Grandmaster Clock Research Articles

Assessment of IEEE 1588-Based Timing System of the ITER Neutral Beam Test Facility

MITICA is one of the two ongoing experiments at the ITER Neutral Beam Test Facility (NBTF) located in Padova (Italy). MITICA aims to develop the full-size neutral beam injector of ITER and, as such, its Control and Data Acquisition System will adhere to ITER CODAC directives. In particular, its timing system will be based on the IEEE1588 PTPv2 protocol and it will use the ITER Time Communication Network (TCN) on a dedicated Ethernet LAN. Following the ITER device catalog, the National Instruments PXI-6683H PTP timing modules will be used to generate triggers and clocks synchronized with a PTP grandmaster clock. The “Lazy Trigger" technique, then, will be adopted to implement event-driven data acquisition without the need of any hardware link in addition to the Ethernet connections used to transfer data and timing synchronization. To evaluate the accuracy over time that can be achieved with different network topologies and configurations, a test system has been set-up consisting of a grand master clock, two PXI-6683H devices and two PTP aware network switches. In addition, a detailed simulation of the network and the involved devices has been performed using the OMNET++ discrete event simulator. The simulation parameters include not only the network and switches configuration, but also the PID parameters used in the clock servo controllers. A comparison between simulated and measured statistics is reported, together with a discussion on the possible optimal configuration strategies.

Distributing and Synchronizing Signals Between the Worlds of SDI and IP

Moving signals between the worlds of serial digital interface (SDI) and Internet Protocol (IP) is not exactly rocket science, but synchronizing these signals may prove to be a challenge. It is these cases that we will discuss in this article and these challenges to which we seek to identify and present a viable and cost-effective solution. We will consider a recent Riedel project with a major U.S. broadcaster. Following the decision to move its operations to ST 2110, this broadcast network experienced synchronization problems between its IP-based flagship station and more than 200 affiliate stations throughout North America relying on SDI. The fact that the remote feed needed to be compressed posed yet another challenge, as it required the decompressed signal to be decoded to ST 2110 before it could be converted to SDI. The Riedel team managed to solve the synchronization issue with a single, powerful device smaller than the size of your thumb: A software-defined processing small form-factor pluggable (SFP) device that enabled the conversion of UHD-1 and ST 2110 signals for bidirectional distribution between the headquarters and the affiliate stations while generating a Precision Time Protocol (PTP) Grand Master clock from the affiliate’s synchronized signal. This greatly reduced both system complexity and the cost of replacing the entire affiliate synchronization system. After a general description of the specific use-case setup, we will present an overview of the various possible solutions and weigh the pros and cons before focusing on the most viable solution. After short explanations of the demarcation switch configuration and the Epoch reference generation at the affiliate sites, we conclude with an outlook on other potential use cases.

Wireless muometric navigation system

While satellite-based global navigation systems have become essential tools in our daily lives, their effectiveness is often hampered by the fact that the signals cannot be accessed in underground, indoor, or underwater environments. Recently, a novel navigation system has been invented to address this issue by utilizing the characteristics of the ubiquitous and highly penetrative cosmic-ray muons. This technique, muometric navigation, does not require active signal generation and enables positioning in the aforementioned environments within a reference coordinate defined by the three-dimensional positions of multiple detectors. In its first phase of development, these reference detectors had to be connected to the receivers via a wired configuration to guarantee precise time synchronization. This work describes more versatile, wireless muometric navigation system (MuWNS), which was designed in conjunction with a cost-effective, crystal-oscillator-based grandmaster clock and a performance evaluation is reported for shallow underground/indoor, deep underground and undersea environments. It was confirmed that MuWNS offers a navigation quality almost equivalent to aboveground GPS-based handheld navigation by determining the distance between the reference frame and the receivers within a precision range between 1 and 10 m.

