Three-Phase EPLL-II

This chapter presents the second member of the three-phase enhanced phase-locked loop (3EPLL) structures. This structure, called the 3EPLL-II, is a direct extension of the 3EPLL-I in order to obviate its major shortcoming with regard to input signal unbalance. The 3EPLL-II inherits all properties of the 3EPLL-I, and in addition to those, it avoids the double-frequency error caused by the negative-sequence component. The 3EPLL-II is comprised of a 3EPLL-I on top and another modified 3EPLL-I on the bottom. The chapter explains the derivation of 3EPLL-II and the modular representation of 3EPLL-II. Representation of the 3EPLL-II in stationary domain is developed and a linear time invariant (LTI) model for the 3EPLL-II is derived for design purposes. The chapter highlights that the performance of the 3EPLL-II is controlled by two gains which makes its design stage very simple.