This study proposes a novel rotor position estimation method for wound-rotor synchronous starter/generator (WSSG). At the starting stage, WSSG needs a resolver to obtain the main machine's (MM's) rotor position. However, the use of resolver increases starting system's complexity, volume, weight and cost. In order to solve this problem, a novel kind of MM's rotor position estimation method is proposed, which considers the structure of WSSG as a resolver. The novel method injects a rotating voltage into MM's stator, detects main exciter's stator current and subsequently processes the current signals to estimate MM's rotor position. Experimental results show that the novel method can estimate rotor position accurately, which are in good agreement with the theoretical analyses and simulation results. Compared to the saliency tracking rotor position estimation method, the novel method does not rely on WSSG's parameters (including MM's saliency), and the signal processing procedures are more simple.

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.

This study presents a low-cost switched reluctance machine (SRM) drive system with reduced current sensors and position sensors. The reduction of current sensors is achieved by rearranging the location of adopted sensors, and each phase current is calculated by decomposing the current from two special positions. The reduction of position sensors is realised by optimising conventional slotted disc. Being different from the conventional three-phase 12/8 SRM drive system, the developed low-cost system only requires two current sensors and one position sensor. First, the proposed phase current detection method is illustrated in details. Second, the measures to solve the three key problems in rotor position sensing strategy are represented considering the forward and reverse direction of SRM. Third, the reliability function and the mean time to failure indicators are compared between the conventional and proposed methods. Finally, the effectiveness of the proposed methods is experimentally validated on a three-phase 12/8 SRM drive. The proposed low-cost system is easily extended to the widely used four-phase 8/6 SRM system. Moreover, the proposed strategies for the low-cost SRM drive system are not relying on the analytical motor model and easy for online implementation without additional hardware.

Wound-rotor synchronous starter-generator (WRSSG) has the advantages of less volume and weight, high safety and low cost in maintenance, so it is becoming increasingly popular in modern aircraft, especially for more-electric aircraft. The main machine (MM) and main exciter (ME) of the aircraft WRSSG are electromechanically coupled seriously, which makes the start control for the WRSSG complex in the starting mode. In this study, a decoupling start control method for aircraft WRSSG based on main field current estimation is proposed to solve the serious coupling problem and improve start control performance. In the proposed decoupling control method, the main field current is estimated first and used in the closed-loop excitation control for the ME to make the main field current meet the MM demand. With the desired field current, the MM is decoupled with the ME and controlled like a traditional synchronous motor to start the aircraft engine under maximum torque per ampere. The feasibility and effectiveness of the proposed decoupling control method is verified by experimental results.

The multiphase synchronous generator-rectifier system could provide an ideal DC power source for more electric aircraft (MEA). When the inter-turn short-circuit fault occurs in phase windings of the generator, a large short-circuit current would be introduced inside the armature windings, which could cause severe damages to the system for overheat in the windings and irons as well as huge electromagnetic forces on the end coils. To improve the reliability of the MEA, this study researches on the inter-turn fault of the multiphase generator-rectifier system including the theoretical analysis, numerical simulation and experiment verification. A 12-phase system is taken, for example, and a multi-loop mathematical model is built up to calculate all voltages and currents in the multiphase synchronous generator-rectifier system with armature inter-turn fault. Many factors are thoroughly considered in the model including the location and short turns of fault, space harmonics of the air-gap magnetic field and the changing circuit topology of the system. Moreover, the mathematical model is verified by fault experiment results. Moreover, the electric characteristics of the fault are summarised, which could provide a quantitative basis for early detection of the inter-turn faults in the multiphase generator-rectifier system.

This paper proposes a drive circuit for single-phase brushless direct current (BLDC) fan motors to reduce their acoustic noise. First, the torque ripple of a single-phase BLDC motor is analysed theoretically. Then, a drive circuit that is capable of regulating the DC-link voltage during commutation to weaken the negative effect of current lag is proposed to reduce the acoustic noise of single-phase BLDC fan motors. Furthermore, the characteristics of the proposed drive circuit are discussed theoretically using a deduced analytical model of the proposed drive circuit. Additionally, simulations based on the finite element method and experiments are performed. The torque ripple and acoustic noise generated by the conventional and proposed drive circuits are compared. The simulation results show that the torque ripple is reduced by 16.1% when the proposed drive circuit is used, and the experimental results illustrate that the acoustic noise generated by the second harmonic of the torque ripple is reduced by 7.3%. Ultimately, the effectiveness of the proposed drive circuit is verified.

