ANALYSIS OF LIMIT CYCLE OSCILLATIONS DUE TO INSTRUMENT'S SATURATION IN DC MOTOR CONTROL SPEED

• Main Author: Mengheang, HAK
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/69940
• Institution: Institut Teknologi Bandung

PID control has been widely used for speed control applications of DC motor over AC motor. However, at the point during operation, the controller may reach a condition called saturation limit that causes the control system to become a nonlinear system. The saturation is called limit cycle oscillations (LCO). The stable LCO phenomenon is mostly undesired. Therefore, it is important to check the possibility of occurrence and characteristics of the LCO phenomenon and to come up with a PID controller that avoids LCO. In this study, the describing function (DF) analysis is selected to analyze the possibility of LCO in the control system. The result shows that the control system can experience LCO since the frequency of LCO can be found as a solution of the analysis. Besides the frequency, the amplitude of LCOs can be calculated from the DFs analysis. The DFs analysis offers the condition for the controller to prevent the control system from experiencing LCOs. To evaluate the performance of DFs analysis, simulation in MATLAB Simulink is performed. The simulation shows that the controller has to follow Routh-Hurwitz instead of DF to avoid LCOs. This result shows the shortfall of DFs for the controller to avoid LCOs. However, the existence and characteristics of LCOs like frequency and amplitude are accurately predicted from DFs analysis. To have a better understanding, and also to replace experiment, Tina-TI program is employed to build an electrical circuit model to represent the control system and simulate the system to compare the results to both DFs analysis and MATLAB Simulink. The results show that the DFs analysis shows a very good agreement with Simulink and Tina-TI.