Isolated Bidirectional Switched-capacitor Flyback Converter

In this paper, high-efficiency, extremely high step-up and step-down bi-directional DC-DC converter is proposed. The proposed converter consists of a flyback and an isolated switched-capacitor cell to achieve high cost competitiveness for the extreme operation. The output of the flyback converter and that of the isolated switched-capacitor is connected in series to obtain a high voltage step-up. In the reverse direction, then, this converter can be an extremely voltage step-down one. For the design of the controller, the small-signal transfer functions of the converter are derived. Finally, a 100W hardware prototype of the proposed converter is implemented. To improve the efficiency of a PV system employing the proposed converter, a maximum Power Point Tracking (MPPT) method is applied with Perturb and Observe (P&O) method. To demonstrate the operation of the bidirectional converter, the main switch current is used for the power control. All of these controls are implemented with a digital signal processor (DSP).