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Saving fuel and reducing emissions are major drivers in the marine industry, with a large number of potential modifications and machinery options available to enable the greening of shipping. Assessing which technology and what combination of solutions gives favourable economic results needs careful consideration of the vessel’s operational profile. Electrification of shipboard systems introduces operational flexibility, offering the potential for fuel savings and emission reductions. Auxiliary drives, energy storage and onshore power supply are three approaches which address the issues of ship fuel consumption/emissions, specifically during in-harbour operation of vessels. In this paper, the impact of these three technologies on ship environmental performance and energy consumption is assessed by considering a real case RoRo vessel sailing a real operational profile. Models of the resultant system are built such that the machinery configurations can be analysed separately or in conjunction with each other. The results stress the importance of the operational profile of the vessel, showing significant fuel and emissions reductions during in-harbour operations but relatively small savings when considering operation through a complete return voyage. The sensitivity of the results to fuel and utility costs are also considered and shown to have a large impact on the economic feasibility (or otherwise) of different solutions.

The efficient utilization of energy is of high importance for shipboard applications, for environmental and economic reasons as well as maximized vessel operation. The electrification of marine systems facilitates the storage and generation of energy from multiple sources, offering the potential for energy savings, due to the flexibility associated with electric systems. In this paper, an energy management system (EMS) based on bond graph system models used in conjunction with a stochastic search algorithm is proposed and developed. The EMS optimizes the configuration of the vessel’s onboard machinery system based on the current operating condition. The approach is universal, with the system model and optimization routine being separate and distinct. The effectiveness of the proposed EMS is demonstrated using a real operating profile of a roll-on/roll-off vessel fitted with a hybrid machinery configuration including energy storage, onshore power supply, and photovoltaic generation. The results show fuel savings of around 23% compared with current fuel consumption levels.

This paper presents a novel predictive model reference adaptive system (MRAS) speed estimator for sensorless induction motor (IM) drives applications. The proposed estimator is based on the finite control set-model predictive control (FCS-MPC) principle. The rotor position is calculated using a search-based optimization algorithm which ensures a minimum speed tuning error signal at each sampling period. This eliminates the need for a proportional–integral (PI) controller which is conventionally employed in the adaption mechanism of MRAS estimators. Extensive experimental tests have been carried out to evaluate the performance of the proposed estimator using a 2.2-kW IM with a field-oriented control (FOC) scheme employed as the motor control strategy. Experimental results show improved performance of the MRAS scheme in both open- and closed-loop sensorless modes of operation at low speeds and with different loading conditions including regeneration. The proposed scheme also improves the system robustness against motor parameter variations and increases the maximum bandwidth of the speed loop controller.

Over the last decade various high-capacitance devices have become available in the market such as supercapacitors, ultracapacitors, and recently, Li-ion capacitors. The cell voltage limit of each of these technologies is a small percentage of the system-level voltage so they must, therefore, be connected in series to attain a high voltage. During charging and discharging, manufacturing tolerances between the cells result in voltage mismatch across the stack. Mismatched voltages are an inefficient use of the energy storage medium and can lead to dangerous failures in the cells if voltages exceed safety limits. Transformer-based voltage equalization techniques are the preferred circuit topologies in applications with low system voltage due to simplicity of control and low number of switches. The drawback of these circuits is the number of isolated windings that are required on a single core. This paper describes for the first time a solution to that problem by using a classical two windings transformer that in principal can be applied to any number of capacitors. This paper describes the operation of the circuit, shows simulation results and practical results based on a prototype with five cells.

One of the most commonly utilised maximum power point tracking (MPPT) algorithms for photovoltaic (PV) generators is the incremental conductance (INC) algorithm. Yet, the operating characteristics of this algorithm at high perturbation frequencies, when the system response to MPPT perturbations is never allowed to settle, have not been addressed in the literature. This study characterises system behaviour in this operating mode experimentally for a standalone PV system with a dc motor–pump load. Results show that the INC algorithm operating at a high perturbation rate offers higher energy utilisation efficiency and better system performance despite the resulting non-periodic waveforms of the system.

