Microgrid energy storage system charge state calibration method based on multi-machine cooperative control

Abstract

The invention discloses a micro-grid energy storage system charge state calibration method based on multi-machine cooperative control. The method comprises the following steps: acquiring operation state data of battery management systems corresponding to all energy storage converters through an energy management system; a virtual synchronous generator main unit is selected, and other energy storage converters are set to be in an active-reactive power mode and form a to-be-calibrated queue; calibrating the first energy storage converter in the queue to be calibrated, and sequentially executing full discharge calibration and full charge calibration; after full-charge and full-discharge calibration of the current calibration energy storage converter is completed, the current calibration energy storage converter is switched to the virtual synchronous generator main unit, and parameters of the original virtual synchronous generator main unit are synchronized to become a new main unit; and repeatedly executing calibration until the charge state calibration of the battery clusters connected with all the energy storage converters is completed. According to the invention, with calibration one by one and alternation of main units as a core, non-stop state-of-charge calibration is realized through calibration queue management and mode switching time sequence control.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and more specifically to a method for calibrating the state of charge of a microgrid energy storage system based on multi-machine collaborative control. Background Technology

[0002] Existing battery state-of-charge (SOC) estimation methods, especially the ampere-hour integration method, suffer from long-term drift due to the accumulation of measurement errors over time, making it impossible to guarantee convergence. While the open-circuit voltage method (OCV) can provide high-precision calibration, it requires the battery to be left to stand for several hours to reach electrochemical equilibrium, which is impractical for microgrid systems that require continuous operation.

[0003] Currently, there are several methods for state-of-charge (SOC) calibration using power converters (PCS) in microgrid energy storage systems. The first method is single-unit calibration: a single PCS is fully charged / discharged, but this is difficult to guarantee the operational stability of other PCS in a multi-PCS parallel system. The second method is grid-connected calibration: relying on the grid as a voltage / frequency reference, a single PCS operates in grid-connected mode, capable of charging and discharging. However, this method is sensitive to power fluctuations at the grid connection point and cannot be performed in islanded operation. The third method is centralized scheduling via an energy management system (EMS): the EMS issues power commands to all PCS to achieve SOC balance, but it lacks a "per-PCS full-charge / discharge calibration" mechanism, which can lead to SOC drift and inaccurate capacity estimation over long-term operation.

[0004] The above-mentioned solutions have shortcomings in both SOC management and capacity calibration, especially in multi-PCS systems, where there is a lack of a control strategy that can accurately achieve full charge / discharge for each battery. The main problems are: first, SOC drift, during long-term operation, due to differences in efficiency and aging, the SOC of different battery packs gradually becomes distorted, specifically manifested as battery SOC jumps, such as a sudden change from 80% to 100%; second, calibration difficulties: there is a lack of a mechanism to safely achieve full charge / discharge in a multi-PCS system; and third, circulating current risk: if multiple PCS are formed simultaneously, inconsistent control parameters can lead to circulating current in the bus current.

