A pwm charge-discharge control strategy based on dynamic reconfigurable battery energy storage system

Abstract

Based on the energy digitization of dynamic reconfigurable battery energy storage technology, the application paradigm of fixed series-parallel connection since the invention of battery is changed, the physical connection between batteries is changed from traditional fixed series-parallel rigid connection to program-controlled flexible connection, and better balance control effect is realized by controlling the time of each battery access to the charge-discharge circuit. The application proposes a PWM charge-discharge control strategy under certain conditions for the dynamic reconfigurable battery energy storage system, and by applying the duty cycle signal to the non-conducting battery monomer, the output power instruction and the balance effect are well balanced. At the same time, compared with the traditional balance control strategy, the balance speed of the improved strategy is also improved, which greatly improves the safety and energy efficiency of the battery energy storage system, and provides a new balance control idea for building large-scale long-life low-cost battery energy storage system.

Description

Technical Field

[0001] This invention relates to the field of equalization control of battery energy storage systems, and in particular to an equalization control strategy under high overload operating conditions. Background Technology

[0002] With the rapid development of electrochemical energy storage, the inherent safety issues of energy storage systems are becoming increasingly prominent. Energy storage battery systems are often composed of several battery modules connected in series and parallel. However, even cells of the same specification and model naturally differ in parameters such as voltage, state of charge, capacity, internal resistance, lifespan, and self-discharge rate. These subtle differences are amplified after being assembled into battery modules, resulting in a high degree of discreteness in the entire battery system. In an energy storage system, the charging and discharging current received by modules connected in series is consistent. However, due to the discreteness, the capacity of each battery module differs, and the charging and discharging capacity of the entire battery system depends on the smallest single cell, thus creating the "weakest link" effect.

[0003] During charging and discharging, the smaller capacity battery module reaches the charge / discharge depth threshold first, limiting the charging and discharging capabilities of other batteries in the battery system. If the battery system cannot be fully charged or discharged for an extended period, it will lose some capacity, causing irreversible damage to the battery system's capacity. This results in inaccurate State of Charge (SOC), decreased depth of discharge, and reduced operating efficiency. Over long periods of operation, the polarization between battery sizes becomes increasingly severe, further reducing the usable capacity of the battery system and leading to issues related to safety and economics. Therefore, battery balancing technology is of paramount importance.

[0004] In recent years, digital energy storage systems based on dynamically reconfigurable battery networks have attracted widespread attention. Dynamically reconfigurable battery networks deeply couple low-power semiconductor devices with the battery, transforming the battery from an electrochemical reaction device into a novel digital device. Through millisecond-level reconfiguration of the battery's physical connection topology, they fundamentally eliminate heat accumulation and thermal runaway problems caused by overcharging and over-discharging, achieving intrinsic safety at the battery system level. Furthermore, dynamically reconfigurable battery networks can quickly diagnose and disconnect faulty batteries while maintaining the normal operation of electrochemical energy storage, greatly improving the system's availability and reliability.

[0005] Traditional digital energy storage balancing strategies employ a N-1 column battery capacity limit for charging and discharging, where N selects N-1 columns and M selects M-1 rows. However, when the power command exceeds the N-1 column battery capacity limit but falls below the N column battery capacity limit, all N columns are put into operation. In this case, the balancing strategy fails, and prolonged operation negatively impacts the lifespan of individual battery cells. Summary of the Invention

[0006] To address the aforementioned problems, this invention improves upon traditional methods by employing PWM charge / discharge control. PWM charge / discharge control divides each delay interval into smaller time scales. When the power command exceeds the capacity limit of N-1 rows of batteries but does not reach the capacity of N rows, the duty cycle of each cell in the non-conducting row is calculated by dividing the excess power into the capacity of a single string. This duty cycle is then used to control the power electronic switches of the non-conducting cells in the non-conducting row. Compared to conventional two-dimensional balancing strategies in digital energy storage, this improved strategy is more suitable for high overload conditions, increases battery utilization, extends battery life, and reduces energy storage costs.

