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بسم الله الرحمن الرحيم. The Islamic University of Gaza Faculty of Engineering Electrical Engineering Department. POWER ELECTRONICS . EELE 5450 — Summer 2012. Instructor: Eng. Jalal Al Roumy. Lecture 20. AUXILIARY IMPULSE COMMUTATED INVERTER.

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## POWER ELECTRONICS

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**بسم الله الرحمن الرحيم**The Islamic University of Gaza Faculty of Engineering Electrical Engineering Department POWER ELECTRONICS EELE 5450— Summer 2012 Instructor: Eng. Jalal Al Roumy Lecture 20**AUXILIARY IMPULSE COMMUTATED INVERTER**A block schematic diagram of the gate pulse control is shown below.**AUXILIARY IMPULSE COMMUTATED INVERTER**A typical commutation interval is shown in three stages T1 is on and T1A is turned on to begin the commutation of T1. The capacitor discharges through an oscillatory circuit, first of all through the load, and then through D1. When T1A is turned on the capacitor current, ic, rises and the current in thyristor T1 falls until it reaches zero, at which point T1 turns off. Capacitor current continues to rise, and the excess of ic over IL flows through diode D1. The discharge current passes through maximum, and begins to fall as the capacitor begins to charge in the reverse direction.**AUXILIARY IMPULSE COMMUTATED INVERTER**Stage2 ic falls below IL, the load inductance acts to keep IL constant, and in so doing it forward biases D2 and load current flows in this diode. When the capacitor is charged in the reverse direction, ic ceases and T1A turns off, leaving the capacitor charged to rather less than Vb.**AUXILIARY IMPULSE COMMUTATED INVERTER**Stage 3 If T2 is turned on just before TIA goes off, a further charge will flow into C to recharge it to Vb. When T1A turns off, the capacitor is charged to a polarity such that T2 can be turned off by firing T2A in the negative half-cycle**The waveforms during a commutation interval. The resonant**frequency half-periodic time is very small compared to the inverter half periodic time. At to, a commutation pulse is fed to the gate of T1A. At t1, ic = I, IT1 = 0 and T1 prepares to turn off. At t2, ic = 0 for the second time and T1 must have turned off by this time; current is transferred from D1 to D2. At t3, T2 is turned on.**AUXILIARY IMPULSE COMMUTATED INVERTER**Laplace transformation: as a circuit in the s domain, when the charged capacitor is switched across T l. The resistance of the coil has been neglected and this of course will damp the oscillation. In this circuit:**AUXILIARY IMPULSE COMMUTATED INVERTER**Laplace transformation**AUXILIARY IMPULSE COMMUTATED INVERTER**Example A single-phase auxiliary-impulse commutated inverter is driven from a 60V centre-tapped d.c. supply. The load is inductive and over the commutation interval the load current can be considered constant at 30 A. The thyristors turnoff time is 40us. Derive suitable values for the commutating components L and C. Assume that the ratio of maximum capacitor current to constant load current is 1.5. Also determine the time taken for the capacitor current to reach the load and maximum currents.**AUXILIARY IMPULSE COMMUTATED INVERTER**solution End of Lecture

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