A Hybrid Multi-loop Current Control of the Grid-Connected Converter with LCL Filter

LCL filter is widely applied in the industry due to the advantages of the small size and high harmonics mitigation, but the system stability results from the filter interaction and grid impedance must be addressed. Although conventional multi-loop current control physically decouples the interaction of the LCL filter, the control performance is limited by the digital controller delay effect. This paper proposes the hybrid multi-loop current control which integrates the one-step predictive current control into the conventional multi-loop current control to compensate for the calculation delay effect. In addition, the observer of capacitor voltage is added into the hybrid multi-loop current control to save the cost, and the noise reduction compensator is also discussed in this paper. Except for making sure of single inverter stability, the passivity-based analysis is applied to prove the system is stable in the weak grid. In the end, the laboratory test results will be used to support the aforementioned analysis.