Energy reshaping based passive fractional-order PID control design and implementation of a grid-connected PV inverter for MPPT using grouped grey wolf optimizer

•A passive fractional-order PID control is proposed for PV system to achieve MPPT.•A storage function is constructed while the beneficial terms are carefully retained.•Error tracking performance is enhanced thanks to the fractional-order PID mechanism.•Satisfactory control performance is realized under various operation conditions. This paper designs a novel passive fractional-order proportional-integral-derivative (PFoPID) controller for a grid-connected photovoltaic (PV) inverter via energy reshaping, such that the maximum power point tracking (MPPT) can be achieved through perturb and observe (P&O) technique under different atmospheric conditions. Based on the passivity theory, a storage function associated with the DC-link voltage and DC-link current, as well as q-axis current is firstly constructed for the PV system, in which the physical property (e.g., heat produced on resistors) of each term is thoroughly investigated and analyzed while the beneficial terms are carefully retained in order to fully exploit the essential characteristics of the PV system. Then, the remaining energy of the storage function is reshaped via an additional input in the context of fractional-order PID (FoPID) control framework, which control parameters are optimally tuned by grouped grey wolf optimizer (GGWO), such that an optimal control performance can be realized. Four case studies, including the solar irradiation variation, temperature variation, power grid voltage drop, and PV inverter parameter uncertainties, are carried out. Simulation results verify the effectiveness and advantages of PFoPID control in comparison to that of conventional PID control, fractional-order PID (FoPID) control, and passivity-based control (PBC), respectively. Lastly, a dSpace based hardware-in-loop (HIL) experiment is undertaken to validate the implementation feasibility of the proposed approach.