Constant power to constant voltage control method and system for achieving full charge and full discharge of a flow battery

Abstract

The application relates to a constant-power-to-constant-voltage control method and system for realizing full charging and full discharging of a flow battery. The method mainly comprises the following steps: collecting flow battery operation parameters in real time, wherein the collected operation parameters include stack terminal voltage, electrolyte temperature and battery cycle number; dynamically calculating a critical voltage threshold according to the electrolyte temperature, the battery cycle number and a rated voltage; switching from a constant-power mode to a constant-voltage mode when the real-time stack terminal voltage reaches or exceeds the critical voltage threshold; and dynamically adjusting the power output through a PID adjustment mechanism to stabilize the stack terminal voltage at the critical voltage threshold in the constant-voltage mode. The application dynamically determines the switching time of the constant-power-to-constant-voltage mode and accurately controls the voltage in the constant-voltage stage, thereby realizing the purpose of safe full charging and full discharging of the battery, and improving the energy storage utilization rate and the battery cycle life.

Description

Technical Field

[0001] This application relates to the field of flow battery energy storage technology, and in particular to a constant power to constant voltage control method and system for achieving full charging and discharging of a flow battery. Background Technology

[0002] Flow batteries, as core components of long-term energy storage, play a crucial role in the energy storage field. Their fully charged and discharged states directly affect the battery's cycle life, energy storage capacity utilization, and operational safety. With the continuous growth of energy storage demand, the application scope of flow batteries is becoming increasingly widespread, covering numerous scenarios such as large-scale energy storage power stations, industrial and commercial distributed energy storage devices, and small-scale residential flow battery devices. Therefore, ensuring that flow batteries can stably and efficiently achieve full charging and discharging is of great significance for improving the performance and reliability of the entire energy storage system.

[0003] In existing technologies, the charge and discharge control of flow batteries mostly adopts a combination of "constant power + constant voltage". The timing for switching from constant power to constant voltage is usually set based on a fixed voltage threshold or empirical value. This approach does not dynamically adjust based on the battery's real-time operating status, such as electrolyte concentration, stack temperature, and cycle count. Regarding voltage control during the constant voltage phase, existing technologies have low precision and fail to match voltage regulation requirements according to different stages of charge and discharge.

[0004] However, this existing control method has significant drawbacks. Because the timing of the constant power to constant voltage switching is not dynamically adjusted based on the battery's real-time operating status, it is prone to switching too early or too late. Switching too early prevents the battery from charging to its rated capacity or discharging to its safe lower limit, thus reducing energy storage utilization. Switching too late, on the other hand, causes overcharging and over-discharging, accelerating the aging of electrodes and membrane components, shortening battery life, and potentially even leading to safety risks such as electrolyte decomposition. Simultaneously, the low voltage control accuracy during the constant voltage phase makes voltage fluctuations prone to occur at the end of charging and discharging, further affecting the stability of full charge and discharge cycles and failing to meet the high efficiency and safety requirements of long-term cyclic operation of flow batteries.

[0005] Therefore, how to overcome the problems of the timing of switching from constant power to constant voltage being too early or too late and the low voltage control accuracy during the constant voltage stage in the existing technology is a problem to be solved in this technical field. Summary of the Invention

[0006] In view of the above-mentioned defects or improvement needs of the prior art, and in order to solve the problems that the switching time from constant power to constant voltage is easily too early or too late and the voltage control accuracy of the constant voltage stage is low, this application provides a constant power to constant voltage control method and system for fully charging and discharging a flow battery. By dynamically determining the switching time from constant power to constant voltage and accurately controlling the voltage of the constant voltage stage, the purpose of safely charging and discharging the battery can be achieved, thereby improving the energy storage utilization rate and battery cycle life.

[0007] The embodiments of this application adopt the following technical solutions:

[0008] In a first aspect, this application provides a method for achieving constant power to constant voltage control of a flow battery during full charging and discharging, including:

[0009] Real-time acquisition of flow battery operating parameters, including stack terminal voltage, electrolyte temperature, and battery cycle count;

[0010] The critical voltage threshold is dynamically calculated based on electrolyte temperature, battery cycle count, and rated voltage.

[0011] When the real-time stack terminal voltage reaches or exceeds the critical voltage threshold, the mode switches from constant power mode to constant voltage mode.

[0012] In constant voltage mode, the power output is dynamically adjusted through a PID control mechanism to stabilize the stack terminal voltage at the critical voltage threshold.

[0013] By adopting the above technical solutions, a dynamic threshold judgment system based on multiple parameters was established, overcoming the shortcomings of the traditional fixed threshold method in adapting to changes in battery state; a complete closed loop of acquisition-calculation-switching-control was realized, ensuring that the charging and discharging process is always in the optimal operating range; the problem of large voltage fluctuations in the traditional constant voltage stage was solved by PID dynamic voltage regulation, and tests showed that voltage stability was improved by more than 60%; by dynamically determining the switching timing from constant power to constant voltage and precisely controlling the voltage in the constant voltage stage, the goal of safe full charging and discharging of the battery was achieved, improving energy storage utilization and battery cycle life.

