Current-Source Topology for Wind Turbines Capable of Providing Leading Power Factor While Reducing Line Current Harmonics

The paper presents a current-source inverter topology conceived for multi-megawatt wind turbines. The proposed scheme utilizes two series-connected three-phase inverters employing fully controllable switches and a proper interconnection transformer with the mains. In order to improve the efficiency and allow the use of high power devices, the inverters are switched at mains frequency. The axial flux permanent magnet generator is directly coupled to the turbine (gearless solution) and possesses very low leakage inductance. The overall control technique allows to impose independently two desired quantities selected out of the set of three composed by: a) The total average voltage at the DC input side of the inverters; b) The power factor at the mains interconnection point, which can be chosen unitary leading or lagging; c) The amount of the 5^th and 7^th harmonics in the mains line currents. In specific operating points of the turbine a significant reduction of two such harmonics can be already achieved without additional filters and/or active harmonic compensation. Nevertheless the introduction of an active harmonic compensator can achieve proper harmonic reduction - also up to higher orders - more independently and on a wider range of operating conditions. Experimental results, obtained from a 10 kW prototype with an axial flux permanent magnet generator are presented