Does the load have much in the way of bypass capacitance? The power that the switching element has to dissipate can be as high as 1/2 FCV^2 where F is the frequency (100Hz), C is the total load capacitance and V is the load voltage (200 V). The dissipation in the switching element can be reduced by adding by adding a series resistor or, even better, a series inductor. Note also that the switching element has to be rated for the peak current that may be drawn while switching.
Cheers,