A Novel Coupled Inductor Based Active Balancing Technique for Ultracapacitors

A novel active buck-boost equalizer with a coupled inductor is proposed here for balancing ultracapacitors (UC) strings connected in the form of a matrix configuration. As a coupled inductor is used instead of an inductor, the number of switches and inductor windings required for balancing is reduced to N/2 and (N-P), respectively, where N is the number of UC cells to be balanced, and P is the number of parallel strings. The proposed balancing circuit requires only a single pair of complementary pulse width modulation (PWM) signals to balance the entire UCs in the UC strings. Hence, control complexities are significantly less as compared to the existing active voltage balancing methods. The effectiveness of the proposed topology is verified in the MATLAB/simulation platform and validated experimentally.