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Modular inverters are presented for grid-connected photovoltaic systems based on the loss-free resistor concept. The basic module consists of a cascade connection of a buck-boost converter operating in discontinuous conduction mode and a push-pull switching inverter. The DC power of the photovoltaic module is transferred by the buck-boost stage to the push-pull converter, which transforms this power into AC power compatible with grid connection. Maximum power point tracking is achieved by matching the panel impedance at the maximum power point and the buck-boost input impedance. Two alternatives for building modular structures for N panels are investigated. Experimental and simulation results of both modular alternatives are presented.