Self-Excitation Criteria of the Synchronous Reluctance Generator in Stand-Alone Mode of Operation

The self-excited synchronous reluctance generator (SynRG) represents an alternative to supply electric power to remote communities. It is robust, simple, and less expensive compared with other types of brushless generators. However, for reliable operation in stand-alone mode, the self-excitation of the machine must be assured, which demands that certain starting conditions are met. It is observed through experiments that the existence of a minimum residual flux in the core, though necessary, is not sufficient to trigger self-excitation. The start-up acceleration also plays an important role since it may create transients in the q-axis flux linkage that can lead to demagnetization of the core and consequent failure in the terminal voltage build-up. This paper studies the effects of these starting conditions on the self-excitation phenomenon and presents criteria in terms of minimum residual flux and maximum start-up acceleration to trigger self-excitation without the risk of core demagnetization. The criteria to ensure the self-excitation for synchronous reluctance machines is developed using the dq-model of the machine and the energetic model. The developed concept is also applicable to other SynRGs operating in stand-alone mode.