This study introduces a method for controlling a system that rectifies electric current where power is transferred from several offshore wind power generation systems through a common offshore AC line, into a diode-based bridge. This modular rectifier comprises one or more uncontrolled modules (such as diode rectifiers). According to the study, the wind power supply systems receive a reactive power reference from a central external regulator to maintain the common AC-line frequency. Although there are other control methods for this topology, the proposed external control uses commercial wind turbine with no changes in their internal control. The power plant control systems use their own algorithm to select the active and reactive power reference, maintaining the original wind turbine control unaltered. This method for controlling the voltage and the frequency of local offshore grid allows the operation of the different rectifiers end of the HVDC link. PSCAD^® simulations are used to prove the technical control and the design concept.

This study presents a new ‘cascaded flywheel energy storage system’ topology. The principles of the proposed structure are presented. Electromechanical behaviour of the system is derived base on the extension of the general formulation of the electric machines. Design considerations and criteria are discussed and a general procedure for designing of such energy storage system is developed. Typical machine is designed and an analogy between it and the conventional one is discussed. Comparison shows significant improvements in energy density and utility requirements of the proposed system in comparison to the conventional structure. Dynamic response of the designed machine is studied in various conditions as the stand-alone and also as the grid-connected system. Finally, a typical three-stage system is designed, prototyped and tested which shows a good agreement between an analytical and experimental analysis.

Winding insulation degradation may lead to phase-to-phase fault in switched reluctance machines (SRMs). First, the fault modes are described considering the connected sequence of the coils and the fault behaviours are analysed in details. Second, the equivalent circuit of three-phase windings is represented and the faulty SRM is modelled based on the derived electromechanical equations. Third, the locations of three current sensors are optimised to calculate the incoming line current and outgoing line current of each phase without utilisation of any extra hardware. The phase-to-phase fault can be detected and located by monitoring the residuals between the two line currents during motor operation. Forth, to improve the post-fault operation performance of the motor, a triple closed-loop control scheme aiming at suppressing the short-circuit current is conducted by modifying the switching states of power transistors. Finally, simulations and comparative experiments on a three-phase 12/8 structure SRM validate the effectiveness of the proposed methods.

Nowadays, after passing more than three decades from discovery of high-temperature superconductors, they are widely used in different fields including power industry. High-temperature superconducting (HTS) bearing is an electromagnetic machine that provides frictionless operation and intrinsic stability without requiring control equipment. Before entering to the fabrication stage, an accurate simulating model can satisfactorily reveal many of practical considerations. This work is based on the results of their previous study, delving into time steps of multi-physical simulations juxtaposing electromagnetic and thermal characteristics of an HTS bearing. This is attainable by using multi-physics analysis of radial HTS bearings based on a semi-analytical method called variational iteration method (VIM). This is accomplished by coupling of the Maxwell equations and thermal equilibrium. The electrical behaviour of the superconductor is described by means of a B–T-dependent modified E–J power-law relation. To verify VIM results, the multi-physics equations are also numerically solved using finite-element method. In this research, two case studies are examined; failure of the cryogenic system and incorporating new materials in the stator part of the bearing in order to improve the cooling efficiency.

Researches on active magnetic bearings (AMBs) are mainly based on equivalent magnetic circuit (EMC) method with the assumption that there is no magnetic saturation in magnetic circuit. However, this assumption about magnetic saturation is no longer valid for special solutions, such as aero-engines. In this case, limitations exist for the application of EMC method. This research focuses on an analytical bearing capacity model for AMBs based on a non-linear magnetic circuit method (NMCM) with magnetic saturation taken into account. First, the error factors of EMC method are analysed by using finite element analysis software when the air gap increased. Then, aiming at the main factors, including fringing flux, flux leakage and magnetic saturation, the air-gap magnetic flux model and the flux leakage model are developed based on the magnetic field division method. On this basis, a NMCM based on magnetic saturation is proposed to create the analytical bearing capacity model of AMBs. Additionally, the analytical model is verified by comparing with the results of finite element analysis and experiments. Eventually, the analytical model of hybrid magnetic bearing with single degree of freedom based on NMCM is verified by experiments.

