New Nonlinear Control Based on Polynomial Approach for Islanded DC Microgrid Robustness and Voltage Stability

This paper aims at developing a novel robust polynomial decentralized control approach for an islanded hybrid DC MicroGrid (MG) with saturation constraint. The investigated MG system consists of a PV unit, a battery and a SuperCapacitor (SC). Each source is controlled by a DC-DC power converter. The challenge is to design a new control approach to enhance the robustness and the stability of the DC MG subject to high nonlinear variations. The main nonlinear control objectives are to: 1) maintain the DC bus voltage to a reference value, 2) ensure the power balance in the system, and 3) warranty the system robustness against perturbations and parametric uncertainties. The Polynomial Control (PC) theory offers an adequate framework to meet the required performances. The resulting control algorithms are simple, and do not need important calculating resources. An extended version of the PC controller is also proposed to make the system Fault Tolerant (FT) w.r.t severe eventual faults, such as a short circuit case at the DC bus level. The design conditions of the developed polynomial controllers are solved using the Sum Of Squares (SOS) approach while verifying the saturation constraint. Stability conditions are ensured based on polynomial Lyapunov functions. Finally, simulations are carried out on MATLAB/Simulink to prove the pertinence and the robustness of the developed control architecture while considering variable loads and solar irradiance. Results are compared to model-based feedback linearization control and sliding mode control techniques.