A method for balancing lithium iron phosphate battery pack and a battery balancing charging system

Abstract

A method for equalizing a lithium iron phosphate battery pack, wherein the battery pack performs battery equalization when the charger is inserted. Battery equalization includes two alternating operating states: equalization and equalization calculation. A battery equalization charging system includes a lithium iron phosphate battery pack, an input and output interface, an MCU module, an analog front-end module, an equalization circuit, a data communication module, and a charge and discharge MOS tube. The system is characterized in that when the battery pack is charged with specific message communication, the MCU module in the battery pack can determine that the battery has been charged in a safe state, and determine whether to equalize the battery based on the voltage value of each battery cell obtained from the analog front end. Long-term equalization can eliminate various inconsistencies generated by the battery itself and during use after the battery is grouped, gradually reduce and eliminate the voltage difference between battery cells, and ensure that the battery charge can be used stably for a long time.

Description

Technical Field

[0001] The patent of this invention belongs to the field of lithium iron phosphate battery management technology, and in particular relates to a balancing method for lithium iron phosphate batteries during use and a battery balancing charging system. Background Art

[0002] When using lithium batteries, the BMS system must protect the battery cells to prevent the battery cells from being damaged by overcharging or over-discharging during the charging or discharging process. The system has overvoltage, undervoltage and other protection functions.

[0003] A lithium battery pack is composed of multiple cells connected in series and in parallel. Due to the different self-discharge rates of the cells in each string and the electrochemical characteristics of the battery during use, the internal resistance of each string of cells will change, resulting in different capacities of each cell. This leads to a large voltage difference between the cells in series during long-term use, which reduces the charge and discharge capacity of the battery. When the battery is plugged in to the charger, it can be identified and judged so that the battery can be balanced for a long time, gradually eliminating various inconsistencies caused by the battery itself and during use after it is grouped, and gradually reducing and eliminating the voltage difference between battery cells, so that the battery can be used normally for a long time.

[0004] The general practice in the industry is to enable the balancing function of the BMS system when the cell voltage reaches a certain high-voltage threshold during battery charging. However, due to the characteristics of lithium iron phosphate batteries, the battery charge and discharge curve is not as smooth and uniform as that of ternary lithium batteries in idle conditions. This will cause the voltage growth rate to increase faster when the battery is charged to the high-voltage end, and the battery cannot be kept in a balanced state for a long time. The balancing function of the BMS system is turned on for a short time each time it is charged, which is not conducive to reducing the voltage difference of battery packs with large voltage differences. Therefore, it is difficult to trigger balancing or the balancing time is very short when using the common lithium battery balancing algorithm, and the battery balancing effect cannot be truly achieved.

[0005] Especially in the field of battery replacement, lithium iron phosphate batteries are heavily used, with high-power discharge and fast charging every day. Therefore, after half a year of use, the problem of battery imbalance will become extremely obvious. Therefore, it is necessary to design an algorithm specifically for the characteristics of lithium iron phosphate batteries to solve the lithium iron phosphate battery balance problem. Summary of the invention

[0006] The purpose of the present invention is to provide a lithium iron phosphate battery pack equalization method and a battery equalization charging system to address the defects of the prior art, so that the lithium iron phosphate battery can be balanced for a long time when the charger is plugged in, thereby increasing the equalization efficiency of the lithium iron phosphate battery and improving the life of the lithium iron phosphate battery.

[0007] In order to achieve the above object, the present invention adopts the following technical scheme:

[0008] A method for balancing a lithium iron phosphate battery pack, characterized in that the lithium iron phosphate battery pack performs battery balancing when a charger is inserted.

[0009] It is further characterized in that: the battery balancing includes two alternating operating states of balancing in progress and balancing calculation;

[0010] In the balancing calculation state, the voltage and current are sampled and calculated, and the balancing time is configured; the unit cells to be balanced are calculated, the required balancing unit cells are configured, and a timer is started; after the timer expires, the balancing state is switched to;

[0011] In the balancing process state, the balancing circuit performs battery balancing on the unit cells according to the configured balancing time and strategy; at the same time, the balancing calculation time is configured, and the balancing calculation state is entered after the battery balancing time expires.

[0012] Further: the battery balancing needs to meet the following four conditions at the same time;

[0013] a. The battery pack is in a normal state without any faults;

[0014] b. The lowest cell voltage of the battery pack is greater than Vbmin and the highest cell voltage is less than Vbmax for a period of t1; Vbmin is the lowest cell voltage threshold of the battery pack, and Vbmax is the highest cell voltage threshold of the battery pack;

[0015] c. The maximum voltage difference of the battery pack cells is greater than Vdiff and lasts for t2 time; Vdiff is the voltage difference threshold of the battery pack cells entering the balanced state, and t2 is the voltage difference stabilization time;

[0016] d. The battery pack communicates with the communication interface for a period of t3, where t3 is the duration of the communication.

