Enhanced hysteresis current controller for a permanent-magnet synchronous machine

With a conventional hysteresis current controller the power output of an inverter fed synchronous machine decreases if the set point of the current becomes to high. This appears because the voltage of the DC link is too low to apply the desired current. Therefore the fundamental component of the current is not in phase with the fundamental component of the voltage. This phase difference increases with increasing set point. This paper describes a method to avoid this increasing phase differnce by changing the conventional hysteresis control. For this purpose the time is calculated from which the current has to be decreased. The theory and some simulation results are shown. The output power can be further increased if the set point of the current leads the fundamental component of the voltage so that the fundamental components of voltage and current are in phase.