D. John Morrow

Telecommunications for Smart Grid: Backhaul solutions for the distribution network

Telecommunications are an essential component of emerging Smart Grid technologies. Up until now, power system telecoms planning have largely focused on transmission with less investment in the distribution network. Presently there is a need for a universal system over which all messaging may be achieved. With the rise of protocols such as IEC 61850 there is growing momentum to start installing telecoms so as to exploit the benefits on offer, but the challenge is now how to correctly engineer a system that can accommodate rapid growth alongside demand for throughput and real-time performance. This paper reviews a number of last-mile access technologies and proposes a model telecoms network for Smart Grids.

Synchrophasor Broadcast Over Internet Protocol for Distributed Generator Synchronization

Synchronous islanded operation involves continuously holding an islanded power network in virtual synchronism with the main power system to aid paralleling and avoid potentially damaging out-of-synchronism reclosure. This requires phase control of the generators in the island and the transmission of a reference signal from a secure location on the main power system. Global positioning system (GPS) time-synchronized phasor measurements transmitted via an Internet protocol (IP) are used for the reference signal. However, while offering low cost and a readily available solution for distribution networks, IP communications have variable latency and are susceptible to packet loss, which can make time-critical control applications difficult. This paper investigates the ability of the phase-control system to tolerate communications latency. Phasor measurement conditioning algorithms that can tolerate latency are used in the phase-control loop of a 50-kVA diesel generator.

Three-Port DC–DC Converter for Stand-Alone Photovoltaic Systems

System efficiency and cost effectiveness are of critical importance for photovoltaic (PV) systems. This paper addresses the two issues by developing a novel three-port dc-dc converter for stand-alone PV systems, based on an improved Flyback-Forward topology. It provides a compact single-unit solution with a combined feature of optimized maximum power point tracking (MPPT), high step-up ratio, galvanic isolation, and multiple operating modes for domestic and aerospace applications. A theoretical analysis is conducted to analyze the operating modes followed by simulation and experimental work. This paper is focused on a comprehensive modulation strategy utilizing both PWM and phase-shifted control that satisfies the requirement of PV power systems to achieve MPPT and output voltage regulation. A 250-W converter was designed and prototyped to provide experimental verification in term of system integration and high conversion efficiency.

Islanding Detection for Distributed Generation

The paper analyzes the performance of a ROCOF relay and looks at the factors that affect its detection capability, such as load type and the impact of load power factors. It also considers how ROCOF can maloperate during system transients. The later section of this paper describes a new LOM detection technique based on a GPS synchronized phasor measurement system that compares the angular difference between the utility network voltage phasors and the distributed generator voltage phasors. The performance of the proposed technique is shown to be more reliable than ROCOF.

Online Thévenin Equivalent Determination Considering System Side Changes and Measurement Errors

This paper presents a new method for online determination of the Thèvenin equivalent parameters of a power system at a given node using the local PMU measurements at that node. The method takes into account the measurement errors and the changes in the system side. An analysis of the effects of changes in system side is carried out on a simple two-bus system to gain an insight of the effect of system side changes on the estimated Thévenin equivalent parameters. The proposed method uses voltage and current magnitudes as well as active and reactive powers; thus avoiding the effect of phase angle drift of the PMU and the need to synchronize measurements at different instances to the same reference. Applying the method to the IEEE 30-bus test system has shown its ability to correctly determine the Thévenin equivalent even in the presence of measurement errors and/or system side changes.

Management of a multiple-set synchronous island

The continuity of power supply can be improved by power system islanding. A possible solution, synchronous islanded operation, enables the islanded system to remain in phase with the main power system while not electrically connected, and so avoids out-of-synchronism re-closure. Specific consideration is required for the multiple-set scenario, and is the topic of this paper. A suitable island management system is proposed, with the emphasis being on maximum island flexibility by allowing passive islanding transitions to occur, facilitated by autonomous control. These transitions include: island detection, identification, fragmentation, merging and return-to-mains. It can be challenging to detect these transitions while maintaining synchronous islanded operation. A Mathworks SimPowerSystems simulation is used to investigate the performance of the island management system. However, return-to-mains is particularly difficult to detect, and so a method based on voltage phase angle variability is explored by using a laboratory demonstration and time stamped phasor measurements.

Performance of phasor measurement units for wide area real-time control

Phasor Measurement Units (PMU) are becoming a basic building block of modern wide area power system protection, monitoring and control schemes. Such systems rely on accurate time synchronized measurements. PMU operation is governed by the IEEE C37.118 standard. The standard sets out the performance requirements for valid phasor measurements under steady state conditions, but does not specify the response of PMUs under transient system conditions. Since most events requiring action by protection and control systems arise from transients it is important that PMUs report these anomalies in an understood and universal manner. This paper discusses the problem of determining phase during a transition from one cyclic state to another.

OpenPMU: Open source platform for Synchrophasor applications and research

Synchrophasor measurement is increasingly becoming a standard tool of the electrical power systems engineer and is attracting much interest in the research community due to the novel new methods and techniques it offers for observing and controlling the power system. A common difficulty in the development of Synchrophasor based technology is the closed environment in which the measurement algorithms and processes governing the operation of Phasor Measurement Units, PMUs, are developed. While most PMUs will support the relevant IEEE standards for Synchrophasor measurement, where transient or dynamic operation is concerned it would be useful to have detailed knowledge of the mathematical transforms and indeed any limitations of the measurement hardware. This can be especially important in developing new protection systems utilizing Synchrophasors, when confidence in the system rests on consistent performance between devices over a long period of service, including device upgrades. The “OpenPMU” described in this paper intends to settle some of these concerns by defining and developing a research orientated platform for Synchrophasor algorithm and application development.

Statistical Analyses of Wind and Solar Energy Resources for the Development of Hybrid Microgrid

In this paper, a procedure for the statistical analyses of wind and solar energy resources are investigated in order to determine the accurate frequency distribution for the development of hybrid microgrid. The frequency distributions used for wind speed data analysis include Weibull, Rayleigh and Gamma distribution functions. On the other hand the frequency distributions used for the analysis of solar radiation data include Weibull, Logistics, lognormal, Beta and Gamma functions. The performance of the probability distributions used in the wind speed analyses are based on the error evaluations between the predicted and the theoretical wind power densities of the site. Similarly, the performance of the probability distribution functions used in the solar radiation data were judged based on Kolmogorov-Smirnov, Anderson-Darling and Chi-Square tests. The goodness of fit tests (GOF) results of the wind speed analyses show that Weibull distribution performed better compared to Rayleigh and Gamma distributions. On the other hand Beta distribution fitted the solar radiation data better than all other distributions models.

The OpenPMU Project: Challenges and perspectives

The OpenPMU project is a platform for the development of Synchrophasor measurement technology, Phasor Measurement Units (PMU), in an open source manner. The project has now been operating for a number of years and has seen increased adoption at Universities and interest from electrical utilities. The OpenPMU device has recently been tested against the IEEE C37.118 standard and shown to operate within the specification. This paper discusses the OpenPMU project from the perspective of the past two years of experience and evaluates successes and opportunities for improvements in both the OpenPMU device and the philosophy of the design.