Document Type : Article
Department of Electrical and Computer Engineering, University of Kashan, Kashan, Iran
Single-phase voltage source inverters (SP-VSIs) are widely used in grid connected solar photovoltaic (PV) systems. This paper deals with the dynamic modeling and stability analysis of single-phase grid connected PV inverters taking the PLL dynamics into account. The PLL structure employed in this paper includes two control branches; the main branch, known as phase estimation loop, extracts the phase and frequency of the grid voltage and the other branch, known as voltage peak estimation loop, determines the grid voltage amplitude. In this way, the paper first proposes design considerations for the dc-link voltage control and PLL control loops. Then, unified dynamic modeling of the SP-VSI system comprising PLL, dc-link dynamics and grid is presented and linearized block diagram of the whole system is extracted. The linearized block diagram depicts the interaction between the control loops of the PLL and dc-link system, where the PLL control loops consist of phase/frequency and amplitude estimation loops of the grid voltage. Next, the small signal stability of the full system is presented, and impacts of grid strength, operating point, and PLL closed loop bandwidth on the performance of SP-VSI are investigated by the modal analysis and time domain simulations.