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Rapporto RSE 17000228

Methods of measurement of conducted disturbances of the devices connected to the network and the characterization of the impedances of the network in the frequency range 2 kHz ÷ 500kHz

Rapporto

2016

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S. Peraboni (RSE SpA) , F. Zanon (RSE SpA), F. Belloni (RSE SpA) , A. Tonello (WiTiKee), H. Shadmehr (RSE SpA), A. Brambilla (RSE SpA)

SMART-DSYS 2016 - Development and management of distribution networks

The report deals with the main results of the activity to evaluate, in the frequency range of 2 kHz ÷ 500 kHz, the possible measurament methods and data analisys for: (i) electronic devices disturbances; (ii) grid and device impedance.

The increasing use of power electronic devices in distribution grids, as loads and distributed generators interface, is leading to a series of relatively new phenomena of interference with other grid connected devices, due to noise in the frequency range from 2 kHz to 500 kHz. Such interference phenomena are not limited to the impossibility to communicate with Power Line Communication devices, but extendalso to malfunctions of electronic devices and to unintentional tripping of grid protection. These problems, of recent interest also for regulatory committees, motivated the study of measurement and estimation methods of the conducted emissions of devices in the frequency range 2 kHz to 500 kHz.

The disturbance emitter was modeled as a linear Norton equivalent, composed of a current source and an internal impedance. The possibility to predict the noise generated by a device is guaranteed once all the elements of this equivalent model are characterized, and once the network impedance is known. For this reason, the research was divided into two main areas, the former covering techniques for measuring harmonic currents and the latter concerning the impedance measurements.

As regards the currents measurement, measurement techniques both in the frequency domain and the time domain were considered. For the latter, most suitable for the purpose of measuring time-varying signals such as those from power electronic devices, the main factors that may affect the noise estimation were analyzed trying to identify possible countermeasures to minimize their impact. Then, different estimation methods for quantifying harmonic emissions in the frequency range of interest were considered, both settled in the frequency domain and in the mixed time-frequency domain. The latter methods emerged as most promising for characterizing time-varying signals, even though their results are more complex to be interpreted than those from frequency domain methods.

For impedance measurement techniques, a study of characterization methods in the mixed time-frequency domain was started. The considered methods are oriented to measure time-variance of network impedance and can be applied in Multi In Multi Out systems. Both methods based on the measurements of the scattering parameters of the grid and on the measurement of voltage pulse propagation were considered in the study. Characterizations of real devices led to the implementation of an experimental set-up for laboratory and “in field” applications.