Microgrid system and method based on distributed control

Abstract

The present application relates to the field of micro-grid control and power electronics, in particular to a micro-grid system and method based on distributed control, comprising a central control module and a plurality of distributed nodes interconnected through a communication network; the distributed nodes collect local bus three-phase voltage, current and extract power quality parameters, transient operating parameters and local communication parameters; switch to a local autonomous control state when the communication delay is greater than 200ms or the packet loss rate is greater than 40%; the central control module generates inertia control table and specific harmonic compensation instructions and issues; when the active power change rate exceeds the threshold value, the local table lookup interpolation obtains the target virtual inertia, generates the voltage phase reference value to adjust the distributed inverter output power; when the total harmonic distortion rate or the negative sequence current is out of limit, the nonlinear load branch is cut off; and the next period inertia control table is updated through frequency calibration.

Description

Technical Field

[0001] This invention relates to the field of microgrid control and power electronics technology, specifically to a microgrid system and method based on distributed control. Background Technology

[0002] Microgrid distributed control technology is a common way to improve the operational stability of new energy access systems. It can coordinate and control distributed inverters, energy storage devices and load branches through information interaction between the central control module and multiple distributed nodes. It can also realize power regulation and power quality management based on local operating parameters such as voltage, current and frequency. It has the flexibility and scalability to support plug-and-play of multiple nodes and dynamic reconfiguration of control topology.

[0003] As the proportion of photovoltaic, wind power, energy storage batteries, and nonlinear loads in the microgrid of the park continues to increase, the operating status of the microgrid is more susceptible to communication delays, packet loss, rapid fluctuations in source and load power, and harmonic disturbances. However, existing microgrid control methods may still rely on central control or real-time interaction between adjacent nodes when communication deteriorates or transient disturbances occur. This can lead to untimely local control response, inaccurate phase reference, insufficient inverter inertia support, and the inability to achieve local autonomous disconnection of nonlinear loads, thereby affecting the stable operation of the microgrid under complex operating conditions. Summary of the Invention

[0004] The purpose of this invention is to provide a microgrid system and method based on distributed control, addressing the following technical problems: Existing microgrid control methods suffer from deficiencies in response timeliness, phase reference accuracy, inverter inertia support, and independence of nonlinear load shedding when facing communication degradation or transient disturbances. These deficiencies include response lag and malfunctions. Therefore, this invention proposes a microgrid system and method based on distributed control that achieves communication degradation autonomy and lookup table control through edge nodes, utilizes internal crystal oscillators to provide stable phase, dynamically calibrates and updates inertia support, and independently shelves disturbed load branches, thereby maintaining stable system operation under complex communication and operating conditions. The objective of this invention can be achieved through the following technical solutions:

[0005] The microgrid system based on distributed control includes a central control module and multiple interconnected distributed nodes. Each node contains an edge detection unit, an edge execution unit, an edge control module containing a state extraction unit, a local judgment unit, and a lookup control unit, as well as distributed inverters and physical relays.

[0006] The edge execution unit is connected to the distributed inverter and the physical relay, and shares the edge control module with the edge detection unit. The edge control module is communicatively connected to the central control module, which includes a parameter calculation unit and a frequency calibration unit.

[0007] The edge detection unit collects the instantaneous values ​​of the three-phase voltage and current of the local bus; the state extraction unit extracts the local power quality parameters, transient operating parameters and local communication parameters based on these and sends them to the central control module.

[0008] The local judgment unit switches to the local autonomous control state when the local communication parameters meet the preset communication degradation conditions.

[0009] The parameter calculation unit generates an inertia control table containing the correspondence between virtual inertia and frequency change rate and specific subharmonic compensation instructions based on the node parameters, and sends them to the edge control module.

[0010] When the active power change rate exceeds the preset power change threshold, the table lookup control unit calculates the target virtual inertia based on the transient operating parameters in the inertia control table, generates a voltage phase reference value, and drives the edge execution unit to adjust the output of the distributed inverter.

[0011] The frequency calibration unit calculates the cumulative frequency deviation based on transient operating parameters and target virtual inertia. When the deviation exceeds a preset tolerance threshold, it adjusts the preset inertia compensation coefficient to update the inertia control table for the next cycle.

[0012] The system controls the distributed inverters and physical relays to maintain operation when the communication degradation conditions or the active power change rate exceeds the limit.

[0013] Optionally, the edge control module further includes a local phase-locked loop and an internal crystal oscillator. After switching to the local autonomous control state, the local judgment unit excludes the off-diagonal weights in the adjacency weight matrix containing the communication topology of adjacent nodes in the local distributed control from the calculation of local control quantities and cuts off the external phase reference input.

[0014] The local judgment unit is also used to lock the phase tracking state of the local phase-locked loop and switch to the standard power frequency phase accumulation signal generated by the internal crystal oscillator to avoid reactive circulating current caused by phase difference deviation due to receiving expired communication data.

[0015] Optionally, the power quality parameters include the fundamental amplitude of the local bus voltage, the frequency offset, the total harmonic distortion rate extracted through a sliding window, and the negative sequence current;

[0016] The transient operating parameters include the rate of change of active power, the rate of change of frequency, and the real-time state of charge of the local energy storage battery.

[0017] The local communication parameters include one-way communication delay with neighboring nodes, packet loss rate statistics, and the current physical switch status of grid connection or islanding; the packet loss rate statistics refer to the percentage ratio of the number of cooperative control data packets that a node failed to receive to the total number of data packets expected to be received within a preset sliding time observation window.

[0018] Optionally, the physical relay is connected in series in the nonlinear load branch of the microgrid; when the one-way communication delay is greater than 200ms or the packet loss rate is greater than 40%, the local judgment unit determines that the preset communication degradation condition is met.

