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This paper presents a transient based protection principle utilising the magnitude of the travelling wave power derivative at only local terminal to formulate a non-unit protection scheme, where the directional transient relay and boundary relay have been involved. In terms of boundary relay, for an internal fault in the forward direction with respect to a local relay, the traveling wave power derivative will exceed a pre-determined setting, otherwise the fault is external to the relay, due to the discontinuity of surge impedance at the boundary point. Directional detection is achieved by the comparison of the forward travelling wave power to the backward travelling wave power. The ratio of forward traveling wave to backward traveling wave is less than unity for all forward directional faults and much greater than unity for reverse directional faults. Simulation studies carried out in PSCAD and the results presented shows the suitability of the proposed protection principle as all fault scenario indicated were detected within 250μs following the application of the faults.

Electrical power to data hall critical loads will often be fed via an uninterruptable power supply (UPS) strings. Therefore, fault tolerance of these machines is of pivotal importance for the data centres uptime. The UPS will be in the middle of a complex electrical distribution system with reliance on other connected components for optimal performance. The data centre owners will also want to know what happens when components on the UPS power string fail and what effects this can have on critical equipment's. The goal is to minimise any negative effective on critical power and achieve 100% operational uptime. This paper investigates a rotary UPS string in terms of fault currents, electrical protection and arc flash.

A high voltage DC-DC converter is a key component of future HVDC grids. This paper presents a comparison of a single-stage and multi-stage converter. Both topologies are based on the Marx principle where charged capacitors are charged in parallel and discharged in series to achieve the voltage transformation. Detailed models of both converter topologies at 50 MW, 6kV/72kV are designed and simulated using Matlab/Simulink package software.

This paper is based on an investigation of load flow, short circuit analysis, and load point reliability of a data centres electrical power distribution network. A series of power system analysis software simulations were undertaken in order to determine the steady state behaviours of the power distribution system. Each load flow model investigated allowed a critique of model results for verification of critical bus-bar Voltage Security Index (VSI) and confirmation of acceptable Voltage limits, in-line with industry standards. Load flow studies highlighted optimal configurations for the electrical distribution networks, short circuit faults were simulated at multiple network locations for both nominal grid feeders, and mesh configurations with standby generators. Results from this research paper have provided recommendations on how to improve Operational Availability (AO) with suggestions given for optimal equipment configuration in terms of achieving improved Voltage security, limiting the required short circuit ratings of network equipment and investigating the improvement of load point reliability.

In order to reduce the cost and visual impact of electrified railway lines, radical changes in infrastructure can be avoided by only removing the catenary wire. This can produce a significant saving in the overall cost of the railway network, reduce maintenance requirements and improve the overall visual impact. On-board energy storage systems have a significant role in providing the required energy during catenary free operation of trams, and in the recovery of regenerated energy from braking. It was found that a 13km journey can be achieved with a battery energy capacity of 39.6kWh with a rated voltage of 495V. Achieving an efficient train control, and optimising the energy management, can improve the energy efficiency of rapid transit systems. This paper presents a novel energy management phase driven method to perform state actions and control the transition between different operating energy supply modes for catenary free tram operation. The StateFlow environment is used to model the energy management, and has been implemented using ANSI C.

Wind power is the most dominant renewable source and the global wind power capacity, both on shore and off shore are rapidly increasing. The United Kingdom is leading the use of off shore wind energy and has the largest off shore wind farm in the world. Power electronics is essential for the harnessing of wind energy for use by the consumers. Power electronic converters required are line commutated thyristor converters, two level and multilevel voltage source converters including energy diverting converters for facilitating fault ride through and reactive power compensators. With the advent of DC grids DC-DC converters are required for interfacing different voltage levels and novel designs are required. All these converters require either series connection or modularization of Thyristors and IGBTS with associated voltage equalization networks.

This paper presents an improved cascaded DC-DC resonant converter for offshore windfarms. The improvements are reduced losses and the number of components. The topology is based on the Marx principle where charged capacitors are charged in parallel and discharged in series to achieve the voltage transformation. The four inductors of the converter are designed to resonate with the capacitors to create resonance forcing current zeros to enable zero current switching thereby reducing switching losses. The operating principles and design considerations of the proposed converter are discussed and the design equations are presented. In order to evaluate the operation of 50 MW converter aimed at connecting a 30 kV DC Busbar in a wind power collection system to a 360 kV high voltage DC bus for transmission to the onshore grid was simulated and the results are presented.

