Research On Undisturbed Switching Of Direct-drive Wind Turbine Sub-controllers

With the consumption of fossil fuels and the aggravation of environmental pollution, wind power generation is getting more and more attention by researchers all over the world because of the low cost of power generation and no pollution to the environment as a new and renewable energy. With the development of wind power generation technology, direct-drive permanent magnet synchronous wind power generation becomes one of the most potential methods for the simplified structure.Wind power generation is a compounded control system with multiple loading conditions and multiple controllers. It is particularly important for the stability of system that switching without disturbance between sub-controllers. This article focus on the sub-controllers based on the two typical loading conditions during the operation of wind turbine, the switching strategy of sub-controllers is mainly researched. The main achievements of the paper are as following:(1) The development status of wind power industry in the world is researched. The design of sub-controllers and the switching strategy between sub-controllers under the loading condition that the wind speed changes from the underrated wind speed to the over-rated wind speed. Based on the analysis of basic structure and working principle of wind turbine system, the mathematical models of wind turbine, permanent magnet synchronous generator (PMSG) and pulse-width modulation (PWM) converter are built. It lays the foundation for the analysis of sub-controllers and switching strategy.(2) The control strategy of sub-controllers under the loading condition that the wind speed changes from the underrated wind speed to the over-rated wind speed is researched and the wind turbine system simulation model with the sub-controllers is established based on Matlab/Simulink. The rotor flux-orientation vector control method is applied to control the generator-side converter for tracking the maximum power point of wind power under the loading condition that the wind speed is under the rated wind speed. At the same time, the voltage orientation control strategy is applied to control the grid-side converter to realize the decoupling control of active power and reactive power and keep the voltage stability of the DC-side capacitance. The pitch angle controller based on fuzzy algorithm is applied under the loading condition that the wind speed is over the rated wind speed, to reduce the wind energy capturing of wind turbine and keep the output power at the rated power.(3) Based on the analysis of the system characteristics and the reason that lead to the mutation of system control variables, the active disturbance rejection controller (ADRC) is applied to arrange transient of rotor current and control the mutation of rotor current caused by the switching process. The mutation of output power caused by the switching process is reduced and the power quality is improved. The simulation model of ADRC is established based on Matlab/Simulink. And the feasibility of switching strategy is verified by simulations.(4) The particle swarm optimization (PSO) algorithm is applied to optimize the parameters of ADRC for the reason of that ADRC has more parameters and it is complex to set. The validity of PSO is verified by simulations.