[0005] Therefore, proposing a full-charge calibration control method for multi-PCS energy storage with one cluster and one management is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] In view of the above problems, this invention is proposed to provide a method for calibrating the state of charge (SOC) of a microgrid energy storage system based on multi-machine collaborative control, which overcomes or at least partially solves the above problems. This method enables sequential full-charge / full-discharge calibration of multiple energy storage inverter battery packs; ensures system voltage and frequency stability during calibration; avoids circulating current and impacts, achieving smooth mode switching; and provides SOC correction and capacity calibration benchmarks to improve system operational reliability.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention provides a method for calibrating the state of charge (SOC) of a microgrid energy storage system based on multi-machine collaborative control. The microgrid energy storage system adopts a one-cluster-one-management architecture, with each battery cluster connected to a corresponding energy storage converter. Each energy storage converter is communicatively connected to an energy management system, and each battery cluster is equipped with an independent battery management system. The calibration method includes the following steps: S1. Collect the operating status data of the battery management system corresponding to all energy storage converters through the energy management system, and generate an initial calibration queue; S2. Select the energy storage converter with the optimal state of charge of the battery from the initial calibration queue as the virtual synchronous generator main unit, and set the remaining energy storage converters to active-reactive power mode and form a calibration queue. S3. Select the first energy storage converter from the queue to be calibrated as the current calibration target, and issue a constant power charging and discharging command through the energy management system to perform full discharge calibration and full charge calibration in sequence; during the calibration process, the virtual synchronous generator main unit dynamically adjusts its own output to compensate for the charging and discharging power of the current calibration energy storage converter. S4. When the corresponding battery management system reports that the current calibration energy storage converter has completed full charge and discharge calibration, the energy management system controls the current calibration energy storage converter to switch from active-reactive power mode to virtual synchronous generator master unit, and synchronizes the parameters of the original virtual synchronous generator master unit to become the new virtual synchronous generator master unit; the original virtual synchronous generator master unit switches to active-reactive power mode and is added to the tail of the calibration queue. S5. Repeat steps S3 to S4 until the state of charge calibration of all energy storage converter connected battery clusters is completed.

[0009] Furthermore, the energy management system includes: The mode scheduling layer is used for mode allocation, issuing role switching instructions, and managing calibration queues. The security verification layer is used to monitor grid voltage, frequency and power fluctuations, battery status and energy storage converter status in real time, and to trigger calibration pause or resumption. The calibration execution layer is used to receive instructions for role switching and charge / discharge calibration.

[0010] Furthermore, in step S1, the operating status data includes: battery voltage, battery current, battery state of charge, and battery aging degree.

[0011] Furthermore, in step S1, the initial calibration queue is prioritized based on the battery state-of-charge estimation error of each battery cluster, historical calibration interval and runtime, and battery aging degree.

[0012] Furthermore, the battery state-of-charge estimation error is obtained by comparing the actual released capacity with the nominal capacity of historical full charge and discharge events.

[0013] Furthermore, in step S3, the full-range calibration includes: Control the current calibrated energy storage converter to discharge at a constant power until the battery management system detects that the battery cell voltage has reached the discharge cutoff voltage or the battery cell state of charge has dropped to a preset lower limit, and maintains this state for a period of time greater than a first preset time.

[0014] Furthermore, in step S3, the full charge calibration includes: After full discharge calibration is completed, the current calibrated energy storage converter is controlled to charge at a constant power until the battery management system detects that the battery cell voltage reaches the charging cutoff voltage, the charging current drops to the trickle charging threshold, or the battery cell state of charge reaches 100%, and is maintained for more than the second preset time.

[0015] Furthermore, in step S4, the parameters of the original virtual synchronous generator main unit specifically include: the voltage amplitude, frequency, and damping coefficient of the original virtual synchronous generator main unit.

[0016] As can be seen from the above technical solution, compared with the prior art, the present invention discloses a method for calibrating the state of charge of a microgrid energy storage system based on multi-machine cooperative control, which has the following beneficial effects: 1. Achieve accurate online SOC calibration without system shutdown.

[0017] This invention uses multiple energy storage converters for coordinated control to complete the full charge and discharge calibration of battery clusters one by one while the microgrid is running continuously (in either islanded or grid-connected mode). This does not require shutdown or interruption of power supply to the load, and significantly improves system availability and operation and maintenance efficiency.

[0018] 2. Ensure the stability of microgrid operation.

[0019] This invention introduces a virtual synchronous generator main unit to dynamically compensate for power fluctuations generated during calibration, effectively maintaining the stability of microgrid voltage and frequency, and avoiding system instability or power quality degradation caused by single-cluster battery calibration.

[0020] 3. Supports fine-grained calibration under the "one cluster, one management" architecture.

[0021] This invention addresses the system structure of independently configuring BMS and PCS for each battery cluster, enabling cluster-by-cluster calibration. This overcomes the overall SOC drift problem caused by battery inconsistency in traditional centralized energy storage, thereby improving the energy dispatch accuracy of the entire system.

