| The development of rich offshore wind energy resources has become a hotspot of resea rch today.With the continuous expansion of the installed scale of offshore wind power,the incorporation of offshore wind power leads to the reduction of the equivalent inertia of the system,and then the stability of the grid frequency is affected,which brings some difficulties to the frequency modulation control of offshore wind power.Doubly fed wind turbine is the main type of offshore wind farm,which does not have the support ability of traditional synchronous generator to grid frequency.At the same time,the inefficient frequency modulation methods will cause the further decline of inertia and frequency modulation ability.Therefore,in order to improve the stability of the offshore wind power system and reduce the load interference,this paper studies the frequency modulation technology of the offshore wind turbine with the virtual inertia control.The main research work of this paper includes:Firstly,according to the characteristics of the marine environment of the offshore wind farm,the four component model of the offshore wind speed and the characteristics of the offshore wind turbine are established.Then,the mathematical models of doubly fed induction generator(DFIG)and grid side converter are established.These mathematical models are the research basis of virtual inertia control of offshore wind power system.Secondly,in order to make the power electronic inverter to simulate the traditional synchronous generator characteristics on the external characteristics,a leading lag fuzzy virtual synchronous generator control method is proposed.This method is used to improve the moment of inertia of the system so that the frequency stability of the system can be maintained.When the parameters of VSG change,it is easy to cause oscillation.When the load is suddenly changed,it is easy to cause power instability.The second-order virtual synchronous motor model is used to analyze the influence of the change of damping coefficient on the power oscillation,and the fuzzy control algorithms is used to adjust the damping parameters.In addition,the response speed of virtual synchronous machine is improved by adding leading and lagging links.The simulation results show that the control method is effective and feasible.Thirdly,in order to reduce the equivalent moment of inertia of power grid,a method of energy storage inertia control based on fuzzy auto disturbance rejection control(ADRC)is proposed.Specifically,the fuzzy ADRC is designed to control the operation of the energy storage system and provide support for the active frequency of the power grid.In order to effectively estimate and compensate the system disturbance and uncertainty caused by the complex and changeable marine environment,fuzzy rules are used to automatically modify the parameters of extended state observer,so as to realize the intelligent distribution of output power and improve the anti-interference ability of the system.Finally,considering that the overshoot and over discharge of energy storage device will directly affect the working life of energy storage battery,a hybrid energy storage system(HESS)coordinated control method based on fuzzy control is proposed.In this method,the fuzzy controller is designed according to the state of charge of the battery and the voltage value of the super capacitor.Specifically,the fuzzy controller is used to adjust the high and low frequency components of DC bus voltage deviation in real time and online,so as to realize the coordinated control between battery and super capacitor.Simulation results show that the fuzzy energy storage coordinated control method effectively solves the problem of over charging and over discharging of energy storage equipment,and improves the operation life of energy storage system. |
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