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A conventional unified power flow controllers (UPFCs) can provide power flow control and voltage regulation in medium voltage (MV) distribution networks using partially rated converters. However, one of the main challenges of using the conventional UPFC is the unique design of the series interfacing transformer. This paper investigates a modified topology of a UPFC suitable for MV distribution networks. The modified UPFC does not need an interfacing series transformer. Hence, it offers a smaller size, lighter weight, and less cost than the conventional UPFC. It consists of single-phase back-to-back series and shunt voltage source converters. The series converters are connected to a distribution network without a series transformer, while the shunt converters are interfaced using a three-phase shunt transformer. The power ratings of the series and shunt converters were investigated considering a distribution network with a low X/R ratio. The modified UPFC was modelled in MATLAB Simulink and was connected to a two-busbar distribution network and the enhanced IEEE 33-bus distribution network. The results showed the ability of the modified UPFC to independently control active and reactive power in a distribution feeder by processing a fraction of the power transfer through the converters.

The cascaded three-level neutral-point-clamped (3L-NPC) converter and the modular multi-level converter (MMC) are attractive solutions for medium-voltage direct-current (MVDC) applications. Due to their low cost compared to MMCs, cascaded 3L-NPC converters have been adopted in ANGLE-DCa 30 MVA MVDC link demonstration project in North Wales, UK. DC voltage imbalance across submodules (SMs) is a common challenge for both types of MVDC converters. Such imbalance is topology dependent and remains under-researched for cascaded 3L-NPC converters. In this paper, small-signal model-based analysis has been done to reveal that the dc voltage imbalance in cascaded 3L-NPC converters is caused by an unstable system pole. Two voltage balancing methods are presented. The first method is based on PI controllers to precisely regulate SMs voltages without influencing output power. However, it relies on communication between a central controller and local controllers within SMs. The second method uses inverse-droop based control to take over the dc voltage regulation upon loss of communication. Both balancing methods are experimentally validated using a 30 kVA testbed based on the ANGLE-DC project. It has been demonstrated that the dc voltages of SMs can be effectively balanced with both methods during changes of load conditions and dc bus voltages.

Several sources of revenue are available for battery storage systems that can be stacked to further increase revenue. Typically, price arbitrage is used to gain revenue from battery storage. However, additional revenue can be gained from participation in ancillary services such as frequency response. This study presents a linear optimisation approach to account for local energy system participation in the wholesale day-ahead electricity market and multiple frequency response services. The methodology was applied to a school case study. A breakdown of market revenue and value of investment is presented for five operating strategies. The value of availability revenue and response energy revenue are distinguished for frequency response services. Finally, the impact of revenue stacking on battery degradation is assessed. The results show that local energy systems can decrease their operating costs and improve battery storage investment viability by stacking multiple revenues, whilst reducing degradation and increasing lifetime.

A method for estimating the heat demand of different types of dwellings is described. Furthermore, an optimal heat supply mix for a local area was determined considering gas and electricity prices and the unique characteristics of the local area in terms of the heat demand and potential heat supply options. These methods were demonstrated on the local authority area of Neath Port Talbot in the UK. The estimated heat demand was validated against real data. The modelling results obtained show that significant financial support is required for low carbon heating technologies such as heat pumps and district heating networks for them to play a major role in the decarbonisation of heat.

The capability of domestic heat pumps to provide dynamic frequency response to an electric power system was investigated. A thermal model was developed to represent a population of domestic heat pumps. A decentralized dynamic control algorithm was developed, enabling the heat pumps to alter their power consumption in response to a system frequency. The control algorithm ensures a dynamic relationship between the temperature of building and grid frequency. The availability of heat pumps to provide low-frequency response was obtained based on data supplied by Element Energy. Case studies were carried out by connecting a representative model of the aggregated heat pumps to the regional Great Britain (GB) transmission system model, which was developed by National Grid. It was shown that the dynamically controlled heat pumps distributed over GB zones have a significant impact on the GB system frequency and reduce the dependency on frequency services that are currently supplied by expensive frequency-sensitive generators. The rate of change of frequency was also reduced when there is a reduction in system inertia.

