Question

Give the operation of single phase full wave bridge controlled converter with RL load with a neat diagram. Also draw its waveform.

Answer 1

Single phase fully control bridge converter with RL load: 1. During positive half cycle of input voltage, T1 and T2 are forward biased and during negative half cycle, T3 and T4 are forward biased. Therefore, T1-T2 pair and T3-T4 pair are fired alternately in positive and negative half cycles of input voltage respectively, as shown in the waveform figure (b). 2. In each half cycle, the respective SCRs are fired at firing or delay angle , as shown. Once SCR pair conducts (at delay angle in each half cycle), the input source voltage appears across load, the current flows and if the load is inductive in nature, the conducting SCRs remain into conduction till the fall of current to zero or firing of next pair of SCRs as shown in the waveform diagram. 3. Due to load inductance, the current lags behind the output voltage and falls to zero after the end of that half cycle. Therefore, during the time interval between voltage zero instant and current zero instant, the reversed supply voltage appears across load for discontinuous conduction. 4. At current zero, the SCRs are turned off and load gets isolated from source, causing load voltage zero till the firing of next pair of SCRs. 5. If load inductance is large, the load current never falls to zero. The current attempts to fall, but before it could fall to zero, the next pair of SCR get fired and we get continuous conduction. 6. In this situation, the reversed voltage appears across load after the end of each half cycle till the firing of next pair of SCRs as shown in the waveform.

Comments

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