Series-Resonant Inverter

OperationT1 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 < (4L/C)

Operation in Mode 1 Fire T1

To find the time when the current is maximum, set the first derivative = 0

To find the capacitor voltage, integrate the currentThe current i1 becomes = 0 @ t=t1m

Operation in Mode 2 T1, T2 Both OFF

t2m

Operation in Mode 3 Fire T2

Summary -- Series Resonant Inverter

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

Series Resonant Inverter Coupled Inductors

Improvement in performanceWhen T1 turned ON, voltage @ L1 is as shown, voltage @ L2 in same direction, adding to the voltage @ CThis turns T2 OFF before the load current falls to 0.

Half-Bridge Series Resonant InverterNote:L1 = L2C1 = C2

This configuration reduces the high-pulsed current from the dc supplyPower 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.

Full-Bridge Series-Resonant Inverter

Characteristics of the full-bridge inverterThis configuration provides higher output power.Either T1-T2 or T3-T4 are fired.Supply current is continuous but pulsating.

Example 8.1 Analysis of the Basic Resonant InverterL1 = L2 = L = 50HC = 6FR = 2Vs = 220Vfo = 7kHztq = 10s

Determine the resonant frequencyThe resonant frequency in Hz

Determine the turn-off time toff

Determine the maximum permissible frequency

Determine the peak-to-peak capacitor voltage

Determine the peak load current

Sketch the instantaneous load current, capacitor voltage, and dc supply current

Calculate the rms load current

Using MATHCAD,Io = 44.1Amperes

Determine the output power

Determine the average supply current

Determine the average, peak, and rms thyristor currents

rms Thyristor CurrentUsing MATHCAD

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