In this paper, an Artificial Neural Network ANN based algorithm is proposed for energy conversion system adapting Oscillating Water Column (OWC) coupled to a Wells turbine. The presented algorithm integrates with the associated P-Q controlled grid connected Doubly Fed Induction Generator (DFIG) by calculating the optimized turbine speed that grantees stalling phenomenon avoidance. The proposed technique effectiveness has been attested by simulating various operation conditions featuring different input differential pressure levels. The presented technique offers simplified tuned algorithm in addition to fast transient response with minimal oscillation during steady state operation.

This paper presents a voltage regulated step up Marx DC-DC converter suitable for HVDC offshore wind farm applications. This configuration has the capability to generate a variable high voltage adding controllability to the standard Marx converter with a fixed gain. For voltage control, an auxiliary controlled buck-boost converter was combined with the Marx converter to regulate the output voltage. The studies were carried out by simulating the converter with the design specifications of 6kV to 30kV voltage on LV and HV sides and 5MW rated power. The simulation results showed good voltage stability on the output DC line when the converter input voltage varies.

A decoupled active-reactive power control technique is proposed for an oscillating water column (OWC) based wave energy conversion system adopting grid connected doubly fed induction generator (DFIG). The effectiveness of the technique is investigated under various rotor speed and reactive power reference commands. The results show enhanced performance, better tracking, and improved transient response.

Interconnecting several offshore wind farms using High Voltage dc (HVDC) connections and forming multi terminal HVDC grid are some of the targets set by industry leaders to be achieved in the near future. Researchers have introduced a few methods of power flow control based on either the control of AC/DC converter stations or the connection of new power electronic equipment to the grid. In this paper, the operation and control of an extended three-port IGBT based current flow control (CFC) device suitable for multi terminal HVDC systems is presented. Features and functionalities of the proposed controller including the balancing of cable currents, limiting the magnitude of cable current and current nulling are demonstrated. The proposed three-port CFC is real time simulated using OP4510 real time simulator. Real time simulation studies explore fast dynamic response and the results show that the CFC studied may have a significant role to play in the control a of power flows in multi terminal high voltage DC systems.

Modular Multilevel Converters (MMC) are considered very suitable for the transmission of bulk power. Increasing the reliability of MMCs forms a real challenge since they are built from series connection of sub-modules. Applying the concept of fault tolerance to the MMC control system can significantly increase the reliability of the MMC as it will be available in normal as well as faulty conditions. This paper presents an analysis of the MMC reliability enhancement gained from applying different fault tolerant control techniques. The reliability is investigated through solving differential equations generated from Markov chains.

This paper presents a novel capacitor voltage estimation using the adaptive linear neuron (ADALINE) algorithm for monitoring of MMC sub-module voltages. The proposed estimation unit requires only three voltage sensors per phase for the arm reactors and the output phase voltages. Measurements of sub-module capacitor voltages and associated communication links with the central controller are not needed. The proposed strategy can be applied to MMC systems that contain a large number of sub-modules. The method uses PSCAD/EMTDC, with particular focus on dynamic performance during boost operation.

The absence of a reliable current flow control method is one of the main problems that need to be solved to allow the realization of multi terminal high-voltage direct current (HVDC) transmission. Industry leaders and researchers have introduced a few methods of power flow control based on either the control of converter station or the connection of new power electronic equipment to the grid. This paper presents the operation and control of an extended three-port IGBT based current flow control (CFC) device suitable for multi terminal HVDC systems. Features and functionalities of the proposed controller including the balancing of cable currents, limiting the magnitude of cable current and current nulling are demonstrated. The three-port CFC is simulated using PSCAD/EMTDC, network simulation software to evaluate its steady state and dynamic performance. Simulation studies explore the fast dynamic response and the results show that the CFC studied may have a significant role to play in the control a of power flows in multi terminal high voltage DC systems.

The main development trend of wind power generation systems is large offshore wind farms (OWFs) with grid connection. However offshore wind farms have grown rapidly due to much better wind conditions. Hence, several large scale offshore wind farms are planned to be built and installed at distances greater than 100 km from the coast. Traditionally, an AC collector scheme collects energy from the wind farm and step up the voltages by power transformers and transmit power via AC submarine cables to the onshore substation. However, this is suitable for shorter distances about 50 km. When the distances are greater the AC transmission of bulk power from the wind farm to the onshore grid via undersea cables is not viable due the reactive power issues. Therefore HVDC transmission is now being considered for the grid connection of wind farms. However as wind farms constitute weak systems Line commutated converter (LCC) based HVDC is not viable and newer Modular Multilevel Converter (MMC) based Voltage Source Converters(VSC) are needed for AC-DC conversion. Opting for dc systems for both power collection and transmission pose a number of technical challenges in terms of developing HVDC breakers and DC -DC converters.

