequence admittance comparison, and the method comprises the steps: obtaining zero-sequence voltage and zero-sequence current sampling values at two ends of a protected section, and determining whether to start the detection of single-phase earth fault positioning or not based on the break variable of the zero-sequence voltage; if the detection of the single-phase earth fault positioning is started, the two ends respectively calculate respective power frequency zero sequence voltage phasors and power frequency zero sequence current phasors, and send the phasors to the opposite end; respectively calculating zero-sequence admittance values of the home terminal and the opposite terminal based on the power frequency zero-sequence voltage phasors and the power frequency zero-sequence current phasors of the home terminal and the opposite terminal; and respectively calculating a differential admittance value and a brake admittance value, respectively comparing the differential admittance value with an admittance threshold value and the brake admittance value, and judging whether the protected section is a fault section based on a comparison result. The differential admittance serves as the action amount, the brake admittance serves as the floating threshold, the difference between internal and external faults is amplified, and reliability and sensitivity are effectively improved.

The invention belongs to the technical field of DC power grid short-circuit current calculation, and particularly relates to a short-circuit current calculation method for a metal backflow four-terminal bipolar DC power grid, and the method comprises the steps: S1, building an MMC equivalent model; s2, constructing and processing an equivalent circuit of a Bergeron lossy transmission line of the DC line to obtain a Bergeron two-port equivalent model of a single-phase transmission line and a Bergeron equivalent model of a three-phase transmission line; s3, establishing an equivalent model of the metal backflow four-terminal bipolar direct current power grid; s4, establishing an accompanying circuit model of the metal backflow four-terminal bipolar direct current power grid; s5, constructing a conductance matrix G, and forming a node voltage equation; and S6, according to the fault type, modifying a node admittance matrix G in the node voltage equation into an equivalent conductance matrix G ', and then solving the modified node voltage equation to obtain the branch current and the node voltage after the fault. According to the method, the problem that the short-circuit current calculation method of the metal backflow four-terminal bipolar direct-current power grid is insufficient in accuracy can be solved.

The invention discloses an impedance characteristic remodeling method, device and equipment and a medium, and is applied to the field of wind turbine generators. Wherein the corresponding rotor reference current is determined according to the electromagnetic reactive power, the active power and the corresponding power reference value; correcting the rotor current according to the rotor reference current by adopting a virtual admittance control mode, and generating a corresponding rotor voltage given value; sequentially performing differentiation, filtering and signal extraction processing on the rotor reference current and the rotor current to obtain an impedance remodeling signal; and correcting the rotor voltage given value based on the impedance remodeling signal so as to enable the corrected rotor voltage given value to serve as the control voltage of a rotor side converter in the medium-voltage doubly-fed wind turbine generator after impedance characteristic remodeling. The virtual admittance control mode and the impedance remolding signal mode are adopted to suppress the negative resistance effect of the rotor side converter in the medium-voltage doubly-fed wind turbine generator under voltage disturbance, and therefore the damping effect on external excitation in the sub-super-synchronous frequency band and the high frequency band is higher.

The invention discloses a wind power system composite oscillation suppression strategy and system based on a static synchronous compensator, and the strategy comprises the steps: firstly constructing a sequence impedance model of a GFM-STATCOM and an equivalent wind turbine generator (EWTG) based on a wind power output system containing the GFM-STATCOM; combining the impedance contribution degree beta, analyzing the interaction between the two, and determining the oscillation risk dominant factor of the sub / super-synchronous frequency band; and finally, performing frequency-band suppression: aiming at the problem of negative damping dominance of the subsynchronous frequency band GFM-STATCOM, adopting a control parameter optimization strategy based on parameter sensitivity, and reducing a reactive loop integral coefficient by increasing virtual resistance so as to reduce a negative damping range. In order to solve the problem of negative damping leading of a super-synchronous frequency band EWTG, a virtual admittance control strategy based on voltage feedforward is adopted to reduce the output impedance amplitude of a GFM-STATCOM, the leading position of positive damping of the GFM-STATCOM is enhanced, and then the negative damping of the system is eliminated. According to the invention, precise suppression of composite oscillation is realized, and the stability of a wind power sending system under a weak power grid is improved.

