Gilsu Choi

Interior permanent magnet synchronous machine rotor demagnetization characteristics under fault conditions

This paper presents the dynamic response of an interior permanent magnet synchronous machine (IPMSM) drive to various fault conditions and their effects on the PM demagnetization characteristics. Attention is focused on modeling the IPMSM drive including nonlinear magnetic behavior under asymmetrical inverter fault conditions, demonstrating the significant risks of irreversible demagnetization caused by the large transient fault currents. Other types of inverter faults are discussed, including phase-leg open-circuit fault and uncontrolled generator (UCG) mode fault. Finite element (FE) analysis is used to simulate the demagnetization characteristics under a variety of fault conditions. Three-phase symmetrical short circuit fault characteristics for several different IPM machine designs are discussed.

Investigation of key factors influencing the response of permanent magnet synchronous machines to three-phase symmetrical short-circuit faults

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.

Demagnetization characteristics of permanent magnet synchronous machines

This paper presents the calculated demagnetization characteristics of different types of permanent magnet synchronous machines (PMSMs) under the influence of demagnetizing MMF contributed by the stator currents (i.e., armature reaction). The demagnetization of NdFeB magnets is quantified in terms of demagnetized magnet volume and loss of magnet remanence using finite element (FE) analysis. The impact of cross-coupled q-axis current and the rotor position are also investigated. The results comparing seven PM machine configurations show that burying the magnets inside the rotor using interior PM (IPM) rotor configurations generally improves the demagnetization performance. In addition, the machine configurations with distributed windings generally provides better demagnetization-withstand capabilities than the configurations with fractional-slot concentrated windings.

Design of electric machines for electric vehicles based on driving schedules

This paper presents a specialized design evaluation tool for electric machines intended for use in electric vehicles that seeks to maximize the machines efficiency in the operating regions that most closely correspond to the vehicles driving schedules. The influences of different designs on a production battery-electric vehicle are studied. A combination of closed form and finite element analysis is applied in the design process to incorporate both vehicle driving patterns and machine electromagnetic characteristics in order to optimize the machine efficiency optimization in the most frequent operating regions. The total required energy and relative losses of each of the candidate machines is calculated for the driving cycles using the predicted machine and vehicle performance characteristics. Finally, the Nissan Leafs energy consumption is calculated using simplified combined city/highway driving schedules and compared to the EPAs published range, demonstrating that the developed analytical model can deliver promising accuracy.

Reduction of Eddy-Current Losses in Fractional-Slot Concentrated-Winding Synchronous PM Machines

This paper presents the results of an investigation focused on the rotor eddy-current losses of a permanent magnet (PM) synchronous machine that is equipped with fractional-slot concentrated windings (FSCWs). Major spatial harmonics that induce the most significant rotor eddy-current losses are identified and evaluated. Time-stepped finite-element analysis results are presented to compare the predicted losses in the proposed FSCW-PM machine designs. It is shown that the lowest total eddy-current losses in the rotor core and magnets are achieved by introducing flux barriers into the rotor back iron along the d -axis.

PM Synchronous Machine Drive Response to Asymmetrical Short-Circuit Faults

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.

A new course on control of wind power generation systems using analysis and simulation

This paper presents a new graduate-level course that is designed, developed, and taught at the University of Wisconsin-Madison to further advance the education for wind power technologies. The objective of this course is to provide an in-depth coverage of control of electric drives for wind turbines with an emphasis using state-of-the-art modeling and simulation techniques. Various generator types and their associated controlling techniques for wind power generation are reviewed in the course. The course begins with a thorough discussion of the performance requirements for electric power generating equipment controls in wind turbine applications. Analyses and simulations of electric generators combined with their controls are incorporated into the class curriculum to provide students with a thorough understanding of the achievable generating system performance. The course capitalizes on the students prior knowledge in drives, power electronics, and electric machines to develop highly skilled, advanced degree graduates that can readily become researchers or developers of next-generation wind power generation systems.

Experimental verification of rotor demagnetization in a fractional-slot concentrated-winding PM synchronous machine under drive fault conditions

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 machines fault-mode response characteristics.

Analysis and design guidelines to mitigate demagnetization vulnerability in PM synchronous machines

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 machines 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 / offer appealingly low values for both of these demagnetization metrics.