Percussive-rotary drilling is an effective method for the hard rock drilling. As hydraulic and pneumatic hammers have many problems especially in the deep core drilling, a new electromagnetic hammer driven by a tube linear motor is introduced in this study. The study mainly covers the mechanical structure and electromagnetic design of the hammer, respectively. Due to the direct use of electric power, the electromagnetic hammer has the advantage of high efficiency while it must meet the minimal percussive energy requirement under the limitation of drill pipe diameter. In this study, the validity of electromagnetic design is verified through the finite-element analysis software Ansoft/Maxwell 2D and numerical calculation of electromagnetic force. The working temperature in deep down-hole is relatively high, the influence of high temperature in deep hole on the electromagnetic thrust of the linear motor is then analysed. A motion model of linear motor hammer is established to calculate and analyse the impact power and frequency under different conditions. The results show that the performance of linear motor hammer can reach or even exceed the one of same diameter hydraulic hammer, especially in the low-frequency range. The prototype test also confirms the validity of the design.

This study presents four-quadrant sensorless control in switched reluctance machine (SRM) drive for startup and low speed. The proposed control method is based on two special flux linkage-current characteristic curves which can be obtained expediently and quickly without the need of external mechanical fixtures. The narrow voltage pulse is injected into the idle phases by the power converter and the rotor position zone within an electrical cycle is determined by comparing the measured flux linkage with the two flux linkage-current curves. The judgment rules and flow-chart of rotor positions estimation are proposed to implement the four-quadrant operation in SRM drive. The effectiveness of the proposed sensorless technique is investigated through a series of experiments on a three-phase 12/8 pole SRM drive platform. The experimental results show that the four-quadrant sensorless control of SRM is implemented without the requirements of additional hardware circuit and complicated computation.

This study analyses the influence of the control parameters on the iron loss of the switched reluctance motor under different control modes by using the motor iron loss model which is suitable for different control modes. The motor iron loss model combines the magnetic equivalent circuit (MEC) method with the finite element (FE) method. First, the static flux density of the motor is obtained by the FE software, and then the relationship between the characteristics of static flux density and dynamic flux density is analysed through the MEC method. In combination with the motor dynamic MATLAB/Simulink model, the dynamic flux density of different feature regions is obtained. Simultaneously, the iron loss model of the motor is established in MATLAB/Simulink according to the loss model so that the motor loss can be calculated rapidly and accurately. Then, the influence of the control parameters on the motor loss is calculated and analysed under angle position control and current chopping control. The accuracy of the loss model and analysis results are verified by experiments.

Accurate brushless doubly fed induction machine (BDFIM) control is considered as a good alternative to traditional generators. Therefore, the knowledge of the parameters accuracy is necessary to design high-performance drives. In this study, an offline identification method to identify the BDFIM parameters is presented. This study investigates the input signal effects on the accuracy of the identified parameters. The similarity between BDFIM frequency model and the standard induction machine frequency model has been verified by comparing the step responses of the corresponding transfer functions. The obtained results would be a motivation for online identification techniques and BDFIM field-oriented control strategies. The proposed identification method has been validated by performing experimental results.

In many engineering applications, the coils of different geometrical shapes are used. Usually, these coils (circular, right etc.) are with the constant currents in different directions. In the literature, there are many papers on the calculations of the magnetic fields of the circular coils with the constant azimuthal currents or the calculations of the mutual inductance and the magnetic force between them. In some applications, where the high intensity magnetic fields are required the circular metal plates and insulating spacers are used with the inverse radial current. Such configurations form an electromagnet named after its inventor Bitter. In this study, the authors calculate the mutual inductance and the magnetic force between the thick Bitter coil of rectangular cross-section with the inverse radial current and the circular filamentary coil with the constant azimuthal current. The semi-analytical and the analytical expressions of these quantities are obtained over complete elliptic integrals of the first and second kind as well as Heuman's lambda function. There is one simple integral which has to be solved numerically. The results of this method are compared by those obtained by the modified filament method for the presented configuration. All results are in an excellent agreement.

