A coordinated control method for AC / DC hybrid microgrid suitable for new energy access

Abstract

The application relates to a coordination control method for AC / DC hybrid micro-grid suitable for new energy access, and belongs to the technical field of wind power generation systems, and comprises the following steps: S1, constructing an AC / DC hybrid micro-grid topology structure comprising a wind power generation unit, a photovoltaic power generation unit, a hybrid energy storage unit and AC / DC loads; S2, adopting a hierarchical coordination control architecture; S3, according to real-time output prediction data of the wind power generation unit and the photovoltaic power generation unit and real-time demand data of the AC / DC loads; S4, adopting a dynamic droop control method to perform charging and discharging power distribution on the hybrid energy storage unit; S5, performing power mutual aid between subnets through a bidirectional AC / DC interconnection converter; and S6, monitoring the state of charge of the hybrid energy storage unit in real time, and realizing SOC equalization control between energy storage units. The coordination control method for the AC / DC hybrid micro-grid suitable for new energy access realizes the coordinated control of the AC / DC hybrid micro-grid in multiple time scales through the construction of the hierarchical coordination control architecture.

Description

Technical Field

[0001] This invention relates to the field of wind power generation system technology, specifically to a coordinated control method for AC / DC hybrid microgrids suitable for new energy access. Background Technology

[0002] With the escalating global energy crisis and increasingly prominent environmental issues, renewable energy sources, represented by wind and solar power, have been widely developed and utilized. However, renewable energy power generation is intermittent and volatile, and large-scale grid connection poses a severe challenge to the safe and stable operation of the power system. Microgrid technology, as a key solution for the efficient integration of distributed energy resources, has received widespread attention and research in recent years. Compared with single AC or DC microgrids, hybrid AC / DC microgrids combine the advantages of both. They can easily connect AC distributed power sources and AC loads, and efficiently connect DC distributed power sources and DC loads. At the same time, through interconnection converters, energy exchange between the two subgrids is achieved, significantly improving the absorption capacity of new energy sources and the operational flexibility of the system.

[0003] Currently, control methods for AC / DC hybrid microgrids are mainly divided into two categories: centralized control and distributed control. Centralized control relies on a central controller to collect global information and make unified decisions, but it suffers from problems such as single-point failure risk, heavy communication burden, and insufficient dynamic response speed. Distributed control achieves collaborative decision-making through local communication between adjacent units, reducing communication dependence and system costs. However, in scenarios with a high proportion of renewable energy integration, traditional distributed control methods often struggle to balance dynamic response speed and steady-state accuracy.

[0004] For the coordinated control of energy storage systems, existing technologies mainly employ control schemes using single-battery energy storage. However, batteries experience severe lifespan degradation under frequent charge-discharge conditions and exhibit slow response to high-frequency power fluctuations. Some technologies attempt to introduce supercapacitors and batteries to form hybrid energy storage, but their power allocation strategies often employ fixed frequency division filtering schemes, failing to dynamically adjust the power allocation ratio based on the state of charge of the energy storage units. This affects the overall efficiency of hybrid energy storage and the long-term economic viability of the system.

[0005] In terms of coordinated control between AC and DC subgrids, traditional methods often employ a strategy that combines per-unit processing with droop control. Power mutual assistance is achieved by comparing the per-unit values ​​of voltage / frequency on both AC and DC sides. However, this method lacks effective coupling of the dynamic characteristics of the two subgrids. When there are sudden load changes or drastic fluctuations in renewable energy output, the response speed and control accuracy of power mutual assistance are difficult to meet the power quality requirements of modern microgrids.

[0006] Therefore, there is an urgent need to propose a coordinated control method that can balance dynamic response speed and steady-state control accuracy, achieve efficient collaboration of hybrid energy storage, and enable adaptive power mutual assistance between AC and DC subgrids, so as to effectively address the technical challenges brought about by the high proportion of new energy access. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a coordinated control method for AC / DC hybrid microgrids suitable for new energy access. It has advantages such as dynamic coordination, adaptive mutual assistance, SOC balancing, and seamless switching, and solves the problems of unreasonable energy storage allocation, slow power mutual assistance response, SOC imbalance, and switching impact in existing technologies.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A coordinated control method for AC / DC hybrid microgrids suitable for new energy access includes the following steps:

[0010] S1. Construct an AC / DC hybrid microgrid topology that includes wind power generation units, photovoltaic power generation units, hybrid energy storage units, and AC / DC loads, wherein the AC / DC hybrid microgrid includes an AC subgrid and a DC subgrid, and the AC subgrid is interconnected with the DC subgrid through a bidirectional AC / DC interconnection converter;

[0011] S2. A hierarchical coordination control architecture is adopted, including an equipment control layer, a coordination control layer, and an energy management layer. The equipment control layer performs local control of wind power generation units, photovoltaic power generation units, hybrid energy storage units, and interconnected converters. The coordination control layer collects the operating status information of each sub-network and performs power coordination allocation. The energy management layer formulates an energy dispatch plan based on the overall system operating data.

[0012] S3. Based on the real-time output prediction data of the wind power generation unit and the photovoltaic power generation unit, as well as the real-time demand data of the AC and DC loads, the power balance status of the system is determined by the coordination control layer, and power reference commands for each unit are generated.

