Analysis and evaluation of the decoupling control strategies for the design of grid-connected inverter with LCL filter

Proportion-integration (PI) controllers in rotating frame have been considered to design the current controllers for the grid-connected VSI with LCL filter. One issue that must be considered is how to eliminate the complicated coupling terms between d-axis and q-axis in the mathematical model in synchronous reference frame. The direct decoupling modeling process eliminates the interaction between d-axis and q-axis by neglecting the coupling terms, directly, such as small external disturbances. The feedforward compensation decoupling modeling process realizes precise modeling by feeding forward compensation for the relevant coupling terms gradually to improve the quality of the grid-connected current. By designing the Simulink models based on dual closed current loop control strategy, these two decoupling methods are verified. At last, a concept of feedforward compensation coefficient, which provides a new selection criterion for the design of decoupling control strategy of the grid-connected inverter with LCL filter, is proposed after comparing the advantage and disadvantage of two decoupling control strategies in eliminating the interaction between output active power and reactive power and improving the quality of grid-connected current.