Extended high-gain observer-based DC-link voltage regulation in dual-stage grid-tied PV system under balanced and unbalanced voltages

This study presents the design and experimental validation of feedback control along with a high-gain observer to regulate the DC-link voltage in dual-stage grid-tied photovoltaic (PV) system. In particular, the composite controller is designed to ensure accurate and fast control of the DC-link voltage in response to abrupt changes in either the delivered active power or grid voltages. The high-gain observer is employed to estimate the unknown disturbance, which is then cancelled by the feedback controller to ensure asymptotic regulation. Fast disturbance estimation is required to retain the nominal transient response specified under the feedback controller, which mandates using high-observer gain. However, high-observer gain magnifies the effect of the measurement noise, which results in poor steady-state performances. This problem is addressed here by using a non-linear gain to allow for on-line adjustment of the observer gain. Specifically, a large observer gain is used during transients to ensure fast disturbance estimation, while a reduced observer gain is employed in the steady-state regime to mitigate the effect of the measurement noise. Experimental results demonstrated the ability of the proposed controller to achieve accurate control, good transient response, fast disturbance rejection, and negligible sensitivity to the measurement noise.