Airborne wind energy is a promising newly emerging wind energy harvesting technology. Due to low material use and high potential harvesting density it aspires to be competitor to the conventional wind turbines we see today. Kitepower bv, a company in the Netherlands, is developing a airborne wind energy system based on a flexible kite. To be able to get a share in the energy market, reliability, safety and long term operation are aspects that are still challenging. The kite is controlled by a robot, called a kite control unit(KCU), that is suspended under the wing and steers the wing inside the wind window to create a traction force. This research focuses on improving long term operation by improving the power supply of this KCU. A wind turbine attached to the KCU is used as a power supply, but the electronic power conversion has not been optimized yet. A maximum power point tracker is optimised for this system, in which a new control model is used. Here the rotational speed is taken as a controlled variable. In addition, a method to protect the battery and the electrical system is implemented when abundant energy is available. This research shows how a converter is designed and how it can be controlled to provide the demanded functionalities.