Series-Resonant Inverter

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Series-Resonant Inverter
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Operation
T1 fired, resonant pulse of current flows
through the load. The current falls to zero at t
t1m and T1 is self commutated. T2 fired,
reverse resonant current flows through the load
and T2 is also self-commutated. The series
resonant circuit must be underdamped, R2 lt (4L/C)
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Operation in Mode 1 Fire T1
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To find the time when the current is maximum, set
the first derivative 0
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To find the capacitor voltage, integrate the
current
The current i1 becomes 0 _at_ tt1m
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Operation in Mode 2 T1, T2 Both OFF
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t2m
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Operation in Mode 3 Fire T2
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Summary -- Series Resonant Inverter
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To avoid a short-circuit across the main dc
supply, T1 must be turned OFF before T2 is turned
ON, resulting in a dead zone.
This off-time must be longer than the turn-off
time of the thyristors, tq.
The maximum possible output frequency is
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Series Resonant Inverter Coupled Inductors
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Improvement in performance

• When T1 turned ON, voltage _at_ L1 is as shown,
  voltage _at_ L2 in same direction, adding to the
  voltage _at_ C
• This turns T2 OFF before the load current falls
  to 0.

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Half-Bridge Series Resonant Inverter
Note L1 L2 C1 C2
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This configuration reduces the high-pulsed
current from the dc supply

• Power drawn from the source during both
  half-cycles of the output.
• Half of the current is supplied from the
  associated capacitor, half of the current is
  supplied from the source.

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Full-Bridge Series-Resonant Inverter
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Characteristics of the full-bridge inverter

• This configuration provides higher output power.
• Either T1-T2 or T3-T4 are fired.
• Supply current is continuous but pulsating.

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Example 8.1 Analysis of the Basic Resonant
Inverter

• L1 L2 L 50µH
• C 6µF
• R 2?
• Vs 220V
• fo 7kHz
• tq 10µs

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Determine the resonant frequency
The resonant frequency in Hz
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Determine the turn-off time toff
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Determine the maximum permissible frequency
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Determine the peak-to-peak capacitor voltage
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Determine the peak load current
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Sketch the instantaneous load current, capacitor
voltage, and dc supply current
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Calculate the rms load current
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Using MATHCAD,
Io 44.1Amperes
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Determine the output power
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Determine the average supply current
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Determine the average, peak, and rms thyristor
currents
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rms Thyristor Current
Using MATHCAD