A grid-connected induction machine capable of operation at unity and leading power factor

This paper presents a method to operate a grid-connected induction machine such that reactive power may be supplied to the grid. Using the principle of series voltage injection, two control approaches are presented. The first control approach is suitable for systems with steady loads and allows the reactive power flow to be dynamically controlled. The second control approach may be applied to systems with variable loads and results in operation with a leading power factor The principle of operation is demonstrated using an induction machine with a three-phase converter and floating DC link inserted into the circuit at the Y-point. The converter is controlled to inject 3-phase voltages at the motor Y-point to introduce a phase-shift between the motor winding voltage and the grid voltage. As the magnitude of the injected voltage is adjusted, the phase angle of the machine current can be shifted to be less lagging, in phase with or leading the grid voltage. The paper presents the theory behind the approach together with simulations and experimental results. The results demonstrate reactive power supply to the grid.