An Electromechanical Network Model of the DC Motor

A dc motor is modeled by means of a network representation of an analogous mechanical system consisting of a velocity source, rotational damper, and rotational spring which derive from the no-load speed, armature resistance, and armature inductance, respectively. It is shown that the reduction in the field due to the cross-magnetization effect of the armature current can be approximated by an additional damper and a controlled torque source. A Thevenin equivalent of the resulting electromechanical network is obtained and applied to common situations. Steady-state applications in which loads are characterized by any combination of coulomb and viscous friction can be solved directly with ease. It is also shown that the response to small changes in armature voltage, field voltage, or both can be obtained directly. Dynamic characteristics are considered by deriving system functions from the equilibrium equations which can be written directly from the network representation of the complete electromechanical system.