Design, Analysis, Implementation and Operation of a Brushless Doubly Fed Reluctance Motor Drive

Abstract

The permanent magnet synchronous motor (PMSM) is a popular choice for variable speed drive (VSD) applications. However, concerns regarding the low availability and price volatility of rare earth permanent magnet materials are encouraging researchers to reduce or even remove the permanent magnets from electrical machines without significantly compromising their performance. The Brushless Doubly Fed Reluctance Machine (BDFRM) can be a promising prospect with its unique advantageous features over other conventional machines. The BDFRM has two stator windings and a reluctance type rotor. It does not consist of brushes, rotor circuits or magnets. This makes the BDFRM an attractive prospect of a controllable, low cost, low maintenance machine which can be even more robust and versatile than the PMSM. If such a machine is commercially realized, it will be highly suitable to operate in locations of limited accessibility or harsh climate. With proper control technique being utilized, it can be an attractive replacement for two important electrical applications: wind power system and electric vehicle. The concept of Brushless Doubly Fed Machine (BDFM) was first introduced more than a century ago. Much of the published literature has analyzed existing designs, rather than focusing on the design process and effective operation of possible commercial machines. This work describes the complete evaluation of a ducted rotor BDFRM design process through time-stepped finite element analysis (FEA), a prototype machine built based on the design, and two-converters based operation of the BDFRM drive in three different operating modes. In this regard, theoretical aspects and control approach are also discussed and explained. Another objective of this work is to investigate the two-converters based frequency sharing operation (Mode-3) of the prototype BDFRM drive. In this case, the total applied frequency is split between the two stator windings with a specific ratio. Thus, the frequency dependent core loss can be reduced. Besides, this approach can provide additional degrees of freedom for control, extend the constant torque region, and increase the machine power density.