Showing papers in "Iet Electric Power Applications in 2019"

Health monitoring and prognosis of electric vehicle motor using intelligent-digital twin

Abstract: Electric mobility has become an essential part of the future of transportation. Detection, diagnosis and prognosis of fault in electric drives are improving the reliability, of electric vehicles (EV). Permanent magnet synchronous motor (PMSM) drives are used in a large variety of applications due to their dynamic performances, higher power density and higher efficiency. In this study, health monitoring and prognosis of PMSM is developed by creating intelligent digital twin (i-DT) in MATLAB/Simulink. An artificial neural network (ANN) and fuzzy logic are used for mapping inputs distance, time of travel of EV and outputs casing temperature, winding temperature, time to refill the bearing lubricant, percentage deterioration of magnetic flux to compute remaining useful life (RUL) of permanent magnet (PM). Health monitoring and prognosis of EV motor using i-DT is developed with two approaches. Firstly, in-house health monitoring and prognosis is developed to monitor the performance of the motor in-house. Secondly, Remote Health Monitoring and Prognosis Centre (RHMPC) is developed to monitor the performance of the motor remotely using cloud communication by the service provider of the EV. The simulation results prove that the RUL of PM and time to refill the bearing lubricant obtained by i-DT twins theoretical results.

Permanent magnet vernier machine: a review

Abstract: Permanent magnet vernier machines (PMVMs) gained a lot of interest over the past couple of decades. This is mainly due to their high torque density enabled by the magnetic gearing effect. This study will provide a thorough review of recent advances in PMVMs. This review will cover the principle of operation and nature of magnetic gearing in PMVMs, and a better understanding of novel PMVM topologies using different winding configuration as well as different modulation poles and rotor structures. Detailed discussions on the choice of gear ratio, slot-pole combinations, design optimisation and role of advanced materials in PMVMs will be presented. This will provide an update on the current state-of-the art as well as future areas of research. Furthermore, the power factor issue, fault tolerance as well as cost reduction will be discussed highlighting the gap between the current state-of-the art and what is needed in practical applications.

Design and implementation of a novel adaptive backstepping control scheme for a PMSM with unknown load torque

Abstract: In this study, a novel adaptive backstepping control method is proposed to handle the position tracking problem of the permanent magnet synchronous motor (PMSM) system with unknown load torque. Firstly, a novel load torque update law which is different from the traditional load torque update law is obtained based on the position error and estimated torque error. Then, a novel adaptive backstepping controller is presented under the circumstance of estimated load torque. The asymptotic stability of the overall system is verified by using Lyapunov stability theory. The novel load torque update law guarantees the accurate estimation and improves the convergence speed of the estimated load torque. The designed controller improves the position tracking performance and ensures stability of the closed-loop system. Finally, real-time experiment results with LINKS-RT platform intuitively exhibit that the proposed control method ensures position tracking performance and retains good load torque disturbance attenuation.

Rolling bearing fault detection of electric motor using time domain and frequency domain features extraction and ANFIS

Abstract: Demands for various products, higher qualities, reduction of costs and competitiveness, have resulted in the use of intelligent fault detection systems. Bearing fault diagnosis as a major component of the electric motors has had an essential role in the operation of production units’ reliability. In addition, vibration analysis is one of the most powerful tools in diagnostics. Advances in signal processing technology and electrical equipment have developed a machinery condition monitoring for defect detection. This study has used the extracted features of vibration signals and the adaptive neuro-fuzzy interface system (ANFIS) network proposing a structure for fault detection and diagnosis of rolling bearings. Time-domain and frequency-domain statistical characteristics have been extracted fault information from vibration signals. Besides, the test data sets are presented to the ANFIS network. Simulation results indicated that the performance of the ANFIS network is acceptable. The results reveal that this method has more accuracy and better classification performance in comparison with other methods proposed in the literature.

