A Lithium-ion Battery Emulator With Improved ESR Control

The performance of a device which contain a lithium-ion battery need to be test, before it is used. If a battery emulator is used instead of a real battery, it would reduce testing costs, reduce environmental pollution, improve testing efficiency and enhance testing flexibility. An emulator is designed which can be used to emulate the output characteristic of a lithium-ion battery in charging and discharging. It could replace a real lithium-ion battery in researching and testing.The characteristic of a lithium ion battery is analyzed and emulated, and then through experimental test get the charging and discharging curve of a kind of lithium-ion battery. According to the basic model of the lithium-ion battery, mathematical models and curve fitting is used to model it. After comparing and analyzing, fitting equation is selected as the model of the lithium-ion battery.Constant-voltage electronic load is used to emulate the charging process of the lithium-ion battery. The outer voltage loop is used to set the output voltage of the circuit, and make the output voltage change along with the battery charging characteristic curve by controlling the reference voltage. In the output side, a current inner loop be used to realize current balance, and take multiphase parallel to realize power expansion of electronic load.A circuit with variable ESR is used to emulate the discharge of the lithium-ion battery. It not only could emulate the discharge with constant current, but could emulate the discharge with dynamic current, while its output voltage would change follow the load current and show the characteristic of true battery with variable ESR. In order to increase the output voltage and power, improved control method of the original circuit ESR, it is combined with VCVS and as the reference input of VCVS to control its ESR and output. So it would fit the constant current discharge and cut-off load process, by setting circuit parameters.Last, the controller is designed and the experimental prototype is built to analyze. The controller through the main program call to each subroutines, according to the sampling voltage and current select the work mode, and calculate the reference voltage of charging and discharging circuit to realize the output characteristic is controlled of the emulator. The prototype is built of 36 V 8.6Ah lithium-ion battery pack, and the constant current charging, the constant current discharge, the cut-off load discharge, and the switch of charging-discharging working modes are emulated to get an accurate result.