The reduction of emissions in harbours is of particular importance due to the proximity to human habitation. Vessels normally run onboard generators, typically using diesel fuel, to provide the service loads while berthed. New and upcoming regulations aim to decrease emissions from shipping, and coupled with increased environmental consciousness of ship owners and harbour operators, shore supply is becoming a more popular and feasible option. Cold ironing provides an alternative locally emission-free solution by having berthed ships plug in to the shore electrical network, such that the onboard electrical energy demand is supplied from land. Electrically, a number of different shore network topologies are possible, providing different infrastructural options of supplying power to multiple berths. This paper examines the electrical characteristics of one such installation and the impact on the shoreside electrical network for an existing port using actual visiting ship power profiles. The paper examines how the cold ironing system influences important electrical network characteristics such as bus voltages and power quality, as well as the potential impact on the rest of the utility distribution system.

A modular current sharing control scheme is proposed in this paper to attain good current distribution between equally rated parallel-connected converters. In this scheme, local information is used by each inverter to achieve the required current control with minimal information sharing between the converters. Unlike conventional current sharing control methods that use a stationary or rotating reference frame representation, the converter currents in the proposed controller are represented by the magnitude of the current space vector. As a result, each converter employs only one proportional–integral compensator to share the load current. The operation of the new current sharing control scheme is demonstrated using two different pulsewidth modulation (PWM) control strategies: conventional space-vector PWM and discontinuous PWM. A mathematical analysis of the proposed control scheme is presented, and the performance of the controller is experimentally verified using a 2.5-kVA test rig. The results show excellent current sharing characteristics with minimal communications between the parallel-connected converters.

This paper presents a new current sharing control strategy for parallel-connected, synchronised three-phase DC-AC converters employing space vector pulse width modulation (SVPWM) without current sharing reactors. Unlike conventional control methods, the proposed method breaks the paths of the circulating current by dividing the switching cycle evenly between parallel connected equally rated converters. Accordingly, any inter-module reactors or circulating current control will be redundant, leading to reductions in system costs, size, and control algorithm complexity. Each converter in the new scheme employs a synchronous dq current regulator that uses only local information to attain a desired converter current. A stability analysis of the current controller is included together with a simulation of the converter and load current waveforms. Experimental results from a 2.5kVA test rig are included to verify the proposed control method.

This paper presents a novel speed estimation scheme for induction motors (IMs) based on back electromotive-force model reference adaptive system (back-EMF MRAS). The scheme is employed for the purpose of sensorless fault-Tolerant torque-controlled drives used in a limp-home mode operation in electric vehicle (EV) applications. The proposed scheme was experimentally tested on a laboratory dynamometer using a 19-kW IM and a 29-kW controller, which are both currently used in the automotive industry for EV applications. The scheme was also implemented on an electric golf buggy which was equipped with a 5-kW IM. A performance comparison was carried out between the proposed and conventional back-EMF MRAS schemes for starting from standstill, sensitivity to parameter variations and constant speed operation with load variations. Utilizing the golf buggy, the behaviors of the new scheme was separately investigated for vehicle starting from standstill, wide speed range including field weakening region, and hill-starting operations. The proposed scheme is computationally easy to implement, robust against sensitivity to parameters variations, inverter nonlinearity and errors due to digitization in the field weakening region. This scheme is not only consistent for vehicle starting from standstill, it also provides a reliable vehicle-drive in the field weakening region and during vehicle hill-starting. The dynamometer and vehicle test-drive results show the suitability of the proposed scheme for the purpose of EV fault-Tolerant limp-home mode operation.

This paper presents a robust sensorless control technique for an Induction Motor (IM) used for Electric Vehicle (EV) applications. In order to estimate the rotor speed, a new back-electromotive-force (back-EMF) based-model reference adaptive system (MRAS) estimator is proposed. The new back-EMF MRAS is independent from the stator resistance and stator inductance parameters. Hence the proposed scheme is immune to these parameters variations. It also is robust against inverter nonlinearity and shows consistency at starting from standstill. The proposed scheme has been experimentally implemented and tested on a 19-kW induction motor (IM), of a type used for the automotive industry for EV applications. A comparison is carried out between the performance of the conventional and the proposed back-EMF MRAS. Tests include sensitivity to stator resistance variation and capability to start from standstill. Experimental results show the improved performance achieved using the proposed sensorless control scheme and its suitability for EV applications.

A near-state three-dimensional space-vector modulation (NS 3-D SVM) switching scheme, which aims to reduce the common-mode noise in a three-phase four-leg voltage source inverter, is proposed. The impact of common-mode noise, which is related to electromagnetic interference issues for a high-voltage level four-leg system, is investigated first. Identification of the section in a 3-D space, selection of the near-state switching vectors, and sequence of the selected switching vectors are then introduced in steps to describe the proposed switching scheme. The proposed switching scheme is based on classical 3-D SVM, producing higher dc-link utilization, less harmonic content, and reduced switching loss compared to sinusoidal PWM. Theory, simulation, and experimental results show that the near-state 3-D SVM can work under both balanced and unbalanced load conditions.

