MATLAB Sample ScriptsWith Electrical Engineering Applications

Shameer A Koya

Introduction This lecture we will do some practice on

Basic MATLAB Scripts. We will start with simple scripts and will

discuss some electrical engineering applications.

More scripts including conditional statements will be discussed in the next lecture.

Please review lectures on basic input and output commands.

Script 1% Program to calculate Height of a Building from time a stone takes to reach the basement. % Use g=9.81and k=0.05 g=9.81; k=0.05; time= input (‘Enter the time taken: ‘); height=g*(time+(exp(-k*time)-1)/k)/k; disp(’Depth of well is ’) disp(depth) disp(’metres’)

Script 2% Program to calculate the BMI (body mass index)

% Input your Height and Weight  weight = input('Type your weight (kg): '); height = input('Type your height (m): '); 

bmi    = weight / height^2;  % Display the BMI   fprintf('Your Body Mass Index is %f\n", bmi); 

Script 3% Program to calculate Electricity bill. w = input('Enter power of your device (in watts): ');h = input('Enter time (in hours): ');r = input('Enter electricity rate (in dollars per KWH): '); ec = w * h/1000 * r;disp(’Your Electricity bill is’)Disp(ec)

Power transfer vs Load resistance curveRL = 1:0.01:10;Vs = 12;Rs = 2.5;P = (Vs^2*RL)./(RL+Rs).^2;plot(RL,P)xlabel('Load resistance')ylabel('Power dissipated')

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Curve fitting% Second order curve fitting%enter the input x and y vectorsx = [0 .1 .2 .3 .4 .5 .6 .7 .8 .9 1];y = [-.447 1.978 3.28 6.16 7.08 7.34 7.66 9.56 9.48 9.30 11.2];n = 2;p = polyfit( x, y, n ) %Find the best quadratic fit to the

dataxi = linspace(0,1,100);yi = polyval(p, xi); % evaluate the polynomialplot(x,y,’-o’, xi, yi, ‘-’)xlabel(‘x’), ylabel(‘y = f(x)’)title(‘Second Order Curve Fitting Example’)

Series RLC circuit % Program to plot current vs frequency semilog

plot of a series RLC circuit

R = input('Enter value of resistance in ohms:'); L = input('Enter value of inductance in Henary:'); C = input('Enter value of capacitance in Farads:'); V = input('Supply voltage in volts:') f = 0 : 1: 1000000; XL = 2 * pi .* f * L; XC = 1./(2 * pi .* f * C); Z = (R^2-(XL-XC).^2).^0.5; I = V ./ Z; semilogx(f,real(I)); title('Current Vs Log frequency plot' ); xlabel('fLogf'); ylabel('Current in A');

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DC Machines CharacteristicsMATLAB program to calculate the characteristics of separately excited DC motor.%Required parameters are Ra, k, Rf, Vt, Ns, k, Vf clc;Ra=0.5 ;Rf=250;Vt=250;k=2;Vf=250;T = 0:100; % vector of torque If=Vf/Rf;Ia=T/k;Ea=Vt-Ia*Ra;w=Ea/k/If;N=w*60/2/pi;plot(T,N)xlabel('Torque')ylabel('Speed in RPM')title('Speed-Torque Curve')plot(T,Ia)xlabel('Torque')ylabel('Armature Current')

study the characteristics of shunt and series DC motors

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Induction MachineTorque-Speed Curve for a squirrel cage Induction Motor Ns=1500; % Synchronous speed; R1=15.6 ;R2=14;X1=18; X2=23;Xm=260;Vt=400/sqrt(3); s = 0.002:0.002:1; % vector of slip N = Ns.*(1-s); % Speed, in RPM Ws = 2*pi*Ns/60; % Synchronous speed in rad/sec Rr = R2./ s; % Rotor resistance Zr = j*X2 + Rr; % Total rotor impedance Za = j*Xm*Zr./(j*Xm+Zr); % Air-gap impedance Zt = R1 + j*X1 +Za; % Terminal impedance Ia = Vt ./ Zt; % Terminal Current I2 = j*Xm*Ia./(j*Xm+Zr); % Rotor Current Pag = 3* (abs(I2)).^2.*Rr; % Air-Gap Power Pm = Pag.* (1-s); % Converted Power Trq = Pag/ Ws; % Developed Torque subplot(2,1,1) plot(N, Trq) xlabel('Speed in RPM') ylabel('Torque (Nm)') subplot(2,1,2) plot(Ia, Trq) xlabel('Load Current') ylabel('Torque (Nm)')

Synchronous Motor%M-file to calculate and plot the terminal voltage % of a synchronous generator as a function of load% for power factors of 0.8 lagging, 1.0, and 0.8 leading.% Define values for this generatorEA = 277; % Internal gen voltageI = 0:2:240; % Current values (A)R = 0.03; % R (ohms)X = 0.25; % XS (ohms)% Calculate the voltage for the lagging PF caseVP_lag = sqrt( EA^2 - (X.*I.*0.8 - R.*I.*0.6).^2 )- R.*I.*0.8 - X.*I.*0.6;VT_lag = VP_lag .* sqrt(3); % Calculate the voltage for the leading PF caseVP_lead = sqrt( EA^2 - (X.*I.*0.8 + R.*I.*0.6).^2 )- R.*I.*0.8 + X.*I.*0.6;VT_lead = VP_lead .* sqrt(3);% Calculate the voltage for the unity PF caseVP_unity = sqrt( EA^2 - (X.*I).^2 );VT_unity = VP_unity .* sqrt(3); % Plot the terminal voltage versus loadplot(I,abs(VT_lag),'b');hold on;plot(I,abs(VT_unity),'k--');plot(I,abs(VT_lead),'r:'); legend('0.8 PF lagging','1.0 PF','0.8 PF leading');grid on;hold off;

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n 12% INPUT THE LINE PARAMETERS Z = input ('Enter Line Impedence, Z line: '); Y = input ('Enter Line Admittance, Y line: '); P = input ('Enter Recieving end Power, Pr: '); VL = input ('Enter Recieving end Voltage, Vr: '); PF = input ('Enter Recieving end Power factor, pfr: '); % CALCULATION OF ABCD CONSTANTS A=(1+Z*Y/2); D=A; B=Z; C=Y*(1+Z*Y/4); A1=acos(PF); VR=VL/sqrt(3); % CALCULATION OF RECEIVING END CURRENT IR= P/(sqrt(3)*VL*PF); IR=IR*(cos(A1)-j*sin(A1)); % CALCULATION OF SENDING END VOLTAGE VS=A*VR+ B*IR; VSA=abs(VS); VSL=sqrt(3)*VSA; % CALCULATION OF VOLTAGE REGULATION VVRR=(VSA/abs(A)-VR)/VR; VREGULATION = VVRR*100; % CALCULATION OF SENDING END CURRENT IS=C*VR+D*IR; ISA=abs(IS); % CALCULATION OF PHASE ANGLE PA=angle(VS)*180/pi; PB = angle (IS) *180/pi; PS=(PA-PB)*pi/180; PFS=cos(PS); PS=sqrt(3)*ISA*VSL*PFS; % CALCULATION OF SENDING END POWER EFFICIENCY=(P/PS)* 100; % CALCULATION OF EFFICIENCY fprintf ('Efficiency is %d\n', EFFICIENCY); fprintf ('Voltage Regulation is %d \n', VREGULATION);