Investigation on control strategies for LCL-filtered voltage-source converter

The grid-connected VSC system with LCL filter has resonance problems which will magnify the harmonics near the resonant frequency and result in a low stability margin and complex design of current regulators. In this paper, a novel control strategy is proposed by introducing the feedforward compensatory controls of state variables and grid voltage, which can not only lessen the system order from the third-order to the first-order but also reject the current distortions arising from grid voltage disturbances, such as surge, sag or harmonics. Therefore, with the proposed strategy, the system stability margin is enlarged and the design of current regulators is simplified greatly. Besides, a sensorless solution is also proposed to lower the cost of the system. Especially, with the sensorless solution, the system can also avoid disturbances from the local load. Theoretical analysis simulation and experimental results verified the proposition.