[0013] S4. Based on the state of charge (SOC) and power response characteristics of the hybrid energy storage unit, a dynamic droop control method is used to allocate the charging and discharging power of the hybrid energy storage unit, wherein the supercapacitor responds to the high-frequency component of the power fluctuation, and the battery responds to the low-frequency component of the power fluctuation.

[0014] S5. When there is a power imbalance between the AC subnet and the DC subnet, the power mutual assistance between the subnets is performed through the bidirectional AC / DC interconnection converter. The interconnection converter adopts a virtual synchronous machine control strategy to convert the voltage deviation of the DC subnet into the frequency deviation of the AC subnet and participate in frequency regulation.

[0015] S6. Real-time monitoring of the state of charge (SOC) of the hybrid energy storage units. When the SOC of any group of energy storage units exceeds the preset safety threshold range, the charging and discharging droop coefficient of the energy storage unit is adjusted through the coordination control layer to achieve SOC balance control among the energy storage units.

[0016] Furthermore, the specific implementation of the dynamic droop control method in step S4 is as follows:

[0017] S41. The power command of the hybrid energy storage unit is decomposed by high-pass filtering and low-pass filtering to obtain high-frequency power components and low-frequency power components. The cutoff frequency of the high-pass filter is dynamically adjusted according to the capacity configuration and power response speed of the supercapacitor.

[0018] S42. Distribute the high-frequency power component to the supercapacitor for response, and distribute the low-frequency power component to the battery for response.

[0019] S43. Based on the real-time state of charge of the supercapacitor and the battery, dynamically adjust the droop coefficient of each energy storage unit. The functional relationship between the droop coefficient and the state of charge is as follows: ; Where, k droop k is the adjusted droop coefficient. base The base droop factor is α, the adjustment factor is SOC, and the real-time state of charge is SOC. ref For reference state of charge.

[0020] Furthermore, the virtual synchronizer control strategy in step S5 includes: S51. Simulate the rotor motion equations of a synchronous generator and establish the mechanical power-frequency regulation characteristics of a virtual synchronous machine: ; Where J is the virtual moment of inertia, ω is the virtual angular frequency, and P m For virtual mechanical power, P e Where ω is the virtual electromagnetic power, D is the damping coefficient, and ω0 is the rated angular frequency; S52. Introduce a DC bus voltage-AC frequency coupling function to map the DC side voltage deviation to the AC side frequency deviation. The expression for the coupling function is: ; Where Δf is the AC frequency deviation, K v2f U is the voltage-frequency coupling coefficient. dc U is the measured value of the DC bus voltage. dc_ref This is the reference value for the DC bus voltage; S53. Based on the AC frequency deviation obtained from the mapping, the active power output of the interconnected converter is adjusted through the virtual synchronous machine control loop to achieve power mutual assistance and frequency support between AC and DC sub-networks.

[0021] Furthermore, the specific implementation method of the SOC equalization control among energy storage units in step S6 is as follows: S61. Real-time collection of state of charge data of each hybrid energy storage unit through the coordination control layer; S62. Calculate the average value and deviation of the state of charge of each energy storage unit. When the state of charge deviation of any energy storage unit exceeds the preset threshold, trigger the SOC equalization control. S63. Adjust the droop coefficient of the corresponding energy storage unit according to the magnitude of the state of charge deviation. Increase the droop coefficient of the energy storage unit with a lower state of charge to increase the charging power, and decrease the droop coefficient of the energy storage unit with a higher state of charge to reduce the charging power or switch to the discharge mode. S64. Set a dead zone for SOC equalization control. When the SOC deviation is less than the dead zone threshold, maintain the current droop coefficient unchanged.

[0022] Furthermore, the method also includes S7: when the output fluctuation of the wind power generation unit or the photovoltaic power generation unit exceeds a preset power fluctuation threshold, the coordination control layer initiates a fast power response mode, including: S71. Prioritize the use of supercapacitors to respond to instantaneous power fluctuations, with a response time of less than 50 milliseconds; S72. When the power fluctuation lasts for more than the preset time threshold or the supercapacitor's state of charge exceeds the safe range, gradually connect the battery to provide power support. S73. During periods of sustained power fluctuations, the energy management layer optimizes and adjusts the reference values ​​of the output power of the wind power generation unit and the photovoltaic power generation unit to achieve dynamic balance of system power.

[0023] Furthermore, the specific method for determining the power balance state in step S3 is as follows: S31. Compare the real-time operating data obtained by the coordination and control layer with the power prediction data issued by the energy management layer to calculate the power deficit or power surplus. S32. When the power deficit is greater than zero, the system is judged to be in a power deficit state, and the hybrid energy storage unit is controlled to discharge or the AC and DC loads are reduced to meet the power balance. S33. When the power surplus is greater than zero, it is determined that the system is in a power surplus state, and the hybrid energy storage unit is charged or the AC / DC load is increased to absorb the surplus power. S34. When both the power deficit and power surplus are less than the preset dead zone threshold, the system maintains its current operating state.

