150Hz Sine wave in MATLAB simulink

When I feed 150 Hz to a sine wave block with scope settings of 0.04 seconds of time span and 0.00166 as sample time, my output wave looks like a triangle wave rather than a sine wave. How do I make it appear as a sine wave?

Answer 1

[Sam Chak]

Hi @Manuprabha Ravikumar

In short, your sinusoidal signal is undersampled. There are only 5 samples in one cycle.

ts  = 1/600     % sample time

ts = 0.0017

t   = 0:ts:0.04;
f   = 150;
P   = 1/150     % Period (1 cycle)

P = 0.0067

sam = P/ts + 1  % number of samples in 1 cycle

sam = 5

y   = sin(2*pi*f*t);
plot(t, y), grid on, xlabel('t')

However, the curve looks smoother if you decrease the sample time by 100 times, as there are 401 samples (> 360 samples) in 1 cycle.

ts  = ts/100    % sample time

ts = 1.6667e-05

sam = P/ts + 1  % number of samples in 1 cycle

sam = 401

t   = 0:ts:0.04;
y   = sin(2*pi*f*t);
plot(t, y), grid on, xlabel('t')

Answer 2

[halleyhit]

Hi Manuprabha, please make sure you feed 150*2*pi to the block, because the unit is rad/s. Then, please use a smaller sample time, and you will have a wave more like sine.

[Manuprabha Ravikumar]

Still the same...