Mixed Harmonic Elimination Control for a Single-Phase 9 Level Grid-Connected Inverter

The power quality requirements are increasingly stringent, due to the continuous growth of devices connected to the grid that introduce harmonics. These devices include DC to AC energy conversion systems, i.e. grid connected inverters. The design, control and operation of these systems must take into account the rules of interconnection to the electricity grid. To improve the quality of the output waveform of the grid-connected inverter, Multilevel Converters (MC) with selective harmonic elimination modulation technique can be used. This paper presents a single-phase nine level grid-connected inverter with DC/DC input stages. The obtained switching angles for THD minimization are independent of the modulation index. The proposed control technique is able to regulate both the active and the reactive power, acting respectively on the control of the DC/DC and the inverter stages.