A modified energy management scheme to support phase balancing in grid interfaced photovoltaic/fuel cell system

Abstract

This paper presents improved energy management for grid-inverter of a hybrid photovoltaic (PV)/fuel cell (FC) energy system with unbalanced sensitive loads. In the system, unbalanced loads draw unbalanced currents at each phase and consume power from energy units at different levels. This condition makes the grid unbalanced, which cannot be compensated by a conventional energy management controller used in grid inverters. For this, a phase balancing control method is proposed in order to improve the grid quality under unbalanced loading conditions. The proposed method calculates power differentiation values based on multiple-frame αβ/dq transform instead of abc/dq transform in the conventional method. Thus, it eliminates negative & zero sequence components in addition to power flow control. Under unbalanced loading conditions, the proposed method removes the deficiency of the conventional energy management method which generates the symmetrical current references to trigger the switching elements of the inverter. In performance results, the system with unbalanced loads is tested for different case studies, which supply different power from energy units to grids. The results show that the proposed method provides power balancing at the grid-side and eliminates negative & zero sequence components at grid-side currents.