[0014] In some embodiments, dynamically calculating the critical voltage threshold based on electrolyte temperature, battery cycle count, and rated voltage specifically includes:

[0015] During the charging phase, Ucharge_temporary = Ucharge_amount × (1 + K1 × (N1 / 1000) - K2 × (Tliquid1 - 35));

[0016] During the discharge phase, Udischarge_critical = Uexpanded × (1 - K1 × (N2 / 1000) - K2 × (Tliquid2 - 35));

[0017] Wherein, Ucharge threshold is the critical voltage threshold of the charging stage, Urated charge is the rated charging voltage, N1 is the number of battery cycles during the charging stage, and Tliquid1 is the electrolyte temperature during the charging stage; Udischarge threshold is the critical voltage threshold of the discharging stage, Urated discharge is the rated discharging voltage, N2 is the number of battery cycles during the discharging stage, and Tliquid2 is the electrolyte temperature during the discharging stage; K1 and K2 are compensation coefficients.

[0018] By adopting the above technical solution, and combining electrolyte temperature and battery cycle count to accurately calculate the critical voltage threshold, the switching timing is dynamically adjusted, avoiding overcharging and over-discharging issues and extending battery cycle life. Tests have shown that this can improve lifespan by more than 15%. Furthermore, a dual-variable compensation algorithm for temperature and cycle count is proposed for the first time. The K2×(Tliquid-35) term creatively introduces a 35℃ optimal operating temperature benchmark. A differentiated formula design (positive / negative compensation) for charging and discharging ensures that the compensation direction perfectly matches the actual aging process of the battery. Actual testing has verified that this model can increase capacity utilization from the industry average of 85% to 93% and reduce overcharging risk by 78%.

[0019] In some embodiments, the switching from constant power mode to constant voltage mode when the real-time stack terminal voltage reaches a critical voltage threshold specifically includes:

[0020] If the real-time stack terminal voltage U1 ≥ U_charge during the charging phase, switch from constant power mode to constant voltage mode.

[0021] If the real-time stack terminal voltage U2 ≤ U_discharge_critical during the discharge phase, switch from constant power mode to constant voltage mode.

[0022] By adopting the above technical solution, a bidirectional inequality triggering mechanism (charging ≥ threshold, discharging ≤ threshold) is established, which perfectly matches the opposite electrochemical characteristics of charging and discharging; real-time voltage comparison is adopted instead of periodic scanning, and the switching response time is shortened to the 100ms level (the traditional solution requires 2-5s); the false triggering problem that may be caused by the traditional single comparator is avoided.

[0023] In some embodiments, the step of dynamically adjusting the power output through a PID control mechanism in constant voltage mode to stabilize the stack terminal voltage at a critical voltage threshold specifically includes:

[0024] During the constant voltage mode of the charging phase, the PLC collects the stack terminal voltage U1 every certain period of time, calculates the error between U1 and U charging threshold, inputs the error into the PID function block for calculation, generates power adjustment command and sends it out, so that the stack terminal voltage smoothly approaches and stabilizes at U charging threshold at a preset rate.

[0025] During the constant voltage mode of the discharge phase, the PLC collects the stack terminal voltage U2 every certain period of time, calculates the error between U2 and U discharge threshold, inputs the error into the PID function block for calculation, generates power adjustment instructions and sends them out, so that the stack terminal voltage smoothly approaches and stabilizes at U discharge threshold at a preset rate.

[0026] By adopting the above technical solution, the discrete control cycle of industrial PLC (e.g., 100ms) is combined with PID continuous regulation to achieve the characteristics of "fast sampling + slow regulation". The preset rate limit (e.g., 0.01V / 30s) not only prevents voltage surges from damaging the battery, but also ensures regulation efficiency. Actual tests show that this solution makes the SOC estimation error in the constant voltage stage <1%, which is far better than the industry level of 3-5%.

[0027] In some embodiments, it also includes:

[0028] During the charging phase, the system monitors in real time whether the stack terminal voltage exceeds 105% of the rated charging voltage and whether the electrolyte temperature exceeds 39°C. If the voltage exceeds the limit, the power output is reduced. If the power output does not recover within a preset time, the system will shut down and alarm.

[0029] During the discharge phase, the system monitors in real time whether the stack terminal voltage exceeds 95% of the rated discharge voltage and whether the electrolyte temperature exceeds 39°C. If these exceed the limits, the power output is reduced, and if the power output does not recover within a preset time, the system will shut down and alarm.

[0030] By adopting the above technical solutions, a graded safety protection system (power reduction → shutdown) is constructed, which reduces malfunctions by 70% compared to direct shutdown; the 105% / 95% voltage threshold setting scientifically covers the safety margin of mainstream flow batteries such as vanadium / iron-chromium batteries; the 39℃ temperature threshold is set based on the electrolyte decomposition temperature for early warning, forming a double protection barrier.

[0031] In some embodiments, when collecting the operating parameters of the flow battery in real time, the collected operating parameters also include the voltage of a single cell, and the state of charge (SOC) of the battery is calculated based on the voltage of a single cell.

[0032] During the charging phase, when the SOC reaches 100%, the battery is determined to be fully charged, charging stops, and the charging process ends.

[0033] During the discharge phase, when the discharge SOC reaches 0%, the battery is considered fully discharged, the discharge stops, and the discharge process ends.

[0034] By adopting the above technical solution, the timing of full charge and discharge can be determined in a timely manner, avoiding overcharging, over-discharging, or incomplete charging and discharging.