The invention provides a network construction type energy storage wide short circuit ratio adaptive stability control method and system, and the method comprises the steps: carrying out the calculation based on a power grid energy storage parameter, power grid impedance and energy storage impedance, and obtaining a dynamic short circuit ratio; according to the dynamic short-circuit ratio, switching the power grid operation condition mode to a power grid operation condition mode corresponding to the dynamic short-circuit ratio; in a power grid operation working condition mode, obtaining optimized virtual inductance resistance parameters or frequency-variable admittance regulator parameters; a corresponding control instruction is generated according to the virtual inductance resistance parameters or the frequency-variable admittance regulator parameters, and self-adaptive stability control is completed; real-time identification and dynamic adjustment of the power grid impedance and the energy storage impedance are achieved, traditional fixed parameter control limitation is broken through, the dynamic short-circuit ratio is obtained through calculation, the problem of power angle instability under the wide short-circuit ratio is solved, corresponding switching of power grid operation working condition modes can be conducted based on the dynamic short-circuit ratio, differential control requirements of a weak power grid and a strong power grid are considered, and the method is suitable for large-scale popularization and application. And the full-working-condition adaptive capacity is improved.

The invention discloses a scattering parameter de-embedding method, device and equipment, and relates to the technical field of semiconductors. The method comprises the following steps: obtaining n de-embedding test structural members; constructing a first ABCD matrix and a second ABCD matrix according to the first admittance and the second admittance; according to the third admittance, the fourth admittance and the length of each transmission line in the n transmission lines, constructing n third ABCD matrixes; the third admittance is the admittance between the unit length transmission line and the ground in the equivalent pi-type circuit corresponding to the unit length transmission line, and the fourth admittance is the admittance of the unit length transmission line; and according to the first ABCD matrix, the second ABCD matrix and the n third ABCD matrixes, solving to obtain a de-embedded ABCD matrix of the to-be-tested device, and converting the ABCD matrix of the to-be-tested device into scattering parameters. According to the embodiment of the invention, scattering parameter de-embedding can be more efficiently and flexibly realized, so that the overall scattering parameter de-embedding efficiency and precision can be effectively improved.

The invention provides a broadband self-adaptive impedance remodeling method based on energy storage, which comprises the following steps of: dividing an impedance frequency band of an energy storage system according to analysis on a PLL (Phase Locked Loop), a voltage loop, a current loop and a filter, and constructing an improved self-adaptive impedance remodeling control strategy based on combination of active damping and virtual admittance based on the divided frequency band; according to the impedance remodeling control strategy, establishing an energy storage inverter system impedance model considering impedance remodeling; based on an impedance model, the frequency band overlapping effect between different frequency bands and between different control links is comprehensively considered, and the impedance near a system oscillation frequency point is remodeled through sequential optimization design of PLL control, virtual admittance control and active damping control. The purposes of broadband oscillation suppression of the diversified new energy cluster sending-out system and safe and stable operation of a power system are achieved.

The invention belongs to the field of stability analysis of a grid-connected system of a grid-building converter, and particularly relates to a grid-building converter grid-connected resonance risk analysis method considering virtual impedance, which comprises the following steps: S1, establishing a three-phase time domain differential equation and simplifying the equation into a single-phase equivalent time domain model; converting into a harmonic state space model of the main circuit; s2, constructing a harmonic state space model of a control system comprising an active power control loop and a reactive power control loop; s3, introducing a virtual impedance control link, and correcting the voltage amplitude reference phasor output by the reactive power control loop; deriving an expression of a modulation signal disturbance phasor; s4, obtaining a complete frequency domain admittance model YGSC of the network construction converter considering the influence of the virtual impedance; an open loop gain TGFM of the grid converter grid-connected system is constructed; and S5, drawing a Nyquist curve based on TGFM, and carrying out resonance risk determination. According to the method, the interaction dynamic characteristics of the network building converter and the power grid under the influence of the virtual impedance can be accurately represented, and the resonance risk of the grid-connected system is evaluated.

Power flow in a power distribution system is controlled using control commands generated based on values of system parameters. In this regard, generation prediction data, load prediction data, and real-time device status of equipment are utilized to generate scheduling data for power generation and power consumption and a network topology of the system is also obtained. The values of the system parameters are generated as an outcome of an unbalanced load flow analysis of the power distribution system using the scheduling data and the network topology. The unbalanced load flow analysis utilizes a compact multi-bus based nodal admittance model to represent relationships between nodal injected currents and nodal voltages at a plurality of non-overlapped phases of buses for a section formed by zero impedance branch connected with impedance branches in the power distribution system.

