Multi-phase Permanent Magnet Research Articles

Analysis and Calculation of Radial Electromagnetic Force of Circular Winding Brushless DC Motor

The circular winding brushless direct current (CWBLDC) motor is a special type of multiphase permanent magnet motors with nonsinusoidal electromotive forces and circularly connected phase windings. The motor does not rely on conventional pulsewidth-modulation inverters and has high torque density and low torque ripple, making it a promising choice for high-power and high-performance applications, such as marine propulsions. This paper studies the radial electromagnetic force of CWBLDC motors. The effect of slot-pole combinations on harmonic contents of the radial force density is analytically derived. Moreover, two computationally efficient numerical methods to calculate the radial electromagnetic force density distribution are proposed based on the space-time symmetry of CWBLDC motors and the superposition principle of the magnetic field, respectively. In order to validate the analysis, vibration testing of a 10-kW CWBLDC prototype is performed.

Inverse Models and Harmonics Compensation for Suppressing Torque Ripples of Multiphase Permanent Magnet Motor

This paper presents two methods to derive an inverse model in harmonic forms for analyzing the interactions between the torque/current gains and currents, and for suppressing the torque ripples of a multiphase permanent magnet (PM) motor. The first method directly calculates the desired current harmonics from a pseudo-inverse model of a multiphase PM motor with no input-voltage saturation, which is independent of its rotor displacements, for torque ripple compensation. The second is an iterative-free method formulating the inverse model as an optimization problem that minimizes the copper loss subject to torque constraints while accounting for the effects of the input-voltage saturation. The formulation and significance of the two methods are illustrated with a multiphase PM motor for which published measurements are available for model validation and compared with three other commonly used current waveforms for benchmark comparison in terms of torque-ripples and copper losses.

Assessment of current and voltage signature analysis for the diagnosis of rotor magnet demagnetization in five-phase AC permanent magnet generator drives

Multiphase permanent magnet generators are becoming attractive alternative for a variety of industry applications. In this context, diagnosing the status of the rotor magnets is necessary to guaranty the required efficiency of the generators. This paper deals with two techniques suitable for quantifying the level of rotor demagnetization in closed-loop controlled five-phase AC permanent magnet machines. More specifically, the paper is aimed to identify the control impact on magnet demagnetization detectability based on voltage and current signature analysis. The analysis shows that the last approach has the advantage of being less dependent on the operating point of the generator. The proposed comparative study is analytically established, and validated by means of numerical simulations thereby.

Dynamic Performance Improvement of Five-Phase Permanent-Magnet Motor With Short-Circuit Fault

Multiphase permanent-magnet (PM) brushless motors are popularly adopted for their high efficiency and high power density. However, short-circuit phase fault results in serious problems, such as increased torque fluctuations and deteriorated dynamic performance. This paper proposes a new vectorial approach to minimize pulsating torque and improve dynamic performance in a five-phase PM motor with short-circuit fault. The novelty of the proposed strategy is voltage feedforward compensation based on the relation of the short-circuit current and its fault-phase back electromotive force. First, the compensatory voltages are used to eliminate the impact of the short-circuit current. Then, its combination with the orthogonal reduced-order transformation matrices derived from fault-tolerant current references can improve the dynamic performance of the faulty PM motor. The effect of the short-circuit phase fault on the PM motor model under rotating synchronous frame is also discussed. This control strategy allows minimal reconfiguration of the control structure from healthy operation to fault-tolerant one and exhibits the improved dynamic performance. The simulated and experimental results are presented as validation for the proposed strategy.

Multi-Phase Modular Drive System: A Case Study in Electrical Aircraft Applications

In this article, an advanced multiphase modular power drive prototype is developed for More Electric Aircraft (MEA). The proposed drive is designed to supply a multi-phase permanent magnet (PM) motor rating 120 kW with 24 slots and 11 pole pairs. The power converter of the drive system is based on Silicon Carbide Metal Oxide Semiconductor Field-Effect Transistor (SiC MOSFET) technology to operate at high voltage, high frequency and low reverse recovery current. Firstly, an experimental characterization test is performed for the selected SiC power module in harsh conditions to evaluate the switching energy losses. Secondly, a finite element thermal analysis based on Ansys-Icepak is accomplished to validate the selected cooling system for the power converter. Thirdly, a co-simulation model is developed using Matlab-Simulink and LTspice® to evaluate the SiC power module impact on the performance of a multiphase drive system at different operating conditions. The results obtained show that the dynamic performance and efficiency of the power drive are significantly improved, which makes the proposed system an excellent candidate for future aircraft applications.

