What is the load value?

If the load is not small enough, the capacitor will stay charged regardless of the duty.

Try to put a 1 ohm load in shunt with the capacitor. You could also reduce the capacitor value

Assuming that the device is all right, the following are the possibilities:

Possibility 1:

The output filter inductor is in discontinuous conduction, in which case the output filter capacitor will try to charge up to the peak of the output pulse (equal to input) rather than to the average value. This situation can be overcome by increasing load current or by increasing inductance value or by switching at a higher frequency to make it operate in continuous conduction.

Possibility 2:

The IGBT may be connected with its Collector and Emitter terminals reversed, in which case the anti-parallel diode is providing a direct connection between input and output.

Luc-Andre Gregoire sir Am using a Resistive load of 50 Ohm, 10A, 

IGBT  shorted ,check  the C E and GATE  .

You tell us the value of the inductor and capacitor but it is necessary to know the switching frequency and the load range to have an idea of what may happen.

Generally at no load condition without bleeder resistor the condition can exist other wise the output voltage should always be lesser than the input.

followed