Broken rotor bar fault detection of the grid and inverter-fed induction motor by effective attenuation of the fundamental component

Abstract: Since electrical machines are the largest consumer of electricity worldwide, their fault diagnostic at the incipient stage and condition monitoring is essential for better reliability, economy, and safety of operation. Out of several condition monitoring techniques, motor current signature analysis is gaining heightened popularity because of its non-invasive nature, the least number of sensors required and versatility of compatible algorithms. In this study, the best characteristics of infinite impulse response (IIR) filter are exploited to observe the broken rotor bar (BRB) frequencies with good legibility in current and voltage spectrum of the grid and inverter-fed motor, respectively. The causes of various harmonics in the stator current spectrum are first investigated for better understanding. The results are taken based on simulation and measurements taken from the laboratory setup. It is observed that a better tuning of IIR filters can make diagnostic algorithms capable of detecting the frequencies of interest by effectively attenuating the fundamental component and reducing its spectral leakage. Moreover, in case of direct torque control-based industrial inverter-fed motors, the current cannot be a good candidate for fault diagnostics rather the phase voltage can be effectively used for the detection of BRBs.

Thermal analysis of fault-tolerant electrical machines for aerospace actuators

Abstract: For safety-critical applications, electrical machines need to satisfy several constraints, in order to be considered fault tolerant. In fact, if specific design choices and appropriate control strategies are embraced, fault-tolerant machines can operate safely even in faulty conditions. However, particular care should be taken for avoiding uncontrolled thermal overload, which can either cause severe failures or simply shorten the machine lifetime. This study describes the thermal modelling of two permanent magnet synchronous machines for aerospace applications. In terms of the winding's layout, both machines employ concentrated windings at alternated teeth, with the purpose of accomplishing fault-tolerance features. The first machine (i.e. Machine A ) adopts a three-phase winding configuration, while a double three-phase configuration is used by the second one (i.e. Machine B ). For both machines, the winding temperatures are evaluated via simplified thermal models, which were experimentally validated. Copper and iron losses, necessary for the thermal simulations, are calculated analytically and through electromagnetic finite-element analysis, respectively. Finally, two aerospace study cases are presented, and the machines' thermal behaviour is analysed during both healthy and faulty conditions. Single-phase open-circuit and three-phase short-circuit are accounted for Machines A and B, respectively.

Modelling and performance analysis on a bearingless fixed-pole rotor induction motor

Abstract: Both torque winding magnetic field and suspension force winding magnetic field induce currents in the rotor in conventional bearingless induction motors (BIMs). Owing to the induced currents of suspension force winding, the air gap magnetic field is affected, which results in amplitude and phase error of torque and radial suspension forces. To overcome such drawbacks, a novel BIM with a fixed-pole rotor is proposed, which is called bearingless fixed-pole rotor induction (BFPRI) motor. First, the structure of the BFPRI motor is designed and introduced. Second, the mathematical models of radial suspension forces and torque are deduced. Third, the corresponding electromagnetic characteristics, including induced currents, radial suspension forces, and torque, are investigated and compared with the conventional BIM. Finally, the prototype motor equipped with a fixed-pole rotor is constructed and experimental research is carried out. According to the finite element analysis and experimental results, for the proposed BFPRI motor, only the torque winding magnetic field induces currents in the rotor, which makes the precision of torque and radial suspension forces higher and improves the accuracy of the BIM control system.

Research on PMSM harmonic coupling models based on magnetic co-energy

Abstract: Modelling of the permanent magnet synchronous motor (PMSM) torque ripple and PMSM current harmonics controlling technology are important branches of PMSM research. Based on the existing linear PMSM model derived from magnetic co-energy, this study considers the variation of PMSM parameters (inductance, permanent magnet flux and cogging torque) caused by magnetic saturation. Then, the harmonic coupling models including flux-current coupling model, voltage-current coupling model and torque-current coupling model are deduced. In these harmonic coupling models, the PMSM parameters no longer vary with rotor position but only with current amplitude and phase. Based on the torque-current coupling model, a novel method of obtaining the required injecting currents which could suppress torque ripple is proposed. The validity of the harmonic coupling models and the injecting current solution method is verified by finite-element method.

