Power Electronics

Draw two-transistor behavioral model of a thyristor.

Why Snubber Circuits are used in Power Electronics?

Draw and explain the turn-off snubber Circuit for thyristor.

Draw the V - I characteristics of Power IGBT.

What are the various implications of heat dissipation in power MOSFET?

What are the desirable features for a semi conductor device to operate as an ideal switch?

Mention the differences between MOSFET and IGBT.

What do you understand by a duty ratio for any given converter?

What do you understand by commutation of SCR?

Explain the latching and holding current in thyristor.

A three-phase controlled rectifier has an input voltage which is $480\text{ V rms}$ at $60\text{ Hz}$. The load is modelled as a series resistance and inductance with $R=10\Omega$ and $L=50\text{ mH}$. Determine the delay angle required to produce an average current of $50\text{ A}$ in the load.

Show that the power factor for the controlled Full wave rectifier with resistive load is $\text{pf}=\sqrt{1-\frac{\alpha }{\pi }+\frac{\sin (2\alpha )}{2\pi }}$.

A half-controlled single-phase bridge rectifier is supplying an R-L load. It is operated at a firing angle $\alpha$ and the load current is continuous. Calculate the fraction of cycle that the free wheeling diode conducts.

A three phase fully controlled bridge converter is feeding a load drawing a constant and ripple free load current of $10\text{ A}$ at a firing angle of $30^{\circ }$. Find out the Total Harmonic Distortion (\%THD) and the rms value of fundamental component of input current.

Explain the working of boost converter with suitable diagram and Waveforms.

Mention in detail, the various applications of DC - DC converters.

A Single-phase inverter is operated in PWM mode generating a single-pulse of width 2d in the centre of each half cycle as shown in figure Q7. It is found that the output voltage is free from 5th harmonic for pulse width $144^{\circ }$. What will be percentage of 3rd harmonic present in the output voltage ($V_{o3}/V_{01\text{ max}}$)?

Design a circuit that will produce an average current that is to vary from $8$ to $12\text{ A}$ in an $8\Omega$ resistor. Single phase ac sources of $120$ and $240\text{ V rms}$ at $60\text{ Hz}$ are available. The current must have a peak-to peak variation of no more than $2.5\text{ A}$. Determine the average and rms currents and maximum voltage for each circuit element.

Design a buck converter to produce an output voltage of $18\text{ V}$ across a $10\Omega$ load resistor. The output voltage ripple must not exceed $0.5\%$. The dc supply is $48\text{ V}$. Design for continuous inductor current. Specify the duty ratio, the switching frequency, the values of the inductor and capacitor, the peak voltage rating of each device, and the rms current in inductor and capacitor. Assume ideal component.

In a full bridge inverter of figure Q3 has a switching sequence that produces a square wave Voltage across a series RL load. The switching frequency is $60\text{ Hz}$, $V_{dc}=100\text{ V},R=10\Omega$, and $L=25\text{ mH}$. Determine (a) an expression for load current. b) The average current in the dc source.

The full bridge inverter is used to produce a $60\text{ Hz}$ voltage across a series RL load using bipolar PWM. The dc output to the bridge is $100\text{ V}$, the amplitude modulation ratio $m_a$ is $0.8$, and the frequency modulation ratio $m_f$ is $21$. The load has a resistance of $R=10\Omega$ and series inductance $L=20\text{ mH}$. Determine the THD of the load current.

Design a bipolar PWM inverter that will produce a $75\text{-V rms }60\text{ Hz}$ output from a $150\text{V}$ dc source. The load is a series RL combination with $R=12\Omega$ and $L=60\text{ mH}$. Select the switching frequency such that the current THD is less than $10$ percent.