Analysis of harmonic transfer in an AC excited generator including speed ripple

AC excited generators are favoured in some applications due to their features including generation at a constant frequency but a variable speed. With the rotor windings supplied from a static power electronic converter, harmonics are one of the major concerns in such systems. Based on a mathematical model of the AC excited machine, a method is developed to analyze the system or stator side harmonics as transferred from the rotor side. The effect of the rotor speed ripple, which can be caused by pulsating torque at low frequencies, is investigated. It is shown that the rotor speed ripple will modify the spectrum of stator current. Experimental tests and simulations are used to illustrate the phenomenon and verify the analysis.