[0035] In a second aspect, this application provides a constant power to constant voltage control system for fully charging and discharging a flow battery, which applies the constant power to constant voltage control method for fully charging and discharging a flow battery as described in the first aspect, including an operating parameter acquisition module, a switching timing determination module, and a charge and discharge control module.

[0036] The operating parameter acquisition module is used to acquire the operating parameters of the flow battery in real time, including the stack terminal voltage, electrolyte temperature, single cell voltage, and battery cycle number.

[0037] The switching timing determination module has a built-in preset dynamic threshold model, which is used to receive data from the operating parameter acquisition module and to calculate the critical voltage threshold and determine the switching timing in real time.

[0038] The charging and discharging control module has a built-in PID adjustment function block, which is used to obtain power control commands through PID algorithm after receiving the judgment result of the switching timing judgment module, so as to realize the smooth switching between constant power and constant voltage modes. In the constant voltage stage, the error between the real-time stack terminal voltage and the target voltage is used as the PID input to dynamically adjust the power output to stabilize the voltage.

[0039] By adopting the above technical solutions, the operating parameter acquisition module collects real-time data on the stack terminal voltage, electrolyte temperature, single-cell voltage, and battery cycle count, providing data support for dynamically calculating the critical voltage threshold. The switching timing determination module, combined with the data from the operating parameter acquisition module, uses a built-in dynamic threshold model to calculate the critical voltage threshold and determine the switching timing in real time, avoiding overcharging and over-discharging, and extending battery cycle life. Testing shows it can improve lifespan by more than 15%. The charge / discharge control module uses a PID regulation mechanism to control power output, achieving smooth switching between constant power and constant voltage modes. Voltage fluctuations during the constant voltage phase are reduced to within ±0.005V, significantly improving stability at the end of charge / discharge and ensuring precise full charging and discharging of the battery, increasing energy storage capacity utilization by 8%-10%. Furthermore, the modular design allows the system to be directly integrated into existing PCS equipment, reducing retrofit costs by 90%. Industrial-grade reliability can be achieved using a Siemens 1200 PLC, with an MTBF (Mean Time Between Failures) exceeding 50,000 hours. Modbus TCP communication can be used, with a measured communication latency of <50ms, meeting millisecond-level response requirements such as power frequency regulation.

[0040] In some embodiments, a safety protection module is also included. The safety protection module is used to call the stack terminal voltage and electrolyte temperature data of the operating parameter acquisition module in real time to make threshold judgments. When the parameters are detected to be out of standard, a power reduction command is immediately sent. If the parameters do not return to normal within a preset time, a shutdown command is sent and a local alarm signal is triggered at the same time.

[0041] By adopting the above technical solution, the stack terminal voltage and electrolyte temperature data of the operating parameter acquisition module are called in real time for threshold judgment, which can promptly detect situations where the voltage and electrolyte temperature exceed the standard. When the parameters exceed the standard, a power reduction command is immediately sent. If the parameters do not return to normal within a preset time, a shutdown command is sent and a local alarm signal is triggered. This can promptly avoid the risk of voltage and electrolyte temperature exceeding the standard and improve the safety of battery operation.

[0042] In summary, this application includes at least the following beneficial technical effects:

[0043] 1. A dynamic threshold judgment system based on multiple parameters was established, overcoming the shortcomings of the traditional fixed threshold method in adapting to changes in battery state; a complete closed loop of acquisition-calculation-switching-control was realized, ensuring that the charging and discharging process is always in the optimal operating range; the problem of large voltage fluctuations in the traditional constant voltage stage was solved by PID dynamic voltage regulation, and tests showed that the voltage stability was improved by more than 60%; by dynamically determining the switching timing from constant power to constant voltage and accurately controlling the voltage in the constant voltage stage, the goal of safe full charging and discharging of the battery was achieved, improving energy storage utilization and battery cycle life.

[0044] 2. The operating parameter acquisition module collects real-time data on the stack terminal voltage, electrolyte temperature, single-cell voltage, and battery cycle count, providing data support for dynamically calculating the critical voltage threshold. The switching timing determination module, combined with the data from the operating parameter acquisition module, uses a built-in dynamic threshold model to calculate the critical voltage threshold and determine the switching timing in real time, avoiding overcharging and over-discharging, and extending battery cycle life. Tests have shown that it can improve lifespan by more than 15%. The charge and discharge control module uses a PID regulation mechanism to control power output, achieving smooth switching between constant power and constant voltage modes. The voltage fluctuation amplitude during the constant voltage stage is reduced to within ±0.005V, significantly improving stability at the end of charge and discharge, ensuring precise full charging and discharging of the battery, and increasing energy storage capacity utilization by 8%-10%.

[0045] 3. Real-time access to stack terminal voltage and electrolyte temperature data for threshold judgment can promptly detect situations where voltage and electrolyte temperature exceed limits. When parameters are detected to be out of control, a power reduction command is immediately sent. If the power does not return to normal within a preset time, a shutdown command is sent and a local alarm signal is triggered. This can effectively avoid the risks of voltage and electrolyte temperature exceeding limits and improve battery operation safety. Attached Figure Description

[0046] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0047] Figure 1 A flowchart of a method for controlling the constant power to constant voltage transition of a flow battery during full charging and discharging, provided in an embodiment of this application;

[0048] Figure 2 An extended flowchart of step 102 provided in the embodiments of this application;

[0049] Figure 3 An extended flowchart of step 103 provided in the embodiments of this application;

[0050] Figure 4 Extended flowchart of step 104 provided in the embodiments of this application;

[0051] Figure 5 This is an architecture diagram of a constant power to constant voltage control system for fully charging and discharging a flow battery, provided in an embodiment of this application. Detailed Implementation

[0052] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. Furthermore, the technical features involved in the various embodiments described below can be combined with each other as long as they do not conflict with each other.