The invention provides a system temporary overvoltage evaluation method under an asymmetric fault, and relates to the field of power systems, and the method comprises the steps: responding to a VSC grid-connected system AC fault, carrying out the equivalence of a VSC fault ride-through reactive power support strategy in a positive sequence network, carrying out the equivalence of a VSC unbalanced voltage suppression strategy in a negative sequence network, and carrying out the equivalence of the VSC fault ride-through reactive power support strategy in the negative sequence network; obtaining a single-machine equivalent model; the single-machine equivalent model is merged into a network admittance matrix, a corrected admittance matrix is constructed, and a corrected impedance matrix is solved; setting short-circuit boundary conditions, calculating short-circuit current increment of a fault point as an equivalent current source, solving voltage increment of each PCC point according to the corrected impedance matrix and the equivalent current source, and synthesizing three-phase voltage; and forming a TOV evaluation result based on the phase voltage maximum value of each PCC point, and calculating a voltage safety index according to the result. According to the invention, comprehensive analysis and evaluation of the temporary overvoltage risk of the new energy grid-connected system are realized.

The invention belongs to the technical field of fan torsional vibration prediction, and particularly relates to a torsional vibration prediction method, device and equipment for a net-forming type direct-driven fan and a storage medium, and the method comprises the steps: constructing a small signal model of the net-forming type direct-driven fan; based on a shafting dual-mass-block model, deducing the relation between the direct-drive fan port voltage and current signals and the direct-drive fan shafting torsional vibration when forced oscillation occurs; when forced oscillation occurs, a transfer function between different power grid node ports is obtained by constructing a wind power plant s domain node admittance model, so that required voltage and current signals of the power grid node ports are calculated, and the calculated voltage and current signals are used as input of a small signal model of a grid-constructing type direct-driven fan. And calculating the torsional vibration of the shaft system of the mesh-forming type direct-drive fan caused by forced oscillation by combining the relationship between the voltage and current signals of the port of the mesh-forming type direct-drive fan and the torsional vibration of the shaft system of the mesh-forming type direct-drive fan. The potential torsional vibration problem can be found and processed in time, and faults are avoided.

The invention provides a power distribution network broadband interference traceability method and system resistant to strong noise influence. The method comprises the steps of obtaining a voltage incidence matrix, a vector of a to-be-estimated quantity and a vector of a three-phase harmonic current; establishing a parameter estimation equation by using the voltage incidence matrix, the vector of the to-be-estimated quantity and the vector of the three-phase harmonic current, and processing the parameter estimation equation to establish a variable weight least square expression; iteratively solving parameters by aiming at the variable weight least square expression, and calculating a residual vector generated by k-th iteration; if the residual vector is within a tolerance range, outputting line parameters under harmonic waves estimated this time, obtaining self-impedance and earth admittance of each node, obtaining a harmonic wave position index by using a fuzzy logic method, inputting the harmonic wave position index into a statistical parameter calculator with abnormal values removed, obtaining a sequence value after the abnormal values are removed, and calculating a threshold value; and filtering the harmonic position index lower than the threshold value, and judging the node where the interference source is located.

The invention belongs to the field of complex electrical impedance tomography, and particularly relates to a complex electrical impedance image reconstruction method based on space-wavelet dual-domain driving. A boundary voltage signal on a sensor is mapped into an initial complex value admittance image by using a complex number Newton-Raphson method, the initial complex value admittance image is used as an input feature of an SWU-Net model to carry out spatial feature coding and wavelet frequency domain feature construction, the SWU-Net model comprises a plurality of residual four-azimuth full convolution encoders, a plurality of rswFormer modules and a plurality of decoders, and the SWU-Net model comprises a plurality of residual four-azimuth full convolution encoders, a plurality of rswFormer modules and a plurality of decoders. Wherein the encoder and the decoder construct and fuse spatial domain features and frequency domain features respectively. Meanwhile, a jump connection module for fusing double-domain features of a space domain and a frequency domain is constructed, and the jump connection module is used for fusing the space low-frequency features and the frequency high-frequency features. The method provided by the invention has better reconstruction performance in the aspects of quantitative indexes and visual visualization effects.

The invention discloses an impedance remodeling method for a grid-connected converter, and relates to the field of fire safety, and the method comprises the steps: respectively recording a virtual impedance transfer function and a virtual admittance transfer function into a current inner loop universal controller structure under a d / q coordinate system, and obtaining a series virtual impedance control structure and a parallel virtual admittance control structure; the series virtual impedance control structure and the parallel virtual admittance control structure are subjected to time domain and frequency domain conversion to obtain a series virtual impedance Norton equivalent circuit and a parallel virtual admittance Norton equivalent circuit respectively; based on the influence of virtual impedance and virtual admittance on the converter, multiple compensation links are added in a control framework of the grid-connected converter, so that the harmonic voltage and harmonic current of a grid-connected point are reduced, and the converter operates more stably.

