Frequency measurement using a frequency locked loop

A phase locked loop method is proposed for fast estimation of utility grid frequency, for control and protection purposes in grid-connected power converters. Using a second order generalized integrator (SOGI) and a `novel´ frequency locked loop (nFLL), which makes the SOGI frequency adaptive, the proposed SOGI-nFLL detects small and large step changes in frequency with fast response and without large overshoot. In this paper, the SOGI-nFLL method is analyzed, simulated and implemented in a Field Programmable Gate Array (FPGA). Its performance is compared with the original SOGI-FLL using simulations and experimental data. The experimental results verify that the proposed method results in smoother transients for frequency detection that may be used to reliably activate over-frequency protection within a half cycle.