The commutatorless motor with an armature induced voltage commutation has found recently many practical applications. However, it has a drawback that its commutation ability is smaller than that of a motor with forced commutation.
Examples of the most commonly used position sensor of a rotor are a device composed of proximity switches or a device composed of lamps and photo-transistors. These devices, however, have a drawback of a fixed leading angle.
The effective leading angle which determines the reverse bias period of commutating thyristor decreases with an increase of load current. If a leading angle is controlled according to the load current automatically, the commutation ability is, much increased than in the case of fixed leading angle.
Along this idea we have conducted an experiment about a new detection method of the rotor's position by detecting the armature induced voltage. This control method compensates the decrease of a leading angle due to the armature reaction by detecting the self adjusted cross point of the induced voltages and requires no mechanical position sensor such as proximity switches, photo-transistors or a sector.
Therefore, this control method enables us to control a conventional synchronous motor as a commutatorless motor only with an addition of control circuits.
According to the theoretical considerations of the criterion of the commutation ability, its maximum current becomes 3.75 times as much as that for a mechanical position sensor and its maximum torque is 3.24 times as much. The most suitable leading angle of this control method is 45∼50 degrees.
We have proposed the starting method of the commutatorless motor which is controlled by this control method and have shown that this starting method enables us to start successfully the commutatorless motor.
We have introduced theoretically the relation between the angular velocity of the motor, the power source voltage, the current and the phase angle in a state of starting and have shown a permissible range of the power source voltage for a stable starting.

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Current source inverter-fed synchronous motors, hereafter we call them commutatorless motors, have come into a wide use in industry as variable speed drives. They can be controlled to give a good to give a good performance as DC motors can and are easy to be maintained as AC motors are.
When this system is used as a variable speed drive, it is important to consider dynamic characteristics as well as steady state ones.
When we consider dynamic characteristics of variable speed drives, two kinds of dynamics should be taken into consideration; one is the electrical dynamics and the other is the electromechanical dynamics. Since a response in electrical dynamics is much faster than that of electromechanical ones, these two dynamics can be discriminated one from another. The electro-mechanical dynamics can be easily obtained from the torque-speed curve of the motor and the torque characteristics of the load. On the other hand, the electrical dynamics can not be easily obtained, since it involves complicated electrical phenomena. However, the electrical dynamics is a very important factor when a high performance of control characteristics like that of DC drives is required of commutatorless motors.
In this paper, first, the transfer function models of commutatorless motors are obtained mainly from the view point of the electrical dynamics and the transfer function model including the electro-mechanical dynamics is discussed later. The models have been derived on the basis of the average behaviours which are represented by continuous dynamic equations. The phenomena during commutation periods are considered to be equivalent with average voltage drops in the circuits. The adequacy of the transfer models has been confirmed by both simulation and experimental results.
The effects of motor parameter on the performance characteristics of the system are also discussed.

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The great advance of the power electronics technics brought about a significant improvement for motor control. Especially, induction motors and commutatorless motors driven by current source inverter have many excellent characteristics on steady and dynamic state, and these driving systems are intended for practical use as ideal variable speed motors. The torque pulsation, however, is considerably large and it has bad influence upon the mechanical system. Many studies have been made in order to reduce the torque pulsation. Some intended to improve the current wave forms, others designed to make a multi-phase system. These methods are very useful to improve the torque pulsation, but there are few reports which examined the experimental results of the instantaneous torque.
Generally speaking, the motor driving system forms a high Q torsional resonator and instantaneous torque on the motor shaft contains a large sinusoidal wave component at the resonance frequency. Cosequently, it is very difficult to measure the instantaneous torque generated by the motor. Many measurement methods have been reported, but they are not sufficient for exactness and laborious.
In this paper, the equivalent circuit of the motor driving system is derived and the system is precisely represented as a second-order equation. A new method is proposed, which compensates the torsional oscillation with band rejection filter. It is proved with the experimental results that this measurement method is very useful and accurate.

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サイリスタモータを安定、高効率、高力率に運転するためには、転流余裕角一定制御が必要であるが、制御性、運転範囲の向上のためには更に空隙磁束を一定にする制御法が有用である。
本文では、この制御法をROMテーブルにより簡単に実現する方法を提案し、更に実験によりこのシステムの有用性を確かめている。

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A self-controlled synchronous motor, which has similar characteristics to a conventional dc motor, is being used in various industrial fields as an adjustable speed motor. The inductances in the motor are changed with the change in the air-gap flux due to magnetic saturation as in the field-weakening region. A new and simple formula representing the inductances (i.e. reactances) in which the effect of magnetic saturation is taken into account is proposed in this paper, and the validity of the formula is shown for the transient performances of a tested motor when the field voltage was stepped down. The effects of the magnetic saturation on the steady-state and dynamic performances are then clarified for a motor having average constants of synchronous machines. It is shown that the steady-state motor speed for small values of dc input current when the magnetic saturation is considered is larger than that for constant parameters. It is also clarified that the field-weakening speed control regions for constant-power driving become narrow if the motor has a property of considerable magnetic saturation. The transient responses when dc input and field voltages are changed, respectively, are finally investigated, and it is shown that if magnetic saturation is considered, the commutation limit of inverter thyristors for a step-down change in the field voltage is widened when compared with the case for constant parameters.

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Using high-speed camera, we have been doing some experiments to clarify the mechanism of the commutation spark generation from the image aspect in universal motor. Previously we mentioned about the cases of single and plural number of sparks generation at single commutator segment This time, we took pictures of all the sparks generated during a single-rotation of the motor and examined sparks generation distribution and their positions of the brush. As a result, we observed that the closer the position to the side where the brush and the armature coil are connected the more sparks are generated. Also we measured the voltage between brush and commutator segment.

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