Design of a five‐phase permanent‐magnet motor for the electric steering of an aircraft nose landing gear

Recently, there has been a growing interest in reducing the number or replacing the hydraulic/pneumatic actuators utilised on aircraft with electric actuators coupled to mechanical gears, which would improve the reliability and performance. This is involved in the concept of more electric aircraft. The electrification of actuators would affect the primary and secondary flight controls, as well as the movement of flight surfaces, retraction of the landing gear, and steering of the nose landing gear, which is also considered in this study. This study considers the design of a multiphase permanent-magnet (PM) motor to be utilised for the electric steering of a commercial aircraft nose landing gear. This multiphase motor would make it possible to achieve a highly reliable actuator and, coupled with a harmonic drive, avoid the use of a multi-motor configuration. Moreover, a multiphase motor would increase the power density and efficiency of the actuator, through improving the torque ripple. The performance variation due to temperature swings is considered, and a design procedure for the PM motor is described using the worse operation case for the electric actuator. The adequate performance of the designed motor and actuator is demonstrated by means of a finite element analysis.

A New Nine-Phase Permanent Magnet Synchronous Motor With Consequent Pole Rotor for High-Power Traction Applications

Although three-phase permanent magnet (PM) motors are quite common in industry, multi-phase PM motors are used in special applications where high power and redundancy are required. Multi-phase PM motors offer higher torque/power density than conventional three-phase PM motors. In this paper, a novel multi-phase consequent pole PM (CPPM) synchronous motor is proposed. The constant power-speed range of the proposed motor is quite wide as opposed to conventional PM motors. The design and the detailed finite-element analysis of the proposed nine-phase CPPM motor and performance comparison with a nine-phase surface mounted PM motor are completed to illustrate the benefits of the proposed motor.

A Novel Asymmetric and Unconventional Stator Winding Configuration and Placement for a Dual Three-Phase Surface PM Motor

Multi-phase permanent magnet (PM) motors are becoming more popular because of their higher torque densities, enhanced efficiency, and fault-tolerant capabilities. In this paper, a novel six-phase PM synchronous motor with a new asymmetric stator ac winding scheme and placement is proposed. Two identical dual three-phase asymmetrical winding sets are placed in two separate half of the stator in 180 mechanical degrees. This approach reduces the phase resistance and thus copper losses. Torque quality of the proposed motor is also analyzed using 2-D finite element method in detail. It can be concluded that the proposed novel asymmetric stator has more advantages to offer than conventional six-phase PM motors.

Design guidelines for fractional slot multi‐phase modular permanent magnet machines

This study presents the design considerations for a fractional slot multi-phase modular permanent magnet (PM) machine with single-layer concentrated windings. The winding factors for various slot/pole number combinations are calculated to identify the optimal slot/pole number combinations for different phase numbers. In addition, the electromagnetic performance influenced by flux gaps (FGs), such as air-gap magneto-motive force, back-electro-motive force, cogging torque, on-load torque and torque ripple etc. are comprehensively investigated by using the two-dimensional finite element (FE) method. Several general rules with respect to the influence of FGs on multi-phase modular PM machines performance are established. The prototypes of modular PM machines are built and the FE results are validated with experiments.

Series‐connected multi‐half‐bridge modules converter for integrating multi‐megawatt wind multi‐phase permanent magnet synchronous generator with dc grid

In this study, a new transformerless wind energy conversion system to integrate high-power multi-phase permanent magnet wind generators to medium-voltage local grids is presented. The proposed converter topology consists of multi-half-bridge modules with a high ac-direct current (dc) boosting capability. Each phase of an open winding multi-phase generator is connected to the ac side of a half-bridge module, whereas the dc sides of the half-bridge modules are connected in series forming the high-voltage dc-link output. The proposed architecture facilitates the employment of semiconductor switches with a relatively low-voltage rating, which equals the dc-link voltage divided by the number of generator phases. A detailed analysis of the proposed architecture along with the required closed-loop control is presented. The proposed architecture is simulated under different operating conditions using a typical 2 MW system, while the experimental validation is carried out using a low-scale prototype converter.

