Research On Control Strategies Of The Direct-drive Permanent Magnet Wind Power Generation System Based On Dual PWM Converter

As the demand for energy increases all around the world, wind power, as the greatcommercial prospect of new energy power generation, has attracted more attention anddeveloped rapidly in recent years. Among them, the direct-drive permanent magnet windpower generation system has been widely used for its simple structure, reliable operationand higher power generation efficiency advantages.In this paper, the research background and the development status of wind powergeneration system are introduced firstly, and then a variety of topologies of thedirect-drive permanent magnet wind power converter is analyzed. In the whole system, asthe converter can convert the output of the generator and the electrical energy of thevariable frequency to constant voltage and constant frequency respectively, and it can alsoimprove the power factor of the system, so it is essential for the stable and high efficientoperation of the entire system. In this paper, the chosen dual PWM converter has the mostadvantageous topology currently, and appropriate control strategies for effective control ofdirect-drive permanent magnet wind power generation system is the key to improve thesystem performance.Secondly, a mathematical model of the various components of the direct-drivepermanent magnet wind power generation system is established. According to thetechnology of coordinate transformation, the mathematical model of the permanentmagnet synchronous motor in the synchronous rotating coordinate system is established aswell. To the motor, zero d-axis current vector control strategy is adapted, and the specificform is dual closed-loop control of the speed of the out ring and the current of inner ring.The output active power of the generator, torque ripple and the wind energy utilization ofthe wind turbine generator system are achieved. A fuzzy PI current regulator is designed toimprove the dynamic performance of the system. Then the mathematical model of thegrid-side PWM converter is analyzed, to the grid-side PWM converter, a vector controlstrategy based on the grid voltage oriented is adapted, the specific form is the dualclosed-loop control of the voltage loop and the inner current loop. By the control of the dual PWM converter DC voltage, the output active power of the generator can betransferred to the grid in time, and by the control of the reactive current component of thegrid, the independent regulation of the reactive power is realized. In order to keepmaintain the DC voltage stable when the change of the wind speed is rather frequent, afuzzy PI voltage regulator is designed.Finally, a simulation analysis of the direct-drive permanent magnet wind powersystem was done in the MATLAB/Simulink environment, and the results show that thecontrol strategy adapted in this paper allows the system to achieve maximum powertracking control and run in the state of the variable speed constant frequency (VSCF)generation. Meanwhile, the output current of the system has good sinusoidal and smallharmonic, the unity power factor to the network is achieved, and the feasibility as well asthe effectiveness of the control strategy is verified.