Active Power Smoothing Control Of A Doubly-Fed Wind Power System

With the large-scale grid connection of wind power,the impact on the big power grid cannot be ignored.In particular,the active power fluctuations of the wind power system usually cause fluctuations in the grid voltage,resulting in a decline in power quality.In severe cases,the entire power system may even collapse.Therefore,it is necessary to smoothly control the power output from the wind power system,thereby reducing the impact on the power grid.In this paper,smooth control strategy for wind power fluctuations and battery-supercapacitor hybrid energy storage system(Hybrid Energy Storage System,HESS)carried out research.In this paper,the working principle of the doubly-fed electric machine is analyzed firstly,and the various components of the doubly-fed wind power generation system and HESS are mathematically modeled to realize the independent control of the stator side of the doubly-fed motor and the rotor-side converter.(RSC)establishes a dual closed-loop control strategy for power and current,and can achieve maximum wind energy tracking control.For grid-side converter(GSC),the main purpose of its control strategy design is to stabilize the DC bus voltage and design voltage and current.Double closed loop control strategy.Finally,the effectiveness of the control strategy is verified by simulation in MATLAB/Simulink.Secondly,the adverse effects of wind power output fluctuating power on grid voltage are analyzed,and the wind power smoothing control strategy is proposed.In this paper,HESS composed of battery-super capacitor is selected for wind power power smoothing control.Through the mathematical derivation of the energy storage characteristics of HESS,the system has the characteristics of high power density and high energy density.Then the common topology of HESS is analyzed and the advantages and disadvantages of each topology are pointed out.Aiming at the energy storage characteristics of batteries and supercapacitors,this paper studies an active cascaded topology.Based on this topology,the HESS energy management scheme is further established and the HESS capacity configuration method is proposed.Then,the overall control scheme of HESS to suppress the wind power fluctuation is proposed.The control strategy of the bidirectional DC/DC converter is established according to the HESS energy management scheme.For the DC/DC(A)converter,a multi-hysteresis current control strategy is designed to enable the battery to operate in the segmented current mode to prevent the supercapacitor state of charge(SOC)from deviating from the set operating interval minimum limit;for DC/ DC(B)converter,design power and current double closed-loop control strategy,so that the super capacitor priority to stabilize the wind power fluctuation power.Due to the low cycle life of the battery,a fuzzy controller that can output variable filter coefficients is designed for HESS,so that the wind power can reduce the smoothness of wind power transmission to the grid under the premise of meeting the requirements of grid connection.Compared with the fixed filter coefficient,the output of HESS can be adjusted in real time,avoiding the frequent charge and discharge of the battery and optimizing the HESS control.Finally,in order to further verify the reliability of the HESS control strategy in practical applications,a HESS-based physics experiment platform for the doubly-fed wind power generation system was built.The experimental verification was carried out to verify the effectiveness of the HESS power smoothing control strategy.