Torque/Power Density Optimization of a Dual-Stator Brushless Doubly-Fed Induction Generator for Wind Power Application

The brushless doubly-fed machine has attractive features to be employed in highly reliable wind turbine systems. However, the existing brushless doubly-fed topologies primarily work by the principle of modulation and suffer from low torque/power density, inferior efficiency, and high level of time and spatial harmonic distortion. This paper presents a simple design optimization approach for torque/power density optimization of a dual-stator brushless doubly-fed induction generator, which, unlike the modulation types, is inherently free of harmonic-related issues. An analytical average torque model with a full set of geometrical, electromagnetic, and thermal constraints is developed based on the power flow of generating operation. The optimized results exhibit comparable torque per volume and torque per weight to standard industrial induction machines with the similar size, synchronous speed, and power loss per-unit area. Mechanical considerations, manufacturing costs, and control aspects are also discussed to show the high potential in superseding existing doubly-fed induction generators. Finite-element analysis and experimental results of a 3.7-kW prototype are used to validate the effectiveness of the optimization.