Multi-objective optimisation design and performance comparison of permanent magnet synchronous motor for EVs based on FEA

Abstract: The requirements of high efficiency, power density, and low price for the motor of electric vehicles (EVs) make the design of the driving motor become a process of multi-objective optimisation. For purpose of the permanent magnet synchronous motor (PMSM) used for EVs has the higher efficiency, wider range of speed regulation with flux-weakening and better cost superiority, a multi-objective optimisation design approach based on finite element analysis (FEA) and modified particle swarm optimisation (MPSO) algorithm which takes efficiency, flux-weakening rate, and price as optimisation objectives is proposed in this study. Five PMSMs with different rotor topologies (V-shape, U-shape, double V-shape, delta-shape, and double tangential-shape) are optimised by the proposed optimisation method and their performance characteristics, including flux-weakening ability, efficiency, price, and anti-demagnetisation ability, are compared. The results suggest that double V-shape rotor topology has the wider constant power range and double-layer PMs topology has stronger anti-demagnetisation ability and wider high efficiency interval, whereas single-layer topology has lower cost price. Furthermore, a PMSM prototype with V-shape PMs is manufactured, so that the feasibility of multi-objective optimisation design approach and accuracy of FEA are verified by prototype experiments.

Analytical modelling and experimental verification of E-type reluctance motors

Abstract: The main objective of this study is the analytical modelling of two short-flux-path two-phase reluctance motors with E-type stators: first, a switched reluctance motor and second, a hybrid-excitation reluctance motor (HRM). The former has no permanent magnets in its structure, whilst in the latter, there are magnets inside the common poles. Firstly, finite element analysis (FEA) is adopted to obtain the flux paths distribution in the proposed structures. Then, a precise magnetic circuit model (MCM), which considers all leakages and fringing effects, is built and the permeances of the machine are calculated for any rotor position based on the predicted flux flow patterns. Torque and inductance curves and steady-state current and voltage waveforms are also carried out. Finally, both motor prototypes are fabricated and the experimental results are obtained and compared with those of MCM and FEA. This comparative study confirms the validity and accuracy of the developed MCMs. In addition, the torque profiles of the proposed structures and two other conventional and C-type reluctance motors are compared. It is shown that the proposed HRM has superior characteristics amongst all compared structures.

Design and optimisation of a novel asymmetric rotor structure for a PM-assisted synchronous reluctance machine

Abstract: This study proposes a novel asymmetric rotor structure with tuning-fork flux barriers for a permanent magnet (PM)-assisted synchronous reluctance machine (PMA-SynRM) to improve the torque characteristics. The proposed asymmetrical rotor structure can effectively decrease the flux leakage inside the rotor, as well as ensure the maximum values of the magnetic torque and the reluctance torque are near the same current phase angle as each other to achieve better utility. To realise this, the frozen permeability method is implemented to separate the total torque into the reluctance torque and the magnetic torque via a two-dimensional finite-element method – JMAG-Designer. To achieve the optimal torque characteristics in the proposed model, the Kriging method and a genetic algorithm are used for getting the optimised model. The contribution of this investigation into motor performance is validated by comparing the proposed model with a conventional PMA-SynRM with a symmetric rotor structure. Beyond that, all machine models are the same size, have the same number of magnets and are operated under the same conditions. A prototype of the proposed model is experimentally verified, i.e. the simulation results agree with the experimental results.

Bi-subspace predictive current control of six-phase PMSM drives based on virtual vectors with optimal amplitude

Abstract: Owing to the low equivalent impedance of six-phase machines in the secondary subspace, in which currents do not contribute to torque production, low-order current harmonics with high amplitude are likely to appear in the stator currents, increasing the harmonic distortion and the losses in the machine. In the case of permanent magnet synchronous machines (PMSMs), the main causes of these harmonics are machine asymmetries, non-linearities of the power converters and back-electromotive force harmonics. The existing predictive control strategies based on virtual vectors for six-phase machines only regulate the currents mapped into the fundamental subspace, responsible for flux/torque production and leave the currents mapped into the secondary subspace uncontrolled. This study proposes a novel bi-subspace predictive control strategy for six-phase PMSMs with optimal amplitude virtual vectors, which is able to effectively regulate the currents in both subspaces simultaneously, leading to a significant minimisation of the current harmonic distortion. Moreover, the proposed control strategy also allows operating the six-phase PMSM with a current unbalance between the two sets of windings. Both simulation and experimental results confirm the much better performance of the proposed strategy in comparison with other state-of-the-art predictive control strategies found in the literature.

