Design method of equalization charging of lithium ion battery pack protection plate


  Author :Iflowpower – Portable Power Station Supplier

Abstract: This paper uses a group of powered lithium-ion batteries. All the lithium-ion batteries require charging overvoltage, discharge under voltage, overcurrent, short circuit protection, and the problem of complement of the unit balanced charging during charging, resolve one Design method for protecting battery pack protection panels with equalized charging function using a single lithium ion battery protective chip to any series of lithium ion batteries. After simulating results and industrial processing, the protection plate is perfect, the work is stable, and the cost performance is high.

0 Introduction Common balance charging techniques include constant shunt resistance equalization, power-off shunt resistance equalization, uniform battery voltage equalization charging, switching capacitance equalization charging, buck 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 the power lithium-ion battery, 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, parsing a use Design method of battery pack protection panels containing equalized charging function for arbitrary series of lithium-ion battery protection chips. Simulation results and industrial processing use certificate, the protective plate protection is perfect, stable, cost-effective, balanced charge error less than 50MV.1 lithium ion battery pack protective plate equalization charging principle structure with single-cell lithium ion battery protection chip design is equilibrium Lithium ion battery pack protection plate structure block diagram shown in Figure 1 below.

Figure 1 Lithium ion battery pack protective plate diagram 4 wherein: 1 is a single lithium ion battery; 2 is a charge overvoltage shunt discharge branch; 3 is a shunt discharge branch control switching device; 4 is overcurrent test protection resistance; 5 is omitted lithium-ion battery protection chip and circuit connection portion; 6 is a single lithium ion battery protective chip (generally including charging control pin Co, discharge control pin DO, discharge overcurrent, short-circuit test pin VM, battery positive End VDD, battery negative VSS, etc.); 7 is a MOS tube gate for charging control in the main circuit after the charging overvoltage protection signal is performed after the photocoupler is isolated; 8 is a discharge under voltage, overcurrent, and short-circuit protection signal After the optocoupler isolation, a series relationship is formed in the main circuit, and the MOS pipe gate is used in the main circuit; 9 is a charging control switching 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-cell lithium-ion battery protective chips determines according to the number of lithium ion battery pack cells, in series, respectively, the charge and discharge, overcurrent, and short-circuit state of the corresponding single-cell lithium ion battery, respectively.

While charging protection, the system is charged by protective chip control shunt discharge branch switching devices, which is different from the conventional practice of balanced charging in the charger end, and reduces lithium-ion battery pack charger. Cost of design. 2 Hardware Design 2.

1 Charging circuit When the lithium ion battery pack is charged, the external power supply positive and negative electrode is connected to the battery pack positive and BAT-end, the charging current flows through the battery pack positive BAT +, the battery pack single-cell ion battery 1 ~ N, discharge control switching device, charging control switch device, battery pack negative BAT-, current flow to Figure 2. Figure 2 Lithium-ion battery pack charging circuitry control circuit partial single lithium ion battery protective chip is used in parallel after latex isolation, and is the on-supply gate voltage of the charging switch device in the primary circuit; If a certain or several lithium-ion batteries entered the overvoltage protection state during the charging process, the overvoltage protection signal is controlled in parallel at the branch conversion branch of the positive and negative electrode of the single-stage lithium ion battery, and will be connected in series The corresponding monomer lithium ion battery in the charging circuit is off the charging circuit. 2.

2 Main circuit and shunt discharge branch lithium ion battery pack in series, ignore the influence of single battery capacity differences, and the battery that is small in the internal resistance is fine. 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. According to the PNGV equivalent circuit model of the battery, the diversary of the split branch resistance is equivalent to the load of the primary single lithium-ion battery, which is discharged by it, and the battery end voltage is maintained in a very small range near the outer 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.

Figure 3 The discharge branch resistance between the primary circuit and the shunt discharge branch single battery can be calculated according to 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 clear; if it is too large, the energy loss of the system is large, the balance efficiency is low, and the heat management requirements for 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 is connected to the battery pack positive BAT + and BAT-end, and the discharge current flow flows through the battery pack negative BAT-, the charging control switch device, the discharge control switch device, the battery pack Lithium ion battery N ~ 1 and battery pack positive BAT +, 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 In the discharge process, there is a special case of overvoltage or overcurrent and short-circuit, and the corresponding single-cell lithium ion battery discharge protection control signal is low, and the gate is not available for the supply of the gate electrical circuit. The bias makes it shut down, the main circuit is disconnected, that is, end the discharge process.

