Stability analysis on parallel of LCL-filter-based grid-connected converters in MW-level direct-drive wind generation using complex vector

With the individual capacity of wind power generation system increasing, the demand for high power grid-connected converters is growing, which is usually limited by the available semiconductor technology. One solution is multiple lower power units connected in parallel. LCL filters can provide much better ripple and harmonic attenuation. Therefore, they are more suitable for high power conversion systems. However, LCL filters may result in resonance, and thus cause the closed-loop control system unstable, especially in the parallel of LCL-filter-based converters which are connected to the grid by one transformer. In this paper, complex vector model of parallel of two LCL-filter-based converters is first introduced in details. Then using the superposition theorem, the performance of LCL filter imposed by separate excited sources is analyzed. Furthermore, current reference step response and voltage feedforward control are discussed. Finally, the related results are verified by simulation and experiment.