Sliding Mode Observer based direct torque control of a Brushless Doubly-Fed Reluctance Machine

Direct Torque Control (DTC) has been extensively researched and applied during the last two decades. However, it was applied to the Brushless Doubly-Fed Reluctance Machine (BDFRM) for the first time only a few years ago in its basic form inheriting its intrinsic flux estimation problems that propagate throughout the algorithm and hence compromise the DTC performance. In this paper, we propose the use of Sliding Mode Observer (SMO) as an alternative to improve the estimation quality and consequently the control performance of the DTC. The SMO is designed around a nominal model, but is shown to be reliable over the whole operating range of the BDFRM. Moreover, we use a modified robust exact differentiator based on Sliding Mode (SM) techniques to calculate the angular velocity from an angular position encoder. Computer simulations are meticulously designed to take into account real-world physical constraints and thus show illustrative supporting results as expected from an experimental setup.