A bidirectional charge equalization circuit based on a bidirectional flyback converter topology is proposed to achieve the balance charging and discharging in series-connected battery bank. The circuit comprises a multi-input transformer, in which the batteries bank are connected to the primary windings via associated active power switches. During discharging, the batteries transfer energy to the load by activating the primary power switches. On the contrary, the batteries are charged by activating the secondary power switch in which the load is replaced by a power source. In order to simplify the control circuit and provide a flexible modulation, a digital signal processor (DSP) with the associated sensors and interface circuits are used as the control kernel. It is used to monitor the variations of battery voltages, and to regulate the duty ratio of the converter to provide a balance charging or discharging among the batteries. A battery bank with four series connected lead-acid batteries is used for illustrating the operation of the bidirectional charge equalization circuit. The experimental results advocate the applicability of the proposed approach.

Charge imbalance may happen to series-connected batteries during charging or discharging due to the discrepancies among batteries. The charge imbalance will cause some batteries being over-charged or over-discharged and is harmful to the battery cycle-life. Moreover, the storage capacity of the battery bank will not be effectively utilized. This thesis brings forth first the concept of charge equalization on discharging for battery banks. Various control strategies are implemented on a flyback converter with a multi-input transformer to provide the balance discharging function as well as output voltage regulation. Each battery of the battery bank is connected to a primary winding of the transformer via an active power switch. The batteries transfer their energy to load according to the residual energy in each battery. Meanwhile, by continually monitoring battery voltages, exhausted batteries can be disconnected to avoid being over-discharged. A battery bank with four series-connected lead-acid batteries is used as an example to illustrate the operation of the balance discharging circuit. The complicated calculations and precise control are accomplished by a digital signal processor (DSP). The experimental results advocate the applicability of the discharging circuit and control strategies.