Novel Winding Design and Analysis of Brushless Wound Rotor Synchronous Machines

Abstract

Synchronous machines are electric machines characterised by a rotating speed proportional to the AC supply and are independent of load. Traditional permanent magnet synchronous machines utilise rare earth minerals for rotor flux generation, posing challenges due to rising costs. In such conditions, wound rotor synchronous machines with electromagnets may offer several economic and operational benefits, particularly for applications requiring a wide range of speeds and better torque density. However, rotor excitation in these machines requires brushes and slip rings, which lead to higher initial and maintenance costs, increased sensitivity to fluctuations, reduced speed regulation, and lower power factor. Existing designs of brushless wound rotor synchronous machines use additional rotor windings, leading to increased complexity and reduced efficiency. Techniques such as third harmonic excitation have been employed to eliminate brushes, but these solutions often suffer from low starting torque and inefficient stator utilisation. To overcome the issues associated with existing brushless wound rotor machines, this article proposes a novel winding scheme that incorporates an additional stator winding to enhance the slot fill factor. Furthermore, the benefits of single and dual inverter-fed designs are analysed, highlighting the reduced cost, size, and simplified circuitry of the single inverter design, along with the improved control and performance offered by the dual inverter design. Finally, an advanced harmonic excitation method is integrated to optimise torque production. A thorough 2D finite element analysis has been conducted to validate the proposed designs and operational principles of the brushless wound rotor synchronous machine, demonstrating its potential for enhanced performance in various electric machine applications.