Kazuto Sakai

Principle of hybrid variable-magnetic-force motors

Reduction in power consumed by motors is required for energy saving in electrical appliances and electric vehicles. The motors used in such appliances and vehicles operate at variable speeds. For reducing energy consumption of electrical appliances, the flux-weakening current that depresses the voltage at high speed leads to significant copper and core losses. Therefore, we have developed a new technique for controlling the magnetic force of a permanent magnet on the basis of the load or speed of the motor. In this paper, we propose a novel motor that can vary the magnetic flux of permanent magnets and clarify the principle and basic characteristics of the motor. Our motor has a permanent magnet magnetized by a magnetizing coil of the stator. The results show that the motor can vary magnetic flux linkage from 37% to 100% and produce high torque. The results of our analysis prove that our novel motor can vary the flux of a permanent magnet on the load and can be used in a variable-speed drive with high performance.

Permanent magnet motor capable of pole changing for high efficiency

To reduce energy consumption, we developed a technique that varies the number of magnetic poles in a permanent magnet (PM) motor. We propose a PM motor that can change the number of magnetic poles and produce two types of torque. When the motor operates with eight poles, it produces a PM torque at low rotational speeds. When the motor changes to four poles, it produces both PM torque and reluctance torque at high speeds. We explain the principle and basic characteristics of the motor by using a finite element method magnetic-field analysis, which consists of a PM magnetized by a pulse d-axis current of the armature winding. The results of our experiment show that the proposed motor reduces core loss by 49% and 33% under no-load and load conditions, respectively, and doubles the speed range of the motor.

Realizing high efficiency using pole-changing hybrid permanent magnet motors

It is necessary to reduce the power consumed by variable-speed motors in electrical appliances and electric vehicles in order to achieve energy saving. Thus, we developed a technique that changes poles in a permanent magnet (PM) motor based on speed. In this paper, we propose a novel pole-changing PM motor and discuss its basic configurations and principles. The proposed pole-changing PM motor has a permanent magnet that is magnetized by the magnetizing coil of the stator. The motor can magnetize just one of the permanent magnets so as to change the number of poles in the motor. Our analytical results confirm that a pole-changing PM motor can vary the induced voltage from 15% to 100%, reduce core loss by approximately 70% over a wide speed range, and increase the speed range in drive. Thus, the proposed motor is suitable for use in a variable-speed drive system to achieve high performance and efficiency.

Effects of pole changing in a permanent magnet motor

To reduce energy consumption, we developed a technique that varies the number of magnetic poles in a permanent magnet (PM) motor. We propose a PM motor that can change the number of magnetic poles and produce two types of torque. When the motor operates with 8 poles, it produces a PM torque at low speeds. When the motor changes to 4 poles, it produces both PM torque and reluctance torque at high speeds. We explain the principle and basic characteristics of the motor, which has a PM magnetized by the pulse d-axis current of the armature winding. The results of our experiment show that the proposed motor reduces core loss by 49% or 33% and triples the speed range of the motor.

Permanent magnet motor with pole changing and variable magnetic force for variable speed

We developed a technique in which the number of poles in a permanent magnet (PM) motor is varied to reduce energy consumption. We propose a PM motor that can change the number of poles and vary the magnetic force in PM. The motor produces a PM torque at low speeds when it operates with eight poles, but it produces both PM torque and reluctance torque at high speeds when it operates with four poles. We explain the principle involved and the basic characteristics of the motor using a magnetic field analysis, which consists of a PM magnetized by a pulse d-axis current in the armature winding. Our results show that the proposed motor reduces iron loss by 46-55%, has triple the speed range than it would without pole changing and variable magnetic force, and has high efficiency over a wide speed range.

Permanent magnet motors capable of pole-changing without changing the connection of the windings for high efficiency

To realize energy saving in electrical appliances and electric vehicles, it is necessary to reduce the power consumption of motors operating at variable speeds. We developed a technique that changes the poles of a permanent magnet (PM) motor depending on the speed. Here, we propose a novel PM motor that changes the number of poles without changing the winding connections and discuss its basic configurations and principles. Pole-changing is accomplished using the d-axis current of the proposed motor for magnetization. Our analysis results confirm that the pole-changing PM motor reduces iron loss by 36% over a conventional PM motor and increases efficiency over a wide range of speeds. Hence, the proposed motor is suitable for use in variable-speed drive systems to achieve high performance and efficiency.

A permanent magnet motor capable of pole changing for variable speed drive

For reduction of energy consumption, we developed a technique that varies the number of magnetic poles in a permanent-magnet (PM) motor in accordance with speed. In this paper, we propose a novel PM motor that can change the number of magnetic poles and produce two types of torque. When the motor operates with 8 poles, it produces a PM torque at low speeds. When the motor changes to 4 poles, it produces both a PM torque and a reluctance torque at high speeds. We explain the principle and basic characteristics of the motor, which has a PM magnetized by the pulse d-axis current of the armature winding. The results show that the proposed motor reduces core losses by 50% and doubles the speed range of the motor.

Winding scheme to reduce voltage and torque ripples

Voltage and torque ripples can reduce control precision and increase vibration and noise in electric vehicles, servo systems, or wind generators. To address this problem, we proposed a novel winding method in which three phase coils are wound around each tooth, with each coil having a different number of turns around a given tooth. The proposed winding scheme may also be applied to toroidal winding. By numerical magnetic analysis, we examined the characteristics of machines using these proposed windings. The results demonstrated a reduction in back-EMF ripple to below 1% of the fundamental components. Torque ripple was reduced by approximately 7% for a four-pole machine and by 2.5% for an eight-pole machine, compared with both the concentrated and toroidal winding schemes. The proposed winding scheme was shown to significantly reduce voltage and torque ripples.

Novel integrated motor design that supports phase and pole changes using multiphase or single-phase inverters

To reduce energy consumption, a novel motor system was proposed using two individual current control technologies involving (1) a multiphase inverter and (2) a single-phase inverter. The multiphase inverter technology comprised two sets of three-phase windings connecting two three-phase inverters. Each set of coils connecting the three-phase inverters formed a rotating field. The two windings allowed the resultant field to generate a rotating field of eight or four poles. In contrast, the single-phase inverter technology connected each coil to a single-phase inverter circuit to control individual current vectors. Motor systems capable of changing their pole and phase operate at higher efficiencies over a wide range of speeds. The single-phase inverter technology additionally reduced torque ripple and vibration by controlling the current of each coil independently. For the multiphase inverter technology, results from both simulation and experimental tests confirmed that the motor is capable of changing the pole and phase during rotation. Experimental test results also confirmed that the single-phase inverter technology reduced iron loss in a motor by 50% during pole change.

Ultralightweight motor design using electromagnetic resonance coupling

To produce an ultra-lightweight motor, we propose a technology that converts electrical energy between the stator and rotor using magnetic coupling. Magnetic coupling causes electromagnetic resonance between the respective multiphase windings of the stator and rotor. Electromagnetic resonance coupling technology allows electric motors to convert energy without magnetic cores, significantly reducing their overall weight. In this study, we proposed a motor design based on magnetic resonance coupling (MRC) and described its operating principles and characteristics. A model of the proposed MRC motor was analyzed using magnetic analysis to verify its rotational energy conversion and understand its fundamental characteristics. Our results confirmed that the proposed MRC motor without a magnetic core is capable of converting electromagnetic energy between the stator and rotor and producing sufficient operating torque.