Cold ironing (or onshore power supply) addresses airborne emissions while ships are berthed in port. By providing the electrical power demands from shoreside electricity, the onboard auxiliary generators can be switched off for a locally emission-free solution. The net emissions will of course be dependent on the actual shoreside electricity mix, but reductions can be realised in most cases. This study looks at the various electrical configurations available for cold ironing of berthed vessels. Shoreside generation using liquefied natural gas as an alternative fuel is also considered as a complement to cold ironing. This provides the possibility of hybridised solutions combining power supply from the grid or from clean, onsite generators. Using real data from an operational European port, the various cold ironing configurations are modelled and optimal trade-off solutions were identified. This is achieved by considering the reduction in emissions and minimisation of component costs as a multi-objective non-linear optimisation problem. The results show that CO2 emissions can be reduced by up to 40% by using cold ironing, while the use of liquefied natural gas shore generation can reduce the sulphur and particulate emissions in port to extremely low levels.

The performance of the doubly fed induction generator (DFIG) during grid faults is attracting much interest due to the proliferation of wind turbines that employ this technology. International grid codes specify that the generator must exhibit a fault-ride-through (FRT) capability by remaining connected and contributing to network stability during a fault. Many DFIG systems employ a rotor circuit crowbar to protect the rotor converter during a fault. Although this works well to protect the generator, it does not provide favorable grid support behavior. This paper describes an experimental investigation of an alternative FRT approach using a brake chopper circuit across the converter dc link to ensure that the dc-link voltage remains under control during a fault. Two different approaches to chopper control are examined and the resulting FRT performance is compared with that of a conventional crowbar approach. The new chopper-based control methods are experimentally evaluated using a 7.5-kW DFIG test rig facility.

Auxiliary drives can provide an alternative propulsion system for marine vessels giving the potential to achieve improved environmental performance during low-speed sailing. In this work, two case vessels were considered for analysis, a Roll-On–Roll-Off ship and a harbour tug boat. Actual sailing operational profiles were used as the basis for energy considerations to assess the potential for lower emissions. An energy-centric simulation model was built to estimate the emission of various pollutants, considering different machinery set-ups. Results have shown that savings are possible, especially for vessels which run on residual fuels, where auxiliary drives provide a way of exploiting the advantages of cleaner sources for manoeuvring instances.

An efficient, cost-effective maximum power point tracking (MPPT) algorithm is required to improve the energy utilization efficiency of low power photovoltaic (PV) systems. This paper presents an experimental evaluation of the incremental conductance MPPT algorithm when employed by a standalone PV pumping system, using an experimental installation comprised of a 1080-Wp photovoltaic array connected to a 1-kW permanent magnet dc motor-centrifugal pump set. Particular focus is given to the evaluation of the two commonly utilized implementation techniques: reference voltage perturbation and direct duty ratio perturbation. The influence of algorithm parameters on system behavior is investigated and the energy utilization efficiency is calculated for different weather conditions. The performance of the incremental conductance algorithm is compared to that of the commonly used perturb and observe MPPT algorithm and the various advantages and drawbacks of each technique are identified.

Synchronous dq-frame controllers are generally accepted due to their high performance compared to stationary αβ-frame ones, as they operate on dc quantities, achieving zero steady-state error. In single-phase systems, however, PI-based dq controllers cannot be directly applied due to the reduced number of input signals available compared to three-phase systems. The common approach in single-phase systems is to create a synthesized phase signal orthogonal to the fundamental signal of the single-phase system so as to obtain dc quantities by means of (αβ to dq) transformation. The orthogonal components in conventional approaches are usually obtained by phase shifting the real signals by a quarter of the fundamental period. The introduction of such delay in the system deteriorates the dynamic response, which becomes slower and oscillatory. In this paper, an alternative dq controller scheme which referred as to simplified dq controller is proposed. The proposed scheme does not require orthogonal quantities to be generated, making it easier to be implemented. The simplified dq control method is experimentally compared to the conventional delay-based dq control method and shown to improve the poor dynamics of the conventional approach while not adding excessive complexity to the controller structure. A single-phase five-level diode-clamped grid-connected PV inverter is considered as an example in this paper.