[0019] When the total harmonic distortion rate (THD) collected locally is greater than 15% or the negative sequence current is greater than 20%, the lookup table control unit outputs a high-level signal to drive the physical relay to disconnect the corresponding nonlinear load branch within a preset time. If neither the THD nor the negative sequence current exceeds the corresponding threshold, the physical relay remains in its original state.

[0020] Optionally, the parameter calculation unit generates a nonlinear relationship between the virtual inertia and the frequency change rate based on the pre-stored system basic inertia constant, the inertia compensation coefficient, the predicted frequency change rate obtained through the transient operating parameters, the available energy storage depth, and the penalty factor used to limit the over-discharge of the energy storage battery.

[0021] The parameter calculation unit discretizes the nonlinear correspondence and extracts multiple inflection point coordinates at equal intervals within the frequency change rate range to generate a two-dimensional inertia control table with a row and column structure.

[0022] Optionally, the edge control module further includes a virtual synchronous generator control model and a space vector pulse width modulation generator; the virtual synchronous generator control model and the space vector pulse width modulation generator are integrated as control algorithm programs in the microprocessor of the edge control module, and are logically located between the lookup control unit and the edge execution unit, and are used to convert the virtual inertia calculation obtained from the lookup into the underlying pulse width modulation signal;

[0023] The lookup control unit writes the inertia control table to a specified memory address of the controller via direct memory access.

[0024] When matching the inertia control table, the table lookup control unit performs linear interpolation based on the locally collected frequency change rate to obtain the target virtual inertia, and generates the voltage phase reference value based on the target virtual inertia and the virtual synchronous generator control model.

[0025] The lookup control unit writes the voltage phase reference value into the register of the space vector pulse width modulation generator to change the duty cycle timing of the switching transistors of the distributed inverter.

[0026] Optionally, the edge control module records the actual physical frequency change curve before and after the control action and reports it to the central control module;

[0027] The frequency calibration unit calculates the cumulative frequency deviation within the transient observation time window based on the actual physical frequency change curve.

[0028] When the accumulated frequency deviation exceeds the preset tolerance threshold, the frequency calibration unit calculates the compensation correction amount based on the accumulated frequency deviation and adds it to the inertia compensation coefficient to achieve closed-loop calibration of the drift of the underlying physical hardware operating parameters; when the accumulated frequency deviation does not exceed the preset tolerance threshold, the inertia compensation coefficient remains unchanged.

[0029] Optionally, the sampling rate of the edge detection unit is configured to be 5000Hz, the period for the state extraction unit to send parameters is configured to be 1s, and the communication period for the parameter calculation unit to send the inertia control table is configured to be 1min.

[0030] The microgrid method based on distributed control, applicable to the microgrid system based on distributed control described in the embodiments, is characterized by including the following steps:

[0031] Step 1: Initial system configuration: Configure the sampling period of the edge detection unit and the communication degradation conditions of the local judgment unit;

[0032] Step 2, Local Status Acquisition: The edge detection unit acquires the instantaneous values ​​of the three-phase voltage and current of the local bus; the status extraction unit extracts the local power quality parameters, transient operating parameters, and local communication parameters accordingly.

[0033] Step 3, Degradation Condition Judgment: When the local communication parameters meet the preset communication degradation conditions, the local judgment unit interrupts the collaborative interaction and switches to the local autonomous control state.

[0034] Step 4: Global parameter calculation: The central control module gathers the parameters of each node, generates an inertia control table containing the relationship between virtual inertia and frequency change rate, and sends specific subharmonic compensation commands to the edge control module.

[0035] Step 5, Lookup Control Execution: When the active power change rate exceeds the preset power change threshold, the lookup control unit calculates the target virtual inertia based on the transient operating parameters in the inertia control table, generates the voltage phase reference value, and drives the edge execution unit to adjust the output of the distributed inverter.

[0036] Step 6, Parameter Feedback Update: The frequency calibration unit calculates the cumulative frequency deviation based on the transient operating parameters and the target virtual inertia. When the deviation exceeds the preset tolerance threshold, the preset inertia compensation coefficient is adjusted to update the inertia control table for the next cycle.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1. When communication is degraded, the present invention switches to local autonomous control state through local judgment unit, locks local phase-locked loop and switches to standard power frequency phase accumulation signal generated by internal crystal oscillator; this setting cuts off external phase reference input, avoids reactive circulating current caused by phase difference deviation due to receiving expired communication data, and ensures stable operation of microgrid when communication is degraded.

[0039] 2. This invention adopts a collaborative control method of central control issuing inertia control tables and edge nodes looking up tables locally; when the active power change rate exceeds the limit, the table lookup control unit directly calculates the target virtual inertia based on transient operating parameters in the local table and adjusts the inverter output; this eliminates the need for nodes to wait for real-time communication responses during transient disturbances, and provides timely and effective inertia support;

[0040] 3. This invention achieves independent control of nonlinear loads through an edge control module; when the locally collected total harmonic distortion rate or negative sequence current exceeds a preset threshold, the lookup control unit directly outputs a signal to drive the physical relay to disconnect the corresponding nonlinear load branch; this reduces the dependence on central coordination and interaction, and realizes local rapid isolation when power quality deteriorates. Attached Figure Description

[0041] The above and other objects, features and advantages of the present invention will become more apparent from the following description of embodiments of the invention with reference to the accompanying drawings, in which:

[0042] Figure 1 A schematic diagram of a microgrid system based on distributed control provided in an embodiment of the present invention.

[0043] Figure 2 This is a flowchart illustrating the microgrid method based on distributed control provided in an embodiment of this application. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0045] like Figure 1As shown, the microgrid system based on distributed control includes a central control module and multiple interconnected distributed nodes. Each node contains an edge detection unit, an edge execution unit, an edge control module containing a state extraction unit, a local judgment unit, and a lookup control unit, as well as distributed inverters and physical relays.