[0007] This invention proposes a PWM charge-discharge control strategy based on a dynamically reconfigurable battery energy storage system. Its key feature is the ability to rapidly achieve energy balance within the storage system while providing high overload power. The strategy mainly includes the following steps:

[0008] 1) Establish a circuit topology model for a dynamically reconfigurable battery energy storage system. This mainly includes establishing an N-parallel M-string battery network topology based on lithium iron phosphate battery cells, and connecting a high-frequency power switch in series with each lithium iron phosphate battery cell. At the same time, every N parallel cells are connected in parallel with a bypass high-frequency power switch. The high-frequency power electronic switches here are all selected as MOSFET devices.

[0009] 2) Monitor and collect various electrical parameters of the energy storage system, including the state of charge (SOC) of each battery cell, the output voltage and current of the energy storage system, and external power commands.

[0010] 3) Establish a traditional digital energy storage equalization control model for a dynamically reconfigurable battery energy storage system. Input the obtained SOC data of each battery cell and the external power command into the control module. Based on the SOC data of each battery cell, the control module controls the switching on and off of MOSFETs to control the input and output of each battery cell, thereby dynamically reconfiguring the battery network and ultimately achieving SOC equalization of the entire energy storage system.

[0011] 4) Establish a bidirectional DC / DC converter control model and construct a current loop based on PID control.

[0012] 5) Constant power control is adopted for the bidirectional DC / DC converter. The external power command collected by monitoring is input into the control model of the bidirectional DC / DC converter. Different current commands are obtained based on different power commands. The energy storage system outputs current to track the current command through the PID current loop, thereby controlling the charging and discharging of the energy storage system.

[0013] 6) Improve the traditional SOC equalization control model by using PWM control of the high-frequency power electronic switch according to the external power command to realize PWM charging and discharging control. When the energy storage system is fully loaded, it operates in full power mode to ensure output power matching. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a flowchart illustrating the overall implementation of the method of the present invention;

[0016] Figure 2 This is a schematic diagram of an energy storage system.

[0017] Figure 3 A comparison chart of traditional series-parallel battery packs and digital energy storage battery packs;

[0018] Figure 4 Reconstructing the structure diagram of digital energy storage batteries;

[0019] Figure 5 This is a flowchart of the reconfigurable battery pack power monitoring and topology reconfiguration process;

[0020] Figure 6 Diagram of traditional digital energy storage balancing strategy;

[0021] Figure 7 Diagram of PWM charge / discharge control balancing strategy. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be described in conjunction with the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0023] Please see Figure 1 This invention proposes a PWM charge-discharge control strategy based on a dynamically reconfigurable battery energy storage system, comprising the following steps:

[0024] Step S10: Establish the circuit topology model of the dynamically reconfigurable battery energy storage system; Step S20: Monitor and collect various electrical parameters of the energy storage system, including the state of charge (SOC) of each battery cell, the system's output voltage and current, and external power commands; Step S30: Establish a traditional SOC equalization control model for the dynamically reconfigurable battery energy storage system; Step S40: Establish a bidirectional DC / DC converter control model; Step S50: Apply constant power control to the bidirectional DC / DC converter; Step S60: Improve the traditional SOC equalization control model to achieve PWM charge and discharge control.

[0025] Step S10 establishes the circuit topology model of the dynamically reconfigurable battery energy storage system, such as... Figure 2 As shown, it includes:

[0026] Step S101: Establish an N-parallel M-string battery network based on lithium iron phosphate battery cells; Step S102: Connect a high-frequency power switch in series with each lithium iron phosphate battery cell, and connect every N parallel cells in parallel with a bypass high-frequency power switch. The high-frequency power electronic switches here are all selected as MOSFET devices.