다상 영구자석 동기 전동기의 자기 및 상호 인덕턴스 계산

다상 영구자석 동기 전동기의 자기 및 상호 인덕턴스 계산

Multiphase permanent magnet synchronous motors with fractional slot windings

Purpose The purpose of this paper is to investigate advantages of multiphase permanent magnet synchronous motors (PMSM) with fractional slot concentrated windings (FSCW). The investigation is based on comparative analysis and assessment of FSCW PMSM wound as 3, 6, 9 and 12 phase machines suited for low speed applications. Design/methodology/approach The investigations are focussed on distortions of back electromotive (emf) and magnetomotive force (mmf) with the torque ripples and motors’ performance taken into account. The finite element models with the aid of customized computer code have been adopted for motor winding design and back emf, mmf and motor performance analyses. Findings The novel multiphase winding layouts were found to offer lower content of sub-harmonics in the mmf waveforms compared with the traditional three-phase machine designs. Moreover, the investigated multiphase machines exhibited higher average value of the electromagnetic torque, while the multiphase PMSM machines with FSCW were further characterized by significantly lower torque pulsations. Originality/value The analyses presented in this paper demonstrate that PMSM with FSCW are advantageous to their counterpart three-phase machines. Specifically, they offer higher performance and are more suitable to work with multiple drives supplying segmented winding system. This ability of using multi-drive supply for one motor offers flexibility and cost reduction while increasing fault tolerant power train system.

Influence of Third Harmonic Back EMF on Modeling and Remediation of Winding Short Circuit in a Multiphase PM Machine With FSCWs

For multiphase open-winding permanent-magnet (PM) machines, both back electromotive force (EMF) and short-circuit current (SCC) contain third harmonic components that interact with each other and produce even-harmonic torque pulsation. This paper investigates the impact of the third harmonic component on SCC prediction, torque pulsation and postfault remediation method in case of a winding short-circuit fault. Analytical modeling of SCC is developed, which shows that the third harmonic SCC increases the maximum value of SCC. It is found that the transient SCC is heavily influenced by the initial phase angle of winding axis and exciting current when the fault is incepted. The braking torque due to the negative q -axis SCC component is investigated, which peaks at low speed as winding inductive impedance goes down. The comparison of two postfault remediation methods for single-phase short-circuit faults shows the importance of considering the third harmonics of SCC and back EMF in terms of torque performance. Finally, the theoretical results of SCC, braking torque, and remediation methods are verified and evaluated with experimental results.

Preparation Analysis of the Overall Characteristics for High Power PMSM With Multi Phase Units

Testing of multiphase high power permanent magnet synchronous motor having multiple units in the laboratory always introduces many problems. In this paper, prediction problems to obtain the overall characteristics for such motor under limited experimental conditions have been analyzed. On the basis of power characteristic analysis and calculation of one independent unit, the calculation of power characteristics for multiunit as well as the prediction of overall power characteristics were realized. Finally, some valuable conclusions resulting from the analysis are provided.

A Novel Dual Three-Phase Permanent Magnet Synchronous Motor With Asymmetric Stator Winding

Although three-phase permanent magnet (PM) motors are dominant in industry, multi-phase PM synchronous motors present higher torque-to-weight ratios, better efficiency, and low torque ripple compared with three-phase conventional PM motors. These features make fault-tolerant multi-phase PM motors become attractive for safety-critical applications. In this paper, a novel PM multi-phase motor design with a dual three-phase asymmetric stator winding is proposed. The winding structure of the proposed motor is unconventional due to selected slot–pole combinations. Therefore, an asymmetric winding is needed. The detailed finite-element analysis of the proposed motor and a performance comparison between the conventional integer-slot (72-slot/12-pole motor) with symmetric winding and the unconventional fractional-slot (78-slot/12-pole motor) PM motors with asymmetric windings is performed to see the benefits of the proposed motor. It was shown that the novel unconventional multi-phase PM motor has excellent torque quality and slightly higher torque density levels.

