Natural Adaptive Observers-Based Estimation Unit for Robust Grid-Voltage Sensorless Control Characteristics in Inverter-Based DG Units

This paper presents a natural adaptive observers- based estimation unit for robust grid-voltage sensorless control characteristics in inverter-based distributed generation (DG) units. First, a rigorous discrete-time model of a current- controlled inverter-based DG unit, including the calculation delay and the nature of the pulse-width-modulation (PWM) as a zero-order-hold, is presented. Second, a novel estimation unit is designed with low computational demand to estimate, in the realtime, the interfacing parameters and the grid voltage simultaneously. A unified solution to the present nonlinear estimation problem is presented by adopting a parallel observers structure. Third, the estimated quantities are utilized within the inner high bandwidth current control loop and the outer power controller to realize a robust grid-voltage sensorless interfacing scheme. Theoretical analysis and evaluation results are provided to demonstrate the validity and usefulness of the proposed interfacing scheme.