[0027] By introducing high-frequency power electronic switching devices, the information and energy of energy storage batteries can be "digitized," such as... Figure 3 As shown, due to the limitations of traditional series-parallel battery pack structures, when the capacity of a single battery cell exceeds its limit, the entire series-connected battery pack will shut down, severely reducing the reliability of the energy storage battery's power supply. Furthermore, the "weakest link" effect of the battery hinders the efficient utilization and economic recovery of energy and resources, leading to a series of problems related to efficiency, safety, reliability, lifespan, and economy. This invention proposes a new energy storage battery topology that uses high-frequency switching to "digitize" control signals. A control switch is added to each battery cell, enabling refined control of the control unit. Through precise capture, transmission, and execution of digital signals, precise control of the battery cell's capacity and independent charging and discharging are achieved.

[0028] In addition, such as Figure 4 As shown, the physical connections between individual cells can also be dynamically reconfigured through software and energy exchange backplanes based on the battery's own condition and external operating conditions, enhancing the adaptability and flexibility of the energy storage system to complex operating conditions.

[0029] Step S20 involves monitoring and collecting various electrical parameters of the energy storage system, including the state of charge (SOC) of each battery cell, the system's output voltage and current, and external power commands.

[0030] Battery power monitoring and topology reconfiguration are prerequisites for two-dimensional equilibrium in energy storage networks. The uneven power distribution among individual battery cells complicates the operational structure of large-scale battery networks. Therefore, achieving dynamic optimization of complex battery network topologies essentially involves monitoring battery power and controlling its deployment and deactivation. To achieve fine-grained and efficient management of individual battery cell power, it is necessary to monitor the characteristics and status of network nodes in real time, as well as the characteristics and performance of different network topologies composed of these nodes. This allows for topology reconfiguration and performance optimization of the battery energy storage system through battery power monitoring and deployment / deactivation logic.

[0031] Therefore, a battery information management system is needed to measure the charge, voltage, and temperature of each battery cell in real time through the battery energy exchange backplane, capture the battery cell charge information, and store it on the information management platform. Furthermore, the battery network controller on the information management platform can accurately estimate and predict the battery's health status and charge information online, providing a platform foundation for optimizing the battery network topology and subsequent two-dimensional balancing.

[0032] Step S30: Establish a traditional SOC equalization control model for a dynamically reconfigurable battery energy storage system.

[0033] The battery management system performs power monitoring and topology reconfiguration. The flowchart for power monitoring in an energy storage battery network is as follows: Figure 5 As shown, the battery power information management system captures individual battery cell power information in real time and stores it on the information management platform. Upper and lower limits for battery power are set at 20% and 80%, respectively. When the battery power falls below 20% or rises above 80%, the system shuts down to prevent the "bottleneck effect" from causing safety and reliability issues in the battery network. Cells with power levels between 20% and 80% are considered ideal, providing charging and discharging guarantees for subsequent load demands under different operating conditions.

[0034] When the battery charge falls below a threshold (i.e., a single battery cell's charge is below 20%), the information management platform reports the number of cells exceeding the limit. If only one cell is below the threshold, the power electronic switch digital logic controls that cell to exit operation, forming a new energy storage battery topology. When multiple cells are below the threshold, the information management platform collects charge data, and cells exit the topology sequentially in ascending order of charge level to prevent system crashes caused by simultaneous exits. When the battery charge exceeds a threshold (i.e., a single battery cell's charge is above 80%), the information management platform reports the number of cells exceeding the limit. If only one cell is above the threshold, the power electronic switch digital logic controls that cell to exit operation, forming a new energy storage battery topology. When multiple cells are above the threshold, the information management platform collects charge data, and cells exit the topology sequentially in descending order of charge level.

