| With the development of various kinds of energy storage devices,lithium battery has caught worldwide attention for its high energy density,long cycle life,large discharge rate,pollution-free advantages.Lithium battery protection system parameters,battery voltage of lithium battery and battery internal resistance are important indexs to evaluate the performance of lithium battery.Testing the lithium battery pack and its protection system provides the technical support for the safe use of lithium battery pack.The main study in this paper is lithium battery pack and its protection system detection technology.In lithium battery pack testing,the main research is lithium battery pack voltage and battery internal resistance detection technology.The function,type and working principle of lithium battery protection system are analyzed in detail.According to the working principle of lithium battery protection system,a scheme to detect the parameters of the protection system is determined by applying the voltage and current excitation signals to the protection system.According to the characteristic of protection system the detection method to detect the protection voltage,recovery voltage,balance voltage,balance current,supply current and over-current protection current are designed.Using special chip to test the voltage of battery is analyzed.The method based on relay and shared A/D chip sequential acquisition mode(sequential acquisition way)to detect the battery voltage is analyzed.The method of detecting the battery voltage by sequential acquisition way is determined,according to the design scheme of this paper.The equivalent circuit model of lithium battery is analyzed in detail.The advantages and disadvantages between the DC method and AC method on the internal resistance testing of lithium batteries are compared and the AC method is chosed to detect the internal resistance of lithium batteries.Aiming at the problem of noise in battery internal resistance testing,the working principle of phase-sensitive detection is analysed,and the way of phase sensitive detection is determined to test the response signal of cell.The hardware circuit of detection system is designed,which is comprised of battery pack simulator,current source control circuit,current detect circuit and protection system action detect circuit for detecting battery protection system.Controllable current sourcecircuit and signal detection circuit for detecting battery internal resistance is designed.The software of detection system is designed,which is comprised of various subprograms for various parameters detecting and the main program of host computer and slave computer.The modbus protocol of the communication between the host computer and slave computer is established,which makes the data transmission between the host computer and slave computer to fulfill the detection setting and the result display.Simulation and experiment are carried out to verify the key circuit of the testing.The system experimental platform is builded to complete the detection experiments of various parameters.According to the comparison of experimental results and theoretical analysis results the correctness of the system detection method,the system detection accuracy and the stability of the system detection are verified.It can be seen from the experiment results that the system testing index has reached the system design requirements. |
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