Unbalance and harmonic mitigation using battery inverters

Slight unbalance in voltage in a distribution system can result in high unbalance in currents due to induction machine loads. Further, a wide spectrum of harmonic components will be generated in currents due to uncontrolled power electronic loads employing diode-bridge rectifiers. Power quality becomes a critical issue for a microgrid if both induction machine loads and rectifier loads exist. Mitigation of unbalanced and harmonic currents without additional investments is of interest of utility companies. With energy storage systems such as batteries installed for peak shaping and valley filling, power quality improvement through voltage source converter (VSC) based battery inverters is proposed in this paper. This paper develops a Unbalanced Current (UC) and Harmonic Current (HC) controller for battery inverters based on the structure of Proportional-Resonance (PR) controller. Real-Time simulations carried out in RT-LAB demonstrate the grid current can be successfully improved to meet the IEEE standard when the negative sequence component of grid voltage is lower than 4% for the study system in this paper.