Shinichi Wakui

Transient-torque analysis for line-starting permanent-magnet synchronous motors

Using the analysis method for resolving the starting torque of line-starting permanent magnet (PM) synchronous machines with starting cage, the electromagnetic torque can be separated into two components, the driving ldquocage torquerdquo and the braking ldquomagnet torquerdquo. The correct saturation of the iron must be considered, when calculating the separate torque components. The sum of the two torque components exhibits a good agreement with the originally calculated starting torque with the Finite Element time stepping technique. This novel method also helps to have a better knowledge of the synchronization mechanism. Results are given for a two-pole prototype motor with PN=5 kW, nN=3000 min-1, VN=200 V, Y-connection.

Analysis of rotor eccentricity on permanent magnet synchronous motor characteristics

This paper describes the influence of rotor eccentricity on permanent magnet synchronous motor characteristics by a magnetic field analysis and several experiments. The rotor eccentricity unbalances the magnetic force and thus increases the mechanical loss. Furthermore, a circulating current generated in two three-phase windings connected in parallel results in an increase of electric power loss in the permanent magnet synchronous motor. Therefore, we presented that the flux barrier rotor is effective to reduce the harmful effect of the rotor eccentricity.

Evaluation of Torque Characteristics in Saturated Magnetic Field for Permanent-Magnet Synchronous Motors

The evaluation of torque characteristics in saturated magnetic field for permanent-magnet (PM) synchronous motors is presented. Using the modified two-axis machine model that considers the cross-coupling effect, two important phenomena resulting from magnetic saturation are indicated: the decrease in magnet torque because of an anomalous flux of PMs and the existence of cross-magnetizing torque. These two kinds of torque characteristics cannot be considered by the conventional two-axis machine model, which assumes a constant value of induced electromotive force due to PMs. Measurement results indicate the validity of the modified method while they demonstrate the conventional method has difficulty in deducing torque components.

Dynamic and steady-state performance of line-starting permanent magnet motors

This paper presents two types of prototype motors for line-starting permanent magnet motors; one is a non-salient- pole machine, and the other is a salient-pole machine. Through both the analyses and the experiments, it is proved that the reluctance torque utility boosts up not only the steady-state characteristics but also the line-starting capability. It is also noteworthy that in the steady-state operation the salient-pole machine can realize not only the better efficiency but also the higher power factor. Results are given for a two-pole prototype motor with PN = 5 kW, nN = 3000 min−1, VN = 200 V, Y-connection.

Influences of rotor eccentricity on permanent magnet synchronous motor characteristics

This paper describes the influence of rotor eccentricity on permanent magnet synchronous motor characteristics. Specifically, we studied the influence of rotor eccentricity on permanent magnet synchronous motor characteristics by conducting a magnetic field analysis and several experiments. The rotor eccentricity unbalances the magnetic force and thus increases the mechanical loss. Furthermore, a circulating current generated in two three-phase windings connected in parallel results in an increase in electric power loss in the permanent magnet synchronous motor.

Development of self-starting permanentmagnet synchronous motors for compressor drives

A lot of saving energy policies are being globally instituted from the viewpoints of global warming and environmental preservation. Although a lot of effort has been put into improving industrial air conditioners, there are still efficiency problems with multisystem air conditioners in buildings where constant speed scroll compressors are used. We present the measurement results of a self-starting permanent magnet synchronous motor applied to a compressor drive. Compared with an isometric induction motor, efficiency improvements of 9% and 7% were confirmed for rated operation under 50 Hz and 60 Hz, respectively. The power factors also increased by 17% and 10% for the same rated operations, respectively. Moreover, the efficiency of the compressor equipped with the proposed motor was 9% and 7% higher than that with the conventional induction motor, under 50 Hz and 60 Hz operations, respectively. This result is consistent with the efficiency improvement of the proposed motor itself.

Analysis of turbine generator steady-state reactances for load conditions

This paper describes variations of turbine generator steady-state reactances for load conditions. When the turbine generator is of small size, magnetic saturation of the stator and rotor core is a problem. Therefore, it is important to understand the variations of the reactances for load conditions. The reactances of a 592-MVA turbine generator are calculated with d- and q-axis equations considering magnetic saturation and two-dimensional numerical magnetic field analysis. The results are as follows. (1) The equivalent synchronous reactances considering cross-magnetizing are smaller than the original synchronous reactances for load conditions. (2) Numerical values of the d- and q-axis mutual reactance and the field and q-axis mutual reactance are at their maximum when the d-axis linkage flux is nearly equal to the q-axis linkage flux under constant voltage. (3) The d-axis synchronous reactance drops with increasing reactive power under constant voltage and active power, but the q-axis synchronous reactance increases. (4) The variation of the equivalent d-axis synchronous reactance with increasing reactive power is similar to that of the d-axis synchronous reactance, but the variation of the equivalent q-axis synchronous reactance is different from that of the q-axis synchronous reactance.