Mathematical modelling is a fundamental issue in the condition monitoring and fault diagnosis of electrical machines. This study presents a multiple coupled circuit approach for the modelling of squirrel cage induction machines (SCIMs) with a single broken bar. Derived by means of winding function, the model is capable of incorporating all the harmonics of air-gap magnetomotive force and describing transient machine behaviours. A d–q reference frame fixed on rotor is introduced. Each stator winding function is decomposed into two parts, a q-axis and a d-axis component, both of which induce currents in each rotor mesh. The q-axis and d-axis equivalent circuits are developed for both healthy and faulty cage rotors. It is also shown that a single-broken-bar fault does not affect the q-axis rotor mesh current distribution. The d-axis equivalent circuit for healthy cage rotor is modified further to determine the deviations in the mesh currents due to bar breakage. A detailed model of a 2.2 kW, four-pole, three-phase, 28-rotor-bar SCIM is implemented in MATLAB/Simulink environment, and a laboratory test bed is set up for this machine. A comparison between the simulation and experimental results verifies the effectiveness of the proposed modelling approach.

This paper deals with the modelling of magnetic saturation in induction motors (IMs) with particular focus on the equivalent or fictitious air-gap permeance technique. Besides, an improved version of this technique is provided so as to account for the transient starting process and the third harmonic saturation factor in addition to the fundamental one. This is for the symmetric case. Under air-gap eccentricities, extension of both saturation models is proposed using the varying saturation factor solution. The 2D-modified winding function approach (2D-MWFA) is the base of the inductance calculation and the state equations are derived from the well-known multiple coupled circuit model (MCCM). Thanks to such considerations, skew effect, rise of the magneto-motive force (MMF) across the slots, all winding harmonics, and many faulty states can be judiciously taken into account. In summary, five derived saturation models are discussed in favour of a good handling of the saturation phenomenon in cage IMs. The work is supported by extensive simulation and experimental results of eccentricity, broken rotor bar, and combined faults.

Deformation of the windings is one of the main causes of the power transformers failure. Here, for the first time, the electromagnetic forces exerted on the windings are computed in ferroresonance condition and compared with that of the inrush current for a typical power transformer. In both cases, the magnetic core of the transformer saturates and the leakage flux around the windings increases, which leads to large forces on the windings carrying high currents. Therefore, precise modelling of the transformer core is required to calculate the forces inside the transformer. For this purpose, the Jiles–Atherton vector hysteresis model is employed in conjunction with finite element method (FEM) to simulate the laminated grain-oriented steel core, and then the radial and axial forces inflicted on the windings are estimated.

This paper proposes a transverse flux machine which has the topology of flux-concentrating and passive rotor, and also conducts a design and optimisation for machine. With working process of the machine introduced, its topology structure and composition are introduced. The optimisation objectives and design parameters are obtained with analysis. Furthermore, the performance equations are deduced to determine the parameters which affect performance. Ten free parameters should be optimised and the number of pole pair is first optimised with preliminary simulation. Subsequently, Taguchi method is applied to reduce the number of free parameters, and four parameters are selected to be further optimised. Three approximation models are created, and the Kriging model is better to predict the simulation results, thereby substitute the simulation to be used to algorithm. Accordingly, NSGA-II and MOPSO are used to acquire the optimal design for the machine, and the best solution of algorithm is determined by the simulation based on the results from the two algorithms. Finally, the prototype experiment is conducted to verify the optimisation method and simulation. The whole optimisation process for design and optimisation of electrical machine which is timesaving in comparison with optimisation with only simulation can provide the reference for electrical machine's design.

