Showing papers by "Stefano Rinaldi published in 2013"

Automation of Distribution Grids With IEC 61850: A First Approach Using Broadband Power Line Communication

Abstract: The IEC 61850 standard allows for a structured grid automation system where critical tasks like grid protections, renewable energy sources management, synchronized measurements, and monitoring applications share the communication network. So far, the use of IEC 61850 has been mainly limited to the primary substations, but more interesting could be the coordinated actions between primary and secondary substations in order to quickly react to faults and to reduce service downtimes for final customers. Unfortunately, the communication networks between primary and secondary substations are today only partially deployed. Considering this context, the broadband power line over medium voltage grid (MV-BPL) could be a suitable solution for closing the communication gaps between substations that use IEC 61850. The main objective of this paper is to present the outcomes of the first phase of a project whose final goal is the implementation in real grids of distribution grid automation based on IEC 61850. A new and comprehensive set of experiments on a real (and in service) medium voltage grid in Italy has been designed and carried out. The practicability of IEC 61850 communication over the distribution grid is assessed comparing the time characteristics of the MV-BPL against the transfer time classes of the IEC 61850, determining which IEC 61850 services may be transported over MV-BPL. The experimental long-term analysis highlights that more than 90% of the service requests are transferred on the network with a round-trip time lower than 40 ms even in the case of four hops, a time which is compatible with the IEC 61850 fast automatic interactions on MV grid.

A New IED With PMU Functionalities for Electrical Substations

Abstract: 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

Multi-sensor system with Bluetooth connectivity for non-invasive measurements of human body physical parameters

Abstract: In the last few years, the availability of powerful personal computing devices, like smartphones, has opened new scenarios to the so called “Body Area Network” (BAN), i.e., sensor networks specifically designed to monitor physical conditions of the user. The traditional methods adopted to monitor physical parameters, like heart beat rate or exertion level, are not suitable for real-time measurements. However, a continuous monitoring of such kind of parameters would allow the athletes to constantly control their physical conditions, furnishing useful information to prevent overstrain and to improve their performance. In this work, a simple, portable and low-cost system for non-invasive and real-time measurement of physical parameters is proposed and experimentally characterized. It is composed of three units: the sensor apparatus, electronic interface circuit, and the data transmission unit. Two different sensors are combined in a unique structure to be placed in a clip-like fashion on the earlobe or other body part of a person. A photoplethysmographic sensor is used to optically measure the changes of blood volume in the arteries, thus to acquire information about heart beat, blood pressure, and arrhythmias. The second sensor is composed of two electrodes, hence an impedance measurement of the tissue is carried out. The impedance estimation can be used to monitor the dielectric properties of biological tissues and fluids, like blood flow. A commercial battery-operated Bluetooth earphone is used both to transmit sensor data and to provide the power supply for the sensors and the first conditioning electronics. Data transmission is operated by the standard Bluetooth Hands-Free profile; therefore, sensor data can be easily acquired, elaborated and visualized by a broad range of commercial devices. In fact, Hands-Free is the only Bluetooth data communication profile supported by any smartphone, from the low-cost ones to the high-end devices. The experimental characterization of the prototype, performed by using a specifically designed application for Android smartphone systems, has demonstrated the validity of the proposed approach.

Low Complexity UWB Radios for Precise Wireless Sensor Network Synchronization

Abstract: Wireless sensor networks are becoming widely diffused because of the flexibility and scalability they offer. However, distributed measurements are significant only if the readout is coupled to time information. For this reason, network-wide time synchronization is the main concern. The objective of this paper is to exploit a very simple hardware implementation of an IR-UWB radio for realizing an accurate synchronization system for wireless sensors. The proposed solution relies on commercial-off-the-shelf discrete electronic components (rather than on specialized transceivers). It is designed for providing accurate timestamping of the packet time of arrival (TOA) to an adder-based tunable clock, which tracks the network time reference. The comprehensive set of experimental results based on prototypes, shows a TOA detection error with a standard deviation well below 1 ns. On the other hand, in the FPGA-based prototype, the synchronization performance reaches an overall synchronization error of few nanoseconds. Finally, in order to highlight the tradeoff between timestamping accuracy, clock stability, and synchronization performance, some additional simulations have been carried out: a synchronization error in the order of 1 ns is possible, if good local oscillator sources are available in the nodes and if the adjustable clock has a sufficient resolution.