[0046] The edge execution unit is connected to the distributed inverter and physical relay, and shares an edge control module with the edge detection unit. The edge control module communicates with the central control module, which includes a parameter calculation unit and a frequency calibration unit.

[0047] The edge detection unit collects the instantaneous values ​​of the three-phase voltage and current of the local bus; the status extraction unit extracts the local power quality parameters, transient operating parameters and local communication parameters based on these and sends them to the central control module.

[0048] The local judgment unit switches to the local autonomous control state when the local communication parameters meet the preset communication degradation conditions.

[0049] The parameter calculation unit generates an inertia control table containing the correspondence between virtual inertia and frequency change rate, as well as specific subharmonic compensation instructions, based on the node parameters, and sends them to the edge control module.

[0050] When the rate of change of active power exceeds the preset power change threshold, the lookup control unit calculates the target virtual inertia based on the transient operating parameters in the inertia control table, generates the voltage phase reference value, and drives the edge execution unit to adjust the output of the distributed inverter.

[0051] The frequency calibration unit calculates the cumulative frequency deviation based on transient operating parameters and target virtual inertia. When the deviation exceeds the preset tolerance threshold, it adjusts the preset inertia compensation coefficient to update the inertia control table for the next cycle.

[0052] The system controls the distributed inverters and physical relays to maintain operation when communication degradation conditions are met or the active power change rate exceeds the limit.

[0053] The edge control module also includes a local phase-locked loop and an internal crystal oscillator. After switching to the local autonomous control state, the local judgment unit excludes the off-diagonal weights in the adjacency weight matrix containing the communication topology of adjacent nodes in the local distributed control from the calculation of local control quantities and cuts off the external phase reference input.

[0054] The local judgment unit is also used to lock the phase tracking state of the local phase-locked loop and switch to the standard power frequency phase accumulation signal generated by the internal crystal oscillator to avoid reactive circulating current caused by phase difference deviation due to receiving expired communication data.

[0055] Power quality parameters include the fundamental amplitude of the local bus voltage, frequency offset, total harmonic distortion extracted through a sliding window, and negative sequence current.

[0056] Transient operating parameters include the rate of change of active power, the rate of change of frequency, and the real-time state of charge of the local energy storage battery;

[0057] Local communication parameters include one-way communication delay with neighboring nodes, packet loss rate statistics, and the current physical switch status of grid connection or islanding. The packet loss rate statistics refer to the percentage of cooperative control data packets that a node fails to receive within a preset sliding time observation window, compared to the total number of data packets expected to be received.

[0058] The physical relay is connected in series in the nonlinear load branch of the microgrid; when the one-way communication delay is greater than 200ms or the packet loss rate is greater than 40%, the local judgment unit determines that the preset communication degradation condition is met.

[0059] When the total harmonic distortion rate (THD) collected locally exceeds 15% or the negative sequence current exceeds 20%, the lookup control unit outputs a high-level signal to drive the physical relay to disconnect the corresponding nonlinear load branch within a preset time. If neither the THD nor the negative sequence current exceeds the corresponding threshold, the physical relay remains in its original state.

[0060] This implementation is used in a park microgrid containing photovoltaic, wind power, energy storage batteries, and multiple nonlinear load branches. Multiple distributed inverters are set up in the park, and each distributed inverter is connected to a corresponding distributed node. The central control module is located in the microgrid dispatch center. Each distributed node is connected to the central control module through a communication network, while data interaction links for distributed collaborative control are maintained between adjacent nodes. Nonlinear load branches include frequency converters, rectifier loads, or single-phase centralized load branches, with physical relays connected in series in the branches. The physical relays are driven by edge execution units.

[0061] In this embodiment, when communication degradation, rapid changes in source load power, and power quality degradation caused by nonlinear loads occur, the system allocates control tasks between the central control module and distributed nodes as follows: the central control module is responsible for parameter calculation and subsequent calibration, while the distributed nodes are responsible for local sampling, state extraction, degradation judgment, and execution control. With the above settings, the distributed nodes do not need to wait for the central control module to return real-time control quantities every time a power disturbance occurs, but instead use the issued inertia control table to perform local judgment and execution.

[0062] The edge detection unit in each distributed node is connected to the local bus voltage and current sampling channel to continuously collect the instantaneous values ​​of three-phase voltage and three-phase current. The state extraction unit extracts the fundamental amplitude of the local bus voltage, frequency offset, total harmonic distortion rate extracted by the sliding window, and negative sequence current based on the above sampled values, and further calculates the active power change rate, frequency change rate, and real-time state of charge of the local energy storage battery.

[0063] In parallel, the edge control module obtains the one-way communication delay and packet loss rate statistics from the heartbeat packets of the communication link or the interaction records of adjacent nodes, and reads the current grid-connected or islanded physical switch status; after the above parameters are processed locally, the edge control module sends them to the central control module through the communication network, and the central control module forms the current operation record of each node based on this.

[0064] The local judgment unit continuously monitors the statistics of one-way communication delay and packet loss rate with neighboring nodes; when the one-way communication delay is greater than... Or the packet loss rate statistic is greater than When the local judgment unit determines that the communication degradation condition is met, the edge control module stops using the collaborative control data sent by the adjacent nodes and switches the current node to the local autonomous control state. If the communication parameters do not exceed the above threshold, the distributed node continues to maintain the original collaborative interaction mode and sends the local status to the central control module according to the original cycle.