[0017] Further: the battery balancing exit meets any of the following conditions:

[0018] (1) The communication interface is disconnected for more than the set time t4;

[0019] (2) The maximum cell voltage difference of the battery pack is less than Vdiff2, where Vdiff2 is the cell voltage difference threshold for the battery pack to exit the balanced state;

[0020] (3) Discharge current is detected or load connection is detected;

[0021] (4) Detection of abnormal protection such as over-current, over-voltage, over-temperature, etc.

[0022] (5) Check that the lowest cell voltage is less than Vbmin or the highest cell voltage is greater than Vbmax for a period of time t1;

[0023] (6) It is checked that the battery balancing lasts for t5; t5 is the battery balancing duration.

[0024] A battery equalization charging system based on the equalization method of the lithium iron phosphate battery pack, characterized in that it includes a lithium iron phosphate battery pack, an MCU module, an analog front-end module, an equalization circuit, a data communication module, a charge and discharge MOS tube, and an input and output interface;

[0025] The lithium iron phosphate battery pack is composed of a plurality of lithium iron phosphate unit cells;

[0026] The analog front-end module is connected to the input-output interface, detects the type of connected load, and transmits it to the MCU module; collects the state parameter information of the battery pack, and transmits it to the MCU module; and sends a control signal according to the instruction of the MCU module to control the operation of the charging and discharging MOS tube; sends a control signal according to the instruction of the MCU module to control the operation of the balancing circuit;

[0027] The input and output interface is used to connect to the load and communicate with the data communication module;

[0028] The charging and discharging MOS tube is used to control the charging and discharging of the lithium iron phosphate battery pack;

[0029] The data communication module is used to communicate with the load and transmit the charge and discharge information to the MCU module;

[0030] The balancing circuit is used to balance multiple lithium iron phosphate unit cells according to the control signal;

[0031] The MCU module is used to determine the charge and discharge status and issue charge and discharge instructions for the battery pack based on the connected load information of the battery pack received; and to comprehensively determine whether the battery pack's balancing is turned on or off based on the battery pack's unit cell voltage difference, charge and discharge status, and data communication module status.

[0032] Its further characteristics are: the load includes power load and charging load; the charging and discharging state includes charging state, discharging state and no-load state.

[0033] The battery equalization charging system enters the equalization judgment step including the following steps:

[0034] Step 1: The analog front-end module collects the real-time status parameter information of the battery pack and feeds it back to the MCU module. The MCU module determines that the battery pack is charging and has no faults, and then proceeds to step 2; if the battery pack is in a faulty or non-charging state, the judgment ends;

[0035] Step 2: The MCU module determines through the data communication module whether the battery pack is charged in a balanced environment. If the battery pack is in a balanced environment, the following step 3 is continued; if the battery pack is not in a balanced environment, the determination is terminated.

[0036] Step 3: The MCU module determines whether the voltage state of the battery pack meets the equalization entry condition according to the voltage value of each unit cell of the battery pack fed back by the analog front-end module. If it is determined that the battery pack voltage meets the equalization entry condition, step 4 is continued; if the voltage of each unit cell of the battery pack does not meet the equalization condition, the judgment is terminated;

[0037] Step 4: The MCU module determines whether the voltage difference meets the equalization entry condition according to the maximum voltage difference value of the battery pack fed back by the analog front-end module. If it is determined that the voltage difference of the unit battery cell meets the condition, the following step 5 is continued; if the voltage difference of the unit battery cell does not meet the equalization entry condition, the judgment is terminated;

[0038] Step 5: The MCU module determines that the battery pack has entered a balanced state, and commands the analog front-end module to turn on the balanced switch of the unit cell that needs to be balanced.

[0039] Further: after judging the equalization entry, the battery pack is first set to the equalization calculation state, and after reaching the equalization calculation state duration, it is converted to the equalization progress state; when the battery pack is in the equalization progress state, the corresponding equalization progress state is judged, and after reaching the set equalization progress state time without exiting the equalization, it enters the equalization calculation state again.

[0040] The equilibrium calculation state includes the following steps:

[0041] The MCU module processes and calculates the battery pack status parameter information collected by the analog front-end module in real time, and determines whether the battery pack has reached the balance exit condition by combining the data communication module online.

