Ac modules (ACM) are state-of-the-art method for implementation of grid connected photovoltaic (PV) systems. Compared with other methods of PV module connection, ACMs have distinct advantages, which make them an optimum option specially in building integrated PV (BIPV) systems. Power Electronic (PE) interface, which is installed on the back of PV-ACM, plays a key role in processing and transferring of the PV power to the grid. PE interfaces, based on the number of power processing stages which they have, are justify; TEXT-INDENT: 18pt; MARGIN: 0cm 0cm 0pt; unicode-bidi: embed; DIRECTION: ltr" dir=ltr Almost without any exception, PE interface in ACMs includes a single-phase inverter. Single-phase inverters face the problem of power pulsation (with double grid frequency) in their input level. PV panel in ACMs have constant output power and voltage. Power pulsation at input of the inverter (output of the panel) will cause deviation of PV voltage from MPP. A conventional method to solve the power pulsation problem is using a bulky electrolytic capacitor at inverter input. This capacitor has short life-time compared with other ACM parts, and from reliability standpoint is problematic for the whole PV system; thus, to guaranty the maximum system reliability and life-time, an active circuit (or filter) - called power decoupling circuit- including a small film capacitor may be used instead of abovementioned electrolytic capacitor. This thesis presents a new power decoupling circuit, designed to be used in a DCM-FI in ACM application, which makes the power decoupling function possible with a small film capacitor. In addition to use a small capacitor- compared with other power decoupling methods- proposed circuit uses only 3 high-frequency switches, while the two other switches at the second side of the flyback transformer work at grid frequency; thus, having negligible switching losses. This circuit is designed with three different configuration of elements; thus, making it possible to evaluate the operation of the structure in three different operating points, and to investigate the effects of variation in key components in the circuit. Results and analysis are verified through the circuit simulation in PSIM software. thesis In this thesis In this thesis In this thesis In this thesis In this thesis In this thesis In this thesis In this thesis In this thesis In this thesis In this thesis. Keywords: PV ac module, power electronic interface, flyback inverter, power decouplin