Single-Stage Voltage Balancer with High-Frequency Isolation for Bipolar LVDC Distribution System

Abstract

Conventional voltage balancers for the bipolar low-voltage dc (LVDC) distribution system have been composed of multiple power stages, which degrades their power density and cost effectiveness. To minimize the power stages, this paper presents a single-stage voltage balancer with high-frequency isolation. This voltage balancer is based on three-level dual-active-bridge converter. Furthermore, for the proposed voltage balancer, an enhanced switching modulation using the two switching patterns α and β is proposed to fully balance the bipolar voltage level under unbalanced load condition and even for when one of the dc poles has no load. Besides, a closedloop control system can be implemented by using output voltage information and proportional-integral controllers. Finally, experimental results using a 3-kW laboratory prototype converter verify the effectiveness of the proposed voltage balancer.