Z.Q. Zhu

• The University of Sheffield

These days, as the application of permanent magnet synchronous machines (PMSMs) and drive systems becomes popular, the reliability issue of PMSMs gains more and more attention. To improve the reliability of PMSMs, fault detection is one of the practical techniques that enables the early interference and mitigation of the faults and subsequently red...

This paper introduces a novel interior permanent magnet synchronous machine (IPMSM) using a parallel configuration of hybrid rare-earth and ferrite permanent magnets (HPMs) and V-shape arrangement of spokes. Aiming at the same torque with lower volume of rare-earth PMs (REPMs) than a double V-shape IPMSM for EV application, the proposed parallel HP...

This paper investigates the mechanism of asymmetric permanent magnet (PM) eddy current loss and temperature distributions of surface-mounted PM synchronous machines (SPMSMs) with different slot/pole number combinations for the first time. A finite element analysis (FEA) based harmonic restoration method is utilized to evaluate and quantify contribu...

This paper investigates the torque contributions of stator and rotor permanent magnets (PMs) in multi-tooth dualPM machines accounting for stator/rotor pole number combinations. The influences of different total PM volume constraints during optimisation, armature pole number, split tooth number, and key parameters are also considered. It is found t...

This paper presents a high-fidelity lumped-parameter (LP) thermal model (HF-LPTM) for permanent magnet synchronous machines (PMSMs) in electric vehicle (EV) applications, where various cooling techniques are considered, including frame forced air/liquid cooling, oil jet cooling for end-winding, and rotor shaft cooling. To address the temperature mi...

This paper investigates the contributions of stator slot permanent magnets (PMs) in multi-tooth dual-PM machines with different stator/rotor pole number combinations. Different stator configurations with and without stator slot PMs are analyzed and compared considering different rotor pole numbers and split tooth numbers. It is found by analytical...

In this paper, novel virtual signal injection methods are proposed for full-parameter estimation of surface-mounted permanent magnet (PM) synchronous machines (SPMSMs) under sensorless control, including virtual resistance, virtual inductance, virtual voltage/current, virtual back-EMF, and virtual flux-linkage. When a positive and a negative virtua...

This paper proposes a high-accuracy lumped-parameter (LP) thermal modelling method to predict maximum winding temperatures and the asymmetric winding temperature distributions under short-circuit (SC) fault conditions for fractional-slot concentrate slot (FSCW) permanent magnet synchronous machines (PMSMs). It is the first time to consider the non-...

Radial-flux fractional slot concentrated winding (FSCW) yokeless counter-rotating dual-rotor permanent magnet (YCDRPM) machines are proposed and investigated in this paper. Counter-rotating operation is required for special applications, such as washing machines, counter-rotating wind power generators, and underwater vehicles. The YCDRPM machine in...

This paper compares the electromagnetic performances of radial-flux, dual-rotor, permanent magnet (DRPM) machines with series (S) and parallel (P) magnetic circuits for two rotors, i.e., SDRPM and PDRPM, accounting for different slot/pole number combinations, stator winding configurations, and machine sizes. The machines are optimized using the fin...

Nowadays, as the application of permanent magnet synchronous machines (PMSMs) and drive systems becomes popular, the reliability issue of PMSMs gains more and more attention. To improve the reliability of PMSMs, fault detection is one of the practical techniques, which enables early interference and mitigation to the faults, and subsequently reduce...

This paper proposes a novel approach to predict the maximum permanent magnet (PM) temperature for surface-mounted PM synchronous machines (SPMSMs). By using the 3-D conduction heat transfer equation, a generic correlation between average and maximum PM temperatures is analytically derived for the first time. It depends on the basic geometric/therma...

This paper investigates a new ventilation cooling technology for modular permanent magnet (PM) machines. Air is pumped into the stator flux gaps and rotor ducts. A significant temperature reduction for the modular machines can be observed by introducing ventilated air. The flux gaps within the modular machines provide extra coolant path, notably mo...

The 150 $^\circ $ mode 12-step control (150-TSC) is suitable for high-speed drives since it can generate a quasi-sinusoidal current waveform compared with the conventional 120 $^\circ $ mode six-step control. However, for high-speed brushless direct current drives, the relatively large commutation angle of 150-TSC will cause a noticeable phase de...

The longitudinal end effect of permanent magnet linear synchronous machines (PMLSMs) induces parameter asymmetry, imparting time-varying and nonlinear characteristics to the machine model. In parameter estimation, parameter asymmetry introduces additional estimated parameters and results in nonlinearity and coupling among the parameters. To enhance...