[0035] Once all batteries outside the threshold have exited, the battery information management platform begins monitoring the battery charge under the latest battery topology. It then uses historical charge data and current charge information to make short-term predictions of battery charge levels, assessing any short-term changes in the energy storage topology. When all battery charges are within the threshold, a 2-second delay is set. If the monitored charge information remains within the ideal range within 2 seconds, the topology reconstruction is complete, and two-dimensional battery charge balancing control begins. If a battery charge exceeds the threshold again within 2 seconds, the single-cell exit command is executed again, forming a new reconstructed topology.

[0036] For traditional digital energy storage balancing strategies, such as Figure 6 As shown, when the power command does not exceed the total power of N columns of batteries, N-select-N-1 (column) and M-select-M-1 (row) charging and discharging control is executed. That is, during normal operation in the discharge state, based on the collected SOC data of each battery cell, the cell with the smallest SOC value among every N parallel battery cells is calculated and selected. The high-frequency power electronic switch of this cell is disconnected to isolate it from the network, thereby achieving column-level discharge balance. Then, the group of cells with the smallest sum of SOC among every N parallel cells is calculated and selected. The bypass power electronic switch of this group of battery cells is closed to isolate it from the network, thereby achieving row-level discharge balance. When the system is in charging mode, based on the collected SOC data of each battery cell, the cell with the largest SOC value among every N parallel battery cells is selected and isolated from the network by disconnecting its high-frequency power electronic switch, thereby achieving the purpose of charging state balancing. Then, the group of cells with the largest sum of SOC among every N parallel cells is selected and isolated from the network by closing the bypass power electronic switch of the group of battery cells, thereby achieving the purpose of row balancing.

[0037] When the power command exceeds the power limit of N-1 rows of batteries but does not reach the power of N rows of batteries, all N rows of batteries will be put into use. At this time, the traditional digital energy storage balancing strategy fails, resulting in a waste of energy storage system capacity and also adversely affecting the lifespan of individual battery cells.

[0038] In step S40, a bidirectional DC / DC converter control model is established, mainly consisting of a Buck-Boost bidirectional DC-DC converter. In step S50, constant power control is applied to the bidirectional DC / DC converter. The external power command collected by monitoring is input into the bidirectional DC / DC converter control model. Based on different power commands, different charging and discharging current commands are obtained, thereby controlling the energy storage system to be in a charging or discharging state.

[0039] In step S60, the traditional SOC equalization control model is improved to achieve PWM charge and discharge control, such as... Figure 7 As shown, it mainly includes:

[0040] When the power command exceeds the power limit of N-1 rows of batteries but does not reach the power of N rows of batteries, all N rows of batteries will be put into use. In this case, the traditional digital energy storage balancing strategy will fail. In order for the energy storage system to retain the balancing function under this condition, the existing control strategy needs to be improved.

[0041] At this point, the balancing strategy is as follows: when the energy storage system is in a discharging state, if the discharge power is less than the upper limit of the power of N-1 clusters of batteries, then the N-1 clusters of batteries with the larger capacity are discharged; if the discharge power is greater than the upper limit of the power of N clusters of batteries, then all N clusters of batteries are discharged; if the discharge power is greater than the upper limit of the power of N-1 clusters of batteries but less than the upper limit of the power of N clusters of batteries, then the battery cluster with the smallest capacity is subjected to PWM discharge. In this case, the duty cycle α of the PWM signal of the power electronic switch is represented by the ratio of the excess power to the power of a single cluster of batteries, i.e.

[0042]

[0043] Similarly, when the energy storage system is in a charging state, if the charging power is less than the upper limit of the power of the N-1 cluster battery strings, then the N-1 cluster battery strings with smaller capacity are charged; if the discharging power is greater than the upper limit of the power of the N cluster battery strings, then all N cluster battery strings are charged; if the charging power is greater than the upper limit of the power of the N-1 cluster battery strings but less than the upper limit of the power of the N cluster battery strings, then the battery string with the largest capacity is charged by PWM. At this time, the duty cycle α of the PWM signal of the power electronic switch is also represented by the ratio of the power excess to the power of a single cluster battery string.

