Research On Improvement Of P＆O Method For MPPT Of Permanent Magnet Direct Drive Wind Power System

Permanent magnet direct drive wind power system is widely used in the field of wind power generation for its simple structure and good reliability.Faced with the fierce competition of wind power industry,maximum power point tracking（MPPT）,a significant technology to improve the economic benefit of wind power generation,has become the focus of research.MPPT is a control method to achieve maximum wind energy capture by adjusting the operation state of wind turbine.Perturbation and observation method（P＆O）is the most widely used algorithm in MPPT.There are many problems in the current research of P＆O method,such as difficult step selection and slow tracking speed,which seriously affect the utilization of wind energy,it is necessary to improve the P＆O method.To improve the efficiency of wind energy utilization,this paper focuses on the improvement of P＆O method.The main work and innovations are as follows:1.Pitch angle and tip speed ratio are the parameters affecting wind energy utilization coefficient.To simplify the algorithm,the current research of P＆O method only takes the tip speed ratio into consideration.Therefore,this paper proposes an improved P＆O method considering pitch angle adjustment,which uses the classification method to control the pitch angle.Considering the performance of tracking speed and accuracy,a group of adaptive step size is introduced in the improved P＆O method,which divides the region in accordance to the estimated wind speed.In the area away from the maximum power point,a larger step size is adopted;in the area close to the maximum power point,a smaller recursive step size is adopted.2.To solve the problem of slow tracking speed of P＆O method,the P＆O method is combined with the tip speed ratio method: when the wind speed changes greatly,the tip speed ratio mode is used to determine the approximate range,and then the P＆O mode is used;when the wind speed changes slightly,only the P＆O mode is used.It is difficult to balance the tracking speed and accuracy by using the fixed step size in the P＆O mode of the combined method.This paper takes Fibonacci sequence with step size factor as the perturbation step size.3.Traditional sliding window method uses fixed initial window and fitting threshold,which makes it slow and inaccurate to obtain information from wind speed,speed and other data.To solve this problem,this paper introduces dynamic initial window and dynamic threshold,and proposes an improved sliding window algorithm.The improved algorithm is more rapid,complete and accurate for data segmentation.The speed difference data after segmentation is used for step size factor design.