Daohan Wang

Reducing Cogging Torque in Surface-Mounted Permanent-Magnet Motors by Nonuniformly Distributed Teeth Method

This paper proposed a novel method for reducing cogging torque in surface-mounted permanent-magnet (PM) motors with nonuniformly distributed teeth. In this method, the width of one tooth tip is different from that of the others while all slot openings are the same. By suitable selection of the teeth width ratio, i.e., the width ratio of the one tooth tip to others, the cogging torque can be greatly reduced. First, the analytical expression of cogging torque was deduced and used to analyze the cogging torque qualitatively. Based on the above, analytical method was proposed to determine the teeth width ratio. To determine the teeth width ratio accurately, numerical method was proposed. Calculation of cogging torque by finite element method (FEM) shows that cogging torque can be greatly reduced by teeth width ratio determined by analytical method, and the teeth width ratio determined by numerical method can reduce the cogging torque further, which proved the effectiveness of the proposed methods. At last, the influences of the stator asymmetry resulted by this method on PM motors were discussed.

Cogging Torque Minimization and Torque Ripple Suppression in Surface-Mounted Permanent Magnet Synchronous Machines Using Different Magnet Widths

Permanent magnet synchronous machines are vulnerable to significant amounts of torque ripple if they are not carefully designed. Even though minimizing cogging torque can help reduce the torque ripple, but can not definitely give rise to a low level torque ripple. This paper presents a simple solution for minimizing the cogging torque and suppressing operation torque ripple simultaneously. The principle of that simple solution is illustrated, where a magnet with different width is used so that the flux density distribution in the machine is substantially changed. The magnet widths for minimizing cogging torque are obtained by using an analytical model. The influence of magnet widths on operation torque ripple and average operation torque is examined by using Finite Element Analysis (FEA) which gives more preciseness to calculations. It is found that the cogging torque and operation torque ripple can be greatly reduced, but with slight average output torque reduction. At last, the Unbalance Magnetic Pull (UMP) is examined, indicating that the presented method can substantially increase the UMP due to the asymmetric distribution of magnets.

Optimization of Magnetic Pole Shifting to Reduce Cogging Torque in Solid-Rotor Permanent-Magnet Synchronous Motors

In this paper, the method of magnetic poles shifting was combined with optimization method to reduce cogging torque in solid-rotor permanent-magnet synchronous motors. Although the finite-element method (FEM) can calculate the cogging torque accurately, to find the peak value of cogging torque, the cogging torque for different relative positions between permanent magnets and slots must be calculated; thus, the optimization will take a long time. To reduce optimization time, a novel analytical method was proposed to determine the initial value and feasible range of the shifting angles. Then the optimization method and FEM were used to minimize the cogging torque. Two prototype motors were analyzed and optimized, respectively. It was proved that the cogging torque can be greatly reduced by the proposed method.

Reducing Cogging Torque in Surface-mounted Permanent Magnet Motors by Teeth Notching

Based on the analytical formulation for cogging torque derived in this paper, the effects of stator teeth notching on cogging torque are studied. When the method of teeth notching is adopted, the most important is to decide how many notches are needed. When k notches are adopted on one stator tooth, only Fourier coefficients Gn(n is the multiple of k+1) are not zero, and the value of these Gn increases by k+1 times. In order to reduce cogging torque effectively, the Gk+1 should have no effect on the cogging torque. At the end, the method is validated by finite element method.

Performance Characteristics and Preliminary Analysis of Low Cost Tubular Linear Switch Reluctance Generator for Direct Drive WEC

This paper presents the performance characteristics of a low cost but high-power density tubular linear switch reluctance generator (TLSRG) for direct drive marine wave energy conversion (WEC). The presented TLSRG consists of series of soft magnetic rings and exhibits higher power density than conventional teeth type TLSRG. There is sole set of round winding in each stator slot, which facilitates manufacturing process, thus, results in low cost. The referred ring segments are both magnetically and electrically isolated with each other so it reduces the phase coupling and increase the capability of fault tolerance that is favorable to be used in harsh conditions as WEC. The characteristics and dynamic performance at WEC mode are examined and discussed, validating that the presented TLSRG is a strong alternative candidate to permanent magnet tubular generator for WEC.

