随着传统化石能源的不断枯竭及环境污染问题的日益突出，太阳能作为一种 储量丰富，清洁环保的可再生能源，受到了世界各国的广泛关注。光伏发电是目 前太阳能最有效的利用方式之一，但由于光伏电池的输出特性具有较强的非线性 特征，其输出功率极易受到外界环境变化的影响，而无法保证光伏发电系统始终 稳定地工作在最大功率点(MPP)处。因此，需要采用最大功率点跟踪(MPPT)技术 来提高光伏发电的效率和电能质量。针对目前所提出的MPPT控制算法普遍存在 跟踪速度慢，稳定性差等问题，本文以独立光伏发电系统为研究对象，设计并改 进了基于滑模变结构控制的MPPT算法。?
本文首先介绍了光伏发电的研究背景及意义，并对光伏电池在不同外界环境 下的输出特性进行仿真分析。其次，通过对比各种DC-DC变换器的优缺点，选择 Boost变换器作为系统的主电路，并对其进行电路设计。再次，对光伏发电系统 MPPT的基本原理进行介绍，并对几种常用MPPT算法的工作原理及优缺点进行 对比分析。然后，对基于滑模变结构控制的MPPT算法进行研究。为保证系统在 外界环境改变的情况下，能够迅速稳定的实现MPPT，利用Boost变换器中的电感 电流与MPP处电流的差值，设计出传统滑模控制算法。同时，为进一步减小系统 在稳定状态下的功率振荡，通过在传统滑模切换函数中加入积分项及采用饱和函 数sat(s)代替指数趋近率中的符号函数sgn(s)，对传统滑模控制算法进行改进，最 终设计出了一种改进型滑模控制算法。最后，在Matlab/Simulink中搭建出MPPT 算法的仿真模型，并对不同MPPT算法的仿真结果进行对比分析。?
仿真结果表明，在外界环境稳定的情况下，改进型滑模控制算法与传统滑模 控制算法相比，在光伏电池输出功率的波动范围上减小了2.7W；同传统扰动观察 法相比，不仅功率的波动范围减小了3.6W，而且MPPT的时间也缩短了0.031s。 在外界环境变化的情况下，改进型滑模控制算法与其他MPPT算法相比，在系统 实现MPPT中，具有更快的跟踪速度和更高的跟踪精度。?
关键词：光伏发电系统；MPPT；滑模变结构控制；指数趋近率?
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With the continuous depletion of traditional fossil energy sources and the growing ?problem of environmental pollution, solar energy, as a kind of renewable energy with ?abundant reserves and clean environment, has received wide attention from all over the ?world. Photovoltaic power generation is one of the most effective ways to use solar ?energy, however, since the output characteristic of photovoltaic cells has strong ?nonlinear characteristics, the output power is extremely susceptible to changes in the ?external environment, and it is impossible to ensure that the photovoltaic power ?generation system always operates stably at the maximum power point (MPP). ?Therefore, maximum power point tracking (MPPT) technology is needed to improve the ?efficiency and power quality of photovoltaic power generation. Aiming at the problems ?of slow tracking speed and poor stability of the proposed MPPT control algorithm, this ?thesis designs and improves the MPPT algorithm based on sliding mode variable ?structure control with independent photovoltaic power generation system as the research ?object.?
This thesis first introduces the research background and significance of ?photovoltaic power generation, and simulation analysis the output characteristics of ?photovoltaic cells in different external environments. Secondly, by comparing the ?advantages and disadvantages of various DC-DC converters, the Boost converter is ?selected as the main circuit of the system, and the circuit design is carried out. Thirdly, ?the basic principle of photovoltaic power generation system MPPT is introduced, and ?the working principle, advantages and disadvantages of several common MPPT ?algorithms are analyzed. Then, the MPPT algorithm based on sliding mode variable ?structure control is studied. In order to ensure that the system can realize MPPT quickly ?and stably under the change of external environment, the traditional sliding mode ?control algorithm is designed by using the difference between the inductor current and ?the current at the MPP in the Boost converter. At the same time, in order to further ?reduce the power oscillation of the system under steady state, the traditional sliding ?mode control algorithm is improved by adding the integral term in the sliding mode ?switching function and replacing the sign function sgn(s) in the exponential approach ?rate with the saturation function sat(s), and an improved sliding mode control algorithm?was designed. Finally, the simulation model of MPPT algorithm is built in ?Matlab/Simulink, and the simulation results of different MPPT algorithms are compared ?and analyzed.?
The simulation results show that when the external environment is stable， compared with the traditional sliding mode control algorithm, the improved sliding ?mode control algorithm reduces the fluctuation range of photovoltaic cell output power ?by 2.7W. Compared with the traditional perturbation and observation method, not only ?the power fluctuation range is reduced by 3.6W, but also the MPPT time is also ?shortened by 0.031s. In the case of changes in the external environment, compared with ?other MPPT algorithms, the improved sliding mode control algorithm has faster ?tracking speed and higher tracking accuracy in the system implementation of MPPT.?
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