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Current energy transitions towards the use of more distributed generation, as well as the decarbonisation of heat and transport, are changing the operation of local energy distribution systems. The impact of these local changes on a national scale energy supply system is not well understood. An energy hub approach was integrated into a national scale gas and electricity transmission networks model (CGEN), to represent local energy distribution systems. The energy hub models the integrated operation of electricity, natural gas and heat distribution systems. The distribution system within a region is described in terms of energy supply sources, conversion technologies and storage systems. Transmission supply points link the energy hubs with the gas and electricity transmission networks. A case study was conducted to investigate the impacts on model outputs by integrating energy hubs into the CGEN model. Preliminary results indicate that the operation of distributed generation and storage in energy hubs have a direct impact on electricity and natural gas supply in the transmission networks. The proposed methodology, therefore, extends the analytical capability of the CGEN model across multiple scales and vectors including heat.

A multi-terminal soft open point (MT-SOP) is a power electronic device, using multiple (3 or more) voltage source converters (VSCs) connected to a common DC busbar and multiple feeders, installed at previously normally open points in distribution networks. Due to its capability of accurate control of power flow, MT-SOPs are able to mitigate voltage and thermal constraints in medium voltage (MV) networks with high penetrations of distributed generators (DGs). The operating set-points were determined using a non-linear programming (NLP) optimization and a Jacobian matrix-based sensitivity analysis. The methodology was demonstrated on an 11 kV test network. Results showed that a three-terminal SOP reduces the network energy losses and enables the distribution network to host a further 20% of DG compared to a two-terminal SOP.

—Increasing amount of Distributed Generation (DG)\ud connected to distribution networks may lead to the voltage and\ud thermal limits violation. This paper proposes a Virtual Energy\ud Storage System (VESS) to provide voltage control in distribution\ud networks in order to accommodate more DG. A VESS control\ud scheme coordinating the demand response and the energy storage\ud system was developed. The demand response control measures the\ud voltage of the connected bus and changes the power consumption\ud of the demand to eliminate voltage violations. The response of\ud energy storage systems was used to compensate for the\ud uncertainty of demand response. The voltage control of energy\ud storage system is a droop control with droop gain values\ud determined by voltage sensitivity factors. The control strategy of\ud the VESS was applied to a medium-voltage network and results\ud show that the control of VESS not only facilitates the\ud accommodation of higher DG capacity in the distribution network\ud without voltage violations or network reinforcements but also\ud prolongs the lifetime of transformer on-load tap changer.

The employment of battery storage is recognized to be a solution for managing the variability of renewable energy sources in power systems. In this paper the feasibility of integrating a battery energy storage system (BESS) into a renewable energy park was investigated. The energy park consists of three wind turbines with a total generating capacity of 6MW and 2MW of solar photovoltaic panels. A maximum power export limit of 5 MW to the grid is enforced. The optimal size of the BESS was calculated to maximize the profit made by the energy park through participating in the electricity spot market. To do this, a linear optimization model embedded within a net present cash flow approach was developed. Optimal size of the battery storage capacity and optimal power rating of the inverter for different battery costs assumptions were examined.

The energy system is a complex network of physical infrastructure and markets interacting closely with one another. Within this network, the gas and electricity systems have become the backbone of modern energy production. Both systems are closely interconnected due to the vast deployment of efficient combined-cycle gas turbines (CCGTs) over the first decade of the 2000s, mainly in Organization for Economic Cooperation and Development countries. This increased interdependence and rapid penetration of variable renewable energy sources (varRE) make the gas-electricity nexus a primary concern and opportunity for energy system flexibility.

This paper presents an algorithm that calculates the nonconcurrent per-node demand and generation hosting capacity of a distribution network. The algorithm is used to appraise the increase in hosting capacity that would result from adding a Soft Open Point (SOP) to link two networks. To visualise non-concurrent per-node hosting capacity, a stress majorization technique is applied to a United Kingdom Generic Distribution System (UKGDS) network. This creates geographically representative layouts which preserve branch length information. It is suggested that applying these techniques to the entire GB 33kV network, whilst allowing for network reconfiguration and for variation of demand and generation across the time of day and day of year, is feasible.

