Research On Frequency Control Of Renewable Power System Considering Demand Response

Recently years,the pentration rate of wind power in the power grid has become higher and higher.The frequency control problem caused by wind power has become a research hotspot.Due to decoupling operation characteristics,wind farms do not have the ability to participate in frequency regulation.Traditional frequency regulation mainly relies on conventional units and energy storage system.Frequency regulation by conventional units requires sufficient reserve capacity of the power system.Energy storage system is expensive.So traditional frequency regulation methods are uneconomical.With the development of smart.grids,demand side resources have also begun to participate in power system frequency control.Being abundant and distributed evenly in power grid,demand side resources are very potential in frequency control.How to make demand side resources participate in frequency control more effectively is an urgent problem to be solved.Firstly,this paper introduces the principle of primary and secondary frequency regulation of power system considering renewable energy source,and establishes a frequency control model of power system including wind farm.Then the principle of demand side resources participating in frequency control is introduced,and the traditional control strategy of demand side resources participating in frequency regulation based on air conditioning loads is established.Traditional control strategy have problems.It's inflexible.Demandside resources are controlled in a long period.And it may cause secondary fall or counter-rebound of frequency.Therefore,this paper proposes a decentralized control strategy.Based on the traditional control strategy,two dynamic frequency trigger signals are established for each demand side equipment,so that each equipment can have equal opportunities to participate in the power system frequency control according to the frequency fluctuation.The quantity of equipment on the demand side depends on the deviation of frequency.Then it can alleviate the problem of the rebound of the frequency in the opposite direction.The state of demand side resources depends on their users or environmental factors to a certain extent.Therefore,it is necessary to coordinate demand side resources with the energy storage system for frequency regulation.A traditional coordination control strategy is introduced.It uses two filters with fixed time constants to divide the grid frequency fluctuation into high frequency fluctuation and intermediate frequency fluctuation.T he two parts are responded by the air conditioning loads and the battery energy storage system respectively.Then a fuzzy control strategy is proposed based on the traditional coordination control strategy.The fuzzy control strategy can change the time constant of the traditional filter in real time,according to the state of charge and the charging/discharging speed.So the air conditioning loads and the battery energy storage system can participate in the frequency control more permanently.And user comfort can be improved.The sevice life of battery energy system can be extended.