[0065] In the local autonomous control state, if the phase reference transmitted from adjacent nodes is still used, communication delays or packet loss may cause the phase reference to lag, resulting in a phase deviation between inverters. This embodiment further sets up a local phase-locked loop and an internal crystal oscillator in the edge control module. In the normal cooperative interaction state, the edge control module of each distributed node calculates the cooperative voltage and frequency reference quantities based on the adjacency weight matrix containing the communication topology relationship of adjacent nodes, where the off-diagonal elements represent the phase and power weight data transmitted by adjacent nodes. After entering the local autonomous control state, the local judgment unit excludes the off-diagonal weights in the adjacency weight matrix containing the communication topology relationship of adjacent nodes in the local distributed control from the calculation of local control quantities and cuts off the external phase reference input.

[0066] At the same time, the local judgment unit locks the current phase tracking state of the local phase-locked loop and switches to the standard power frequency phase accumulation signal generated by the internal crystal oscillator; this process enables the node to use the local stable phase source during communication degradation, instead of continuing to use potentially lagging data from neighboring nodes.

[0067] After receiving the power quality parameters, transient operating parameters and local communication parameters uploaded by each node, the parameter calculation unit in the central control module generates an inertia control table that includes the correspondence between virtual inertia and frequency change rate, and generates specific harmonic compensation instructions. The inertia control table and specific harmonic compensation instructions are sent to the corresponding edge control module through the communication network, and the edge control module saves them as control data that can be directly called locally.

[0068] After receiving a specific harmonic compensation command, the edge control module extracts the required harmonic order and amplitude through its internal command parsing unit, converts them into a compensation current reference value, and superimposes it onto the input of the space vector pulse width modulation generator to drive the distributed inverter to output an anti-phase harmonic current to cancel the specific harmonic in the microgrid bus.

[0069] If a node fails to receive the new inertia control table in the current distribution cycle, the node can continue to use the saved inertia control table from the previous cycle to ensure that local table lookup control does not stop due to a communication failure; after the next communication cycle resumes, the central control module will re-distribute the updated table data.

[0070] When the rate of change of active power in the local transient operating parameters exceeds the preset power change threshold, the lookup table control unit reads transient operating parameters such as the local frequency change rate and the state of charge of the energy storage battery, and performs matching and interpolation in the local inertia control table to obtain the target virtual inertia. The lookup table control unit generates a voltage phase reference value based on the target virtual inertia, which is transmitted to the edge execution unit, which adjusts the output power of the distributed inverter. If the rate of change of active power does not exceed the preset power change threshold, the lookup table control unit does not trigger the inertia compensation action, and the distributed inverter maintains the current control mode.

[0071] For power quality degradation caused by nonlinear loads, the lookup control unit also reads the locally acquired total harmonic distortion (THD) and negative sequence current; when the THD is greater than... Or the negative sequence current is greater than At this time, the lookup control unit outputs a high-level signal to the edge execution unit, and the edge execution unit drives the physical relay to disconnect the corresponding nonlinear load branch within a preset time.

[0072] The edge execution unit contains an optocoupler isolation circuit and a power amplifier drive circuit, which are used to electrically isolate and boost the low-voltage logic high-level signal from the lookup control unit, and convert it into a control voltage sufficient to drive the physical relay coil.

[0073] If the total harmonic distortion rate and negative sequence current do not exceed the corresponding threshold, the physical relay remains in its original state and does not perform the disconnection action; this process separates the nonlinear load disconnection and inverter inertia control to avoid mutual coupling and delay between the two control actions in terms of timing.

[0074] The frequency calibration unit obtains the actual physical frequency offset based on transient operating parameters and calculates the theoretical frequency deviation based on the target virtual inertia obtained from the lookup control unit. The central control module accumulates the difference between the actual physical frequency offset and the theoretical frequency deviation within the same observation time range to form the cumulative frequency deviation. When the cumulative frequency deviation exceeds the preset tolerance threshold, the frequency calibration unit adjusts the inertia compensation coefficient, and the parameter calculation unit regenerates the inertia control table in the next cycle. If the cumulative frequency deviation does not exceed the preset tolerance threshold, the inertia compensation coefficient remains unchanged, and the inertia control table can continue to be generated according to the original compensation coefficient in the next cycle.

[0075] In the aforementioned microgrid in the park, when extreme weather causes a decline in the quality of communication between nodes, the affected nodes directly enter a local autonomous control state based on local communication latency and packet loss rate, and stop relying on data from neighboring nodes; when changes in photovoltaic or wind power output cause the rate of change in active power to exceed a threshold, the edge control module quickly obtains the target virtual inertia through the inertia control table and adjusts the inverter output; when nonlinear loads cause the total harmonic distortion rate or negative sequence current to exceed a threshold, the physical relay disconnects the corresponding branch; all of the above processes are completed within the same microgrid operation scenario, with the central control module responsible for parameter generation and subsequent correction, and distributed nodes responsible for local execution;

[0076] In this embodiment, the parameter calculation unit generates a nonlinear relationship between virtual inertia and frequency change rate based on the pre-stored system basic inertia constant, inertia compensation coefficient, predicted frequency change rate obtained through transient operating parameters, energy storage available depth, and penalty factor used to limit over-discharge of energy storage battery.

[0077] The parameter calculation unit discretizes the nonlinear correspondence and extracts multiple inflection point coordinates at equal intervals within the frequency change rate range to generate a two-dimensional inertia control table with a row and column structure.

[0078] The edge control module also includes a virtual synchronous generator control model and a space vector pulse width modulation generator. The virtual synchronous generator control model and the space vector pulse width modulation generator are integrated into the microprocessor of the edge control module as control algorithm programs. Logically, they are located between the lookup control unit and the edge execution unit and are used to convert the virtual inertia calculation obtained from the lookup into the underlying pulse width modulation signal.

