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Top1. Introduction
The different process variables are maintained by the operation of the different manual and automatic control loops at the desired values in order to obtain the high quality product at lesser cost along with all the safety aspects of the plant operation and the PID controller (Bindu & Namboothiripad, 2012; Matousek, Minar, Lang, & Pivonka, 2011; Malhotra, Singh, & Singh, 2011; Thomas & Poongodi, 2009; Astrom & Hagglund, n.d.; Bera & Chattopadhyay, 2001; Bera & Chattopadhyay, 2004) is one of the most important components of any automatic control loop. Different research works are going on about the design and tuning of PID controllers; some of them are being reported.
Direct current machines (Bimbhra, 2010; Considine, 1974) are the most versatile energy conversion devices. Their outstanding advantage is that the volt-ampere or speed-torque characteristics of these machines are very much flexible and easily adaptable for both steady state and dynamic operations. Due to these excellent characteristics of a DC motor, it has been widely used in industry even though its maintenance costs are higher than the induction motor. Their inherent characteristics can be modified further by making use of the feedback control circuits. Permanent magnet direct current motors PMDC have been widely used in high-performance electrical drives and servo system, whose poles are made of permanent magnets. The permanent magnets of PMDC motor are magnetized and mounted on the inner periphery of the cylindrical steel stator. The rotor has a conventional DC armature, with commutator segments and brushes. Most of the PMDC motors operate on 6V, 12V, 24V DC supply obtained from batteries or rectifiers. There are many different types of DC motor (Bimbhra, 2010; Considine, 1974) available in the market and all with it good and bad attributes. Such bad attribute is the lag of efficiency.
In order to overcome this problem, a controller is introduced to the system. There are also many types of controller used in industry but PID controller (Thomas & Poongodi, 2009; Singh Chauhan & Semwal, 2013; Jairath, 2009; Comanescu, Keyhani, & Dai, 2003; Bera & Chattopadhyay, 2004) is the most widely used control algorithm in the process industry and improvements in tuning of PID controllers will have a significant practical impact on its performance. The PID controller has three principal control effects. The proportional P action gives a change in the controller output directly proportional to the control error. The integral I action gives a change in the controller output proportional to the integral error, and its main purpose is to eliminate offset. The less commonly used derivative D action is used in some cases to speed up the response or to stabilize the system, and it gives a change in the controller output proportional to the derivative error.
There are lot of design techniques of speed control system of a DC motor using different types of controller. J. Singh Chauhan et al. (2013), proposed microcontroller based speed control of DC geared motor through RS-232 interface with PC.
Here PWM based speed control of DC motor through RS232 with PC, replaced the role of electrical drives in industrial automation. A. K. Dewangan et al. (2012), presented PWM based automatic closed loop speed control of DC motor. Here implementation of the ATmega8L microcontroller for speed control of DC motor fed by a DC chopper has been used. Here a constant speed of the DC motor is maintained instead of varying the amount of load. N. Afrasiabi et al. (Afrasiabi & Yazdi, 2013) proposed DC Motor Control Using Chopper, where the speed of DC motor is controlled by using a chopper circuit, which performs as a converter.