Research On Integrated Control Of Doubly Fed Wind Turbines Participating In Grid Frequency Regulation

With the rapid growth of wind power market in the world,the installed capacity of wind turbine is also increasing,when they are connected to the grid on a large scale,the stability of grid frequency will also be affected inevitably,Therefore,it is necessary to put forward higher requirements for the grid connection of wind turbine,that is,when the grid frequency falls,the wind turbine can maintain stable operation and provide power support for the recovery of grid frequency to some extent.First of all,this paper takes doubly fed wind turbine as the research object,the problem of doubly fed wind turbine participating in grid frequency regulation is studied deeply,and proposes a virtual synchronous control strategy for the rotor side converter of doubly fed wind turbine,which makes doubly fed wind turbine have similar interface characteristics of synchronous generator,and can provide necessary inertia support in response to grid frequency fluctuation,by this way,the problem of equivalent inertia reduction caused by large-scale wind power grid connection will be sloved.Secondly,considering that in the same wind farm,most of the wind turbines are running in different working conditions,the wind energy obtained is different,resulting in their different active frequency regulation capabilities.In order to ensure the stable operation of the wind turbine after participating in active frequency regulation,this paper practically considers the situation of the wind turbine operating conditions and the frequency regulation requirement of power system,and takes the wind speed and frequency deviation values as the input signals of the fuzzy logic controller to adjust the rotational inertia parameters in the virtual synchronous control accordingly,so as to realize the adaptive control of the inertia support of the doubly-fed wind turbine.Then,considering that the doubly-fed wind turbines lack the ability to participate in the primary frequency regulation of the power grid,this paper further studies the adaptive control of the pitch of the doubly-fed wind turbines,by using the constant load reduction coefficient to maintain the load reduction operation of the wind turbine,its standby power changes with the wind speed,the reserve power changes with the wind speed,what's more,the size of the load reduction factor of the wind turbines is adjusted proportionally according to the size of the grid deviation value,the primary frequency regulation function of the double fed wind turbine is realized through the variable pitch adaptive control.Finally,by combing the adaptive control of virtual synchronous generator and pitch adaptive control,a integrated control strategy of doubly fed wind turbines is proposed to take full advantage of both.the control scheme designed in this paper is conducive to maintaining the stability of grid frequency after wind power grid connection and promoting the long-term development of wind power industry.