Design of DC excitation controllers for grid-connected wound-rotor induction generators

This paper presents analyzed results for the design of a DC excitation controller for a grid-connected wound-rotor induction generator (GCWRIG). The DC excitation controller is performed by using a micro-controller with reduced instruction set chip (RISC) to control the conduction time of a MOSFET switch in a DC-to-DC buck converter. Due to high-speed modulation capability of the proposed RISC micro controller on DC excitation, the characteristics of the studied GCWRIG can be effectively improved than the ones of a conventional grid-connected induction generator (GCIG) with AC excitation capacitors only. Transient characteristics of the studied GCWRIG connected to a practical three-phase low-voltage utility grid are analyzed. The studied GCWRIG system is practically implemented in a laboratory 300 W wound-rotor induction machine driven by a DC motor of 500 W and is practically connected to three-phase, 220 V, 60 Hz distribution system. From the analyzed results using field measurements and computer simulations, it can be concluded that the GCWRIG with the proposed DC excitation controller can provide effective control than the conventional induction generators containing only excitation capacitors under various operation conditions.