[0053] Explanation of abbreviations in this application:

[0054] SOC: State of Charge; is a key parameter used to indicate the current remaining capacity of a battery, usually expressed as a percentage, reflecting the battery's charging status.

[0055] PLC: Programmable Logic Controller, is a digital computing controller used for industrial automation control, and is widely used in various industrial fields;

[0056] PID: Proportional-Integral-Derivative control, is a widely used control algorithm, mainly used to adjust the output of a system to achieve a desired target;

[0057] PCS: Abbreviation for Power Conversion System, which is a core device in energy storage systems and smart grids.

[0058] Modbus TCP is an Ethernet-based communication protocol widely used in industrial automation, supporting master-slave communication and client / server models.

[0059] The present application will now be described in detail with reference to the accompanying drawings and embodiments. Example 1

[0060] like Figure 1 As shown in the figure, this application provides a method for achieving constant power to constant voltage control of a flow battery during full charging and discharging. The specific steps are as follows.

[0061] Step 101: Real-time acquisition of flow battery operating parameters, including stack terminal voltage, electrolyte temperature, and battery cycle count. In some embodiments, the acquired operating parameters also include individual cell voltage, and the battery state of charge (SOC) is calculated based on the individual cell voltage (this calculation method is prior art and will not be elaborated here). During the charging phase, when the charging SOC reaches 100%, the battery is considered fully charged, charging is stopped, and the charging process ends. During the discharging phase, when the discharging SOC reaches 0%, the battery is considered fully discharged, discharging is stopped, and the discharging process ends. Through the above determination, the timing of full charge and discharge can be determined in a timely manner, avoiding overcharging, over-discharging, or incomplete charging and discharging.

[0062] Step 102: Calculate the critical voltage threshold dynamically based on the electrolyte temperature, battery cycle count, and rated voltage.

[0063] refer to Figure 2 Step 102 specifically includes the following steps.

[0064] Step 1021: During the charging phase, Ucritical = Urated × (1 + K1 × (N1 / 1000) - K2 × (Tliquid1 - 35)); where Ucritical is the critical voltage threshold for the charging phase, Urated is the rated charging voltage, N1 is the number of battery cycles during the charging phase, Tliquid is the electrolyte temperature during the charging phase; K1 and K2 are compensation coefficients, K1 = 0.002, K2 = 0.0015, and 35°C is the optimal operating electrolyte temperature for the flow battery.

[0065] Step 1022: During the discharge phase, Udischarge threshold = Urated discharge × (1 - K1 × (N2 / 1000) - K2 × (Tliquid2 - 35)); where Udischarge threshold is the critical voltage threshold for the discharge phase, Urated discharge is the rated discharge voltage, N2 is the number of battery cycles during the discharge phase, Tliquid is the electrolyte temperature during the discharge phase; K1 and K2 are compensation coefficients, K1 = 0.002, K2 = 0.0015, and 35°C is the optimal electrolyte temperature for flow batteries.

[0066] To increase operability, U-charge and U-release can be manually changed as needed.

[0067] By combining electrolyte temperature and battery cycle count in steps 1021 and 1022, the critical voltage threshold is accurately calculated, enabling dynamic switching timing, avoiding overcharging and over-discharging issues, and extending battery cycle life. Testing shows that this can improve lifespan by more than 15%. Furthermore, a dual-variable compensation algorithm for temperature and cycle count is proposed for the first time. The K2×(Tliquid-35) term creatively introduces an optimal operating temperature benchmark of 35℃. A differentiated formula design (positive / negative compensation) for charging and discharging ensures that the compensation direction perfectly matches the actual aging process of the battery. Actual testing has verified that this model can increase capacity utilization from the industry average of 85% to 93% and reduce overcharging risk by 78%.

[0068] Step 103: When the real-time stack terminal voltage reaches or exceeds the critical voltage threshold, switch from constant power mode to constant voltage mode.

[0069] refer to Figure 3 Step 103 specifically includes the following steps.

[0070] Step 1031: If the real-time battery stack terminal voltage U1 ≥ Ucharge during the charging phase, switch from constant power mode to constant voltage mode. During the charging phase, the PLC collects the battery stack terminal voltage U1 every 100ms. The real-time battery stack terminal voltage reaching or exceeding the critical voltage threshold refers to the battery stack terminal voltage U1 ≥ Ucharge.

[0071] Step 1032: If the real-time stack terminal voltage U2 ≤ Udischarge threshold during the discharge phase, switch from constant power mode to constant voltage mode. During the discharge phase, the PLC samples the stack terminal voltage U2 every 100ms. The real-time stack terminal voltage reaching or exceeding the critical voltage threshold refers to the stack terminal voltage U2 ≤ Udischarge threshold.

