For all those people who are terrified of seeing big graph , I am writing this note. I will try to explain in simple terms what is happening...
1. The capacitor is charged with +Edc voltage by triggering chopper T2. So current flows through +Es-->C-->T2-->LOAD-->-Es.
2.After C is charged, the T2 is turned off as current from C decreases.
3.Now T1 is triggered. So C discharges through T1.
4.after C is completely discharged, C is charged -Edc by the path Es-->T1-->L-->D-->Vc.
5. Now when T2 is triggered again, voltage accross T1 is -Edc. So T1 is turned off.
6. Now C starts discharging through T2. So total voltage accross load is 2Edc. but C slowly discharges to 0. Now Es charges C to +Edc.after c is charged, the charging current becomes zero and so T2 is turned off and again the cycle repeats..