  This letter proposes a new design of frequency-locked loop (FLL) which is
based on synchronous (dq) reference frame instead of stationary
({\alpha}\b{eta}) reference frame. First, a synchronous reference frame FLL
(briefly called SRF-FLL0) equivalent to the conventional FLL is proposed. Then
the SRF-FLL0 is improved by utilizing the phase error to acquire a better
performance. The small-signal modeling and parameter tuning of the improved
synchronous reference frame FLL (SRF-FLL) are presented. Finally, the
theoretical analysis and experiment results verify the superiority and
effectiveness of proposed SRF-FLL.
