Grid current unbalance compensation using a fuzzy controlled smart transformer

Abstract

This paper proposes a novel method that uses a hybrid fuzzy controller (FC) to control a smart transformer (ST) to compensate three-phase medium voltage (MV) currents arising from unbalanced renewable generation in the low voltage (LV) grid. An averaged macro-model of the ST is used to handle current unbalances in the LV secondary, while providing balanced share of active power in the MV primary. The ST benefits from proportional derivative (PD)-like plus Integrator fuzzy controllers (FPD+I) to provide a regulated voltage in LV grid in addition to unity power factor in MV grid and one PD-like plus gain update mechanism to balance currents in MV grid. Moreover, a three-phase power-sharing strategy is proposed to guarantee active power equality in both sides of ST. The proposed ST macro-model is tested by two modified IEEE 5-bus and IEEE 33-bus with an unbalanced LV grid connected through an ST. Three different scenarios for imbalance conditions are considered. The effectiveness of the proposed scheme is verified by measuring the current unbalance factor (CUF) indices. The proposed controller shows almost 1% reduction in the voltage unbalance factor (VUF) and 9% in CUF, while the response time is reduced to 20 ms.