PROJECT TOPIC- INSIGHT INTO THE DYNAMIC PERFORMANCE OF A CLOSED LOOP SPEED CONTROLLED SEPARATELY EXCITED DC MOTOR WITH P, I & PI CONTROLLERS
In this paper, the dynamic performance of a speed controlled separately excited dc motor is analytically investigated under open and closed loop conditions. The closed loop control arrangement considered is of two types: one with a speed controller only and the other with a speed controller and an inner current loop controller. In this closed loop arrangement, the relative merits and demerits of the proportional, the integral and the
proportional plus integral controllers are investigated and highlighted. Use of the integral (I) controller alone has the advantage of giving zero steady state error and excellent speed regulation but results in significantly degraded system response speed, high response oscillations and/or total system instability. The proportional (P) controller alone, for a given control arrangement, gives relatively faster transient response speed but at the expense of higher transient armature current and appreciable steady state errors that increase with decrease in the controller gains. The proportional plus integral (PI) controller combines the advantages of the P and I controllers and these advantages include system fast response speed, excellent speed regulation and absence of steady state errors. For P and PI controllers, the inner current loop control arrangement shows faster speed response and good stability over a wide range of controller gain variation than the arrangement without inner current loop. Illustrative dynamic performance curves are given for a 230V, 204 1500 rpm separately excited dc motor.
Because of its simplicity of analysis and ease of control the dc motor is widely used in industrial drives [i,2,3,<5]. Also, the brushless dc motor, which is electrically-modeled as the conventional dc motor, has further raised deep interest in dc motor-like industrial drives because of its low maintenance requirements [6,7]. Extensive research interest in dc motor drives (including dc servo motor drives) has therefore continued to be sustained. In this paper, the dynamic performance of a speed controlled seporrtely excited dc motor with constant field excitation is investigated. Two closed loop control schemes are considered.
These are the closed loop control with and without the inner current loop. The effects of the proportional, the integral and the proportional plus integral controllers on the motor stability and dynamic response to step changes in the armature terminal voltage, speed setpoint and load torque are comparatively highlighted. A 230V, 204 1500 rpm separately excited motor is used as an example motor in the study. The PI controller is seen to give drive performance that combines th httrantages of the proportional and the integral controllers. Also, the inner current ldhr ;;:I arrangement significantly showed superior drive performance than the arrangtm~:lt~ ~;thouant inner current loop. To the control engineer on dc industrial drives, the rmlta of the study provide useful guide on how to select speedcurrent controllers for specified dc drive applications.