Source topology for wind turbines with decreased mains current harmonics, further reducible via functional minimization

The paper presents a current-source inverter topology tailored for large multi-megawatt wind turbines. The proposed topology can inherently benefit from the distance between the generator and the mains because the consequent length and possible layout of the power cables may enable the realization of a significant portion of the dc-link inductance. In order to improve the efficiency and to allow the possible utilization of rugged inexpensive thyristors, pulsewidth modulation (PWM) modulation is not used. Unity fundamental power factor at the mains is guaranteed at any load condition while the fifth and seventh harmonics of the mains line currents can be reduced by proper system design at a desired turbine speed, considered most suitable for its operation. Further harmonic reduction is achievable through an active filter controlled via a newly proposed PWM methodology that does not belong either to a carrier-based or to a classical space vector modulation approach. Such a controller relies on a real-time minimization of a proper functional and is capable of implementing true-feedback current regulation. Experimental results from a 10 kW prototype are presented and validate the developed analytical computations.