[0044] In summary, employing a PWM charge / discharge control strategy in a dynamically reconfigurable battery energy storage system improves battery utilization, effectively compensates for differences between individual battery cells, achieves balanced charge levels, and significantly extends battery life. Since this strategy does not require additional equipment, it offers a cost advantage in terms of construction, thereby reducing the overall construction cost of the energy storage system.

[0045] The aforementioned PWM charge-discharge control strategy based on a dynamically reconfigurable battery energy storage system can be implemented and has broad application prospects.

[0046] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A PWM charge / discharge control method based on a dynamically reconfigurable battery energy storage system, characterized in that... The system can quickly achieve power balancing in an energy storage system while providing high overload power, including the following steps: Step S10: Establish the circuit topology model of the dynamically reconfigurable battery energy storage system; Step S20: Monitor and collect various electrical parameters of the energy storage system, including the state of charge (SOC) of each battery cell, the system's output voltage and current, and external power commands. Step S30: Establish a traditional SOC equalization control model for a dynamically reconfigurable battery energy storage system; Step S40: Establish a bidirectional DC / DC converter control model; Step S50: Constant power control is applied to the bidirectional DC / DC converter; Step S60: Improve the traditional SOC equalization control model to achieve PWM charge and discharge control; Step S10 includes: Step S101: Establish an N-parallel M-string battery network based on lithium iron phosphate battery cells; Step S102 involves connecting a high-frequency power electronic switch in series with each lithium iron phosphate battery cell, and connecting every N parallel cells in parallel with a bypass high-frequency power electronic switch. The high-frequency power electronic switches here are all MOSFET devices. Step S60 includes: Step S601: When the power command exceeds the output power of the N-1 column of batteries, PWM control is applied to the high-frequency power electronic switch to increase the output power of the energy storage system. Step S602: After full load, operate in full power mode to ensure that the output power matches the power command; At this point, the balancing strategy is as follows: when the energy storage system is in a discharging state, if the discharge power is less than the upper limit of the power of N-1 clusters of battery strings, then the N-1 clusters of battery strings with the larger capacity are discharged; if the discharge power is greater than the upper limit of the power of N clusters of battery strings, then all N clusters of battery strings are discharged; if the discharge power is greater than the upper limit of the power of N-1 clusters of battery strings but less than the upper limit of the power of N clusters of battery strings, then the battery string with the smallest capacity is discharged via PWM. In this case, the duty cycle α of the PWM signal of the power electronic switch is represented by the ratio of the excess power to the power of a single cluster of battery strings, i.e.: 。 2. The method according to claim 1, characterized in that, Step S20 includes: Step S201: Monitor and collect the SOC of the lithium iron phosphate battery cell; Step S202: Monitor and collect the output voltage and current of the dynamically reconfigurable battery energy storage system; Step S203: Monitor and collect external power commands.

3. The method according to claim 1, characterized in that, Step S30 includes: Step S301: Input the SOC data of each battery cell obtained in step S20 and the external power command into the control module. Step S302: Based on the above data, the switching on and off of MOSFETs is controlled to control the input and output of each battery cell, thereby realizing dynamic reconfiguration of the battery network.

4. The method according to claim 1, characterized in that, Step S40 includes: Step S401: Establish a current loop based on PID control.

5. The method according to claim 1, characterized in that, Step S50 includes: Step S501: Input the monitored and collected external power command into the bidirectional DC / DC converter control model, and obtain different current commands based on different power commands; Step S502: Control the charging and discharging of the energy storage system according to different current commands.

6. The PWM charge / discharge control method based on a dynamically reconfigurable battery energy storage system according to claim 1, characterized in that, The hardware structure of the battery energy storage system is mainly divided into the main circuit and the control program. The main circuit consists of a dynamically reconfigurable battery energy storage system and a bidirectional DC / DC converter.

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