Research On The Influencing Factors And Evaluation Of Power Quality For Small Wind Turbine

The application constrained problem of small wind turbines has arisen due to its poor power quality.In order to find power quality optimization measures,the research on influencing factors and evaluation method of power quality has become an important subject in the field of wind power generation.Based on international and national standards,firstly,the indicators of power quality conform to the operating characteristics of small wind turbine are selected.Then the relevant test indexes of external characteristics and power quality in some kinds of wind turbines,which consisting of several permanent magnet synchronous generators(PMSG)and different airfoils of wind wheel,are obtained.And the valid data is analyzed to acquire some interaction between the wind power coefficient,test indexes and influencing factors.In addition,above results are verified by MATLAB/Simulink simulation,and the evaluation criteria of each test index are proposed.Then the reliable evaluation indexes of small wind turbine are presented based on experiment results and simulation.Finally,the paper puts forward the Multi-target evaluation of power quality by MATLAB program,which can be used to explore ways and accumulate the experience for evaluation and improvement of power quality in small wind turbines.There is various factors’ influence on several power quality indicators and its’ mechanism is analyzed.To begin with,the special experimental study on power quality of wind turbine units with several structures of generator and different wind wheels is achieved.Afterwards the conclusions relating to each influencing factor are proposed.Such as adjusting the tip speed ratio or wind speed,slotting the airfoil of wind wheel and changing the number of pole pairs,starting torque or rated power,whether there is some relevance to the variation of power quality indexes,including the current and voltage total harmonic distortion,voltage negative-sequence and zero-sequence unbalance degree and power factor,as well as how to explain the existing relevance.The simulation model of wind turbine power quality is built and its parameters are set up so that the simulation indicators are obtained and experimental results are confirmed.Based on the wind turbine,PMSG and AC load model,the power quality simulation of small wind turbines is studied by means of Simulink circuit model.For the sake of ensure that the simulation coincides with the test,the power coefficient of the wind turbine model is set up according to the external characteristic experiment.Besides,the PMSG and load model parameters are adjusted in accordance with the rated parameters and factory reports of testing generators.Ensure that the simulation variables and data processing methods are consistent with the experiments so that the simulation indicators of power quality and testing results can corroborate with each other.The evaluation indexes of power quality are selected,and the influencing weight of different factors to each indexes are obtained.According to international and national standards,along with experimental and simulation results,the evaluation standards of power quality indicators for small wind turbines to explore are discussed.Accordingly,the current and voltage total harmonic distortion,voltage negative-sequence unbalance degree and power factor are chosen as the evaluation indexes,and the wind power coefficient is selected as the auxiliary evaluation index.On the basis of entropy method,the restriction of generators’ structure parameters to the voltage total harmonic distortion and voltage negative-sequence unbalance degree,the weight of wind speed influence on power factor and the correlation between the tip speed ratio and power coefficient are analyzed.The evaluation process of power quality for small wind turbines is presented,and it is applied to evaluate testing data.In order to ascertain all kinds of conditions of power quality optimum,accordingly the weight analysis theory combine analytic hierarchy process(AHP)and entropy method,a multi-target evaluation method can determine the difference of power quality is put forward.Furthermore,the evaluation process is achieved by MATLAB,and experiment results proved that the power quality evaluation method is reliable.