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Due to the increasing number of power electronics-based devices in modern power systems, there are concerns about the impact of higher-frequency interactions on system stability. The typically-used algebraic representation of networks fails to capture these newly emergent issues, but dynamically modelling the entire network with differential equations will lead to a prohibitively long simulation time. This paper proposes a computationally-efficient analysis framework to determine the system loadability in power electronics-rich, large networks with the consideration of multiple types of stabilities. The framework developed in this paper identifies the critical network elements based on the eigenvalue sensitivity in order to exploit a hybrid modelling approach. Within the hybrid model, only the critical network portion is modelled dynamically with the rest of the network represented by algebraic equations. Bifurcation theory is used to simultaneously analyze both small-disturbance rotor angle and small-disturbance voltage stability. The results obtained show that the high-frequency interactions are accurately captured with the pro-posed framework. Additionally, applying this methodology results in a small dimension for the system matrix and a reduction in the computational burden. Two test networks, a three-bus system and the IEEE 39-bus system, are used to illustrate and verify the analysis framework.

Outdoor water use, especially for lawn and landscaping irrigation, accounts for a substantial proportion of residential water use and often peaks during summer months. Understanding how to reduce outdoor water use can play a critical role in balancing the increasing demand for and subsequent protection of water resources. This study aims to find out if information-based strategies can be effective in reducing homeowners’ water use as well as identifying the key determinants that can enhance water conservation campaigns. Using online survey data from 2077 randomly selected urban homeowners with home lawns in a relatively water-rich state, we found that social norm-based information is generally more effective to promote household water conservation behavior than education information. Moreover, the results showed that the households’ water-saving actions, lawn watering knowledge, awareness for local water scarcity, attitudes toward water conservation, socio-demographics, and landscape characteristics all play a role in determining household water conservation intention.

It is anticipated that a large number of voltage source converters (VSCs) will be integrated into future power sys-tems, which can potentially be detrimental to system stability. Pre-vious work has utilized an impedance-based approach to analyze the feasibility region boundaries of power systems with multiple VSCs. However, impedance-based modeling limits the analysis of the system feasibility region to just two or three dimensions. Hence, this paper develops a methodology based on bifurcation theory that enables the system multi-dimensional feasibility region to be identified efficiently with consideration of multiple different varying parameters. The developed methodology is generalized so that it can be applied to identify system feasibility region bounda-ries in other power systems with multiple varying parameters. The partial Spearman correlation coefficient is adopted in this paper to identify the key parameters that affect the feasibility region boundary. Additionally, the calculated correlation indices quan-tify the interactions between the control loops VSCs in the system. The proposed methodology is verified against other analytical methods and the impact of key parameter variation on the system feasibility region boundaries is discussed.

This article studies the influence of fiber Bragg grating (FBG) head length on insulated gate bipolar transistor (IGBT) direct on-chip thermal sensing performance of FBG sensors. To this end, the surface of a commercial IGBT chip is thermally simulated and experimentally characterized. Uniform FBG sensors with three head sizes are then tested in two promising thermal sensing locations. The study has found that the large thermal gradients in this application create an additional constraint when using longer head lengths. A distortion in the reflected spectrum of the 5-mm FBG sensor is used to illustrate the underlying physical effect, which causes this limitation for IGBT junction temperature measurement. This additionally affects the length of head sizes providing accurate temperature readings of the IGBT surface hotspots, and significantly, this limit is location-dependent in a given IGBT geometry.

Policy interventions on the water are commonly associated with restricting watering on specific days with a limited time window, yet very few existing studies focus on water conservation behavior in the context of the length of watering schedule intervals. People make decisions periodically, and their intertemporal time preferences may affect their decisions. In this study, we investigate the impact of the watering schedule interval on water use both theoretically and empirically. First, we incorporate intertemporal time preferences and subjective distortion of objective probabilities into a theoretical model that simulates the watering decision-making process. Our theoretical model shows that homeowners are more likely to postpone their irrigation as they become more impatient if the expected cost of having an over-watered lawn is relatively low. Second, we empirically test to which extent people’s water conservation behavior changes as the duration of water restrictions increase. We examine three types of watering schedules, i.e., odd-even day watering restriction, restricted hours watering, and voluntary watering restriction. The results show that longer watering schedule intervals increase irrigation frequency and even more water consumption. Yet, we also found that for people who prefer an immediate reward instead of a more valuable reward in the future, shortening the watering schedule intervals may be effective in reducing their irrigation frequency and promoting water conservation.JEL: D12, D15, Q31, Q50, R21

An IGBT finite element model aimed at facilitating the assessment of Fibre Bragg Grating sensing based direct on-chip temperature monitoring is first presented in this paper. A commercial off-the-shelf IGBT module geometry is characterised, and a thermo-electrical finite element model is then established using its features. The model is subsequently employed to evaluate the local thermal disturbances that may be introduced by the installation of the optical based temperature sensor directly on the top surface of the IGBT chip. The effects of the sensor thermal interface material characteristics, e.g., thermal conductivity and size, in the local temperature environment are investigated.

