Multirate State Estimator Applied to the Current Control of PWM-VSI Connected to the Grid

This paper proposes a multirate state estimator for grid connected PWM inverters with LCL-filter usually found in high power variable speed wind turbines. The proposed state estimator reduces significantly the high frequency components resulted from the PWM operation on the estimated state variables. Furthermore, the proposed multirate estimator does not introduce additional dynamics under nominal conditions and it is predictive. As a result, it can compensate the time delay of digital implementation and the closed loop system is robust for grid impedance uncertainties. It is demonstrated that even with constant feedback gains it is possible to ensure stable operation from stiff to weak grid conditions. Experimental results from a 10 kW grid connected inverter is presented to demonstrate the good performance of the closed loop system with the proposed multirate estimator.