Phase angle, frequency and amplitude of the utility voltage are a critical piece of information for the operation of the grid-connected inverters. In such applications, an accurate and fast tracking of this information is essential to ensure the correct operation of the control system. This paper presents a novel phase-locked-loop (PLL) algorithm suitable for single-phase grid connected systems. The proposed algorithm generates the orthogonal voltage component using a structure based on a programmable cascaded low-pass filter (PCLPF), which possesses the following advantages: simple digital implementation and, therefore, low computational burden; - high filtering capability allowing a satisfactory harmonic distortion rejection- besides, the proposed structure is not affected by the frequency changes. The performance of the proposed PCLPFPLL algorithm is evaluated by extensive experimental tests, with various utility grid disturbances, such as voltage harmonics, voltage sag, phase jumps and frequency variations to validate the effectiveness of the proposed algorithm.

Different schemes of modified conventional sorting algorithms with low complexity are proposed in order to balance the voltages of submodule (SM) capacitors for the modular multilevel converter (MMC). Two different procedures are investigated in this study. The main idea is to achieve voltage balance within the MMC arms with fewer current sensors. The two different methods are examined under different operating conditions; for instance, with a sudden change in the DC-source or when different load values are applied. The advantage of such sensor-less control methods is to simplify hardware communications in general. Moreover, the reliability of the MMC is also improved. Simulation analyses of a single-phase four-level MMC are conducted to show the effectiveness of the proposed methods.

This paper has described a laboratory-scale DFIG test facility commissioned to investigate the low voltage fault behavior of a DFIG wind turbine generator. In this DFIG test facility, a dc motor driven by a four-quadrant dc drive is used as a prime mover to replicate the torque input from a wind turbine's drive shaft. A mechanical model created in Simulink is executed by the dSpace controller. The IGBT power converter and dc-link capacitors are over-rated to withstand various grid faults. The fault emulator permits a flexible approach to the application of grid faults and also provides an opportunity to mimic the typical grid connection impedance of a wind turbine.

This paper proposes a novel online condition monitoring system of dc-link metallized polypropylene capacitors in fault-tolerant drives for aerospace applications. The estimation technique makes use of voltage and current sensors which are already in place for protection and control purposes. The novel aspect of the proposed technique relates to monitoring capacitors in real time while the motor is operational. No external interferences, such as injected signals or special operation of the drive, are required. The condition monitoring system is independent of torque and speed and hence independent of a variation in the load. The condition monitoring system is validated using manual calculations, simulation, low-voltage experimentation, and high-voltage implementation on an aerospace drive.

This paper presents an overview of motor drive technologies used for safety-critical aerospace applications, with a particular focus placed on the choice of candidate machines and their drive topologies. Aircraft applications demand high reliability, high availability, and high power density while aiming to reduce weight, complexity, fuel consumption, operational costs, and environmental impact. New electric driven systems can meet these requirements and also provide significant technical and economic improvements over conventional mechanical, hydraulic, or pneumatic systems. Fault-tolerant motor drives can be achieved by partitioning and redundancy through the use of multichannel three-phase systems or multiple single-phase modules. Analytical methods are adopted to compare caged induction, reluctance, and PM motor technologies and their relative merits. The analysis suggests that the dual (or triple) three-phase PMAC motor drive may be a favored choice for general aerospace applications, striking a balance between necessary redundancy and undue complexity, while maintaining a balanced operation following a failure. The modular single-phase approach offers a good compromise between size and complexity but suffers from high total harmonic distortion of the supply and high torque ripple when faulted. For each specific aircraft application, a parametrical optimization of the suitable motor configuration is needed through a coupled electromagnetic and thermal analysis, and should be verified by finite-element analysis.

The energy utilization efficiency of commercial photovoltaic (PV) pumping systems can be significantly improved by employing simple perturb and observe (P&O) maximum power point tracking algorithms. Two such P&O implementation techniques, reference voltage perturbation and direct duty ratio perturbation, are commonly utilized in the literature but no clear criteria for the suitable choice of method or algorithm parameters have been presented. This paper presents a detailed theoretical and experimental comparison of the two P&O implementation techniques on the basis of system stability, performance characteristics, and energy utilization for standalone PV pumping systems. The influence of algorithm parameters on system behavior is investigated and the various advantages and drawbacks of each technique are identified for different weather conditions. Practical results obtained using a 1080-Wp PV array connected to a 1-kW permanent magnet dc motor-centrifugal pump set show very good agreement with the theoretical analysis and numerical simulations.

