Grid-connected Single Phase Photovoltaic Inverter

Nowadays, on account of the problems of environmental pollution and exhaustion of energy resources becoming worse and worse, exploring and using of new energy become more and more important, solar energy is accepted commonly for its advantages such as economical and cleanness, and the inverter is the most important power converter in the PV generator system, whose performance will directly influence the efficiency of the use of solar power. This paper focus on single-phase grid-connected system which can work on not only the photovoltaic grid-connected system but also the photovoltaic independent system, the control method of virtual value outer loop and instantaneous value inner loop, which can eliminate the static error, as well as make the output wave well. So, this paper analyzed the topology of the system, control strategy and the key technology of grid-connected such as Digital PLL and anti-island.Firstly, the significance and good foreground of the solar power using is narrated, the main content of this subject is simply introduced, and the topology and operating principle of main circuit are analyzed in detail, the structure of control circuit is simply introduced, the structure and the calculate course of parameters of output filter for operation independently or grid-connected are given, and the design was testified by simulations and experiments.Based on the analysis of the main circuit work, the needed conditions of grid-connected and the control target of the inverter were presented, several relatively popular control methods of inverter are simply introduced using block diagram. Based on SPWM, voltage or current control can make the switch of operation independent and grid-connected easy, and have some advantages, such as invariable switching frequency, simplify signification, and easy realized. This method made the output wave well, and also made the system have a fast dynamic response. Subsequently, DPLL was introduced in detail. The structure of phase locked loop circuit and operating principle were researched. Using the capture function of DSP, considered the time-delay of the synchronous signals of grid which was sampled by circuit, analyze its reasons, the method of leading α are used, gave the diagram of program, the experiment results testify that the output current of the inverter have the same phase with the gird, the efficiency of the inverter is 1, this method is availability.Islanding effect should be well solved in grid-connected photovoltaic system. This paper presents the meanings and the criterion of the islanding effect, shows the causations of islanding effect happened, shows its hazards, testifies the needed of anti-islanding effect, analyses the active and passive detecting methods separately, then testifies the validity of active frequency drift by MATLAB.Finally, TMS320LF2407A of TI incorporated is used as the main controller, a 1kW experimental prototype is produced, the experimental waveforms of operation independent and grid-connected are obtained. It shows that the control strategy and the designed circuit can satisfy the design requests, this prototype works safely and stably.