The invention relates to a three-level SVG multistage WARD equivalent modeling method based on an L / C constant admittance model. An ANPC type three-level converter model is an important part of various types of power electronic equipment, and is applied to scenes such as a three-level static var generator (SVG) and the like. In small-step offline simulation, an existing simulation modeling technology cannot consider precision and efficiency at the same time. Aiming at the problem that the simulation speed is extremely low in an offline simulation platform, a three-level SVG electromagnetic transient simulation acceleration model equivalent to a multi-stage nested fast simultaneous solution algorithm is provided based on a device Norton equivalent circuit. Firstly, an L / C equivalent constant admittance model is used for carrying out equivalent processing on a switching device, first-time WARD equivalence is carried out, then an equivalent circuit is connected with other transformer and filter inductance circuit parts, WARD equivalence is carried out again, and finally a Norton form equivalent circuit is formed.

The invention discloses a grounding fault judgment method and system of a distribution line grounding system, a storage medium, electronic equipment and a computer program product. According to the ground fault judgment method, the ground fault judgment system determines a zero-sequence voltage abrupt change value and a zero-sequence voltage amplitude according to the collected zero-sequence voltage of the distribution line; under the condition that the zero-sequence voltage abrupt change value meets a preset zero-sequence voltage abrupt change value condition, determining a transient grounding judgment result and a zero-sequence admittance value according to the collected zero-sequence current and zero-sequence voltage of the distribution line; determining the classification condition of the zero-sequence admittance value according to the transient grounding judgment result; under the condition that the zero-sequence voltage amplitude meets a preset zero-sequence voltage amplitude condition, determining a zero-sequence admittance judgment result according to the classification condition of the zero-sequence admittance value and the zero-sequence admittance value; determining a grounding comprehensive result according to the transient grounding judgment result and the zero-sequence admittance judgment result; and determining a grounding fault condition of the distribution line according to the grounding comprehensive result and a preset grounding result condition.

The invention discloses an MMC AC-DC admittance model establishment method considering AC frequency and related equipment, and the method comprises the steps: obtaining a main circuit small signal model, a voltage loop small signal model and a current loop small signal model of a modular multilevel converter, and carrying out the rewriting of the models through a harmonic state space method, according to the method, the working condition of alternating-current side rated operation frequency change is considered, the method is suitable for stability analysis of a flexible direct-current transmission sending-out system considering frequency change of a new energy collection system, then unknown numbers in a rewritten model are obtained based on a steady-state theory solving method, and finally a modular multilevel converter mixed admittance model is established. The method is not influenced by AC side and DC side power grid admittance, is only determined by a steady state working point, a control structure and converter parameters of the modular multilevel converter, and better meets the requirements of fully protecting user privacy and commercial confidentiality during system stability analysis.

The invention discloses an optimal locating and sizing planning method for an energy storage system and distributed power generation. The method comprises the following steps: representing the condition of installing an energy storage and distributed power supply in each node in a topological graph of a power system through a decision vector; establishing an admittance matrix according to the topological graph of the power system, and then performing conversion to obtain an impedance matrix of the nodes; and by taking the lowest operation cost as an objective function and combining constraint conditions, optimizing decision vectors by combining sensitivity analysis of an impedance matrix and a simulated annealing algorithm to obtain an optimal locating and sizing scheme of the energy storage system and distributed power generation. According to the method, the overall operation environment of a power grid and physical limitations of equipment are more considered, including consideration of the capacity of a transformer, and it is ensured that the safe operation range of the transformer is not exceeded while BESS and DG are increased; greater flexibility is provided, and the number and scale of energy storage and power generation facilities are allowed to be dynamically adjusted.

The invention discloses a direct-driven fan system impedance modeling method considering frequency coupling, and the method comprises the steps: S1, obtaining a mathematical expression of a blade tip speed ratio and output power according to a wind turbine airflow model of a direct-driven fan; s2, according to equivalent circuit topology modeling under a dq coordinate system of the permanent magnet synchronous motor, obtaining an expression of electromagnetic torque and electromagnetic power; s3, according to the control structures of the machine-side converter and the grid-side converter of the direct-drive fan, modeling is carried out respectively, and an equivalent admittance mathematical expression of the machine-side converter and six disturbance admittance expressions in the direct-drive fan are obtained; and S4, based on the mathematical expressions of the output power, the electromagnetic power, the equivalent admittance and the disturbance admittance obtained in S1, S2 and S3, establishing the equivalent admittance / impedance of the direct-drive fan system. According to the method, multi-time-scale control and full-working-condition frequency domain port characteristics of the direct-driven fan system can be effectively represented, and the equivalent impedance model can accurately analyze the stability of the system.