Distributed selective harmonic mitigation and decoupled unbalance compensation by coordinated inverters in three-phase four-wire low-voltage networks

Considering the high penetration of distributed generators in low-voltage grids, establishing a coordinated operation of their grid-tied inverters has become imperative to move towards the implementation of smart grids. Yet, knowing that mitigation of power quality issues such as reactive power, current unbalance and harmonics is of importance within such a context, this work proposes a master/slave control approach, which uses a communication means of low-bandwidth, to flexibly coordinate four-leg inverters dispersed in three-phase four-wire networks. Their coordination is attained by means of a current-based approach, allowing the sharing of active, reactive, harmonic and unbalance currents drawn by loads. The control strategy also regulates the power flow at the point of common coupling of the low-voltage network, while proportionally steering inverters according to their nominal capabilities. In addition to the offering of selective harmonic mitigation, the control approach provides distributed and decoupled unbalance compensation, in partial or total portion, based on concepts from the Conservative Power Theory. Consequently, extraction of sequence components or implementation of virtual impedance control loops are not required. The proposed strategy is evaluated based on multiple simulation results, considering the CIGRE's European low-voltage distribution benchmark, including six distributed inverters, as well as linear and nonlinear loads.