[0024] Furthermore, the method also includes S8: when the AC / DC hybrid microgrid is operating in islanded mode, a multi-mode seamless switching control strategy is adopted, including: S81. Real-time detection of voltage and frequency at the point of common coupling (PCC) to determine the connection status with the main power grid; S82. When a power grid failure is detected, the bidirectional AC / DC interconnection converter is controlled to switch from grid-connected mode to islanded mode. During the switching process, pre-synchronization control is used to eliminate phase difference and amplitude difference. S83. In islanded mode, the AC subgrid uses frequency-active power droop control as the primary regulation method, and the DC subgrid uses voltage-active power droop control as the primary regulation method. The coordination control layer acts as the secondary regulation center to correct the droop reference value of each unit. Step S84: When the main grid is detected to have resumed power supply, the frequency and phase of the microgrid are synchronized with the main grid through pre-synchronization control, and then the microgrid is switched back to grid-connected mode.

[0025] Furthermore, the method also includes S9: when the deviation between the predicted output and the real-time output of the wind power generation unit or photovoltaic power generation unit exceeds a preset prediction error threshold, a rolling optimization correction mechanism is initiated, specifically including: S91. The coordination control layer re-collects real-time output data and load data of each unit at preset time intervals. S92. Compare the newly collected data with the energy management system's scheduling plan and calculate the prediction error; S93. Based on the magnitude of the prediction error, the power allocation command is rolled over and corrected using the model predictive control algorithm, and the power reference value of each unit is updated.

[0026] Furthermore, the wind power generation unit adopts a permanent magnet synchronous wind turbine, which is connected to the AC subgrid or DC subgrid through an AC / DC rectifier and a DC / AC inverter. The maximum power point tracking control of the wind power generation unit adopts an improved hill climbing search algorithm, which dynamically adjusts the search step size according to the wind speed change rate.

[0027] Furthermore, the hybrid energy storage unit includes a supercapacitor energy storage module and a battery energy storage module. The supercapacitor energy storage module is connected to the DC bus through a bidirectional DC / DC converter, and the battery energy storage module is connected to the DC bus through another set of bidirectional DC / DC converters. The coordinated control of the AC / DC hybrid microgrid is achieved through information interaction between the central coordinating controller and each local controller. The central coordinating controller and each local controller communicate through industrial Ethernet, and the communication protocol adopts the Modbus TCP / IP or IEC 61850 standard.

[0028] Compared with existing technologies, this invention provides a coordinated control method for AC / DC hybrid microgrids suitable for new energy access, which has the following advantages: 1. This coordinated control method for AC / DC hybrid microgrids with new energy access achieves coordinated control of AC / DC hybrid microgrids across multiple time scales by constructing a hierarchical coordinated control architecture (equipment control layer, coordinated control layer, and energy management layer). The equipment control layer is responsible for millisecond-level local rapid response, the coordinated control layer is responsible for power coordination and allocation from second to minute level, and the energy management layer is responsible for energy scheduling optimization from minute to hour level. An effective collaborative mechanism is formed among the three layers, which not only ensures the system's rapid response capability to instantaneous disturbances but also achieves economic optimization for long-term system operation.

[0029] 2. This coordinated control method for AC / DC hybrid microgrids applicable to new energy access adopts a power frequency division and allocation strategy based on dynamic adjustment of state of charge. It allocates high-frequency power fluctuations to the supercapacitor response and low-frequency power fluctuations to the battery response, and dynamically corrects the droop coefficient according to the real-time state of charge of the energy storage unit. This strategy fully leverages the advantages of supercapacitors, such as fast response speed and long cycle life, effectively reduces the capacity decay of batteries under frequent charge and discharge conditions, extends the service life of batteries, and ensures the power response capability of the hybrid energy storage system under different states of charge.

[0030] 3. This coordinated control method for AC / DC hybrid microgrids applicable to new energy access introduces a virtual synchronous machine control strategy and designs a voltage-frequency coupling function in the bidirectional AC / DC interconnected converter. This maps the voltage deviation of the DC subgrid to the frequency deviation of the AC subgrid, which participates in frequency regulation. This strategy enables the interconnected converter to have inertial and damping characteristics similar to a synchronous generator, enhances the dynamic coupling between the AC and DC subgrids, and enables adaptive power mutual assistance between the two subgrids when the system experiences power fluctuations. This effectively improves the dynamic stability and anti-disturbance capability of the system.

[0031] 4. This coordinated control method for AC / DC hybrid microgrids applicable to new energy access achieves automatic state of charge balancing by dynamically adjusting the droop coefficient of each energy storage unit. This mechanism avoids the problem of some energy storage units being overcharged or over-discharged while other units have idle capacity, improves the overall utilization efficiency of the hybrid energy storage system, extends the overall service life of the energy storage system, and simplifies the management complexity of the energy storage system.

