A simple and low-cost PLL structure for single-phase grid-connected inverters

This paper presents a new PLL structure for single-phase grid-connected systems. Its peculiarity consists in the presence of an orthogonal signal generator, not dependent on the frequency of the input grid voltage and realized by simple and low-cost analog and digital devices. The paper gives a detailed description of the proposed PLL structure, also dealing with the appropriate design of the analog section that includes integrator and derivator circuits. The effectiveness of the proposal is validated by laboratory experiments on a prototypical realization of the proposed PLL structure.