[0042] If the equilibrium exit condition is not met, voltage sampling is performed;

[0043] Calculate the cells that need to be balanced;

[0044] Configure the unit cells that need to be balanced;

[0045] Configure the balancing state time.

[0046] The equilibrium process includes the following steps:

[0047] The MCU module determines whether the battery pack has reached the balancing exit condition based on the collected fault information and the data communication module information;

[0048] If the balancing exit condition is not met, configure the balancing calculation state time and perform battery balancing normally.

[0049] The above-mentioned data communication module includes but is not limited to RS485 communication module, CAN communication module, UART communication module, one-line communication module, etc., preferably RS485 communication module.

[0050] Advantages of the present invention:

[0051] 1. When the battery pack is in the battery swap cabinet, it can be continuously balanced during the entire charging process to improve the balancing efficiency.

[0052] 2. Effectively reduce the voltage difference between unit cells.

[0053] 3. Using specific data communication instructions as the judgment for entering the balance function can effectively prevent the balance function from being turned on by mistake.

[0054] 4. Battery balancing can automatically and freely configure the balancing time ratio and control the balancing rate.

[0055] 5. Effectively improve the service life of the battery pack. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] FIG1 is a block diagram of the battery equalization charging system of the present invention.

[0057] FIG. 2 is a flow chart of the present invention entering into the balance judgment process.

[0058] FIG. 3 is a flow chart of the determination in battery balancing of the present invention.

[0059] FIG. 4 is a flow chart of the balanced calculation state judgment of the present invention.

[0060] FIG. 5 is a flow chart of the state determination of the equalization of the present invention. DETAILED DESCRIPTION

[0061] like Figure 1 As shown, a battery balancing charging system includes a lithium iron phosphate battery pack, an MCU module, an analog front-end module, a balancing circuit, an RS485 communication module, a charging and discharging MOS tube, and an input and output interface.

[0062] The lithium iron phosphate battery pack is composed of multiple lithium iron phosphate unit cells.

[0063] The analog front-end module is connected to the input and output interface. When the battery pack is connected to an external load, the analog front-end module outputs high and low potentials to one end of the input and output interface, and transmits the feedback potential signal to the MCU module; the MCU module determines whether the battery pack is in a discharge state or a charge state based on the potential signal. The state parameter information of the battery pack is collected and transmitted to the MCU module; and a control signal is issued according to the instruction of the MCU module to control the operation of the charge and discharge MOS tube; a control signal is issued according to the instruction of the MCU module to control the operation of the balancing circuit.

[0064] The input and output interface is used to connect the power load or charging load and communicate with the RS485 communication module.

[0065] The charging and discharging MOS tube is used to control the charging and discharging of the lithium iron phosphate battery pack.

[0066] The RS485 communication module is used to communicate with the load and transmit the charge and discharge information to the MCU module.

[0067] The balancing circuit is used to balance multiple lithium iron phosphate battery cells according to a control signal.

[0068] The MCU module is used to determine whether the battery pack is in a charging state, a discharging state, or an unloaded state according to the connected load information of the battery pack, and issue a charge and discharge instruction for the battery pack. The battery pack's equalization is turned on or off based on the battery pack's cell voltage difference, charge and discharge state, and RS485 communication module status.

[0069] A method for balancing a lithium iron phosphate battery pack, wherein the lithium iron phosphate battery pack performs battery balancing when a charger is inserted.

[0070] The following four conditions must be met at the same time for battery balancing to be enabled:

[0071] a. The battery pack is in a normal state without any faults;

[0072] b. The lowest cell voltage of the battery pack is greater than Vbmin and the highest cell voltage is less than Vbmax for a period of t1; Vbmin is the lowest cell voltage threshold of the battery pack, and Vbmax is the highest cell voltage threshold of the battery pack;

[0073] c. The maximum voltage difference of the battery pack cells is greater than Vdiff and lasts for t2 time; Vdiff is the voltage difference threshold of the battery pack cells entering the balanced state, and t2 is the voltage difference stabilization time;

[0074] d. The battery pack communicates with the communication interface for a period of t3, where t3 is the duration of the communication.

[0075] The battery balancing exits when any of the following conditions are met:

[0076] (1) The communication interface is disconnected for more than the set time t4;

[0077] (2) The maximum cell voltage difference of the battery pack is less than Vdiff2, where Vdiff2 is the cell voltage difference threshold for the battery pack to exit the balanced state;

[0078] (3) Discharge current is detected or load connection is detected;

[0079] (4) Detection of abnormal protection such as over-current, over-voltage, over-temperature, etc.

