This paper investigates the three-phase symmetrical short-circuit (SSC) characteristics of a permanent magnet synchronous machine (PMSM). Closed-form solutions are derived to predict both the steady-state and transient response of a PMSM to three-phase SSC faults. The developed expressions account for the impact of prefault operating conditions and include provisions for incorporating magnetic saturation effects. The influences of machine parameters and prefault operating conditions are studied to identify the key factors that have a major influence on the steady-state and peak transient values of the fault currents. It is shown that higher machine characteristic current values, reduced stator resistance, higher q-axis prefault current, and higher magnetic saturation all increase the peak transient value of the demagnetizing d-axis current. Time-stepped finite element (FE) simulation is performed to investigate the rotor demagnetization characteristics of PMSMs under SSC fault conditions. Both two-dimensional (2-D) and three-dimensional (3-D) FE simulations are used to build confidence in the fault current predictions of the developed analytical model, accompanied by experimental verification.

A design approach is presented to mitigate demagnetization vulnerability in permanent magnet synchronous machines (PMSMs) by proper selection and design of stator windings and rotor configurations. First, a comparative analysis of the stator demagnetizing MMFs and leakage inductances for surface PM machines equipped with integral-slot distributed windings (ISDW) and fractional-slot concentrated windings (FSCW) is performed under the constraint of equal magnet flux linkage. Finite element analysis is used to build confidence in the predicted variation of flux density over the magnet surfaces in the two machines. The higher leakage inductance in the FSCW machine reduces the negative impact of its higher peak demagnetizing MMF, but not enough to offset the ISDW machine's advantage of lower demagnetizing MMF. Overall, two convenient metrics are proposed to evaluate the relative amplitude of peak demagnetizing MMF and potential rotor temperature rise due to eddy-current losses. This study shows that the FSCW-PM machine is more vulnerable to rotor demagnetization compared to the ISDW-PM machine because of the higher peak demagnetizing MMF applied by the stator winding currents and rich spatial harmonics that increase rotor losses. Finally, it is shown that the FSCW-PM machines with slot-per-phase-per-pole values of 1/2 offer appealingly low values for both of these demagnetization metrics.

This paper investigates the impact of machine topology and parameters on the fault-mode characteristics of permanent-magnet synchronous machines (PMSMs) exposed to asymmetrical short-circuit (ASC) faults, one of the most dangerous faults in terms of peak current amplitudes and demagnetization risks. Simulations using an equivalent circuit model combined with finite-element (FE) analysis are used to explore the differences between the ASC fault-mode responses of three major types of PM machines. The effects of several different rotor and winding configurations have been studied to identify the key machine parameters that have a major influence on the fault current amplitudes. Results indicate that fractional-slot concentrated winding (FSCW) PM machines tend to exhibit lower peak currents compared to distributed winding (DW) machines during ASC fault events. Finally, the results from three different types of short-circuit faults are summarized and compared for several PM machine configurations to provide information that will be helpful for choosing the best machine for new applications. Experimental results are provided for constrained ASC fault conditions that build confidence in the models and their predictions.

This paper presents the results of experimental tests designed to verify analytical predictions of the rotor demagnetization characteristics of a 0.6 kW (cont.) 9-slot/6-pole fractional-slot concentrated winding (FSCW) interior permanent magnet (IPM) synchronous machine. The demagnetization characteristics of the rotor magnets in this commercially produced FSCW-IPM machine are measured using a test configuration that is designed to conduct multiple demagnetization tests on the same test machine under controlled temperature conditions. In this paper, finite-element (FE) predictions of the rotor demagnetization characteristics of the experimental machine during three-phase symmetrical short-circuit and single-phase asymmetrical short-circuit faults are presented. These results are compared with experimental test measurements of the postfault currents and the magnet flux density distribution following demagnetization, demonstrating very good agreement of many key features. These comparisons also confirm that 3-D effects and magnet material properties such as the magnet thermal coefficients have a significant impact on some details of the FE predictions of the machine's fault-mode response characteristics.

This paper presents a detailed process for the design of interior permanent magnet synchronous machines (IPMSMs) for electric vehicle (EV) applications. First, a comprehensive design process featuring two objectives and three constraints is proposed to realize an optimal IPMSM design that can satisfy the key performance requirements for an EV application. The objectives and constraints were carefully selected and designed to obtain a balance between performance, efficiency, and cost. Because the inductances and magnet flux linkage of the machine are key design parameters for attaining optimal flux-weakening capability, the impact of the machine dimensions on these two parameters is thoroughly investigated and explained using both analytical and numerical techniques. Additional analyses including normalized key performance metrics and the impact of short-circuit faults in PM machines with three different characteristic current values (1, 1.3, and 2.6 pu) are also provided, highlighting the advantages and limitations of the three baseline designs.

Safety is a critical feature for all passenger vehicles, making fail–safe operation of the traction drive system highly important. Increasing demands for traction drives that can operate in challenging environments over wide constant power speed ranges expose permanent magnet (PM) machines to conditions that can cause irreversible demagnetization of rotor magnets. In this paper, a comprehensive analysis of the demagnetization vulnerability in PM machines for an electric vehicle (EV) application is presented. The first half of the paper presents rotor demagnetization characteristics of several different PM machines to investigate the impact of different design configurations on demagnetization and to identify promising machine geometries that have higher demagnetization resistance. Experimental verification results of rotor demagnetization in an interior PM (IPM) machine are presented in the latter half of the paper. The experimental tests were carried out on a specially designed locked-rotor test setup combined with closed-loop magnet temperature control. Experimental results confirm that both local and global demagnetization damage can be accurately predicted by time-stepped finite element (FE) analysis.