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1
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How many pulses per half cycle in the single PWM?
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One
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2
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How the gate signal is generated in the single PWM technique?
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The gate
signal is generated by comparing rectangular reference signal and triangular
carrier signal.
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3
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Explain the term : amplitude modulation index and frequency
modulation index
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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
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4
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Describe the effect of harmonic as the output voltage
decreases in the single PWM?
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As the output
voltage decreases the harmonic increases whereas the harmonics decreases as
the output voltage increases.
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5
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How the gate signals are generated in the multiple PWM?
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The gate signals
in the MPWM are generated by comparing rectangular reference signal with
triangular carrier signal.
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6
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Which signal determines numbers of pulses per half cycle in
the MPW?
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Triangular
carrier signal
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7
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Why the MPWM is also called as symmetrical PWM?
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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.
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8
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Describe the number of pulses per half cycle on the harmonics in
the MPWM?
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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.
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9
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In which method of PWM, the width of the all pulses is not
same?
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Sinusoidal PWM
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10
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What do you mean by term ‘series’ inverter?
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Series inverter
- The
commutating components L and C are connected in series with the load so it is
called as series inverter.
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11
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Whether the output waveform of the series inverter is
sinusoidal?
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The output
waveform of the series inverter is approximately sinusoidal particularly at
very high frequency.
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12
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Write the condition for the under damped circuit in the series
inverter.
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The condition
for the under damped circuit in the series inverter is
R2 < √ ( L
/ C)
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13
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Why the series inverter is called as load commutated inverter
or self commutated inverter?
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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.
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14
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Describe the effect of load current on the capacitance voltage
in the series inverter.
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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 )
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15
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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?
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In order to
avoid short circuit of the input supply
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16
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What is meaning of the dead zone of the series inverter?
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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.
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17
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What should be rating of the capacitor in the series inverter?
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Rating
of capacitor
- The rating of
capacitor should be greater than the twice supply voltage.
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18
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Describe the limitations of the series inverter.
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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.
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19
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State the applications of the series inverter.
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Applications
- High frequency
heating
- Ultrasonic
generators
- Fluorescent
lighting
- Sonar trans
meter
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20
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Describe the difference between commutating circuit in the
modified series inverter and series inverter.
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The mutual
coupled inductance L1 and L2 is used in place of inductor L in the modified
series inverter.
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