This paper investigates the interaction effects of permanent magnet (PM) tolerances and rotor eccentricities of 12-slot/10-pole PM machines by finite element method (FEM) and phasor analysis. It is found that the relative location between diversified PMs and eccentric rotor have a significant effect on cogging torque. (a) When a weak (e.g., thin th...

This paper investigates the ability for elimination of unwanted magneto-motive force (MMF) harmonics in fractional slot dual m -phase single-layer PM machines. By doubling the number of slots and applying stator shifting, the 1st order and one unwanted higher order winding MMF harmonic can be suppressed. Then, through the addition of a second con...

This paper proposes a novel magnetization state (MS) control method to eliminate the unintentional demagnetization (UD) of low-coercive force permanent magnet (PM) for variable flux memory machine (VFMM). In the proposed method, the amplitude of demagnetization d -axis current pulse is determined from a look-up table with the relationship between...

This paper proposes a simple inductance asymmetry compensation method for minimizing the second-order harmonic current responses and the corresponding position errors in high frequency signal injection sensorless controlled dual three-phase interior permanent magnet synchronous machines (IPMSMs). It is found that the second-order harmonics of HF cu...

A Taguchi‐based robust design strategy is proposed to minimise the torque ripple of a 6‐slot/2‐pole modular high‐speed permanent magnet motor in mass production, accounting for manufacturing tolerances of split gap (Δg), misalignment (Δm), and offset angle (Δα). Firstly, the effects and interactions of manufacturing tolerances are calculated, indic...

This paper investigates the benefits and challenges of the multi‐MW direct‐drive offshore wind Vernier generators. It is worth noting that the comparison of generator topologies presented in ref. [1] was for the same power level and therefore a reduced machine volume for the surface‐mounted permanent magnet Vernier (SPM‐V) generators. This would ma...

Finite control set model predictive current control has fast dynamics and is simple to implement. However, it requires accurate machine parameters for the current prediction, any parameter mismatch will cause a current prediction error resulting in deteriorated control performance. Particularly, PM flux-linkage is commonly required by the predictio...

This paper proposes a novel analytical fault model for permanent magnet machines with inter-turn short-circuits that considers the influence of various factors on the fault current. These factors include (1) mutual inductances between the faulted turns and the remaining healthy windings (faulted and healthy phases), (2) load current, and (3) PWM ha...

This paper investigates the use of fractional-slot concentrated windings (FSCWs) in large-scale (MW level) offshore wind generators. It focuses specifically on a power rating of 3 MW and uses an existing direct-drive synchronous PM machine (DD-SPM) with 480s/160p and dual three-phase integer-slot winding (ISW) as a baseline. A multiple of the commo...

This paper proposes an improved position-offset based parameter estimation (POPE) method for permanent magnet synchronous machines. In the proposed method, dq -axis inductances and permanent magnet flux linkage can be estimated simultaneously based on three machine states corresponding to injections of zero, positive, and negative position offset...

In this paper, a novel magnetization state (MS) control method is proposed by utilizing torque deviation to achieve the MS closed-loop control for variable flux memory machine. Firstly, the relationship between the MSs and the demand magnetizing current pulses is built into a look-up table, which also contains information on the flux linkages and t...

This paper compares the electromagnetic performance of 6-slot/2-pole slotted high-speed permanent magnet (HSPM) motors with toroidal and tooth-coil windings. Both HSPM motors are optimized for maximum torque by analytical and finite element (FE) methods considering maximum winding temperature allowance. It is found that under the stator loss and th...

This paper proposes an analytical multi-element thermal modelling method for predicting the sleeve and magnet thermal fields for high-speed permanent magnet machines (HSPMMs). The analytical model is developed based on the conduction heat equations and the continuity equations of heat transfer. The rotor temperature distributions and hotspots can b...

The authors investigate a semi‐flooded cooling technology for modular permanent magnet machines using flux gaps (FGs) in alternate stator teeth for extra cooling channels. The investigated machine is separated into stationary and rotational components by a polyether ether ketone sleeve. Liquid is directed into the stationary component to achieve a...

In this paper, the electromagnetic performance of variable flux memory (VFM) machines with series-magnetic-circuit is investigated and compared for different rotor topologies. Based on a V-type VFM machine, five topologies with different interior permanent magnet (IPM) arrangements are evolved and optimized under same constrains. Based on two-dimen...

Uncertainty is a key issue in thermal analysis and management for permanent magnet (PM) synchronous machines (PMSMs) and always occurs in both conduction and convection heat transfers. However, this issue has not been evaluated thoroughly, especially for outer rotor PMSMs. Therefore, this paper presents a comprehensive sensitivity analysis with unc...