The increasing decarbonisation of the power and heat sectors in Great Britain poses numerous uncertainties about the future of the gas network. An optimisation model was developed for investigating the operation of future low carbon electricity, gas and heat supply systems. The model was employed to quantify the impacts on the operation of the gas network in Great Britain of transitioning to low carbon power and heat. The modelling results show that the decarbonisation of the power and heat sectors affects the operation of the high and low pressure gas networks differently. A highly electrified heat sector, only slightly changes the gas load duration curve for the high pressure gas transmission network, but significantly affects the load duration curve for low pressure gas distribution networks. In addition, in a future energy system with a large capacity of variable wind and solar generation, and highly electrified heat supply, although the annual volume of gas supply decreases, the peak gas supply during low wind and cold spells remains the same or even exceeds the current figure. This is mainly due to gas-fired power plants operating to their maximum capacity to complement the wind resource and also supply electricity for heat pumps.

The electrification of heat supply is a widely discussed strategy for decarbonizing the heat sector in the Great Britain (GB). This impacts the electricity load duration curve and affects the optimal mix of power generation technologies. Additionally, the price of electricity and the emission from the grid determine whether the electrified heat is cost-effective and low carbon. These interdependencies necessitate adopting an integrated approach for long term planning of heat and electricity supplies to ensure cost-effective decarbonization. In this work, we have developed an iterative approach for investigating optimal mix of technologies in electricity and heat sectors considering the interactions between these sectors. This approach was applied to GB as a case study. Firstly, the capacity and operation of various technologies for electricity generation were determined to supply electricity demand (including electricity demand for heating) with a minimum annualized cost. Then, using the levelized cost of electricity calculated in the power generation mix optimization problem, the optimal heat supply mix was determined through the minimization of annualized cost. The iterative optimization of electricity and heat was continued until an equilibrium was achieved. The results were compared with a centralized optimization model that heat and electricity supply problems are solved simultaneously.

—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.

© 2017 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. Electrical resonances may compromise the stability of HVDC-connected offshore wind power plants (OWPPs). In particular, an offshore HVDC converter can reduce the damping of an OWPP at low-frequency series resonances, leading to the system instability. The interaction between offshore HVDC converter control and electrical resonances of offshore grids is analyzed in this paper. An impedance-based representation of an OWPP is used to analyze the effect that offshore converters have on the resonant frequency of the offshore grid and on system stability. The positive-net-damping criterion, originally proposed for subsynchronous analysis, has been adapted to determine the stability of the HVDC-connected OWPP. The reformulated criterion enables the net damping of the electrical series resonance to be evaluated and establishes a clear relationship between electrical resonances of the HVDC-connected OWPPs and stability. The criterion is theoretically justified, with analytical expressions for low-frequency series resonances being obtained and stability conditions defined based on the total damping of the OWPP. Examples are used to show the influence that HVDC converter control parameters and the OWPP configuration have on stability. A root locus analysis and time-domain simulations in PSCAD/EMTDC are presented to verify the stability conditions.

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.

An agent-based control system that manages the battery charging of electric vehicles in power distribution networks is presented. The electric vehicle battery charging schedules are calculated according to electricity prices and distribution network technical constraints. The design of the multi-agent system is described. The real-time operation of the multi-agent system was demonstrated in a test-bed of a laboratory micro-grid.

A methodology was developed and tested for controlling the emissions from a group of micro-generators aggregated in a Virtual Power Plant. The methodology is based on the EU Emissions Trading Scheme. A multi-agent system was designed and simulations were performed. The operation of the system was demonstrated experimentally using micro-generation sources installed in two laboratories. Two days of experiments were performed. Results show that system emissions have been controlled with a good accuracy, since only small deviations between desired and actual emissions output were observed. It was found that Virtual Power Plant controllability increases significantly by increasing the number of participating micro-generators.

An approach for minimisation of the capital costs and energy consumption in a district heating network is presented using a case study based on a district heating network in South Wales, UK. A number of different design cases were simulated using the PSS SINCAL, taking into account different supply and return temperatures and target pressure losses. The operation of the district heating network was synthesised under different design cases using four district heating operating strategies. Optimisation was conducted to obtain the optimal flow rate and supply temperature for the variable flow and variable supply temperature operating strategy. The optimisation model was formulated using the FICO™ Xpress optimisation suite. The objective of optimisation was to minimise the annual total energy consumption and costs. Using each operating strategy, the annual pump energy consumption, heat losses and the equivalent annual cost were found and compared. A variable flow and variable supply temperature operating strategy was found to be beneficial in all cases. Design cases with minimum annual total energy consumption and cost used small pipe diameters and large pressure drops. Further, by increasing temperature difference between supply and return pipes, the annual total energy consumption and the equivalent annual cost were reduced.

The control and operation of a multiterminal VSC-HVDC grid for offshore wind power under normal and fault conditions are described. The paper addresses maintaining the DC voltage during electrical faults and power reduction methods using fixed speed induction generators.

