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, Th_M is ON and Th_A is OFF. The turn-off time available to Th_M in microseconds, when Th_A is triggered, is________ (rounded off to the nearest integer).

GATE EE 2024

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

GATE EE 2023

A buck converter, as shown in Figure $$(a)$$ below, is working in steady state. The output voltage and the inductor current can be assumed to be ripple free. Figure $$(b)$$ shows the inductor voltage $${V_L}$$ during a complete switching interval. Assuming all devices are ideal, the duty cycle of the buck converter is ________.

GATE EE 2016 Set 1

In the following chopper, the duty ratio of switch $$S$$ is $$0.4.$$ If the inductor and capacitor are sufficiently large to ensure continuous inductor current and ripple free capacitor voltage, the charging current (in Ampere) of the $$5$$ $$V$$ battery, under steady-state, is_____

GATE EE 2015 Set 1

A step-up chopper is used to feed a load at $$400$$ $$V$$ $$dc$$ from a $$250$$ $$V$$ $$dc$$ source. The inductor current is continuous. If the ‘off’ time of the switch is $$20\,\,\mu s,$$ the switching frequency of the chopper in $$kHz$$ is ________.

GATE EE 2014 Set 2

The power electronic converter shown in the figure has a single-pole double-throw switch. The pole $$P$$ of the switch is connected alternately to throws $$A$$ and $$B.$$ The converter shown is a

GATE EE 2010

A step down chopper is operated in the continuous conduction mode in steady state with a constant duty ratio $$D.$$ If $${V_0}$$ is the magnitude of the $$dc$$ output voltage and if $${V_s}$$ is the magnitude of the $$dc$$ input voltage, the ratio $${{{V_0}} \over {{V_s}}}$$ is given by

GATE EE 2002

In a thyristor $$dc$$ chopper which type of commutation results in best performance?

GATE EE 1996

Consider the chopper circuit of figure. The chopper operates at $$400$$ $$Hz$$ and $$50$$% duty cycle. The load current remains almost ripple free at $$10A.$$ Assuming the input voltage to be $$200V$$ and the devices to be ideal, the turn-off time available to the thyristor $$Th$$ $$M$$ is____________ $$\mu s$$

GATE EE 1995

A $$dc$$ to $$dc$$ transistor chopper supplied from a fixed voltage $$dc$$ source feeds a fixed resistive-inductive load and a free-wheeling diode. The chopper operates at $$1$$ $$kHz$$ and $$50$$% duty cycle. Without changing the value of the average $$dc$$ current through the load, if it is desired to reduce the ripple content of load current, the control action needed will be

GATE EE 1995

Match the following

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

GATE EE 1994

A chopper operating at a fixed frequency is feeding an $$R$$-$$L$$ load. As the duty ratio of the chopper is increased from $$25\% $$ to $$75\% $$, the ripple in the load current

GATE EE 1993

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).

GATE EE 2024

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).

GATE EE 2023

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).

GATE EE 2022

The figure shows two buck converters connected in parallel. The common input dc voltage for the converters has a value of 100 V. The converters have inductors of identical value. The load resistance is 1 $$\Omega $$. The capacitor voltage has negligible ripple. Both converters operate in the continuous conduction mode. The switching frequency is 1 kHz, and the switch control signals are as shown. The circuit operates in the steady state. Assuming that the converters share the load equally, the average value of $${i_{S1}}$$, the current of switch S1 (in Ampere), is _____ (up to 2 decimal places).

GATE EE 2018

A dc to dc converter shown in the figure is charging a battery bank, B2 whose voltage is constant at 150 V. B1 is another battery bank whose voltage is constant at 50 V. The value of the inductor, L is 5 mH and the ideal switch, S is operated with a switching frequency of 5 kHz with a duty ratio of 0.4. Once the circuit has attained steady state and assuming the diode D to be ideal, the power transferred from B1 to B2 (in Watt) is ___________ (up to 2 decimal places).

GATE EE 2018

In the circuit shown all elements are ideal and the switch $$S$$ is operated at $$10$$ $$kHz$$ and $$60$$% duty ratio. The capacitor is large enough so that the ripple across it is negligible and at steady state acquires a voltage as shown. The peak current in amperes drawn from the $$50$$ $$V$$ $$DC$$ source is ________. (Give the answer up to one decimal place.)

