Integrated Aerodynamic And MPPT Control Design For Low Wind Speed Wind Turbines

The exploitation of wind energy in low-wind-speed region has gradually become an important approach for the future development of wind power in China.However,the energy loss of low-wind-speed wind turbine(LWSWT)during the process of maximum power point tracking(MPPT)is aggravated by the change in wind condition and the corresponding increase of wind turbine size.Following the traditional idea of separated design for wind turbine physical and servo control system,this problem cannot be solved in a more effective way by mainly depending on the optimization of MPPT controller parameters.Considering the significant effects of the wind turbine physical parameters on the MPPT performance,it is worthy exploring the approaches that take advantage of the coordination between the wind turbine's physical and MPPT control system and conduct the integrated design of the physical parameters and the MPPT controller parameters in order to effectively improve the efficiency of wind energy extraction for LWSWTs.It should be pointed out that,smaller cost of physical parameters adjustment for the improvement of control performance can be achieved by finding out the parameters that are sensitive to control performance and adding them into the integrated design.Moreover,the inherent constraints of wind turbine physical design can be satisfied more easily.In this paper,the mechanism of the wind turbine physical parameters affecting the effectiveness of MPPT control is studied and the sensitive parameters that significantly affect MPPT performance are extracted.Furthermore,the integrated design of sensitive physical parameters and MPPT control strategy is investigated in order to explore a feasible approach for achieving high efficiency of LWSWTs.Major contributions of this paper are as follows:(1)The mechanism of wind turbine physical parameters affecting MPPT performance is explored and analyzed and the parameters sensitive to control effectiveness are extracted.It is found that the aerodynamic parameters of the wind turbine are more sensitive to the MPPT performance and are more easily to be adjusted comparing with the structural parameters.Therefore,the integrated design of aerodynamic and MPPT control not only facilitates the coordination and improvement of wind energy extraction efficiency,but also has great practical significance in satisfying the inherent constraints of wind turbine physical design and achieving overall engineering feasibility.(2)Aerodynamic optimization methods of wind turbine blades considering the effects of sensitive aerodynamic parameters on MPPT are proposed.Based on the existing aerodynamic design methods,the objective function is adjusted with consideration of the effects of sensitive aerodynamic parameters on MPPT and the optimization model without specific controller parameters is established.In this way,the closed-loop performance of the system can be further enhanced while the principles of classic separate design are preserved.In addition,this integrated design approach makes the results more general because it does not depend on specific control strategy.The optimization methods proposed in this paper are introduced as follows:A.Multi-angle-of-attack(Multi-AOA)airfoil design considering the effects of airfoil geometry on MPPT.It has been found that MPPT performance can be significantly improved by the fine tuning of airfoil shape.Then,based on the existing multi-AO A design methods,the distribution law of the airfoil's operational AO A and its description based on the proportion of the inflow wind energy are investigated in order to determine the multiple design AO As and their weighting coefficients in the objective function so that the existing airfoil multi-AOA designs that mainly rely on engineering experience can be improved.B.Aerodynamic optimization of wind turbine blades considering the effects of the flatness of wind power coefficient curve on MPPT.Based on the closed-loop wind turbine system,the influence of the flatness at the top of wind power coefficient curve on MPPT is analyzed.The dispersive distribution of the tip-speed-ratio(TSR)and its description based on the proportion of inflow wind energy are investigated.On these basis,a multi-point aerodynamic optimization method with a weighted sum of power coefficients at multiple TSRs as the objective function is proposed in order to improve the existing blade optimization method without considering MPPT dynamics and only optimize the aerodynamic performance of single working point.C.Aerodynamic optimization of wind turbine blades considering the effects of optimal TSR on MPPT.Based on the conventional inverse blade design method,the mean efficiency of wind energy capture,a closed-loop performance index of wind turbine,is used as the objective function by considering the effects of the optimal TSR on both the static aerodynamic performance and MPPT dynamics of the wind turbine.Moreover,the former separate optimization of TSR,chord,and twist angle is improved to a joint optimization.D.Multi-point aerodynamic optimization of wind turbine blades considering the effects of wind power coefficient curve flatness and optimal TSR on MPPT.Based on the proposed method in B,the influence of the varying optimal TSR on the dynamics of MPPT is taken into account.The mean efficiency of wind energy capture is utilized as the objective function and it is transformed to the weighted sum of wind power coefficient at multiple TSRs.The design TSRs and their weights in the objective function can be dynamically adjusted according to the varying distribution of the operational TSR so that better coordination of static aerodynamic performance with MPPT dynamics and correspondingly higher wind energy production can be achieved.Simulation results based on the commercial software Bladed show that,compared with the MPPT controller optimization where the efficiency increment is generally about 1.0%,the integrated design scheme proposed in this paper can finally improve the efficiency more than 2.0%and thus significantly alleviate the unfavorable effects of low wind speed on the power conversion efficiency for the wind power generation system.Engineering analysis and dynamic model experiments are suggested to further verify the overall engineering feasibility of the new integrated design sheme.