Wen L. Soong

Pulsating torque minimization techniques for permanent magnet AC motor drives-a review

Permanent magnet AC (PMAC) motor drives are finding expanded use in high-performance applications where torque smoothness is essential. This paper reviews a wide range of motor- and controller-based design techniques that have been described in the literature for minimizing the generation of cogging and ripple torques in both sinusoidal and trapezoidal PMAC motor drives. Sinusoidal PMAC drives generally show the greatest potential for pulsating torque minimization using well-known motor design techniques such as skewing and fractional slot pitch windings. In contrast, trapezoidal PMAC drives pose more difficult trade-offs in both the motor and controller design which may require compromises in drive simplicity: and cost to improve torque smoothness. Controller-based techniques for minimizing pulsating torque typically involve the use of active cancellation algorithms which depend on either accurate tuning or adaptive control schemes for effectiveness. In the end, successful suppression of pulsating torque ultimately relies on an orchestrated systems approach to all aspects of the PMAC machine and controller design which often requires a carefully selected combination of minimization techniques.

Field-weakening performance of interior permanent-magnet motors

This paper compares the field-weakening performance under rated and overload conditions of synchronous reluctance and interior permanent-magnet motors against that of a baseline 2.2-kW induction machine. Four prototype rotors based on axially laminated and multiple-barrier designs were built and tested in the same induction machine stator. Field-weakening performance was estimated based on 50-Hz load tests at reduced voltage. It was found that the performance of the axially laminated synchronous reluctance machine was comparable with the induction machine while the interior permanent-magnet motors offered significantly better output power above rated speed. The multiple-barrier interior permanent-magnet motor design gave the most promising field-weakening performance.

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.

Comparison of Five Topologies for an Interior Permanent-Magnet Machine for a Hybrid Electric Vehicle

This paper presents a detailed comparison of the characteristics of five different rotor topologies for a distributed winding permanent-magnet (PM) machine for high-performance traction applications, including hybrid electric vehicles. These rotor topologies include one surface PM topology and four single-layer interior PM topologies (conventional, segmented, V shape, and W̅ shape). The performance characteristics, which include the back-electromotive force and its harmonics, magnet mass, iron loss, and ripple torque are compared and analyzed. A 7.5-kW interior permanent-magnetic (IPM) prototype using the conventional rotor topology was tested and the finite-element analysis results were compared. The aim of the paper is to give some guidance and reference for machine designers who are interested in IPM machine selection for high-performance traction applications.

Fault tolerant motor drive system with redundancy for critical applications

Some of the recent research activities in the area of electric motor drives for critical applications (such as aerospace and nuclear power plants) are focused on looking at various motor and drive topologies. This paper presents a motor drive system, which provides an inverter topology for three-phase motors, and also proposes an increased redundancy. The paper develops a simulation model for the complete drive system including synthetic faults. In addition, the hardware details including the implementation of DSP based motor controller, inverter module, and brushless PM motor system are provided and some experimental results are presented.

Design of a new axially-laminated interior permanent magnet motor

The design of an axially-laminated interior permanent magnet motor drive optimised for its field-weakening performance is described. A 7.5 kW motor was built based on low-cost, flexible rubber-bonded ferrite magnet sheet. It achieved an extremely wide constant power speed range of greater than 7.5:1, in contrast to the 2.5:1 obtained both with an axially-laminated synchronous reluctance motor and a standard induction motor. The excellent field-weakening performance makes this type of motor a serious contender for applications such as machine-tool main spindle drives and traction.<<ETX>>

Torque prediction using the flux-MMF diagram in AC, DC, and reluctance motors

This paper uses the flux-MMF diagram to compare and contrast the torque production mechanism in seven common types of electric motor. The flux-MMF diagram is a generalized version of the flux-linkage versus current (/spl psi/-i) diagram for switched-reluctance motors. It is illustrated for switched-reluctance, synchronous-reluctance, induction, brushless AC, brushless DC, interior PM and commutator motors. The calculated flux-MMF diagrams for motors with the same electromagnetic volume, airgap, slotfill, and total copper loss are shown and are used to compare the low-speed torque and torque ripple performance. The motor designs used were reasonably optimized using a combination of commercially available motor CAD packages and finite-element analysis.

Automatic Classification and Characterization of Power Quality Events

This paper presents a new technique for automatic monitoring of power quality events, which is based on the multiresolution S-transform and Parsevals theorem. In the proposed technique, the S-transform is used to produce instantaneous frequency vectors of the signals, and then the energies of these vectors, based on the Parsevals theorem, are utilized for automatically monitoring and classification of power quality events. The advantage of the proposed algorithm is its ability to distinguish different power quality classes easily. In addition, the magnitude, duration, and frequency content of the disturbances can be accurately identified in order to characterize the disturbances. The paper provides the theoretical background of the technique and presents a wide range of analyses to demonstrate its effectiveness.

Unified theory of torque production in switched reluctance and synchronous reluctance motors

A method is described for calculating the average and instantaneous torque of the synchronous reluctance motor from a knowledge of the trajectory of the phase flux-linkage versus phase current [i-/spl psi/] waveform, i.e., the same method as used with the switched reluctance motor. This allows a direct comparison between torque production in the two motors to be made. Analytical and finite-element analysis both show that the [i-/spl psi/] loci of the synchronous reluctance motor are ellipsoidal in shape and are not limited to the first and third quadrants as in the switched reluctance motor. The [i-/spl psi/] loci of the synchronous reluctance motor are not bounded by the magnetization curves in the same sense as in the switched reluctance motor and rely upon mutual coupling between phases for correct operation. >

Torque Ripple Reduction in Interior Permanent Magnet Synchronous Machines Using the Principle of Mutual Harmonics Exclusion

The interior permanent magnet (IPM) synchronous machine is vulnerable to developing significant amounts of current-induced ripple torque depending on the details of the machine design. Building on the contributions of earlier researchers, this paper approaches the problem of torque ripple reduction in IPM machines by applying the principle of mutual harmonics exclusion. First, this paper develops a useful analytical expression for the torque ripple that highlights the stator-rotor harmonic interactions. Next, an analytical design procedure for IPM rotors with multiple flux barriers is proposed that applies the mutual harmonics exclusion principle in combination with stator windings that use odd numbers of slots per pole pair. Finally, the technique is applied to two example IPM machines to investigate the effectiveness of this approach using finite element analysis. Promising results predict that a low peak-to-peak torque ripple can be achieved using relatively small numbers of stator slots and rotor flux barriers for the full range of current control angles, including deep flux weakening.