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In this paper is analyzed and simulated on the computer the operation of a three level H-bridge converter as well as its parallel operations. Based on the simulation results the operating behavior between a) a three level H-bridge neutral point clamped converter, b) a three level H-bridge neutral point clamped converter with parallel elements and c) two three level H-bridge neutral point clamped converters parallel connected is being compared. From the simulation results is obvious that in the first two cases the ripples, the distortion in primary and secondary winding currents, and the power factor are quite satisfactory and almost identical to each other. In the third case as compared with the first two, we observe that current harmonics with higher amplitude appear in the primary winding of the transformer.

In this paper, a photovoltaic (P/V) system, with maximum power point tracking (MPPT), connected to a three phase grid is presented. The connection of photovoltaic system on the grid takes place in one stage using voltage source inverter (VSI). For a better utilization of the photovoltaic system, the control strategy applied is based on p-q theory. According to this strategy during sunlight the system sends active power to the grid and at the same time compensates the reactive power of the load. In case there is no sunlight (during the night for instance), the inverter only compensates the reactive power of the load. The advantage of this strategy is the operation of the photovoltaic system the whole day. In this paper the p-q theory is proposed, which does not demand the use of PLL and introduces simple algebraic calculations.