C. M. De Dominicis

On the Use of IEEE 1588 in Existing IEC 61850-Based SASs: Current Behavior and Future Challenges

The International Electrotechnical Commission (IEC) 61850 standard describes the communication inside the substation automation system (SAS) setting the base for new interoperating devices that share information using the Ethernet network infrastructure. More recently, the request of time synchronization among SAS components for the timestamping of critical events or synchrophasor measurement has generated a very high interest in the IEC 61850 working group for distributed synchronization protocols like IEEE 1588. This paper analyzes the current situation, matching different implementations of the IEEE 1588, and their respective accuracy, with the requirements of typical SAS applications: from the millisecond synchronization accuracy required by fault recorder application to the microsecond required by the sampled values (SV). The main focus of this paper is on the integration of IEEE 1588 with real already existing systems, and the goal is the performance comparison of different architectures. For these reasons, experimental tests have been carried out using a real SAS network infrastructure [redundant gigabit optical fiber Ethernet network managed using rapid spanning tree protocol (RSTP)]. The results show that, under ideal conditions, the IEEE 1588 protocol can achieve synchronization accuracy slightly worse (80 ns) than legacy IRIG-B systems (15 ns). However, IEEE 1588 makes possible a great cabling reduction and a simplified maintenance when synchronization is directly transferred on the SAS system bus. On the other hand, experiments highlight that nodes connected through a legacy RSTP infrastructure, which does not support IEEE 1588 messages, can lose the time synchronization in the case of network traffic or reconfiguration of the network. Therefore, the integration of IEEE 1588 over existing IEC 61850 station bus is basically a tradeoff between installation costs and performance since it requires the replacement of already installed Ethernet infrastructure. In the last part, this paper analyses the challenges for the next SAS generation that has to combine on the same plants the high accuracy IEEE 1588 implementation with high-availability protocols based on IEC 62439. Since the lifetime of an SAS is more than ten years and the adoption of these technologies takes several years, some solutions that introduce synchronization and high-availability protocols guaranteeing compatibility with existing technologies have been analyzed, too. For instance, an adaptation block that (when attached to a high-availability network) reconstructs the interface signals (e.g., synchronization signals) required by traditional bay has been proposed.

Investigating WirelessHART coexistence issues through a specifically designed simulator

In this paper, the WirelessHART communication scheme is investigated. The protocol is at first described, in order to underline the key aspects of its design; then, a simulation tool is presented: it enables analysis that accounts for both protocol and physical layers issues. In particular, interference effects on protocol choices can be easily analyzed. The experimental results, obtained from simulations, highlight improvements of WirelessHART with respect to IEEE 802.15.4 standard, concerning the Packet Error Ratio (PER) degradation of interfering networks.

Evaluation of Bluetooth Hands-Free profile for sensors applications in smartphone platforms

Nowadays, the wide diffusion of smartphones has completely changed the interaction of people with the surroundings. In fact these devices are equipped with a large number of sensors, like GPS receiver, 3-axis accelerator, which can enrich the user experience, collecting data from the external environment. Moreover, additional sensors can be used to enlarge the set of data providing information usually not available in a smartphone, like biomedical data. Usually, Bluetooth is used to connect external sensors to smartphone. Several commercial solutions are already available on the market. Unfortunately, different types of smartphone require the use of dedicated external sensors, due to the different Bluetooth data profile supported by the different Operative System (iOS, Android). In this paper the Bluetooth Hands-Free profile has been evaluated to transmit sensor information to smartphone, since it is the only profile supported both by Android as well as iOS devices. A prototype of a photoplethysmographic sensor with Hands-Free interface has been realized and interfaced to commercial smartphone, showing the feasibility of this approach.

On the development of a wireless self localizing streetlight monitoring system

The growing interest towards green and efficient use of electrical energy has recently pushed the industry of street light control systems. In the past, very simple on/off switching mechanism based on daylight sensing and cyclic preventive maintenance procedures were adopted. Nowadays, intelligent control systems offering remote supervision have strongly contributed to a change in perspective in maintenance engineering form a traditional “Fail and Fix” view to a “Predict and Prevent” approach. However, most of the infrastructure is already in place and replace street light with improved units has to be economical feasible. Traditional solutions exploit Power Line Communications (PLCs). In this paper we propose a wireless retrofitting of lamps, which has some advantages due to the independence from power line faults. In addition, the service provider usually ignores the exact location of the lamp poles and the integration with Geographic Information System (GIS) databases requires a preliminary on-site survey. The novelty of our proposal relies on the exploitation of nodes self location capability. Radios based on Chirp Spread Spectrum (CSS) modulation are used in order to achieve a good spatial resolution without the adoption of expensive GPS modules. In particular, experimental results are focused on the ranging capabilities of such devices, showing the feasibility of the proposed approach. Open field trials, mimicking real world applications, have shown an overall accuracy on the order of one meter.

