A Method of Determining the Transfer Function Parameters of a Capacitor Servomotor

Abstract

The aim of this paper is to establish a simple method for the calculation of the transfer function parameters of the capacitor servomotor. The equivalent circuits of a group of twelve capacitor servomotors of widely different parameters are simulated on a transformer analogue network analyser. An empirical formula expressing the reference voltage in terms of the motor speed, control voltage and the capacitance value is obtained. A torque equation for the capacitor servomotor is deduced by introducing the obtained formula in the torque equation of the two-phase servomotor derived by Saleh and Yuferov. The gain and time-constant of the capacitor servomotor are deduced from the proposed torque equation. Effects of the control voltage, as well as the effects of the capacitive reactance on the gain and time-constant, are also discussed. The torque-speed characteristics of a drag-cup capacitor servomotor are computed for different values of the control voltage and different capacitances using the proposed torque equation, and compared with those obtained experimentally. The experimental results are in good agreement with the theoretical calculations.