[0032] 5. This coordinated control method for AC / DC hybrid microgrids applicable to new energy access designs employs a seamless switching control strategy in both grid-connected and off-grid modes. During the switching process, pre-synchronization control eliminates phase and amplitude differences, avoiding current surges and voltage sags common in traditional switching methods. This strategy ensures a smooth transition between grid-connected and islanded modes, improving the power supply reliability for sensitive loads. Detailed Implementation

[0033] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] I. System Topology: This embodiment provides a coordinated control method for AC / DC hybrid microgrids suitable for new energy access. The applicable AC / DC hybrid microgrid system includes an AC subgrid and a DC subgrid, which are connected via a bidirectional AC / DC interconnect converter. The AC subgrid includes an AC bus, on which wind power generation units (accessed via AC / DC rectifiers and DC / AC inverters), photovoltaic power generation units (accessed via DC / AC inverters), battery energy storage units (accessed via bidirectional AC / DC converters), and AC loads are connected. The DC subgrid includes a DC bus, on which photovoltaic power generation units (accessed via DC / DC converters), supercapacitor energy storage units (accessed via bidirectional DC / DC converters), battery energy storage units (accessed via bidirectional DC / DC converters), and DC loads are connected. The wind power generation units use permanent magnet synchronous wind turbines. The AC output is converted to DC by an AC / DC rectifier, and then converted back to AC by a DC / AC inverter before being connected to the AC subgrid, or directly connected to the DC subgrid via a DC / DC converter.

[0035] In this embodiment, the AC / DC hybrid microgrid is connected to the main grid through the point of common coupling (PCC), enabling it to operate in both grid-connected and islanded modes.

[0036] II. Hierarchical Coordination and Control Architecture: This embodiment adopts a hierarchical coordination control architecture, which includes three layers: the equipment control layer, the coordination control layer, and the energy management layer.

[0037] (1) Equipment control layer The equipment control layer, located at the bottom layer, is responsible for the local control of each distributed power source, energy storage unit, and interconnect converter. Specifically, it includes: Control of the wind power generation unit: A maximum power point tracking (MPPT) control strategy is adopted. The speed of the wind turbine is regulated by controlling the duty cycle of the AC / DC rectifier, ensuring that the wind turbine always operates at its maximum power output point under different wind speed conditions. This embodiment employs an improved hill-climbing search algorithm, which dynamically adjusts the search step size based on the wind speed change rate: when the wind speed change rate is greater than a preset threshold, a large step size is used to quickly track the maximum power point; when the wind speed change rate is less than the preset threshold, a small step size is used to reduce output power fluctuations and improve steady-state accuracy.

[0038] Photovoltaic power generation unit control: An MPPT control strategy is employed, controlling the duty cycle of the DC / DC converter or DC / AC inverter to ensure the photovoltaic array operates at its maximum power point. In grid-connected mode, the photovoltaic power generation unit can also receive power dispatch commands from the coordination control layer for power limiting control.

[0039] Control of the hybrid energy storage unit includes the control of the supercapacitor energy storage module and the battery energy storage module. The supercapacitor energy storage module is connected to the DC bus through a bidirectional DC / DC converter, and the battery energy storage module is connected to the DC bus through another set of bidirectional DC / DC converters. Both adopt a dual closed-loop control structure (voltage outer loop, current inner loop) to achieve precise control of charging and discharging power.

[0040] Control of bidirectional AC / DC interconnection converter: A virtual synchronous machine control strategy is adopted to enable the interconnection converter to have inertia and damping characteristics similar to a synchronous generator, so as to realize power mutual assistance between AC and DC sub-networks.

[0041] (2) Coordination and control layer The coordination and control layer is located in the middle layer and is responsible for collecting the operating status information of each subnet (including AC bus voltage and frequency, DC bus voltage, power of each branch, state of charge of each energy storage unit, etc.), and generating power reference commands for each unit according to the power balance status of the system, and sending them to the equipment control layer for execution.

[0042] The main functions of the coordination and control layer include: (a) Power balance judgment and power allocation: Based on the real-time output data of wind power generation and photovoltaic power generation and the real-time demand data of AC and DC loads, calculate the power deficit or power surplus of the system, and formulate the power allocation scheme for each unit accordingly. (b) Hybrid energy storage power distribution control: Based on the frequency characteristics of power fluctuations and the state of charge of each energy storage unit, the power command is decomposed into high-frequency components and low-frequency components, which are then distributed to the supercapacitor and the battery, respectively. (c) Power balance control between subnets: When there is a power imbalance between the AC subnet and the DC subnet, power balance between subnets is performed through a bidirectional AC / DC interconnection converter; (d) SOC equalization control: Real-time monitoring of the state of charge of each energy storage unit. When the state of charge deviation exceeds the threshold, the droop coefficient is dynamically adjusted to achieve SOC equalization.

[0043] (3) Energy Management System The energy management layer, located at the top level, is responsible for formulating the overall energy dispatch plan for the system (typically on a timescale of 15 minutes to 1 hour) based on ultra-short-term forecast data for wind and solar power generation, load forecast data, and the operating status of the main power grid. This dispatch plan is then distributed to the coordination and control layer as a reference for power allocation. The energy management layer is also responsible for information exchange with the power dispatch center and participating in demand response and ancillary services in the electricity market.

