Characteristics of DC Series Motor Operating with Thyristor Chopper Source

With the rapid improvement of thyristor elements, it has become a frequent practice to drive a DC series motor by the chopper power supply. The static and dynamic performances of a DC series motor driven by the chopper power supply must be different from those driven by the pure DC power supply.In this paper, firstly the theoretical analysis of the static performance of a DC series motor operating with the thyristor chopper is presented. Especially, the general equation on the speedtorque characteristic is derived. The calculated results from it are compared with the measured ones. Secondly we obtained the dynamic characteristic of the motor subjected to small variations around the working point of supply voltage and load torque. Consequently we found that the transfer function of the DC series motor is approximated practically by the form of first order lag and that experimental values agree well with the calculated result.