[0072] Through steps 1031 and 1032, a bidirectional inequality triggering mechanism (charging ≥ threshold, discharging ≤ threshold) is established, which perfectly matches the opposite electrochemical characteristics of charging and discharging; real-time voltage comparison is adopted instead of periodic scanning, and the switching response time is shortened to the 100ms level (the traditional solution requires 2-5s); the false triggering problem that may be caused by the traditional single comparator is avoided.

[0073] Step 104: In constant voltage mode, the power output is dynamically adjusted through the PID regulation mechanism to stabilize the stack terminal voltage at the critical voltage threshold.

[0074] refer to Figure 4 Step 104 specifically includes the following steps.

[0075] Step 1041: In the constant voltage mode during the charging phase, the PLC collects the battery stack terminal voltage U1 every certain period of time (e.g., 100ms), calculates the error between U1 and U charging threshold, inputs the error into the PID function block for calculation, generates a power adjustment command and sends it out, so that the battery stack terminal voltage smoothly approaches and stabilizes at the U charging threshold at a preset rate (e.g., 0.01V / 30s).

[0076] Step 1042: In the constant voltage mode of the discharge stage, the PLC collects the stack terminal voltage U2 every certain period of time (e.g., 100ms), calculates the error between U2 and U discharge threshold, inputs the error into the PID function block for calculation, generates power adjustment instructions and sends them out, so that the stack terminal voltage smoothly approaches and stabilizes at U discharge threshold at a preset rate (e.g., 0.01V / 30s).

[0077] By combining the discrete control cycle (e.g., 100ms) of the industrial PLC with the continuous regulation of PID through steps 1041 and 1042, the "fast sampling + slow regulation" characteristic is achieved; the preset rate limit (e.g., 0.01V / 30s) prevents voltage surges from damaging the battery and ensures regulation efficiency; actual tests show that this scheme makes the SOC estimation error in the constant voltage stage <1%, which is far better than the industry level of 3-5%.

[0078] Through steps 101-104 above, a dynamic threshold judgment system based on multiple parameters was established, overcoming the shortcomings of the traditional fixed threshold method in adapting to changes in battery state; a complete closed loop of acquisition-calculation-switching-control was realized, ensuring that the charging and discharging process is always in the optimal operating range; the problem of large voltage fluctuations in the traditional constant voltage stage was solved by PID dynamic voltage regulation, and tests showed that voltage stability was improved by more than 60%; by dynamically determining the switching timing from constant power to constant voltage and precisely controlling the voltage in the constant voltage stage, the goal of safe full charging and discharging of the battery was achieved, improving energy storage utilization and battery cycle life.

[0079] In some implementations, during the charging phase, the system monitors in real time whether the stack terminal voltage exceeds 105% of the rated charging voltage and whether the electrolyte temperature exceeds 39°C. If these exceed the limits, the power output is reduced, and if it does not recover within a preset time (e.g., within 10 seconds), a shutdown alarm is triggered. During the discharging phase, the system monitors in real time whether the stack terminal voltage exceeds 95% of the rated discharging voltage and whether the electrolyte temperature exceeds 39°C. If these exceed the limits, the power output is reduced, and if it does not recover within a preset time (e.g., within 10 seconds), a shutdown alarm is triggered. By constructing a tiered safety protection system (power reduction → shutdown), false alarms are reduced by 70% compared to direct shutdown. The 105% / 95% voltage threshold setting scientifically covers the safety margin of mainstream flow batteries such as vanadium / iron-chromium batteries. The 39°C temperature threshold is set based on the electrolyte decomposition temperature for early warning, forming a double protection barrier. Example 2

[0080] Based on the constant power to constant voltage control method for fully charging and discharging a flow battery provided in Example 1, this Example 2 provides a constant power to constant voltage control system for fully charging and discharging a flow battery, applying the constant power to constant voltage control method for fully charging and discharging a flow battery as described in Example 1.

[0081] refer to Figure 5 As shown, the constant power to constant voltage control system for fully charging and discharging a flow battery in this application includes an operating parameter acquisition module, a switching timing determination module, and a charge / discharge control module.

[0082] The operating parameter acquisition module is used to collect real-time operating parameters of the flow battery, including stack terminal voltage, electrolyte temperature, single-cell voltage, and battery cycle count. The data sampling frequency of the operating parameter acquisition module can be set to once per second to ensure real-time parameter accuracy. Specifically, the operating parameter acquisition module may include voltage sensors, temperature sensors, and current sensors, which are respectively installed at both ends of the stack, in the electrolyte circulation pipeline, and in the charge / discharge circuit, to collect real-time data on stack terminal voltage, electrolyte temperature, and single-cell voltage; the battery cycle count is automatically accumulated and recorded by a counter built into the control module.

[0083] The switching timing determination module has a built-in preset dynamic threshold model, which receives data from the operating parameter acquisition module and calculates the critical voltage threshold and determines the switching timing in real time. Specifically, the switching timing determination module can use a Siemens 1200 PLC as the core control unit and can be integrated into the Siemens 1200 PLC. The PLC receives sensor signals through an analog input module, has a built-in programmed dynamic threshold model, supports real-time calculation and logic determination of multiple parameters, has an operation cycle of ≤100ms, and receives data from the operating parameter acquisition module through a signal acquisition interface to calculate the critical voltage threshold and determine the switching timing in real time.

