Ryoso Masaki

Development of a position sensorless control system on an electric vehicle driven by a permanent magnet synchronous motor

This paper presents a new position sensorless control system of an interior permanent magnet synchronous motor (IPMSM) for electric vehicles. The proposed control system is based on an injected voltage vector that is synchronized with a PWM carrier of an inverter. The pole position is estimated from the relation between the injected voltage vector and the saliency of the rotor. The first current difference vector is detected when the injected voltage vector in the estimated pole position direction is added to the motor control voltage vector. Next, the second current difference vector is detected when the injected voltage vector in the opposite direction of the estimated pole position is added to the same motor control voltage vector. Then, the pole position of the rotor with anti-saliency can be estimated from the first and second current difference vectors. This control needs neither motor parameters nor band pass filters. The anti-salient pole type IPMSM can be operated over a wide speed range including zero speed, with a quick response. Good driving of electric vehicles is realized using the proposed system.

Development of an Axial Gap Motor With Amorphous Metal Cores

This paper presents a novel motor design concept that utilizes amorphous cut cores in the stator and ferrite magnets in the rotor to obtain a high-efficiency motor. This motor employs a six-pole nine-slot axial gap construction and aims to provide 90% efficiency with decreased size and low cogging torque for fan motor applications. Amorphous cut cores are applied to the stator to decrease iron loss and save motor space. Skewed magnets are employed to decrease cogging torque. Three-dimensional finite element analysis was used to analyze motor performance. In order to verify the accuracy of the design, a trial motor was constructed, and a large range of experiments was conducted to measure the motor characteristics. The results of the trial motor meet the design goals.

A torque controller suitable for electric vehicles

A torque controller suitable for electric vehicles is studied. The controller ensures that an induction motor generates motor torque efficiently, stably and accurately. The torque control system feeds back an assumed motor torque calculated using the secondary magnetic flux and the torque current detected from current sensors of the primary currents. The motor torque is controlled by using the torque current reference determined from the generated secondary magnetic flux and the magnetizing current reference. The magnetizing current reference is determined on the basis of the torque current reference so that motor torque generation efficiency is always optimal. The magnetizing current regulator is operated according to the magnetizing current reference. This ensures the motor generates the motor torque stably even in transient states. Fundamental performance characteristics, such as response, accuracy and efficiency of the motor torque are verified by simulation and experiments. The torque controller is judged suitable for the drive system of electric vehicles.

Evaluation of experimental permanent-magnet brushless motor utilizing new magnetic material for stator core teeth

We prepared motors with experimental cores using a soft magnetic composite and an amorphous metal and evaluated their performance. We measured the magnetic and motor characteristics, such as iron loss, when the new materials were used in the stator core teeth. The amorphous metal was found to have very high permeability and low iron loss, whereas the soft magnetic composite had low permeability and had a comparable iron loss as low-grade magnetic steel. The soft magnetic composite had the added benefits of being able to form a three-dimensional shape and having relatively low core loss in high frequency conditions. The magnetic properties we measured were able to predict the motor characteristics with high accuracy based on numerical and finite-element-method analysis.

Characteristics of a Permanent-Magnet Synchronous Motor with a Dual-Molding Permanent-Magnet Rotor

A dual-molding magnet rotor was evaluated as a soft magnetic composite for the magnetic material of the rotor of a motor. Especially the possibility of using a dual-molding magnet rotor as means to improve motor efficiency was investigated. A dual-molding magnet rotor was a one-piece permanent magnet rotor made with bonded NdFeB magnet and soft magnetic composite core. A permanent-magnet synchronous motor was targeted for evaluation, and three types of dual-molding magnet rotors with different magnetic orientations were evaluated using the finite element method (FEM) and a trial model of test motor. It was confirmed that the cogging torque originated in the variation of the rotor element decreased because the pole-pitch accuracy and the outer-size accuracy were improved by utilizing a one-piece molding in the dual-molding magnet rotor. In spite a difference in the maximum energy products of the three magnets of about three times, the difference between maximum efficiency of the sintered rare-earth radial ring magnet and the isotropic-multi-pole oriented magnet and that between the former and the anisotropic-pole-concentrate oriented magnet are within 1%. The evaluation results show that the structure of dual-molding-magnet-rotor is superior to sintered rare-earth radial ring magnet rotor.

A Microprocessor-Based Current Controller with an Internal Current-Rate Loop for Motor Drives

A new current-control method that is suitable for microprocessor-based speed regulation of motor drives is described. The method achieves fast-response and high-accuracy performance by using a major current loop and an internal current rate loop. The former loop is used to control precisely the mean value of the motor current by employing a current feedback signal obtained from a smoothing filter of the rippled current. The latter loop is used to stabilize the major loop with a high gain and to limit the variation rate of the motor current by employing the current feedback signal obtained from the instantaneous current without time delay. A current controller using a microprocessor was trail-manufactured and tested with a thyristor-converter-driven dc motor. It was found that fast-controlled current response can be obtained, even with a relatively long sampling period.