Richard McMahon’s research while affiliated with The University of Warwick and other places

This paper presents a method to estimate the BDFM equivalent circuit rotor current from rotor bar current measurements. Rotor currents are measured using a specially designed hardware that incorporates Rogowski coils and Bluetooth wireless transmission. The measurement of rotor currents enables the parameters in the BDFM's full equivalent circuit to be extracted unambiguously. In particular, stator and rotor leakage inductances can be estimated from experimental tests, which was not possible before from terminal measurement. The method is presented for a nested-loop rotor design and experimental measurements are shown for a prototype D180 frame BDFM.

A Brushless Doubly-Fed Induction Machine (BDFIM) has wide application potential in wind turbines, industrial drives, small hydro power plants, power supply of ships, aircraft starters, and electric vehicles. In electric vehicles, a BDFIM offers a robust structure without needing permanent magnet materials, slip-rings, and brushes, which makes it particularly suitable for heavy vehicles, such as buses, agriculture and construction vehicles, where the low power density of a BDFIM is of less significance compared to that in passenger cars. To effectively analyze and control a BDFIM in various applications, it is essential to develop its accurate electrical equivalent circuit models. This paper presents a comprehensive review on various electrical equivalent circuit models of BDFIMs in the literature with different level of complexity. A full order model is complex, but can represent the complete electrical behavior of a BDFIM. By simplifying the full order model and neglecting certain parameters, a reduced order model requires fewer state variables due to practical approximations. Dynamic behavior of BDFIMs under various operating conditions are demonstrated in the paper to showcase the effectiveness of these existing models. This review emphasizes the significance of electrical equivalent circuit models in the design, analysis and control of BDFIMs. Future research directions for the model refinement are recommended.

This study studies, using experimentally verified finite element (FE) analysis, various performance measures of the brushless doubly fed induction generator (BDFIG) when magnetic wedges are used for closing stator open slots. The BDFIG is an attractive generator solution for offshore wind power and can replace doubly fed slip-ring induction generators. It is shown in this study that the use of magnetic wedges, commonly used in large induction machines, reduces the stator windings magnetising currents in a BDFIG, reflected in the values of magnetising inductances. They also increase the leakage flux in the stator slots, leading to a larger series inductance in the equivalent circuit. The series inductance significantly affects the BDFIG performance as well as the rating of its converter. The effects of magnetic wedges on BDFIG air-gap flux, synchronous torque, and stator tooth top saturation is also investigated. Two-dimensional FE analysis of an experimental 250 kW BDFIG is used in this study, verified by experimental measurements.