Optimal Control For Large-inertia Wind Turbine Generation System Covering The Whole Wind Speed Range

Developing renewalble energy,such as wind power,is an essential approach to solve the environmental problems caused by energy source utilitzation.On one hand,the randomness and intermittent of wind speed brings many challenges for power system operating.On the other hand,wind power limitation and grid-friendly requirements,such as power smoothing,impose adverse influence on economic and environment benefits.With the increasing of wind turbine capacity,large inertia of wind turbine augments this contradiction mentioned above.Therefore,study on the large-inertia wind turbine control system in different wind speed situation is significant to consider both inconomic,invironmental benefits and grid friendliness.This paper presents a novel control framework for large-inertial wind turbine covering the whole wind speed situation in terms of two dimentions including wind profile and wind fluctuations.The balance of wind energy conversion efficiency and power smoothing is taken into account below rated wind speed.In the region above or around rated wind speed,power fluctuations and mechnical loads are alleviated appendently.The main research works are as follows:1.The mathmetical model of wind turbine generator system is established,and the characteristics of rotational inertia are analyzed.Then a nonlinearity assessment method based on gap metric is proposed.Finally,a flexible control framework covering the whole wind speed environment is designed for large-inertia wind turbine generator system.2.In the operating region below rated wind speed,the impacts of large inertia on traditional OTC-MPPT control performance are analyzed firstly.The MPPT efficiency is enhanced by adopting a dynamic gradient estimator.Secondly,a high-efficiency MPPT strategy taking power smoothing into account is proposed by employing T-S fuzzy inference system.The stability and contro performance are porved by small signal analysis.3.Adaptive Multi-objective model predictive control(MPC)strategy based on proposed torque compensating structure is designed,to balance efficiency enhancement and power smoothing caused by large inertia.Furthermore,the stability and performance of presented controller is analyzed.The proposed control strategy refrains from ensuring stability the same as traditional MPC controller.4.In the region above rated wind speed,the fixed steady states for MPC are loosed as a set of half-freedom steady states based on large-inertia characteristics.This method is to reduce the pitch actions,and alleviate power fluctuations and mechanical loads.In addition,the computing speed of MPC solver at each sampling time is much enhanced by employing blocking strategy.5.To diminish power fluctuations and mechnical loads in the operating region around rated wind speed,a undisturbed switching control strategy based on event-driven method.The switching strategy defines two events:wind speed up-crossing event and down-crossing event.The dynamic switching region is established around rated wind speed.When the system is switched into this region,the operating points(OPs)are to move along with a dynamic vector until system OPs achieve to target region.Then the system controller can switch without any extra fluctuations between below and above rated speed region.The stability and control performance of proposed switching strategy are also analyzed.