Jagadeesh K. Tangudu

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.

Comparison of interior PM machines with concentrated and distributed stator windings for traction applications

This paper presents a detailed design comparison of two types of high-performance interior permanent magnet (IPM) synchronous machines designed to meet demanding FreedomCAR traction machine specifications, one with fractional-slot concentrated windings (FSCW) and the other with integral-slot distributed windings (ISDW). An IPM rotor that was originally designed for an FSCW stator with a slots-per-pole-per-phase (SPP) value of 2/5 and double-layer windings is used in all four of the studied designs. This comparative investigation is carried out using finite element analysis with both single- and double-layer winding configurations. Key performance metrics are compared including the predicted back-EMF, the characteristic current, cogging torque, and highspeed losses under full load operating conditions.

Design, analysis and loss minimization of a fractional-slot concentrated winding IPM machine for traction applications

This paper presents details of the design and analysis of a high-performance fractional-slot concentrated winding (FSCW) interior permanent magnet (IPM) machine that has been designed to meet demanding FreedomCAR traction machine specifications. Attention is focused on the design of the IPM rotor, including investigations of the impact of varying the magnet height and the depth of the magnet chevron midpoint on key performance metrics. This paper also addresses interaction between the electromagnetic and structural characteristics of the rotor as bridge and post widths are varied. Predicted performance characteristics of the machine are presented and design techniques are described for improving the machine efficiency at high operating speeds. Test results gathered from an experimental machine exhibit promising agreement with the predicted performance.

Lumped parameter magnetic circuit model for fractional-slot concentrated-winding interior permanent magnet machines

This paper presents a simplified lumped-parameter magnetic circuit model (MCM) of a fractional-slot concentrated-winding (FSCW) interior permanent magnet (IPM) machine that provides rapid estimates of machine performance for use in machine design optimization software. This model incorporates several key nonlinear phenomena including (i) magnetic saturation; (ii) cross-saturation effects between the d- and q-axes affecting both flux linkages and inductances; (iii) stator slotting effects; and (iv) localized effects due to rotor bridges. A coupled permeance element is proposed that captures the cross-coupling saturation effects along with airgap modeling that captures both radial and tangential airgap flux densities. The MCM is configured to predict key machine performance variables including airgap flux densities, back-EMF, phase and dq-axis inductances, characteristic current, and torque. Finite element (FE) analysis results are presented that match the MCM results quite closely, building confidence in the MCM model.

Segregation of torque components in fractional-slot concentrated-winding interior PM machines using frozen permeability

Torque is produced in interior permanent magnet (IPM) machines as a result of stator current interactions with the rotor permanent magnets and rotor electromagnetic reluctance. Separation of the torque into its permanent magnet (PM) and reluctance components is helpful to machine designers but is complicated by the nonlinearity of magnetic saturation. This paper proposes a magnetic circuit model (MCM) to predict machine characteristics under frozen permeance conditions to help segregate machine torque components into PM and reluctance torques. Strengths and limitations of previously proposed techniques for performing this torque segregation are compared, including techniques based on finite element (FE) analysis. An alternative technique is proposed for delivering torque segregation results for fractional-slot concentratedwinding (FSCW) IPM machines that compares very well with the FE frozen permeability results but with significantly faster computation time. FE analysis is used to compare the characteristics of four alternative torque segregation techniques.

Unsaturated and saturated saliency trends in fractional-slot concentrated-winding interior permanent magnet machines

This paper presents an investigation of trends in the unsaturated and saturated magnetic saliency values of interior permanent magnet (IPM) synchronous machines with fractional-slot concentrated windings (FSCW). This paper investigates alternative slot-pole combinations for FSCW-IPM machines, highlighting the key observation that the saliency of these machines is generally lower than their counterpart IPM machines with conventional distributed windings. The relative merits and challenges of FSCW-IPM machines are examined, with a focus on the contribution of reluctance torque to the total machine torque. A key design metric that proves useful in this discussion is “unsaturated saliency ratio”, defined as the ratio Lq/Ld in the limiting case of near zero stator current and “saturated saliency ratio”, defined as the ratio Lq/Ld at high stator current. An important objective is to use this parameter to help machine designers choose the most appropriate slot-pole configuration for an FSCW-IPM machine in order to achieve the desired performance requirements.

Modeling power semiconductor losses in HEV powertrains using Si and SiC devices

Silicon carbide (SiC) power semiconductor devices are known to have potential benefits over conventional silicon (Si) devices, particularly in high power applications such as hybrid electric vehicles (HEVs). Recent literature studying the use of SiC JFETs in HEV inverters indicate a substantially increased gas mileage. This paper further investigates this change in inverter efficiency due to the adoption of SiC using analytical loss models and empirical loss data obtained from experimental Cree 1200V 10A DMOSFETs and Schottky diodes. A motor inverter efficiency map is developed and used in the VEHLIB simulator to evaluate fuel consumption benefits. Distribution of conduction and switching losses in both Si and SiC inverters is explored.

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.

Core loss prediction using magnetic circuit model for fractional-slot concentrated-winding interior permanent magnet machines

This paper presents a promising technique for estimating the cores losses of a fractional-slot concentrated-winding (FSCW) interior permanent magnet (IPM) machine using a simplified lumped-parameter magnetic circuit model (MCM). This model incorporates several key nonlinear phenomena including (i) magnetic saturation; (ii) cross-saturation effects between the d- and q-axes affecting both flux linkages and inductances; (iii) stator slotting effects; and (iv) localized effects due to rotor bridges. The MCM is configured to predict the flux densities waveforms in the iron as the rotor rotates. Fourier transformation is then applied to extract the frequency components of the flux density in each iron core permeance element, followed by estimation of the losses in each element. These permeance losses can then be combined to provide the estimated iron losses in the total core. Very good agreement is demonstrated between core loss predictions delivered by this model for a target FSCW-IPM machine and those provided by finite element (FE) analysis.

Scalable, low-cost, high performance IPM Motor for Hybrid Vehicles

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 an overview of the DoE/GE project to develop scalable, low-cost, high-performance next generation IPM traction motors for hybrid applications. The goal is to leap frog the state of the art and meet the FredomCar 2020 specifications. The paper will include the analytical and test results of the first proof-of-principle machine, analytical and preliminary test results for the second proof-of-principle machine as well as next steps.