Perturb and Observe-Based Control of Four-Leg Grid-Feeding Inverters to Mitigate Voltage Imbalances in Low-Voltage Microgrids

Unbalanced distribution of single-phase loads and the presence of nonlinear loads causes voltage unbalance in a low-voltage microgrid. Unbalanced voltages at distribution nodes severely affect the operation of many power system installations, hence requiring correction. This paper proposes a perturb and observe-based control strategy, suitable for four-leg inverters to reduce the voltage imbalances in the microgrid. The proposed method requires measurement of the voltage unbalance factor at the point of connection of the inverter to the microgrid, and injection of negative-sequence current. The negative-sequence current to be injected is generated by the superposition of two orthogonal components. These components are perturbed in four incremental neighborhoods, and the corresponding voltage unbalance factors observed. The system is shifted toward the minimum of the observed voltage unbalance points from where the system is perturbed, observed, and shifted again until the system reaches and stays at the minimum unbalance neighborhood. The shape of the 3D surface obtained by plotting voltage unbalance factor with respect to these negative-sequence current components current has been explored to develop the algorithm. Different case studies have been performed on a 25-bus, IEEE-13 bus, IEEE-34 bus, and 19-bus unbalanced radial distribution system configured as a microgrid to study the effectiveness of the proposed algorithm. © 2022, The Institution of Engineers (India).