Analysis of balanced charging method for power lithium ion battery pack

ଲେଖକ: ଆଇଫ୍ଲୋପାୱାର - Furnizor centrală portabilă

Common balanced charging technologies include constant shunt resistance equalization, disconnect shunt resistance equalization, average battery voltage equalization charging, switching capacitance equalization charging, step-down converter equalization charging, inductance equalization charging, etc. When the lithium ion battery in group is charged in series, it should ensure that each battery is balanced, otherwise it will affect the performance and life of the whole set of batteries during use. The existing single-cell lithium-ion battery protective chip does not contain equalization charging control functions, multi-segment lithium-ion battery protective chip equalization charging control functions to be external CPU; through serial communication (such as I2C bus) by protective chips, Increased the complexity and design difficulty of protection circuits, reducing the efficiency and reliability of the system, adding power consumption.

In this paper, for the use of power lithium-ion batteries, each lithium-ion battery requires charging overvoltage, discharge under voltage, overcurrent, short circuit protection, and the problem of balance charging of the whole group during charging, introduces a use Design method of battery pack protective panels containing equalized charging function on arbitrary series of lithium-ion battery protective chips. Simulation results and industrial production application have proven that the protective board has perfect, stable work, high cost performance, and balanced charging error less than 50mV. 1 Lithium ion battery pack protective plate equilibrium charge principle wherein: 1 is a single lithium ion battery; 2 is a charge overvoltage shunt discharge branch resistance; 3 is a shunt discharge branch control switch device; 4 is overcurrent detection protection resistance 5 is omitted lithium ion battery protection chip and circuit connecting portion; 6 is a single lithium ion battery protection chip (generally including charging control pin CO, discharge control pin DO, discharge overcurrent, short-circuit detection pin VM, battery Positive VDD, battery negative VSS, etc.

); 7 is a MOS pipe gate for charging control in the main circuit after the charging overvoltage protection signal is formed by photocoupless relationship to the main circuit; 8 is a discharge under voltage, overcurrent, and short-circuit protection signal After the optical coupling is separated, the electrically conductive MOS pipe gate is formed in the main circuit of the main circuit; 9 is a charging control switch device; 10 is a discharge control switch device; 11 is a control circuit; 12 is a primary circuit; 13 is a shunt discharge branch. The number of single lithium-ion battery protective chips determines according to the number of cells of the lithium ion battery pack, in series, respectively, respectively, protects and discharge, overcurrent, and short-circuit state of the single-cell lithium ion battery, respectively. While charging protection, the system is charged by protective chip control shunt discharge branch switching device, which is different from which the conventional method of achieving equalization charging in the charger end, reducing lithium ion battery pack charger.

Design application cost. 2 Hardware Design 2.1 Charging circuit When charging the lithium ion battery group, the external power supply positive and negative electrode is connected to the battery pack, and the charging current flows through the battery pack positive BAT +, the battery pack single-cell lithium-ion battery.

1 ~ N, discharge control switching device, charging control switch device, battery pack negative BAT-, current flow to Figure 2. In the system, the charging overvoltage protection signal of a single lithium ion battery protective chip is used in parallel, and the gate voltage of the charging switch device in the primary circuit is mainly used; such as a certain or several lithium The ion battery enters the overvoltage protection state during the charging process, and the overvoltage protection signal is discharged in parallel discharge branches in parallel in the positive and negative electrode of the single-cell lithium ion battery, and the corresponding monomer is connected in series in the charging circuit. Lithium-ion battery breaks the charging circuit.

2.2 Main circuit and shunt discharge branch lithium ion battery pack series charge, ignore the influence of single battery capacity differences, generally charged the battery. At this time, the corresponding overvoltage protection signal is controlled by the switching device of the shunt discharge branch, and one shunt resistor is connected in parallel at both ends of the original battery.

Depending on the PNGV equivalent circuit model of the battery, the diversion branch resistance is equivalent to the load of the first one-piece lithium ion battery, which is discharged, so that the battery end voltage is maintained in a very small range near the state. Assuming that the 1st, the lithium-ion battery is charged first, enter the overvoltage protection state, then the main circuit and the current flowing branch are flowed towards Figure 3. When all single cells are charged into the overvoltage protection state, all single lithium ion battery voltages are completely equal in the error range, and the control signals of each section protection chip are lowered and cannot be a charging control switch in the main circuit.

The device supply gate bias makes it turned off, the main circuit is disconnected, that is, the power-over charging, the charging process is completed. The discharge branch resistance between the two ends of the single-section battery can be calculated from the charging voltage size of the lithium ion battery charger and the size of the lithium ion battery and the magnitude of the discharge current. Balanced current should be reasonable, if it is too small, the equalization effect is not obvious; if it is too large, the energy loss of the system is large, the equalization efficiency is low, and the heat management requirements of the lithium ion battery are high, and the general current can be designed between 50 and 100 mA.

2.3 Discharge Circuit When the battery pack is discharged, the external load separates the battery pack positive and negatives BAT + and BAT-both ends, and the discharge current flows through the battery pack negative BAT-, charging control switching device, discharge control switching device, battery pack in units Lithium ion batteries N ~ 1 and battery pack positive bats, current flow to Figure 4. The discharge underrupted electrical protection, overcurrent and short-circuit protection control signals of the single-cell lithium ion battery protective chip are connected in series after the optical coupling, and the power supply gate voltage of the discharge switch device in the main circuit; once the battery The group encounters special circumstances such as an undervoltage or overcurrent and short circuit such as a single lithium ion battery during the discharge, and the corresponding single-cell lithium ion battery discharge protection control signal is low, and the gate is not supplied to the discharge control switch device in the main circuit.

