Choppers and Commutation Techniques · Power Electronics · GATE EE
Marks 1
A forced commutated thyristorized step-down chopper is shown in the figure. Neglect the ON-state drop across the power devices. Assume that the capacitor is initially charged to 50 V with the polarity shown in the figure. The load current ($I_L$) can be assumed to be constant at 10 A. Initially, ThM is ON and ThA is OFF. The turn-off time available to ThM in microseconds, when ThA is triggered, is________ (rounded off to the nearest integer).

The chopper circuit shown in figure (i) feeds power to a 5 A DC constant current source. The switching frequency of the chopper is 100 kHz. All the components can be assumed to be ideal. The gate signals of switches S$$_1$$ and S$$_2$$ are shown in figure (ii). Average voltage across the 5 A current source is





List $$-$$ $${\rm I}$$
$$A.$$ Commutation
$$B.$$ $$V$$ $$-$$ Curves
$$C.$$ Free wheeling diode
$$D.$$ Overlap
List $$-$$ $${\rm II}$$
$$P.$$ Resistive load
$$Q.$$ Inductive load
$$R.$$ Capacitive load
$$S.$$ Inter pole
$$T.$$ Source Inductance
$$U.$$ Synchronous motor
Marks 2
In the DC-DC converter shown in the figure, the current through the inductor is continuous. The switching frequency is 500 Hz. The voltage ($V_o$) across the load is assumed to be constant and ripple free. The peak inductor current in amperes is __________ (rounded off to the nearest integer).

The circuit shown in the figure has reached steady state with thyristor 'T' in OFF condition. Assume that the latching and holding currents of the thyristor are zero. The thyristor is turned ON at $$t=0$$ sec. The duration in microseconds for which the thyristor would conduct, before it turns off, is _________ (Round off to 2 decimal places).
The steady state current flowing through the inductor of a DC-DC buck boost converter is given in the figure below. If the peak-to-peak ripple in the output voltage of the converter is 1 V, then the value of the output capacitor, in $$\mu$$F, is _________. (round off to nearest integer).





Under steady state operating conditions, the average voltage across the indicator and the capacitor respectively, are






The PEAK-TO-PEAK source current ripple in $$Amps$$ is

The average source current in Amps in steady-state is


The initial current through the inductor is zero, while the initial capacitor voltage is $$100$$ $$V.$$ The switch is closed at $$t = 0.$$ The current $$i$$ through the circuit is:

The $$L$$-$$C$$ circuit $$Q.13$$ is used to commutate a thyristor, which is initially carrying a current of $$5A$$ as shown in the figure below. The values and initial conditions of $$L$$ and $$C$$ are the same as in $$Q.13.$$ The switch is closed at $$t = 0.$$ If the forward drop is negligible, the time taken for the device to turn off is

what should be the theoretical minimum value of $${C_1}?$$. Assume current ripple through $${L_0}$$ to be negligible.


The average voltage across the load and the average current through the diode will respectively be
$$T{h_M}$$ is $$ON$$
$$T{h_AUX}$$ is trigged at $$t=0.$$ $$T{h_M}$$ is turned $$OFF$$ between.


The minimum time in $$\mu $$ sec for which the $$SCR$$ $$M$$ should be ON is

The average output voltage of the chopper will be





Marks 5
(a) The on-time $${t_{ON}}$$ of the switch
(b) The value of the peak current $${{\rm I}_p}$$


(a) Evaluate the circuit turn off time for the main thyristor $$T{h_1}$$
(b) Calculate the value of inductor $$L,$$ if the peak current through the main thyristor $$Th,$$ is limited to $$180$$% of the load current.
(c)Calculate the maximum instantaneous output voltage of the chopper