추정 선로 정수 기반 변전소 간 페이저 시각 오차 대응 기법

Time synchronization error between adjacent substations may cause the mal-operation on transmission line protective IEDs. To solve this problem, this paper assumes a situation where time synchronization error occurs between substations due to GPS/Master clock fail, etc., and estimates the changing transmission line constant due to weather, and uses them to estimate the voltage/current phasor of adjacent substations. The estimated voltage/current phasor of adjacent substation are compared with the IEC 61850-based received voltage/current phasor of adjacent substation to estimate the time synchronization error between substations. In this paper, to verify the schemes proposed, the testbed was built with IMU (implemented with AM572X, ADS8688), grand master clock (LANTIME M1000-IMS), network switch (Ruggedcom RSG 2488), RTDS and the target power system was modelled with RSCAD. The results of this research are expected to provide a good guide to constructing the full digital substation.

Clock Synchronization in Virtualized Distributed Real-Time Systems using IEEE 802.1AS and ACRN

Virtualization of distributed real-time systems enables the consolidation of mixed-criticality functions on a shared hardware platform thus easing system integration. Time-triggered communication and computation can act as an enabler of safe hard real-time systems. A time-triggered hypervisor that activates virtual CPUs according to a global schedule can provide the means to allow for a resource efficient implementation of the time-triggered paradigm in virtualized distributed real-time systems. A prerequisite of time-triggered virtualization for hard real-time systems is providing access to a global time base to VMs as well as to the hypervisor. A global time base is the result of clock synchronization with an upper bound on the clock synchronization precision. We present a formalization of the notion of time in virtualized real-time systems. We use this formalization to propose a virtual clock condition that enables us to test the suitability of a virtual clock for the design of virtualized time-triggered real-time systems. We discuss and model how virtualization, in particular resource consolidation versus resource partitioning, degrades clock synchronization precision. Finally, we apply our insights to model the IEEE~802.1AS clock synchronization protocol and derive an upper bound on the clock synchronization precision of IEEE 802.1AS. We present our implementation of a dependent clock for ACRN that can be synchronized to a grandmaster clock. The results of our experiments illustrate that a type-1 hypervisor implementing a dependent clock yields native clock synchronization precision. Furthermore, we show that the upper bound derived from our model holds for a series of experiments featuring native as well as virtualized setups.

Clock Synchronization in Virtualized Distributed Real-Time Systems Using IEEE 802.1AS and ACRN

Virtualization of distributed real-time systems enables the consolidation of mixed-criticality functions on a shared hardware platform, easing system integration. Time-triggered communication and computation can act as an enabler of safe hard real-time systems. A time-triggered hypervisor that activates virtual CPUs according to a global schedule can provide the means to allow for a resource-efficient implementation of the time-triggered paradigm in virtualized distributed real-time systems. A prerequisite of time-triggered virtualization for hard real-time systems is providing access to a global time base to VMs and the hypervisor. A global time base results from clock synchronization with an upper bound on the clock synchronization precision . We present a formalization of the notion of time in virtualized distributed real-time systems. We use this formalization to propose a virtual clock condition that enables us to test the suitability of a virtual clock for the design of virtualized time-triggered real-time systems focusing on clock synchronization. We discuss and model how virtualization, particularly resource consolidation versus resource partitioning, degrades clock synchronization precision. Finally, we apply our insights to model the IEEE 802.1AS clock synchronization protocol and derive an upper bound on the clock synchronization precision of IEEE 802.1AS in a virtualized distributed real-time system. We present our implementation of a dependent clock for ACRN that can be synchronized to a grandmaster clock. The results of our experiments illustrate that a type-1 hypervisor like ACRN implementing the dependent clock paradigm yields native clock synchronization precision. Furthermore, we show that the upper bound of clock synchronization precision derived from our model holds for a series of experiments featuring native and virtualized setups.

