Research On Converter Control Of Direct-driven Permanent Magnet Wind Generation System Without Speed Sensor

With the non-renewable energy resource exhausting, the use and development ofrenewable energy get the worldwide attention, wind power technique develops fasterthan the others at present. Direct-driven permanent magnet wind power system is a vscfwind power system, it can realize the maximum power tracking and work without gearbox, so its maintenance cost is small, and it also has small effects on power grids andstrong low voltage operation ability, so it has got great public attention. In this paper,the control strategy of converter system for direct-driven permanent magnet wind powergeneration system and sensorless control method of the permanent magnet synchronousgenerator is studied, the main research contents are as follows:First the overall structure and the main components of the direct-driven permanentmagnet wind power system is analysed, and then mathematical model of the main partsconsist of wind turbine, transmission shaft, the permanent magnet synchronousgenerator and the PWM converter is built.The control strategy of back to back PWM converter is studied, it mainly dividesinto the control of the generator side converter and the power grid side converter. Thenuse mathematical model of the permanent magnet synchronous generator in two phaserotation coordinate and the field-oriented principle to analyse vector control theory ofthe permanent magnet synchronous generator, choose tip speed ratio as the maximumpower tracking method, last the double closed loop control strategy is set up, the outerring is speed and inner ring is current, the simulation results verify the effectiveness ofthe control strategy. Use mathematical model of the PWM converter connected to thepower grid and voltage vectordirectional principle to set up the double closed loopcontrol strategy of the power grid side converter, the outer ring is voltage and inner ringis current, the simulation results verify the effectiveness of the control strategy.The basic principles, the basic properties and the design method of the slidingmode variable structure control theory is analysed. The control goal is that the outputpower of generator fastly track the reference power, then the double closed loop controlstrategy is set up, the outer ring is power and inner ring is current, The simulationresults show that the output power of generator can fast track the maximum power, theerror is zero when the wind speed change, the response of the output power is fast andthe fluctuation of the output power is small.In order to overcome shortcomings and the insufficiency of the photoelectricencoder, sensorless control method of direct-driven permanent magnet wind powergeneration system is studied. Use the sliding mode observer to achieve the rotor speedand position estimation, first the traditional sliding mode observer equation is set up,then the existing chattering problem is analyzed, use modified saturation function to weaken the chattering strength. In order to better restrain the strength of the highfrequency chattering noise, the adaptive law of switch gain following the referencevalue of the angular velocity is designed and the expansion equation of the sliding modeobserver is built, then the adaptive law of the back emf and the electricity angularvelocity is designed. Last the sensorless control performance of direct-driven permanentmagnet for wind power system is simulated, the simulation results show that theproposed adaptive sliding mode observer can realize the rotor speed and positionaccurate estimation, and has strong robustness against the parameters change ofgenerator stator.