Figure 4 Battery pack discharge circuit General lithium ion battery with constant current-constant voltage (TAPER) charge control, constant voltage charging, reduced charging current approximation index regularity. The switching device of the charge and discharge main circuit in the system can be satisfied with the maximum operating current and operating voltage selection of the external circuitry. A single-term 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 protector circuit simulation According to the basic principle of the above equilibrium charging protector circuit, the system simulation model is built in the MATLAB / SIMULINK environment, and the case of protecting the protective board during the charging of lithium-ion battery packs, verifying the design method. Feasibility.

For the sake of simplicity, the lithium ion battery pack is given only by the 2-segmental ion battery, as shown in Figure 5. Figure 52 Section of the tandem of the lithium ion battery, replace the single-cell lithium ion battery, simulate battery charge and discharge. In Fig.

5, the RS is the battery total internal resistance 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 models for tight logic operation modules, symbol function modules, one-dimensional check module, integral module, delay module, switch module, mathematical operation module, etc.

to simulate timing and logic of protection action. Since there is a certain difference between the simulation environment and the true circuit, do not filter and strong weak electrical isolation, and excess modules can easily lead to the length of 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, you should pay attention to the input output data of different modules and the signal type may have differences. If the connection order of the module is not properly arranged, the data type is converted, and the voltage test module is used in the model to implement 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 using an overcurrent amplifier branch in the battery pack, which can be seen that a method of using an overcurrent discharge circuit is available. Figure 6 Lithium Ion Battery Voltage Test Simulation Results 4 System Test Reconstruction In response to the demand for a brand electric bicycle plus factory, the design has achieved 2 groups of consolidated, 10 series 36V8A · H manganese acid lithium-ion battery pack protective plate Among them, the single-cell lithium-ion battery protective chip uses Japanese Seiko's S28241, the protective plate is composed of main circuit, control circuit, shunt discharge branch, filter, optocoupler isolation, and level conditioning circuit, etc.

, its basic structure is shown 7. The discharge branch current is selected from 800mA, and the 510Ω resistor string is connected in parallel. Figure 7 Lithium-ion battery pack protection plate adjustment debugging work is divided into voltage detection and current detection two parts.

Voltage detection includes charging performance test overvoltage, basic charge, discharge performance test under voltage two steps. You can choose to use the battery analog power supply instead of the actual battery pack. Due to the multi-cell battery, the method of detecting the probe cost is higher.

It is also possible to detect in a fashionable battery pack. When the battery pack circulation is charged and discharge, the protective device is not normal, record the real-time voltage of each battery, and determine the performance of the equalization charging during the recording of overcharm protection. But this method has a long time to spend longer.

When the battery pack is charged, the 3-bit half-precision voltmeter is used to monitor the charging voltage of 10 batteries. It 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 detection portion includes overcurrent testing and short circuit test. The overcurrent test can be connected in series in the resistor load and the power supply back, slowly reduce the load, when the current increases to an overflow value, the current table does not indicate the flow. Short-circuit testing can be straight and short-connected battery pack is a negative electrode to observe current table status.

Under the premise of determining that the device is intact, the circuit welding is correct, it can also be discharged through the state of the power source indicator on the protective plate. 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 is not operating, the switching devices on the protective plate are in the off state, so the static loss is almost 0. When the system is working, it is a main circuit that is pondered on two MOS tubes in the primary circuit. When the charging state 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 within the periodic level of the battery pack.

Detected, the design of the protection circuit can meet the maintenance of the serial lithium ion battery pack protection, the protection is complete, can reliably overcharge, over-discharge protection, and achieve equalization charging function. According to the use of the usage, after changing the protective chip model and the series, the power level of the switching device and the energy consumption element, the power lithium ion battery pack of any structure and voltage level can be achieved. If the FS361A single-section lithium-ion battery protective chip is used with Fujing, 3 groups of consolidated, 12 string phosphate ion battery pack protection plate design, etc.

The ultimate various industrial products are reasonably priced, and the products are not repaired by the 3-year market inspection. 5 Conclusions This paper uses a single lithium-ion battery protection chip design to achieve a multi-segment-lithium-ion battery in series, in addition to completing the necessary overvoltage, undervoltage, overcurrent, and short-circuit protection, it can also achieve equalization charging. Function.

The simulation and experimental results verify the feasibility of the approach, and the market use is verified the stability of the design.

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