A closed-loop robust distribution state estimator was investigated. An approach that is suitable for medium voltage distribution networks which are either under-determined with limited real-time measurements or over-determined but with delayed information from smart meters was developed. The state estimator was designed to be robust against the effect of measurement errors, the type, location and accuracy of measurements, as well as temporary failure of the smart metering communication system. A machine learning function provides reliable input information to a robust state estimation algorithm. The output of the state estimator is then fed back to the machine learning function creating a closed-loop information flow which improves the performance of the state estimator. Test results and analysis on a 33-node system are provided.

Torsional dampers are employed in wind turbines to damp vibrations in the drive-train. The conventional design is based on band-pass filters (BPF); however, its effectiveness can be compromised due to parametric uncertainty. To restore the performance of the damper, it is a common practice to re-tune it during the commissioning of wind turbines. To overcome this shortcoming, a model-based torsional damper was designed and its performance compared to the conventional approach when subjected to model uncertainty. A stability analysis was conducted and simulations were performed in Simulink. A real-time hardware-in-the-loop experiment was carried out, with experimental and simulation results showing good agreement. The proposed model-based torsional vibration damper showed a superior performance over the conventional BPF-based approach. Results also showed that the model-based damper can eliminate the need for retuning procedures associated with BPF-based designs.

In Great Britain (GB), increased levels of wind penetration require substantial reinforcements for transmitting power from Scotland to England. In the National Grid 2020 Vision, offshore and onshore infrastructure reinforcements have been proposed, the inland reinforcement including series compensation (fixed capacitors). A possible detrimental effect of onshore series compensation is the appearance of subsynchronous resonance (SSR). SSR caused by the interaction between turbogenerators and a series-compensated electrical network is studied. A three-machine system representing the onshorereinforced mainland GB system is examined. The effect of series compensation equipment on SSR is assessed. The effects of quadrature boosters in the network are also investigated. Time-domain simulations are carried out in power systems computed aided design (PSCAD) whereas system modelling and eigenvalue analyses are conducted in MATLAB.

Mathematical modeling of synchronous and induction generators for wind turbines using state-space representations is presented. Emphasis is given to those models suitable for control schemes of variable-speed wind turbines and their application for different power system studies. The state-space representations provide a convenient way to assess different configurations of fixed and variable-speed wind turbines based on synchronous and induction generators. The modeling approach here presented allows both transient and small-signal stability analysis. As a case study, the performance of fixed and variable-speed wind turbines under faults and voltage sags is assessed. The state-space models are used to investigate the capability of different wind turbine technologies to satisfy Grid Code requirements. An eigenanalysis is included to show the flexibility of the models.

This paper analyzes the frequency support characteristics of multiterminal voltage source converter HVdc (VSC–HVdc) (MTDC) schemes using the energy transferred from wind turbine rotating mass and other ac systems. An alternative coordinated control (ACC) scheme that gives priority to a frequency versus active power droop fitted to onshore VSCs is proposed to: transfer wind turbine recovery power to undisturbed ac grids, and allow correct control operation of MTDC systems during multiple power imbalances on different ac grids. The fast frequency response capability of MTDC systems equipped with the proposed ACC scheme is compared against a coordinated control scheme, which uses a frequency versus dc voltage droop. The frequency control schemes are demonstrated on an experimental test rig, which represents a three-terminal HVdc system. Also, the MTDC frequency support capability when wind farms do not provide extra power is tested using a four-terminal HVdc system.

Voltage source converter, multi-terminal HVDC transmission (MTDC) for the connection of large offshore wind farms to the terrestrial grid is investigated. Induction generators without the need of wind turbine converters are installed in the wind farms due to the supports from the voltage source converters of the HVDC. A control system is designed which incorporates the voltage–current characteristics of the voltage source converters and the power reduction from the wind turbines during a fault. During normal operation, grid side converters control the DC voltage and coordinate the power sharing to the terrestrial grids. During abnormal operation, wind farm side converters take over the DC voltage control and coordinate the power reduction between wind farms. The control system removes the requirement for fast communication between the converters and achieves automatic coordination. The dynamic performance of a MTDC with the control system is tested through simulations using PSCAD/EMTDC.

Three configurations of voltage source converter multi-terminal HVDC transmission for large offshore wind farms are studied. The voltage-current characteristics of the converters are shown and the operation of the converters with different power output from the wind farms is discussed. The control system is designed to achieve automatic coordination between the converters without the need of fast communication between them. The operation of the multi-terminal HVDC transmission with the control system is tested through simulations using PSCAD/EMTDC and through experiments on a three-terminal test rig. The simulation and experimental results show good agreement.

