the evolution from dc drives to various forms of
ac drives has been motivated by the continuing need
for simultaneous performance, simplicity, and reliability. In
practice, these needs have often proved to encompass mutually
exclusive goals. Therefore, new developments often strive to
improve the available mix of advantages versus disadvantages.
Direct torque control represents a recent step in mix
improvement. Fig. 1 shows drive evolution as a basic four-step
process. This viewpoint is simplistic, but useful for comparison
purposes.