Sensorless Control of Brushless Doubly-Fed Reluctance Machines using an Angular Velocity Observer

The brushless doubly-fed reluctance machine (BDFRM) has been considered by academic and industrial communities as a potential alternative to conventional doubly-excited wound rotor induction machines (DEWRIM) in variable speed applications with limited speed ranges such as large pumps and wind turbines. While offering similar cost benefits, afforded by the use of partially-rated power electronics, the BDFRM has the following important advantages over DEWRIM-brushless design and consequent maintenance-free operation. The main purpose of this paper is to further improve the reliability and cost- effectiveness of the BDFRM drive by proposing a new observer based algorithm for speed and direct torque (and flux) control (DTC) of this machine without a shaft position sensor using a maximum power factor control strategy as a case study. The developed sensorless control scheme has been experimentally verified on a small BDFRM prototype, and obtained test results have shown that it can perform very well down to zero applied frequency to the inverter-fed winding this being difficult or impossible to achieve with traditional DTC concepts.