Final year project Analysis and simulation of a converter fed dc motor drive by using MATLAB

Introduction Converter-fed dc motor drives are extensively used in special heavy duty application The ac-dc converters also known as controlled rectifiers are generally used for the speed control of dc motors The speed of dc motors changes due to the changes of load torque When the torque is increased, the speed of the motor is decreases due to the voltage drop in the armature resistance To maintain the constant speed of the motor, the armature voltage should be varied continuously by varying the alpha angle of a ac-dc converters. Thus, the controller must be added to control the alpha angle

Objectives To develop the transfer function of the dc motor with and without feedback To design controller with a speed feedback (closed loop feedback) using PI controller and simulate the drive under different loading and reference speed. To conduct experiments to verify results with the simulated responses.

Methodology Literature Survey – References from library and IEEE website - Through guidance from lecturers Simulation – Using MATLAB M-file and SimPowerSystems

,where (1) (2) (3) Substituting all equations above; (4)

Transfer Function Using Laplace transform; Then, the transfer function becomes;

Transfer functions of: Proportional Integral Controller (PI)

Block Diagram of dc motor Block diagram of converter

Block Diagram of a converter-fed dc motor

Torque – speed characteristic The graph shown below is the effect of armature voltage speed control on a separately excited dc motor’s torque-speed characteristic. Speed ω Va1 Va2 Va3 Torque Τ

Effect of change the load torque due to the speed of the motor Dc motor with speed-feedback controller Change the load torque ω Time

Project Research Using Matlab M-File Using Simulink (Simpowersystem) Design requirement with 1 rad/sec step reference, settling time less than 3 sec and steady-state error less than 2 %. Using Simulink (Simpowersystem) Block diagram of dc motor drive with and without feedback with 100 rad/sec speed reference. Simulation of converter fed dc motor under different loading and speed references.

Control input voltage = ±10V MOTOR RATINGS FOR SIMULATION USING M-FILE AND BLOCK DIAGRAM TRANSFER FUNCTION 240 V, 8.3 A, 60 Hz, 5hp Control input voltage = ±10V Maximum current permitted in the motor is 20A. Moment of Inertia (J) = 0.0607 (kg-m2) Machine frictional torque coefficient (Bt) = 0.0869 (N.m/rad/sec) Armature resistance (Ra) = 4 Ω Armature Inductance (La) = 0.072 H Kb = 1.26 V/rad/sec

Simulation Using M-File Open loop transfer function of dc motor Settling time>3 sec Speed<1rad/sec

Proportional Integral (PI) Controller with Kp=100 and Ki=150 Settling time<3sec Speed=1 rad/sec

Simulation using Simulink Block diagram without feedback Block diagram of speed controller dc motor drive

Simulation results Without feedback Settling time>3sec Speed>100 rad/sec

With feedback (speed and current controller) Settling time<3 sec Speed= 100rad/sec

DC Motor ratings

Simulation using SimPowerSystems Without feedback

Result

With feedback

Results Constant speed and torque with Kp=2 and Ki=20

Constant speed with changing load torque (Kp=2 and Ki=20)

Step speed reference with constant torque (Kp=2and ki-20)

Step speed reference with changing load torque (kp=2 and ki=20)

Kp=2 Ki=20 6% 0.385sec 10% Kp=30 Ki=50 5% 0.175sec 2% Kp=100 Ki=150 Comparison results of using different value of Kp and ki. Overshoot Settling time Steady state error Kp=2 Ki=20 6% 0.385sec 10% Kp=30 Ki=50 5% 0.175sec 2% Kp=100 Ki=150 oscillates 1.9% Good controller

Experimental results The speed with and without load when using PI controller PI-controller parameters Speed (ω) without load (rpm) Speed (ω) with load (rpm) Kp=100,Ki=200 1506 1501 Kp=100, Ki=20 1517 1520 Kp=5,Ki=10 1509 1511 Kp=1, Ki=5 1498 1502

Conclusion A Proportional plus Integral (PI) controller is design to reduce the system errors and improve the dynamics responses. The constant KP and KI in PI controller can be changed to meet the acceptable performance. This project compares a various study in designing the converter-fed dc motor drive with and without system feedback and simulates drive under different loading and speed references. By increasing the constant KP and KI tends to reduce the systems errors and improve the overshoot and settling time. However, large KP and KI will worsen the transients’ stability. A good controller will change back the motor speed to the normal value due to the change of load torque. The proposed converter is designed and tested in the lab using the separately excited dc motor. The experimental results are shown to be in good agreement with the simulated results.

Future Research More extensive follow-up studies can be done so that the proposed approach is always up-to-date. Further fine tuning of the speed controller. Example, design the Proportional Integral and Derivative (PID) controller in order to enhance and improved the transients stability. The automatic tuning is also can be done by using the Non-linear Control Design (NCD) in Simulink Blockset. Further research in designing the four quadrant three phase rectifier in SimPowerSystems simulation.

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Theodore Wildi. 2006. Electrical Machines, Drives, and Power Systems Theodore Wildi. 2006. Electrical Machines, Drives, and Power Systems. 6th Edition. Prentice Hall. W. Shepherd, L.N. Hulley, and D.T.W. liang. 2002. Power Electronics and motor control. 2nd Edition. Cambridge University Press.

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