In this paper, a novel pulse-width-modulation (PWM) strategy to operate in overmodulation range with low switching-to-fundamental frequency ratio is developed for permanent magnet synchronous machine drives based on a two-level voltage source inverter (VSI). The proposed strategy is able to operate at low switching-to-fundamental frequency ratio an...

This paper presents a novel method for addressing the challenge of dq -transformation in fractional-slot machines with star-delta connected concentrated windings. These machines have no neutral point, preventing direct measurement of mutual inductance between phases. This complicates the calculation of d - and q -axis inductances, which are c...

This paper systematically investigates the effect of multi-tooth numbers on electromagnetic performances of conventional and consequent-pole (CP) vernier permanent magnet (PM) synchronous machines (VPMSMs), including average torque, overload torque capability, PM utilization, loss, efficiency, and power factor, etc. In particular, the influence of...

The applications of real-time thermal models (RTTMs) to sensorless temperature monitoring are limited due to unknown initial temperatures. To address this issue, this paper proposes a method to determine initial temperatures for all main components, only relying on one thermal sensor installed in a specific component, ideally in the active or end w...

In this paper, the generic relationship between the average and maximum stator slot winding temperatures in electrical machines is analytically revealed for the first time. It is shown that the difference between average and maximum temperatures can be presented by the product of copper loss with a function related to basic winding geometric and th...

This paper presents a general rule for the design of m-phase machines supplied by n-converters that employ a hybrid star-polygonal winding in each m-phase set. This rule shows that for any m-phase machine supplied by n-converters, there exists a set of feasible slot-pole numbers in conjunction with the star-polygonal connection that allows for opti...

This paper proposes a novel magnetization state (MS) control method for a hybrid magnet memory machine (HMMM) based on modified voltage limitation. The effect of the voltage limitation on the MS manipulation is analyzed. The circumcircle of voltage vector hexagon is utilized as the modified voltage limitation instead of the inscribed circle to simp...

The unipolar end flux leakage of dual-permanent magnet (PM) consequent-pole (CP) vernier machines is investigated in this article. The relationship between the stator and rotor pole number combinations and significances of unipolar end flux leakages generated by stator PMs and rotor PMs is revealed for the first time. It is found that the unipolar...

This paper investigates the influence of randomly distributed additional air gaps (AAGs) between stator teeth and back-iron on cogging torque in 12-slot/10-pole modular permanent magnet machines by using Taguchi method. It has been observed that with uniform AAGs, a maximum cogging torque exists, while non-uniform AAGs significantly affect cogging...

Lumped-parameter thermal models (LPTMs) have been widely used for thermal analysis and management in various electromagnetic devices and systems, e.g., electrical machines and power electronic modules. However, the existing LPTMs suffer from significant temperature misestimation issues due to assumptions of independent and uniform heat flows and/or...

The novel lumped-parameter thermal models (LPTMs) have been developed for a general cuboidal component in Part I. In this paper (Part II), the proposed thermal modelling method is developed for general cylindrical components in all 1-D directions, 2-D planes, and the 3-D solid. By introducing two compensation thermal resistances, both average and m...

This paper presents a comparative analysis of electromagnetic performance of radial flux dual-rotor surface-mounted permanent magnet (SPM) machines with fractional slot non-overlapping windings, with reference to external- and internal-rotor SPM machines. All machines are optimised by genetic algorithm using finite element analysis under various de...

This paper focuses on torque maximization of electrically excited (EE) machines considering variable stator/rotor copper loss ratio (SRCLR) in design optimization. Firstly, two EE machines are optimized with SRCLR fixed to 1 (EE1) and variable SRCLR (EE2) based on a baseline interior permanent magnet (IPM) machine, which proves that an optimal SRCL...

Pulse width modulation (PWM) effect plays a critical role not only in permanent magnet (PM) loss but also in PM temperature distribution. This paper proposes an analytical method to fast predict transient PM temperature distributions in surface-mounted PM synchronous machines (SPMSMs) accounting for the PWM effect. The proposed method is obtained b...

This paper proposes a novel model-based Luenberger state observer for interturn short-circuit (ITSC) fault diagnostics. The residuals between the observed currents and the measured currents in the α- and β-axes serve as fault indicator, which can be used to detect ITSC faults not only at an early stage with contact resistance but also at the fully...

This paper firstly investigates unipolar end leakage flux of consequent pole (CP) permanent magnet machines (PMMs) with different slot-pole number combinations and winding configurations. It shows that unipolar end leakage flux, mainly due to CP rotor, is affected by slot-pole number combinations, while the armature reaction has negligible effect o...