GATE EE 2017 Set 2

The input voltage $${V_{DC}}$$ of the buck-boost converter shown below varies from $$32$$ $$V$$ to $$72$$ $$V.$$ Assume that all components are ideal, inductor current is continuous, and output voltage is ripple free. The range of duty ratio $$D$$ of the converter for which the magnitude of the steady state output voltage remains constant at $$48$$ $$V$$ is

GATE EE 2017 Set 1

The circuit shown is meant to supply a resistive load $${R_L}$$ from two separate $$DC$$ voltage sources. The switches $$S1$$ and $$S2$$ are controlled so that only one of them is ON at any instant. $$S1$$ is turned on for $$0.2$$ $$ms$$ and $$S2$$ is turned on for $$0.3$$ $$ms$$ in a $$0.5$$ $$ms$$ switching cycle time period. Assuming continuous conduction of the inductor current and negligible ripple on the capacitor voltage, the output voltage $${V_0}$$ (in Volt) across $${R_L}$$ is __________.

GATE EE 2015 Set 1

A self commutating switch $$SW,$$ operated at duty cycle $$\delta $$ is used to control the load voltage as shown in the figure

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

GATE EE 2015 Set 1

A buck converter feeding a variable resistive load is shown in the figure. The switching frequency of the switch $$S$$ is $$100$$ $$kHz$$ and the duty ratio is $$0.6.$$ The output voltage $${V_0}$$ is $$36$$ $$V.$$ Assume that all the components are ideal, and that the output voltage is ripple-free. The value of $$R$$ (in $$Ohm$$) that will make the inductor current ($${{\rm I}_L}$$) just continuous is _______.

GATE EE 2015 Set 1

For the switching converter shown in the following figure, assume steady-state operation. Also assume that the components are ideal, the inductor current is always positive and continuous and switching period is $${T_s}.$$ If the voltage $${V_L}$$ is as shown, the duty cycle of the switch $$S$$ is __________.

GATE EE 2015 Set 2

Figure (i) shows the circuit diagram of a chopper. The switch $$S$$ in the circuit in figure (i) is switched such that the voltage $${V_D}$$ across the diagram as the wave shape as shown in figure (ii). The capacitance $$C$$ is large so that the voltage across it is constant. If switch $$S$$ and the diode are ideal, the peak to peak ripple (in A) in the inductor current is ________.

GATE EE 2014 Set 1

In the figure shown below, the chopper feeds a resistive load from a battery source. $$MOSFET$$ $$Q$$ is switched at $$250$$ $$kHz,$$ with a duty ratio of $$0.4.$$ All elements of the circuit are assumed to be ideal.

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

GATE EE 2013

The average source current in Amps in steady-state is

GATE EE 2013

In the circuit shown, an ideal switch $$S$$ is operated at $$100$$ $$kHz$$ with a duty ratio of $$50%$$. Given that $$\Delta {i_c}$$ is $$1.6$$ $$A$$ peak-to-peak and $${{\rm I}_0}$$ is $$5 A$$ $$dc,$$ the peak current in $$S$$ is

GATE EE 2012

A voltage commutated chopper circuit, operated at $$500Hz,$$ is shown below. If the maximum value of load current is $$10A,$$ then the maximum current through the main $$(M)$$ and auxiliary $$(A)$$ thyristors will be

GATE EE 2011

The L-C circuit shown in the figure has an inductance $$L=1mH$$ and a capacitance $$C = 10\mu F.$$

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

GATE EE 2010

The L-C circuit shown in the figure has an inductance $$L=1mH$$ and a capacitance $$C = 10\mu F.$$

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:

GATE EE 2010

In the chopper circuit shown, the main thyristor $$\left( {{T_M}} \right)$$ is operated at a duty ratio of $$0.8$$ which is much larger than the commutation interval. If the maximum allowable reapplied $${{dV} \over {dt}}$$ on $${T_M}$$ is $$50$$ $$V/\mu s,$$
what should be the theoretical minimum value of $${C_1}?$$. Assume current ripple through $${L_0}$$ to be negligible.

GATE EE 2009

In the circuit shown in the figure, the switch is operated at a duty cycle of $$0.5.$$ A large capacitor current is connected across the load. The inductor current is assumed to be continuous.