[0044] III. Dynamic droop control of hybrid energy storage: In this embodiment, the power distribution of the hybrid energy storage unit adopts a droop control method based on dynamic adjustment of state of charge. The specific implementation steps are as follows: Step 1: Power fluctuation frequency division processing The coordination control layer sets the cutoff frequency f of the high-pass filter based on the power fluctuation characteristics of the system. c The cutoff frequency is dynamically adjusted based on the supercapacitor's capacity configuration and power response speed, and its value typically ranges from 0.1 Hz to 1 Hz.

[0045] The coordination control layer calculates the instantaneous power imbalance ΔP(t) of the system, and processes it through a high-pass filter and a low-pass filter respectively to obtain the high-frequency power component ΔP. H (t) and low-frequency power component ΔP L (t), satisfying: ; Among them, the high-frequency power component ΔP H (t) is allocated to the supercapacitor for response, low-frequency power component ΔP L (t) is allocated to the battery for response.

[0046] Step 2: Dynamic adjustment of droop coefficient based on state of charge In this embodiment, the droop coefficients of the supercapacitor and the battery are dynamically adjusted based on their respective real-time state of charge. The droop coefficient adjustment function is as follows: ; ; Where, k droop_SC and k droop_BAT These are the adjusted droop coefficients for the supercapacitor and the battery, respectively, k. base_SC and k base_BAT Based on the droop coefficient, α SC and αBAT The adjustment factor (typically ranging from 0.1 to 0.5) is used for SOC. SC and SOC BAT For real-time state of charge, SOC ref_SC and SOC ref_BAT This is used as a reference state of charge (usually set to 0.5~0.6).

[0047] Step 3: Generation of charge / discharge power commands Calculate the power commands for the supercapacitor and battery based on the adjusted droop factor: ; ; in, This is the power command for the supercapacitor. This is the power command for the battery. A positive power command indicates discharging, and a negative power command indicates charging.

[0048] IV. Virtual Synchronous Machine Control of Interconnect Converters: In this embodiment, the bidirectional AC / DC interconnect converter adopts a virtual synchronous machine control strategy, enabling the interconnect converter to possess inertial and damping characteristics similar to a synchronous generator. The specific implementation steps are as follows: Step 1: Establishment of the Mathematical Model of the Virtual Synchronizer Establish the rotor motion equations and electromagnetic equations of the virtual synchronous machine.

[0049] The rotor motion equations are as follows: ; Where J is the virtual moment of inertia (typically ranging from 0.1 to 10 kg·m²), ω is the virtual angular frequency (rad / s), and P... m For virtual mechanical power (W), P e Let ω0 be the virtual electromagnetic power (W), D be the damping coefficient, and ω0 be the rated angular frequency (314.159 rad / s).

[0050] The electromagnetic equations are as follows: ; Where E is the virtual internal potential, U is the AC output voltage of the interconnect converter, X is the virtual reactance, and I is the output current.

[0051] Step 2: Design of voltage-frequency coupling function A DC bus voltage-AC frequency coupling function is introduced to map the DC-side voltage deviation to the AC-side frequency deviation. The expression for the coupling function is: ; Where Δf is the AC frequency deviation (Hz), Kv2f U is the voltage-frequency coupling coefficient (typically ranging from 0.5 to 5 Hz / kV). dc U represents the measured value of the DC bus voltage (V). dc_ref This is the reference value (V) for the DC bus voltage.

[0052] The design principle of the coupling function is that when the DC bus voltage drops due to power deficit in the DC subgrid, U dc dc_ref When Δf < 0, this negative frequency deviation causes the interconnect converter to increase the active power delivered from the AC subnet to the DC subnet through the virtual synchronous machine control loop; conversely, when the DC subnet has a power surplus that causes the DC bus voltage to rise, the interconnect converter increases the active power delivered from the DC subnet to the AC subnet. This achieves adaptive power balance between the AC and DC subnets.

[0053] Step 3: Power Control Loop Design

[0054] The mapped AC frequency deviation Δf is superimposed on the actual AC frequency fac to obtain the reference frequency f of the virtual synchronizer. ref : ; f ref The virtual synchronous machine control loop is input, and it adjusts the active power output of the interconnect converter according to the frequency deviation. The mathematical relationship for power adjustment is as follows: ; in, For the active power command of the interconnect converter, K p and K i These are the proportional coefficient and integral coefficient, respectively, and f0 is the rated frequency (50 Hz).

[0055] Step 4: Reactive Power-Voltage Control The reactive power-AC voltage control of the interconnected converter adopts a traditional droop control strategy: ; in, K is the reactive power command for the interconnect converter. q U is the reactive power droop factor, U0 is the rated voltage of the AC bus, and U ac This is the measured value of the AC bus voltage.

[0056] V. SOC Equalization Control Among Energy Storage Units: ​In this embodiment, when the AC / DC hybrid microgrid includes multiple sets of hybrid energy storage units (such as multiple battery energy storage units operating in parallel), to prevent uneven power distribution and overcharging / over-discharging problems caused by differences in state of charge among the energy storage units, the coordination control layer implements SOC equalization control among the energy storage units. The specific implementation steps are as follows: Step 1: Acquisition and Calculation of State of Charge Data The coordination and control layer collects state-of-charge (SOC) data in real time through the local controllers of each energy storage unit and calculates the average SOC of all energy storage units. avg : = ; Where n is the number of energy storage units, and SOC i This represents the state of charge of the i-th energy storage unit.