Grid-connected wind turbine doubly fed induction generators (DFIGs) are sensitive to dips in supply voltage, so-called “grid faults”. Fault ride through systems must be designed to manage the large and potentially dangerous fault currents in both stator and rotor circuits. However, DFIG fault response has been only partially or summarily treated in contemporary literature. This paper presents a detailed analytical analysis of wind turbine DFIG grid-fault response. The physical behavior of the machine is presented through a description of the flux-linkage response and later developed with analytical solutions of the generalized DFIG machine equations operating under fault conditions showing that the frequencies of the decay components of current deviate from pure dc and rotor speed due to magnetic drag effects. The analysis is experimentally verified and evaluated using a 7.5-kW test facility.

This paper presents a comparative investigation of the performance characteristics of a directly connected photovoltaic (PV) pumping system and a scheme utilizing a constant voltage maximum power point tracking algorithm. A simple and accurate model is developed for each individual component of the system based on its measured characteristics and the system is simulated numerically. System performance is analyzed and energy utilization efficiency is calculated for different weather conditions. A detailed comparison identifying the advantages and drawbacks of each technique is presented. Experimental results obtained using a 1080-Wp PV array connected to a 1-kW permanent magnet dc motor-centrifugal pump set show very good agreement with the numerical simulation of the systems.

Doubly fed induction generator (DFIG) technology is the dominant technology in the growing global market for wind power generation, due to the combination of variable-speed operation and a cost-effective partially rated power converter. However, the DFIG is sensitive to dips in supply voltage and without specific protection to “ride-through” grid faults, a DFIG risks damage to its power converter due to overcurrent and/or overvoltage. Conventional converter protection via a sustained period of rotor-crowbar closed circuit leads to poor power output and sustained suppression of the stator voltages. A new minimum-threshold rotor-crowbar method is presented in this paper, improving fault response by reducing crowbar application periods to 11-16 ms, successfully diverting transient overcurrents, and restoring good power control within 45 ms of both fault initiation and clearance, thus enabling the DFIG to meet grid-code fault-ride-through requirements. The new method is experimentally verified and evaluated using a 7.5-kW test facility.

This paper considers the electrical actuation of aircraft wing surfaces, with particular emphasis on flap systems. It discusses existing hydraulic and electrohydraulic systems and proposes an electrical alternative, examining the potential system benefits in terms of increased functionality, maintenance, and life-cycle costs. This paper then progresses to describe a full-scale actuation demonstrator of the flap system, including the high-speed electrical drive, step-down gearbox, and flaps. Detailed descriptions of the fault-tolerant motor, power electronics, control architecture, and position sensor systems are given, along with a range of test results, demonstrating the system in operation.

This paper employs a Kalman filter (KF) algorithm to estimate the capacitance of submodule (SM) capacitors in modular multilevel converters (MMCs). The proposed method can be used in the health condition monitoring technique of the capacitors. This proposed scheme estimates the capacitance of each individual capacitor from data of arm current and the corresponding voltage across the targeted capacitor. The arm current is used to calculate the capacitor current from the upper state of the SM switch. The proposed method has shown very good performance under normal operating conditions. The effectiveness of the proposed technique is validated via a MATLAB simulation analysis of a single-phase four-level MMC.

In recent years, integrated passive components technology has gained significant popularity in integrated drives research. An integrated drive may be considered to be a full mechanical integration of the machine, power electronic converter and passive components into a single package. This approach is important for applications such as traction motors, aerospace, electric vehicles and cars where space, mass or volume constraints are high. Incorporation of electromagnetic components, such as line filters, into electric machines can be achieved by sharing the existing machine's magnetic circuit with the filter component. In this paper part of an LCL line filter has been chosen to be integrated with a permanent magnet synchronous machine. An LCL filter has been selected as it has lower inductance compared to other input filter types such as LC and L filters. This paper also presents a several novel techniques for integrating the largest portion of LCL input power filter which is the 3-phase ac inductors located in the drive side producing a single mechanically packaged unit without significant increase in size and loss which in turn achieves high power density. Different integrated 3-phase input inductors designs have been simulated with finite element analysis to prove the effectiveness of integration of passives within the machine structure. In each case the design has been iteratively optimised to determine the optimal mass of copper and core for the integrated filter inductors targeting parity in power density when compared to a traditionally separated package. The paper demonstrates that an approach utilising a double slot machine with input filters wound into the outermost slots was the most appropriate choice in terms of power density compared to other proposed methods.

