Robust Servomechanism Multivariable Control Scheme for Grid-Following Photovoltaic LCL-Voltage Source Converter

This paper proposes the robust multivariable controller for the single-stage grid connected photovoltaic (PV) energy systems. The PV generator is interfaced to the grid through the three-phase LCL filtered voltage sourced converter (VSC). The proposed controller is designed to optimally control the active and reactive power injected to the grid notwithstanding the PV generator and grid system dynamics. Specifically, the proposed multivariable control scheme is designed to trade-off between control input effort and converter/grid states regulation by merely deciding appropriate quadratic performance indices. Similarly, the servomechanism approach is introduced at the outer-loop to track the DC-link dynamics interacting with the PV generator maximum power point tracker dynamics. To enhance the closed-loop system stability and robustness, the optimal state feedback observer based on H-infinity approach is designed to minimize cost and improves system reliability. The resulting augmented observer-based multivariable control scheme features tracking ability (1.25% SSE and 10ms settling time) and robustness against grid and PV dynamics. Unlike the conventional multi-loop vector controllers for the grid-tie LCL-VSC structure, the proposed scheme does not require any special damping compensators, which makes it simple to design and implement. Finally, the comparative results are presented to validate the performance of the proposed scheme.