Smartphone based localization solution for construction site management

Abstract: 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.

Toward smart metering application exploiting IPv6 over wM-bus

Abstract: In the last years, the increasing focus on energy savings is the key factor in the transformation of the legacy distribution grid toward the so called smart grid. One of the most evident, it is the wide diffusion, in some countries, of smart metering technologies for monitoring of customer electrical consumption. The proven benefits of this technology suggested to the Italian regulative agency the adoption of similar smart solutions for water and gas meters. Currently, the transmission technology which seems to satisfy the strict constraints of power consumption and wide range is the wM-bus operating in different frequency bands, including the recently standardized portion of the spectrum around 169 MHz. This technology provides a low-power and reliable communication channel, but it is not integrated with the IP-based protocols. This may represent a limit since all the ongoing standardization efforts consider the IP suite the unifying framework for the very different network tiers of a Smart Grid. In this paper, the mapping of IPv6 protocol, over wM-bus has been proposed and evaluated in a dedicated simulation environment. The results confirm the feasibility of the proposed approach: the transmission of a typical DLMS/COSEM packet takes only few additional resources compared to wM-bus solution, although the medium access technique of wM-bus decreases the communication performance.

Experimental characterization of time synchronization over a heterogeneous network for Smart Grids

Abstract: Nowadays, the growing presence of distributed energy resources (DER) makes the management of the distribution grid more complex, thus requiring distributed monitoring and controlling capabilities. The deployment of locally distributed intelligent devices over a large area involves a high performance network infrastructure (typically based on heterogeneous communication technologies) in order to provide the most appropriate level of communication. In addition, monitoring and control applications need a common sense of time to coordinate the activities among distributed devices, but accurate time synchronization in a heterogeneous network is still a challenge. Network Time Protocol (NTP) can distribute time information with accuracy in the order of milliseconds on a Wide Area Network (WAN). In this work, an experimental characterization of NTP synchronization performance on a real network for Smart Grids has been done. The first analysis highlights the synchronization capabilities span from 1 ms to 20 ms depending on the technology adopted for the deployment of the network (e.g. fiber optics links, BPL links and Wi-Fi).

Performance analysis of a clock state estimator for PROFINET IO IRT synchronization

Abstract: Clock synchronization is essential to support time-based medium access scheduling and distributed control over industrial networks relying on Real-Time Ethernet (RTE). PROFINET IO is one of the most widely used field-buses in large automation plants. The PROFINET IO Isochronous Real Time (IRT) implementation includes a Precision Transparent Clock Protocol (PTCP) for network-level synchronization. A similar scheme is also used in the second version of the Precision Time Protocol (PTP), standardized as IEEE 1588-2008. Unfortunately, synchronization uncertainty typically grows in the case of long chains of cascaded clocks. In this paper, the accuracy of a clock state estimator based on a Kalman filter is analyzed in the context of PROFINET IO IRT networks. The proposed estimator can be used to compensate the time offsets of every node with respect to the reference master, thus improving synchronization accuracy in the case of long linear topologies beyond the limits of other existing solutions. The presented results are obtained from multiparametric simulations based on the features of real hardware devices.