Design and Performance Evaluation of a Tubular Linear Switched Reluctance Generator with Low Cost and High Thrust Density

This paper presents the design and performance evaluation of a tubular linear switch reluctance generator (TLSRG) with ferromagnetic rings to a conventional teeth-type TLSRG. The referred ferromagnetic rings are magnetically isolated with each other thus eliminate the stator yoke and make better utilization of material. Since only one set of ring windings are housed in the translator, no electric insulation measures are required. A standard analytical design procedure is developed for the presented generator and two demonstrators with identical dimensions are designed. The performance characteristic of the two generators are obtained and compared to each other in terms of inductance, load force, output current, and power density. The results demonstrate that the presented generator is superior to the teeth-type generator as linear generation systems such as electromagnetic dumper and wave energy conversion.

Design and Comparison of a High Force Density Dual Side Linear Switched Reluctance Motor for Long rail propulsion Application

Linear switched reluctance motors (LSRMs) have been an attractive solution for linear driving systems. This paper presents the design and performance comparison of dual side mover and segmental stator LSRM. A conventional teeth-type LSRM, which has identical dimensions, is designed and compared. A design process is developed based on the linear inductance model, and then a standard power equation of this kind of machine is derived, giving a guideline for the design process of the presented LSRM. Using the designed process obtained, a prototype machine is designed and manufactured. Finally, the experimental results from the prototype validate the design procedures and analysis.

Performance analysis of a high power density tubular linear switch reluctance generator for direct drive marine wave energy conversion

Marine wave energy is a promising renewable source of energy in the world since it is characterized by high power density and worldwide distribution. Alternative to the well know permanent magnet linear synchronous machine and linear induction machine, a high power density tubular linear switch reluctance machine (TLSRM) is presented in this paper as direct drive marine wave energy generator. The translator of the machine consists of series of ring segments and there is only one set of round concentric winding in each stator slot, which significantly reduces the end of winding and manufacturing cost. It has been revealed that the presented machine exhibits high power density and low cost, thereby, to be a potential candidate for marine wave generator. Numerical optimization is used to determine the key dimensions which affect the machine performance. The performance of the presented machine are evaluated and compared with the traditional teeth type linear reluctance machine, validating that the presented machine shows significant advantages as marine wave energy generator.

Topology analysis and performance evaluation of a high thrust force density linear switched reluctance machine for low cost conveyor applications

Linear switched reluctance machine (LSRM) offer advantages to be used in harsh conditions and low cost applications, but subject to low force density because of the nature of force production which resemble the well-known rotary SRM. A new kind of LSRM with different structure and magnetic circuit topology is presented in this paper. The presented machine incorporates a simple concentric winding and concrete ferrite-magnetic segmentations instead of the teeth type stator. Compared to teeth type linear reluctance machine, it features unique magnetic circuit and higher thrust force density. This paper analyze the principle and evaluate the performance of the presented machine. The results show that the presented linear reluctance machine gains a favorable superiority over the teeth type linear reluctance machine in terms of high force density, high reliability and low cost. The presented machine with different structural configurations are given and their performance are evaluated and discussed.

Performance Analysis and Design Optimization of an Annular Winding Bilateral Linear Switch Reluctance Machine for Low Cost Linear Applications

Linear switch reluctance machine (LSRM) has been an alternative actuator for linear transportation systems such as mine hoist applications and urban ropeless elevator system. This paper proposes a novel bilateral LSRM, which stator consists of series of concrete ferrite-magnetic segments rather than laminated teeth type structures. The referred segments are magnetically isolated between each other and, thereby, eliminate the stator yoke and make much better utilization of magnetic circuit. It is found that the proposed machine features lower mass of stator core but achieves much higher thrust than a conventional teeth type LSRM. An optimization procedure is performed and is compared with results from initial design ranging from inductance characteristics, statistic force, normal force to force density and force ripple. The presented machine has gained superiority over teeth type LSRM in terms of higher propulsion force density, utilization of magnetic material, capability of fault tolerance, and low manufacturing and assembling cost.