Sliding Mode Control and Immersion & Invariance Observer for Grid-Tied Inverters in Photovoltaic Applications: Continuous Operation for Power Quality Enhancement

This work proposes a model-based control scheme using a sliding mode controller (SMC) and an immersion and invariant (I&I) observer. The objective of the proposed control scheme is to be applied to a three-phase grid-tied inverter, which could operate as a shunt active power filter when the photovoltaic array is not generating power (night-time operation). The grid-tied inverter always remains operational, ensuring continuous support of the power quality improvement, as well as current harmonic compensation due to nonlinear loads and power factor correction. An external control loop is included to keep the voltage of the DC-link capacitor regulated. As can be explained in detail along with the work, a battery stack is avoided in this proposed research. Thus, a decision stage is added to the control scheme to select the night or day operation. Simulation results are carried out using Altair-PSIM© to demonstrate the effectiveness of the proposed control scheme in several scenarios.