| Nowadays, on account of the problems of environmental pollution and exhaustion of energy sources become worse, the photovoltaic application has been a hot spot that most countries compete against each other to develop. As the main development trend of photovoltaic applications, grid-connected photovoltaic system will certainly be promoted rapidly.This paper focuses on single-phase grid-connected system. The topology, control strategy and parameter selection of grid-connected photovoltaic system are analyzed and studied in detail. The main contents are as follows:(1) The principles and characteristics of different main circuit topologies of grid-connected photovoltaic systems are analyzed at length. The parameter selection of main circuit in the system will concerns directly whether the system can work properly, and influences the quality of output current. The designing ideas and processes of the filters on both DC and AC sides are studied in this paper, and the formulas of the key parameters of the main circuit are derived and given out.(2) The tracking control of grid-connected current is the central technology that is studied in this system. This paper has studied several control strategies of single-phase grid-connected system, analyzed and researched the control method of zero error of current tracking, presented a method that combining the feed forward control of the power grid voltage with the power grid current, and treating the grid-connected system as an passive inverting system, could lighten the burden of adjuster, reduce the interference of noise and improve the shape of current wave. The simulation model of system is established in this paper and the experiments are carried out.(3) The characteristics of solar cell are strong nonlinear, and the output power is influenced by an intensity of illumination, the temperature of junction and other environmental conditions. Two of the most routine methods of maximum power point tracking (MPPT) are studied in this paper: perturbation and observation (P&O) method and incremental conductance (IncCond) method, which are the study and development foundation of other MPPT. This paper adopted a variable step method that is based on the average power to track the MPP of the solar arrays. This method guarantees the stability and rapidity of tracking process, and the experiments proved the method had a good performance of tracking.(4) Islanding effect should be prevented in grid-connected photovoltaic system, the active andpassive detecting methods in use nowadays are analyzed in this paper. According to the characteristics of the grid and load, this paper presented an islanding-effect detecting method based on phase leading, analyzed the principle of this method, and proved it through experiments. The phase-locked loop method of random phase angles is put forward, by which the sinusoidal quantity of random phase angles can be calculated, and phase leading can be realized and locked at random phase angles.(5) Monitoring subsystem is developed which is based on the DSP TMS320LF2407A, ATmegal64 and personal computer; it makes local and remote monitoring of grid-connected photovoltaic system come true, and simplifies display, communication and storage of the real-time operating data and analyse of history dada; also, it implements on-line setup and alteration of system parameter.(6) A set of software and hardware of grid-connected photovoltaic system is also developed here that is based on DSP TMS320LF2407, and it realizes the digital control of the whole system. The system has been operating without any fault for about 1 year. The results of the system and the analysis of data show that every index of the system, which is of high reliability and stability, is definitely fit to design demand.
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