Battery Management System HIL Test Solution

    The Battery Management System (BMS) is an increasingly important key part in electric vehicles and a core component in key technologies for monitoring operation and protecting batteries.

Figure 1-1 BMS functions

    There are many disadvantages to using real battery packs to test BMS:

• Extreme operating condition simulation brings safety risks to testers, such as overvoltage, overcurrent and overtemperature, which may cause battery explosion.

• The SOC estimation algorithm verification takes a long time, and the actual battery pack charge and discharge test takes a week or even longer.

• It is difficult to simulate specific working conditions, such as the slight SOC difference between battery cells during the equalization function test, and the slight temperature difference between the battery cell and the battery pack during the battery thermal balance test.

• As well as other BMS functional tests, such as battery pack operating voltage, single cell voltage, temperature, SOC calculation function, charge and discharge control, battery thermal balance, high voltage safety function, equalization function, communication, fault diagnosis, sensors and other tests, OEMs are faced with many challenges.

2. Solution

    In the face of the above challenges, Hirain Technology provides a BMS HIL test solution based on TestBase. The system solution mainly includes the following parts:

• Real-time simulation platform: Developed based on the PXI bus series boards provided by NI , it consists of real-time processors, real-time I/O boards, etc., and can perform fast data calculations.

• Battery simulation board: used for single cell simulation. Combined with the battery simulation model, it can dynamically output the voltage and temperature of the single cell; 

• Battery simulation model: It adopts the equivalent circuit principle to model and calculate the voltage, current, temperature, SOC and other state quantities of the battery when it is working.

Figure 2-1 Overall solution for battery simulation

    The above system solution uses the battery cell simulation module independently developed by Hirain Technology, which has been successfully applied to the BMS HIL projects of new energy vehicles of multiple OEMs.

    Application Areas

• Simulation of battery modules or cells;

• BMS balancing, insulation and SOC estimation algorithm verification;

• BMS charging and discharging, high voltage safety testing;

• Communication and functional verification based on actual vehicle conditions.

    Features

• Achieve voltage simulation of up to 150 cells by connecting in series;

• Conveniently and accurately realize battery temperature and insulation detection;

• Realize high voltage power on/off and pre-charge relay control;

• Accurately simulate the characteristics of each battery cell and simulate each sensor;

• Meet CAN, LIN and SENT communication protocols;

• IO and equipment can be customized according to the customer's actual BMS.

3. Product features and advantages

3.1.Battery simulation model principles and characteristics:

    The battery simulation model is based on the equivalent circuit method and takes into account the impact of factors such as polarization loss and self-discharge loss at different stages of the battery cell on the battery voltage and SOC, which significantly improves the steady-state and transient response of the battery model. The modeling principle is shown in Figure 3-1.

Figure 3-1 Battery simulation model principle

    The battery model function is shown in Figure 3-2:

Figure 3-2 Battery simulation model characteristics [page]

    The comparison between the battery single-cell pulse discharge test simulation curve and the real single-cell pulse discharge curve is shown in Figure 3-3:

Figure 3-3 Battery model simulation comparison curve

3.2. Battery simulation board functions and features:

    After the battery model calculation is completed, the status information of the single battery in the battery model is output to the battery simulation board, such as the single battery voltage signal, and the single battery voltage signal is sent to the BMS daughter board to realize the simulation and test of the single battery voltage. The battery simulation board function is shown in Figure 3-4:

Figure 3-4 Battery board functions and indicators

    By combining the resistance simulation board and the insulation resistance simulation board, the temperature and insulation resistance of the single cell can be simulated. The specific parameter indicators are shown in Figure 3-5:

Figure 3-5 Specific parameters of the battery simulation module

4. Summary

    Compared with BMS testing using real batteries, HIL testing using battery simulation technology has the following obvious advantages:

• Safe and energy-saving: Avoid high-power charging and discharging processes, and avoid potential safety hazards to testers;

• Easy to create various BMS faults, so as to comprehensively test the BMS diagnostic function;

• Realize simulation of battery packs of various specifications (number of cells, voltage level) through software and hardware configuration;

• Battery status, such as SOC, temperature, etc., can be modified quickly online to improve test efficiency;

• By modifying the model parameters, the battery aging, cell inconsistency and other phenomena can be simulated;

• Can simulate the whole vehicle operating environment.