A direct load management scheme with two-way communication, with consideration of end-user comfort, is proposed. First, the control algorithm is developed and the data required to be transmitted between system operator and controllable loads are identified. Then, the actions of controllable air conditioners and the power adjustment of dispersed generators to eliminate overloads in a substation transformer are simulated. The results indicate that the proposed load management technique performs effectively to reduce overloads on the transformer while maintaining energy consumption in each load, and the performance is improved by coordination with the output of dispersed generators. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 176(3): 19–28, 2011; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21139

Voltage–current characteristics and equilibrium points for the DC voltages of multiterminal HVDC systems using voltage source converters are discussed. The wind farm rectifiers and grid connected inverters are analyzed through their operating modes, governing equations and graphical characteristics. Using the converter equations and the HVDC grid conductance matrix the equilibrium voltages and currents are found. Case studies are presented considering wind power generation, loss of a converter and voltage sags in the AC grid.

Topologies of multiterminal HVDC-VSC transmission systems for large offshore wind farms are investigated. System requirements for multiterminal HVDC are described, particularly the maximum power loss allowed in the event of a fault. Alternative control schemes and HVDC circuit topologies are reviewed, including the need for HVDC circuit breakers. Various topologies are analyzed and compared according to a number of criteria: number and capacity of HVDC circuits, number of HVDC circuit breakers, maximum power loss, flexibility, redundancy, lines utilization, need for offshore switching platforms and fast communications.

A direct load management scheme with two-way communication while considering end users comfort is proposed. First, the control algorithm is developed and the data required to be transmitted between system operator and controllable loads is identified. Then, the actions of controllable air conditioners and the power adjustment of dispersed generators to eliminate overloads in a substation transformer are simulated. The results indicate that the proposed load management technique performs effectively to reduce overloads on the transformer while maintaining energy consumption in each loads, and the performance is improved by coordination with the output of dispersed generators.

Distributed generation (DG), whose installed capacity is increasing rapidly, can be defined as low rating generation that is neither planned nor dispatched centrally and is usually connected to the distribution network. Appropriate control of DG can improve the performance of DG units without violating network constraints, and facilitate the effective participation of DG in power system and market operation. Two control levels, DG unit control and network control, are summarized. DG unit control is introduced based on three technologies: induction generators, synchronous generators and power electric converters. Effective network control can be built based upon active management concept. Finally, three DG control paradigms, MicroGrid, cell and virtual power plant, are discussed.

A multi-time period combined gas and electricity network optimisation model was developed. The optimisation model takes into account the varying nature of gas flows, network support facilities such as gas storage and the power ramping characteristics of electricity generation units. The combined optimisation is performed from an economic viewpoint, minimising the costs associated with gas supplies, linepack management, gas storage operation, electricity generation, and load shedding. It is demonstrated on the GB gas and electricity network.

The aim of the paper is to demonstrate the way in which mechanical power variations, due to tower shadow and wind turbulence, influence control performance of power system stabilizer (PSS) loops for doubly-fed induction generators (DFIGs). The PSS auxiliary loops are applied on a specific DFIG control scheme, the flux magnitude and angle controller (FMAC). However, since the PSS signal is applied at the output of the basic controller, the PSS performance characteristics displayed are deemed typical for DFIG control schemes in general. The relative capabilities of PSS controllers based on stator power, rotor speed, and network frequency, when the DFIG turbine is subjected to aerodynamic torque variations, are investigated via simulation studies. A two-generator aggregate model of a wind farm is introduced, which enables the influence of tower shadow and wind turbulence on both an individual turbine and on the overall wind farm itself to be assessed.

The United Kingdom is leading Europe in its power market reforms and is currently engaged in addressing issues of DG integration through development of innovative approaches to network planning, operation, regulation, and pricing. This article draws on these recent advances to explore active management technologies, developing regulatory arrangements for network operation, and new commercial opportunities emerging from the low-carbon climate change agenda. It explores the changing role of the distribution system operator (DSO) in response to increasing penetration of DG and identifies the transitions currently taking place in the United Kingdom toward integration of DG that has wider implications for extrapolation across Europe.