Electromagnetic and thermal analysis and design of a novel-structured surface-mounted permanent magnet motor with high-power-density

Abstract: A segmented-core (SC) structure has been widely used for high-power-density (HP) motors. However, the SC motor is associated with a number of problems due to the complexity of both the structure and the manufacturing process. To address these issues, a novel structure of a HP motor is proposed, referred to as the ring-coupled segmented-stator (RSS) model here. The proposed RSS can increase the reliability, the stability, and the manufacturability of motor. Furthermore, useful thermal analysis and design flow which take into account the RSS and asymmetric overhang structure of the motor are proposed in this research. The proposed lumped parameter thermal network (LPTN) for the thermal analysis shows a good agreement with experimental data within 9.8% difference. The proposed analysis and design method can be used for the diverse kinds of motor requiring the HP. The usefulness of the proposed RSS motor, the analysis method, and the design method are verified through the experiment in this research.

Axial flux switched reluctance machines: a comprehensive review of design and topologies

Abstract: Axial flux switched reluctance machines (AFSRMs) exhibit unique characteristics that specify their superiority over other topologies in specific applications. A number of researchers have studied the efficient design and constructed structures in different types of AFSRMs. Each of such studies seeks to produce a motor with improved characteristics. Here, a comprehensive study is performed in AFSRMs, including their design considerations, sizing equations and the structural changes. The sensitivity of parameters for efficient operation is investigated. Also, the comparisons among topologies are provided for each of the identified metrics. This study ends with a comparison summary, which shows the performance indices evaluation of different topologies to utilise in various applications.

Conception of an electric propulsion system for a 9 kW electric tractor suitable for family farming

Abstract: This study presents an updated review of the application of electric tractors. A customised drive system for the conception of a novel low-power electric tractor suitable for family farms is also introduced and discussed. The introduced system comprises several aspects regarding energy generation, transmission, conversion, storage, utilisation, conservation, and management, as well as sustainability issues. A 9 kW prototype composed of two three-phase induction motors, two independent inverters, and a lead–acid battery bank is presented. Flexible and safe operation is ensured by using an electronic control unit specifically designed for this project, as a dedicated control algorithm is also developed to provide greater versatility under common rural activities. Also, a supervisory system is proposed for data storage and performance analysis. To verify the proper performance of the electric tractor, the methodology used for conducting drawbar tests has been based on document CODE 2 by Organisation for Economic Co-operation and Development (OECD). Experimental results are presented and discussed; thus, demonstrating that the proposed electric tractor is technically feasible in terms of performance when compared with a similar internal combustion engine one.

Design and multi-objective optimisation of switched reluctance machine with iron loss

Abstract: In this study, the design optimisation of a switched reluctance machine (SRM) with the layered method has been studied. Firstly, a multi-physical analytical model for the SRM is established. The proposed model consists of an electromagnetic model, an electrical model, a loss model, and a thermal model. Then a layered optimisation design method suitable for the SRM is proposed in combination with the multi-physical field simulation model. Taguchi method is used to analyse the influence degree of the main geometric dimensions on the dynamic performance, and the parameters are divided into high-sensitivity parameters (HSPs) and low-sensitivity parameters. The non-dominated sorting genetic algorithm-II algorithm is used to optimise the HSP by the proposed model. The iron loss, average torque, average torque per unit mass, torque ripple and efficiency are taken as the objective functions. Finally, the prototype is manufactured and a testing platform is built. The flux linkage of several special positions of the machine is verified experimentally, and the accuracy of the electromagnetic model in the multi-physical field model is verified. The temperature experiments are carried out on the machine, and the accuracy of the equivalent heat circuit model in the multi-physical field model is verified.

Review on the evolution of technology advancements and applications of line-start synchronous machines

Abstract: Line-start synchronous machines (LSSMs) emerged as an efficient alternative for induction machines in numerous constant speed applications. This study reviewed evolution, technological advancements, design concepts, optimisation techniques, and possible applications in a comprehensive manner. A case study on the reviewed LSSM has been carried out based on its suitability in agricultural applications in India. Further, the performance comparison and significant advantages between the existing induction machine and LSSM are finally discussed.

