Modeling And Simulation Of Direct-driven Permanent Magnet Synchronous Generator And Study Of Low Voltage Ride-through

With the global fossil energy depletion and environmental problems worsen,the development and utilization of renewable energy represented by wind and solar energy have attracted more and more attention.In the already installed wind turbines,permanent magnet direct drive wind turbines which have eliminated the speed gearbox,due to the use of multipole low speed permanent magnet synchronous generators,thus reducing the cost of maintenance and manufacturing.The use of fully-rated converter in variable-speed constant-frequency power generation,not only improve the reliability of the operation,but also greatly improve the efficiency of wind energy utilization.Therefore,permanent magnet direct drive wind power generation system has become increasingly popular and abstracted largely research.In this paper,the control strategy of permanent magnet direct drive wind power generator is studied,and the simulation research is done in DIgSILENT,which provides the theoretical basis for practical application.Firstly,the structure and characteristics of permanent magnet direct drive wind power generation system is analyzed by this thesis.Then,the mathematical model of wind power generation system which contains variable pitch system,wind turbine and transmission chain is established and modeled in DIgSILENT.Then,the coordinate transformation theory commonly used in the control of wind power generation system and several commonly used reference coordinate systems in DIgSILENT are introduced.The mathematical model of permanent magnet synchronous motor(PMSM)and converter is established in abc three-phase static coordinate system and dq rotating coordinate system.According to the above analysis,the control strategy of machine side and grid side converter is studied.In order to realize the decoupling control of active and reactive power,the grid voltage orientation strategy is applied to grid side converter.After analysis the maximum power point tracking principle and rotor flux orientation and principle,the zero d axis current control strategy is proposed to machine side converter.The correctness and feasibility of the controlling strategy are validated by the simulation analysis of the above model under variable wind speed by DIgSILENT.Then,according to the requirements of the Namibian grid code,a wind farm containing three permanent magnet direct-drive wind turbine wind turbines was established in DIgSILENT.The grid-connected controller including power factor control,active control and frequency response is designed,and the above-mentioned grid-connected controller is simulated by software platform to verify whether it meets the requirements of grid connection.Finally,this paper introduces the basic principle and related standards of low voltage ride through.The dynamic characteristics of grid side converter and DC side are analyzed.This paper presents a scheme of DC-Chopper,which is based on the DC-side protection scheme with dual energy dissipation resistance,and proposes an estimation method for the resistance value of energy dissipation.Finally,the feasibility and correctness of the proposed scheme are verified by simulation.