High Voltage Hybrid Generator and Conversion System for Wind Turbine Applications

This paper presents the design of a high voltage hybrid generator (HG) and conversion system for wind turbine applications. The HG combines wound field (WF) and permanent magnet (PM) rotor excitations. At any given speed, the PM induces a fixed stator voltage while the WF induces a variable controlled stator voltage. The HG alternating output is rectified via a passive rectification stage, hence the machine net DC output voltage is controlled over a prescribed, but limited range. The split ratio between PM and WF rotor sections is considered as varying from a fully WF rotor, or traditional synchronous generator (SG), to some ratio of PM to WF excitation. The turbine operational characteristics and maximum wind velocity variations between turbines in a wind farm are used to define the WF to PM split ratio. Both a 3-phase and a 9-phase stator winding design are investigated. The 9-phase winding results in 4.2% higher output RMS voltage that yields a more power dense solution. It further yields lower rectified DC-link voltage ripple. The HG mass, loss audits and efficiency discussions are presented. In order to investigate the feasibility of the HG concept a small scale laboratory prototype is designed and operational test results presented that show good agreement with the simulation model results.