Time synchronization for transmission substations using GPS and IEEE 1588

Time synchronization systems that utilize the global navigation satellite systems (GNSS) are widely used in the monitoring, control, and protection of transmission networks. They ensure that phasor measurement units (PMUs) can accurately monitor voltage phase angles, increase the accuracy of fault locators, enhance the capabilities of disturbance recorders, and allow differential feeder protection to use re-routable communication networks. However, concern about the reliability of GNSS receivers used in intelligent electronic devices (IEDs) have been reported; problems include mal-operations of differential protection, erroneous satellite timing/location messages, inappropriate installations, and blocking of satellite signals due to illegal use of GNSS jammers in vehicles. Utilities now require a timing system less dependent on the use of low cost GNSS receivers integrated into IEDs, but one that uses Grandmaster clocks, slave and transparent clocks, and an Ethernet communication network. The IEEE 1588-2008 synchronization protocol uses the Ethernet to disseminate a global time reference around a substation. A future substation will probably include duplicate 1588 grandmasters, each incorporating stable oscillators with GNSS and terrestrial receivers, in conjunction with a 1588 compliant Ethernet data network with slave and transparent clocks, and redundancy boxes for interfacing with IEDs. Although IEEE 1588 protocol is promising for future substation automation systems, its performance and impact has to be fully evaluated before it can be used in real substations. This paper describes how an IEEE 1588 time synchronization testbed is designed, constructed, and tested. Testing involves measuring the time offset when the Ethernet is heavily loaded with other traffic and the holdover capability of 1588 clocks. Additional delay introduced by IEEE 1588 traffic is also measured. As there is limited testing on GPS receivers within the power industry, this paper also uses the testbed to evaluate the steady state and transient behavior of GPS receivers. The results show a 1588 time synchronization system is accurate, secure, and ideally suited for protection and control applications, compared to a timing system merely based on GPS receivers. The information described in this paper should increase a utility's confidence in applying IEEE 1588 timing in a real substation.

Developing a power monitoring and protection system for the junction boxes of an experimental seafloor observatory network

A power monitoring and protection system based on an embedded processor was designed for the junction boxes (JBs) of an experimental seafloor observatory network in China. The system exhibits high reliability, fast response, and high real-time performance. A two-step power management method which uses metal-oxide-semiconductor field-effect transistors (MOSFETs) and a mechanical contactor in series was adopted to generate a reliable power switch, to limit surge currents and to facilitate automatic protection. Grounding fault diagnosis and environmental monitoring were conducted by designing a ground- ing fault detection circuit and by using selected sensors, respectively. The data collected from the JBs must be time-stamped for analysis and for correlation with other events and data. A highly precise system time, which is necessary for synchronizing the times within and across nodes, was generated through the IEEE 1588 (precision clock synchronization protocol for networked measurement and control systems) time synchronization method. In this method, time packets were exchanged between the grandmaster clock at the shore station and the slave clock module of the system. All the sections were verified individually in the laboratory prior to a sea trial. Finally, a subsystem for power monitoring and protection was integrated into the complete node system, installed in a frame, and deployed in the South China Sea. Results of the laboratory and sea trial experiments demonstrated that the developed system was effective, stable, reliable, and suitable for continuous deep-sea operation.

Precision Time Protocol support hardware for ATCA control and data acquisition system

An in-house, Advanced Telecom Computing Architecture (ATCA) based control and data acquisition (C&DAQ) subsystem has been developed at Instituto de Plasmas e Fusão Nuclear (IPFN), aiming for compliance with the ITER Fast Plant System Controller (FPSC). Timing and synchronization for the ATCA modules connects to ITER Control, Data Access and Communication (CODAC) through the Timing Communication Network (TCN), which uses IEEE 1588-2008 Precision Time Protocol (PTP) to synchronize devices to a Grand Master Clock (GMC). The TCN infrastructure was tested for an RMS jitter under the limit of 50ns. Therefore, IPFN's hardware, namely the ATCA-PTSW-AMC4 hub-module, which is in charge of timing and synchronization distribution for all subsystem endpoints, shall also perform within this jitter limit. This paper describes a relevant upgrade, applied to the ATCA-PTSW-AMC4 hardware, to comply with these requirements – in particular, the integration of an add-on module “RMC-TMG-1588” on its Rear Transition Module (RTM). This add-on is based on a commercial FPGA-based module from Trenz Electronic, using the ZHAW “PTP VHDL code for timestamping unit and clock”, which features clock offset and drift correction and hardware-assisted time stamping. The main advantage is that timestamps are generated closer to the Physical Layer, at the Gigabit Ethernet Media Independent Interface (GMII), avoiding the timing uncertainties accumulated through the upper layers. PTP code and user software run in a MicroBlaze™ soft-core CPU with Linux in the same FPGA, adding programmability and quick implementation of the desired features and upgrades. The paper briefly presents an overview of the ATCA C&DAQ, presenting the PTP and time stamping solution and how it was hardware-implemented, resulting in the RMC-TMG-1588 module. Finally it will describe the synchronization performance tests and results obtained at ITER site as well as indicating further developments to the system, in order to fulfil ITER's requirements.

