# Dynamic Impedance Estimation: Challenges and Considerations
## 5 Conclusions  
This paper addressed the main challenges in harmonic synchrophasor estimation (HSpE) and presented some paths for research evolution. The first aspect to be considered when estimating the harmonic phasor concerns the voltage and current transducers' imperfections. The transducers present in the transmission substations or the distribution networks were designed to respond accurately to the fundamental component, presenting an inadequate frequency response for the harmonic range considered today in the PQ analysis (up to 50 th harmonic). This paper presented the adaptive equalization method through algorithms already established in digital signal processing theory adapted to power networks as a proposed solution. For this, the installation of a reference transducer in a previously chosen point of the network and using a satellite synchronization system and availability of a data communication channel to carry out the equalization in a supervised and online manner is suggested. The initial results in this field are auspicious. The second aspect considered was related to the estimation algorithms of the harmonic phasor itself. The harmonic synchronized phasor measurements are still incipient, and further efforts are needed to improve the magnitude and phase estimation algorithms. One of the problems pointed out in this work concerns the error introduced by the resampling system in the magnitude and phase of the harmonic presence in the presence of noise. These errors can generate a TVE greater than 12% for a 40 dB SNR, especially if the harmonics present in the network have low energy, such as less than 5%. It was observed that these errors were introduced in the resampling circuit that is necessary to reduce the leakage error due to the asynchronous sampling rate. In this regard, the proposed solution was using an oversampling technique to reduce the noise level, although the search for new HSpE algorithms is also an exciting path. Finally, two possibilities of estimating the network impedance were presented, one passive using ICA and the other active through the injection of small pulses in the system with controlled frequency content. In particular, the importance of online estimation of network impedance and harmonic transfers was highlighted. The knowledge of these quantities in an online and dynamic way will make it possible to explain phenomena of harmonic propagation in the network and identify polluting agents over time and how each agent contributes to increase or reduce the total harmonic distortion of the network.  
Dynamic impedance estimation will continue to be a great challenge for the power systems engineer as the system complexity increases with the massive insertion of power electronic inverters and the associated required filtering. Real-time signal processing will be an effective tool to determine the dynamic self or transfer impedance.  
[PERSON], [PERSON] and [PERSON] have worked on the Dynamic Impedance Estimation section; [PERSON] and [PERSON] have worked on the Transducers Online Equalization section; [PERSON] and [PERSON] have worked on the Harmonic Synchrophasor Estimation; [PERSON] and [PERSON] have supervised all works and worked on the general review of the article. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The authors also would like to thank CAPES, CNPq, FAPEMIG, INERGE for providing academic and laboratory support.  
The authors declare no conflict of interest.