This paper proposes a novel control of a direct grid-connected photovoltaic (PV) system using solely a three-phase inverter. Considering the large amount of energy transmitted to the network, we use the so-called discontinuous pulse width modulation (DPWM) technique for driving the inverter in closed loop, which reduces the number of commutations by about 33 %, resulting in an important decrease of the switching losses. The operation of the PV source at the maximum power point (MPP) and the control of the reactive energy injected into the network are performed using a designed robust sliding mode controller (SMC). The performances of the proposed system are evaluated through some simulation results, which highlight the effectiveness of the proposed SMC to achieve good control of the grid connected PV system. Additionally, the generalized discontinuous pulse width modulation strategy implemented in closed loop opens a new approach to the reduction of the switching losses in the PV inverter and may apply in other converters topologies for renewable energy systems.

Keywords: Discontinuous pulse width modulation, Photovoltaic system, Sliding mode control, Switching losses, Dc-ac inverter