Fault ride-through (FRT) is required for large wind farms in most power systems. Fixed speed wind turbines (FSWTs) are a diminishing but significant sector in the fast-growing wind turbine (WT) market. State-of-art techniques applied to meet grid requirements for FSWT wind farms are blade pitching and dynamic reactive power compensation (RPC). Blade pitching is constrained by the onerous mechanical loads imposed on a wind turbine during rapid power restoration. Dynamic RPC is constrained by its high capital cost. These present technologies can therefore be limiting, especially when connecting to smaller power systems. A novel alternative technology is proposed that inserts series resistance into the generation circuit. The series dynamic braking resistor (SDBR) dissipates active power and boosts generator voltage, potentially displacing the need for pitch control and dynamic RPC. This paper uses a representative wind farm model to study the beneficial effect of SDBR compared to dynamic RPC. This is achieved by quasi-steady-state characterization and transient FRT stability simulations. The analysis shows that SDBR can substantially improve the FRT performance of a FSWT wind farm. It also shows that a small resistance, inserted for less than one

The capability of islanding detection has become a requirement for grid connection of inverters utilized in distributed generation (DG) systems. The parallel RLC resonant circuit comprised, as a local load, in the standard test of islanding detection schemes offers lower impedance for higher frequency harmonics. With the presence of such a parallel RLC circuit, the full power balance between the distributed generation and local load will never be satisfied when the voltage at the point of common coupling is slightly distorted. In this paper, the performance of grid-connected inverter during islanding detection routine test is analyzed with sinusoidal and marginally distorted grid voltage. The results presented in this paper show that grid background harmonics may have significant impacts on inverter control and islanding detection algorithms.

This paper presents a control system of an Induction Machine (IM) with predictive controller-estimator. A novel speed estimator is proposed, and the estimator operation is examined at different operational conditions. The new estimator shows an improvement in the speed estimation during the transient operation compared to the conventional estimators, and it also shows a satisfactory operation at different operating conditions. Simulations results are presented and the proposed experimental rig is described.

This paper discusses the design of a fault-tolerant electric motor for an aircraft main engine fuel pump. The motor in question is a four-phase fault-tolerant motor with separated windings and a six-pole permanent magnet rotor. Methods of reducing machine losses in both the rotor and stator are introduced and discussed. The methods used to calculate rotor eddy current losses are examined. Full three-dimensional finite-element (FE) time stepping, two-dimensional (2-D) FE time stepping, and 2-D FE harmonic methods are discussed, and the differences between them and the results they produce were investigated. Conclusions are drawn about the accuracy of the results produced and how the methods in question will help the machine designer

Power electronic inverters are commonly used for the interfacing of distributed generation systems to the electrical power network. These electronic inverters operate in a current controlled mode to inject unity power factor sinusoidal current into the network. To prevent possible dc current injection, a mains frequency isolation transformer is often employed at the inverter output. This isolation transformer is a costly component. An alternative approach is to use current sensing and control techniques to eliminate the dc current component. One method is to use a current controller to force the output dc current to zero. Current controllers are prone to errors associated with nonlinearity and offsets in the current transducers. This paper considers a novel auto-calibrating dc link current sensing technique that eliminates the errors associated with the current transducer, and helps avoid dc current injection into the grid when using a transformerless grid connect inverter system

In grid connected multiple inverter systems, it is normal to synchronize the output current of each inverter to the common network voltage. Any current controller deficiencies, which result in low order harmonics, are also synchronized to the common network voltage. As a result the harmonics produced by individual converters show a high degree of correlation and tend to be additive. Each controller can be tuned to achieve a different harmonic profile so that harmonic cancellation can take place in the overall system, thus reducing the net current total harmonic distortion level. However, inter-inverter communication is required. This paper presents experimental results demonstrating an alternative approach, which is to arrange for the tuning within each inverter to be adjusted automatically with a random component. This results in a harmonic output spectrum that varies with time, but is uncorrelated with the harmonic spectrum of any other inverter in the system. The net harmonics from all the inverters undergo a degree of cancellation and the overall system yields a net improvement in power quality.

This paper discusses the design and testing of an aircraft electric fuel pump drive. The drive is a modular, four-phase, fault-tolerant system which is designed to meet the specification with a fault in any one of the phases. The motor employed has a permanent-magnet rotor with the magnets arranged in a Halbach array to maximize the air-gap flux density. Exceptionally high electric loadings are obtained by flooding the entire motor with aircraft fuel, which acts as an excellent cooling agent. Theoretical results are compared with test results gained in conditions approaching those found in an aircraft. Tests are carried out on the unfaulted drive and with one of several fault scenarios imposed. The electrical and thermal performance of the drive is assessed, showing how the flooded fuel cooling has excellent performance without introducing significant drag on the rotor.