Impedance Source Based Multi Phase Inverter Fed Variable Speed PMBLDC Motor Using Advance controller for Torque Ripple Minimization

This paper presents the advance controlling system for multiphase PMBLDC motor. This permanent magnet synchronous motor has copper losses in stator, current vibration and harmonics due to wrong selection of rotor shape is generated by the voltage saturation and more torque ripple. This voltage saturation affects the performance of the motor. The proposed multiphase permanent magnet BLDC motor is to reduce the voltage saturation and also to minimize the torque ripple. The multiphase motor have more handling capacity, high reliability and to produce high torque at same ampere volume of machine. This multiphase topology is requiring high dc source and effective control method for high speed operation. The introduced Z-source topology is used to improve source voltage boost up ability without using any DC/DC converters. Further, it reduces the line harmonics, enhance the load power factor, gives ride through ability in the course of input voltage sags and increases inverter reliability. The IFOC control strategy is possible to achieve high reliable operation at input voltage sag conditions. The proposed Z-source networks as well as IFOC scheme based multi phase motor to attain the minimum torque ripples and high voltage gain in ASD (adjustable speed drive) are analyzed in MATLAB/ SIMULINK environment.

Enhanced Availability of Drivetrain Through Novel Multiphase Permanent-Magnet Machine Drive

This paper deals with a novel multiphase permanent-magnet (PM) machine drive to enhance drivetrain availability in electric traction applications. It describes the development of new winding configurations for six-phase PM brushless machines with 18 slots and eight poles, which eliminate and/or reduce undesirable space harmonics in the stator magnetomotive force. In addition to improved power/torque density and efficiency with a reduction in eddy current loss in rotor PMs and copper loss in end-windings, the developed winding configuration also enhances availability of drivetrain, in a variety of applications requiring a degree of fault tolerance, by employing it as two independent three-phase windings in a six-phase interior-PM machine, which is designed and optimized for a given set of specifications for an electric vehicle, under thermal, electrical, and volumetric constraints. This paper also describes the design and development of a six-phase inverter with independent control for both sets of three-phase windings. The designs of the motor and the inverter are validated by a series of preliminary tests on the prototype machine drive.

Generalized Vectorial Formalism – based multiphase series-connected motors control

Multiphase drives are more and more used in specific applications leading to a necessity of control strategy development. This paper presents the Generalized Vectorial Formalism (GVF) theory to control multiphase series-connected permanent magnet synchronous motors (PMSM) fed by one voltage source inverter (VSI). Based on a decomposition of multiphase machine, a proposed control strategy has been achieved. Some experimental results are given to illustrate this control method.

Modeling and Fault Diagnosis of Interturn Short Circuit for Five-Phase Permanent Magnet Synchronous Motor

Taking advantage of the high reliability, multiphase permanent magnet synchronous motors (PMSMs), such as five-phase PMSM and six-phase PMSM, are widely used in fault-tolerant control applications. And one of the important fault-tolerant control problems is fault diagnosis. In most existing literatures, the fault diagnosis problem focuses on the three-phase PMSM. In this paper, compared to the most existing fault diagnosis approaches, a fault diagnosis method for Interturn short circuit (ITSC) fault of five-phase PMSM based on the trust region algorithm is presented. This paper has two contributions. (1) Analyzing the physical parameters of the motor, such as resistances and inductances, a novel mathematic model for ITSC fault of five-phase PMSM is established. (2) Introducing an object function related to the Interturn short circuit ratio, the fault parameters identification problem is reformulated as the extreme seeking problem. A trust region algorithm based parameter estimation method is proposed for tracking the actual Interturn short circuit ratio. The simulation and experimental results have validated the effectiveness of the proposed parameter estimation method.

Global Fault-Tolerant Control Technique for Multiphase Permanent-Magnet Machines

In this paper, a global fault-tolerant control (FTC) technique is proposed for multiphase permanent-magnet (PM) machine drives. The goal of the proposed FTC is to find a general closed-form solution for healthy phase currents under steady-state post fault conditions. Healthy phase currents are found through an optimization problem to produce ripple-free output torque with minimum ohmic losses. A comprehensive FTC approach should be able to provide fault-tolerant currents for multiphase machines with any number of phases. In addition, it needs to find currents based on fault type (open-circuit/short-circuit), fault locations [phase(s) and/or line(s)], connection of stator windings, and even different control objectives. An important feature of the proposed method is its flexibility and simplicity in dealing with all possible fault conditions. The proposed method is a great tool to evaluate fault-tolerant capability of different drive systems in terms of maximum available ripple-free torque and copper losses. Due to its simplicity and flexibility, it is also well-suited for real-time implementation. A five-phase PM machine is used as an example to investigate the validity of the proposed solutions through finite-element analysis and experimental tests.