High-precision UWB-based timestamping

The work presented in this paper is related with time synchronization for wireless networks. In particular, it is focused on the proposal and experimental evaluation of a low-cost and high precision timestamping technique based on Ultra Wide Band (UWB) signalling. In recent years, the use of such systems has gained an increasing success thanks to their robustness to interferers and multipath. In this paper a new hybrid wireless node is proposed; a traditional IEEE802.15.4 radio, the reference physical layer for wireless sensor networks, is supported by an UWB transceiver. The former is used for communication purposes and allows to preserve compatibility with already installed infrastructures/networks; the latter is used for time of arrival estimation. Hardware prototypes have been realized and experimental tests have shown a sub-nanosecond accuracy. A comparison with commercial solutions has shown a performance improvement with respect to conventional approaches.

Integration of existing IEC61850-based SAS within new high-availability architectures

The introduction of the standard IEC 61850 for the communication of Substation Automation System (SAS) opens new scenarios in which products of different vendors can communicate on the same network infrastructure, based on Ethernet technology. The recent improvements in industrial communications are going to deeply influence two of the key points in the development of SAS: synchronization and availability. The challenge of SASs of the future is to combine on the same plants high accuracy synchronization protocols (e.g. IEEE 1588) with high-availability systems in order to increase the overall performance. The integration in real plants is hindered because of the large base of traditional SASs already deployed in the field. In this paper the implementation of mixed scenario SASs, with high-available synchronized Bays together with legacy Bays, is analyzed and a solution for smooth integration is proposed. The idea is based on the use of an adaptation block that, when attached to a high-availability network, reconstructs the interface signals (e.g. synchronization signals) required by traditional Bay.

Smartphone based localization solution for construction site management

Managing a large building construction site is a really complex task. Nowadays, many controllers have to daily check the site collecting information in order to inform managers about the construction progress. Recently, several software applications, compatible and integrated in most of commercial CAD tools, have been developed to help managers in collecting information. These tools furnish the managers on-site access to technical documentation, but are standalone tool very poorly connected with the site infrastructure. For this reason, some proposals have been suggested in literature to enable real-time data collection about site status exploiting communication facilities (e.g. wireless sensor networks). The work discussed in this paper extends this approach including localization-aware and task-aware mobile computing based on the use of smartphones and tablets. These devices natively offer intuitive and user-friendly interfaces, dramatically reducing time in personnel training. In particular, ranging and localization techniques on most diffused smart platforms have been successfully tested, also by means of external hardware plugins.

Experimental evaluation of synchronization solutions for substation automation systems

In the last year the automation systems in power substation start to rely on networks thanks to the introduction of the IEC 61850 standard. Besides, it generates a general interest on synchronization also in the field of substation automation systems. In fact, timestamping of critical events or synchrophasor measurements can have a great advantage from distributed synchronization protocols like IEEE 1588. This paper analyzes the current situation and proposes new architecture for the test of IEEE 1588 solutions before introduction in the market. The focus is mainly on compatibility with real existing systems and its goal is the performance comparison of different implementations. First experimental results on real substation automation system show a great cabling reduction and a simplified maintenance in the IEEE1588-based systems. On the other hand, the synchronization performance are slightly worse: the maximum time difference among clocks of the system is about 80 ns for IEEE1588 with respect to 15 ns of typical IRIG-B-based system.

Timestamping performance analysis of IEEE 802.15.4a systems based on SDR platforms

An increasing number of distributed measurement and control applications requires that network nodes are able to estimate the position and the time measured by other devices on a common spatio-temporal reference frame. Accurate packet timestamping is a necessary condition to achieve this goal. However, in the case of wireless networks, timestamping accuracy is generally quite poor due to the combination of multiple uncertainty sources (e.g., variable signal attenuation and interferences) affecting wireless message propagation. Various communication schemes have been proposed to improve performance. One of the most recent and promising is the Chirp Spread Spectrum (CSS) modulation. In this paper, the timestamping accuracy of CSS signals similar to those defined in the standard IEEE 802.15.4a is analyzed experimentally using two different platforms based on a Software Defined Radio (SDR). Some results confirm that CSS can be successfully employed for accurate time synchronization and ranging.

Acquisition and elaboration of cardiac signal in android Smartphone devices

Today, the broad proliferation of Smartphones and Tablets has determined a wide availability of software applications for numerous purposes. Thanks to this, Smartphones are now essential devices for many aspects of everyday life and not just advanced mobile phone terminals. The presence of powerful processing units, embedded sensors as well as the availability of many standard communication interfaces has recently attracted the interest of the scientific community. Several projects based on Smartphone systems have been proposed in different fields and many more application scenarios are being explored. A critical aspect still unresolved is the possibility of acquiring external information, such as data from other sensors. Due to their nature of consumer devices, Smartphones provide digital and high level communication interfaces, such as USB and Bluetooth. Sensor interface is therefore possible if a suitable front-end able to digitize sensor data and to handle the communication with the Smartphone is employed. In order to lower the complexity and the cost of the front-end as well as to reduce its power consumption, an effective method for the acquisition of external sensor signals through the Smartphone audio input is proposed in this paper. As a proof of concept, a sensor system composed by a photoplethysmographic sensor for cardiac signal monitoring and a pair of electrodes for tissue impedance estimation has been used. Specific software routines for Android operating system have been developed to process the acquired sensor signals providing visualization, data storage and simple data analysis, and thus demonstrating the feasibility of the proposed approach.