Proportional Complex Integral Based Control of Distributed Energy Converters Connected To Unbalanced Grid System

Abstract

The high penetration of distributed energy resources (DERs) consisting of photovoltaic and fuel cell and wind power plants into the modern power grid results in several challenges such as stability and reliability. In this regard, this paper proposes proportional complex integral (PCI)-based control scheme of distributed energy inverter (DEI) connected to the utility grid to overcome limitations of synchronous rotating coordinate systems based control schemes. The dynamic performance, power quality and stability of the grid connected DEI are enhanced in contrast to proportional integral (PI)-based control scheme during unbalanced and distorted grid voltages. A noteworthy contribution of this paper is that the third-order (3rd) current harmonic stemmed from the DC-link voltage (DC-LV) oscillations is eliminated at the grid side. Elimination of the DC-LV oscillations contributes to reducing the size of the DC capacitance and increasing the lifetime of the power conversion system. Active power reference is calculated in a closed-loop control system based on the DC-LV controller or based on maximum allowable active power injection according to the control objectives. Another contribution to previous studies is to eliminate the need for a phase locked loop (PLL). The complexities and additional hardware requirement for phase estimation are reduced. The performance comparison for two control schemes has been evaluated in terms of dynamic response, removing active power oscillations (APOs) for the DC-side voltage stability, removing reactive power oscillations (RPOs) for the AC side voltage stability, reducing the DC-LV oscillations for the elimination of third-order current harmonic and protection of the inverter from overcurrent. The effectiveness and availability of the proposed control scheme are confirmed through a set of case studies.