Frequency estimation for grid-connected converters under time-varying harmonics and inter-harmonics

In order to allow the power flow control of grid-connected converters, this paper presents an improved scheme for grid fundamental frequency tracking. A comparison under frequency variation and time-varying harmonic and inter-harmonic condition is also discussed in order to show the method robustness. The scheme is based on a frequency-locked loop operating integrated with a decomposition core, which utilizes a recursive implementation of a modified Hanning filter. The frequency value information is used to perform the modulation and demodulation required to make de decomposition into the core. The compared frequency estimation scheme is based on a zero-crossing with an interpolation correction. Simulation results show that the proposed scheme is able to estimate the fundamental component, including relative quadrature companion signal and the frequency value more accurately and stably than the scheme used to perform the comparison.