Kum-Kang Huh

Comparison of Interior and Surface PM Machines Equipped With Fractional-Slot Concentrated Windings for Hybrid Traction Applications

Electric drive systems, which include electric machines and power electronics, are a key enabling technology for advanced vehicle propulsion systems that reduce the petroleum dependence of the ground transportation sector. To have significant effect, electric drive technologies must be economical in terms of cost, weight, and size while meeting performance and reliability expectations. This paper will provide details of the design, analysis and testing of two permanent magnet (PM) machines that were developed to meet the FreedomCar 2020 specifications. The first machine is an Interior PM (IPM) machine and the second machine is a surface PM (SPM) machine. Both machines are equipped with fractional-slot concentrated windings (FSCW). The goal of the paper is to provide a quantitative assessment of how achievable this set of specifications is as well as a comparison with the state of the art. The paper will also quantitatively highlight the tradeoffs between IPM and SPM FSCW machines especially in the context of traction applications.

A novel method for initial rotor position estimation for IPM synchronous machine drives

Novel methods for initial position estimation during start-up are presented for interior permanent magnet synchronous machine drives. The magnet cavities in the IPMSM rotor create a sizable difference in the inductances of the two orthogonal rotor axes. This spatial saliency based on the rotor position makes it possible to use persistent, rotating or pulsating vector, carrier frequency image tracking techniques to reliably identify and track the orientation of the d and q axes even when the rotor is at standstill. However, additional details in the saliency image must be used to identify the polarization of the magnets in order to distinguish the north and south poles. The magnet polarity is identified by using magnetic saturation effects on the saliency image to uniquely identify the magnet pole polarity being tracked. Carrier currents for both rotating and pulsating voltage carrier injection are derived by using IPM machine model including saturation and verified by measured carrier current components. Experimental results show that the proposed algorithms are capable of reliable and fast initial position estimation including the polarity at standstill.

Advanced High-Power-Density Interior Permanent Magnet Motor for Traction Applications

Electric drive systems, which include electric machines and power electronics, are a key enabling technology for advanced vehicle propulsion systems that reduce the petroleum dependence of the ground transportation sector. To have significant effect, electric drive technologies must be economical in terms of cost, weight, and size while meeting performance and reliability expectations. This paper will provide details of the design, analysis and testing of an advanced interior permanent magnet (IPM) machine that was developed to meet the FreedomCar 2020 specifications. The 12 slot/10 pole machine has segmented stator structure equipped with fractional-slot concentrated-windings (FSCW). The rotor has a novel spoke structure. Several prototypes with different thermal management schemes have been built and tested. The paper will cover the test results for all these prototypes and highlight the tradeoffs between the various schemes.

Effect of Number of Layers on Performance of Fractional-Slot Concentrated-Windings Interior Permanent Magnet Machines

Interior PM machines equipped with fractional-slot concentrated-windings are good candidates for high-speed traction applications. This is mainly due to the higher power density and efficiency that can be achieved. The main challenge with this type of machines is the high rotor losses at high speeds/frequencies. This paper will thoroughly investigate the effect of number of winding layers on the performance of this type of machines. It will be shown that by going to higher number of layers, there can be significant improvement in efficiency especially at high speeds mainly due to the reduction of the winding factor/magnitude of the most dominant stator mmf subharmonic component. It will also be shown that there is significant improvement in torque density. Even though there is reduction in the winding factor of the stator synchronous torque-producing mmf component, this is more than offset by increase in machine saliency and reluctance torque. The paper will provide general guidelines regarding the optimum slot/pole/phase combinations based on torque density and efficiency. Sample designs of various slot/pole combinations are used to quantify the benefit of going to higher number of layers in terms of torque density, efficiency, and torque ripple.

Reduced Rare-Earth Flux-Switching Machines for Traction Applications

There has been growing interest in electrical machines that reduce or eliminate rare-earth material content. Traction applications are among the key applications where reducing cost and, hence, reduction of rare-earth materials are key requirements. This paper will assess the potential of different variants of flux-switching machines (FSMs) that either reduce or eliminate rare-earth materials in the context of traction applications. Two designs use different grades of dysprosium-free permanent magnets (PMs), and the third design is a wound-field variant that does not include PMs at all. A detailed analysis of all three designs in comparison to the required set of specifications will be presented. The key opportunities and challenges will be highlighted. The impact of the high pole-count/frequency of the FSMs will also be evaluated. Experimental results for one of the designs with dysprosium-free PMs will also be presented.

