Abstract: A method of detecting a diode fault in an AC signal rectifier circuit, the AC signal rectifier circuit including a plurality of diodes, and being arranged to supply a rectified output voltage to a load, wherein the method includes the steps of deriving an operating value indicative of the ratio of the voltage magnitudes of a first harmonic frequency and another harmonic frequency of the rectified output voltage across the load; and determining whether a fault has occurred in one or more diodes on the basis of the derived operating value. The first harmonic frequency is preferably the fundamental harmonic frequency, and/or the another harmonic frequency is preferably the 6th harmonic frequency.

Abstract: A thermal controller for driving a gate control unit of a gate-driven semiconductor switching device, the thermal controller comprising a junction temperature estimation module for generating an estimated junction temperature for the switching device, a gate voltage control module for modifying a gate voltage of the switching device, a switching frequency control module for modifying a switching frequency of the switching device, and a duty cycle control module for modifying the duty cycle of the switching device. In use, the thermal controller is adapted to activate one of the gate voltage control module, switching frequency control module and duty cycle control module dependent upon the estimated junction temperature in order to maintain the actual junction temperature below a pre-determined limit.

Abstract: A thermal controller for driving a gate control unit of a gate-driven semiconductor switching device, the thermal controller comprising a junction temperature estimation module for generating an estimated junction temperature for the switching device, a gate voltage control module for modifying a gate voltage of the switching device, a switching frequency control module for modifying a switching frequency of the switching device, and a duty cycle control module for modifying the duty cycle of the switching device. In use, the thermal controller is adapted to activate one of the gate voltage control module, switching frequency control module and duty cycle control module dependent upon the estimated junction temperature in order to maintain the actual junction temperature below a pre-determined limit.

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.