[0022] 4. Enable seamless role switching and collaborative scheduling among multiple machines.

[0023] This invention utilizes a dynamic rotation mechanism between the virtual synchronous generator master unit and the active and reactive power slave units, enabling a calibrated PCS to immediately take over the system master role. This ensures a continuous and smooth calibration process without the need for additional backup equipment. By employing a "rotation calibration" strategy, it guarantees that at least one PCS is always in virtual synchronous generator mode acting as the master unit, maintaining voltage and frequency stability in the microgrid and achieving seamless integration of maintenance and operation. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0025] Figure 1 This is a flowchart of the state-of-charge calibration method for a microgrid energy storage system based on multi-machine collaborative control provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the state-of-charge calibration method for a microgrid energy storage system based on multi-machine collaborative control provided in this embodiment of the invention. Figure 3 This is a flowchart illustrating the node jump process of the state-of-charge calibration method for a microgrid energy storage system based on multi-machine collaborative control, as provided in this embodiment of the invention. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0027] Before introducing the embodiments of the present invention, it is necessary to clarify the following terms: Battery Management System (BMS) is a system that manages batteries and systems that manage batteries.

[0028] An energy storage converter is a type of power conversion system, also known as a Power Conversion System (PCS).

[0029] Energy Management System, abbreviated as EMS.

[0030] The state of charge of a battery, also known as SOC, is the state of charge of the battery.

[0031] Virtual Synchronous Generator (VSG)

[0032] The active-reactive power mode, abbreviated as PQ mode, is used in energy calculations. Active power is represented by P and reactive power by Q.

[0033] This invention discloses a method for calibrating the state of charge (SOC) of a microgrid energy storage system based on multi-machine collaborative control. The microgrid energy storage system adopts a one-cluster-one-management architecture, with each cluster of batteries connected to a corresponding energy storage converter. Each energy storage converter is communicatively connected to the energy management system, and each battery cluster is equipped with an independent battery management system. (Refer to...) Figure 1 As shown, the calibration method includes the following steps: S1. Collect the operating status data of the battery management system corresponding to all energy storage converters through the energy management system and generate an initial calibration queue; S2. Select the energy storage converter with the optimal state of charge of the battery from the initial calibration queue as the virtual synchronous generator main unit, and set the remaining energy storage converters to active-reactive power mode and form a queue to be calibrated. S3. Select the first energy storage converter from the queue to be calibrated as the current calibration target, and issue a constant power charging and discharging command through the energy management system to perform full discharge calibration and full charge calibration in sequence; during the calibration process, the virtual synchronous generator main unit dynamically adjusts its own output to compensate for the charging and discharging power of the current calibrated energy storage converter. S4. When the corresponding battery management system reports that the current calibration energy storage converter has completed full charge and discharge calibration, the energy management system controls the current calibration energy storage converter to switch from active-reactive power mode to virtual synchronous generator master unit, and synchronizes the parameters of the original virtual synchronous generator master unit to become the new virtual synchronous generator master unit; the original virtual synchronous generator master unit switches to active-reactive power mode and is added to the tail of the calibration queue. S5. Repeat steps S3 to S4 until the state of charge calibration of all energy storage converter connected battery clusters is completed.

[0034] This embodiment describes a microgrid energy storage system in an industrial park, employing a modular design with one cluster per management module. Each cluster of batteries corresponds to a PCS (Power Control System). While there is no communication between PCS, each cluster's BMS (Battery Management System) and PCS communicate with the EMS (Energy Management System). The core idea of ​​this embodiment is that, under normal microgrid operation, all PCS operate as the grid power source in Virtual Synchronous Generator (VSG) mode. During SOC (State of Charge) calibration, a portion of the PCS are set to Active-Quick Power (PQ) mode as current sources, allowing for full charge / discharge calibration of the batteries connected to the PQ-mode PCS without system shutdown. After calibration, roles are reversed: PCS originally in VSG mode switch to PQ mode for calibration, while PQ-mode PCS that have completed calibration switch back to VSG mode to assume main unit responsibility. This cycle continues until all PCS are calibrated.