[0079] The lookup control unit writes the inertia control table to a specified memory address of the controller via direct memory access.

[0080] When matching the inertia control table, the lookup control unit performs linear interpolation based on the locally acquired frequency change rate to obtain the target virtual inertia. Based on the target virtual inertia and the virtual synchronous generator control model, it generates a voltage phase reference value.

[0081] The lookup control unit writes the voltage phase reference value into the register of the space vector pulse width modulation generator to change the duty cycle timing of the switching transistors in the distributed inverter.

[0082] The edge control module records the actual physical frequency change curves before and after the control action and reports them to the central control module;

[0083] The frequency calibration unit calculates the cumulative frequency deviation within the transient observation time window based on the actual physical frequency change curve.

[0084] When the cumulative frequency deviation exceeds the preset tolerance threshold, the frequency calibration unit calculates the compensation correction amount based on the cumulative frequency deviation and adds it to the inertia compensation coefficient to achieve closed-loop calibration of the drift of the underlying physical hardware operating parameters; when the cumulative frequency deviation does not exceed the preset tolerance threshold, the inertia compensation coefficient remains unchanged.

[0085] The sampling rate of the edge detection unit is configured to 5000Hz, the period for the state extraction unit to send parameters is configured to 1s, and the communication period for the parameter calculation unit to send the inertia control table is configured to 1min.

[0086] Based on the system of the embodiment, this implementation further defines the generation, distribution, memory writing, inverter driving, and frequency deviation correction process of the inertia control table. According to the scheme of the embodiment only, the distributed node can perform table lookup control when the active power change rate exceeds the threshold. However, if the inertia control table only uses fixed empirical values, the inertia value in the table may not match the current operating conditions when the state of charge of the energy storage battery decreases or the frequency change rate changes beyond the preset linear threshold range.

[0087] In this implementation, the parameter calculation unit generates a nonlinear relationship between virtual inertia and frequency change rate based on the system's basic inertia constant, inertia compensation coefficient, predicted frequency change rate, available energy storage depth, and penalty factor used to limit excessive discharge of energy storage batteries. This relationship is then converted into a two-dimensional inertia control table that can be directly read by the edge control module.

[0088] The central control module stores the system's basic inertia constant, which is related to the number of currently grid-connected micro-sources and the system configuration. The parameter calculation unit obtains the frequency change rate and the real-time state of charge of the energy storage battery from the transient operating parameters of each node, and uses this to obtain the predicted frequency change rate and energy storage availability depth. The inertia compensation coefficient is used to adjust the virtual inertia increment, and the penalty factor is used to limit the over-discharge of the energy storage battery under low charge conditions. When generating the nonlinear correspondence between virtual inertia and frequency change rate, the parameter calculation unit multiplies the system's basic inertia constant with the inertia compensation coefficient to obtain the reference dynamic inertia.

[0089] Define the trigger boundary of the penalty factor when the available energy storage depth is greater than, for example... When setting the safety threshold, the penalty factor is set to When the available depth of energy storage is less than or equal to When the energy storage depth decreases, the penalty factor decays exponentially. Specifically, the penalty factor is calculated by multiplying the difference between the current energy storage depth and the set safety threshold of 40% by a preset decay response coefficient of 6.93, with the natural constant as the base, so as to quickly reduce the discharge intensity.

[0090] A nonlinear mapping rule for the rate of frequency change is established, using the absolute value of the predicted rate of frequency change as input. When the absolute value of the rate of frequency change is, for example, less than... During the normal fluctuation range, no additional inertia is provided. When the range is exceeded, the inertia gain is calculated by multiplying the square of the excess by the set inertia adjustment constant. This inertia gain is then multiplied by the penalty factor and added to the reference dynamic inertia, thereby forming a nonlinear correspondence between virtual inertia and frequency change rate.

[0091] For example, in a single parameter calculation, the fundamental inertia constant is... The inertia compensation coefficient is The reference dynamic inertia is The predicted frequency change rate at this time is Exceeding the normal fluctuation range The excess part The squared term multiplied by the set inertia adjustment constant Calculations show that an increase is needed. The inertia; and at this time the usable energy storage depth is That is, lower than Triggering a penalty, the penalty factor decays to The actual applied inertia gain is then... Multiply equal Ultimately, the target virtual inertia corresponding to this specific frequency change rate is Add equal ;

[0092] Based on the above calculation rules, the parameter calculation unit extracts multiple inflection point coordinates at equal intervals within the set frequency change rate range; each inflection point coordinate contains a frequency change rate value and its corresponding virtual inertia value, and multiple inflection points are arranged in a row and column structure to form a two-dimensional inertia control table.

[0093] The generated two-dimensional inertia control table is sent from the central control module to the edge control module according to the communication cycle. After receiving the table data, the edge control module's table lookup control unit writes the inertia control table to a designated memory address of the controller via direct memory access, so that subsequent table lookup processes do not require re-parsing of communication messages. If the table data fails verification during the writing process, the table lookup control unit does not overwrite the currently valid table data and continues to retain the inertia control table available in the previous cycle. After receiving the table data again in the next communication cycle, the overwrite is then performed. This process avoids the control table in the controller's memory becoming unusable due to a single table data anomaly.

[0094] The sampling rate of the edge detection unit is configured as follows: The state extraction unit extracts power quality parameters and transient operating parameters based on the sampled data, and uses them as... The parameter calculation unit sends parameters to the central control module periodically; the communication cycle for issuing the inertia control table is configured as follows: This periodic configuration ensures that local sampling and local control maintain a first preset update frequency, while the inertia control table is updated only at a second preset update frequency, reducing the impact of the communication link on real-time control.

