A Balanced, Unity Power Factor, 3-phase Bridgeless AC/DC Step-up Transformer-less Converter with Magnetic-Coupled Soft-Switched Step-up Rectifiers for Wind Farm with a MVDC Grid

摘要

High voltage gain, high-power AC/DC converters are the key components for medium voltage (MV) step-up power conversion in wind systems with a MVDC grid. This paper presents a new, three-phase bridgeless AC/DC soft-switched, step-up resonant converter with magnetically coupled high-gain output rectifier modules for MV step-up conversion. In the proposed circuit, the output high-gain rectifier stage in all phases are coupled together to improve the output current and voltage balancing issues. While each phase (i.e. each module) has its own dedicated controller to regulate the output voltage in each phase, the coupled magnetics is able to ensure that the output current in each phase is balanced. Similarly, the inductor in the input power factor correction stage in all three phases are also coupled together to reduce the overall number of magnetic components. The operating stages of the proposed converter, and the design of the coupled magnetics will be discussed in this paper. Simulation results are first given on a 1.8MW, 690V_AC/44kV_DC system to highlight the performance of the proposed converter. Hardware experimental results on a laboratory-scale prototype with an output voltage of 1.2kVDC are finally presented to verify with the proposed converter's performance.