The developments of large-scale renewable energy cause significant challenges for the operation of power system. Demand Side Response (DSR) based Thermostatically Controlled Loads (TCLs) may offer a broad range of potential benefits on system operation and reliability. This paper investigates the modelling of aggregated small loads, such as Heat Pump (HP). The simplified thermodynamic model of a residential single Air Source Heat Pump (ASHP) was developed and simulated using Matlab. A decentralized temperature control algorithm was used to control the ON/OFF cycle of the heat pump offering comfort to the customer. The behaviour of a population of controlled heat pumps was examined. Seven case studies were conducted to identify a suitable number of individual heat pump models that can be used to represent the total number of heat pumps in the UK according to the National Grid 2030 medium uptake scenario. Simulation results showed that an aggregation model of 5,000 individual heat pumps is suitable to represent the total number of heat pumps in the GB power system.

Wind power integration has been increasing over the recent years. Although a significant number of wind turbines (WTs) are AC connected to the grid either as fixed-speed induction generators or doubly fed induction generators (DFIGs), the use of permanent magnet synchronous generators (PMSGs) is being considered. As variable-speed WTs displace fossil fuel conventional plants, they are expected to comply with Grid Code requirements and contribute to the provision of ancillary services. In this paper, dynamic models and control schemes for DFIG and fully rated converter (FRC) PMSG-based WTs, rated at the same level, are presented. The dynamic responses and the fault ride-through capabilities of both technologies are assessed and compared. The inertia support capabilities of FRC PMSG-based WTs in the GB system have also been investigated.

The stability of an HVDC-connected Offshore Wind Power Plant (OWPP) is compromised if there are interactions between the power converters and the resonances of the offshore grid. This paper analyses the voltage stability of the offshore HVDC converter due to low frequency electrical resonances. An impedance-based representation is used to identify the resonances and study the stability. The effect of the offshore converter control and OWPP parameters is analysed through the root locus of the system. The positive-net-damping criterion is used to determine the stability conditions due to electrical resonances. Also, time-domain simulations in PSCAD/EMTDC are presented to verify the stability conditions.

Electric power systems will need to accommodate large amounts of renewables and a growing number of DC loads with reduced costs and losses. Medium-voltage DC distribution lines can play a key role. Moreover, a higher availability and reliability of the power supply can be achieved with energy storage systems (ESSs). In this paper, a hybrid configuration merging both concepts is evaluated. A medium-voltage DC distribution system with an integrated ESS has been proposed, modelled, and simulated. Voltage source converters have been used for the AC/DC conversions. The ESS is connected to the DC bus through a dual active bridge enabling bidirectional power flow while covering a large voltage gap. The controllers for all converters and a supervisory control scheme have been implemented. Simulations show the capability of the hybrid configuration to fulfill variable grid demand regardless of the wind power generation, thus transforming a fluctuating source into a dispatchable supply.

This paper demonstrates a scaling method for an experimental test rig to represent the steady state operation of different HVDC transmission systems. The method is based on a parameter conversion between the experimental rig and the HVDC system under study. A virtual resistance is added to the DC cable resistance of the experimental test rig in order to achieve the same steady state operation as the real HVDC system. A droop control correction in the VSCs was used to implement the virtual resistance. A Hardware-in-the-loop set-up formed by laboratory-scale power electronic devices and a Real Time Simulator was used to test this scaling method. Three case studies modelled in PSCAD/EMTDC were used to verify that the results show good agreement.

Multiterminal HVDC (MTDC) schemes are intended to transfer power from offshore wind farms to land and interconnect the grids of adjacent countries, through Voltage Source Converters (VSC). The modular multilevel converter (MMC) topology of VSCs is a more recent development which has low harmonics, reduced losses and occupies less space. This paper analyses the frequency support characteristics of MMC-based multiterminal HVDC schemes, using the energy transferred from the capacitance of the MMCs, wind turbine rotating mass and other AC systems. A generic formulation of an equivalent synthetic inertia constant is proposed to determine the energy transferred from the MTDC scheme. A 3-terminal MMCHVDC system is utilised to study the influence of cell capacitance of the submodules and the proposed synthetic inertia constant of the MTDC system on the frequency support capability of the MMC capacitors. The time response and energy capability of the different energy sources of the MTDC system are compared.