Improving attitude detection performance for spherical motors using a MEMS inertial measurement sensor

Abstract: A spherical motor has multiple degrees of freedom. Its motion control requires an accurate attitude detection system. This study proposes a low-cost microelectromechanical system (MEMS) inertial measurement sensor to detect the attitude of the spherical motor. The proposed sensor combines a three-axis gyroscope and a three-axis accelerometer to obtain raw position data of spherical motors to estimate rotor's attitude. To improve the accuracy of the estimated attitude from the raw position data, the authors reduce the inclination angle error between the motor's rotor and MEMS sensor's coordinate systems by compensating axial angle error. A high-speed camera that generally provides high accuracy of the attitude is used as a calibration device for comparison and validation. Experimental results show that the MEMS inertial measurement sensor can achieve accurate attitude estimation that is suitable for motion control of a spherical motor.

Methods for overcoming misalignment effects and charging control of a dynamic wireless electric vehicle charging system

Abstract: A new method of power control for wireless power transmission (WPT) system has been proposed and analysed. The circuit and method suggested in this study holds good promise of reducing switching loss in the high-frequency converter of WPT. The effect of misalignment between transmitter and receiver coils has been analysed and a simple remedial method has been proposed. The desirability of frequency tuning of converter's output voltage under varying degrees of misalignment has been highlighted. The conventional perturb and observe method for maximum power point tracking has been gainfully employed here to achieve the required frequency tuning of the proposed converter. The proposed methods are implemented and tested on laboratory scale. Some suggestions have been given for augmenting driver assistance system aimed at limiting lateral misalignment in dynamic WPT system. The suggested algorithm is tested in a laboratory environment using a simple communication system.

Switched capacitors 9-level module (SC9LM) with reduced device count for multilevel DC to AC power conversion

Abstract: Switched capacitors (SCs)-based modules are being increasingly used for multilevel DC to AC power conversion, especially for low input voltage applications. Many of these topologies operate in two stages involving H-bridge switches, which endure high-voltage stress. The SC 9-level module (SC9LM) presented here operates in a single stage with one DC source and two capacitors. In addition, the peak inverse voltage of all power switches is confined to the voltage of the input DC source. The proposed 9-level module ensures a reduced number of power switches. In addition, with appropriate utilisation of states, two of the eleven switches in the module operate at fundamental switching frequency, thereby minimising the switching losses. A single SC9LM achieves a voltage gain of two. The proposed module is validated through circuit analysis followed by simulation and experimental results.

Dual-stator consequent-pole Vernier PM motor with improved power factor

Abstract: The Vernier permanent-magnet (VPM) machines are recently attracting more attention for utilisation in low-speed, high-torque applications including renewable energy conversion systems, electric vehicles and elevators. Although, the VPM machines present interesting advantages, they suffer from lower power factor (PF) in comparison to the conventional permanent-magnet (PM) drives. In this study, a novel structure of the VPM machine with dual-stator and consequent-pole (CP) rotor topology is proposed with enhanced PF. The objectives in this new structure are achieving higher torque density per PM volume, higher efficiency, simpler and more robust installation of PM pieces, lower cogging torque and simpler rotor core laminations compared to the previously proposed VPM structures with reasonably improved PF. The low PF issue of VPM machines is analysed in details and the novel CP-VPM geometry is designed to diminish this drawback. Then analytical relations are derived based on the magnetic-equivalent-circuit for evaluating the flux density distribution, induced back electromotive force, magnetising reactance and PF. The effectiveness of the novel structure in enhancing the operating features is validated using analytical and 2D-FE simulation results. Finally, it is concluded that the performance of the optimally designed structure can be enhanced reasonably so that to consider it as a good choice for direct-drive applications.