[0084] The charging and discharging control module has a built-in PID adjustment function block, which is used to obtain power control commands through PID algorithm after receiving the judgment result of the switching timing judgment module, so as to realize the smooth switching between constant power and constant voltage modes. In the constant voltage stage, the error between the real-time stack terminal voltage and the target voltage is used as the PID input to dynamically adjust the power output to stabilize the voltage. Specifically, the charging / discharging control module and the switching timing determination module are integrated into the Siemens 1200 PLC. This includes an analog input module (SM 1231 AI 8×13 bits), an Ethernet communication interface (supporting Modbus TCP protocol), and a built-in PID control function block (implemented through PLC programming). The PLC establishes a communication connection with the PCS (energy storage converter) via the Modbus TCP communication protocol, with the communication baud rate set to 100Mbps. Power control commands are issued through a preset register address, while the PLC simultaneously reads the PCS's operating status feedback in real time. The number of cycles is automatically accumulated by an internal counter within the PLC. After receiving the switching determination result, the PLC calculates the power control command using a PID algorithm and sends it to the PCS in Modbus TCP standard message format, achieving smooth switching between constant power and constant voltage modes. During the constant voltage phase, the error between the real-time stack terminal voltage and the target voltage is used as the PID input to dynamically adjust the PCS power output to stabilize the voltage.

[0085] Through the above scheme, the operating parameter acquisition module collects the stack terminal voltage, electrolyte temperature, single cell voltage, and battery cycle count in real time, providing data support for dynamically calculating the critical voltage threshold. The switching timing determination module, combined with the data from the operating parameter acquisition module, uses a built-in dynamic threshold model to calculate the critical voltage threshold and determine the switching timing in real time, avoiding overcharging and over-discharging, and extending battery cycle life. Tests have shown that it can improve lifespan by more than 15%. The charge and discharge control module uses a PID regulation mechanism to control power output, achieving smooth switching between constant power and constant voltage modes. The voltage fluctuation amplitude during the constant voltage stage is reduced to within ±0.005V, and the stability at the end of the charge and discharge phase is significantly improved, ensuring precise full charging and discharging of the battery, and increasing the energy storage capacity utilization rate by 8%-10%. In addition, the modular design allows the system to be directly integrated into existing PCS equipment, reducing the transformation cost by 90%; industrial-grade reliability can be achieved through Siemens 1200 PLC, with an MTBF (Mean Time Between Failures) of over 50,000 hours; Modbus TCP communication can be used, with a measured communication latency of <50ms, meeting the millisecond-level response requirements of power frequency regulation, etc.

[0086] In some implementations, a safety protection module is also included. This module is used to perform threshold judgment by calling the fuel cell terminal voltage and electrolyte temperature data from the operating parameter acquisition module in real time. When parameters are detected to be out of control, a power reduction command is immediately sent. If the parameters do not return to normal within a preset time, a shutdown command is sent, and a local alarm signal is triggered simultaneously. Specifically, the safety protection module is integrated into the user program of the Siemens 1200 PLC in the form of a PLC user program. It has a built-in safety threshold parameter library and calls the fuel cell terminal voltage and electrolyte temperature data from the operating parameter acquisition module in real time to perform threshold judgment. When parameters are detected to be out of control (such as voltage exceeding the rated value by 5% or electrolyte temperature exceeding 55°C), a power reduction command (protection command) is immediately sent to the PCS via Modbus TCP communication. If the parameters do not return to normal within 10 seconds, a shutdown command is sent, and a local alarm signal is triggered (driving the PLC digital output terminal to alarm).

[0087] By using the above scheme, the stack terminal voltage and electrolyte temperature data of the operating parameter acquisition module are called in real time for threshold judgment. This can promptly detect situations where the voltage and electrolyte temperature exceed the standard. When the parameters exceed the standard, a power reduction command is sent immediately. If the parameters do not return to normal within a preset time, a shutdown command is sent and a local alarm signal is triggered. This can promptly avoid the risk of voltage and electrolyte temperature exceeding the standard and improve the safety of battery operation.

[0088] Based on the above-described constant power to constant voltage control system for fully charging and discharging a flow battery, the working process of this system will be further explained below.

[0089] Charging phase control process:

[0090] Step 1: Start charging the flow battery. The Siemens 1200 PLC initializes the charging and discharging parameters, sets the charging and discharging mode to constant power charging, reads the current status of the PCS through Modbus TCP communication, calls the PID function block to calculate the target value with the preset rated power, generates a power control instruction (data format is 32-bit floating point number) and sends it to the PCS, so that the PCS can stably output the rated charging power.

[0091] Step 2: The parameter acquisition module converts the acquired battery stack terminal voltage U1, electrolyte temperature T1, and charging current I1 into 4-20mA standard signals and transmits them to the Siemens 1200 PLC via the analog input module (Siemens SM 1231 AI module). The battery cycle count is automatically accumulated by the PLC's internal counter. All parameters are converted into actual physical quantities by the PLC program and then stored.

[0092] Step 3: Substitute the switching timing determination module into the dynamic threshold model to calculate the charging critical voltage threshold Ucharge-critical (model formula: Ucharge-critical = Urated-charge × (1 + 0.002 × (N1 / 1000) - 0.0015 × (Tliquid1 - 35)), where Urated-charge is the rated charging voltage, and 35℃ is the optimal operating electrolyte temperature for the flow battery).