this paper reports a distributed thermal monitoring scheme for power electronic modules (PEMs) in wind turbine converters. The sensing system is based on utilizing electrically non-conductive and electromagnetic interference immune fiber Bragg Grating (FBG) sensing technology embedded in the PEM baseplate. The design and implementation features of the proposed scheme are presented first. The scheme is then applied in a commercial PEM operating within an inverter bridge, equipped also with a conventional distributed thermal monitoring system using a multiple point thermo-couple (TC) sensor suite. A range of tests are performed to evaluate the performance of the FBG distributed thermal monitoring system and correlate it to TC measurements under steady-state and transient operating conditions representative of PEM operation in an actual wind turbine application. It is shown that the proposed FBG monitoring system can offer practical operational improvements in establishment of distributed thermal sensing schemes for wind turbine PEM.

In-situ temperature near the chips in a multiple-chip power semiconductor module is important information for thermal design validation, condition monitoring and overheat protection. Due to the compact packaging structure and clamping force, online detection of the temperature is challenging for a press pack module. This study attempts to achieve measurement by integrating optical Fiber Bragg Grating (FBG) sensors into the device. Different integration schemes are examined using experiments and theoretical analysis to show the effects on the transient performance. It is shown that FBG sensors with plate housing can effectively indicate the transient temperature ripple in normal converter operation, owing to the fast dynamic response of a small size sensor. The package integration has only minimal effects on the original distributions of electrical, thermal and mechanical quantities within the power module.

HVDC circuit breakers are of increasing importance, as multi-terminal high voltage DC (HVDC) transmission becomes a commercial reality. Multiple HVDC breaker technologies have been developed, and are starting to appear as proof-of-concept installations on real networks. Information about them is however distributed widely in the literature. This article describes the underlying challenges, the leading candidate solutions, and discusses the requirements and construction of the component sub-assemblies. Its goal is to provide a comprehensive overview of the field.

This paper details the design, construction, and test of a lightweight, low energy usage Thomson Coil actuator for the operation of a commercial medium-voltage vacuum switch. A novel latching design, directly linked to the actuator armature, helps to keep the actuator mass at minimum. Experimental results show that 125 J of electric energy is sufficient for operation of a commercial 27 kV vacuum interrupter in times suitable for medium-voltage dc protection applications. The use of high conductor density coils is shown to play a key role on the observed actuator performance. Finite element simulations are used to demonstrate that shorter operation times are feasible, without augmenting the consumed electrical energy, by further increasing coil conductor density.

Representations are special functions on groups that give us a way to study abstract groups using matrices, which are often easier to understand. In particular, we are often interested in irreducible representations, which can be thought of as the building blocks of all representations. Much of the information about these representations can then be understood by instead looking at the trace of the matrices, which we call the character of the representation. This paper will address restricting characters to subgroups by shrinking the domain of the original representation to just the subgroup. In particular, we will discuss the problem of determining when such restricted characters remain irreducible for certain low-rank classical groups.

This paper uses FEA simulations to investigate the behaviour of a high-speed, high-power Thomson coil (TC) actuator suitable for HVDC protection applications, when excited by a double discharge. The influence of the resulting pulse train on the amplitude of observed armature vibration is investigated. The significance of the pulse train on the device electrical to mechanical energy conversion efficiency is assessed and compared with the efficiency obtained using the conventional single discharge approach.

Large, converter-based, renewable energy generation devices will be incorporated into future power systems. This may lead to undesirable interactions between the new and existing conventional power devices. While many papers have analyzed the specific impacts of the integration of the converter-based devices, no previous paper has reviewed the current progress on research into the interactions within mixed complex AC/DC grids with considerable renewable energy. This paper classifies the current research about the interactions in a mixed complex AC/DC network with high penetration of renewable resources examined from two aspects: (i) the problems and issues that have been analyzed; and (ii) the methodological analysis techniques used. Based on this structured review, the current research gaps with respect to the analysis of interactions in networks with considerable renewable energy sources are identified and analyzed, and suggestions for future research are proposed.

The increasing importance of cascaded multilevel converters (CMCs), and the sub-category of modular multilevel converters (MMCs), is illustrated by their wide use in high voltage DC connections and in static compensators. Research is being undertaken into the use of these complex pieces of hardware and software for a variety of grid support services, on top of fundamental frequency power injection, requiring improved control for non-traditional duties. To validate these results, small-scale laboratory hardware prototypes are often required. Such systems have been built by many research teams around the globe and are also increasingly commercially available. Few publications go into detail on the construction options for prototype CMCs, and there is a lack of information on both design considerations and lessons learned from the build process, which will hinder research and the best application of these important units. This paper reviews options, gives key examples from leading research teams, and summarizes knowledge gained in the development of test rigs to clarify design considerations when constructing laboratory-scale CMCs. Published version This work was supported in part by The University of Manchester supported by the National Innovation Allowance project ‘‘VSC-HVDC Model Validation and Improvement’’ and Dr. Heath’s iCASE Ph.D. studentship supported through Engineering and Physical Sciences Research Council (EPSRC) and National Grid, in part by the Imperial College London supported by EPSRC through the HubNet Extension under Grant EP/N030028/1, in part by an iCASE Ph.D. Studentship supported by EPSRC and EDF Energy and the CDT in Future Power Networks under Grant EP/L015471/1, in part by University of New South Wales (UNSW) supported by the Solar Flagships Program through the Education Infrastructure Fund (EIF), in part by the Australian Research Council through the Discovery Early Career Research Award under Grant DECRA–DE170100370, in part by the Basque Government through the project HVDC-LINK3 under Grant ELKARTEK KK-2017/00083, in part by the L2EP research group at the University of Lille supported by the French TSO (RTE), and in part by the Hauts-de-France region of France with the European Regional Development Fund under Grant FEDER 17007725.

