Variable speed control of a small wind turbine
An electronic controller has been developed for a wind turbine which uses a passive pitching mechanism and a permanent magnet generator. The turbine rotor is a 3 bladed, down wind horizontal axis design with a diameter of 3.4m. The machine, manufactured by Proven Engineering Ltd., produces 2.2kW at a wind speed of 12m/ s and a rotor speed of 30Orpm. Passive regulation is achieved through a variation of blade pitch controlled by balancing the aerodynamic, centrifugal and spring forces acting on each blade. A production machine has been instrumented and laboratory and field test data collected; from this data a mathematical model has been derived. A power electronic interface (DC-DC booster) was designed and built to transform the generator voltage to a fixed DC voltage. A controlled load is used together with feedback to the booster to set an appropriate load resistance according to operating conditions. Current demand from the generator (used in the control) is derived either from the difference between the rotor speed and a reference speed, or directly as a function of the rotor speed (feed-forward control). This thesis deals with the design and testing of the 3 compensators which govern the wind turbine control using both simulated and measured results. The overall objective of the controller is to maximise the energy yield from the wind turbine, subject to realistic constraints imposed by the power electronic design in the context of this particular design.