Single-Phase Grid-Tied Inverters: Guidelines for Smoother Connection and Suitable Control Structure

This paper presents an analysis of grid connection synchronization characteristics to provide guidelines with a suitable control structure for single-phase grid-tied inverters. Thus, it is analyzed the grid voltage phase for a smooth connection. Moreover, different active power references and the arising of a DC grid current that may occur in the grid synchronization are also considered. Furthermore, it is discussed the effect of the grid voltage phase on the DC current magnitude, as well as the effect of the grid resistance, the grid inductance and their relation to weak grids. Therefore from the grid connection analysis a adequate control structure is suggested. To attain the grid synchronization this paper applies a resonant phase locked loop (PLL). Moreover, a current reference generation in the stationary frame is detailed. A proportional resonant controller is used for the current loop which can additionally provide selective harmonic compensation achieving the pursued control structure. Simulations results present the inverter and grid waveforms for the aforementioned analysis and control structure.