Using drones for infrastructure inspection is becoming routine, driven by the benefit of reducing risk and costs. In this paper, the business case for drone-based inspection is examined from the perspective of the wind farm operator and the Drone Service Provider (DSP). A physical and financial model of an offshore wind farm is built using techno-economic analysis and activity-based costing, and data from the open literature. Drone operational models are developed based on domain specific knowledge of operation practices and the predicted physical environment. Rope-access inspection is used as a baseline and accounts for 0.7% of the wind farm operational expenditure. Replacing rope-access inspection with drones reduces costs by up to 70% and decreases revenue lost due to down-time by up to 90%. Increasing autonomy of drones increases the speed at which inspections can be performed but increases costs and complexity. For wind farm operator there is marginal economic benefit (2% reduction in inspection costs) in moving towards a fully autonomous drone-based inspection system from the current visual line of sight operation of single drone. However, from the point of view of the DSP, fully autonomous operations allow greater scalability of the business and enables higher utilisation of the fleet.

Lack of representative and sufficient failure data is a common problem faced by researchers in the area of HVDC systems reliability analysis. To alleviate this problem, researchers usually resort to the collection of data from different publicly available sources, such as organizations reports and from other research articles. However, homogeneity of the information gathered in this way is not guaranteed, given the diverse sources; the generality of any conclusions based on this data is thus affected. In this paper, the adequacy of publicly available failure data for use in reliability analyses of LCC based HVDC systems is assessed. To this end, failure data available in public domain is first collated. Results from the reliability analysis of two bi-pole topologies of LCC based HVDC systems, with different levels of redundancy and operating voltages, are reported.

This paper analyzes sub-synchronous resonance (SSR) in fu-ture wind power plants (WPPs) using bifurcation theory, a non-linear analysis approach. SSR, and in particular the Induction Generator Effect (IGE) is likely to occur more frequently as large amounts of wind power are incorporated into power net-works, supported by series compensation to improve power transfer capability. A nonlinear 10th order modified IEEE first benchmark model is developed. Bifurcation analysis reveals the critical conditions resulting in IGE are identified as a Hopf bifurcation point, verified by considering the trajectory of sys-tem eigenvalues and also through transient time domain simu-lation. The application of bifurcation theory is compared with the linear Nyquist stability criterion. The results from the Nyquist approach show that both analytical methods are in agreement with each other. However, the nonlinear bifurcation analysis determines system stability with respect to any param-eters of interest, whereas the Nyquist stability criterion only determines the system stability at a specific operating point.

Hardware implementation of controllers for modular multilevel converter voltage source converters is a non-trivial task, which requires a thorough evaluation of the real-world performance of control hardware. This paper presents a new processor-in-the-loop system developed at The University of Manchester which enables real-time evaluation of power converter control algorithms implemented on a target hardware platform from within a PSCAD/EMTDC simulation. The developed system has been used to measure the execution times of sorting algorithms implemented within the capacitor balancing control loop of an MMC. The system is a low-cost alternative to commercial real-time hardware-in-the-loop systems, and can be used to bridge the gap between offline simulation and final controller implementation in hardware. The developed system can be extended to support any control algorithm of interest, implemented on a wide range of target hardware platforms which may include: embedded microcontrollers, digital signal processors, and field-programmable gate arrays. Applications include control systems for power electronics connected to power systems including HVDC, renewable energy and smart grids.

This paper proposes a secondary Model Predictive Control (MPC) based architecture to provide DC voltage and DC power control to MT VSC-HVDC networks interfacing wind power generation. The proposed architecture places the controller at a supervisory level, thus providing coordination amongst existing converters’ local droop controllers. Droop control is a type of decentralized DC voltage/power control. Hence, in case of secondary controller failure, droop control acts as a contingency control scheme. A simplified linear dynamic model of the MT VSC-HVDC network is utilised for the MPC's design, thus minimizing computational effort needed to compute secondary control action. Updates of droop gains and offshore and onshore “AC” variables, in the dq domain, are explicitly considered as measured input disturbances within the formulation of the MPC controller, thus, ensuring appropriate control response in order to minimise adverse impact of their variation on the overall system's performance, particularly under wind power variations. Simulation results show that MPC, whose design is based on the system's simplified linear model, is capable of delivering satisfactory performance when applied to the high fidelity non-linear full order model of a six-terminal VSC-HVDC network simulated in PSCAD.