It is now more than a decade since distributed generation (DG) began to excite major interest amongst electric power system planners and operators, energy policy makers and regulators as well as developers. This paper presents an overview of the key issues concerning the integration of distributed generation into electric power systems that are of most interest today. The main drivers behind the focus on DG integration, especially of the renewable type, in many countries around the world are discussed. A synopsis of the main challenges that must be overcome in the process is presented. Particular emphasis is placed on the need to move away from the fit and forget approach of connecting DG to electric power systems to a policy of integrating DG into power system planning and operation through active management of distribution networks and application of other novel concepts. The paper also analyses the repercussions in transmission system operation and expansion that result from the connection of large amounts of DG of different energy conversion systems focusing on issues related with impacts in steady state operation, contingency analysis, protection coordination as well as dynamic behaviour analysis. A discussion on the possibility of provision of ancillary services by DG is also included. Some results from studies performed in the interconnected Portuguese transmission system are presented and discussed. Some of the opportunities that could be exploited in support of the integration and hence greater penetration of DG into electric power systems are also explored.

A power system stabilizer (PSS) for a wind turbine employing a doubly fed induction generator (DFIG) is presented. It is shown that this PSS can significantly influence the contribution that a DFIG-based wind farm can make to network damping. A simple, generic test network that combines synchronous and wind farm generation is used to demonstrate system performance contributions. The results of both eigenvalue analysis and time response simulation studies are presented to illustrate contributions to network dynamic and transient performance that the DFIG controller with its PSS can make. Performance capabilities superior to those provided by synchronous generation with automatic voltage regulator and PSS control are demonstrated.

The nature and control of existing distribution networks limits the amount of distributed generation that can be connected. To increase the penetration of distributed generation a distribution management system controller (DMSC) can be used. The use of a DMSC requires a state estimator algorithm that provides an estimate of the network state in real time. In this paper, a state estimation algorithm based on the methods used on transmission networks is presented. The application of these methods into distribution networks requires existing measuring systems to be supplemented with the addition of new real-time measurements, and the use of load estimates. Copyright © 2006 John Wiley & Sons, Ltd.

This paper addresses the design and implementation of a novel control scheme for a doubly fed induction generator (DFIG), of the type employed with wind turbines, to provide support to power system operation. It is shown that this controller provides a DFIG-based wind farm with operational and control compatibility with conventional power stations, the ability to contribute to voltage support and recovery following network faults, the ability to provide a power system stabilizer capability that improves overall system damping, and the capability of contributing short-term frequency support following loss of network generation. A simple but realistic test network that combines synchronous and wind farm generation has been modeled and used to assess dynamic performance. Simulation results are presented and discussed that demonstrate the capabilities and contributions of the new DFIG controller to network support.

This paper describes a model of photovoltaic (PV) generation suitable for studying its interactions with the power system. Experimental results suggest that the maximum power point tracking part of the control system of the PV generator dominates the dynamic behavior of the system. These experimental results are used to develop and validate the proposed model. It is shown that the model accurately reflects the behavior of the generator following both small and fast changes in irradiance and AC grid voltage. The proposed model is designed to be integrated in a dynamic simulation program.

Technological advances and environmental pressures are driving the interconnection of renewable energy sources to the distribution network. The interconnection of large amounts of non-traditional generation however causes problems in a network designed for ‘conventional’ operation. The use of power electronics interfaces and the ‘bundling’ of micro-generation and loads into so-called Microgrids, offers a potential solution. Each Microgrid is designed to operate as a ‘good citizen’ or near ideal conventional load. This paper discusses the various elements of the new Microgrid concept and presents suggestions for some typical control strategies for the various system elements.

With increasing concern over climate change, a number of countries have implemented new renewable energy targets, which require significant amounts of wind generation. It is now recognized that much of this new wind generation plant will be variable speed type using doubly fed induction generators (DFIG). In order to investigate the impacts of these DFIG installations on the operation and control of the power system, accurate models are required. A fifth order and reduced order (3rd) machine models are described and the control of the wind turbine discussed. The capability of the DFIG for voltage control (VC) and its performance during a network fault is also addressed.

A modified voltage space vector pulse-width modulated (PWM) algorithm for a four-wire dynamic voltage restorer (DVR) is described. The switching strategy based on a three-dimensional (3-D) /spl alpha//spl beta/O voltage space is applicable to the control of three-phase four-wire inverter systems such as the split-capacitor PWM inverter and the four-leg PWM inverter. In contrast to the conventional voltage space vector PWM method, it controls positive, negative and zero sequence components of the terminal voltages instantaneously. Three 3-D modulation schemes are analyzed with respect to total harmonic distortion (THD), weighted total harmonic distortion (WTHD), neutral line ripple and switching loss over the whole range of the modulation index when the DVR experiences both balanced and unbalanced sags with phase angle jumps. Experimental results from a 9 kW DVR system using a split-capacitor PWM inverter are presented to validate the simulation results.