The average voltage across the load and the average current through the diode will respectively be

GATE EE 2008

The circuit in the figure is current commutated $$dc$$ $$-$$ $$dc$$ chopper where, $$T{h_M}$$ is the main $$SCR$$ and $$T{h_AUX}$$ is the auxiliary $$SCR$$. The load current is constant at $$10$$ $$A.$$
$$T{h_M}$$ is $$ON$$
$$T{h_AUX}$$ is trigged at $$t=0.$$ $$T{h_M}$$ is turned $$OFF$$ between.

GATE EE 2007

A voltage commutation circuit is shown in figure. If the turn off time of the $$SCR$$$$s$$ is $$50$$ $$\mu \sec $$ and as safety margin of $$2$$ is considered, what will be the approximate minimum value of capacitor required for proper commutation?

GATE EE 2006

A voltage commutated chopper operating at $$1$$ $$kHz$$ is used to control the speed of $$dc$$ motor as shown in figure. The load current is assumed to be constant at $$10$$ $$A.$$

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

GATE EE 2006

A voltage commutated chopper operating at $$1$$ $$kHz$$ is used to control the speed of $$dc$$ motor as shown in figure. The load current is assumed to be constant at $$10$$ $$A.$$

The average output voltage of the chopper will be

GATE EE 2006

The given figure shows a step $$-$$ down chopper switched at $$1$$ $$KHz$$ with a duty ratio $$D = 0.5.$$ The peak - peak ripple in the load current is close to

GATE EE 2005

Figure shows a chopper. The device $${S_1}$$ is the main switching device. $${S_2}$$ is the auxiliary commutation device. $${S_1}$$ is rated for $$400V, 60A.$$ $${S_2}$$ is rated for $$400V, 30 A.$$ the load current is $$20$$ $$A.$$ The main device operates with a duty ratio of $$0.5.$$ The peak current through $${S_1}$$ is

GATE EE 2004

Figure shows a chopper operating from a $$100$$ $$V$$ $$dc$$ input. The duty ratio of the main switch $$S$$ is $$0.8.$$ The load is sufficiently inductive so that the load current is ripple free. The average current through the diode $$D$$ under steady state is

GATE EE 2004

A chopper is employed to charge a battery as shown in figure. The charging current is $$5A$$. The duty ratio is $$0.2.$$ The chopper output voltage is also shown in figure. The peak to peak ripple current in the charging current is

GATE EE 2003

In the chopper circuit shown in fig the input $$dc$$ voltage has a constant value $${{V_s}}$$. the output voltage $${{V_0}}$$ is assumed ripple free. The switch $$S$$ is operated with a switching time period $$T$$ and a duty ratio $$D.$$ What is the value of $$D$$ at the boundary of continuous and discontinuous conduction of the inductor current $${i_L}$$?

GATE EE 2002

A step down chopper operates from a $$dc$$ voltage source $${V_s}$$ feeds a $$dc$$ motor armature with a back $$e.m.f$$ $$\,\,{E_b}.$$ From oscilloscope traces, it is found that the current increases for time $${t_r}$$ falls to zero over time $${t_f},$$ and remains zero for time $${t_0}$$ in every chopping cycle, then the average $$dc$$ voltage across the freewheeling diode is

GATE EE 2000

Marks 5

In fig, the ideal switch $$S$$ is switched on and off with a switching frequency $$f = 10 kHz.$$ The switching time period is $$\,T = {t_{ON}} + t{}_{off} = 100\,\,\mu s.$$ The circuit is operated in steady state at the boundary of continuous and discontinuous conduction, so that the inductor current i is as shown in Fig.P20. Find

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

GATE EE 2002

A voltage commutated thyristor chopper circuit is shown in fig. The chopper is operated at $$500$$ $$Hz$$ with $$50\% $$ duty ratio. The load takes a constant current of $$20A$$

(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

GATE EE 2001

A $$dc$$ motor with armature resistance $${R_a}$$ is fed from a step down chopper in the continuous mode, and operates at some known speed and known excitation current. The motor current rises from $${I_{\min }}\,\,$$ to $${I_{\max }}\,\,$$ in the $${T_{on}}$$ period Ton of the chopper; and drops from $${I_{\max }}\,\,$$ to $${I_{\min }}\,\,$$ in the $${T_{off}}$$ period Toff of the same circuit. Both the rise and fall of the current may be assumed to be approximately linear. What is the average power loss in the machine armature?

GATE EE 2000