Combined Armature and Field Speed Control of DC Motor For Efficiency Enhancement

This paper presents the comparison of armature voltage control and combined armature voltage and field control of a separately excited dc motor using PI controller. This research paper is a comparison analysis so on comparing the two systems it is found that the efficiency of DC motor is enhanced by controlling both armature voltage and field voltage simultaneously which are decided by PI controller.In this paper power electronics converter (BUCK CHOPPER) are utilized to control armature voltage and field voltage simultaniously.GTO is used as a power electronics switch in this paper.The MATLAB simulation of armature voltage control and combined armature and field voltage control are compared and the simulation results of speed and enhancement of efficiency are also analyzed in this paper. Keywords—separately excited dc motor, speed control of DC motors, PI controller, hysteresis current controller, Efficiency enhancement. I.INTRODUCTION DC motors are used in many applications like electric railway traction and many more industrial fields such as rolling mills, paper industries etc, because they can provide a high starting torque. The big and practical advantage of DC motor over AC motors that the range of speed control. In DC motor we can control the speed below and above the rated speed by using different methods and techniques.The speed control above the rated speed can be achieved by using field current control method and below the rated speed by varying the armature voltage known as armature voltage control method. The speed of DC motor is directly proportional to the armature voltage(Va) and inversely proportional to the field current(If). In armature voltage control, the rage of speed control is from zero to rated speed.While in the field control, the speed control range from constant reference speed up to 120%-130% rated can be achieved but with loss of the motor developed torque. DC motors are used in many applications like electric trains, vehicles, cranes and robotics manipulators. They require controlling of speed to perform their tasks. Initially speed control of DC motor has been done by voltage control[1]. Semiconductors too like MOSFET, IGBT and GTO have been used as switching devices to control speed[2]. In this paper the combined armature and field speed control of separately excited DC motor using PI controller is discussed and the comparison between armature control of DC motor is performed and it is found that the efficiency of combined armature and field method is found better in comparison to the armature control of the dc motor. DC motors have a long tradition of use as adjustable speed machines and a wide range of options have evolved for this purpose. In these applications, the motor should be precisely controlled to give the desired performance. Many varieties of control schemes such as proportional (P), proportional integral (PI), proportional derivative integral (PID), adaptive and fuzzy logic controller (FLCs) have been developed for speed control of DC motors [3]. Speed control means intentional change of the drive speed to a value required forperforming the specific work process. Speed control is a different concept from speedregulation where there is natural change in speed due change in load on the shaft.Speed control is either done manually by the operator or by means of some automaticcontrol device. One of the important features of DC motor is that its speed can be controlled with relative ease. II MATHEMATICAL MODEL OF THE SEPARATELY EXCITED DC MOTOR In this section the main equations of a separately excited DC motor will be explained in detail, It is important to know the main relationship between armature voltage(Eb), field voltage(Ef), speed of motor, and developed torque. Figure (1) shows the equivalent circuit diagram of a separately excited DC motor. SSRG International Journal of Electrical and Electronics Engineering (SSRG-IJEEE) – volume 1 Issue 6 -August 2014 ISSN: 2348 – 8379 www.internationaljournalssrg. org Page 35 Fig. 1. Equivalent circuit diagram of a separately excited dc motor Ra --------------(1) --------------(2) ------------(3) -------------(4) -------------(5) Efficiency= 100 % --------(6)