Parameter Identification and Digital Control of Speed of a Permanent Magnet DC Motors Sanel Galijašević, Šemsudin Mašić, Senad Smaka, Abdulah Akšamović, and Dinko Balić Department for Electrical Power Engineering Faculty of Electrical Engineering Sarajevo Sarajevo, Bosnia and Herzegovina {sg14950, smasic, ssmaka, aaksamovic, db15045}@etf.unsa.ba Abstract— The digital control of speed of a permanent magnet DC motor based on a digital computer is analyzed in this paper. Datasheet information about the DC motor was initially unknown. Therefore, the parameter identification and parameter estimation of the motor was done. A type of PID controller, which parameters were optimized (PI), was used in process of controlling the speed of the motor. DAQ acquisition card was used for the purposes of motor’s parameter identification and realization of computer control of motor speed in closed feedback loop. Manipulations with the same DAQ card were done using Matlab/Simulink software package. Experimental results were compared with the results obtained by simulation. Keywords - Permanent magnet DC motor; DAQ; parameter identification; PID control. I. INTRODUCTION DC motors are type of collector motors attached to DC voltage. They are the oldest types of electrical machines and were invented after the invention of the first sources of DC current, galvanic elements. Thanks to their advantage over other AC machines in controlling the rotating speed, they found applications in many areas of industry. They are used for driving many working mechanisms, where the rotating speed must be changeable in a wide range. They find their place in many products like consumer goods and are used for industrial, medical and military purposes [1]. The most frequent requirement is the possibility to be able to control both the rotation speed and the direction [2]. Apart from these, it is also possible to control the position of a rotor and electromagnetic torque. However, the rotation speed of rotor is the most important control variable, and the variable which was being controlled in this paper [3] – [6]. In spite of the problems related with the complexity of collector – brush system (commutator) which needs constant maintenance, high production costs and problems related with the commutation as the power and speed limiter [7], the advantages of DC motors in controlling the rotation speed in wide range make it concurrent to cheaper AC machines. The DC motor being tested drives no load, except for two gear wheels, which means it does not operate in regime of ideal idling. The value of armature current is less than 20 mA, so it is possible to drive this motor with voltage signal coming directly from the analog output of the acquisition card (the maximum value of the current through the acquisition card is then limited to 30 mA). By using this approach, a better understanding of proposed principles of automatic control of analyzed DC motor is achieved, because the transfer function of power amplifier, which would separate the power part from the signal part, is not taken into consideration [8]. Although all the specifications of the controlled object – DC motor were unknown, using corresponding electrical sensors integrated on to the analyzed DC motor (tachogenerator and encoder), relevant information about the motor being controlled in closed loop are acquired. After that, by knowing the mathematical model of a permanent magnet DC motor [9], the process of motor’s parameter estimation can begin [10], [11]. The process of identifying motor parameters using Siemens PLC S7 200 CPU is the subject of paper given in [12]. After the parameter identification process of the DC motors, the type of controller is being selected (PI controller was chosen) [13], [14], and its parameters are optimized [15]. Design of the fuzzy logic control for a permanent magnet DC motor is given in [16]. The paper is organized as follows. The mathematical model and parameter identification procedure are described in the Section II. The design of PI controller and optimization of PI controllers parameters are presented in Section III. The Section IV shows the simulation model and results. Comparison of simulation and experimental results are shown in section V. The conclusions are written in Section VI. II. PARAMETER IDENTIFICATION OF DC MOTOR A. The transfer function of a DC motor The mathematical model of a permanent magnet DC motor is described by the following set of equations: a a aa a mech di u Ri L c dt ω = + + , (1) a l mech d ci T J dt ω = + , (2) where u a and i a are current values of armature voltage (V) and current (A), c is the construction constant of the motor (V·s/rad), ω mech is the mechanical angular speed of the motor’s shaft (rad/s), T l is the current value of the load torque (N·m),