A cascaded doubly-fed induction machine (CDFM) is a connection of two wound rotor induction machines. The rotors of the two individual machines are electrically and mechanically coupled so that brushes for the rotor sliprings are no longer required. This paper describes the steady state behaviour of such a cascaded machine arrangement. Frequency and slip values are defined. A per-phase equivalent circuit, based on the common induction machine equivalent circuit, helps to gain understanding of the machine quantities. Measurements on a CDFM confirm simulations with the equivalent circuit experimentally. Saturation effects are discussed to show the limitation of the simple equivalent circuit model. By studying the power flow within the CDFM and taking machine utilisation into consideration allows to suggest that a CDFM has to consist of two identical machines.

Since 1994 Econnect has, in conjunction with Northern Electric PLC, investigated the use of consumer load control as a new and innovative method to actively regulate distribution system voltage when affected by the operation of embedded generators [1],[2]. There are a number of issues that can limit the installed capacity of embedded generators; these are often voltage related, and the most common is steady state voltage rise. A number of techniques can be applied to limit steady state voltage rise, some of which are static in time (e.g., network reinforcement) and some dynamic (e.g., power factor control). This paper discusses the issue of excess steady state voltage rise and the methods of limitation that can be applied with specific reference to wind generation. The new and innovative approach using consumer load control is discussed and compared with the existing methods using a simulation case study.

This paper compares various types of current controllers, including a novel method based on flux control. A proportional integral (PI) control method is used initially, to control the current in a high-speed permanent-magnet synchronous machine. The performance of this simple PI loop is presented, Various improvements to the PI controller are investigated, and the change in performance examined. A new current control scheme based on a flux-linkage model of the machine is introduced. The performance of the model-based control is demonstrated and compared with the performance of the PI current controller. Factors affecting the accuracy of the model-based control are given. By incorporating these factors into the model, the performance of the flux controller is further enhanced.

This paper examines winding faults in a demonstrator drive, based on a specification for an aircraft fuel pump. This drive has been designed with a degree of inherent fault tolerance and is capable of continued operation in the presence of a variety of faults. Some of the most severe faults arise from winding insulation failure within a phase of the machine. A method of detecting turn to turn short circuits which can result from winding insulation breakdown is presented, along with a strategy for continued post fault operation of the drive. The detection method operates in real time, requires no additional sensors and is sufficiently sensitive to detect even a single shorted turn.

This paper evaluates the incremental conductance (INC) maximum power point tracking (MPPT) algorithm using an experimental installation comprised of a 540-Wp photovoltaic array connected to a resistive load. Particular focus is given to the assessment of the two commonly utilized implementation techniques: reference voltage perturbation and direct duty ratio perturbation. The impact of algorithm parameters on system behaviour is investigated and the energy utilization efficiency is calculated for different weather conditions. The various advantages and drawbacks of each technique are identified.

Nowadays, it is a general trend to increase the Distribution Generator (DG) based on renewable energy such as photovoltaic (PV) system. This generator can affect the grid by causing a number of problems due to injection of DC current into the grid. If this DC current is not properly prevented, result problems in distribution network such as increased corrosion in underground equipment and transformer saturation. This paper reviews the minimization methods which employ to minimize the output DC current component in single-phase grid-connected inverters photovoltaic applications. These methods are categorized into four classifications. The basic approach is to make use of an isolating transformer to prevent the DC current. Another technique is to use a half-bridge inverter which has the capability of blocking the DC current flow to the AC side. It is also possible to use a DC blocking capacitor in the inverter output. A more recent method is to use current sensing and control techniques to monitor and calibrate the DC link current sensors.

Domestic scale DG (Distributed Generation) installations include a multitude of technologies, many of which are based on a RES (Renewable Energy Source). The energy generation of a DG installation doesn't necessarily coincide with local power consumption; grid connection allows surplus local power to be distributed using the wider power network. A power electronics interface is necessary to achieve connection between the DG unit and the distribution network. The majority of grid connection standards stipulate that the power electronics interface must include a robust LOM (Loss Of Mains) detection routine. This paper presents a Matlab/Simulink simulation model that has been designed to mimic a standard laboratory setup that is used verify the adherence to the LOM grid connection standards. Multiple in-the-loop based LOM detection methods are presented, analysed and compared. Experimental verification of the simulation results is presented to demonstrate the closeness of the model.