[0057] Step 2: SOC Deviation Judgment Calculate the state of charge deviation ΔSOC of each energy storage unit. i : ; Set the SOC deviation threshold. th (Typically set to 0.05~0.1), when the |ΔSOC of any energy storage unit i |SOC th At that time, SOC equalization control is triggered.

[0058] Step 3: Dynamic adjustment of droop coefficient Based on the state of charge deviation ΔSOC i Adjust the droop factor of the corresponding energy storage unit. The adjustment function is as follows: ; Where, k droop,i Let k be the adjusted droop factor for the i-th energy storage unit. base,i β is the base droop coefficient, and β is the balance coefficient (the value range is generally 0.2~1.0).

[0059] In discharge mode: energy storage units with a higher state of charge (ΔSOC) i >0) Increasing the droop factor results in more power output; energy storage units with lower state of charge (ΔSOC) i <0) Reduce the droop factor and reduce power output.

[0060] In charging mode: Energy storage units with lower state of charge (ΔSOC) i <0) Increase the droop factor to absorb more power; energy storage units with a higher state of charge (ΔSOC) i >0) Reduce the droop factor and reduce power absorption.

[0061] Step 4: Dead Zone Setting To prevent SOC equalization control from frequently actuating in steady state, a dead zone threshold SOC is set for SOC equalization control. dead (Typically set to 0.01~0.03). When |ΔSOC i | <SOC dead At this time, the current droop coefficient remains unchanged, and SOC equalization control is not triggered.

[0062] VI. Seamless switching control between parallel and offline modes: In this embodiment, when the AC / DC hybrid microgrid operates in islanded mode, a multi-mode seamless switching control strategy is adopted to ensure smooth switching of the microgrid when the main grid loses or restores power. The specific implementation steps are as follows: Step 1: PCC Status Detection The voltage amplitude, frequency, and phase at the point of common coupling (PCC) are monitored in real time to determine the connection status with the main power grid. The monitoring content includes: (a) Voltage amplitude detection: When the PCC voltage amplitude is lower than 85% of the rated value or higher than 110% of the rated value, it is judged as an abnormality of the power grid; (b) Frequency detection: When the PCC frequency is below 49.5 Hz or above 50.5 Hz, it is judged as an abnormality of the power grid; (c) Phase detection: Real-time monitoring of the phase angle of the PCC.

[0063] Step 2: Switching from Grid-Connected to Island-Connected Systems When a power outage is detected in the main power grid, the following switching steps are performed: (a) Disconnect the static switch to electrically isolate the AC / DC hybrid microgrid from the main grid; (b) Control the bidirectional AC / DC interconnect converter to switch from grid-connected mode to islanded mode, and keep the output voltage and frequency of the interconnect converter consistent with those before the switch during the switching process; (c) In islanded mode, the AC subgrid uses frequency-active power droop control as the primary regulation means, and the DC subgrid uses voltage-active power droop control as the primary regulation means. The coordination control layer acts as the secondary regulation center to correct the droop reference value of each unit and eliminate steady-state error.

[0064] The switching process is kept within 20 milliseconds to ensure power supply continuity for sensitive loads.

[0065] Step 3: Island-to-Grid Pre-Synchronization Control Once the main grid is detected to have restored power, pre-synchronization control is executed to synchronize the microgrid with the main grid. This includes: (a) Detecting the voltage amplitude U of the large power grid gridFrequency f grid and phase θ grid ; (b) Detecting the voltage amplitude U of the microgrid AC bus mg Frequency f mg and phase θ mg ; (c) Calculate the voltage amplitude deviation ΔU=U grid -U mg Frequency deviation Δf = fgrid − fmg and phase difference Δθ = θ grid −θ mg ; (d) By coordinating the control layer, the control parameters of each unit in the microgrid are adjusted, and ΔU, Δf and Δθ are gradually reduced until the synchronous closing conditions are met: |ΔU|<0.05pu, |Δf|<0.1Hz, |Δθ|<5∘; (e) Close the static switch to reconnect the microgrid to the main grid and switch the interconnect converter back to grid-connected mode.

[0066] VII. Rolling Optimization and Correction Mechanism: In this embodiment, when the deviation between the predicted output and the real-time output of the wind power generation unit or photovoltaic power generation unit exceeds a preset prediction error threshold, a rolling optimization correction mechanism is activated. The specific implementation steps are as follows: Step 1: Prediction Error Calculation The coordination and control layer re-collects real-time output and load data of each unit at preset time intervals ΔT (e.g., 5 minutes), and compares them with the forecast data issued by the energy management layer to calculate the forecast error. ;

[0067] Where, ε P P represents the percentage of prediction error. real For real-time output, P forecast To contribute to prediction.

[0068] Step 2: Error threshold determination

[0069] Set the prediction error threshold ε th (e.g., 15%), when ε P >ε th At that time, scrolling optimization corrections are triggered.

[0070] Step 3: Model Predictive Control Correction

[0071] Model predictive control (MPC) algorithm is used to perform rolling corrections on power allocation commands. MPC takes the current system state as the initial state, predicts the system state and output in the time domain as the optimization objects, solves for the control sequence that minimizes the objective function, and executes only the first control variable in the control sequence.