[0080] (5) Check that the lowest cell voltage is less than Vbmin or the highest cell voltage is greater than Vbmax for a period of time t1;

[0081] (6) It is checked that the battery balancing lasts for t5; t5 is the battery balancing duration.

[0082] like Figure 2 As shown, the battery equalization charging system enters the equalization judgment including the following steps:

[0083] Step 1: The analog front-end module collects the real-time status parameter information of the battery pack and feeds it back to the MCU module. The MCU module determines that the battery pack is charging and has no faults, and then proceeds to step 2; if the battery pack is in a faulty or non-charging state, the judgment ends.

[0084] Step 2: The MCU module determines through the RS485 communication module whether the battery pack is charged in a balanced environment. If the battery pack is in a balanced environment, the following step 3 is continued; if the battery pack is not in a balanced environment, the judgment is terminated.

[0085] Step 3: The MCU module determines whether the voltage state of the battery pack meets the balancing entry condition according to the voltage value of each unit cell of the battery pack fed back by the analog front-end module. If it is determined that the battery pack voltage meets the balancing entry condition, step 4 is continued; if the voltage of each unit cell of the battery pack does not meet the balancing condition, the judgment is terminated.

[0086] Step 4: The MCU module determines whether the pressure difference meets the equalization entry condition according to the maximum pressure difference value of the battery pack fed back by the analog front-end module. If it is determined that the cell pressure difference meets the condition, the following step 5 is continued; if the cell pressure difference does not meet the equalization entry condition, the judgment is terminated.

[0087] Step 5: The MCU module determines that the battery pack has entered a balanced state, and commands the analog front-end module to turn on the balanced switch of the unit cell that needs to be balanced.

[0088] like Figure 3 As shown, battery balancing includes two alternating operating states: balancing state S1 and balancing calculation state S2. After the battery balancing charging system determines that it has entered the battery balancing state, it first enters the balancing calculation state S2.

[0089] In the balancing calculation state S2, the voltage and current are sampled and calculated, and the balancing time is configured; the unit cells to be balanced are calculated, the required balancing unit cells are configured, and the timer is started; after the timer expires, it switches to the balancing state S1.

[0090] In the balancing state S1, the balancing circuit performs battery balancing on the unit cells according to the configured balancing time and strategy; at the same time, the balancing calculation time is configured, and the balancing calculation state is entered after the battery balancing time expires.

[0091] like Figure 4 As shown, the equilibrium calculation state S2 includes the following steps:

[0092] The MCU module processes and calculates the battery pack status parameter information collected by the analog front-end module in real time, and determines whether the battery pack has reached the balance exit condition by combining the RS485 communication module online.

[0093] If the equilibrium exit condition is not met, voltage sampling is performed;

[0094] Calculate the cells that need to be balanced;

[0095] Configure the unit cells that need to be balanced;

[0096] Configure the balancing state time ts1.

[0097] like Figure 5 As shown, the balancing process state S1 includes the following steps:

[0098] The MCU module determines whether the battery pack has reached the balancing exit condition based on the collected fault information and RS485 communication module information;

[0099] If the balancing exit condition is not met, configure the balancing calculation state time ts2 and perform battery balancing normally.

Claims

1. A method for equalizing a lithium iron phosphate battery pack, characterized in that: The lithium iron phosphate battery pack performs battery balancing when the charger is inserted; The battery balancing includes two alternating operating states: balancing in progress and balancing calculation; In the balanced calculation state, sampling and calculating the voltage and current are performed, and the balanced time is configured; And calculate the unit cells that need to be balanced, configure the required balanced unit cells, and start the timer; after the timer expires, switch to the balancing state; When the balancing is in progress, the balancing circuit performs battery balancing on the unit cells according to the configured balancing time and strategy; and at the same time, the balancing calculation time is configured, and the balancing calculation state is entered after the battery balancing time expires; The battery balancing activation needs to meet the following four conditions at the same time: a. The battery pack is in a normal state without any faults; b. The lowest cell voltage of the battery pack is greater than Vbmin and the highest cell voltage is less than Vbmax for a period of t1; Vbmin is the threshold value of the lowest cell voltage of the battery pack, Vbmax is the threshold value of the highest cell voltage of the battery pack, and t1 is the voltage stabilization time; c. The maximum voltage difference of the battery pack cells is greater than Vdiff and lasts for t2 time; Vdiff is the voltage difference threshold of the battery pack cells entering the balanced state, and t2 is the voltage difference stabilization time; d. The battery pack communicates with the communication interface for a period of t3, where t3 is the duration of the communication.