Distributed Generation (DG) systems include several technologies, many based on renewable energy sources. Due to the intermittent nature of many DG systems, it is necessary to include energy storage devices. This results in a multitude of DG units that require grid connection. Single phase power converters are necessary to achieve connection between domestic scale DG units and the grid. The majority of utility connection standards state that the DG unit must detect a loss of mains (LOM) event and stop feeding energy into the grid. This paper presents a laboratory setup that has been specifically designed to verify the adherence to grid connection standards. Multiple in-the-loop based LOM detection methods are presented, analysed and compared. A harmonic injection technique is introduced and its merits discussed. (5 pages)

This paper presents a current-controlled parallel connected three phase converters scheme. Two voltage source inverters with a front end diode rectifier are directly paralleled without intermodule reactors. The proposed method divides the switching cycle evenly between the equally rated converters, and each converter employs just one PI regulator to get good current characteristics, both in steady states and transient states. Unlike in most previous studies, the converters utilize local feedback information to obtain equal current sharing without using any circulating current control scheme. Using MATLAB/Simulink, simulation results are given to verify the control proposed. (5 pages)

Single-phase current controlled, voltage source inverters are commonly used to feed unity power factor sinusoidal current into the distribution network from PV sources. A large 50Hz transformer is often used at the inverter output for galvanic isolation and to prevent dc current injection into the distribution network. This transformer increases cost, size and overall power losses of the system. For this reason, transformerless inverters are of increasing interest. When an output transformer is not present it is important that the output current is controlled accurately in order to minimise the DC component. The accuracy of the DC current sensor then becomes important to achieving this. A scheme is proposed in which DC link current sensing and current control are used to minimise the output DC current component. Current controllers are affected by errors associated with nonlinearity and offset in the current sensors. This paper applies an auto-calibrating DC link current sensing technique to minimise the errors produced by current sensors in the single-phase, 3-level half-bridge inverter. Characteristics of the proposed method are illustrated using simulation and experimental results with a resistive load.

The sensitivity of the DFIG to the grid disturbances such as a voltage dip restricts network stability and risks damage to generator converters during the fault period due to the over-current and/or over-voltage. It is now a requirement that wind turbine manufacturers demonstrate what is commonly called `Fault Ride Though' (FRT) capability in their turbine systems. The rotor crowbar, as a cost-effective and reliable method of protecting the power converters of the DFIG, was employed as a part of the FRT scheme. A computer model created in Matlab/Simulink was validated with the results of a 7.5kW experimental system.

Hill-climbing algorithms are the most commonly utilized maximum power point tracking (MPPT) control schemes in photovoltaic (PV) applications. Two techniques have been adopted in the literature for implementing such hill-climbing algorithms: reference voltage perturbation where a reference value for the PV generator output voltage is used as the control parameter and direct duty ratio perturbation where the duty ratio of the MPPT converter is used directly as the control parameter. This paper presents a detailed comparison between these two techniques on the basis of system stability. Practical results obtained using a 540Wp PV experimental setup with a resistive load show very good agreement with the theoretical analysis and numerical simulations. (6 pages)

This paper considers existing More Electric technologies in commercial aircraft, observing recent technologies adopted by aerospace and discussing the reasons restricting the application of other designs. Fault tolerant drives are considered, assessing where reliability may affect application in aerospace. Failure conditions and design issues are proposed which will present challenges in the evolution of laboratory prototypes to actual aerospace hardware. Results are presented from fault tolerant drives, highlighting some of these design considerations.

Power switching devices in dc/dc power converters for Hybrid Electric Vehicles (HEVs) are fluid cooled. Fluid cooled heatsinks make up nearly a third of the volume and weight of DC/DC converters. The design of heatsinks in automotive applications is therefore of paramount importance in order to gain high power-to-volume and high power-to-weight ratios. Literature on heatsink designs often present test results that are based on one set of input data only (e.g. fluid inlet temperature, flow rate and fluid mixture). The fluid inlet temperature and flow rate, however, can vary substantially in an automotive fluid cooled system and the heatsink may therefore not perform well. Fluctuation of theses parameters must therefore be considered in the design of fluid cooled heatsinks in order to allow optimal cooling performance under all conditions. This paper describes the design of a heatsink that is optimised for one set of parameters. The heatsink is then tested at temperature and flow rate variations to emulate the fluctuation in a vehicle cooling system. (6 pages)