Torque prediction using the flux-MMF diagram in AC, DC, and reluctance motors

This paper uses the flux-MMF diagram to compare and contrast the torque production mechanism in seven common types of electric motor. The flux-MMF diagram is a generalized version of the flux-linkage versus current (ψ-i) diagram for switched-reluctance motors. It is illustrated for switched-reluctance, synchronous-reluctance, induction, brushless AC, brushless DC, interior PM and commutator motors. The calculated flux-MMF diagrams for motors with the same electromagnetic volume, airgap, slotfill, and total copper loss are shown and are used to compare the low-speed torque and torque ripple performance. The motor designs used were reasonably optimized using a combination of commercially available motor CAD packages and finite-element analysis

Comparison of switched-mode rectifier and inverter control of surface PM generators

This paper compares the performance of surface PM generators when operated with a switched-mode rectifier and an inverter. An analytical model including losses for the surface PM generator and power electronics controller is developed and validated against simulations and experimental results. This is used to generate efficiency maps as a function of output power and speed for the generator operating with four control methods: rectifier, conventional and phase advance controlled switched-mode rectifiers, and an inverter. The efficiency maps and the required control parameters to achieve maximum efficiency are presented and discussed.Lujie Chen and Wen L. Soon

Fault remedial strategies in a fault-tolerant brushless permanent magnet AC motor drive with redundancy

In this paper the fault-tolerant brushless permanent magnet AC motor drive with redundancy is investigated. The motor modules are designed to provide both magnetic and electrical isolation between phases and the redundancy is achieved by using two motor modules connected on a common shaft. The effect of potential faults on the output torque and torque ripple factor are examined and the fault analysis shows that the output torque will be reduced and the torque ripple will be increased after fault(s). Three fault remedial strategies are proposed to compensate the torque loss due to the fault(s) and their features are discussed as well. Zero torque ripple with minimum copper loss fault remedial strategy is the most suitable method which can result in minimum torque ripple factor with only a modest increase in copper loss comparing with the minimum possible value. The experimental setup of the motor drive is developed and the experimental test results are provided to verify the analysis results and the validity of the proposed fault remedial strategies.Jingwei Zhu, Nesimi Ertugrul and Wen Liang Soon

Maximum-torque-per-ampere control of phase advance modulation of an SPM wind generator

Surface permanent-magnet (SPM) machines are normally operated by controlling the d- and q-axis currents. This paper examines the control of SPM generators based on controlling the terminal voltage magnitude V and power-factor angle 8. This is well suited for generator operation when using a switched-mode rectifier and avoids the need for a rotor position sensor. The parameters required for generating a given value of torque with minimum phase current in order to minimize copper losses are derived in this paper. This will be achieved by controlling V and 8 to keep the d-axis current equal to zero at low speed, before switching to field-weakening control at higher speeds. Simulated and experimental results will be used to verify the control strategy and the efficiency achieved.Mehanathan Pathmanathan, Wen L. Soong and Nesimi Ertugru

Efficiency Maps of Electrical Machines: A Tutorial Review

Efficiency maps (EffMs) illustrate the maximum efficiencies of electric machines over a range of torque-speed operating points. This article reviews the available techniques for efficiency map calculation and gives a general understanding of EffM modelling and interpretation for traction motors. It shows the accuracy versus calculation effort trade-off for different methods. The process of efficiency map calculation for sample induction motor and permanent magnet synchronous machines is explained. Calculation of EffMs using commercial software is also covered. Finally, possible future research opportunities in this field are suggested.Emad Roshandel, Amin Mahmoudi, Solmaz Kahourzade and Wen L. Soon

Axial-flux synchronous reluctance motors: Introduction of a new machine

This paper presents the design and analysis of a novel axial-flux synchronous reluctance motor (AFSynRM). A magnetic equivalent circuit (MEC) model for the proposed axial-flux machine is derived. The feasibility of fabrication is discussed. Finite-element analysis is applied to predict the performance of the proposed motor design. This paper provides a baseline study by comparing the performance of the proposed AFSynRM design with a similar rating radial-flux motor. The motors are designed to have similar volume and both have three rotor barriers. The operating parameters are obtained through static and dynamic FEA. The power, torque, power factor and efficiency of the motors are studied. The saturation and flux distribution in the motor structures are investigated.Amin Mahmoudi, Solmaz Kahourzade, Emad Roshandel, Wen L. Soon

Saturation consideration in modeling of the induction machine using subdomain technique to predict performance

In this article, the analysis of induction machines using five separated subdomains including the rotor slot, rotor slot opening, airgap, stator slot opening, and stator slot regions is considered. The Maxwell equations of each region are solved considering the boundary conditions. Uniform distributions of the current density in the rectangular slots of both the rotor and stator are considered to find the energy of the winding and to calculate the machine inductances using the energy equation. The calculated flux density of each subdomain is used to find the flux distribution. The calculated magnetic flux intensities are required to estimate the saturation level of the motor cores and correct the saturation-related values such as the leakage and magnetizing inductances. The machine core losses are calculated based on the Steinmetz equation at the no-load condition. The calculated inductances and resistances are used in the equivalent circuit of the squirrel-cage induction machine (SCIM) for the performance prediction. The results demonstrate the reliability of the saturation model in the prediction of the saturation influence in a wide range of magnetization levels. The accuracy of the proposed model in the prediction of the performance of the SCIM is validated using two-dimensional (2-D) and 3-D finite-element analysis results. A sensitivity analysis with 75 different geometries was conducted to show the capability of the model for the performance prediction of a wide range of induction machines.Emad Roshandel, Amin Mahmoudi, Solmaz Kahourzade, Wen L. Soon

Unbalanced Axial Forces in Axial-Flux Machines

This paper performs an analysis of the variation of unbalanced forces with airgap length in axial-flux machines. A simple analytical approach is used to provide insights into these key parameters and the results compared with finite-element results for both axial-flux permanent magnet (PM) and induction machines. For PM and current-driven induction machines, the two most important parameters are the ratio of the effective magnet/core magnetic path length to the nominal airgap, and the ratio of the saturation flux density to the nominal airgap flux density. For voltage-driven induction machines, the key parameter is the ratio of stator leakage inductance to the nominal magnetising inductance.Wen L. Soong, Zhi Cao, Emad Roshandel, Amin Mahmoudi, Solmaz Kahourzad