Laboratory control implementations for doubly-fed machines

Brushless doubly-fed machines attempt to achieve the benefits of adjustable speed drives while minimizing power converter rating and cost. However, since only one set of stator windings is controllable, control of the resulting motor drive is potentially more complex than for conventional singly-fed systems. While the doubly-fed machine system is open-loop stable, dynamic response and steady state performance can be far from optimum in the open-loop mode of operation. This has prompted the development of closed-loop control algorithms ranging from simple stabilizing speed feedback and power factor adjustment to fast, predictive torque control based on instantaneous error. The present paper discusses the laboratory implementation of proposed control schemes for brushless doubly-fed drives