[0072] VIII. Communication Architecture:

[0073] In this embodiment, the coordinated control of the AC / DC hybrid microgrid is achieved through information exchange between a central coordinating controller and each local controller. The central coordinating controller is deployed in the control room, while each local controller is deployed on the local side of each distributed power source, energy storage unit, and interconnecting converter. The central coordinating controller and each local controller communicate via industrial Ethernet, using Modbus TCP / IP or IEC 61850 standards to meet the power system's requirements for real-time communication and reliability. The communication network employs a redundant ring network structure; when any communication link fails, the system can automatically switch to a backup communication path to ensure the normal transmission of control commands.

[0074] In summary:

[0075] This invention significantly improves the power coordination response speed, energy storage system lifespan, renewable energy absorption capacity, and the smoothness and stability of grid-connected and off-grid switching of AC / DC hybrid microgrids through hierarchical coordinated control, dynamic frequency-division hybrid energy storage, virtual synchronous machine adaptive mutual assistance, and SOC balancing strategies.

[0076] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0077] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A coordinated control method for AC / DC hybrid microgrids suitable for new energy access, characterized in that, The method includes the following steps: S1. Construct an AC / DC hybrid microgrid topology that includes wind power generation units, photovoltaic power generation units, hybrid energy storage units, and AC / DC loads, wherein the AC / DC hybrid microgrid includes an AC subgrid and a DC subgrid, and the AC subgrid is interconnected with the DC subgrid through a bidirectional AC / DC interconnection converter; S2. A hierarchical coordination control architecture is adopted, including an equipment control layer, a coordination control layer, and an energy management layer. The equipment control layer performs local control of wind power generation units, photovoltaic power generation units, hybrid energy storage units, and interconnected converters. The coordination control layer collects the operating status information of each sub-network and performs power coordination allocation. The energy management layer formulates an energy dispatch plan based on the overall system operating data. S3. Based on the real-time output prediction data of the wind power generation unit and the photovoltaic power generation unit, as well as the real-time demand data of the AC and DC loads, the power balance status of the system is determined by the coordination control layer, and power reference commands for each unit are generated. S4. Based on the state of charge (SOC) and power response characteristics of the hybrid energy storage unit, a dynamic droop control method is used to allocate the charging and discharging power of the hybrid energy storage unit, wherein the supercapacitor responds to the high-frequency component of the power fluctuation, and the battery responds to the low-frequency component of the power fluctuation. S5. When there is a power imbalance between the AC subnet and the DC subnet, the power mutual assistance between the subnets is performed through the bidirectional AC / DC interconnection converter. The interconnection converter adopts a virtual synchronous machine control strategy to convert the voltage deviation of the DC subnet into the frequency deviation of the AC subnet and participate in frequency regulation. S6. Real-time monitoring of the state of charge (SOC) of the hybrid energy storage units. When the SOC of any group of energy storage units exceeds the preset safety threshold range, the charging and discharging droop coefficient of the energy storage unit is adjusted through the coordination control layer to achieve SOC balance control among the energy storage units.

2. The coordinated control method for AC / DC hybrid microgrids suitable for new energy access according to claim 1, characterized in that, The specific implementation method of the dynamic droop control method in step S4 is as follows: S41. The power command of the hybrid energy storage unit is decomposed by high-pass filtering and low-pass filtering to obtain high-frequency power components and low-frequency power components. The cutoff frequency of the high-pass filter is dynamically adjusted according to the capacity configuration and power response speed of the supercapacitor. S42. Distribute the high-frequency power component to the supercapacitor for response, and distribute the low-frequency power component to the battery for response. S43. Based on the real-time state of charge of the supercapacitor and the battery, dynamically adjust the droop coefficient of each energy storage unit. The functional relationship between the droop coefficient and the state of charge is as follows: ； Where, k droop k is the adjusted droop coefficient. base The base droop factor is α, the adjustment factor is SOC, and the real-time state of charge is SOC. ref For reference state of charge.

3. The coordinated control method for AC / DC hybrid microgrids suitable for new energy access according to claim 1, characterized in that, The virtual synchronous machine control strategy in step S5 includes: S51. Simulate the rotor motion equations of a synchronous generator and establish the mechanical power-frequency regulation characteristics of a virtual synchronous machine: ； Where J is the virtual moment of inertia, ω is the virtual angular frequency, and P m For virtual mechanical power, P e Where ω is the virtual electromagnetic power, D is the damping coefficient, and ω0 is the rated angular frequency; S52. Introduce a DC bus voltage-AC frequency coupling function to map the DC side voltage deviation to the AC side frequency deviation. The expression for the coupling function is: ； Where Δf is the AC frequency deviation, K v2f U is the voltage-frequency coupling coefficient. dc U is the measured value of the DC bus voltage. dc_ref This is the reference value for the DC bus voltage; S53. Based on the AC frequency deviation obtained from the mapping, the active power output of the interconnected converter is adjusted through the virtual synchronous machine control loop to achieve power mutual assistance and frequency support between AC and DC sub-networks.

