A SOGI-FLL-Based Type-3 Synchronization System for Single-Phase Grid-Connected Applications

Synchronization systems are crucial for the efficient functioning of grid-connected power converters, typically designed around the phase-locked loop (PLL) concept. While type-2 PLLs are commonly featured in literature, the need for enhanced phase tracking, such as in applications like more-electric aircraft, necessitates the exploration of type-3 PLL designs. Designing advanced type-3 PLLs with high filtering capabilities is challenging; the shift from type-2 to type-3 PLLs adversely impacts stability, and incorporating additional filtering elements to achieve greater filtering ability may exacerbate this issue. This article focuses on single-phase ($\boldsymbol{1\phi}$) applications and suggests a straightforward yet effective approach using the second-order generalized integrator-based frequency locked loop (SOGI-FLL) concept to develop advanced type-3 synchronization systems with high filtering ability. To validate this approach, theoretical investigations based on linear time-invariant (LTI) and linear time-periodic (LTP) modeling are presented, along with comparative results showcasing the performance against state-of-the-art $\boldsymbol{1\phi}$ type-3 PLLs.