2. The equalization method for a lithium iron phosphate battery pack according to claim 1, characterized in that: The battery balancing exit meets any of the following conditions: (1) The communication interface is disconnected for more than the set time t4; (2) The maximum cell voltage difference of the battery pack is less than Vdiff2, where Vdiff2 is the cell voltage difference threshold for the battery pack to exit the balanced state; (3) Discharge current is detected or load connection is detected; (4) Detection of charging overcurrent, overvoltage, and overtemperature abnormal protection; (5) Check that the lowest cell voltage is less than Vbmin or the highest cell voltage is greater than Vbmax for a period of time t1; (6) It is checked that the battery balancing lasts for t5; t5 is the battery balancing duration.

3. A battery equalization charging system based on the equalization method of the lithium iron phosphate battery pack according to claim 1 or 2, characterized in that: Including lithium iron phosphate battery pack, MCU module, analog front-end module, equalization circuit, data communication module, charging and discharging MOS tube, input and output interface; The lithium iron phosphate battery pack is composed of a plurality of lithium iron phosphate unit cells; The analog front-end module is connected to the input-output interface, detects the type of connected load, and transmits it to the MCU module; collects the state parameter information of the battery pack, and transmits it to the MCU module; and sends a control signal according to the instruction of the MCU module to control the operation of the charging and discharging MOS tube; sends a control signal according to the instruction of the MCU module to control the operation of the balancing circuit; The input and output interface is used to connect to the load and communicate with the data communication module; The charging and discharging MOS tube is used to control the charging and discharging of the lithium iron phosphate battery pack; The data communication module is used to communicate with the load and transmit the charge and discharge information to the MCU module; The balancing circuit is used to balance multiple lithium iron phosphate unit cells according to the control signal; The MCU module is used to determine the charge and discharge status and issue charge and discharge instructions for the battery pack based on the connected load information of the battery pack received; and to comprehensively determine whether the battery pack's balancing is turned on or off based on the battery pack's unit cell voltage difference, charge and discharge status, and data communication module status.

4. The battery equalization charging system according to claim 3, wherein: The load includes power load and charging load; the charging and discharging state includes charging state, discharging state and no-load state.

5. The battery equalization charging system according to claim 3 or 4, characterized in that Entering equilibrium judgment includes the following steps: Step 1: The analog front-end module collects the real-time status parameter information of the battery pack and feeds it back to the MCU module. The MCU module determines that the battery pack is charging and has no faults, and then proceeds to step 2; if the battery pack is in a faulty or non-charging state, the judgment ends; Step 2: The MCU module determines through the data communication module whether the battery pack is charged in a balanced environment. If the battery pack is in a balanced environment, the following step 3 is continued; if the battery pack is not in a balanced environment, the determination is terminated. Step 3: The MCU module determines whether the voltage state of the battery pack meets the equalization entry condition according to the voltage value of each unit cell of the battery pack fed back by the analog front-end module. If it is determined that the battery pack voltage meets the equalization entry condition, step 4 is continued; if the voltage of each unit cell of the battery pack does not meet the equalization condition, the judgment is terminated; Step 4: The MCU module determines whether the voltage difference meets the equalization entry condition according to the maximum voltage difference value of the battery pack fed back by the analog front-end module. If it is determined that the voltage difference of the unit battery cell meets the condition, the following step 5 is continued; if the voltage difference of the unit battery cell does not meet the equalization entry condition, the judgment is terminated; Step 5: The MCU module determines that the battery pack has entered a balanced state, and commands the analog front-end module to turn on the balanced switch of the unit cell that needs to be balanced.

6. The battery equalization charging system according to claim 5, wherein: After judging that balancing has been entered, the battery pack is first set to a balancing calculation state, and after reaching the duration of the balancing calculation state, it is converted to a balancing in progress state; when the battery pack is in the balancing in progress state, the corresponding balancing in progress state judgment is performed, and after reaching the set balancing in progress state time without exiting balancing, it enters the balancing calculation state again.

7. The battery equalization charging system as claimed in claim 6, characterized in that The equilibrium calculation state includes the following steps: The MCU module processes and calculates the battery pack status parameter information collected by the analog front-end module in real time, and determines whether the battery pack has reached the balance exit condition by combining the data communication module online. If the equilibrium exit condition is not met, voltage sampling is performed; Calculate the cells that need to be balanced; Configure the unit cells that need to be balanced; Configure the balancing state time.

8. The battery equalization charging system as claimed in claim 6, characterized in that The equilibrium process includes the following steps: The MCU module determines whether the battery pack has reached the balancing exit condition based on the collected fault information and the data communication module information; If the balancing exit condition is not met, configure the balancing calculation state time and perform battery balancing normally.

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