The modular multilevel converters (MMC) form the backbone of the modern voltage source converter (VSC) based HVDC system due to their unique features. Faults within the MMC affect the performance of the HVDC system. In this paper the fault types that can occur in the MMC are investigated. The reported work focuses on sub-module faults. A nine level MMC was simulated using PSCAD/EMTDC in this investigation.

Some significant problems prevent the formation of multi terminal high voltage DC grids until now. Absence of power flow control is considered one of the main challenges that have to be solved in the near future to allow building of an efficient DC grid. This paper investigates different power flow control methods. Simulation of series insertion of AC/DC converters is carried out using MATLAB/SIMULINK software package and results are discussed.

Removal of overhead electrical installations (catenaries) is a major consideration of light railway industries. This is driven by continuing focus on environmental concerns and reduction of energy consumption. For catenary free operation of rapid transit trains, on-board energy storage has a significant role to provide the required power and recover the regenerated energy from braking. An efficient train control and optimised energy management can improve the energy efficiency of rapid transit system. The main aspects of catenary free operation of DC traction systems are described in this paper.

This paper details the areas of advanced research in control systems engineering and the practical application of Proportional Integral Derivative (PID) controllers for the temperature control of data storage units, which is a mission critical facility in the Royal bank of Scotland's data centre. Loop tuning techniques inclusive of the Ziegler Nichols were applied to obtain optimum system response, thus maximising efficiency of the cooling system. The business objective was to reduce the control systems offset to ensure the temperature set point within the ‘cold aisle’ containment remained within a ± 1°C error band. This ensured optimum climate conditions for the IT servers and optimised plant efficiency thus reduced the facilities energy demand. The control system comprised of a number of networked logic controllers, each with individual PID loop modules. Existing control system deficiencies highlighted the severe oscillations from inadequately tuned controllers; this led to uncontrolled cooling valves which ascertained a 5°C error band within the data storage ‘cold aisle’ containment. Application of temperature transducer calibration techniques, analytical equations, advanced tuning logarithms and software tuning provided a substantial improvement of stability control. Post Modification coefficients obtained an 18.4 % improvement with respect to decreasing the error band in all PID controllers. An expected lifecycle reduction of energy consumption from post modification tuning loops was calculated to be a value in excess of £238k.

Grid codes imposed by utilities regulate the operation of Voltage Source Converter - High Voltage Direct Current (VSC-HVDC) interconnected offshore wind farms. Fault ride-through (FRT) specifications require the adoption of specific measures to avoid over-voltages of the HVDC link during faults in order to protect the HVDC equipment. Implementing Energy Diverting Converters (EDC), for instance Dynamic Braking Resistor (DBR) circuits, at the DC link is an established method to comply with the grid codes, where the excess energy of the wind farm is diverted into the parallel circuit during the fault. In this paper an evaluation of three different state-of-the-art DBR circuits is performed in order to establish the advantages and disadvantages of each circuit. The evaluation has shown that although the three solutions meet the FRT requirements, the modular topologies generate reduced slope current and voltage step changes during their operation, while being larger in size and requiring a higher number of semiconductors as compared to the traditional DC chopper circuit employing hard switched series connected semiconductor arrangements.

This paper describes a novel technique for interrupting direct currents (D.C.) with an electromagnetically convoluted arc in air at atmospheric pressure. Investigations are reported on the effects of using a separate current for producing the arc convolving electromagnetic field (B-field) to that being interrupted and using a separate R, L, C circuit in parallel with the arc contacts. Experimental results are presented for the time variation of currents flowing through the arc gap, the B-field coil and the parallel R, L, C circuit, along with the voltage across the arc gap.

The service maintenance of a 3-phase induction motor is limited when compared with other types of motors. The overhaul process needs to be developed to ensure that the motor will perform in service without failure. This is achieved by undertaking a number of tests and examinations, as part of the overhaul operation to guarantee the reliability of he motor. This paper reviews a number of tests that have been developed, as part of the overhaul processes on the 3 phase induction motor to improve it's in service reliability. This paper will also explore the areas that have been found to be problematic.

Energy saving motor controllers for refrigeration and air-conditioning applications operate at the minimum input power point by finding the optimum firing angle of the thyristors in the motor controller. Consequently, the distorted input current contains harmonics, sub-harmonics, and interharmonics whose frequencies change with the motor speed. Therefore passive filters are not suitable and the best solution is to use an active filter. A single phase active filter with simple constant frequency switching is able to reduce waveform distortion by eliminating a sufficient range of frequencies and offers a low cost solution. Theoretical analysis of the full-bridge and half-bridge topologies led to the development of design equations and curves. Simulation of a half-bridge active filter confirmed the design equations