One
How the gate signal is
generated in the single PWM technique?
The
gate signal is generated by comparing rectangular reference signal and
triangular carrier signal.
Explain the term : amplitude modulation index and frequency modulation index
Amplitude modulation index
It
is defined as the ratio of the reference voltage to the carrier voltage.
M = VR / VC
M = Modulation index
VR = Reference voltage
VC = Carrier voltage
Frequency modulation index
It
is defined as the ratio of the carrier frequency to the output frequency.
mf
= fc / fo
mf
= Frequency modulation index
fc = Carrier
frequency
fo
= Output frequency
Describe the effect of
harmonic as the output voltage decreases in the single PWM?
As
the output voltage decreases the harmonic increases whereas the harmonics
decreases as the output voltage increases.
How the gate signals are
generated in the multiple PWM?
The
gate signals in the MPWM are generated by comparing rectangular reference
signal with triangular carrier signal.
Which signal determines
numbers of pulses per half cycle in the MPW?
Triangular
carrier signal
Why the MPWM is also called
as symmetrical PWM?
Symmetrical PWM
The
width of the all pulses and number of pulses are same in the MPWM therefore it
is also called as symmetrical PWM.
Describe the number of
pulses per half cycle on the harmonics in the MPWM?
Effect of number of pulses on the harmonics
As
the number of pulses increases, lower order harmonics decreases whereas the
higher order harmonics increases. However the higher order harmonics is
completely eliminates by using filter. As the number of pulses increases,
switching of the semiconductor also increases therefore the switching losses
increases.
In which method of PWM, the
width of the all pulses is not same?
Sinusoidal
PWM
What do you mean by term
‘series’ inverter?
Series inverter
The
commutating components L and C are connected in series with the load so it is
called as series inverter.
Whether the output waveform
of the series inverter is sinusoidal?
The
output waveform of the series inverter is approximately sinusoidal particularly
at very high frequency.
Write the condition for the
under damped circuit in the series inverter.
The
condition for the under damped circuit in the series inverter is
R2 < √ ( L / C)
Why the series inverter is
called as load commutated inverter or self commutated inverter?
Self commutated inverter
As
the anode current becomes zero itself in this inverter, the SCR turns off
automatically. Therefore the series inverter is called as self commutated or
load commutated inverter.
Describe the effect of load
current on the capacitance voltage in the series inverter.
Effect of anode current on the capacitance voltage in the series inverter
As the anode current reaches up to maximum, the capacitor charges up to supply voltage. As the anode current starts to decreases zero from its peak value, the voltage across capacitor still increases up to twice the supply voltage. The capacitor voltage remains constant during zero anode current. ( The voltage across capacitor remains maximum during switching off of the both thyristors )
Why there
should be enough time delay between turn off of the one thyrisor and turn on of
the other thyrisor in the series inverter?
In
order to avoid short circuit of the input supply
What is meaning of the dead
zone of the series inverter?
Dead zone
It
is time duration between turn off of the one thyrisor and turn on of the other
thyrisor. This time duration is called as dead zone of the series inverter. The
dead zone time must be more than the turn off time of the thyristors.
What should be rating of
the capacitor in the series inverter?
Rating
of capacitor
The
rating of capacitor should be greater than the twice supply voltage.
Describe the limitations of
the series inverter.
Limitations of the series inverter
The
load current flows from supply source only during positive half cycle. The
current drawn from the supply source is not continuous. The SCR T2 turns on
only when the SCRT1 turns off otherwise, the DC supply source is short
circuited. As the load current passes through commutating components, the
rating of the commutating components should be large. The load waveform gets
distorted if the dead zone time or SCR turn off time is higher. The maximum
output frequency of the inverter is less than the ringing frequency. If the
inverter output frequency is greater than the ringing frequency, the supply
source is short circuited. The peak amplitude of the load current during each
half cycle depends upon the load parameters, it will results in poor output
regulation.
State the applications of
the series inverter.
Applications
High
frequency heating
Ultrasonic
generators
Fluorescent lighting
Sonar trans meter
Describe the difference between commutating circuit in the modified series inverter and series inverter.
The mutual coupled inductance L1 and L2 is used in place of inductor L in the modified series inverter.
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