DLGCJS电力工程技术Electric Power Engineering Technology2096-3203电力工程技术编辑部中国江苏dlgcjs-42-3-1792096-3203(2023)03-0179-0910.12158/j.2096-3203.2023.03.020TM615A智能电网技术Smart Grid Technologies基于ESO和分数阶PID的改进P&O控制策略Improved P&O control strategy based on extended state observer and fractional order PID施昕昕SHIXinxin
为了提高光伏电池转换效率、降低能量损失,有必要研究最大功率点跟踪(maximum power point tracking, MPPT)方法。针对传统扰动观察法(perturbation observation method, P&O)存在无法兼顾跟踪速度与稳态精度、在光照度发生较大变化时会产生误判现象的问题,文中提出一种能适应环境变化的变步长P&O控制策略。首先,利用光伏电池刚启动时类似恒流源的特性获取当前光照度下的短路电流,通过固定电流法推导出最大功率点(maximum power point, MPP)的参考电压;其次,当光照度突变时,提出功率修正方法,并给出突变时的变步长调整策略;最后,设计基于线性扩张状态观测器(linear extended state observer, LESO)的分数阶比例积分微分(fractional order proportion integration differentiation, FOPID)控制器,可以对算法输出的参考电压进一步进行跟踪补偿。仿真结果表明,所提控制策略可以提高稳态精度和跟踪速度,有效提高光伏电池的输出功率。
In order to improve the conversion efficiency of photovoltaic cells and reduce the energy loss, the maximum power point tracking (MPPT) method needs to be studied. Aiming at the problem that the tracking speed and steady-state accuracy of the traditional perturbation observation method (P&O) cannot be balanced, and misjudgment occurs when the environment changes greatly, a variable-step P&O control strategy that can adapt to the environmental changes is proposed. Firstly, the short-circuit current under current illumination is obtained by using the characteristics of the photovoltaic cell similar to the constant current source when it first starts, and the reference voltage of the maximum power point (MPP) is derived by the fixed current method. Secondly, when the illuminance changes abruptly, the power correction method is proposed, and the variable step size adjustment strategy is given. Finally, a fractional order proportion integration differentiation (FOPID) controller based on linear extended state observer (LESO) is designed, which can further track and compensate the reference voltage output by the algorithm. Simulation results show that the proposed control strategy can improve the steady-state accuracy and tracking speed, and effectively improve the output power of photovoltaic cells.
变步长扰动观察法(P&O)线性扩张状态观测器(LESO)功率修正分数阶比例积分微分(FOPID)控制最大功率点(MPP)variable step-sizeperturbation observation method (P&O)linear expansion state observer (LESO)power correctionfractional order proportion integration differentiation (FOPID) contorlmaximum power point (MPP)国家自然科学基金资助项目61873120国家自然科学基金资助项目(61873120)引言
目前,全球都面临着传统能源日益短缺、环境污染愈发严重的问题,绿色可再生能源的开发与利用获得越来越多国内外学者的关注[1]。太阳能因其分布广且可持续、无污染的特点成为研究重点。光伏电池是一种基于光生伏特效应,将太阳光能转换为电能的装置。为了提高光伏电池的转换效率,光伏发电系统须尽可能地工作在系统的最大功率点(maximum power point, MPP)处。
常用的最大功率点跟踪(maximum power point tracking, MPPT)算法[2-3]主要有电导增量法(incremental conductance method, INC)[4]、扰动观察法(perturbation observation method, P&O)[5-9]、固定电压法(constant voltage method, CVT)等。其中P&O由于控制逻辑简单且硬件实现方便,在工程上得到大量应用,但其存在扰动步长的设定无法兼顾跟踪速度和稳态精度、在较大光照度变化下会产生方向误判的问题。为了提高传统P&O的跟踪效率,很多学者对其进行了改进。常见的改进方向为算法结合,如文献[10]将CVT与P&O相结合,可以加快跟踪速度,但须额外采集开路电压或者短路电流,并且当光伏组件变化时,算法须进行一定的改动,算法移植性很差。另外,文献[11]在P&O中加入功率预测法也是一种改进方向,其可以防止算法在光照度突变时发生误判,但这种方法须在2次采样周期中间增加1次采样,增加了算法运行时间,并且无论当前光照度是否产生较大变化都会额外进行采样,导致跟踪速度变慢。
文中针对传统P&O存在的缺点,提出一种能自适应环境的变步长P&O控制策略。该控制策略分为启动阶段和运行阶段。首先,启动阶段利用光伏电池刚启动时类似恒流源的特性获取当前光照度下的短路电流,通过固定电流法推导出MPP处的参考电压。其次,在光照强度发生突变时引入功率修正法,避免了算法发生误判[12],并给出光照度发生突变时的变步长调整策略。当算法进入运行阶段,对MPP处电压进行分区,以便系统在出现故障后能快速重新到达MPP处。最后,设计基于线性扩张状态观测器(linear extended state observer, LESO)的分数阶比例积分微分(fractional order proportion integration differentiation, FOPID)控制器对当前环境下的参考电压进一步跟踪修正,并在Matlab/Simulink平台中进行仿真,验证了该方法具有良好的动稳态性能,同时能快速应对外界环境的变化。
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