This work enhances the knowledge of the diagnostic potential of the broken bar fault in induction motors. Since a series of studies have been published over the years regarding condition monitoring and fault diagnostics of these machines, it is essential to reach a common ground on why – sometimes – different techniques render different results. In this context, an investigation is provided with regards to the optimal window that should be adopted for the implementation of a proper time–frequency analysis of the monitored signals. On this agenda, this study attempts to set lower and upper bound limits for proper windowing from the digital signal processing point of view. This is done by proposing a formula for the lower limit, which is derived according to the specific frequencies one desires to put under inspection and which are the fault-related signatures. Finally, a discussion on the upper bound is put onwards; results from finite-element simulations are examined with the discussed approach in both the transient regime and the steady state, while experimental results verify the simulations with satisfying accuracy.

This study addresses an optimisation method for interior permanent magnet synchronous generators (IPMSGs) to improve the efficiency of the electric power generating system of a range-extended electric vehicle. The target operating point of the IPMSG is specified with an optimal operating line (OOL) of the newly developed two-cylinder engine. The performance and efficiency of the IPMSG throughout the OOL are numerically identified in association with finite element analysis (FEA). For optimal design, intelligent mesh adaptive direct search with clustering and elastic net, which has been validated as a global searching optimisation algorithm with fast convergence on electric machines, is applied for IPMSG to maximise efficiency based on FEA. Furthermore, the optimised prototype is experimentally validated via the resultant efficiency map built up by the static and dynamic dynamometer tests.

The electromagnetic noise of an axial-flux in-wheel motor (AFWM) is reduced by combining various pole-arc coefficients and circumferential shifting of permanent magnets (PMs) here. First, the analytical model of the air-gap magnetic field for the AFWM with various pole-arc coefficients and circumferential shifting of PMs is established. The influence of edging effect and stator slotting is taken into account through the radial correction function and complex relative permeance function, respectively. Subsequently, the torque and electromagnetic noise of the AFWM are derived analytically. A multi-objective optimisation of the AFWM is then implemented by the NSGA-II (non-dominated sorting genetic algorithm) based on the proposed analytical approach. Finally, the electromagnetic performance and vibroacoustic characteristics of the initial and optimised motors are compared and analysed. The results show that the proposed method by combining various pole-arc coefficients and circumferential shifting of PMs can reduce the noise of axial-flux motors effectively, without sacrificing the output torque. This study is of great significance for the vibration and noise reduction of axial-flux motors.

This study investigates direct voltage control of stand-alone doubly-fed induction generator (DFIG) system subject to asymmetric loads. An improved voltage regulator is designed based on non-singular terminal sliding mode control and an improved extended state observer (ESO). Due to the salient features of the improved ESO, the rotor current transducer is not required and the sinusoidal fluctuation in the sliding surface caused by asymmetric loads is eliminated. As a result, satisfactory balanced stator voltage can be generated under asymmetric loads. The proposed method is characterised by the rapid dynamic response and the elimination of sequence decomposition operations. Finally, the proposed method is applied to a 6 kW DFIG-based hardware system under various loads and varying speed conditions. Both simulation and experiment results are given to validate the effectiveness and robustness of the proposed method for stand-alone DFIG system.

This paper presents a reduced-switch motor drive system, which is made up of a single-phase half-bridge rectifier circuit, ripple power decoupling unit, three-phase inverter circuit, and three-phase motor. Due to the ripple power decoupling unit, the DC-bus of drive system could also provide DC power supply for other DC loads. The ripple power decoupling unit almost shares all components with rectifier and inverter circuit, so this is a low-cost solution. Considering the strong coupling of all kind of components in the system, a hybrid model predictive control (MPC) is introduced to coordinate the operation of the decoupling circuit, rectifier, and inverter circuits. The effectiveness of this scheme is verified with the experimental results.