Soft Normally-Open Points (SNOPs) are power electronic devices installed at normally-open points in a distribution network. Such power-electronic devices are able to control power flow to balance loads between feeders, reduce network losses and regulate voltage. The performance of SNOPs for feeder load balancing in a medium voltage distribution network was investigated. Steady state models of two different types of SNOP were developed: a back to back voltage-source converter and unified power flow controller. The benefits of using SNOPs were quantified by solving a combinational nonlinear optimization using Powell's direct set method. The IEEE 33-bus power system was used to demonstrate the effectiveness of SNOPs. Different numbers and types of SNOP devices were considered. The superiority of using SNOP was shown by comparing them with the conventional network reconfiguration.

Control of the grid connected load in a power system is an effective means of contributing to the grid frequency control that is conventionally provided by frequency sensitive generation. The availability of domestic refrigerator and industrial bitumen tank load to provide frequency response services was investigated. The time of a day that the load is available to provide frequency response without interfering with its inherent function was measured through field investigations by Open Energi. Based on the measured periods of availability, the number of frequency responsive loads to be aggregated for frequency response over a day was estimated. Decentralised dynamic controllers were then developed which enable loads to vary their power consumption in proportion to the variation of grid frequency. The availability of the dynamically controlled refrigerator and bitumen tank load for frequency response was modelled. Variation of the availability during a severe frequency incident was simulated. The results showed that the aggregated loads were able to provide dynamic response to grid frequency continuously and repetitively over a day.

This paper models the energy systems of Great Britain (GB) and Greece in EnergyPLAN for the year 2020. EnergyPLAN is an analysis tool that simulates energy systems on a national scale. Future alternative scenarios were developed considering smart charging of Electric Vehicles (EVs). The model was run with a range of Renewable Energy Sources (RES) integration and with three different scenarios for the transport sector: reference model with no EVs, the model with EVs without Vehicle to Grid (V2G), and the model with EVs with V2G capability. In the EV charging scenarios, the charging rates of 3kW, 7kW, 11kW and 22kW were considered. The results for GB and Greece were analyzed in terms of Critical Excess Electricity Production (CEEP) and CO2 emissions, and the conclusions show that EVs with V2G option have the potential to increase the penetration of fluctuating RES, and decrease CO2 emissions.

Road transport today is dominated by oil-delivered fuels and internal combustion engines and such a high level of dependence on one single source of primary energy carries strategic, climatic and economic risks [1]. Electric mobility offers an opportunity for diversification of the primary energy sources used in transport, but also brings new risks, technological challenges and commercial imperatives. Large penetration of Electric Vehicles (EV) will increase the electricity demand and load forecasting plays a central role in the operation and planning of electric power. This paper proposes a short-term load forecast model using Support Vector Machines, an artificial intelligence technique. A realistic scenario is studied to test the performance of the suggested model. The accuracy of the method is evaluated through a comparison with a Monte Carlo forecasting technique.

The development of the North Sea Supergrid is closely linked to three main topological ideas: (i) Business as Usual; (ii) Local Coordination; and (iii) Fully Integrated. In this paper, the three proposed topologies were simplified, analysed and compared for power export from offshore wind farms unto onshore grids. A review on the state-of-the-art HVAC and HVDC offshore transmission technologies was carried out. The national offshore network development strategies of the six countries surrounding the North Sea were summarised. The number of HVAC and HVDC assets required for all three topologies were calculated. It was evident from calculations that, by 2030, the Fully Integrated Topology will achieve approximately 8% asset savings than the Local Coordination Topology.

Frequency excursions on electrical power systems are traditionally controlled using governors on central, often steam driven, generators. However, if the proportion of steam driven plant is reduced, there is a need to provide frequency response by other means. Distributed frequency response is under-utilised; this is partly because it is difficult for system operators to schedule demand side frequency response capability and verify its operation. Smart meters provide a means to overcome these difficulties, if the meters have an adequate hardware specification. A scheme to enable System Operators to specify demand side frequency response, become aware of its availability and verify its operation is put forward. A model is developed in which demand side frequency response operation is verified using `Frequency Response Verification Packets' (FRVPs) - data packets created by smart meters that quantify changes in demand following a detected frequency excursion. The model is used to simulate a situation where 20% of all domestic washing machines in Britain can pause for 30 minutes following a frequency excursion. For a frequency deviation at 1830 hrs on a weekday in the month of March, 291778 FRVPs were created (corresponding to 135 MW total demand reduction within 2 seconds of the frequency excursion).

