Mitigation of unbalanced currents in three-phase asynchronous generator supplying single-phase nonlinear load

When a three-phase asynchronous generator (AG) feeds a single-phase load, using any one of the known single-phase operation modes, the currents and voltages are grossly unbalanced. The unbalances become more prominent when the machine is feeding single-phase nonlinear loads. In this paper, analysis of a STATCOM based unbalance mitigation technique has been presented which successfully eliminates the unbalances, especially on the current waveforms. This is an encouraging result as the current unbalances are more severe compared to that of voltage unbalances as the former would otherwise lead to overheating of the machine windings which will eventually cause puncture of the insulation and accelerate ageing of the machine. The STATCOM is designed based on calculating the direct-axis and quadrature-axis components of reference currents which are converted to three-phase reference source currents with the help of Inverse Park Transformation and then compared with the actual machine currents to generate the required pulses to trigger the IGBTs of the Voltage Source Inverter (VSI). A single-phase rectifier based load is considered. The scheme is modeled using Matlab/Simulink PSB and the simulation results are presented.