The bias makes it shut down, the main circuit is disconnected, that is, end the discharge process. Generally, the lithium-ion battery uses constant current-constant voltage (TAPER)-type charging control, constant voltage charging, the charging current approximation index law decreases. The switching device of the charge and discharge main circuit in the system can meet the maximum operating current and operating voltage selection requirements according to the external circuitry.

The single-cell lithium-ion battery protection chip of the control circuit can be selected according to the voltage level of the single-cell lithium ion battery to be protected. Distribution discharge branch resistance can be implemented with power resistance or resistance network. Here, the resistance network is used to realize the resistance of the shunt discharge branch.

It can effectively eliminate the effects of resistance deviation. In addition, it can reduce the use of thermal power consumption. 3 Equilibrium charging protection plate circuit simulation According to the basic principle of the above equilibrium charging protection plate circuit, the system simulation model is built in the MATLAB / SIMULINK environment, and the case of simulating the protection plate during charging and discharge process of lithium-ion battery is verified.

Feasibility. For the sake of simplicity, the simulation model of the lithium-ion battery pack is only connected in series from 2 lithium ion batteries, as shown in Figure 5. In the model, the controlled voltage source is replaced by a single lithium ion battery, and the simulation of battery charge is discharged.

In Fig. 5, RS is the battery headner of the series battery pack, and RL is a load resistor, and Rd is a shunt discharge branch resistance. The single lithium-ion battery protection chip S28241 is encapsulated into a subsystem, making the overall model when it is more concise.

Protective chip subsystem model Important use logic arithmetic module, symbol function module, one-dimensional check module, integration module, delay module, switch module, math operation module, etc. simulate timing and logic of protection. Since there is a certain difference between the simulation environment and the real circuit, do not filter and strong weak electrical isolation, and the extra modules can easily lead to the length of the simulation time.

Therefore, in the actual simulation process, the circuit is removed from filtering, optocoupler isolation, level conditioning and other circuits, and the resistance network designed for large current shunt is changed to a single resistance, and the complexity of the simulation system is reduced. When establishing a complete system simulation model, pay attention to the input and output data of different modules may have differences. It must correctly arrange the connection order of the module.

If necessary, the conversion of data types is necessary, and the voltage detection module is used in the model to realize a strong signal. Conversion connection problem. The given signal of the controlled voltage source in the simulation model can have a small difference in the premise of the waveform, to represent the difference in charging and discharging of the battery.

Figure 6 is a method of detecting a single battery voltage detection simulation in the battery pack, which can be seen using an overcurrent discharge circuit, which is working properly. 4 In practical applications of system experiments, two groups of 36V8A. H manganese acid lithium battery pack protection plates were designed for one group, 10 sections, which were designed for a single-piece and 10 series.

S28241 of Japan Seiko Company, the protective board is important by the main circuit, control circuit, shunt discharge branch, and filtered, optocoupler isolation and level conditioning circuits, and the basic structure is shown in Figure 7. The discharge branch current is selected from 800mA, and the 510 resistor string is connected in parallel. The debugging work is important to voltage testing and current test two parts.

Voltage tests include charging performance detecting overvoltage, basic charge, and discharge performance detection of undervoltage. You can choose to test the actual battery pack by battery analog power supply. It is also possible to test directly with the installed battery pack, and the battery pack is recycled, and the protection device is observed whether the device is normal, and the real-time voltage of each battery is recorded, and the performance of equalization charging is determined.

But this method takes a long time test. When charging performance detection of the battery pack, the 3-bit half-precision voltage meter is used to monitor the charging voltage of the 10-cell battery, which can be seen that each battery is within the normal operating voltage range, and the difference between the monomers is small, during charging The voltage deviation is less than 100mV, full charge voltage 4.2V, voltage deviation is less than 50mV.

The current test portion includes overcurrent detection and short-circuit detection. Overcurrent detection can be connected in series in the resistor load and the power back to the power back, slowly reduce the load, when the current increases to the overflow value, watch the current table indicates the discoloration. Short-circuit detection can directly short-circuit battery set positive and negative electrode to observe current table status.

Under the premise of determining that the device is intact, the circuit welding is correct, the current test can be directly tested directly on the state of the power source indicator on the protector. In actual use, it is considered that external interference may cause the battery voltage unstable, which causes the voltage extremely short-time overvoltage or undervoltage, resulting in a battery protection circuit error determination, so the protective chip is equipped with a corresponding delay. Logic, if necessary, add a delay circuit on the protector, which will effectively reduce external interference to cause the possibility of malfunction of circuit errors.

Since the battery pack does not work, each switch device on the protective plate is in the disconnected state, so the static loss is almost 0. When the system works, the important loss is the paccand loss on 2 MOS tubes in the main circuit, when charging When the equalization circuit is working, the electric resistance heat loss in the shunt branch is large, but the time is short, and the overall dynamic loss is in the periodic level within the battery pack. Tested, the design of the protection circuit can meet the maintenance of the serial lithium ion battery pack, the protection is complete, can reliably perform overcharge, over-discharge protection, and achieve equalization charging function.

According to the application, after changing the protective chip model and the number of lines, the switching device and the power level of the switching device and the energy consumption element can be protected and allocated to the power lithium ion battery pack of any structure and voltage level. If the FS361A of Taiwan FS361A is used to protect the chip to achieve 3 groups of parallel, 12 string phosphate ion battery pack design, etc. The ultimate various industrial products are reasonably priced, and the products are not repaired by the 3-year market inspection.