On the Control System of the Thyristor Brush Type dc Machine

Abstract

The conventional do machine has the advantage of the most accurate controllability for industrial power applications in various kinds of electrical machine. It can easily be controlled by the amount of armature voltage or field current, over the wide range of speed, torque and power. The commutatorless motor applied by thyristors is proposed as the maintenance-free machine to improve a disadvantage of the conventional do machine. Its driving characteristics are similar to those of the synchronous machine, that is, the instantaneous torque ripple appears by considerable amount to cause shaft vibration especially under low driving speed region, while the machine is drove by the square wave inverter circuit.
The thyristor brush type do machine, proposed by authors, is a species of the commutatorless motor and is composed of the same armature winding and air gap flux distribution as the conventional do machine, and of the polyphase thyristor switching circuit, which produce the similar characteristics as that of the do machine.
In this paper, the methods of thyristor gate control and effective number control of divided armature coils on the thyristor brush type do machine are reported with respect to its industrial applications as the equivalent do machine. The latter control is applied to improve driving stability in higher speed region by decreasing the number of control phases and to reduce instantaneous torque and speed vibration in lower speed region by increasing the number of control phases. The characteristics of the machine are discussed mainly on the machine with armature coils divided by eighteen. Instantaneous torque of the machine is also analyzed, and observed torque ripple of the experimental machine is lower than the expected value. The instantaneous shaft torque keeps nearly constant at merely ten per cent speed of rated value.