A robust resonance damping of LCL-filter based grid-connected converter with linear active disturbance rejection control

초록

LCL-filter is frequently employed for the grid-connected converter (GcC) compared to L-filter as an interfacing element. However, increased filter order may cause resonance which may affect the stability of the system and result in poor dynamics. In addition, the resonance effect requires the proper design of LCL-filter and may put a limit on maximum bandwidth achieved with single loop PI control. With converter side current as feedback, the delay in the loop gain further deteriorates the stability of the controller if the higher resonance frequency is adopted for the design. Due to such discrepancy, different controller structures are suggested for L-filter and LCL-filter type GcC with conventional PI control. In this paper, model-independent linear active disturbance rejection control for LCL-filter based GcC is introduced. It is explained by frequency response analysis that the characteristics of the control even with change in the resonance frequency by adopting different filter capacitance. The proposed method treats the system as a simple integrator by estimating all the dynamics of the system with linear extended state observer and compensating them in the control law of ADRC. The robustness of the proposed controller is compared with the conventional PI controller and verified under different filter parameters via simulation and hardware prototype.