[0035] This embodiment takes "calibrating one PCS at a time and rotating the main unit" as its core, relies on the three-layer EMS control architecture, and achieves non-stop calibration of multiple PCS systems through calibration queue management, mode switching timing control and full-process safety monitoring.

[0036] Before introducing the specific steps of this embodiment, we will first introduce the Energy Management System (EMS) of this embodiment, which is responsible for global scheduling, calibration triggering, queue generation, and fault decision-making; including: Mode Scheduling Layer: A core layer under EMS, responsible for PCS mode (VSG / PQ) allocation, role switching command issuance, and calibration queue management.

[0037] Safety verification layer: A protection layer under EMS, which monitors system voltage / frequency / power fluctuations, battery status and PCS faults in real time, and triggers calibration pause or resumption.

[0038] PCS Execution Layer: The bottom-level execution unit, which includes all energy storage converters (PCS), receives commands from the upper layer to perform mode switching and charge / discharge calibration.

[0039] Reference Figure 2 As shown, the specific steps are as follows: Step 1: System initialization.

[0040] Initiating the calibration procedure: The EMS mode scheduling layer initiates the "capacity calibration procedure". The safety verification layer first confirms that the system is fault-free, such as stable voltage / frequency and no PCS faults, and the calibration process is officially started.

[0041] Status identification and queue generation: EMS collects the operating status of all PCS through the PCS execution layer, and at the same time receives the BMS data (battery voltage, current, SOC, aging degree) corresponding to each PCS, and generates calibration queues according to the priority of SOC distortion degree; such as PCS2, PCS5, PCS7...

[0042] Initial mode allocation: The mode scheduling layer designates one PCS with the best state (such as PCS01) as the initial VSG master unit "PCS1-VSG" to maintain the stability of the microgrid voltage / frequency; all other PCS are included in the calibration queue, and the initial state is set to the PQ mode to be calibrated "PCSx-PQ". This completes the initial configuration of selecting one PCS from the queue as the PQ mode and the rest as the VSG mode.

[0043] Figure 2 The symbols and terms in the text are explained below: PCS1-VSG: The PCS initially acts as the "master unit," operating in VSG mode to maintain microgrid voltage / frequency stability. In this embodiment, PCS1 is the initial VSG master unit.

[0044] PCSx-PQ: The PCS cluster to be calibrated, where x is a variable, such as PCS2 or PCS5. It operates in PQ mode and receives charge / discharge commands. In this embodiment, PCS2 is the first PQ unit to be calibrated.

[0045] PCS-new: The new master unit PCS that has been switched to VSG mode after calibration is completed. The parameters of the original VSG master unit need to be synchronized.

[0046] Full charge calibration trigger: The calibration start signal initiated by EMS triggers the mode scheduling layer to generate a calibration queue and execute the calibration process.

[0047] Calibration queue: A list of PCS to be calibrated (e.g., PCS2, PCS5, PCS7...), sorted by priority, and calibration is performed on each PC one by one.

[0048] Synchronize VSG parameters: The new VSG master unit (PCS-new) synchronizes the control parameters such as voltage amplitude, frequency, and damping coefficient with the original master unit (such as PCS1-VSG) to avoid switching shocks.

[0049] Activating the new host of VSG: After the mode scheduling layer confirms the parameter synchronization, the instruction PCS-new officially assumes the role of VSG master unit and takes over the responsibility of microgrid stability.

[0050] Step 2: Refer to Figure 3 As shown, calibrate the PQ unit.

[0051] Selecting a calibration target: The mode scheduling layer extracts the first PCS from the calibration queue, such as PCS02, as the current calibration unit.

[0052] Issuing charge / discharge commands: Based on the battery status data uploaded in real time by the BMS, the EMS issues precise charge / discharge commands to the PCS02 through the coordination controller. Full discharge calibration: Control PCS02 to discharge at a constant power (e.g., 10kW) until the BMS detects that the battery voltage has reached the discharge cutoff voltage (e.g., 2.5V / cell) or the SOC has dropped to the lower limit (e.g., 5%), and maintain this state for 30 minutes to ensure complete discharge.

