Paolo Castello

Impact of the Model on the Accuracy of Synchrophasor Measurement

Phasor measurement units (PMUs) are becoming one of the key issues of power network monitoring. They have to be able to perform accurate estimations of quantities of interest either under steady-state or transient conditions. Among all the sources which may contribute to the uncertainty introduced by PMUs, this paper analyzes the impact of the phasor estimation models on the accuracy of these devices, focuses on algorithms proposed in the literature for the estimation of dynamic phasors, and studies their performances under several different conditions.

A Fast and Accurate PMU Algorithm for P+M Class Measurement of Synchrophasor and Frequency

The IEEE Standard C37.118.1 defines two performance classes, P and M, for phasor measurement units (PMUs), respectively for protection and monitoring oriented applications. The goal of this paper is to define an algorithm that allows the requirements of both classes to be met simultaneously, thus avoiding an a priori selection of either the fast response time of class P or the accuracy of the class M. The designed PMU consists of two digital channels that process in parallel the acquired samples with different algorithms: the first one allows accurate measurements of steady state signals, while the second one is better suited to follow the fast signal changes. Then, a detector identifies the possible presence of dynamic situations and selects the most appropriate output for the actual operating condition. The validation of the solution, performed by means of simulations in all the static and dynamic conditions defined in the standard, confirms that the method is able to comply with all the limits indicated for both classes for synchrophasor and frequency measurement. As for the rate of change of frequency, again the compliance to P-class is fully verified, while for the M-class the only exception is represented by the tests with out-of-band disturbances.

A New IED With PMU Functionalities for Electrical Substations

This paper proposes a new distributed architecture to measure synchrophasors in power substations, inspired by the standards IEC 61850. The new scheme is implemented in the process bus, where a high performance merging unit (MU), synchronized by precision time protocol (PTP), according to the standard IEEE 1588-2008, sends the sampled values (SVs) to an intelligent electronic device (IED) enabled to behave as a phasor measurement unit (PMU). The synchrophasors are evaluated in the IED through an algorithm based on the Taylor Fourier Transform and suitably modified to have high performance also in terms of response time in presence of step change conditions. Different tests and considerations are presented to evaluate the various elements of uncertainty that a distributed architecture can introduce and, finally, to ensure the feasibility of the proposed approach.

Performance comparison of algorithms for synchrophasors measurements under dynamic conditions

Synchrophasor measurement is becoming one of the key issue of power network monitoring. The actual standard IEEE C37.118 concentrates on phasor estimation requirements under steady state conditions. The standardization process is going towards a complete framework that keeps into account dynamic conditions. This paper focuses on algorithms proposed in literature for the estimation of dynamic phasors and analyzes their performance under several different conditions.

Adaptive Taylor-Fourier synchrophasor estimation for fast response to changing conditions

This paper proposes a modified version of the synchrophasor estimation algorithm which uses the non-orthogonal transform defined as a Taylor-Fourier Transform (TFT) and which is based on a Weighted Least Squares (WLS) approximation respect to a second order of Taylor model. The aim of the proposed changes is to improve the performance of the algorithm in presence of fast transient events. Several tests are presented, in different test conditions, to show the improvements achievable with the proposed method.

An IEC 61850-Compliant distributed PMU for electrical substations

This paper proposes a novel architecture, compliant to IEC 61850, for a distributed IED based phasor measurement unit to be used in electrical substations. In particular, a measurement architecture based on process bus and sampled values synchronized with IEEE 1588-2008 is proposed, so that voltage and current signals are acquired by a Merging Unit, while the signal processing is performed on a IED (Intelligent Electronic Device) that uses a new algorithm for synchrophasor measurement, in compliance with IEEE C37.118.1-2011.

Toward a class “P + M” Phasor Measurement Unit

In this paper solutions aiming at achieving a Phasor Measurement Unit that is simultaneously compliant with both M and P classes of the standard IEEE C37.118.1, for synchrophasor estimation at a fixed reporting rate, are presented. In particular, a new version of the Taylor-Fourier Transform (TFT) based adaptive algorithm previously proposed by the authors is used for synchrophasor estimation, while frequency and Rate of Change of Frequency (ROCOF) are estimated using the higher derivatives outputs of the adaptive TFT. Frequency estimation feedback is used to tune the algorithm and achieve better performance. The proposed approaches are validated by means of simulations in all the static and dynamic conditions defined in the Standard.

A Distributed PMU for Electrical Substations With Wireless Redundant Process Bus

Protection and measurement systems in electrical substations are required to have high availability. In an all-digital substation protection system, all the components (instrument transformers, processing units, merging units, intelligent electronic devices, communication network, and synchronization source) may affect the overall availability level. In this paper, a solution to enhance distributed PMU availability, during wired network failures, is presented. In the proposed scheme, the process bus has two parallel networks: 1) the classic wired Ethernet link and 2) a wireless link (implemented with industrial grade IEEE 802.11 devices), for sampled values packets, which carry measurement information. The time synchronization is carried out only through the wired Ethernet link, but the proposed solution is still able to compensate temporary failures of one of the communication links. Experimental tests have been performed to verify the performance of additional IEEE 802.11 link using different protocols and configurations. Communication parameters that can affect the PMU performance, like propagation latency, are characterized. It is shown that, if the measurement algorithm is opportunely designed, depending on the wireless link quality, it is possible to comply, with a single output, with M and P classes of the synchrophasor standard also during network restoration or, at least, to safeguard protection applications if higher latency occurs.

PMU-Based Distribution System State Estimation with Adaptive Accuracy Exploiting Local Decision Metrics and IoT Paradigm

A novel adaptive distribution system state estimation (DSSE) solution is presented and discussed, which relies on distributed decision points and exploits the Cloud-based Internet of Things (IoT) paradigm. Up to now, DSSE procedures have been using fixed settings regardless of the actual values of measurement accuracy, which is instead affected by the actual operating conditions of the network. The proposed DSSE is innovative with respect to previous literature, because it is adaptive in the use of updated accuracies for the measurement devices. The information used in the estimation process along with the rate of the execution are updated, depending on the indications of appropriate local metrics aimed at detecting possible variations in the operating conditions of the distribution network. Specifically, the variations and the trend of variation of the rms voltage values obtained by phasor measurement units (PMUs) are used to trigger changes in the DSSE. In case dynamics are detected, the measurement data are sent to the DSSE at higher rates and the estimation process runs consequently, updating the accuracy values to be considered in the estimation. The proposed system relies on a Cloud-based IoT platform, which has been designed to incorporate heterogeneous measurement devices, such as PMUs and smart meters. The results obtained on a 13-bus system demonstrate the validity of the proposed methodology that is efficient both in the estimation process and in the use of the communication resources.

IoT cloud-based distribution system state estimation: Virtual objects and context-awareness

This paper presents an IoT cloud-based state estimation system for distribution networks in which the PMUs (Phasor Measurement Units) are virtualized with respect to the physical devices. In the considered system only application level entities are put in the cloud, whereas virtualized PMUs are running in the communication network edge (i.e. closer to the physical objects) in order to have a certain degree of local logic, which allows to implement a bandwidth-efficient and smart data transmission to the involved applications in the cloud. The major contributions of the paper are the following: we demonstrate that a cloud-based architecture is capable of achieving the QoS level required by the specific state estimation application; we show that implementing a certain local logic for data transmission in the cloud, the result of the state estimation is not degraded with respect to the case of an estimation that takes place frequently at fixed intervals; we show the results in terms of latency and reduced network load for a reference smart grid network.