Reduced cost current-source topology improving the harmonic spectrum through on-line functional minimization

The paper presents a current-source inverter (CSI) topology tailored for large multi-megawatt wind turbine applications. The cable distance between the generator and the mains enables 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, PWM modulation is not used in the main conversion chain. Unity fundamental power factor at the mains is guaranteed at any load condition while the 5^th and 7^th harmonics of the mains line currents are reduced by choosing a proper nominal operating point for the turbine. Further harmonic reduction is achieved through an active filter controlled via a newly proposed methodology suitable for digital signal processor (DSP) implementation. Such a controller relies on a real-time minimization of a proper functional and is capable of implementing true-feedback current regulation. A part of design simulation results, aimed at constructing a 10 kW prototype, are presented.