[0053] Full charge calibration: After discharging, switch to constant power charging, such as 8kW, until the BMS detects that the battery voltage has reached the charging cutoff voltage, such as 3.65V / cell, the charging current has dropped to the trickle charging threshold, such as 0.05C, or the SOC has reached 100%, and maintain this for 20 minutes to ensure that the battery is fully charged.

[0054] System balance assurance: During calibration, the initial VSG main unit PCS1-VSG follows the "maintain VSG mode" command and compensates for the charging and discharging power of PCS02 by adjusting its own output. For example, when PCS02 discharges 10kW, PCS1-VSG reduces its output by 10kW to ensure the stability of microgrid voltage / frequency and maintain system power balance.

[0055] Figure 3 The following are explanations of the terms used in the calibration process: The decision node, or process branch control node, includes "Has the calibration of the battery cluster been completed?" and "Is the queue empty?". The process jumps according to the actual status.

[0056] BMS data: Battery status data collected by the battery management system, including voltage, current, SOC (state of charge), temperature, etc.

[0057] Charging / discharging power commands: Constant power control commands (such as "10kW discharge" and "8kW charge") issued by the EMS to the PQ mode PCS through the mode scheduling layer.

[0058] VSG unit output adjustment: During calibration, the VSG main unit adjusts its own active / reactive output to compensate for the charging and discharging power of the PQ mode PCS and maintain system power balance.

[0059] Remove from calibration queue: After the PCS completes calibration and switches to VSG mode, it is removed from the list of pending calibrations and will no longer participate in this cycle of calibration.

[0060] Step 3: Switch roles.

[0061] Calibration completion judgment: When the BMS reports that PCS02 has completed full charge-discharge calibration, the mode scheduling layer initiates a role switching command.

[0062] Mode switching execution: PCS02: Switches from PQ mode to VSG mode and synchronizes the control parameters of PCS1-VSG, such as voltage amplitude, frequency, damping coefficient, etc., to become the new main unit PCS-new.

[0063] PCS1-VSG: Switches from VSG mode to PQ mode, enters the tail of the calibration queue, and awaits subsequent calibration.

[0064] Safety verification: During the switching process, the safety verification layer monitors voltage / current changes in real time. If fluctuations exceed the threshold (such as voltage sudden change ±5%), the switching is immediately suspended and the current VSG main unit stabilizes the voltage to ensure no impact or circulating current risk.

[0065] Step 4: Execute repeatedly.

[0066] Next round of calibration starts: After PCS1-VSG switches to PQ mode, the mode scheduling layer extracts the next PCS from the calibration queue, such as PCS05, as the new calibration target, and repeats the second step of the "full discharge → full charge" calibration process.

[0067] The queue is cleared in a cyclic manner: each time a PCS completes calibration and role switching, that PCS is removed from the calibration queue until all PCS have completed calibration.

[0068] Special scenario handling: If only one PQ mode PCS remains in the calibration queue, it can be directly set as the VSG master unit during the switch, without needing to switch other PCS.

[0069] Step 5: System monitoring and protection.

[0070] Real-time monitoring: The security verification layer monitors three core states throughout the entire process: ① Battery status: voltage, temperature, and SOC uploaded by the BMS to prevent overcharging and over-discharging; ② System status, microgrid voltage / frequency, bus current, to avoid circulating current; ③PCS status, mode switching success rate, and charging / discharging power accuracy.

[0071] Emergency response: If a drastic power fluctuation (such as a sudden power change of ±15% at the grid connection point) or a fault (such as a PCS fault or battery overheating) is detected, the calibration process should be immediately suspended, and the current VSG master unit should be prioritized to maintain system stability; after the fault is resolved, calibration should be resumed from the suspended node.