A double stator linear-rotary permanent magnet motor, which has a long tuber ferromagnetic mover core with permanent magnets (PMs) arranged on its inner and outer surfaces, is proposed for two degree of freedom drive in this study. Due to the topology of the long tuber mover, the end-effects, including the interaction between the outer stator end and the mover, the effects of the inner PM length, and the interaction between the inner stator end and the mover, are presented and analysed. Based on the three-dimensional (3D) finite-element method, the influences of the end-effects on the electromagnetic characteristics, such as the flux distributions, flux density, electromagnetic force and torque, and output power, are investigated. Meanwhile, the topology with the minimised end-effects is given, and a prototype is built. The dynamic performances of the prototype are tested via a specific experimental platform. The results are in agreement with that of the 3D finite-element analysis.

To relieve the serious saturation in stator teeth of stator-permanent-magnet flux-switching (SPM-FS) machines due to the co-existence of magnets and armature windings in stator, this study proposes and analyses a novel rotor-permanent magnet flux-switching (RPM-FS) brushless machine. Different from the conventional SPM-FS machines, the magnets are removed from stator to rotor, and magnetised in a unique direction, resulting in a significant alleviation of stator tooth saturation level for the RPM-FS machines. The concentrated armature windings are still wound around stator teeth with an even shorter end-part winding length due to the absence of magnets. To evaluate the advantages and disadvantages of RPM-FS machines, a comprehensive comparison between a RPM-FS machine, a SPM-FS machine, and an interior permanent magnet machine used in Toyota-Prius 2004 hybrid electric vehicle, is conducted and the electromagnetic performances of three machines are investigated by finite element analysis. The predicted results indicate the proposed RPM-FS machine exhibits the largest power density, greatest torque capability, highest efficiency under rated operation, and improved flux-weakening ability. Therefore, the RPM-FS machine is a promising candidate for EV and hybrid electric vehicles applications especially for direct driven systems where the superior overloaded performance is crucial.

Development of power networks increases short circuit level and makes use of fault current limiters (FCLs) inevitably. FCLs should have low impedance in the normal condition of the network and high impedance quickly after the short circuit. For this purpose, a variable reactor has been proposed. In this scheme, the reactor impedance is dependent on the reactor air gap. In the normal condition, the reactor has a large air gap and has low impedance. When a fault occurs and the current increases immediately, a strong force is produced between the fixed and moving parts of the reactor and the air gap is decreased. This leads automatically to an increase in the reactor impedance. After the fault is cleaned, the reactor returns to its previous state by a spring and is recovered easily. An optimal design has been performed here to reach the FCL with desirable performance. To this end, analytical relations of the reactor are implemented and the optimum values are calculated by using genetic algorithm. The designed reactor has been simulated by the finite-element method to verify the analytical calculations. The results confirm the proposed scheme and indicate that the reactor limits the fault current very well.

The study proposes a non-isolated three-phase integrated battery charger (IBC) based on electric vehicle drivetrains that have two permanent magnet synchronous motors with shafts coupled via a torque coupler. The windings of both machines are used as input filter inductances after reconfiguration and connected to a three-phase grid in charging mode. Their existing traction inverters are operated as a three-phase charger that controls the charging power from the grid. The total torque produced on the shaft during operation is analysed and a strategy to eliminate it is proposed. The strategy not only maintains a zero-average torque but also eliminates the pulsating torque component on the shaft during operation. The topology allows conversion of the existing drive to an IBC through minor reconfiguration and provides an opportunity to reduce the effective THD injection into the grid via interleaving for machines with low winding inductance. A power balancing control is also proposed to reduce the second harmonic on the DC power output due to machine non-ideality. Simulation and experimental results validate that the topology can be used as both a battery charger and as a distributed resource, while the resultant torque on the shaft remains eliminated by the proposed strategy.

