Amplitude/Phase Estimation Decoupling and Damping Improvment of Discrete-Time Three-phase Multi-Resonant Frequency-Locked-Loop

Frequency-locked loops (FLLs) are widely used for the synchronization of the renewable energy generations (REGs). Despite the design concept, they can be broken down into a pre-filter and a frequency adaptive controller (FAC). The structure of the pre-filter determines the amplitude/phase estimation decoupling (APED) ability and the degree of freedom to adjust the damping property of the whole FLL system. This paper provides a new framework for pre-filter design to achieve a discrete-time multi-resonant FLL with the APED ability as well as a fast and well-damped dynamic response, which cannot be achieved simultaneously by the existing design. The proposed FLL can also operate stably under long-sampling-period condition, because the discrete-time design makes the resonant frequency realized accurately.