This study proposes an adaptive soft starter control for induction motors using a multifunctional series compensator (MFSC). The proposed MFSC can operate in two modes: (i) the compensation mode for voltage sags and (ii) the virtual impedance mode for soft starting. Various MFSC functions are obtained by controlling the output characteristics of the series inverter. In the voltage sag compensation mode, a voltage is injected in series with the fault phase; as a result, the terminal voltage of the motor remains constant. In the soft-starter mode, the proposed converter injects adjustable virtual impedance in each phase; as a result, the starting current can be limited to the desired value. A novel control scheme and the optimal parameter selection of the MFSC are also presented. The design methodology of the proposed MFSC is verified using simulations conducted in MATLAB/Simulink software. Experimental results prove the capability and effectiveness of the proposed MFSC.

Short moving primary and rigid low-cost secondary are important requirements of linear machines designed for long stroke applications. In the race, linear permanent magnet flux switching machine (LPMFSM) is a competitive candidate by confining excitation sources to short mover, thus making stator robust and low cost (made of only iron). However, single-sided LPMFSM exhibit a demerit of high normal (attraction) force due to its topology. In order to rectify the problem and enhance thrust force profile, two novel double-sided LPMFSMs are proposed with dual stator and dual mover topologies. After stator pole study, both topologies with same design dimensions are analysed and compared by 2-D finite element method here. Detailed analysis revealed that 12/14 DMLPMFSM exhibit low numerical values of thrust force ripples and detent force while maintaining average thrust force value. Hence, 12/14 DMLPMFSM is selected and optimised by structure-based deterministic optimisation (SBDO) approach to further enhance thrust force profile. Finally, comparison of initial and optimised design of 12/14 DMLPMFSM is presented to validate optimisation procedure.

In this study, an initial rotor position estimation at standstill condition is presented for reliable operation of switched reluctance motor (SRM) without initialising machine parameters for light electric vehicle (LEV) applications. The prime objective of this method is to startup an SRM without using the mechanical position sensor, and eliminate the starting hesitation and starting jerk issues from standstill condition. In the proposed method, the initial rotor position at standstill is determined by injecting a single pulse dc voltage simultaneously into all stator phase windings for a very short period (microsecond). The obtained current envelope data is then used to calculate the initial rotor position with the quadratic polynomial interpolation technique without any prior knowledge of other motor parameters. The experimental results for a 3.5 kW, 6/4 SRM are provided to substantiate the overall good performance. The developed system can be considered as a strong candidate for high precision LEV applications.

In recent years, ultra-wideband (UWB) systems have been proposed for online monitoring of power transformers. This study aims at a new UWB-based method to determine the axial displacement (AD) extent in the transformer high-voltage (HV) winding. In the proposed design, two receiving antennas and one transmitting antenna are used. Two receiving antennas receive signals at two different positions due to axial displacement occurrence, and the displacement extent is determined using an analytical method known as hyperbolic method, which is based on signals time difference of arrival. The proposed method is initially studied by simulations using computer simulation technology software. Finally, the experimental results show the effectiveness of the proposed method to detect the AD extent in an actual transformer winding.

Although the antilock braking system (ABS) has been commonly used in electric vehicles (EVs), most of the vehicles still use the traditional hydraulic-based disc brake in which the driving and the braking systems are two individual modules. A novel integrated driving and braking control system with an ABS for EVs was developed, and an electric scooter was used as the experimental object. While braking, the motor acts as a generator. The autonomously generated inertial energy was used to generate a reverse magnetic braking torque and realise an antilock braking control with fast response. Compared with the existing regenerative and short-circuit braking methods, the proposed method uses back electromotive force to yield a reverse magnetic braking torque in a sophisticated manner. In the proposed method, a capacitor-aided regenerative braking strategy was used in an antilock braking controller. For the ABS control design, the slip ratio was maintained within an optimal range for obtaining the best tyre–road surface adhesion using a fuzzy slip ratio controller to prevent the wheel from skidding during emergency braking. For real-world verification, the electric scooter was subjected to various on-road tests to examine the performance of the proposed method.

