Research On Control Of Converter For Direct-driven Permanent Magnet Synchronous Wind Generation System

Over the last twenty years, renewable energy sources have beenattracting great attention due to the cost increase, limited reserves, andadverse environmental impact of fossil fuels. Wind energy isenvironmentally friendly, inexhaustible, safe, and capable of supplyingsubstantial amounts of power and is one of the fastest growing renewableenergy sources. The direct-drive wind power system which doesn’t needgear-box to improve system efficiency and reduces investment andmaintenance costs has become one of the hot spot in common severalkinds of wind power system structure. In the direct driving wind powersystem, the converters are employed to control the speed/torque of thegenerator and also the active/reactive power to the grid. Theimprovements of converter control technology ameliorate efficiency ofthe unit and power quality.Firstly, the current situations of wind power industry at home andabroad were described in this paper. By the development of wind powertechnology, the paper analyzes the kind of different inverter topologies inwind power system and it focuses on the structure of back-to-back PWMconverter topological. The wind turbine, permanent magnet synchronousgenerator and PWM converter which their mathematical models underthe three-phase static coordinate system and two-phase rotatingcoordinate system were builted in Simulink. Space vector pulse widthmodulation (SVPWM) control technical is adopted by the back-to-backPWM converter.Secondly, the double closed-loop control based on the rotormagnetic field oriented control strategy in the generator side and theclosed-double loop control based on the voltage oriented control strategyin the grid side were designed. Then the simulation model of the systemon the MATLAB was established and the simulation results show that thegenerator could follow the wind speed, capture the maximum windenergy. The gird-side could achieve unity power factor control and thevoltage of DC-bus could keep constant. Thirdly, the model based on direct power control in grid was buildeddue to slow response and the harmonic problem. Then an improvement ofthe direct power control (DPC) system was given out and the model ofsimulate based on the SVPWM was builded in Simulink. The results ofsimulation show that the system power harmonic rate was reduced.Finally, by studying the hill-climb searching algorithm (HCS), animprovement of traditional HCS was gaven out in this paper to achievethe maximum power point tracking (MPPT). This paper puts forward avariable step HCS hill-climb searching algorithm (HCS) and build thesimulate models. The results of simulation show that the variable stepperturbation MPPT method could track the change of wind speed andimprove the precision and rapidity of tracking the maximum power point.