Multifunction Single-phase Grid-connected Device For Photovoltaic Power Generation

Under the background of the global energy situation, the use of new energy has become the important measure to solve the problem of energy crisis and solar energy has become one of the key object of the development of new energy with its endless reserves, clean, safe and pollution-free characteristics. At the same time, more and more distributed energy as well as non-linear loads are connected to the electricity grid, which makes the harmonic wave increase massively in power grid and cause serious harm to power system. This paper analysis the structure and working principle of photovoltaic grid inverter and shunt APF, summarizes the differences and similarities of the two, studys the unified control strategy, so as to make the photovoltaic grid power generation system have two functions of grid-inverter generation and active filtering, which not only purifies the power grid, improves the utilization rate of equipment and reduces the equipment cost,but also in a certain extent promotes the development of photovoltaic industry.For harmonic current detection of mul-tifunction grid-connected power generation device,this paper analyzes the single-phase harmonic detection method based on instantaneous reactive power theory, and carries on the improvement, at the same time,this paper proposes a harmonic detection method based on the theory of the Fryze reactive power, the method is better than the detection method of instantaneous reactive power theory in harmonic detection accuracy and the corresponding speed.Compared with the L filter, LCL filter has higher ability of high frequency attenuation and parameter design and main control circuit is also more complex. For LCL filter parameter design, this article obtains the value scope of each parameter from the LCL mathematical model, through the graphic analysis method to analysis of the coupling relationship between each parameter, based on the fundamental wave and limit conditions of harmonic output, and then painted out the relationship of the curves that the harmonic frequencies and the harmonic attenuation rate produce when each parameter changes in the same figure, which produces the best effect of LCL parameters within the certain scope of the resonance frequency and harmonic attenuation. This paper puts forward a kind of active damping control based on capacitive current feedback to suppress the LCL filter resonant. In order to achieve good tracking effect of instruction current, this paper employs the command current repetitive control strategy. Through the simulation of the multifunctional photovoltaic (pv) grid power generation unit under the different ways including the model of the single photovoltaic power generation, single active filter and the photovoltaic power generation with the active filtering, results verify the validity of the parameters and the feasibility of the control strategy. Finally, it simply decribes the design of system hardware circuit.