Recently, the speed control systems using separately excited DC motor driven by the thyristor DC power supply are employed in many industries, because they have more advantages when the conventional motor-generator speed control system.
On the other hand, on account of the backward interceptive characteristics of the diode and the thyristor, the armature circuit is separated from the power supply during one cycle of the pulsating power supply. As a result of the above, the armature current often flows discontinuously. When the armature current is discontiuuous, the static and dynamic characteristics of the motor become fairly different from the case of continuous armature current.
In this paper, the dynamic characteristics of the speed control system using the separately excited DC motor operated by the thyristor chopper controlled by means of the pulse width modulation are described. The authors turn their attention to the response of the motor speed for three input or disturbance signals; the variation of the load torque, the conductive period of the thyristor chopper, and the voltage of DC power supply. The transfer functions obtained to the above input signals are approximated by the first order lag, and the comparisons and the discussions of the measured dynamic characteristics and their transfer functions derived theoretically are given.
However, the time constants and the gain constants of the tested motor are widely variable due to the operating conditions. Therefore, detailed datum to grasp the tendency of these variations and to obtain the characteristics of the separately excited DC motor correctly is offered here.
