A multiphase quasi-resonant (QR) zero-current switching (ZCS) switched capacitor (SC) bidirectional dc-dc converter structure is proposed to reduce current ripple and switching loss, and significantly increase converter efficiency and power density. This approach provides a more precise output voltage to obtain voltage conversion ratios from the double-mode versus half-mode to n-mode versus 1/n mode. This is accomplished by adding a different number of switched capacitors and power MOSFET switches with a small series connected resonant inductor for forward and reverse schemes. The size and cost can be reduced when the proposed converter is designed with coupled inductors. Simulation and experimental results demonstrate four-phase with and without coupled inductor interleaved QR ZCS SC converter performance for bidirectional power flow control applications. A battery energy storage system for a bidirectional power flow control application is demonstrated.