Optimal Voltage Unbalance Suppression Control Using PV Inverter in Distribution Network

Distribution networks exhibit unbalance issues due to arbitrarily connected devices. This paper advances the control strategy of optimal voltage unbalance (VU) suppression using PV inverters. This matter is formulated as an optimization problem to minimize the negative sequence voltage at the point of common coupling (PCC), subject to current limiting, power oscillation, power balance and circuit theorems. To solve this problem, the underlying geometry properties of constraints are explored. Then the boundaries of trajectory of compensating current are obtained under different VU conditions, which proves the availability of the optimal solution acquired by P&O method. Next, by accurately calculating the injected negative sequence currents of the PV inverter, the minimum unbalanced voltage at PCC is obtained by proposed control strategy, which can be implemented without the information of grid impedance and ensuring maximum output power of PV array. Finally, the applicability of gird fault and multiple inverters are investigated. The effectiveness is valid by hardware-in-loop(HIL) tests and experiments based on actual scale-down microgrid.