Direct current control strategy of LCL‐type converter for harmonic suppression under distorted grid condition

The grid voltage distortion represents a significant cause of the grid quality degradation when a renewable energy system is incorporated into the traditional grid. In this paper, a direct harmonic current control strategy is proposed for an LCL converter under distorted grid conditions. The proposed strategy improves the power quality and enhances the converter robustness under the non-ideal grid conditions. Traditionally, in the harmonic suppression strategy, the capacitor current is commonly used as a harmonic information source to control and suppress harmonics, which not only realises active damping, but also provides harmonic current suppression. Unlike the existing technologies, the proposed strategy realises the closed-loop control and harmonic current suppression by sampling the converter-side current. The proposed strategy can achieve a more efficient harmonic suppression than the traditional methods without requiring additional sensors and hidden danger of resonance. The impedance characteristics of multi loops are analysed when a distorted voltage is applied to the LCL converter. Then, the corresponding control strategy is proposed. The similarities and differences in harmonic suppression and stability between the proposed strategy and the traditional strategies are presented and discussed. Finally, the effectiveness and feasibility of the proposed strategy are verified by the simulation and experimental results.