Mustafa K. Guven

Torque Ripple Reduction in Interior Permanent Magnet Synchronous Machines Using Stators With Odd Number of Slots Per Pole Pair

This paper develops analytical principles for torque ripple reduction in interior permanent magnet (IPM) synchronous machines. The significance of slot harmonics and the benefits of stators with odd number of slots per pole pair are highlighted. Based on these valuable analytical insights, this paper proposes coordination of the selection of stators with odd number of slots per pole pair and IPM rotors with multiple layers of flux barriers in order to reduce torque ripple. The effectiveness of using stators with odd number of slots per pole pair in reducing torque ripple is validated by applying a finite-element-based Monte Carlo optimization method to four IPM machine topologies, which are combinations of two stator topologies (even or odd number of slots per pole pair) and two IPM rotor topologies (one- or two-layer). It is demonstrated that the torque ripple can be reduced to less than 5% by selecting a stator with an odd number of slots per pole pair and the IPM rotor with optimized barrier configurations, without using stator/rotor skewing or rotor pole shaping.

Reducing Harmonic Eddy-Current Losses in the Stator Teeth of Interior Permanent Magnet Synchronous Machines During Flux Weakening

Interior permanent magnet (IPM) synchronous machines can experience large harmonic eddy-current losses in the stator teeth under flux-weakening operation, significantly depressing the efficiency of these machines at high operating speeds. This paper presents a new analytical/finite-element hybrid design approach to reduce the harmonic eddy-current losses in IPM machine stator teeth during flux-weakening operation. The proposed technique achieves this objective by three steps: 1) developing an analytical index for the harmonic eddy-current losses in IPM machine stator teeth; 2) designing the spatial distribution of the rotor MMF to minimize the analytical index; and 3) synthesizing the rotor geometry to implement the desired rotor MMF function while maintaining the basic machine characteristics unchanged. It will be shown that two-layer rotors, if properly optimized, are significantly more effective than one-layer rotors for the purpose of reducing the harmonic eddy-current losses in IPM machine stator teeth during flux-weakening operation at high speeds.

Design and Experimental Verification of a 50 kW Interior Permanent Magnet Synchronous Machine

This paper presents the design details for an IPM machine designed to deliver 50 kW constant power over a 5:1 speed range extending from 850 rpm to 4250 rpm, with a gradual reduction in the required output power up to 8000 rpm (25 kW). Electromagnetic, thermal, and structural considerations have been included in the design optimization process. The resulting machine is designed with two magnet layers per pole and a distributed stator winding. Special features of the machine include its deep stator slots and four-layer winding, made necessary by the desire to minimize the machines moment of inertia. Test results available to date demonstrate that the machine is capable of delivering the required output torque and power, and the agreement between the predicted and measured machine parameters is generally quite good. Calculated iron losses for high-speed flux-weakening operation are presented in the final section of the paper, illustrating the challenges associated with minimizing the impact of high-frequency harmonic flux density components

Impact of Maximum Back-EMF Limits on the Performance Characteristics of Interior Permanent Magnet Synchronous Machines

Interior permanent magnet (IPM) synchronous machines are vulnerable to uncontrolled generator (UCG) faults at high speed that can damage the inverter. One approach to reducing this risk is to impose limits on the maximum machine back-EMF voltage at top speed. This paper presents the results of a comparative design study that clarifies the nature and extent of the penalties imposed on the IPM machine metrics and performance characteristics as a result of imposing progressively tighter values of back-EMF voltage limits. As an alternative to limiting back-EMF and penalizing machine designs, this paper also investigates the effectiveness of the system-side protection approach to the same UCG fault problem

Experimental verification of deep flux-weakening operation of a 50 kW IPM machine by using single current regulator

This paper analyzes critical control issues associated with the deep flux-weakening operation of Interior Permanent Magnet (IPM) synchronous machines. Then we review the single-current-regulator control algorithm which controls the d-axis current actively and gives a fixed q-axis voltage command. To achieve better operational efficiency and performance, improvements are made to choose an optimal qaxis voltage for variable speeds and loads. The control algorithm is implemented on a 50 kW IPM machine. Test results available to date including 7:1 Constant Power Speed Ratio (CPSR) operation are presented to verify the theoretical analysis.

Comparing Various PM Synchronous Generators: A Feasible Solution for High-Power, Off-Highway, Series Hybrid, Electric Traction Applications

Different disc-type axial flux permanent magnet (AFPM) generators are designed and compared in this article for a Caterpillar D7E track-type tractor (TTT) electric drive model. The design of several feasible generators with multiple stators and rotors are completed for the given electrical and mechanical specifications and compared with a conventional permanent magnet (PM) generator in terms of power density, torque density, loss distribution, efficiency, heat dissipation, volume, inertia, and weight. Electromagnetic, mechanical, and thermal analyses are also accomplished to finalize the designs. The results reveal the benefits of axial gap PM generators over radial gap generators for a hybrid electric traction application.