The Research On Power Conversion Technique In Direct-driven Grid-connected Wind Turbine

High-power grid-connected wind turbine is the best economic way of cosmically wind power energy utilization. It has become the main way of wind energy utilization in the world nowadays. At the same time, the most of high-power grid-connected wind turbine works as constant speed and constant frequency (CSCF) including up-speed gear. It has low efficiency, makes mechanism spoilage and much noises. So the low-speed permanent magnet synchronous generator (PMSG) direct-driven grid-connected wind turbine which can track the maximal power point of wind power when the wind speed is slower than safe speed quickly becomes one of the hotspots of wind power generation technique research. This paper researches its high-power conversion circuit and its best control system.At first, this paper introduces the work principle, subassemblies and sorts of grid-connected wind turbine. Then, it compares the characteristics of many kinds of variable-speed and constant frequency (VSCF) wind turbine and concludes that the direct-driven PMSG wind turbine is the best choice. This paper then compares three kinds of power conversion circuit applied in it and advances a main circuit which is based on IGBT's power grade nowadays and is applied in high power direct-driven grid-connected wind turbine. It is made up of a six-phase rectifier, two paralleled BOOST chopper circuits and two paralleled SPWM inverters. This paper analyzes their work principle and optimizes the control system of the two paralleled BOOST chopper circuit. This paper also analyzes the two control methods: indirect-current control and direct-current control which are often used in voltage source SPWM inverter, explains its realization and compares their characteristics in detail. Then, this paper simulates the whole power conversion circuit in practice condition in PSIM which includes the two control methods. The simulation results indicate that the direct-current control method is better than indirect-current control not only in dynamic response, anti-disturbs, but also in restraining circumfluence which is often founded in paralleled inverter. So the paper concludes that the direct-current control method is the best control method of provided conversion circuit. At last, the paper designs the hard and soft realization of the whole control system primary which is based on direct-current control method and lists its hard principle and software flow charts. It can be referenced by the exploders of the practiced equipment.