Question

The full bridge inverter is used to produce a 50 Hz voltage across a series R-L load using bipolar PWM. The dc input to inverter is 100 V, the amplitude modulation ratio $\left(m_a\right)$ is 0.8, the frequency modulation ratio $\left(m_f\right)$ is 21. The load has resistance of R = 10 $\Omega$ and inductance L = $\frac{1}{10\pi }H$, with the help of given below data. The peak value of harmonic voltage ${}^{\prime }{V}_{21}$' will be (Use given table of normalized Fourier coefficients $\frac{V_n}{V_{dc}}$ for bipolar PWM).

	$m_a=1$	0.9	0.8	0.7
n = 1	1	0.9	0.8	0.7
n = $m_f$	0.61	0.71	0.82	0.92
$n=m_f\pm 1$	0.32	0.27	0.22	0.17

• A. 6.06 V
• B. 82 V
• C. - 89 V
• D. 22 V

Answer 1

The correct option is B 82 V

With $m_f=21,$ the first harmonics are at n = 21, 19, 23
$V_{21}=(m_{f}correspondsto{m}_f=0.8)\times V_{dc}$
$V_{21}=0.82\times 100=82V\left(peakvalue\right)$