Research On System Modeling And Control Strategy Of The Fresnel Concentration Photovoltaic System

Nowadays,concentration photovoltaic(CPV)technique as the third generation of photovoltaic technique is rapidly becoming a new focus of attention in the field of solar power generation.The CPV system has a lot of advantages,such as high power generation efficiency,less floor space,long component life,and so on.In the view of the problems found,this papers according this main line “mathematical model of the solar trajectory-analysis of focal spot shift and distortion in Fresnel concentrator-design of variable frequency control strategy-analysis and elimination of tracking error for dual-axis system” to expand.First,this paper systematically analyzes the celestial sphere and its related coordinate system in the mathematical model of the solar trajectory.Then deduces a mathematical model of the solar trajectory based on the previous documents.Finally,the simulation results show that the model can accurately calculate the solar trajectory,correctly capture and predict the sun's position,laying a foundation for further research.In the field of concentration photovoltaic system,the existing tracking device and tracking control strategy can not achieve zero error tracking.For a concentrator which has an incident error angle,almost no one analysis and research on the effect factors of the focal spot's offset and distortion.In order to enable the different tracking devices to choose the right concentrator and design parameters,this article chooses the common three types of Fresnel concentrators as a basis.By comparing and analyzing the focal spot's changes in the shape,uniformity and efficiency of the light-garthering on the receiving surface under the factors such as the concentrator type,incident angle,receiving surface calibration error,concentrator radius,focal length and the others to determine the main factors that cause the offset and distortion of the focal spot.The analysis can provide a basis in the selection of the concentrator for tracking devices with its tracking accuracy,which has high practicability and feasibility.Compared to the traditional time controlled tracking control strategy and fixed step tracking control strategy,a new control strategy for concentration photovoltaic tracking system using variable tracking frequency is presented.In this strategy,the solar trajectory can be discretized by sampling time and the threshold interval can be built by using the incident threshold angle of photovoltaic panel.By setting the error angle between the incidence light and the PV surface normal as a controlled volume,the strategy use the look-up table and iterative algorithm to compute and control this volume change in the threshold interval,and then the solar tracking system can achieve the solar tracking in variable frequency.By simulation and analysis,the strategy superior to the fixed-step tracking in the tracking accuracy,it can keep the PV modules output ratio above the set value.It's also better than the traditional time controlled tracking in the tracking consumption.Therefore,this strategy can reduce the system energy consumption and mechanical wear effectively.it has higher practicability and application prospect.In addition,some problems were found in research.In the past study,the researchers paid more attention on the optimization and accuracy of the tracking algorithm,but most of them ignored the system error brought by the time accuracy,the latitude and longitude error,the installation position error and the others.The major factors of system error should be taken into account,because the solar trajectory mathematical model and the time control algorithm were used as the basis of this research.In the end of this paper,we also presented a tracking error elimination method which can regulate the installation error.The experiment has showed that this method has good practicability and can eliminate the system error effectively.