4. The coordinated control method for AC / DC hybrid microgrids suitable for new energy access according to claim 1, characterized in that, The specific implementation method of the SOC equalization control among energy storage units in step S6 is as follows: S61. Real-time collection of state of charge data of each hybrid energy storage unit through the coordination control layer; S62. Calculate the average value and deviation of the state of charge of each energy storage unit. When the state of charge deviation of any energy storage unit exceeds the preset threshold, trigger the SOC equalization control. S63. Adjust the droop coefficient of the corresponding energy storage unit according to the magnitude of the state of charge deviation. Increase the droop coefficient of the energy storage unit with a lower state of charge to increase the charging power, and decrease the droop coefficient of the energy storage unit with a higher state of charge to reduce the charging power or switch to the discharge mode. S64. Set a dead zone for SOC equalization control. When the SOC deviation is less than the dead zone threshold, maintain the current droop coefficient unchanged.

5. The coordinated control method for AC / DC hybrid microgrids suitable for new energy access according to claim 1, characterized in that, The method further includes S7: when the output fluctuation of the wind power generation unit or the photovoltaic power generation unit exceeds a preset power fluctuation threshold, the coordination control layer initiates a fast power response mode, including: S71. Prioritize the use of supercapacitors to respond to instantaneous power fluctuations, with a response time of less than 50 milliseconds; S72. When the power fluctuation lasts for more than the preset time threshold or the supercapacitor's state of charge exceeds the safe range, gradually connect the battery to provide power support. S73. During periods of sustained power fluctuations, the energy management layer optimizes and adjusts the reference values ​​of the output power of the wind power generation unit and the photovoltaic power generation unit to achieve dynamic balance of system power.

6. The coordinated control method for AC / DC hybrid microgrids suitable for new energy access according to claim 1, characterized in that, The specific method for determining the power balance state in step S3 is as follows: S31. Compare the real-time operating data obtained by the coordination and control layer with the power prediction data issued by the energy management layer to calculate the power deficit or power surplus. S32. When the power deficit is greater than zero, the system is judged to be in a power deficit state, and the hybrid energy storage unit is controlled to discharge or the AC and DC loads are reduced to meet the power balance. S33. When the power surplus is greater than zero, it is determined that the system is in a power surplus state, and the hybrid energy storage unit is charged or the AC / DC load is increased to absorb the surplus power. S34. When both the power deficit and power surplus are less than the preset dead zone threshold, the system maintains its current operating state.

7. The coordinated control method for AC / DC hybrid microgrids suitable for new energy access according to claim 1, characterized in that, The method further includes S8: when the AC / DC hybrid microgrid is operating in islanded mode, a multi-mode seamless switching control strategy is adopted, including: S81. Real-time detection of voltage and frequency at the point of common coupling (PCC) to determine the connection status with the main power grid; S82. When a power grid failure is detected, the bidirectional AC / DC interconnection converter is controlled to switch from grid-connected mode to islanded mode. During the switching process, pre-synchronization control is used to eliminate phase difference and amplitude difference. S83. In islanded mode, the AC subgrid uses frequency-active power droop control as the primary regulation method, and the DC subgrid uses voltage-active power droop control as the primary regulation method. The coordination control layer acts as the secondary regulation center to correct the droop reference value of each unit. Step S84: When the main grid is detected to have resumed power supply, the frequency and phase of the microgrid are synchronized with the main grid through pre-synchronization control, and then the microgrid is switched back to grid-connected mode.

8. The coordinated control method for AC / DC hybrid microgrids suitable for new energy access according to claim 1, characterized in that, The method further includes S9: when the deviation between the predicted output and the real-time output of the wind power generation unit or photovoltaic power generation unit exceeds a preset prediction error threshold, a rolling optimization correction mechanism is initiated, specifically including: S91. The coordination control layer re-collects real-time output data and load data of each unit at preset time intervals. S92. Compare the newly collected data with the energy management system's scheduling plan and calculate the prediction error; S93. Based on the magnitude of the prediction error, the power allocation command is rolled over and corrected using the model predictive control algorithm, and the power reference value of each unit is updated.

9. A coordinated control method for AC / DC hybrid microgrids suitable for new energy access according to claim 1, characterized in that, The wind power generation unit adopts a permanent magnet synchronous wind turbine, which is connected to the AC subgrid or DC subgrid through an AC / DC rectifier and a DC / AC inverter. The maximum power point tracking control of the wind power generation unit adopts an improved hill climbing search algorithm, which dynamically adjusts the search step size according to the wind speed change rate.

10. A coordinated control method for AC / DC hybrid microgrids applicable to new energy access according to claim 1, characterized in that, The hybrid energy storage unit includes a supercapacitor energy storage module and a battery energy storage module. The supercapacitor energy storage module is connected to the DC bus through a bidirectional DC / DC converter, and the battery energy storage module is connected to the DC bus through another set of bidirectional DC / DC converters. The coordinated control of the AC / DC hybrid microgrid is achieved through information interaction between the central coordinating controller and each local controller. The central coordinating controller and each local controller communicate through industrial Ethernet, and the communication protocol adopts the Modbus TCP / IP or IEC 61850 standard.

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