In this study, two simple methods for the steady-state analysis of self-excited induction generators (SEIGs) are proposed. These methods neither require lengthy mathematical derivations nor any advanced optimisation techniques to solve the equivalent circuit of SEIGs. First method involves a simple linear search algorithm and the second method employs a binary search algorithm to find the operating frequency at any given rotor speed, leading to the performance predetermination of SEIGs. To start the search techniques, a systematic approach has been formulated for fixing the boundary values required for the unknown pu frequency. The efficacy of the proposed methods has been demonstrated by presenting the predetermined performance characteristics of a three-phase, 230 V, four-pole, 50 Hz SEIG. The same SEIG was also tested in the laboratory using a DC motor as the prime mover. The closeness observed between the predetermined values and the experimental results further confirms the validity of the search algorithms. It has also been shown that the proposed methods can be extended with the same simplicity, for carrying out the performance predetermination of the short-shunt configuration of SEIGs, used for obtaining improved voltage regulation with lagging power factor loads.

Variable speed drives (VSDs)-based direct photovoltaic (PV) fed water pumping systems (WPS) are of increasing importance for the socio-economic growth in remote areas. Due to the absence of windings and magnets on the rotor, switched reluctance motor (SRM) is emerging as a viable economic alternative in VSD systems. Thus, this study proposes and presents a simplified pulse width modulation-based maximum power point tracking (MPPT) control for direct PV-fed SRM-WPS using modified lookup table (MLUT) approach. The proposed control technique offers lesser phase peak, near same phase rms, reduced torque ripple and noise, better efficiency and reduced DC-link current ripple in contrast to single pulse mode technique. In addition, the proposed system does not require an intermediate converter and current sensors. Thus, results in reduced noise, reduced size and hence the cost of WPS. Further, it also provides a reduced memory size due to MLUT and an effective MPPT with the good dynamic response for a change in atmospheric conditions. The proposed system is modelled and simulated in MATLAB/Simulink environment and the prototype is built to validate experimentally using field programmable gate array controller. The performance analysis of the proposed system has been carried out and presented.

This study proposes a new configuration for line start permanent magnet (PM) motors with low consumption of PM material, providing improved performance. The configuration is developed by analysing PM flux density distribution in the machine airgap and focusing on the d-axis armature reaction flux path and also different magnetisation types in the PM poles. It features double flux barriers for each rotor pole to facilitate near sinusoidal flux density distribution. Main characteristics of a motor with the proposed configuration are analysed by finite element method (FEM) and compared with the characteristics of a motor with the conventional configuration. Finally, the motor is built and tested. The FEM and experimental results verify the advantages of the proposed configuration. The results show that the required PM material reduces by one-third, while desirable performance is provided. The machine is capable of working with delta connection causing negligible circulating current and low torque ripples.

This study describes a technique to determine the core loss in different parts of an induction motor (IM) for any types of electric power supply. To calculate the core loss, flux density waveforms are determined in different parts of the motor. Different forms of Steinmetz equation are used for the core-loss calculation. The coefficients of these Steinmetz equations are determined using the loss data given by the electrical steel manufacturer. Since, the manufacturer data are available for a limited number of frequencies; a curve fitting technique is used here to determine the loss data at required frequency. The proposed technique is tested on an IM with sinusoidal excitation for different load torques and with sine pulse-width modulation inverter supply at different switching frequencies. The core loss obtained from with this technique is also compared with other techniques reported in the literature. A good accuracy is obtained between the measured and calculated core loss using proposed technique comparing to other techniques.