Optimal third harmonic injection based nearest level control of large-scale solar photovoltaic multilevel converter

Abstract

This paper presents a new control approach with an optimal third harmonic injection-based nearest level modulation (OTHI-NLM) technique for a large-scale solar photovoltaic (SPV) system. This system uses a single-source multilevel converter to feed solar power into the grid. The merits of the optimal third harmonic injection (OTHI) and nearest level modulation (NLM) are considered for switching the SPV converter. A unique analysis to have an adaptive optimal injection with varying solar irradiance is conducted and compared with the well-known carrier-based high-frequency switching technique. The variations of harmonics for OTHI-NLM, an optimal third harmonic pulse width modulation (OTHI-PWM), and a constant third harmonic injection method are analysed at different irradiance levels. This optimal injection provides benefits such as enhanced DC bus utilization (DBU), better harmonics performance at different solar irradiance levels. The detailed methodology of the OTHI algorithm, nearest level modulation (NLM) technique with an optimal quotient calculation, and an instantaneous optimal third harmonic injection (THI) in closed-loop are presented. The comparative analysis shows the effectiveness of the SPV grid-tied structure over well-known ones. The power quality of the renewable energy system is investigated in dynamic solar irradiations. Moreover, simulation results are presented and validated in a real-time test bench.