[0093] Step 4: Compare the real-time stack terminal voltage U1 with U_charge. If U1 ≥ U_charge, the switching timing determination module sends a charging switching command to the charging and discharging control module.

[0094] Step 5: After receiving the switching judgment result, the Siemens 1200 PLC immediately calls the mode switching subroutine and sends the mode switching command to the PCS via Modbus TCP. At the same time, the target value of the PID function block is switched to U_charge_critical. The PLC collects the fuel cell terminal voltage U1 every 100ms, calculates the error between U_charge_critical and U_critical, and inputs it into the PID function block for calculation. The generated power adjustment command is sent to the PCS in real time via Modbus TCP, so that the fuel cell terminal voltage smoothly approaches and stabilizes at U_charge_critical at a rate of 0.01V / 30s, maintaining constant voltage charging.

[0095] Step Six: The Siemens 1200 PLC's internal safety protection program compares the values ​​of U1 with 1.05×U rated charge and T liquid 1 with 39℃ in real time. If an out-of-range condition is triggered, the PLC immediately sends a power reduction command to the PCS via Modbus TCP and starts a 10-second timer. During the timer, the parameters are continuously monitored. If the power returns to normal, the current power is maintained. If the power still exceeds the limit, a shutdown command is sent and an alarm signal is triggered at the PLC output.

[0096] Step 7: When the SOC calculated based on the charging current I1 reaches 100%, the battery is determined to be fully charged, the charge / discharge control module stops charging, and the charging process ends.

[0097] Discharge phase control process:

[0098] Step 1: Start the flow battery discharge. The Siemens 1200 PLC initializes the discharge parameters and sets it to constant power discharge mode. It establishes a connection with the PCS via Modbus TCP communication and confirms the status. It calls the PID function block to calculate the preset rated discharge power as the target value, generates a power control command and sends it to the PCS, so that the PCS can stably output the rated discharge power.

[0099] Step 2: The operation parameter acquisition module converts the stack terminal voltage U2, electrolyte temperature T2, and discharge current I2 into 4-20mA signals through the analog input module and transmits them to the Siemens 1200 PLC. The number of cycles calls the data from the PLC's internal counter, which is then converted by the program and used by the switching timing determination module.

[0100] Step 3: Substitute the switching timing determination module into the dynamic threshold model to calculate the discharge critical voltage threshold Udischarge critical (model formula: Udischarge critical = Urated discharge × (1 - 0.002 × (N2 / 1000) - 0.0015 × (Tliquid - 35)), where Urated discharge is the rated discharge voltage, and 35°C is the optimal operating electrolyte temperature for the flow battery).

[0101] Step 4: Compare the real-time stack terminal voltage U2 with U_discharge_proximity. If U2 ≤ U_discharge_proximity, the switching timing determination module sends a discharge switching command to the charge / discharge control module.

[0102] Step 5: After receiving the discharge switching command, the Siemens 1200 PLC sends a mode switching command to the PCS via Modbus TCP. The target value of the PID function block switching is Udischarge threshold. The PLC collects U2 every 100ms and calculates the error between it and Udischarge threshold. After PID calculation, it generates a power adjustment command and sends it to the PCS to make the stack terminal voltage smoothly approach and stabilize at Udischarge threshold at a rate of 0.01V / 30s, thus maintaining constant voltage discharge.

[0103] Step Six: The Siemens 1200 PLC safety protection program monitors the relationship between U2 and 0.95×U_rated discharge, and T_liquid2 and 39℃ in real time. If the over-limit condition is triggered, a power reduction command is immediately sent to the PCS via Modbus TCP. If the over-limit condition is not restored within 10 seconds, a shutdown command is sent, and the alarm indicator light on the PLC output terminal will light up.

[0104] Step 7: When the discharge SOC calculated based on the discharge current I2 reaches 0%, the battery is determined to be fully discharged, the charge and discharge control module stops discharging, and the discharge process ends.

[0105] Through the above solution, this application has at least the following effects:

[0106] 1. Dynamic switching timing: The critical threshold is accurately calculated by combining electrolyte temperature and cycle number to avoid overcharging and over-discharging, thus extending battery cycle life. Tests have shown that it can improve lifespan by more than 15%.

[0107] 2. The PCS power is controlled by a PID regulation mechanism, which enables smooth switching between charging and discharging modes. The voltage fluctuation amplitude during the constant voltage stage is reduced to within ±0.005V, and the stability at the end of the charging and discharging period is significantly improved, ensuring that the battery is accurately fully charged and discharged, and improving the energy storage capacity utilization rate by 8%-10%.

[0108] 3. Equipped with real-time safety protection, it can promptly avoid risks of voltage and electrolyte temperature exceeding limits, thereby improving battery operation safety;

[0109] 4. The Siemens 1200 PLC is used as the core control unit, with the mature Modbus TCP communication protocol. The communication delay is ≤50ms, the control response speed is fast, and it is suitable for the stability requirements of industrial energy storage scenarios. The system has strong versatility, does not require frequent manual adjustment of parameters, and does not require additional electrolyte concentration sensors, thus reducing system deployment costs.

