Due to the bypass diodes, the partially shaded photovoltaic (PV) string exhibits multiple peaks in the P-V curve. And the conventional Maximum Power Point Tracking (MPPT) methods are not capable of tracking the global peak (GP) under partially shaded condition (PSC). In order to track the GP fast and efficiently under uniform irradiance condition (UIC) and PSC, a modified incremental conductance (INC) method is proposed in this paper. This method can not only detect the occurrence of PSC, but also determine if the other peaks need to be tracked under PSC by using the relationship between the minimum current at other peaks and the short circuit current to enhance the tracking speed. In order to improve efficiency, the converter duty cycle will be regulated slightly to ensure that the operating point reaches in the vicinity of GP, after the approximate GP is located. The Matlab simulation results show that the proposed method is faster and more efficient than other methods. It only requires 3 and 11 sampling cycles to locate the GP under UIC and PSC, respectively. Its overall tracking efficiency is increased by 13.61%, 4.28% and 0.42% under UIC, PSC and one-day irradiance profile respectively, compared to the conventional INC method. INDEX TERMS PV string, maximum power point tracking (MPPT), global peak (GP), uniform irradiance condition (UIC), partially shaded condition (PSC)

The maximum power point tracking (MPPT) is a strategy that allows imposing the PV array operation point on the maximum power point (MPP) or close to it under any environmental condition. The conventional incremental conductance (INC) algorithm is the most popular algorithm. But due to the fixed step size, its response speed is low under the rapid change of the solar irradiation level or load resistance. In this paper, a new MPPT technique is proposed to enhance the response speed. It consists of two stages: (1) the computing stage and (2) the regulating stage. The computing stage includes the coarse positioning operation and fine positioning operation. And an initial value of the duty cycle is generated in the computing stage, according to the characteristics of the DC-DC converter and the characteristics of the I‐V curve. The regulating stage regulates the duty cycle of the DC-DC converter with a small step size, which can improve the tracking efficiency. And the computing stage can enhance the response speed. A simulation comparison of the proposed MPPT technique with other techniques is carried out in MATLAB/Simulink under different scenarios. The simulation results reveal that the response of the proposed algorithm is 4.6 times faster than that of the INC under these scenarios, and the proposed algorithm has higher efficiency.

This paper examines approximation-based fixed-time adaptive tracking control for a class of uncertain nonlinear pure-feedback systems. Novel virtual and actual controllers are designed that resolve the meaninglessness of virtual and actual controllers at the origin and in the negative domain, and the sufficient condition for the system to have semiglobal fixed-time stability is also provided. Radial basis function neural networks are introduced to approximate unknown functions for solving the fixed-time control problem of unknown nonlinear pure-feedback systems, and the mean value theorem is used to solve the problem of nonaffine structure in nonlinear pure-feedback systems. The controllers designed in this paper ensure that all signals in the closed-loop system are semiglobally uniform and ultimately bounded in a fixed time. Two simulation results show that appropriate design parameters can limit the tracking error within a region of the origin in a fixed time.

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