基于统一不平衡/谐波电压-电流下垂的构网型变流器电能质量控制

In power systems, unbalanced and nonlinear loads might lead to voltage and current imbalance and harmonic distortions, which will affect the operation of some critical equipment. To improve the power quality of a system consisting of multiple grid-forming (GFM) converters, it is necessary to reasonably share the load current’s fundamental negative-sequence and harmonic component while reducing the voltage imbalance and harmonics at the point of common coupling (PCC) as much as possible. To solve this problem, a power quality control strategy for GFM converters based on unified unbalanced/harmonic voltage-current droop is proposed in this paper. By establishing a unified droop relationship of fundamental negative-sequence and harmonic component between PCC voltage and output current, unbalanced and harmonic current is shared in accordance with the capacity of each converter while suppressing imbalance and harmonics of PCC voltage. The proposed method can be applied to multiple converters in both the islanded and grid-connected modes without extracting the fundamental negative-sequence or individual harmonic sequences separately. Compared with the existing control methods, this method is simpler and easy to implement in embedded controllers. The design scheme for control parameters based on closed-loop the pole analysis is discussed in detail. Moreover, through a comparison with the existing methods, it is shown that the proposed method has superior dynamic performance and less computation resources. Finally, the effectiveness of the proposed control method was verified by experimental results.