The brushless doubly fed induction machine as generator for small hydro power - machine design and experimental verification

Abstract

This paper presents the brushless doubly fed induction machine (BDFM) as an alternative choice as generator for small hydro power plants. Looking at this application, the BDFM offers many advantages, mainly the fact that a speed-variable operation in a convenient speed range is possible with a fractionally-rated inverter without the need for slip rings and brushes. An introduction to analytic modeling of the brushless doubly fed machine is given by using an equivalent circuit model, and a machine design process is shown. At first, the main dimensions of the machine and its rating are discussed considering the tangential stress in the air gap. Afterwards the parameters for the equivalent circuit are derived from the machine's geometry. Because of the complex fields in the BDFM, the well-known calculation approaches for standard machines have to be extended. The model and the design process are verified using finite elements simulations and experimental tests with the implemented prototype machine on the test bench.