Harmonics Estimation in Transient Conditions using Static and Dynamic Frequency-domain Techniques

Harmonics estimation during transients (e.g. caused by power quality events such as dips and swells) is a well-known, although less explored measurement problem in power systems, which deserves greater attention due to the changeable operating conditions of future smart grids. The classic frequency-domain harmonics estimator in nonstationary conditions is the Short-Time Fourier Transform (STFT). In this paper, the results achieved with this technique to estimate the amplitude of time-varying harmonics are compared with those returned by an extended version of the so-called Interpolated Dynamic Discrete Fourier Transform (IpD2FT), which in principle is more suitable to track phasor variations over time. Several simulation results show indeed that the IpD2FT exhibits better responsiveness and it is more accurate than the STFT in estimating the fundamental and odd-order harmonics. On the contrary, for weak even-order harmonics the STFT looks preferable. This scenario suggests that both techniques could be advantageously used together.