Research On A New Mode Of Direct-drive Permanent Magnet Synchronous Generators Wind Turbine Connected To Grid

Wind power has been developed for many years. The changeovers of wind power techniques from fixed pitch to controlled pitch and from constant speed constant frequency (CSCF) to variable speed constant frequency (VSCF),have been ongoing. Direct-drive permanent magnet synchronous generators wind turbine (D-PMSG), as a typical controlled pitch and VSVF wind turbine,has been paid increasing attention due to its remarkable advantage.With a D-PMSG connected to power grid by two back-to-back converters as the research subject, the main contents of this paper is as follows:The mathematical model of double PWM converter D-PMSG is established(including the wind turbine aerodynamics model, mathematical model of permanent magnet generators, PWM converter model), the D-PMSG complete control methods is researched.Wind turbine has been rated for safe operation in more than rated wind speed, through thevariable pitch angle control, the rotor position oriented space vector pulse-width modulation is adopted to achieve decoupling control of generator active and reactive power and generator speed. The grid voltage oriented SVPWM is applied to grid side inverter to achieve decoupling control of active and reactive power.Current domestic and international D-PMSG gird-connection have been analyzed, a new D-PMSG gird-connection has been proposed, through the advantages and disadvantages of various methods for comparison. This gird-connection process is:when the stator voltage and low-frequency bus voltage satisfied the condition of quasi-synchronization the AC-DC-AC converter was shorted in the main circuit by controlling the AC-DC-AC double PWM converter. The generator stator was directly connected to box-type transformer, the low-frequency power energy was transmitted to the back-to-back convertor station. The power energy was converted into 50Hz and transmitted into grid. The incorporation processes were simulated by using PSCAD/EMTDC software, the technical feasibility of this mode was verified.Grid-connection method presented in this paper eliminates the traditional D-PMSG full power converter for each unit, but all the units on one low-frequency bus are equivalent to a generator have the same speed, back to back converter station control the various unified synchronous generator speed, lead to some units can not run in the best characteristics of wind energy, some wind energy is lost, at the same time, a large-capacity converter station is increased. The initial investment, annual power output, investment return are analyzed by economic comparison of tradition and new grid-connection structure. Conclusion is that a new grid-connection structure has economically feasibility.