Influence of control bandwidth on stability of permanent magnet brushless motor drive for “more electric” aircraft systems

This paper investigates the influence of control bandwidth on stability of permanent magnet brushless motor drives which are fed from a DC power source via a passive LRC filter. It is shown that if the current and speed control bandwidths of the drive is sufficiently high, the drive behaves like a constant power load, and the system stability margin decreases with the increase in output power. When the control bandwidth is modestly in a practical range, the system stability margin is influenced critically by the drive's characteristic impedance as well as its output power. Under this conditions, the minimum stability margin may occur at low speed and does not coincide with the maximum output power In addition it is shown that a digital filter in a DC-link voltage feedback loop also influences stability boundaries.