Investigation of Harmonics Content in PWM Natural and Regular Sampling including Dead Time and Load Current Phase

Modern wind power plants typically comprise of type IV wind turbines and therefore switched power converters form an integral part of these plants. These converters produce harmonics in output voltage and currents, which can trigger electrical resonances formed by cable capacitances and transformer inductances. Lower frequencies above the fundamental (referred to as baseband) have a high quality factor, Q, thus these frequencies are poorly damped. It is therefore essential to know the harmonic spectrum of the converter. This paper investigates harmonics generated due to widely used non-symmetrical regular sampling, taking into consideration the effect of dead time (when switching the semiconductors) and the phase of the output current relative to the fundamental voltage reference. The investigation has been performed in theory, through simulations and laboratory measurements. A detailed discussion of the results obtained through the three methods has been provided. New contributions in this paper are the investigation of harmonic amplitude and phase due to the phase of the load current together with coupling of both baseband and sideband harmonics.