[0072] This embodiment effectively corrects SOC estimation errors through periodic mandatory full-charge and discharge calibration, ensuring a high degree of consistency in the capacity state of all battery packs and significantly improving the overall usable capacity of the system. It avoids performance degradation and inconsistent degradation caused by some batteries not being fully charged or over-discharged for extended periods, thus extending the overall lifespan of the energy storage system.

[0073] This invention employs a "rotational calibration" strategy, ensuring that at least one PCS is always in VSG mode as the master unit to maintain the voltage and frequency stability of the microgrid, achieving seamless integration of maintenance and operation. The entire calibration process is automatically executed by the energy management system or coordinating controller without manual intervention, improving operational efficiency; it is particularly suitable for clusters of varying numbers of PCS, and expansion can be easily achieved by simply adjusting the control logic.

[0074] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0075] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for calibrating state of charge of a microgrid energy storage system based on multi-machine cooperative control, characterized in that, The micro-grid energy storage system adopts a cluster management architecture, each battery cluster is connected to an energy storage converter, each energy storage converter is in communication connection with an energy management system, and each battery cluster is equipped with an independent battery management system; the calibration method comprises the following steps: S1, collecting the running state data of the battery management system corresponding to all energy storage converters through the energy management system, and generating an initial calibration queue; S2, selecting the energy storage converter with the optimal battery state of charge from the initial calibration queue as a virtual synchronous generator master unit, and setting the remaining energy storage converters to active-reactive power mode and forming a calibration queue; S3, selecting the first energy storage converter from the calibration queue as the current calibration object, issuing a constant power charge-discharge instruction through the energy management system, and sequentially performing full discharge calibration and full charge calibration; during the calibration process, the virtual synchronous generator master unit dynamically adjusts its output to compensate for the charge-discharge power of the current calibration energy storage converter; S4, when the corresponding battery management system feedbacks that the full charge and full discharge calibration of the current calibration energy storage converter is completed, the energy management system controls the current calibration energy storage converter to switch from active-reactive power mode to virtual synchronous generator master unit, and synchronizes the parameters of the original virtual synchronous generator master unit to become a new virtual synchronous generator master unit; the original virtual synchronous generator master unit switches to active-reactive power mode and joins the tail of the calibration queue; S5, repeating steps S3 to S4 until the state of charge calibration of all battery clusters connected to the energy storage converter is completed.

2. The method of claim 1, wherein, The energy management system comprises: a mode scheduling layer for mode allocation, role switching instruction issuing and calibration queue management; a security verification layer for real-time monitoring of grid voltage, frequency and power fluctuation, battery state and energy storage converter state, triggering calibration suspension or resumption; a calibration execution layer for receiving instructions to execute role switching and charge-discharge calibration.

3. The method of claim 1, wherein, In step S1, the running state data includes: battery voltage, battery current, battery state of charge and battery aging degree.

4. The method of claim 1, wherein, In step S1, the initial calibration queue is prioritized according to the battery state of charge estimation error, historical calibration interval and running time, and battery aging degree of each battery cluster.

5. The method of claim 4, wherein, The battery state of charge estimation error is obtained based on the actual release capacity and nominal capacity comparison method of historical full charge and full discharge events.

6. The method of claim 1, wherein, In step S3, the full discharge calibration comprises: controlling the current calibration energy storage converter to discharge at a constant power until the battery management system detects that the battery cell voltage reaches the discharge cutoff voltage or the battery cell state of charge drops to the preset lower limit, and maintaining for more than a first preset time.

7. The method of claim 6, wherein, In step S3, the full charge calibration comprises: after the full discharge calibration is completed, controlling the current calibration energy storage converter to charge at a constant power until the battery management system detects that the battery cell voltage reaches the charge cutoff voltage, the charge current drops to the trickle charge threshold or the battery cell state of charge reaches 100%, and maintaining for more than a second preset time.

8. The method of claim 1, wherein, In step S4, the parameters of the original virtual synchronous generator master unit specifically include a voltage amplitude, a frequency, and a damping coefficient of the original virtual synchronous generator master unit.

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