Research On Medium-voltage Battery Charging And Discharging Equipment Control System

With the widespread of lithium battery used in electric vehicles successfully, research of the lithium battery energy storage system in the traction on the train is also on the agenda. But the DC link voltage of the traction power supply is high (1500V), the charger of lithium power battery under medium-voltage condition hasn’t researched. In addition, with the continuous emergence of new switching device, digital control chip and etc., three level techniques has gained rapid progress since the last century80’s, which has become the preferred topology in the use of battery charger under medium-voltage condition. As the technology of the three level PWM converter is mature, this thesis only discussed the general control system. The emphasis of the thesis is the control of three level Buck-Boost BDC, including PWM modulation strategy, control mode, the digital control system. The difficulty lies in the divided capacitor voltage balancing strategy, realize the rapid conversion of charging and discharging, high precision control, good robustness and so on.On the other hand, charger control not only includes the underlying power driving part, namely the realization of three-phase AC power rectifier to charge the batteries and battery discharge to the grid through the boost, but also includes the application of the battery charge and discharge maintenance. This thesis proposes a multiple degree of freedom combination and active equalization battery charging control strategy based on BMS, which can customize the battery charging curve, avoid the single cell damage in the fast charge and discharge, reduce the inconsistency of the cell voltage through the active equalization so as to improve the cycle performance of the battery group. In the system of high precision measurement of battery, this thesis proposes a design method based on error analysis. As long as the error of voltage, current is certain and effective (synchronous sampling), the precision of power, capacity and energy calculated by DSP or other processor is determined, which can cancel the power acquisition board in the charger. The power acquisition function can be integrated in the system application, thereby saving the cost and improving the utilization rate of resources.