It is now recognized that many large wind farms will employ doubly fed induction generator (DFIG) variable speed wind turbines. A number of such wind farms are already in operation and more are planned or under construction. With the rising penetration of wind power into electricity networks, increasingly comprehensive studies are required to identify the interaction between the wind farm(s) and the power system. These require accurate models of doubly fed induction generator wind turbines and their associated control and protection circuits. A dynamic model has been derived, which can be used to simulate the DFIG wind turbine using a single-cage and double-cage representation of the generator rotor, as well as a representation of its control and protection circuits. The model is suitable for use in transient stability programs that can be used to investigate large power systems. The behavior of a wind farm and the network under various system disturbances was studied using this dynamic model. The influence of the DFIG control on the stability of the wind farm was also investigated by considering different control gains and by applying network voltage control through both stator side and rotor side converters.

Owing to increased levels of generation in Scotland, substantial onshore and offshore reinforcements to the Great Britain (GB) transmission network have been proposed. Possible inland reinforcements include the use of series compensation through fixed capacitors. This potentially can lead to subsynchronous resonance (SSR). Offshore reinforcements are proposed by high-voltage direct-current (HVDC) links. In addition to its primary functions of bulk power transmission, a voltage source converter-based HVDC link can be used to provide damping against SSR, and this function has been modelled. Simulation results have been carried out in Power Systems Computer-Aided Design, with system analysis conducted in MATLAB. A real-time hardware-in-the-loop real-time digital simulator-HVDC test rig has been used to implement and validate the proposed damping scheme on an experimental platform. The simulation and experimental results show good agreement.

Autonomous renewable energy systems such as wind, solar, and micro-hydro require control methods to maintain stability, due to the real time variation of input energy and load, while maximizing the use of renewable energy. This paper describes the application of load control using a novel frequency and voltage-sensing device. The device uses a low cost microcontroller to monitor the system frequency and voltage. Load switching is carried out based on this information. Software was developed for frequency and voltage measurements and tested on a 18 kW, single phase, 50 Hz, micro-hydro system. A fuzzy control system was then developed which makes intelligent load switching decisions using inputs from the measurement algorithms coupled with expert knowledge expressed in the form of control rules. This load control system was then tested on the same micro-hydro system and on a site powered by a 60 kW, 3 phase, 50 Hz wind turbine only.

A laboratory model of an advanced static VAr compensator (ASVC) was constructed to examine its capability for voltage sag mitigation. In this paper, the main structure of the laboratory ASVC is described briefly. Its mitigation effect on voltage sags of different magnitude is then demonstrated. The influences of its initial operation point, system impedance, and DC capacitance are considered. The behaviour of this laboratory ASVC during a phase-angle jump associated with a voltage sag is examined.

For pt. I see ibid., vol.9, no.3, p.145-50 (1995). This is the second of two tutorial articles dealing with the technical aspects of generation embedded in distribution networks. Generators with a rating of up to 10 MW and a connection voltage of 33 kV or below are considered. The first article discussed the characteristics of electrical plant commonly found in embedded generation schemes. In this second article some aspects of the integration of embedded generators with the distribution network are considered, including: power flows, voltage rise in radial circuit, automatic voltage control, power quality, generator and network protection, and earthing of embedded generators.

Synchronous and fixed-speed induction generators release the kinetic energy of their rotating mass when the power system frequency is reduced. In the case of doubly fed induction generator (DFIG)-based wind turbines, their control system operates to apply a restraining torque to the rotor according to a predetermined curve with respect to the rotor speed. This control system is not based on the power system frequency and there is negligible contribution to the inertia of the power system. A DFIG control system was modified to introduce inertia response to the DFIG wind turbine. Simulations were used to show that with the proposed control system, the DFIG wind turbine can supply considerably greater kinetic energy than a fixed-speed wind turbine.

This tutorial article deals with the technical aspects of generation embedded in distribution networks. Generators with a rating of up to 10 MW and a connection voltage of 33 kV or below are considered. A second article will consider some practical aspects of connecting small generating plant to distribution networks.

This article considers the technical aspects of using photovoltaic systems for small power supplies where a connection from a main electricity distribution network is not appropriate. The technology of the various components of a photovoltaic power system is discussed and the overall system design considered. Typical applications of photovoltaic systems are described.