Wind Turbine Control Theory

Chapter 1

Introduction.

In this chapter the basic knowledge of the wind turbine control theory and principles of control of variable-speed, variable blade-pitch-to-feather wind turbine will be described. The previous result made by Matthew Carl Homola, that describing work of standard turbine controller, will show that it is important to modify standard baseline controller. The advanced controller strategy with FAST simulation will be explain in chapter 5. In this chapter I will try to explain control principles by simple language in order to provide good understanding of main idea of the master thesis.

1.1 Control of wind turbine and its challenges

Control strategy is a brain of wind energy conversion system. Properly choosed and

The pitch angle is controlled in such a way as to maintain constant generator power.

1.3.2 Control measurement filter

From the figure 1.4 we can see that the generator speed measurement goes through filter first. It is single-pole low-pass filter with exponential smoothing, which reduce high-frequency disturbances the control systems. It is very important to filter the generator speed measurement , because both the generator-torque and blade- pitch controllers use the generator speed measurement as the feedback input.

According to publication [4] the discrete-time recursion (difference) equation for this filter is: (1.6) with (1.7) where u is the unfiltered generator speed (input), y is the filtered generator speed (output measurement), a is the low-pass filter coefficient, n is the discreet- time-step counter, Ts is the discrete time step, fc is the corner frequency.

Define the filter state, (1.8)

Derive a discreet-time state space representation of this filter: (1.9) where is the discrete-time state matrix, is the discrete-time input matrix, is the discrete-time output state matrix, is the discrete-time input transmission

The diploma thesis task is to modify the torque controller, thus regions 1 1/2 and 2 will be studied. The control objective of torque controller is to maximize power capture. It means to hold a constant value of that corresponds optimal power coefficient for the rotor. Do not pay attention to external damping simplify equation 1.5. Thus in steady state rotor rotation is in balance between aerodynamic torque applied by wind and the electrical torque applied by generator. (1.10) The power coefficient is the relation between mechanical power and power of the wind, it is the measure of mechanical power delivered by the rotor to the low speed shaft of the wind turbine: (1.7) The wind turbine's mechanical depends on the blade's and aerodynamic parameters of wind turbine design. With fixed parameters of the blade (the aerodynamic shape, taper, and twist distribution) is a determined function of the blade tip speed ratio (ratio of blade tip speed to wind speed) with a single maximum value. In variable-speed turbine it is possible to vary ω in order to have constant value of Thus standard control should follow the control low according to following