Research On Ripple Power Control Strategy For Single-phase Single-stage PV System

PV (Photovoltaic) rooftop on-grid system is considered to be the most popular form of PV power generation technology in the future. In such PV system as PV roofs, the PV cell is connected to a single phase power grid or the load via an inverter. As a key component in the PV system, the inverter has a direct impact on performance, efficiency and cost of the overall PV system. Single-phase single-stage inverter featuring of low cost, high reliability and flexible configuration is the most promising topology in the PV system. This paper consider the application of PV rooftop on-grid system as the background, and single-phase single-stage grid-connected PV systems as the object of study, and improve overall system performance and output power quality as the crucial point. Single-phase single-stage grid-connected PV inverter topology with the function of ripple power suppression based on a symmetrical half bridge circuit was proposed, and work principle, control methods, model analysis and system design methods of single-phase single-stage PV inverter were studied deeply.For the DC voltage ripple problem of single-phase full-bridge grid-connected PV inverter, on the basis of the research result of suppress output ripple DC voltage in single-phase rectifier, a novel single-phase single-stage grid-connected PV inverter topology structure to eliminate the secondary voltage ripple of DC side of the inverter were proposed. The working principle of the topology was explicated in detail and the mathematical model of the topology was analyzed. The key technologies, including the mathematical model and the output characteristics of the PV cell, the maximum power point tracking algorithm, the DC voltage control, the grid current control and phase-locked loop were studied deeply.On the basis of the analysis of working principle of the topology, the decoupling current control technology based on fuzzy self-adaptive PI control was proposed, and the new PV inverter topology was simulated in Matlab/Simulink environment. Accuracy and validity of theory of eliminating of the secondary ripple of DC voltage and the simulation results were analyzed.The last, design of hardware of this novel single-phase single-stage PV inverter topology was implemented from three aspects of the main circuit, control circuit and driving circuit, and the design of the system controllers parameters was implemented, and software flow diagram of the system was given out. Based on that, a single-phase PV system prototype with 200W power rating was developed. The digital control system with the core of DSP+CPLD is constructed. The experimental results show that the prototype has obvious advantages in efficiency and output power quality.