Grid integration of renewables using dual DC bus neutral point clamped inverter with improved power quality

Power electronic converters interfacing renewable power sources to the utility must comply with a series of standards imposed by grid operators. Power quality is one such parameter that has to meet these standards. The injected grid current may have lower-order harmonics due to various non-idealities, like grid voltage harmonics, ripple in the DC link voltages and dead-time in PWM. Normally, grid-side filters are not designed to attenuate these harmonics. Hence, these harmonics have to be actively attenuated through a grid converter. In this presentation, lower-order harmonic elimination techniques are applied to a three-level neutral point clamped (NPC) converter that integrates a dual DC renewable bus to the utility grid. The three-level NPC offers certain advantages which are especially very attractive for high-power applications such as central inverters. Also, the dual renewable bus topology allows interfacing of the renewable sources at a lower DC voltage, i.e. half of the central inverter DC link voltage. The present topology, along with the proposed control scheme, is an efficient way of interfacing renewable sources to the utility grid while maintain high power quality. Simulation results are presented and an experimental validation is done on a 3-kWp solar installation.