[0095] When changes in photovoltaic output or load access within the park's microgrid cause the local active power change rate to exceed a preset power change threshold, the lookup control unit reads the locally collected frequency change rate and searches for its range in the inertia control table written to a specified memory address. If the local frequency change rate falls between two adjacent inflection points, the lookup control unit calculates the target virtual inertia using linear interpolation. If the local frequency change rate is less than the minimum frequency change rate in the table or greater than the maximum frequency change rate in the table, the lookup control unit can use the virtual inertia corresponding to the table endpoint as the current target virtual inertia to avoid interrupting the control process when the range of the table is exceeded.

[0096] The edge control module includes a virtual synchronous generator control model and a space vector pulse width modulation generator. After obtaining the target virtual inertia from the lookup table control unit, the target virtual inertia is substituted into the rotor motion equation of the virtual synchronous generator control model. The model calculates the angular frequency deviation based on the active power reference value, the actual output active power, and the damping term. The specific calculation rule is as follows: first, calculate the difference between the active power reference value and the actual output active power, and subtract the damping power term determined by the product of the damping coefficient and the current angular frequency deviation to obtain the unbalanced power; then, divide the unbalanced power by the target virtual inertia to obtain the rate of change of the angular frequency; the angular frequency deviation is obtained by integrating the rate of change of the angular frequency over time; the lookup table control unit further integrates the angular frequency deviation to generate the voltage phase reference value.

[0097] The lookup control unit writes the voltage phase reference value into the register of the space vector pulse width modulation generator. The space vector pulse width modulation generator changes the duty cycle timing of the distributed inverter's switching transistors, so that the output power of the distributed inverter is adjusted according to the new phase reference value.

[0098] When only lookup table control is performed, if the line impedance, battery internal resistance, or actual inverter response deviates from the original set conditions, the theoretical frequency deviation corresponding to the target virtual inertia may not be consistent with the actual frequency change. In this implementation, the edge control module records the actual physical frequency change curve before and after the control action and reports the curve to the central control module. The frequency calibration unit compares the actual physical frequency change curve with the theoretical frequency deviation within the transient observation time window and calculates the cumulative frequency deviation, that is, the difference between the actual frequency and the theoretical frequency at each sampling point is integrated over time.

[0099] When the cumulative frequency deviation exceeds the preset tolerance threshold, the frequency calibration unit calculates the compensation correction amount based on the cumulative frequency deviation. The specific calculation process is based on the preset proportional-integral control logic, taking the cumulative frequency deviation as the input error amount, multiplying it by the system's preset proportional gain constant, and adding the product of the historical integral terms of the cumulative amount exceeding the limit and the integral gain constant. The result is the compensation correction amount.

[0100] This compensation correction amount is directly added to the inertia compensation coefficient; for example, if the current tolerance threshold is... The actual calculated cumulative frequency deviation is If the tolerance threshold is exceeded, then... Input proportional-integral control logic, assuming the proportional gain is... And when there is no historical integral term, the following occurs: The compensation correction amount, thereby changing the original inertia compensation coefficient from Adjusted to The updated inertia compensation coefficient is used by the parameter calculation unit to generate the inertia control table for the next cycle. If the cumulative frequency deviation does not exceed the preset tolerance threshold, the frequency calibration unit will not change the inertia compensation coefficient to avoid frequent modifications to the inertia control table.

[0101] In a microgrid scenario within the same industrial park, the central control module regenerates the inertia control table every minute based on the most recently uploaded node parameters; the edge control module continuously updates the table based on local parameters between update cycles. The sampling data extracts the frequency change rate, and when the source load changes, it directly reads the table data from the specified memory address to complete the interpolation and inverter drive; after the control action is completed, the edge control module sends the actual physical frequency change curve to the central control module with the next parameter up process, so that the frequency calibration unit can calculate whether the inertia compensation coefficient needs to be corrected in the next cycle.

[0102] like Figure 2 As shown, the microgrid method based on distributed control, applicable to the microgrid system based on distributed control in the embodiment, includes the following steps:

[0103] Step 1: Initial system configuration: Configure the sampling period of the edge detection unit and the communication degradation conditions of the local judgment unit;

[0104] Step 2, Local Status Acquisition: The edge detection unit acquires the instantaneous values ​​of the three-phase voltage and current of the local bus; the status extraction unit extracts the local power quality parameters, transient operating parameters, and local communication parameters accordingly.

[0105] Step 3, Degradation Condition Judgment: When the local communication parameters meet the preset communication degradation conditions, the local judgment unit interrupts the collaborative interaction and switches to the local autonomous control state.

[0106] Step 4: Global parameter calculation: The central control module gathers the parameters of each node, generates an inertia control table containing the relationship between virtual inertia and frequency change rate, and sends specific subharmonic compensation commands to the edge control module.

[0107] Step 5, Lookup Control Execution: When the active power change rate exceeds the preset power change threshold, the lookup control unit calculates the target virtual inertia based on the transient operating parameters in the inertia control table, generates the voltage phase reference value, and drives the edge execution unit to adjust the output of the distributed inverter.

[0108] Step 6, Parameter Feedback Update: The frequency calibration unit calculates the cumulative frequency deviation based on the transient operating parameters and the target virtual inertia. When the deviation exceeds the preset tolerance threshold, the preset inertia compensation coefficient is adjusted to update the inertia control table for the next cycle.

[0109] This implementation describes the method execution process of the above system in a park microgrid. The method runs in the order of initial configuration, local data acquisition, degradation judgment, parameter calculation, table lookup execution, and parameter update. The results are transmitted between each step through local status records, inertia control tables, and frequency change records. The central control module is not required to participate in real-time calculations when each transient disturbance occurs.

