Hiroyuki Mikami

Dynamic harmonic field analysis of a cage type induction motor when magnetic slot wedges are applied

Applying magnetic slot wedges to stator slot openings is an effective means to reduce the slot ripple harmonic components in the magnetic field. To investigate the effect of the wedges in detail, this paper proposes a new harmonic field analysis method that considers the rotor movement dynamically and the harmonic components of the secondary current as induced current by a two-dimensional finite element method (2D-FEM) using a time stepping technique. The differences in harmonic characteristics due to the use of plural wedges (a nonmagnetic wedge and magnetic slot wedges in different dimensions) for the stator slot opening of a three-phase cage induction motor are evaluated using the method. Suitable wedge dimensions to reduce the slot ripple harmonics are determined. From the comparison of calculated and experimental results of secondary current, the proposed method is shown to be appropriate and useful for the quantitative estimation of harmonic fields for induction motors.

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.

Dynamic harmonic field analysis of an inverter-fed induction motor for estimating harmonic secondary current and electromagnetic force

The distorted power waveform from an inverter includes many time harmonic components which became a factor in increasing losses and generating noise. To evaluate the effect of these harmonic components quantitatively, this paper proposes a new harmonic field analysis method that considers the rotor movement dynamically and the harmonic components of the secondary current as induced current by a 2-dimensional finite element method (2D-FEM) using a time stepping technique. The proposed method is applied to the analysis of a cage induction motor supplied by a PWM inverter. As a result, the harmonic components of the secondary current and the electromagnetic force are shown quantitatively. These calculated results are confirmed by experiments measuring the secondary current and the sound level. From the comparison of calculated and experimental results, the proposed method is shown to be appropriate and useful for quantitative estimation of harmonic fields for inverter-fed induction motors.

Reluctance Torque Utility for Line-Starting Permanent Magnet Motors

This paper presents two types of prototype line-starting permanent magnet motors for compressor drives; one is a nonsalient-pole machine, and the other is a salient-pole machine. It is proved through both the analyses and experiments that the utility of reluctance torque not only boosts steady-state characteristics but also line-starting capabilities. It was also noteworthy that the salient-pole machine in the steady-state operation could achieve not only better efficiency but also a higher power factor. Finally, the designed motors achieved a 4% to 5% increase in efficiency over all operational points, which prevented a rise in temperature by 30 K, compared with a conventional two-pole induction motor. The results are given for a two-pole prototype motor with PN = 5 kW, nN = 3000 min -1, VN = 200 V, and Y-connection.

Dynamic harmonic field analysis of an inverter-fed induction motor considering all harmonic components in the secondary current

This paper describes a quantitative method to analyze the harmonic fields of induction motors dynamically, considering all the higher harmonic components in the secondary current under the given analysis conditions. The method consists of two parts. Firstly, a magnetic field calculation is performed using a 2D-finite element method considering rotor movement, and then a harmonic analysis is carried out by considering the space and time harmonic components using results from the first part of the calculation. Dependence of periodicity on the magnetic fields, under the load conditions considering the rotor slip, is discussed. The relationships between the analysis period, the method of mesh division, and the periodicity are then clarified to facilitate calculation of the magnetic fields. The computation time needed to solve the magnetic field can be reduced by using these relationships. The method is applied to the analysis of a 240 kW cage induction motor supplied by a PWM inverter. From comparison of calculated and experimental results, the proposed method is shown to be appropriate and useful for the quantitative estimation of the harmonic fields in inverter-fed induction motors.

Starting torque analysis of cage induction motor using permeance model considering magnetic saturation by leakage flux

This paper describes a method to analyze harmonic components of the air-gap flux density distribution and the torque of 3-phase cage induction motors, considering the influence of circumferential slot arrangement, stator winding pattern, and distribution of air-gap permeance due to leakage flux. The proposed method is based on an analytical model of the permeance and magnetomotive force distributions. The proposed method considers magnetic saturation caused by the main and leakage magnetic flux. As a result, the harmonic components of the torque in the starting condition can be determined quantitatively. From the comparison between the calculated and experimental results, the proposed method is shown to be appropriate and useful for quantitatively estimating harmonic torque for cage induction motors.

Magnetic flux density analysis of wound rotor induction motor by permeance model

A fast calculation method for parametric survey is needed when designing motors. We propose a new method for analyzing the harmonic components of air-gap flux density distribution in three-phase wound rotor induction motors. The proposed method is based on analytical equations for permeance and magnetomotive force distribution, considering the influence of the circumference slot arrangement and winding pattern of the motor. Thus, the harmonic components of the air-gap flux density distribution can be analyzed in a short time. The analysis results of the proposed method are in agreement with those of finite element magnetic analysis in on-load condition. Consequently, this method is shown to be suitable for quantitatively estimating the flux density of wound rotor induction motors and useful for parametric survey when designing wound rotor induction motors.

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.

Magnetic field analysis of a squirrel cage induction motor considering rotor skew and higher harmonics in the secondary current

This paper describes a method to analyze harmonic magnetic fields of squirrel cage induction motors considering rotor skew and higher harmonics in the secondary current. The proposed method is based on a two-dimensional finite element method. The rotor skew structure is expressed by multiple 2D finite element mesh models, produced in suitable axial positions, and the magnetic field in each mesh model is calculated by the revised secondary current taking into account the skew effect. The secondary currents, magnetic flux densities, and electromotive forces are calculated by the proposed method. Then the differences between a skewed rotor and a nonskewed rotor are discussed. From the comparison between the calculated and the experimental results, the proposed method is shown to be appropriate and useful for quantitative estimation of harmonic components of induction motors.

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.