Developers of distributed generator schemes often wish to increase the size of their generators, in order to make their projects more economically attractive. This work reported the coordination of the operation of independent distributed generators connected to the same circuit, so as to maximise the amount of electrical energy they deliver without exceeding the power limit of that circuit. An Aggregator, owned by the generators, schedules the generators that can be dispatched in times of reduced output of the other generation. The coordination leads to an additional income from the surplus of electrical energy that is able to be produced. The Aggregator runs a cooperative game with transferable utility to allocate this amount, considering the electrical power produced and the type of each generator. The results of a numerical example showed that all generators have an economic incentive to operate in a coordinated manner.

The potential of Fully Rated Converter-based wind turbines (FRC-WTs) on the mitigation of subsynchronous resonances (SSR) in the power system having series-compensated transmission line. IEEE First Benchmark Model (FBM) was featured with Aggregated FRC-WTs to perform the studies. The potential occurrence and mitigation of the SSR in steam turbine were investigated. The Linear Quadratic Regulator (LQR) was used to damp SSR oscillations occurred at steam turbines. MATLAB code was used to perform Eigenvalue analysis and digital time-domain simulations were used to test the control strategy.

Three approaches for grid integration of Electric Vehicles (EVs) through a Virtual Power Plant (VPP) concept are introduced. A classification of these different ways for realizing a VPP based on the control structure, resource type, and the aggregation approach is discussed. This is followed by a description of the three VPP approaches, which are referred to as direct, hierarchical, and distributed control approaches. For each of the three approaches, the necessary operational steps are discussed and the differences are highlighted. Finally, a case study is presented to demonstrate EV integration through a VPP concept.

Electric Vehicles are anticipated to have a considerable percentage of the vehicle market sales in the forthcoming years. The additional energy requirements for charging their batteries may affect the network operation, in terms of stability and reliability, especially when these are synchronized with the system peak demand. This issue will present power system operators with the challenge to efficiently integrate Electric Vehicles into power systems by exploiting their ability to behave as manageable loads. The Multi-Agent System technology has been proven a promising way to manage distributed energy resources in electrical networks. A multi-agent system approach to manage the charging of the Electric Vehicle batteries is described. The types of agents required to satisfy the technical operation and the market participation of Microgrids with Electric Vehicles are provided.

A combined gas, district heating and electricity distribution network design model was developed. The model determined cost optimal infrastructure component specifications, financial performance and carbon emissions. Consumers were grouped into clusters of similar load profile. Distribution network specifications were estimated using peak load flow conditions. Community combined heat and power units and heat only boiler units were optimised against the district heat network load profile. The model is demonstrated using an example case study based on a real UK new build community development.

The different operation modes of multiterminal HVDC-VSC systems for large offshore wind farms are analyzed. Control schemes for each power converter are proposed. The wind farm VSCs inject the power to the HVDC grid and are controlled as ideal voltage sources that absorb all the incoming power in normal operation, and reduce the injected power whenever a fault occurs and the DC voltage rises. The grid-side VSC inject the power to the main grid and control the DC voltage using a droop control scheme. The proposed controllers are tested in a case study by means of dynamic simulations with a four terminal system. The results show good performance for changing wind speeds, a voltage sag and a loss of a converter.

The feasibility of using delayed smart meter measurements for distribution state estimation is investigated. It was assumed that smart meters take local measurements, store them, and transmit a batch of information twice a day. An 11 kV underground network (the UK Generic Distribution Network) with various numbers of distributed generators connected was used for the study. The error and standard deviations of the voltage estimates are reported for a varying number of near realtime measurements from the distributed generators. Simulations results for different loads and generation outputs are also reported. The results shows that the voltages of a distribution network can be estimated reliably by a state estimator using the previous day's smart meter measurements and a small number of near real-time measurements.