[0110] In step one, the initial system configuration includes configuring the sampling period of the edge detection unit and configuring the communication degradation conditions of the local judgment unit. The sampling period is used to determine the frequency at which the edge detection unit collects the instantaneous values ​​of the three-phase voltage and the instantaneous values ​​of the three-phase current. The communication degradation conditions are used to determine whether a node needs to stop its collaborative interaction with neighboring nodes. After the configuration is completed, the sampling period is written into the sampling control parameters of the edge detection unit, and the communication degradation conditions are written into the judgment parameters that the local judgment unit can read.

[0111] In step two, the edge detection unit collects the instantaneous values ​​of the three-phase voltage and three-phase current of the local bus in real time according to the configured sampling period; the state extraction unit extracts power quality parameters and transient operating parameters based on the above sampled values, and simultaneously obtains local communication parameters; the power quality parameters include the fundamental amplitude of the local bus voltage, frequency offset, total harmonic distortion rate, and negative sequence current; the transient operating parameters include the rate of change of active power, the rate of change of frequency, and the real-time state of charge of the local energy storage battery; the local communication parameters include the one-way communication delay with adjacent nodes, packet loss rate statistics, and the current grid-connected or islanded physical switch status; the extracted parameters are stored in the local state record of the edge control module and uploaded to the central control module according to the sending period;

[0112] In step three, the local judgment unit reads the communication parameters in the local state record and compares them with the preset communication degradation conditions. When the communication degradation conditions are met, the local judgment unit interrupts the collaborative interaction with neighboring nodes and switches to the local autonomous control state. If the communication degradation conditions are not met, the distributed nodes continue to perform collaborative interaction with neighboring nodes. If the communication parameters fail to form a valid statistical value within a certain sampling period, the local judgment unit can retain the previous valid judgment result and re-judge after obtaining valid communication parameters in the next statistical period to avoid frequent state switching caused by missing data in a single period.

[0113] In step four, the central control module aggregates the parameters uploaded by each node; the parameter calculation unit calculates the correspondence between virtual inertia and frequency change rate based on the transient operating parameters of each node, and generates an inertia control table; at the same time, it generates specific harmonic compensation instructions based on power quality parameters; the inertia control table and specific harmonic compensation instructions are sent to the edge control module through the communication network; after receiving them, the edge control module saves the table data to the local controller memory for subsequent table lookup control execution; if a node does not receive new table data in the current cycle, the node continues to use the inertia control table of the previous valid cycle;

[0114] In step five, the lookup control unit reads the active power change rate from the transient operating parameters. When the active power change rate exceeds the preset power change threshold, the lookup control unit interpolates the value in the inertia control table based on transient operating parameters such as the local frequency change rate to obtain the target virtual inertia. The lookup control unit generates a voltage phase reference value based on the target virtual inertia and transmits the voltage phase reference value to the edge execution unit, which adjusts the output power of the distributed inverter. If the active power change rate does not exceed the preset power change threshold, the lookup control action is not executed. For cases where the total harmonic distortion rate or negative sequence current exceeds the corresponding threshold, the edge control module drives the physical relay to disconnect the corresponding nonlinear load branch according to the issued compensation command and the local threshold judgment result.

[0115] In step six, the edge control module reports the actual physical frequency changes before and after the control action to the central control module; the frequency calibration unit obtains the actual physical frequency offset based on the transient operating parameters and calculates the theoretical frequency deviation based on the target virtual inertia obtained in step five; the frequency calibration unit calculates the cumulative frequency deviation between the two; when the cumulative frequency deviation exceeds the preset tolerance threshold, the frequency calibration unit adjusts the inertia compensation coefficient, and the parameter calculation unit updates the inertia control table in the next cycle; when the cumulative frequency deviation does not exceed the preset tolerance threshold, the inertia compensation coefficient remains unchanged, and the system enters the next cycle with the original parameters;

[0116] During the operation of the above method, the central control module in the same park microgrid is only responsible for aggregating parameters, generating inertia control tables, and making subsequent parameter corrections. When communication deteriorates or the rate of change of active power exceeds the threshold, each distributed node completes the judgment and execution based on the local status record and the local inertia control table. This method enables the sampling, judgment, table lookup and execution processes to run continuously locally on the distributed nodes, and enables the table update results of the central control module to continue to affect each node in the next cycle.

[0117] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A microgrid system based on distributed control, characterized in that, It includes a central control module and multiple distributed nodes interconnected by communication. Each node contains an edge control module with an edge detection unit, an edge execution unit, a state extraction unit, a local judgment unit, and a table lookup control unit, as well as a distributed inverter and physical relays. The edge execution unit is connected to the distributed inverter and the physical relay, and shares the edge control module with the edge detection unit. The edge control module is communicatively connected to the central control module, which includes a parameter calculation unit and a frequency calibration unit. The edge detection unit collects the instantaneous values ​​of the three-phase voltage and current of the local bus; the state extraction unit extracts the local power quality parameters, transient operating parameters and local communication parameters based on these and sends them to the central control module. The local judgment unit switches to the local autonomous control state when the local communication parameters meet the preset communication degradation conditions. The parameter calculation unit generates an inertia control table containing the correspondence between virtual inertia and frequency change rate and a specific subharmonic compensation instruction based on the node parameters, and sends it to the edge control module. When the active power change rate exceeds the preset power change threshold, the table lookup control unit calculates the target virtual inertia based on the transient operating parameters in the inertia control table, generates a voltage phase reference value, and drives the edge execution unit to adjust the output of the distributed inverter. The frequency calibration unit calculates the cumulative frequency deviation based on transient operating parameters and target virtual inertia. When the deviation exceeds a preset tolerance threshold, it adjusts the preset inertia compensation coefficient to update the inertia control table for the next cycle. The system controls the distributed inverters and physical relays to maintain operation when the communication degradation conditions or the active power change rate exceeds the limit.