Generalized Approach of Stator Shifting in Interior Permanent-Magnet Machines Equipped With Fractional-Slot Concentrated Windings

Electrical drive systems, which include electrical machines and power electronics, are a key enabling technology for advanced vehicle propulsion systems that reduce the petroleum dependence of the ground transportation sector. To have significant effect, electric drive technologies must be economical in terms of cost, weight, and size while meeting performance and reliability expectations. Interior permanent magnet machines with fractional-slot concentrated windings have been shown to be good candidates for hybrid traction applications. One of the key challenges is the additional stator magnetomotive force sub- and superharmonic components that lead to higher losses in the rotor as well as saturation effects. This paper tries to address this issue by looking into the concept of stator shifting. The generalized concept of stator shifting in the context of the harmonic components that are targeted for cancellation is presented; the focus is on single-layer and double-layer windings that have stator space subharmonics. It is shown that the stator shifting can reduce the loss-producing harmonics on the rotor as well as help the flux weakening performance of the fractional-slot concentrated winding designs. The cancellation of the loss harmonics is introduced as a method in which a particular harmonic can be targeted as well as reduce the phase inductance of the machine allowing for more room in terms of the operating voltage at higher speed. The concept of stator shifting will be explained, and the effect of varying the shift angle on the various harmonic components and winding factors will be investigated. Various designs, arising out of single-layer and double winding layer 10-pole, 12-slot configuration (targeting the FreedomCAR specifications) with varied shift angles are evaluated. The comparison between these designs in terms of their power density, efficiency, and torque ripple is presented.

Advanced high power-density interior permanent magnet motor for traction applications

Electric drive systems, which include electric machines and power electronics, are a key enabling technology for advanced vehicle propulsion systems that reduce the petroleum dependence of the ground transportation sector. To have significant effect, electric drive technologies must be economical in terms of cost, weight, and size while meeting performance and reliability expectations. This paper will provide details of the design, analysis, and testing of an advanced interior permanent magnet (PM) machine that was developed to meet the FreedomCAR 2020 specifications. The 12-slot/10-pole machine has segmented stator structure equipped with fractional-slot nonoverlapping concentrated windings. The rotor has a novel spoke structure/assembly. Several prototypes with different thermal management schemes have been built and tested. This paper will cover the test results for all these prototypes and highlight the tradeoffs between the various schemes. Due to the high machine frequency (~1.2 kHz at the top speed), detailed analysis of various loss components and ways to reduce them will be presented. In addition, due to the high coolant inlet temperature and the fact that the machine is designed to continuously operate at 180 °C, detailed PM demagnetization analysis will be presented. The key novelty in this paper is the advanced rotor structure and the thermal management schemes.

Rotor End Losses in Multiphase Fractional-Slot Concentrated-Winding Permanent Magnet Synchronous Machines

Fractional-slot concentrated windings (FSCW) have been gaining a lot of interest in permanent magnet (PM) synchronous machines. This is due to the advantages they provide including shorter nonoverlapping end turns, higher efficiency, higher power density, higher slot fill factor, lower manufacturing cost, better flux-weakening capability resulting in wider constant power versus speed range, and fault tolerance. This paper focuses on eddy-current losses in the rotor clamping rings. Additionally, the loss in the nonmagnetic shaft with the option of i) metallic, ii) nonmetallic, and iii) metallic with shielding laminations clamping rings is analyzed. The study is based on finite element analysis (FEA). Desirable slot/pole combinations for different number of phases with both single- and double-layer windings are investigated. Experimental results for a three-phase 12 slot/10 pole design are presented to confirm that the losses in the rotor clamping rings can be very significant in case of FSCW machines and should not be overlooked during the design phase.

Comparison of interior and surface PM machines equipped with fractional-slot concentrated windings for hybrid traction applications

Electric drive systems, which include electric machines and power electronics, are a key enabling technology for advanced vehicle propulsion systems that reduce the petroleum dependence of the ground transportation sector. To have significant effect, electric drive technologies must be economical in terms of cost, weight, and size while meeting performance and reliability expectations. This paper will provide details of the design, analysis and testing of two permanent magnet (PM) machines that were developed to meet the FreedomCar 2020 specifications. The first machine is an Interior PM (IPM) machine and the second machine is a surface PM (SPM) machine. Both machines are equipped with fractional-slot concentrated windings (FSCW). The goal of the paper is to provide a quantitative assessment of how achievable this set of specifications is as well as a comparison with the state of the art. The paper will also quantitatively highlight the tradeoffs between IPM and SPM FSCW machines especially in the context of traction applications.

Gear Fault Diagnostics Integrated in the Motion Servo Drive for Electromechanical Actuators

This paper presents contributions made in gear fault diagnostics for motion servos with continuously variable speed as used for aerospace and automotive electromechanical actuators. As the first step for motion servo diagnostics, an observer-based kinematic error estimator is developed whereby this estimated kinematic error is proposed as an operating point-independent gear surface fault signature. As the second step, a signal processing method is developed for real-time implementation of spatial domain resampling of regular time domain samples, and this method is combined with spatial domain synchronous averaging methods, which are shown to be very effective in filtering out unwanted asynchronous signatures. Lastly, a motion servo actuator with a gear surface failure is tested, and the proposed methods are shown to successfully extract the kinematic error profiles of the defective gear during motion servo operation over a wide range of continuously varying velocity.