A high-efficiency synchronous rectifier for supercapacitor voltage equalizer in urban rail

This paper presents a novel rectifying circuit that aims to reduce power losses of Supercapacitor voltage equalizer in urban rail. High-efficiency is achieved by designing a synchronous rectifier with MOSFET instead of diode and chiefly by optimizing MOSFET switching performance. A switching model that takes MOSFET parasitic capacitances and inductances, circuit stray inductances, and reverse current of parasitic diode into consideration is given to analyze the MOSFET switching characteristics. Furthermore, major power losses during MOSFET working including the moment of switching and the state of conduction are calculated. In order to reduce power losses, precise Zero Current Detection (ZCD) is applied. Meanwhile, blanking time is set to avoid the MOSFET accidentally switching. The operational principles of the proposed synchronous rectifier are presented, and high-efficiency is verified by the experimental results in a supercapacitor voltage equalizer experimental system with eight series-connected supercapacitors cell.