2. The microgrid system based on distributed control according to claim 1, characterized in that, The edge control module also includes a local phase-locked loop and an internal crystal oscillator. After switching to the local autonomous control state, the local judgment unit excludes the off-diagonal weights in the adjacency weight matrix containing the communication topology relationship between adjacent nodes in the local distributed control from the calculation of local control quantities, and cuts off the external phase reference input. The local judgment unit is also used to lock the phase tracking state of the local phase-locked loop and switch to the standard power frequency phase accumulation signal generated by the internal crystal oscillator to avoid reactive circulating current caused by phase difference deviation due to receiving expired communication data.

3. The microgrid system based on distributed control according to claim 1, characterized in that, The power quality parameters include the fundamental amplitude of the local bus voltage, frequency offset, total harmonic distortion rate extracted through a sliding window, and negative sequence current. The transient operating parameters include the rate of change of active power, the rate of change of frequency, and the real-time state of charge of the local energy storage battery. The local communication parameters include one-way communication delay with neighboring nodes, packet loss rate statistics, and the current physical switch status of grid connection or islanding; the packet loss rate statistics refer to the percentage ratio of the number of cooperative control data packets that a node failed to receive to the total number of data packets expected to be received within a preset sliding time observation window.

4. The microgrid system based on distributed control according to claim 3, characterized in that, The physical relay is connected in series in the nonlinear load branch of the microgrid; when the one-way communication delay is greater than 200ms or the packet loss rate is greater than 40%, the local judgment unit determines that the preset communication degradation condition is met. When the total harmonic distortion rate (THD) collected locally is greater than 15% or the negative sequence current is greater than 20%, the lookup table control unit outputs a high-level signal to drive the physical relay to disconnect the corresponding nonlinear load branch within a preset time. If neither the THD nor the negative sequence current exceeds the corresponding threshold, the physical relay remains in its original state.

5. The microgrid system based on distributed control according to claim 1, characterized in that, The parameter calculation unit generates a nonlinear relationship between the virtual inertia and the frequency change rate based on the pre-stored system basic inertia constant, the inertia compensation coefficient, the predicted frequency change rate obtained through the transient operating parameters, the available energy storage depth, and the penalty factor used to limit the over-discharge of the energy storage battery. The parameter calculation unit discretizes the nonlinear correspondence and extracts multiple inflection point coordinates at equal intervals within the frequency change rate range to generate a two-dimensional inertia control table with a row and column structure.

6. The microgrid system based on distributed control according to claim 1, characterized in that, The edge control module also includes a virtual synchronous generator control model and a space vector pulse width modulation generator. The virtual synchronous generator control model and the space vector pulse width modulation generator are integrated into the microprocessor of the edge control module as control algorithm programs. Logically, they are located between the lookup control unit and the edge execution unit, and are used to convert the virtual inertia calculation obtained from the lookup into the underlying pulse width modulation signal. The lookup control unit writes the inertia control table to a specified memory address of the controller via direct memory access. When matching the inertia control table, the table lookup control unit performs linear interpolation based on the locally collected frequency change rate to obtain the target virtual inertia, and generates the voltage phase reference value based on the target virtual inertia and the virtual synchronous generator control model. The lookup control unit writes the voltage phase reference value into the register of the space vector pulse width modulation generator to change the duty cycle timing of the switching transistors of the distributed inverter.

7. The microgrid system based on distributed control according to claim 1, characterized in that, The edge control module records the actual physical frequency change curves before and after the control action and reports them to the central control module. The frequency calibration unit calculates the cumulative frequency deviation within the transient observation time window based on the actual physical frequency change curve. When the cumulative frequency deviation exceeds a preset tolerance threshold, the frequency calibration unit calculates a compensation correction amount based on the cumulative frequency deviation and adds it to the inertia compensation coefficient to achieve closed-loop calibration of the drift of the underlying physical hardware operating parameters. When the cumulative frequency deviation does not exceed the preset tolerance threshold, the inertia compensation coefficient remains unchanged.

8. The microgrid system based on distributed control according to claim 1, characterized in that, The sampling rate of the edge detection unit is configured to be 5000Hz, the period for the state extraction unit to send parameters is configured to be 1s, and the communication period for the parameter calculation unit to send the inertia control table is configured to be 1min.

9. A microgrid method based on distributed control, applicable to the microgrid system based on distributed control as described in any one of claims 1 to 8, characterized in that, Includes the following steps: Step 1: Initial system configuration: Configure the sampling period of the edge detection unit and the communication degradation conditions of the local judgment unit; Step 2, Local Status Acquisition: The edge detection unit acquires the instantaneous values ​​of the three-phase voltage and current of the local bus; the status extraction unit extracts the local power quality parameters, transient operating parameters, and local communication parameters accordingly. Step 3, Degradation Condition Judgment: When the local communication parameters meet the preset communication degradation conditions, the local judgment unit interrupts the collaborative interaction and switches to the local autonomous control state. Step 4: Global parameter calculation: The central control module gathers the parameters of each node, generates an inertia control table containing the relationship between virtual inertia and frequency change rate, and sends specific subharmonic compensation commands to the edge control module. Step 5, Lookup Control Execution: When the active power change rate exceeds the preset power change threshold, the lookup control unit calculates the target virtual inertia based on the transient operating parameters in the inertia control table, generates the voltage phase reference value, and drives the edge execution unit to adjust the output of the distributed inverter. Step 6, Parameter Feedback Update: The frequency calibration unit calculates the cumulative frequency deviation based on the transient operating parameters and the target virtual inertia. When the deviation exceeds the preset tolerance threshold, the preset inertia compensation coefficient is adjusted to update the inertia control table for the next cycle.

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