parallel inverter

The inverter plays a vital role in Uninterrupted Power Supply (UPS). It is used to convert the direct current (DC) to alternating Current (AC) of required voltage. The basic single phase parallel inverter circuit consists of two SCRs T1 and T2, an inductor L, an output transformer and a commutating capacitor C. The output voltage and current are V
parallel inverter - schematic

o and Io respectively. The function of L is to make the source current constant. During the working of this inverter, capacitor C comes in parallel with the load via the transformer. So it is called a parallel inverter. The operation of this inverter can be explained in the following modes. In this mode, SCR T1 is conducting and a current flow in the upper half of primary winding. SCR T2 is OFF. As a result an emf Vs is induced across upper as well as lower half of the primary winding. At time to, T2 is turned ON by applying a trigger pulse to its gate. At this time t=0, capacitor voltage 2Vs appears as a reverse bias across T1, it is therefore turned OFF. A current Io begins to flow through T2 and lower half of primary winding. Now the capacitor has charged (upper plate as negative) from +2Vs to -2Vs at time t=t1. Load voltage also changes from Vs at t=0 to Vs at t=t1. When capacitor has charged to Vs, T1 may be tuned ON at any time. When T1 is triggered, capacitor voltage 2Vs applies a reverse bias across T2, it is therefore turned OFF. After T2 is OFF, capacitor starts discharging, and charged to the opposite direction, the upper plate as positive.

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