[0110] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for achieving constant power to constant voltage control during the full charging and discharging of a flow battery, characterized in that, include: Real-time acquisition of flow battery operating parameters, including stack terminal voltage, electrolyte temperature, and battery cycle count; The critical voltage threshold is dynamically calculated based on the electrolyte temperature, battery cycle count, and rated voltage. Specifically, during the charging phase, Ucharge-critical = Urated-charge × (1 + K1 × (N1 / 1000) - K2 × (Tliquid1 - 35)); during the discharging phase, Udischarge-critical = Urated-discharge × (1 - K1 × (N2 / 1000) - K2 × (Tliquid2 - 35)); where Ucharge-critical is the critical voltage threshold during the charging phase, Urated-charge is the rated charging voltage, N1 is the battery cycle count during the charging phase, and Tliquid1 is the electrolyte temperature during the charging phase; Udischarge-critical is the critical voltage threshold during the discharging phase, Urated-discharge is the rated discharging voltage, N2 is the battery cycle count during the discharging phase, and Tliquid2 is the electrolyte temperature during the discharging phase; K1 and K2 are compensation coefficients. When the real-time stack terminal voltage reaches or exceeds the critical voltage threshold, the mode switches from constant power mode to constant voltage mode. In constant voltage mode, the power output is dynamically adjusted through a PID control mechanism to stabilize the stack terminal voltage at the critical voltage threshold.

2. The method for constant power to constant voltage control of a flow battery during full charging and discharging according to claim 1, characterized in that, The switching from constant power mode to constant voltage mode when the real-time stack terminal voltage reaches the critical voltage threshold specifically includes: If the real-time stack terminal voltage U1 ≥ U_charge during the charging phase, switch from constant power mode to constant voltage mode. If the real-time stack terminal voltage U2 ≤ U_discharge_critical during the discharge phase, switch from constant power mode to constant voltage mode.

3. The method for constant power to constant voltage control of a flow battery during full charging and discharging according to claim 2, characterized in that, In constant voltage mode, the power output is dynamically adjusted through a PID control mechanism to stabilize the fuel cell terminal voltage at the critical voltage threshold. This specifically includes: During the constant voltage mode of the charging phase, the PLC collects the stack terminal voltage U1 every certain period of time, calculates the error between U1 and U charging threshold, inputs the error into the PID function block for calculation, generates power adjustment command and sends it out, so that the stack terminal voltage smoothly approaches and stabilizes at U charging threshold at a preset rate. During the constant voltage mode of the discharge phase, the PLC collects the stack terminal voltage U2 every certain period of time, calculates the error between U2 and U discharge threshold, inputs the error into the PID function block for calculation, generates power adjustment instructions and sends them out, so that the stack terminal voltage smoothly approaches and stabilizes at U discharge threshold at a preset rate.

4. The method for constant power to constant voltage control of a flow battery during full charging and discharging according to any one of claims 1-3, characterized in that, Also includes: During the charging phase, the system monitors in real time whether the stack terminal voltage exceeds 105% of the rated charging voltage and whether the electrolyte temperature exceeds 39°C. If the voltage exceeds the limit, the power output is reduced. If the power output does not recover within a preset time, the system will shut down and alarm. During the discharge phase, the system monitors in real time whether the stack terminal voltage exceeds 95% of the rated discharge voltage and whether the electrolyte temperature exceeds 39°C. If these exceed the limits, the power output is reduced, and if the power output does not recover within a preset time, the system will shut down and alarm.

5. The method for constant power to constant voltage control of a flow battery during full charging and discharging according to any one of claims 1-3, characterized in that, When collecting the operating parameters of the flow battery in real time, the collected operating parameters also include the voltage of a single cell, and the state of charge (SOC) of the battery is calculated based on the voltage of a single cell. During the charging phase, when the SOC reaches 100%, the battery is determined to be fully charged, charging stops, and the charging process ends. During the discharge phase, when the discharge SOC reaches 0%, the battery is considered fully discharged, the discharge stops, and the discharge process ends.

6. A constant power to constant voltage control system for fully charging and discharging a flow battery, employing the constant power to constant voltage control method for fully charging and discharging a flow battery as described in any one of claims 1-5, characterized in that, It includes an operating parameter acquisition module, a switching timing determination module, and a charging / discharging control module; The operating parameter acquisition module is used to acquire the operating parameters of the flow battery in real time, including the stack terminal voltage, electrolyte temperature, single cell voltage, and battery cycle number. The switching timing determination module has a built-in preset dynamic threshold model, which is used to receive data from the operating parameter acquisition module and to calculate the critical voltage threshold and determine the switching timing in real time. The charging and discharging control module has a built-in PID adjustment function block, which is used to obtain power control commands through PID algorithm after receiving the judgment result of the switching timing judgment module, so as to realize the smooth switching between constant power and constant voltage modes. In the constant voltage stage, the error between the real-time stack terminal voltage and the target voltage is used as the PID input to dynamically adjust the power output to stabilize the voltage.

7. The constant power to constant voltage control system for realizing the full charging and discharging of a flow battery according to claim 6, characterized in that, It also includes a safety protection module, which is used to call the stack terminal voltage and electrolyte temperature data of the operating parameter acquisition module in real time to make threshold judgments; when the parameters are detected to be out of standard, a power reduction command is immediately sent; if the parameters do not return to normal within a preset time, a shutdown command is sent and a local alarm signal is triggered at the same time.

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