A Power-Derived Virtual Impedance Scheme With Hybrid PI-MPC Based Grid Forming Control for Improved Transient and Steady State Power Sharing

With the increased percentage of inverter-based generation, it would be practical to focus on improving the functionality of traditional power-generating inverters and utilize them to their full potential without compromising on power quality. The proposed novel adaptive power-derived virtual impedance (PDVI) based scheme maintains proportional power sharing among distributed generators (DGs) with a hybrid proportional-integral (PI) and model predictive control (MPC) based grid forming control. The proposed approach results in enhanced fundamental and non-fundamental (harmonic and unbalanced) load power sharing in transient and steady states. The need to tune multiple proportional resonant controllers at harmonic frequencies is thus eliminated. The proposed PDVI strategy is simple in application, independent of communication, and does not require tie-line lengths or network configuration information. The hybrid PI-MPC control provides a high dynamic response and results in lower THD, maintaining power quality within the limits prescribed by standards. Extensive simulations on a two DG system and CIGRE low voltage network in MATLAB/Simulink validates the proposed control strategy. Further, we compare hybrid PI-MPC control and PDVI performance with recent MPC-based grid forming controls and an existing virtual impedance approach, respectively. Sensitivity analysis of the PDVI parameters is also studied, showing their impact on voltage drop, total harmonic distortion and voltage unbalance factor at the point of common coupling. Experimental verifications show the efficacy of the proposed control strategy in the presence of non-linear and unbalanced loads.