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This report describes initial results with simulation of power system control using wind farms with grid support.

This report is the final report of a Danish research project “Operation and control of large wind turbines and wind farms”. The objective of the project has been to analyse and assess operational strategies and possibilities for control of different typesof wind turbines and different wind farm concepts. The potentials of optimising the lifetime/energy production ratio by means of using revised operational strategies for the individual wind turbines are investigated. Different strategies have beensimulated, where the power production is decreased to an optimum when taking loads and actual price of produced electricity into account. Dynamic models and control strategies for the wind farms have also been developed, with the aim to optimise theoperation of the wind farms considering participation in power system control of power (frequency) and reactive power (voltage), maximise power production, keep good power quality and limit mechanical loads and life time consumption. The projectdeveloped models for 3 different concepts for wind farms. Two of the concepts use active stall controlled wind turbines, one with AC connection and one with modern HVDC/VSC connection of the wind farm. The third concept is based on pitch controlled windturbines using doubly fed induction generators. The models were applied to simulate the behaviour of the wind farm control when they were connected to a strong grid, and some initial simulations were performed to study the behaviour of the wind farms whenit was isolated from the main grid on a local grid. Also the possibility to use the available information from the wind turbine controllers to predict the wind speed has been investigated. The main idea has been to predict the wind speed at a windturbine using up-wind measurements of the wind speed in another wind turbine.

This report describes models and control strategies for 3 different concepts of wind farms. Initially, the potential in improvement of grid integration, structural loads and energy production is investigated in a survey of opportunities. Then simulationmodels are described, including wind turbine models for a fixed speed wind turbine with active stall control and a variable speed wind turbine with doubly-fed induction generator. After that, the 3 wind farm concepts and control strategies are described.The 3 concepts are AC connected doubly fed turbines, AC connected active stall turbines and DC connected active stall turbines. Finally, some simulation examples and conclusions are presented.

The three different controller designs presented herein are similar and all based on PI-regulation of rotor speed and power through the collective blade pitch angle and generator moment. The aeroelastic and electrical modelling used for the time-domainanalysis of these controllers are however different, which makes a directly quantitative comparison difficult. But there are some observations of similar behaviours should be mentioned: • Very similar step responses in rotor speed, pitch angle, and powerare seen for simulations with steps in wind speed. • All controllers show a peak in power for wind speed step-up over rated wind speed, which can be almost removed by changing the parameters of the frequency converter. • Responses of rotor speed, pitchangle, and power for different simulations with turbulent inflow are similar for all three controllers. Again, there seems to be an advantage of tuning the parameters of the frequency converter to obtain a more constant power output. The dynamicmodelling of the power controller is an important result for the inclusion of generator dynamics in the aeroelastic modelling of wind turbines. A reduced dynamic model of the relation between generator torque and generator speed variations is presented;where the integral term of the inner PI-regulator of rotor current is removed be-cause the time constant is very small compared to the important aeroelastic frequencies. It is shown how the parameters of the transfer function for the remaining controlsystem with the outer PI-regulator of power can be derived from the generator data sheet. The main results of the numerical optimisation of the control parameters in the pitch PI-regulator performed in Chapter 6 are the following: • Numericaloptimization can be used to tune controller parameters, especially when the optimization is used as refinement of a qualified initial guess. • The design model used to calculate the initial value parameters, as described in Chapter 3, could not berefined much in terms of performance related to the flapwise blade root moment (1-2 %) and tilt tower base moment (2-3 %). • Numerical optimization of control parameters is not well suited for tuning from scratch. If the initial parameters are too faroff track the simulation might not come through, or a not representative local maximum obtained. The last problem could very well be related to the chosen optimization method, where more future work could be done.

This report presents a new developed Saber Toolbox for wind turbine applications. This toolbox has been developed during the research project “Simulation Platform to model, optimize and design wind turbines”. The report provides a quick overview of the Saber and then explains the structure of this simulation package, which is different than other tools e.g. Matlab/Simulink. Then the structure of the toolbox is shown as well as the description of the developed models. The main focus here is to underline the special structure of the models, which are a mixture of Saber built-in blocks and new developed blocks. Since the developed models are based on Saber built-in blocks, a description of the libraries from Saber is given. Then some simulation results using the developed models are shown. Finally some general conclusions regarding this new developed Toolbox as well as some directions for future work are made.

Models for wind power installations excited by transient events have been developed and verified. A number of cases have been investigated, including comparisons of simulations of a three-phase short circuit, validation with measurements of tripping ofsingle wind turbine, islanding of a group of two wind turbines, and voltage steps caused by tripping of wind turbines and by manual transformer tap-changing. A Benchmark model is also presented, enabling the reader to test own simulation results againstresults obtained with models developed in EMTDC and DIgSILENT. This survey on of generator and power electronic concepts was carried out in co-operation between Aalborg University and Risø National Laboratory in the scope of the research programmeElectric Design and Control.

A dynamic model of the wind farm Hagesholm has been implemented in the dedicated power system simulation program DIgSILENT. The wind farm con- sists of six 2MW NM2000/72 wind turbines from NEG-Micon. The model has been verified using simultaneous powerquality measurements on the 10 kV terminals of a single wind turbine and power performance measurements on two wind turbines. The verification shows a generally good agreement between simulations and measurements, although the simulations at higher windspeeds seem to underestimate the power and voltage fluctuations. A way to improve the simulation at higher wind speeds is suggested.