Novel speed estimation technique for vector-controlled switched reluctance motor drive

Abstract: This article discusses the speed-sensorless vector-controlled SRM-drive. The use of position/speed sensors have few concerns related to it in terms of cost, reliability, and compactness, a few to mention. Therefore, it is necessary to have some estimation strategy which estimates the speed/position. Since the control of the machine is done in dq 0-reference frame, so by utilising these dq 0-variables a novel speed/position estimation technique i.e. `P n -MRAS (Net-input-Power-based Model-Reference-Adaptive-System) speed-estimator' is developed for the vector-controlled SRM-drive. The speed-estimator implemented is simple, no look-up table is required and no external circuitry is required for injection of the diagnostic signal. Also, the estimator is free from differentiator and integrator terms. The proposed speed-estimator is stable in all the four quadrants of operation which is proved by performing the stability analysis. The estimator is dependent on two machine parameters (stator-resistance and amplitude of AC-component of self-inductance). The estimator is made robust to changes in stator-resistance by estimating the resistance online by proposed V 0 -MRAS resistance-estimator. The drive has been extensively simulated in MATLAB/SIMULINK and results are also verified experimentally through a dSPACE-1104-based laboratory prototype.

Discrete sliding mode control based on exponential reaching law and time delay estimation for an asymmetrical six-phase induction machine drive

Abstract: This study deals with the problem of controlling rotor speed and stator currents of an asymmetrical six-phase induction machine with uncertain dynamics, disturbances, and unmeasurable rotor currents and proposes a robust non-linear variable structure controller. First of all, an outer control loop based on a proportional–integral regulator is performed to control the rotor speed and to construct the desired stator current references. Then, the inner loop is performed based on the proposed method that combines the time delay estimation method and discrete sliding mode control based on exponential reaching law. This structure allows an accurate and simple estimation of uncertainties and rotor currents, a high-tracking precision, a convergence of the stator currents to their known desired references in finite-time and chattering reduction. The design procedure is detailed step by step and the stability analysis and the convergence time are established for the current closed-loop system. Experimental work was carried out on an asymmetrical six-phase induction motor drive to show the effectiveness and performance of the proposed robust non-linear discrete method. The results obtained highlighted the good tracking performance of the stator currents.

Experimental behaviour analysis for optimally controlled standalone DFIG system

Abstract: Metaheuristic optimisation techniques such as the Grey Wolf optimiser (GWO) and artificial bee colony (ABC) algorithms have been developed for enhancing the dynamic behaviour of wind energy conversion system. The stand-alone doubly fed induction generator (DFIG) control system based on the direct voltage control is experimentally validated for the robust independent control of the stator voltage amplitude and the consequent rotor current regulation. The GWO and ABC are used for selecting the optimal gains of the proportional-integral (PI) regulator to improve the dynamic performance and the robust stability of the DFIG system in the presence of step voltage variation and sudden load operation. Through, MATLAB™/Simulink numerical simulations, the dynamic performances of the GWO-PI and ABC-PI applied to stand-alone DFIG systems are compared with the conventional PI controller under different disturbances. Using a 3 kW DFIG test bench DSPACE DS1104 card prototype, the experimental validation justifies the superiority of proposed novel GWO-PI and ABC-PI controllers over the conventional PI control in terms of steady-state errors, maximum overshoots, settling time and rise time.

Eccentricity fault diagnosis indices for permanent magnet machines: state-of-the-art

Abstract: Eccentricity fault with 10% severity is probably the only existing fault in a brand new healthy electrical machine that is acceptable as a manufacturing tolerance. This fault can be developed due to a continuous pull between stator and rotor, even in a de-energized machine. So, it must be diagnosed,and its severity monitored. The authors introduced and criticized various indices for eccentricity fault diagnosis. Advantages, drawbacks, and ambiguous points of each index and potential ground for improvement of these techniques are addressed. Moreover, different eccentric PM machine modelling techniques are reviewed and environmental factors affecting the eccentricity fault detection process are discussed. This survey covers all direct current and alternating current PM machines. It provides information about the researches performed since 1986 and it is helpful to newcomers to this field, artisans, and protection system designers. Considering the given information, the readers achieve enough understanding of the weaknesses and strong points of each eccentricity fault diagnosis index. Then, these indices are evaluated through assigning weight coefficients under various scenarios. Interested individuals can modify these weight coefficients based on the specifics of the application and decide which index is the most appropriate.

