A control system for an electric motor comprises a current controller which produces a set of voltage demands for the motor, a current sensing means arranged to produce a current sensing output indicative of electric current in the motor, and a current signal processing means arranged to process the current sensing output signal to produce a modified current signal in which at least one harmonic component present in the current sensing output signal due to inaccuracies in the current measurement is removed or substantially reduced. The modified current signal is combined with a demanded motor current to provide the input to the current controller.