DC source-based stand-alone microgrid control using I-PD scheme for a MIMO system

This paper presents an approach to regulate the voltage in a stand-alone microgrid system with a distributed energy resource (DER) unit. The DER applies a switching-function based Voltage-sourced Converter (VSC) to convert DC source to the three-phase AC voltage. The multiple input multiple output (MIMO) control model represents the real system with linear approximation by estimating the transfer functions. A linear controller based on the Integral-Proportional-Derivate (I-PD) scheme is proposed. In this control scheme, proportional and derivative actions are put into the feedback line to reduce the dynamics due to the uncertainties of the load and voltage reference. The nonlinear system dynamics is transformed to d-q axis coordinates making linear controller easy to design. The study focused on the theoretical and simulation analysis aspect by comparing uncompensated and compensated system. The simulation in MATLAB software environment shows that the compensated system has an excellent set-point signal tracking capability and robustly maintains voltage magnitude during the load parameter uncertainties. The power quality of the compensated system also fulfills the required standard according to the IEEE recommendation. Bode diagrams provide more specific control performance characteristics. From the system responses and control performances, the controllers can significantly reduce the coupling effects.