Master Failure Detection Protocol in Internal Synchronization Environment

Abstract: During the last decades, the wide advance in the networking technologies has allowed the development of distributed monitoring and control systems. These systems show advantages compared with centralized solutions: heterogeneous nodes can be easily integrated, new nodes can be easily added to the system, and no single point of failure. For these reasons, distributed systems have been adopted in different fields, such as industrial automation and telecommunication systems. Recently, due to technology improvements, distributed systems are also adopted in the control of power-grid and transport systems, i.e., the so-called large-scale complex critical infrastructures. Given the strict safety, security, reliability, and real-time requirements, using distributed systems for controlling such critical infrastructure demands that adequate mechanisms have to be established to share the same notion of time among the nodes. For this class of systems, a synchronization protocol, such as the IEEE 1588 standard, can be adopted. This type of synchronization protocol was designed to achieve very precise clock synchronization, but it may not be sufficient to ensure safety of the entire system. For example, instability of the local oscillator of a reference node, due to a failure of the node itself or to malicious attacks, could influence the quality of synchronization of all nodes. In recent years, a new software clock, the reliable and self-aware clock (R&SAClock), which is designed to estimate the quality of synchronization through statistical analysis, was developed and tested. This statistical instrument can be used to identify any anomalous conditions with respect to normal behavior. A careful analysis and classification of the main points of failure of IEEE 1588 standard suggests that the reference node, which is called master, is the weak point of the system. For this reason, this paper deals with the detection of faults of the reference node(s) of an of IEEE 1588 setup. This paper describes and evaluates the design of a protocol for timing failure detection for internal synchronization based on a revised version of the R&SAClock software suitably modified to cross-exploit the information on the quality of synchronization among all the nodes of the system. The experimental evaluation of this approach confirms the capability of the synchronization uncertainty, which is provided by R&SAClock, to reveal the anomalous behaviors either of the local node or of the reference node. In fact, it is shown that, through a proper configuration of the parameters of the protocol, the system is able to detect all the failures injected on the master in different experimental conditions and to correctly identify failures on slaves with a probability of 87%.

High availability IEEE 1588 nodes over IEEE 802.1aq Shortest Path Bridging networks

Abstract: The modern industrial and substation automation Ethernet networks have demanding requirements about high availability. Recently, the IEEE 802.1 WG proposes the IEEE 802.1aq, also known as Shortest Path Bridging, to manage Ethernet redundant networks. The IEEE 1588 protocol can exploit the SPB capabilities to manage multiple paths in order to improve synchronization availability. In the paper, the possibility to send copies of IEEE 1588 messages over multiple paths has been analyzed. In particular, the attention has been focused on the combining algorithms in the slaves, which is used to recover the time from multiple sources. In details, some specific fault tolerant combining algorithms, based on synchronization quality estimation have been proposed. The considered solutions are compared to traditional approaches under fault conditions by means of a specifically developed simulation environment.

Analysis of synchronization performance in redundant networks for substation automation

Abstract: In modern real-time Ethernet networks for substation automation, several protocols are adopted to guarantee the strict synchronization and availability requirements imposed by applications. The management of these networks is more and more complex, since several (cross-influencing) configuration parameters affect the performance of the overall system. In this paper the attention has been focused on synchronization systems applied to redundant network infrastructures for substation automation: in these systems the reconfiguration of the network after a fault may affect the synchronization performance of the nodes. As a test case the SNTP (Simple Network Time Protocol) synchronization has been simulated (with different fault conditions) using two network topologies typically adopted in Substation Automation Systems: RSTP (Rapid Spanning Tree Protocol) and PRP (Parallel Redundancy Protocol). The performance of the two cases has been compared by means of suitable metrics: PRP, as opposed to RSTP, guarantees seamless synchronization performance in case of a single fault.

Characterization of multi-standard Power Line Communication on low-voltage grid

Abstract: In the last years, the introduction of distributed energy resources increases the complexity of distribution grid management system, which requires performing communication infrastructures. Moreover, an optimal power management requires a direct data exchange with home and industrial automation and energy systems. A well known technology, the Power Line Communication (PLC), seems to be able to satisfy large parts of these demands. Nevertheless, several PLC solutions have been proposed over the years, each of them satisfying the requirements of specific applications. A measurement method able to characterize the communication performance of different PLC protocols is required due to the increasing complexity of the PLC modern infrastructures. In this work, an approach based on Software Defined Radio has been proposed. This solution is able to characterize several PLC systems, based on different physical modulations, using the same experimental set-up. The characterization of a PLC system, based on DBSK modulation, in a real environment, clearly demonstrated the feasibility of the proposed approach.

