A Brushless Synchronous Generator for Standalone DC Applications

Owing to several advantages like easy integration with renewable energy systems, requirement of less number of power conversion stages, better stability and inter-connectivity etc., dc grids are becoming popular. This paper presents an alternative generating systems for dc applications. A recently proposed brushless and permanent magnet-less synchronous generator is used for such purpose. The machine is basically a synchronous machine where an induction machine (that is embedded in the same machine structure) is used for providing controlled excitation to the synchronous machine. The synchronous and induction machines are wound for different number poles such that they remain magnetically decoupled. The field winding of the synchronous machine (SM) is fed by the rotor-induced-emf of the induction machine (IM) through a rotating diode rectifier. For any operating speed, the IM has the ability to operate in different modes simply by varying its stator frequency. In the present work, the synchronous generator (SG) is connected to a dc load through a diode bridge rectifier (DBR). A simple controller is proposed that maintains the load-side dc voltage under different loading conditions. The q-axis component of the stator current of IM is used to regulate the field-excitation of SM using rotor-flux-oriented-control technique. Extensive PLECS simulations are presented to demonstrate the working of the proposed controller. A sample experimental results from the prototype shows the usefulness of the developed generator for dc-grid application.