A Model Predictive Controlled Bidirectional Four Quadrant Flying Capacitor DC/DC Converter Applied in Energy Storage System

Abstract

Energy storage system (ESS) has been widely used in photovoltaic system to ensure stable power generation. This article proposes a flying capacitor bidirectional buck–boost converter (FCBBC), aiming at making the ESS work with bidirectional four quadrant in the wide dc+bus voltage variation condition. With the symmetrical modulation strategy, the proposed FCBBC can achieve seamless switching between buck and boost mode to match the voltage changes at energy storage and dc bus side. Meanwhile, considering the ESS application requirements, a fixed frequency model predictive control (MPC) strategy based on binary search algorithm is proposed to achieve the control purpose. The decoupling relationship between flying capacitor (FC) and output voltage is derived so that the proposed MPC strategy can control the voltage of two FCs simultaneously. In addition, the adoption of binary search algorithm effectively reduces the computation load of the proposed MPC strategy. Finally, the effectiveness of the proposed converter and MPC strategy are verified with a downscaled ESS experimental platform.