基于改进型LCL滤波器的并网变换器共模谐振电流抑制与效率提升

Three-level grid-tied converters (GTCs) with modified LCL (MLCL) filters are widely used in photovoltaic generation due to their effectiveness in attenuating leakage currents. However, MLCL filters also introduce a significant common-mode (CM) resonant current (CMRC), which poses a risk to system stability. Furthermore, the discontinuous pulse width modulation (DPWM) technique, originally developed to improve converter efficiency, is incompatible with MLCL filters and exacerbates the CMRC. Consequently, a conflict arises between CMRC suppression and efficiency enhancement. In this article, we propose a filter-based DPWM strategy and a robust CM-loop controller to address this problem. Specifically, the filter-based DPWM effectively reduces CMRC excitation sources while still ensuring a prolonged clamping time for each phase. The CM-loop controller, developed using loop-shaping theory, successfully suppresses CMRC and guarantees robust stability of the CM loop. The synergy between the filter-based DPWM strategy and the CM-loop controller simultaneously achieves CMRC suppression and efficiency enhancement. Experimental results demonstrate that the CMRC is reduced to below 300 mA, and the converter efficiency is improved by 2% under the light load condition and 0.5% under the heavy load condition.