LCL-RL filter design for the medium-voltage wind energy conversion system based on dual modules parallel using PS-SVPWM

摘要

The switching frequency of the medium-voltage high power converter is seriously limited, e.g. below 1kHz, due to the switching loss and therefore thermal constraint. Popular LCL filter is difficult to meet grid codes with normal parameters and size, instead, large system volume and expense are unavoidable. However, LCL-RL (RL damping LCL) filter with the same physical size has better filter effect, especially at low switching frequency. In addition, modules parallel technology is generally used in high power converters because of the capacity limitation of a single converter module, accordingly the phase-shifted modulation can be adopted to improve the equivalent switching frequency. In this paper, to reduce the THD of grid current with small filter size and low damping loss, the LCL-RL filter of a medium-voltage multi-megawatt NPC back-to-back converter for a wind energy conversion system (WECS) is designed combined the dual modules technology with PS-SVPWM (Phase-Shifted SVPWM). Simulation results demonstrate the validity of the optimized LCL-RL filter as well as the effectiveness of modules parallel operation using PS-SVPWM.