THE INVESTIGATION OF APPROPRIATE CONTROL ALGORITHMS FOR THE SPEED CONTROL OF WIND TURBINE HYDROSTATIC SYSTEMS

Abstract

This report consists of two chapters. The first is concerned with a new approach to pipe flow modelling and the second has to do with the simulation of the hydrostatic system which will be applied to a wind turbine.For the pipe flow model, the main focus has been to create a flow model which accounts for the frequency dependent friction, i.e. the fluid friction which occurs at non-steady conditions. The author is convinced that the solution to this problem lies in the velocity profile, as the friction is a direct result of the shear stresses in the pipe. At the same time, it is possible to keep track of the velocity profile in the pipe as the pressure evolves in time and space.The new model utilizes the continuity equation for pipe flow and the equation of motion for axisymmetrical flow of a Newtonian fluid to find both a pressure distribution in the pipe and velocity profiles throughout the pipe. There are uncertainties whether the approach to find these velocity profiles done in the new model is correct.The modelling of the hydrostatic transmission to a wind power turbine is done using SIMULINK software. The design of the system and basics of the modelling are described inthe second chapter. The motor speed is regulated using a PID-controller and the generator torque is varied based on the pressure drop over the hydraulic motor. The PID-controller for motor speed seems be of good-enough quality and speed deviations are within acceptablelimits.Simulation results are given for one certain case with an initial rotor torque of 20kNm and an additional step torque of 20kNm.