Abstract: A method of controlling an AC machine that includes a stator and a rotor, wherein the method includes, whilst operating the AC machine according to an overmodulation technique: determining a reference speed for controlling the operation of the AC machine; filtering the reference speed such that if the reference speed exceeds a speed limit of the AC machine, the reference speed is reduced towards that speed limit; and controlling the operation of the AC machine based on the filtered reference speed. It has been found that controlling the AC machine in this way helps to inhibit “windup” of a controller used to implement the method, even if the overmodulation technique sets a non-constant maximum voltage.

Abstract: A method of controlling an AC machine that includes a stator and a rotor. The method includes observing a stability parameter that is indicative of the stability of the AC machine and dependent on a current state of the AC machine; and controlling the AC machine based on the observed stability parameter so as to promote stable operation of the AC machine. The method may include controlling the AC machine to operate as a motor or as a generator. The AC machine may be a permanent magnet synchronous machine. A controller suitable for performing the method is also disclosed.