Multicarrier wave dual reference very low frequency PWM control of a nine levels NPC multi-string three phase inverter topology for photovoltaic system connected to a medium electric grid

The multilevel multi-string inverter has gained much attention in recent years due to its advantages in lower switching loss, better electromagnetic compatibility, higher voltage capability, and lower harmonics. Solar Energy is one of the favorable renewable energy resources and the multilevel inverter has been proven to be one of the important enabling technologies in photovoltaic (PV) utilization. This paper proposes a three phase nine levels NPC grid connected photovoltaic inverter topology with a multicarrier dual reference pulse-width modulated (PWM) control scheme. Eight carrier waves of the same frequency and different amplitudes are compared with two references (a sine wave and its opposite) for generating the control signals of the switches. Some DC/DC boost converters are used to amplify the voltage produced by the photovoltaic generators. Each of these converters is controlled by an MPPT algorithm in order to track the maximum power point of the GPV. Results of simulation in Matlab environment are given and discussed.