This study proposes an integration design of sensorless closed-loop drives for rail transit application employing interior permanent magnet synchronous machine (IPMSM), which works under low switching frequency. Due to the long signal sampling period in high-speed region, the individual back-EMF observer cannot ensure the sensorless closed-loop control stability. In order to increase the speed dynamic response and decouple the d–q axes currents accurately, a fast non-singular terminal sliding mode control is designed. It combines a linear sliding mode factor with conventional non-singular terminal sliding mode and is applied uniformly to position observer, speed and currents regulators. Then, considering the effect of inverter non-linearity on position observer, the observed position error caused by dead-time is analysed, and a compensation method based on q-axis voltage error is proposed. Based on the above methods, a comparison analysis of position observer, speed and currents regulators is given. Finally, a 3.7 kW IPMSM is tested to verify the feasibility of the improved sensorless method.

A detailed analysis is presented for the inductance calculations of rectangular coils with parallel end faces, with the coils of parallel sides as the special case. Integral solutions are given by the theory of second-order scalar potential. The authors further provide the series solutions for the inductance, which are based on the truncated region eigenfunction expansion method. These series are quite concise and accurate, and with higher computational efficiency by comparison with the integrals. The integral and series solutions are also obtained for the planar rectangular coils. The numerical results of both methods are compared with those of the experimental data, and the proposed methods prove to be accurate and efficient enough for practical applications.

The operation of an interior permanent magnet synchronous motor included in an electric power steering system is related to two demanding requirements: (i) the low-voltage DC source pushes the motor to a deep flux weakening region, and (ii) the motor is so optimised that it can withstand only few cycles at nominal torque. Owing to that, maximum torque per ampere (MTPA) and maximum torque per volt (MTPV) current reference generation strategies are common in this type of application. Most of the published MTPA or MTPV strategies are applied to standard voltage motors, so stator resistance is typically neglected, leading to simpler equations. Other works consider the stator resistance but, as the resulting equations are complex, look-up tables or numerically adjusted polynomials are employed in current generation tasks. This work presents analytical expressions allowing the exact computing of current references. These expressions include stator resistances. The battery voltage is considered as an input variable, together with motor speed and reference torque, and direct and quadrature current references are the output variables. Contrary to look-up tables or numerically adjusted polynomials, the proposed expressions can take into account any parameter variation during real-time operation. Simulation and experimental results validate the proposed approach.

A modified explicit torque control (ETC) scheme for permanent magnet (PM) machine with non-sinusoidal back emf is investigated in this article. The conventional ETC scheme for the PM machines with non-sinusoidal back emf furnishes a wide band for the switching frequency and offers a faster response in the torque. In this article, a modified scheme for switching vector selection is proposed to reduce the switching frequency while maintaining the advantage of faster torque response. Other than the conventional two-phase excitation, which uses opposite vectors for switching to get the speedier response in torque, the modifications proposed for the ETC of PM machine are (i) a closer vector selection from the available two-phase vector plane and (ii) a combination of two phase and three phase excitation. Both these modifications gives a faster response in the torque as that of conventional ETC, while this offers a reduction in the switching frequency. Switching frequency variations are expressed mathematically, and experimental results are presented for the modified schemes of ETC and for the conventional ETC based to validate the proposed scheme.

Rotational systems such as aircraft engine drivetrains are subject to vibrations that can damage shafts. Torsional vibrations in drivetrains can be excited by the connection of loads to the generator due to electromechanical interaction. This problem is particularly relevant in new aircraft because the drivetrain is flexible and the electrical power system (EPS) load is high. To extend the lifespan of the aircraft engine, the electromechanical interaction must be considered. Since real-time constants of the electrical and mechanical systems have very different magnitudes, the simulation time can be high. Furthermore, highly detailed models of the electrical system have unnecessary complexity for the study of electromechanical interactions. For these reasons, modelling using reduced order systems is fundamental. Past studies of electromechanical interaction in aircraft engines developed models that allow the analysis of the torsional vibration, but these are difficult to implement. In this study, a reduced order electromechanical interaction system for aircraft applications is proposed and validated using experimental results. The proposed system uses a reduced drivetrain, simplified EPS, and sensorless measurement of the vibrations. The excitation of torsional vibrations obtained is compared with past studies to prove that the reduced order system is valid for studying the electromechanical interactions.