Split ratio optimisation of high-speed permanent magnet brushless machines considering mechanical constraints

Abstract: The split ratio of rotor outer diameter to stator outer diameter is one of the most important design parameters due to its significant impact on machine torque density and efficiency. It has been optimised analytically in existing papers with due account given only for the thermal limitations. Here, the optimised split ratio for high-speed permanent magnet machines (HSPMM) with consideration of the mechanical constraints is investigated analytically. In addition, the influences of flux density ratio, maximum operating speed and sleeve material on the optimised split ratio are discussed in detail. The analytical results are verified by finite-element analyses. It is demonstrated that the optimised split ratio as well as the achievable torque of HSPMM is significantly reduced when the mechanical constraints are taken into consideration. The experimental results on a 6/slot-4pole HSPMM confirm the validity of previous analyses.

Online maximum torque per power losses strategy for indirect rotor flux-oriented control-based induction motor drives

Abstract: Among the conventional loss minimisation algorithms (LMAs), the model-based approaches have the advantages of fast response and high accuracy. Here, a novel online model-based power losses minimisation approach is presented for indirect field-oriented control (IFOC) of induction motor (IM) drives. The proposed method is introduced as maximum torque per power losses (MTPPL) in which the power losses for a given torque are minimised. The results demonstrate that the proposed approach preserves the LMA merits, while the criterion for the MTPPL scheme is achieved. The mentioned criterion is investigated by a gradient approach so that while the gradient vectors of the torque and power losses are parallel, the MTPPL strategy is realised. The closed-loop IFOC of the MTPPL approach is implemented in real time for a laboratory 2.2 kW three-phase IM drive. The experimental results show the capability and validity of the proposed control scheme.

Designing and experimentally testing a flux-focusing axial flux magnetic gear for an ocean generator application

Abstract: The torque density characteristics for an axial flux magnetic gear using a flux-focusing topology is experimentally studied when using neodymium iron boron (NdFeB) rare-earth magnets. A geometric parameter sweep analysis was utilised in order to maximise both the calculated volumetric and mass torque density. The calculated torque and torque density was 628.6 N·m and 173.02 N·m/L while the experimentally measured torque and resultant torque density was 553.2 N·m and 152.3 N·m/L.

Unipolar sinusoidal excited switched reluctance motor control based on voltage space vector

Abstract: In order to improve the operation performance and decrease the torque ripple of switched reluctance motor (SRM), a new current control method for SRM based on voltage space vector was proposed. In which the stator windings are excited by sinusoidal current with a DC offset to realise the unipolar current excitation. In this control system, zero vectors were used to control zero-sequence current alone and non-zero voltage space vector was selected to control d–q-axis current considering coupling. The reluctance torque component was offset by injecting third harmonic current into the DC bias current, and copper loss was minimised by selecting appropriate current ratio. Experiences verified that the new method can effectively control SRM current. The torque ripple can be reduced with third times harmonic current injection, but the efficiency is also decreased. Compared with the traditional control method, the proposed method is simple, easy to implement, and can effectively suppress torque ripple.

Application of the inductive high current testing transformer for supplying of the measuring circuit with distorted current

Abstract: The increasing number of non-linear loads and renewable energy sources causes a decrease in the power quality in the power networks. Therefore, tests of current transformers should be performed in similar conditions. This requires generation by a high current testing transformer of distorted currents that rms values are from a few hundred to several thousands of amperes with a given harmonics levels. However, its frequency band of operation is limited by inductances of its windings and connected load that result from the length and parameters of the used current track and connected device under test. To ensure the constant rms value of higher harmonic of distorted secondary current with the increase of its frequency proportional increase of the rms value of this harmonic in distorted primary voltage of the high current testing transformer is required. However, the maximum permissible value of primary voltage is limited by the dielectric strength of insulation of the primary winding. The purpose of presented studies is to determine the factors that condition the frequency band of operation of a high current testing transformer and limits the range of higher harmonics while testing of the transformation accuracy of instrument current transformers for distorted currents.