Research On Control Strategy Of TL Single-phase Grid-connected Inverter

With the development of PV grid technology and the state vigorously promoting distributed power generation applications especially in recent years, the household kilowatt-class power grid-connected inverter is increasingly becoming a hot research. However, the isolated single-phase grid-connected inverter topology which is getting more and more attention is becoming main choice for lower-power grid-connected inverter due to the light weight and high efficiency. It is also the development direction of the grid-connected inverter in future.Some basic problems of the non-isolated single-phase grid-connected inverter such as circuit topology, PWM algorithm, grid current control, suppression of common mode current and maximum power point tracking are analyzed in this paper.First of all, this paper focuses on the Boost-based two-stage non-isolated grid-connected inverter topology as the development trend of the households low power photovoltaic power generation system. Basic operating principle of the front stage and inverter topology SPWM modulation of the latter stage are respectively analyzed.This paper analyses control strategy of single-phase inverter in the synchronously rotating and stationary coordinate. As the existence of a steady-state error in the conventional PI control, this paper proposed the Quasi-resonant proportion control scheme that can track current without steady-state error. This paper established mathematical model of the TL single-phase current-grid inverter to simulate PI controller and PR controller, to verify the correctness of the theoretical analysis. The results of the simulation proved the correctness of the theoretical analysis.As common-mode current is a inevitable problem in non-isolated photovoltaic grid-connected system, this paper takes non-isolated single-phase full-bridge topology as a model to analyze the reason for the common-mode current in the single phase full bridge TL inverter, and then summed up the different influences in different modulation modes and main circuit topologies. Analysis of two kinds of topology that can eliminate common mode current provides the general rule for common-mode suppression. For the defects in these two types of topological, this paper studied a novel H6topology that can alleviate leakage current issue. Results from theoretical and simulation show that the proposal is correct.Finally, on the base of mathematical model and volt-ampere characteristics, this paper studied the maximum power point tracking technology in the PV grid, proposed a simple adaptive variable step-size algorithm which make maximum power point tracking speed and steady-state accuracy can be guaranteed at the same time in PV system.