This study presents daily optimal operation of biomass combined heat and power (CHP) with thermal storage in a spot market. Since CHP mainly relying on environmental condition as well as spot price is fluctuating under influence of so many factors, optimal operation of CHP district heating systems is not easy to achieve. In this paper operation of medium scale biomass CHP in spot price with and with out storage for a typical day in winter, autumn/spring and summer is investigated. Further, the impact of spot price variability on thermal storage utilization is examined. For this purpose, a residential community in the UK with known heat and electricity profile is being considered. Results of the study show that by making flexibility in CHP operation such as flexible operating point and installing large thermal storage, its partnership in competitive market in an economic way would be achievable much easier. Moreover, thermal storage utilization for CHP operation in competitive market is varied significantly versus variability in spot price and demand profile which contribute to the difficulty of optimal sizing of CHP and thermal storage in deregulated market.

In Great Britain, increased wind generation, up to 34 GW, is planned. Offshore and onshore infrastructure reinforcements have been proposed, the inland reinforcement including series compensation (fixed capacitors), as discussed in the UK National Grid 2020 Vision. Interaction of series fixed capacitors with the quadrature boosters that are already installed in the GB transmission grid is assessed, with particular emphasis on the occurrence of subsynchronous resonance.

Large capacity of wind generation is expected to be installed across Great Britain by 2020. Wind generation is variable, therefore fast ramping generation plants will be required to balance electricity demand. Gas-fired generation plants will most likely be used to compensate for wind generation variability because of their ramping capability and large installed generation capacity. This will cause comparable gas demand swings in the gas network as wind varies. A combined gas and electricity network optimisation model (CGEN) is used to quantify impacts of wind variability on gas network operation. Analysis is performed on mitigation measures such as greater dual fuel capable gas-fired power plants and gas storage capacity in order to reduce gas network constraints and provide alleviation against wind generation variability.

The current status of the development of Smart Grids in the UK and China was reviewed. The definitions, policy and technical drivers, technology composition, incentive mechanisms and industry actors of Smart Grids are discussed and contrasted. The comparison shows considerable divergence in the emphasis placed on different aspects of Smart Grids between the two countries. In particular the UK emphasizes developments within distribution networks, including the demand side, while China also emphasizes the UHV transmission.

Battery charging of Electric Vehicles (EVs) will increase the power demand in distribution networks. It is anticipated that this will cause voltage drops, thermal overloads and an increase in losses. These impacts will be affected by the behaviour of the owners of EVs. A typical 3-phase LV residential distribution network model is used to evaluate the effects of EV battery charging on distribution networks with Distributed Generation (DG). The uncertainties associated with the ownership of EVs, the rating of charging equipment, the occurrence and the duration of charging, together with the spatial distribution uncertainties of DG installation, were addressed with a probabilistic approach. A case study was performed for the year 2030, considering three EV and two DG penetration levels. A control function which reschedules EV battery charging was defined based on customer preferences and distribution network constraints. Thermal overloads, voltage drops, and losses associated with each case were reported. The effects of the coordinated EV battery charging on these impacts were analysed.

The electromechanical transients during a deloading of a DFIG turbine and the Fault Ride Through (FRT) capability of a DFIG wind farm connected through HVDC transmission lines are discussed. The electromechanical oscillations during a deloading operation of a DFIG wind turbine generator are simulated using BLADED software. Then power reduction control during a fault was achieved by reducing the power from the wind farm as a whole and by deloading the individual wind generator. A new power blocking technique applied at the offshore converter station was used to reduce the wind farm power output. Simultaneous control of the wind farm and wind turbine power outputs enabled a smooth power reduction during the fault.

Information and communication technologies (ICT) play a critical role within SmartGrids. However the current weak ICT infrastructure retards the implementation of SmartGrid functions. Smart meters with real-time communication capability are beneficial in many ways for the SmartGrid future, although there is limited agreement on the role of smart meters in system operation. Smart meters and PLC based ICT infrastructure is modeled in OPNET. The model is integrated with a robust state estimator and an OPF tool to set up a platform for analysing the feasibility and performance of the SmartGrid ICT infrastructure. The proposed method can be used to design and evaluate ICT infrastructure for smart distribution network operation.

