# IpDFT-Tuned Estimation Algorithms for PMUs: Overview and Performance Comparison
## 6 Conclusions  
Recent research results have shown that if a preliminary fundamental frequency measurement is performed to compensate for the effect of static off-nominal frequency deviations, the accuracy of some of the most common estimation algorithms for PMUs can be greatly improved. Till now, to the best of Authors' knowledge, no clear performance comparisons between estimation algorithms exploiting the benefits of a preliminary frequency measurement have been reported in the scientific literature. In this paper, the performances of three alternative techniques for the estimation of AC waveform amplitude, phase, frequency and ROCOF based on an a prior 2-point Interpolated Discrete Fourier Transform (IpDFT) stage are evaluated in the very same _P Class_ or _M Class_ testing conditions specified in the IEEE/IEC Standard 60255-118-1:2018 and using data records of the same size. The algorithms considered in this study are: the corrected IpDFT (IpDFTc), the tuned Taylor Weighted Least Squares (TWLS) estimator, and the frequency Down-Conversion and low-pass Filtering (DCF) technique with two alternative types of low-pass filter. The performance comparison shows that the IpDFTc and the tuned TWLS methods are generally more accurate and exhibit shorter transients than the DCF technique, although the latter one still fulfills the Standard requirements in most testing conditions. Quite importantly, the behavior of the DCF algorithm is strongly affected by the chosen low-pass filter and it could be further improved by adopting custom optimization strategies for FIR filter design. The IpDFTc technique is preferable over short intervals and it overcomes the others  
Figure 2: Maximum TVE, \(|\)FE1, and \(|\)RFE1 values obtained with the IpDFTc algorithm, the tuned TWLS estimator and the DCF technique (using either the LSF or the STD filter), over 1000 experimental 4-cycle and 8-cycle data records with system frequency in the range [47 Hz, 52 Hz] and THD \(\approx\) 9.4%. The THD level slightly exceeds the limits specified in the Standard EN.  
when the analyzed waveform is affected by steady-state harmonic and inter-harmonic disturbances. However, it is considerably worse than the tuned TWLS estimator in the presence of amplitude or phase oscillations and it is not able to ensure compliance to the IEEE/IEC Standard in a few testing conditions. On the contrary, the tuned TWLS estimator is much more effective in dynamic conditions, it exhibits shorter synchrophasor and RO-COF response times (although with greater overshoots) and, assuming a reporting rate of 50 readings/s, it returns fully compliant results in the _P Class_ and _M Class_ tests described in the IEEE/IEC Standard over 4-cycle and 8-cycle observation intervals, respectively.  
Conceptualization, D.B., D.M. and D.P.; methodology, D.B., D.M. and D.P.; software, D.B. and D.M.; validation, D.B. and D.M.; writing--original draft preparation, D.B., D.M. and D.P. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The authors declare no conflict of interest.