On the use of PRIME PowerLine Communication in industrial applications: Modbus a first testcase

Abstract: PLC is the acronym for "PowerLine Communication" and means data communications via power wiring. PLC was initially used for tele-protection and tele-monitoring of electrical substations by means of high voltage power lines, in order to avoid costs of microwave or fiber optic links. More recently, PLC has been also adopted for automatic smart metering. However, only with the advent of low-cost digital devices capable to implement complex modulation schema, the offered throughput has reached performance comparable with traditional communication solutions. In this paper the use of the PRIME standard, classified as medium-speed narrow-band PLC, is suggested for industrial applications. A test bench based on proof-of-concept prototypes has been arranged to verify the feasibility of the proposed approach. Results show performance comparable with many wired fieldbuses. In particular, a Modbus implementation has shown a round trip time of 64ms for a read coil function.

Advanced networks for distributed measurement in substation automation systems

Abstract: The adoption of IEC 61850 in the deployment of Substation Automation System opens new scenarios to system design. The presence of a communication infrastructure connecting Intelligent Electronic Device (IED), sensors and protections may suggest the development of distribute measurement devices, where the sampling of the physical quantities and the elaboration of the sampled value could be performed by different physical devices. Nevertheless, such architecture is based on an ideal communication infrastructure, which can transfer the information among the distributed devices without affecting the measurement performance. On the contrary a real network infrastructure could suffer from several failure conditions, mainly to the harsh environment of substations where the installed network devices are not periodically replaced. In the following paper, the effects of network faults on a distributed measurement system in electrical substations are considered. The behavior of network infrastructure and the quality of the service offered in the case of the most common network failures has been analyzed using a simulation environment. The results demonstrate that the commonly adopted Rapid Spanning Tree Protocol (RSTP) is not suitable for the most demanding measurement applications due to the loss of measurement samples during the network reconfiguration time (up to 200 ms). On the contrary, more advanced redundancy protocols, like Parallel Redundancy Protocol (PRP), are able to satisfy also the most strict availability requirements, as suggested by the simulation results.

Co-simulation of network infrastructure for substation automation systems

Abstract: Real-time networks for substations automation systems are based on ICT technologies and they may take great advantages from ultra recent network technological improvements. A careful evaluation of the performance enhancement is required. Due to cost and system complexity, such an analysis can be performed only using a dedicated simulation environment, but the currently available simulation libraries are not focused on lower layers (L1, PHY, and L2 MAC). The main objective of this work is to introduce the architecture of a modular network simulator, with suitable models of L1 and L2 Ethernet layers, for the simulation and co-simulation of substation automation Real-time Ethernet networks. The modular simulator includes interfaces for both co-simulation with FPGA-hardware board and real network, and co-simulation with automation application software (e.g. IEC61850 SCADA system, etc.).

Time of arrival estimation in power line communication systems for home smart grids

Abstract: This paper deals with time synchronization of devices attached to a smart grid, whose accuracy tightly depends on the accurate estimation of the Time of Arrival (ToA) of the synchronization related messages sent over the power line communication systems. Usually smart grids are quite complex “systems of heterogeneous systems”: the aim of this paper is to suggest a ToA detection mechanism that can use to forward time synchronization to the “last mile” link and inside the end user home. In particular in this paper, the use of a chirp-based preamble, borrowed from wireless communications (which suffer from multipath and noise like in power line communication) is proposed and tested by means of simulations and real experiments with narrowband PRIME technology. The results show very interesting performance even with narrowband chirps: the standard deviation of the ToA estimation is always in the order of 150 ns, even with loaded electrical grids.

Robust synchronization for IEEE 802.15.4 CSS wireless sensor networks

Abstract: In a wireless network, synchronization accuracy can be significantly affected by impairments affecting the physical layer. It is well known that path delay asymmetry adversely affects timing protocols based on two-way message exchanges but, unfortunately, bounds to link asymmetry are hard to ensure when timing messages are exchanged through wireless links. It would then be desirable to be able to flag the corresponding timestamps as unreliable. This paper discusses the application of a timestamp validation approach in the synchronization of the nodes in a wireless network employing physical-level timestamping in a IEEE 802.15.4 Chirp Spread Spectrum. Because a Kalman filter is employed as a servo for the local clock, differences between the timestamp received through the network and the predicted local time can be compared to statistical thresholds referred to the Kalman filter innovation process. Thus, a detector decision rule can be successfully based on well-defined statistical criteria, as shown by experimental data presented in the paper.