A future perspective micro-grid with a medium-term prediction for 2030 is described. The present state of intentional islanding is briefly reviewed. Distributed Generators (DGs) and Electric Vehicles (EVs) to sustain the local distribution system in the event of interruption of supply are considered. Projections regarding their availability are presented and different penetration scenarios are addressed. Environmental benefits of a future micro-grid are described through a comparison of the maximum and minimum EV and micro-generation penetration predictions.

With the increased penetration of wind power, wind turbines are now expected to provide ancillary services presently performed by large synchronous generators. Among the ancillary services, frequency duties are vital and a number of papers are available in the literature to demonstrate the possibility of using DFIG based wind turbine for inertia, primary and secondary frequency support. This paper describes the possibility of using DFIG based wind turbine for supplying spinning reserve. The mode of operation is described and simulation results are included.

Developments in wind turbine technology are facilitating the increase of power generation capacity from renewable energy sources. However an electrical utility grid is generally unable to accept a large amount of wind power without imposing strict conditions. Voltage fluctuation, reactive power compensation and fault ride through are the main areas of concern. Variable speed generators, STATCOMs and crowbar circuits are used to comply with grid code requirements. This paper discusses a number of wind turbine topologies and grid code requirements for large scale integration of wind power.

Wind farms are presently an important component of the world's source of electric energy from renewables. With the increasing size of wind turbine generators (leading to bigger wind farms), it has become essential for Transmission System Operators (TSOs) to be able to control, regulate and monitor wind farms like any other modern power plant. For this to be possible, suitable communication facilities are essential to allow the exchange of information between control, regulation, monitoring, visualization and data storage systems. A concise review is presented of the communications requirements and available technology for the Operation and Maintenance (O&M) of modern wind farms (either onshore or offshore).

The extent of distributed generation (DG) that can be connected to a distribution network is often limited by the permissible voltage limits. The DG not only raises voltage but also modifies network fault current and may cause problems on existing distribution network protection schemes. Voltage control by active management can increase the level of DG penetration but requires an assessment of the voltage at each point on the network. Active management of the distribution network (DN) must also be practicable for the generators and the network operator. The paper presents possible solutions to some of the problems of active management and protection of distribution networks with higher penetration of DG. The paper also addresses the issues of costs and benefits of active management and DG islanded operation.

Microgrids are attracting substantial interest because they have the potential to increase the use of renewable generation and micro-CHP. They can also defer investment in distribution capital plant and can improve local power quality. However the primary operational requirement of power systems is that they must operate safely from a user point of view, even during contingencies. Yet electrical safety of microgrids has received little attention to date. This paper addresses this important area. The fault current distribution in a generic microgrid is investigated for different fault contingencies during grid-connected and islanded operation. Based on an extensive investigation of earthing systems, a grounding electrode system is then developed for the microgrid study-case so that safe step and touch potentials are obtained

The grounding system plays an important role in the quality of power produced by windfarms, since overvoltages caused by a fault situation, have to be successfully dispersed into the ground. In this paper the effect of grounding system design in transient overvoltages appearing in windfarm electrical installations is studied. In particular, the effect of interconnecting individual wind turbine grounding systems via horizontal strips on transferred overvoltages is examined.

In this paper, the analytical and practical design issues of a software phase-locked loop (SPLL) for DVR are presented. A SPLL model that uses a lag/lead loop controller, is derived in order to analyse the system performance and filtering characteristic by the use of bode diagrams and root-locus methods. In DVR applications, parameters of the design of the SPLL controller are not only dependent on the steady state and dynamic state, but also on practical conditions such as utility unbalance, voltage sag/swell magnitude, voltage harmonics, phase jumps and frequency variations. Therefore, the practical aspect of the SPLL implementation has also been discussed. Experimental results demonstrate its phase tracking capability.

This paper addresses the issue of load modeling. Various load models have been proposed in the past based on the load responses and subsequent parameter estimation. First and second order generic load models are developed in the MATLAB/SIMULINK environment based on simulated measurement responses obtained from PSCAD/EMTDC. The influence of measurement delays influenced by transducers and other instrumentation on estimated load model parameters is investigated. The comparison between simulated and measured responses showed big influence of instrumentation settings on estimated load model parameters.