Electrical machines equipped with fractional slot concentrated windings (FSCW) have shown great promise at low power levels to improve the electromagnetic performance of PM machines. Principally, they offer shorter end windings, greater manufacturing simplicity, and improved fault tolerance than distributed windings. At high power level, for exampl...

Rotor position error under sensorless control will lead to parameter identification errors of surface-mounted permanent magnet (PM) synchronous machines (SPMSMs). In this article, a novel signal injection method is proposed for the first time, i.e., two additional virtual back-electromotive forces (EMFs) with equal amplitudes as perturbation signal...

High-order lumped-parameter thermal models (LPTMs) can be used to predict spatial temperature distribution and hot spot temperatures for critical components and account for spatial temperature variations in medium- to large-sized electrical machines. However, all existing high-order LPTMs require over-discretisation levels to reduce estimation erro...

To eliminate the influence of parameter mismatches and inverter nonlinearity on fundamental model based sensorless control, a novel virtual Extended-EMF injection-based position error adaptive correction method is proposed for interior permanent magnet synchronous machines in this paper. Specifically, when square wave virtual Extended-EMF is inject...

Compared with conventional non-modular machines, the flux gaps in alternate stator teeth of the modular machines can increase the winding factor and provide flux focusing effect, and hence can increase the torque/power density. In addition, the flux gaps can also be used as cooling channels to improve the thermal performance. This paper investigate...

A general analytical model is developed in a concise block matrix form for surface‐mounted permanent magnet (SPM) machines with series‐parallel coil connections under inter‐turn short circuit (ITSC) fault. In the model, branch currents are used as state variables and inductances of different series‐parallel coil connections are calculated using an...

This paper presents coupled electromagnetic (EM)–thermal modelling of the steady-state dynamic performances, such as torque speed curve and the efficiency map, for surface-mounted permanent magnet machines. One important feature of such a model is that it considers the demagnetization caused by magnet temperature rise at different rotor speeds. EM-...

This paper presents a general analytical fault model in a compact matrix form for surface-mounted permanent magnet (SPM) machines with parallel-connected coils, which is useful to study the machine performance under the inter-turn short circuit (ITSC) fault. To simplify the fault model, the multiphase Clarke transformation has been proposed. In the...

This paper proposes a dual 3-phase SPM machine with star-delta windings. The machine is based on the widely adopted 12s/10p configuration and employs a number of methods to suppress the two largest core loss causing MMF harmonics. Firstly, stator shifting is used to reduce the 7th order harmonic, which is then completely suppressed through the use...

In this paper, contributions of stator and rotor PMs in dual-permanent magnet (PM) machines with different stator/rotor pole number combinations are identified and investigated based on a multi-torque component decomposition method. The relationship between additive and cancellation effects of unmodulated rotor PM field component, contributions of...

This paper investigates magnet demagnetization characteristics of the modular permanent magnet machine. The influence of flux gaps on magnet flux density, losses distribution, torque and demagnetization are analyzed for different operating conditions. The magnet demagnetizations caused by three sources, such as the PM field, the armature field, and...

Split ratio, i.e. the ratio of stator inner diameter to outer diameter, has a closed relationship with electromagnetic performance of permanent magnet (PM) motors. In this paper, the toroidal windings with short end-winding axial length are employed in the 6-slot/2-pole (6s/2p) PM motor for high speed applications. The split ratio is optimized toge...

This paper investigates the influence of different permanent magnet (PM) segmentations on electromagnetic performances of 2-pole high-speed PM motors, considering parallel and perpendicular PM segmentations referring to diametric magnetization direction. Meanwhile, taking into account the manufacturing process, the influence of the gap between two...

In order to analyze the DC winding induced voltage in the wound-rotor synchronous machine, this paper uses the air-gap field modulation principle to investigate its operation mechanism and harmonic order. By establishing the analytical magneto-motive force (MMF)-permeance model, the DC winding induced voltage per electrical cycle under open-circuit...

Permanent magnet (PM) machines have been extensively used for various applications. Nevertheless, thermal effect, particularly hotspot temperature, not only severely restricts power/torque density but also leads to deteriorations in electromagnetic performance, service life, and reliability. Starting with foundations of PM machines and heat transfe...

This paper proposes a general analytical model of surface-mounted permanent magnet (SPM) machines with series-connected coils under inter-turn short circuit (ITSC) fault. One prominent feature of this fault model is that the air-gap and slot-leakage components of inductances under fault are calculated separately, and the influences of pole number a...

The effect of slot and pole number combination on the airgap vibration forces of permanent magnet synchronous machines at no-load condition is studied in this paper. This analysis is carried out using finite element method for three external-rotor topologies, i.e. integer-slot, fractionalslot, and fractional-slot with modular stator. Firstly, a com...