Ground-based Step-down AC-AC Power Electronic Converter for High Altitude Wind Energy Harvesting System

High altitude wind power (HAWP) generating system poses several benefits over conventional wind power (CWP) generating system. An air-borne electric generator is held at high altitude above the ground surface with buoyancy provided by light gas filled blimp/aerostat. In order to minimize the size of the blimp and to reduce the number of electric components in the air-borne system, generation of electrical power is carried out at three phase medium voltage AC (MVAC) and transmitted to the ground station (without any power conversion) using electromechanical tethers. Thus, transmitted power is interfaced into the distribution level grid at 415 V and 50 Hz. This paper evaluates possible power electronic converter (PEC) topologies that can be used to convert variable voltage and variable frequency three phase medium voltage AC power into constant frequency distribution level grid voltage. Three different PEC topologies are proposed that allow generation and grid side current control and generation side maximum power point tracking (MPPT) control. In addition, the proposed PECs provide step down of voltage and electrical isolation with the distribution grid. Suitable active and passive components are selected for 100 kW HAWP system and overall semiconductor losses are evaluated. The converters are simulated using computer software programs PSIM-9 and MATLAB. The converter that exhibits good efficiency, easy control of generation and grid side current as well as facilitates MPPT control of HAWP generation side is selected for grid interface of isolated HAWP system.