Monitoring and control applications in modern power systems rely on a distributed infrastructure that needs to be accurately synchronized. However, traditional time/frequency dissemination techniques may prove to be insufficient to attain the desired level of accuracy and resilience. In this context, the present paper discusses the benefits enabled by adopting the White Rabbit (WR) protocol, which guarantees excellent time synchronization through the accurate estimation and correction of the time-delays between each node. Different hardware architectures have been proposed, implemented and compared, and experimental results highlight the remarkable timebase stability and accuracy achievable through WR. The standard deviation of the offset from the time reference is about 10 nanoseconds, which may be further improved through higher performance hardware. Finally, starting from these results, this paper shows that WR technology, supported by Field Programmable Gate Array-based instruments, can complement Global Navigation Satellite System and Precision Time Protocol Power Utility Profile in future power system applications, including high-performance merging units, harmonic synchrophasor estimation, and traveling wave-based fault location.
Phasor measurement units (PMUs) provide high-accuracy frequency and rate of change of frequency (ROCOF) measurements under quasi-stationary operating conditions. However, their measurement uncertainty can increase by up to two orders of magnitude during fast transients, thus degrading the reliability of wide area monitoring, protection, and control systems. To address this issue, this article proposes event-triggered adaptive Kalman filters (AKFs) that, installed at PMU-equipped buses, dynamically augment local ROCOF measurements with information received from adjacent PMUs when relevant transient conditions are detected. By leveraging spatial correlation in system dynamics, the proposed strategy mitigates the reduced tracking capability of classical model-based prediction during transient events with minimal communication overhead and with no scalability problems. Simulation results on modified IEEE five-bus and 14-bus systems show a substantial reduction in ROCOF estimation uncertainty (up to one order of magnitude in very noisy environments and if the PMU estimates are performed over data records of no more than four nominal cycles each), together with a moderate improvement in frequency estimation accuracy. Application to real-world PMU data further confirms the stable and consistent behavior of the algorithm.
The pervasive deployment of power electronicsbased converters is likely to induce faster dynamics in power systems. Thus, PMUs must be designed to measure synchrophasor, frequency, and rate of change of frequency (ROCOF) under abrupt transients as well. The present paper introduces a new PMU algorithm that is specifically designed to deal with the step test conditions prescribed by IEC/IEEE 60255-118-1:2018 standard. It adopts Taylor-Fourier models and asymmetric observation windows that involve past (left) and future (right) samples with respect to a detected step instant. A merging approach allows combining left and right estimates at each timestamp only under steady-state or slowly-varying conditions, whereas the potentiality of asymmetric windows is triggered in the presence of a step, achieving an exemplary reaction to fast changes even in the presence of wideband noise. Zero synchrophasor, frequency, and ROCOF response times are obtained for M-class algorithms, thus combining accurate measurement under slow variations with remarkable tracking in the presence of abrupt transitions. The main outcome of the proposed solution is providing valid and accurate estimates even under the critical conditions considered by the standard.
In modern power systems, monitoring and control applications are subject to stringent requirements in terms of responsiveness and accuracy. The reference technology in this sense is represented by the phasor measurement units (PMUs), which produce time-stamped measurements of the synchrophasor, frequency, and rate of change of frequency. The delay introduced by different PMU acquisition and processing stages can be characterized in laboratory-controlled conditions as per the relevant standards. This information, however, is hard to integrate into online routines without prior knowledge of the system's operating condition. To address this issue, this article presents a PMU prototype that implements an online trustworthiness metric, which can be used to preliminarily assess the measurement accuracy and track the settling time due to external disturbances. The results confirm the robustness of the proposed approach and its potential applicability to an emerging use case involving the online estimation of power system inertia level.
Indium tin oxide (ITO), a transparent conductive oxide, is widely used in optoelectronic applications due to its electrical conductivity, optical transparency, and chemical stability. This study employs spectroscopic ellipsometry (SE) to analyze ITO layers, enabling nondestructive determination of film thickness, dielectric functions, and bulk conductivity. Electrical properties derived from SE are compared with those obtained using the four-point probe method (4PM) to improve metrological tools for nanotechnology applications and optimize deposition process monitoring for better control of film properties. This work also investigates the chemical stability of ITO layers under etching conditions and explores the development of new sheet resistance standards for scanning microwave microscopy (SMM). The results show that ITO resistivity, calculated from fitted SE data, increases with oxygen flow rate up to 5 cm3(STP) min-1. Good agreement is observed between sheet resistance values obtained by SE and 4PM up to 3 cm3(STP) min-1. Additionally, the sheet resistance values of a distinct set of microstructured ITO samples with different ITO layer thicknesses are determined by SMM, which are highly consistent with those obtained by the 4PM.
