Observer-based grid voltage disturbance rejection for grid connected voltage source PWM converters with line side LCL filters

This work presents an extended disturbance observer design for grid voltage disturbance rejection of voltage source PWM converters with LCL filters. The proposed observer design leads to a cascaded extended disturbance observer using either the converter side current or the line side current for feedback. Theoretical aspects including the LCL filter system observability, observer pole placement strategy and practical implementation are discussed to achieve an observer formulation. The analysis presented is based on a fully analytical observer formulation in the discrete time-domain. The discrete state-space modeling of the LCL filter dynamics is discussed and a step-by-step observer formulation is presented. The theoretical analysis is verified on a 22 kW laboratory type adjustable speed drive system where the control algorithms are implemented on a dSpace system. The analysis reveals excellent disturbance rejection capabilities of the proposed cascaded extended disturbance observer design for both feedback cases.