how to reduce the stress...HELP

[cutiegal]

From the figure, switch S6 will ON first for a short period b4 Switch S5 is turned ON. Switch S5 has a high voltage stress, can someone tell me how the auxiliary switch(S6) help to reduce the stress of switch S5 so that S5 can turn on or off at zero voltage. the technique employed is Zero Voltage Switching (ZVS).
10sssssssssss

 

[VVV]

The caps and the inductor form a series resonant LC tank. C6 is charged, C5 discharged. When you turn on S6, the tank begins its oscillation, because there is energy in C6, and so a quarter of a cycle later, the voltage across each capacitor reaches zero, at which point you can turn on S5. C6 is usually the Coss of S6. The energy present in it before swithing would be dissipated in S6, because S6 has to discharge C6, too, when it turns on.