Kan Akatsu

Design and Evaluation of a Variable-Flux Flux-Intensifying Interior Permanent-Magnet Machine

This paper presents a design approach for interior permanent magnet (IPM) machines with variable-flux characteristics using low coercive force magnet material for improved efficiency and extended operating speed range. A flux-intensifying interior permanent (FI-IPM) type having Ld >; Lq is used in the design due to positive Id operation and reduced load Iq effects. Design consideration of machine structures and variable-flux machine attributes are discussed. In addition, leakage flux in a rotor is specially designed to obtain another degree-of-freedom in variable-flux control as well. Evaluation of the designed machine is provided using FEA simulations and experimental evaluation of a proof-of-principle prototype machine. The designed machine shows benefits in improving efficiency and extending the range of the torque-speed map when magnetization level of the low coercive force magnet is operated at the optimal levels.

Rare Earth Reduction Using a Novel Variable Magnetomotive Force Flux-Intensified IPM Machine

This paper presents a novel variable magnetomotive force flux-intensifying interior permanent-magnet (IPM) (VFI-IPM) machine, which uses only low-coercive force magnets to reduce usage of rare earth metals. The VFI-IPM machine is designed with a characteristic of

Suppressing pulsating torques: Torque ripple control for synchronous motors

L_{d} > L_{q}

Basic Properties of an Axial-Type Switched Reluctance Motor

, which is typical for FI-IPM machines and uses low-coercive force magnets with magnetization level control. A theoretical magnet operating point analysis was conducted to investigate the design methodology. A proof-of-principle prototype machine was then designed based on these principles. Simulation and experimental results show that the VFI-IPM prototype can achieve a wide torque–speed envelope and variable torque–speed characteristics while not requiring high-coercive force magnets that would include far more expensive rare earth materials, such as dysprosium.

Design and evaluation of a variable-flux flux-intensifying interior permanent magnet machine

This article proposes a novel control technique for suppressing pulsating torques in permanent magnet synchronous motors (PMSMs) and synchronous reluctance motors (Syn-RMs). This torque-control system is based on instantaneous torque estimation with a rigorous analytical model that can account for spatial harmonics. Using this novel analytical model, the produced torque can be accurately estimated from simple preknowledge and some measurable online information. Ultimately, superimposed currents obtained from the torque estimation can smooth out the pulsating torque. The effectiveness of the proposed technique is evaluated by performing both simulations and experiments.

Efficiency contours and loss minimization over a driving cycle of a variable-flux flux-intensifying interior permanent magnet machine

This paper describes the design of an axial-type switched reluctance motor (SRM) with the aim of improving the output torque characteristic. The axial-type structure has several advantages, including a large air-gap area due to the dependence on the radial length, whereas the air-gap area of the radial-type motor depends on the axial length. This advantage is expected to increase the inductance and the output torque. This paper shows a method to design an axial-type SRM and basic properties of the designed motor by comparing the results of the finite-element analysis with those obtained by experiments.

Efficiency Contours and Loss Minimization Over a Driving Cycle of a Variable Flux-Intensifying Machine

This paper presents a design approach for interior permanent magnet (IPM) machines with variable-flux characteristics using low coercive force magnet material for improved efficiency and extended operating speed range. A flux-intensifying interior permanent (FI-IPM) type having L d > L q is used in the design due to positive I d operation and reduced load I q effects. Design consideration of machine structures and variable-flux machine attributes are discussed. In addition, leakage flux in a rotor is specially designed to obtain another degree-of-freedom in variable-flux control as well. Evaluation of the designed machine is provided using FEA simulations and experimental evaluation of a proof-of-principle prototype machine. The designed machine shows benefits in improving efficiency and extending the range of the torque-speed map when magnetization level of the low coercive force magnet is operated at the optimal levels.

Secondary resistive losses with high-frequency injection-based self-sensing in IPM machines

In this paper, experimental evaluations for the efficiency of a novel interior permanent magnet (IPM) machine with variable-flux characteristics using low coercive force magnets is presented. The variable-flux characteristics allow improving the efficiency of machine and also reducing the usage of rare-earth material in the high-coercive magnets, which are currently used for the IPM machines in electrified vehicles. A flux-intensifying interior permanent magnet (FI-IPM) type having positive saliency is employed for a positive d-axis current to mitigate a demagnetizing field in the magnet due to a q-axis current. A proof-of-principle machine is designed, fabricated and evaluated. A series of experiments are conducted to capture the efficiency contours with different magnetization states of the low coercive force magnets. The designed machine shows benefits in improving efficiency when the magnetization state is optimally operated. With these results, the loss over a driving cycle is then simulated and the benefits of changing the magnetization state are quantified.

Efficiency comparison between Brushless dc motor and Brushless AC motor considering driving method and machine design

In this paper, experimental evaluations for the efficiency of a novel interior permanent-magnet (IPM) machine with variable-flux characteristics using low-coercive-force magnets are presented. The variable-flux characteristics allow improving the efficiency of a machine. A flux-intensifying IPM type having positive saliency is employed for a positive d-axis current to mitigate a demagnetizing field in the magnet due to a q-axis current. A proof-of-principle machine is designed, fabricated, and evaluated. A series of experiments are conducted to capture the magnetization and demagnetization properties of the low-coercive-force magnets by applying control d-axis current pulse. The efficiency contours with different magnetization states (MSs) of the magnets are then experimentally obtained. The designed machine shows benefits in improving efficiency when the MS is optimally operated. With these results, the loss over a driving cycle is then simulated, and the benefits of changing the MS are quantified.

Self-Sensing Comparison of Fractional Slot Pitch Winding Versus Distributed Winding for FW- and FI-IPMSMs Based on Carrier Signal Injection at Very Low Speed

This paper investigates the impact of high-frequency injection-based self-sensing on secondary resistive losses associated with the high-frequency carrier component in interior permanent magnet (IPM) machines. Two types of salient machines, the flux-weakening IPM (FW-IPM, Lq > Ld) and the flux-intensifying IPM (FI-IPM, Lq < Ld) are investigated. Simulation with 3D finite-element analysis (FEA) is used to analyze loss characteristics of the machines. Iron losses and eddy-current losses in permanent magnets dominate during high-frequency carrier signal injection. The magnet eddy-current loss is found to be dependent on the magnet locations and sensitive to loading, while the iron loss is dependent on stator and rotor structural designs and less sensitive to loading. This characteristic can be used to improve position and magnet temperature sensing. Experimental evaluation of losses on a built FI-IPM machine is used to evaluate the simulation results.