Quantitative Assessment of Fault Tolerant Precision Timing for Electricity Substations

Advanced substation applications, such as synchrophasors and IEC 61850-9-2 sampled value process buses, depend upon highly accurate synchronizing signals for correct operation. The IEEE 1588 Precision Timing Protocol (PTP) is the recommended means of providing precise timing for future substations. This paper presents a quantitative assessment of PTP reliability using fault tree analysis. Two network topologies are proposed that use grandmaster clocks with dual network connections and take advantage of the best master clock algorithm (BMCA) from IEEE 1588. The cross-connected grandmaster topology doubles reliability, and the addition of a shared third grandmaster gives a nine-fold improvement over duplicated grandmasters. The performance of BMCA mediated handover of the grandmaster role during contingencies in the timing system was evaluated experimentally. The 1 μs performance requirement of sampled values and synchrophasors are met, even during network or GPS antenna outages. Slave clocks are shown to synchronize to the backup grandmaster in response to degraded performance or loss of the main grandmaster. Slave disturbances are less than 350 ns provided the grandmaster reference clocks are not offset from one another. A clear understanding of PTP reliability and the factors that affect availability will encourage the adoption of PTP for substation time synchronization.

Use of Precision Time Protocol to Synchronize Sampled-Value Process Buses

Transmission smart grids will use a digital platform for the automation of high-voltage substations. The IEC 61850 series of standards, released in parts over the last ten years, provide a specification for substation communication networks and systems. These standards, along with IEEE Std 1588-2008 Precision Time Protocol version 2 (PTPv2) for precision timing, are recommended by both the IEC Smart Grid Strategy Group and the National Institute of Standards and Technology Framework and Roadmap for Smart Grid Interoperability Standards for substation automation. IEC 61850, PTPv2, and Ethernet are three complementary protocol families that together define the future of sampled-value (SV) digital process connections for smart substation automation. A time synchronization system is required for an SV process bus; however, the details are not defined in IEC 61850-9-2. PTPv2 provides the greatest accuracy of network-based time transfer systems, with timing errors of less than 100 ns achievable. The suitability of PTPv2 to synchronize sampling in a digital process bus is evaluated, with preliminary results indicating that steady-state performance of low-cost clocks is an acceptable 300 ns but that corrections issued by grandmaster clocks can introduce significant transients. Extremely stable grandmaster oscillators are required to ensure that any corrections are sufficiently small that time synchronizing performance is not degraded.

Ultraprecise Absolute Time Synchronization for Distributed Acquisition Systems

In this paper, we describe an algorithm built on top of a precision time protocol (PTP) implementation that allows for synchronization, syntonization and absolute time referencing to coordinated universal time (UTC), including the estimation of timestamp uncertainty. We call this the software grandmaster (SWGM) algorithm, since it provides similar services to a PTP grandmaster clock. We show that SWGM allows timestamps to be coordinated between multiple participants in a distributed measurement system with typical performance of plusmn 86 ns [root mean square (rms)] over commodity switched Ethernet connections using hardware PTP and hardware-derived timestamps. We further show that when software-derived timestamps are used the uncertainty in the timestamps is primarily driven by the latency of the system calls to read the PTP hardware, and may be on the order of 15-25 s (rms) depending on process priority, hardware bus speed, and host processor clock rate. We also show that SWGM is robust against dropped network packets up to approximately 60% loss of packets.