Multilevel Inverter with Direct Nonlinear Controller For Connecting Solar Farms To The Grid

The solar photovoltaic (PV) farm delivers its harvested DC energy to the AC grid via power electronic interfaces. With insolation as well as ambient temperature variations, these power electronic converters should regulate operating point at optimal point to extracting maximum power from PV cells. In this paper, a direct nonlinear control method is developed for cascaded H-bridge multilevel inverter with a LCL output filter. Multilevel inverters produce less harmonic voltages, so the size of output filter can be reduced. Moreover, operating in higher voltage levels gives the opportunity of omitting the step-up transformer in the grid with medium voltage. In the proposed control method, DC terminals of cascaded multilevel inverter can be controlled, independently. So, solar farm can be divided into distinct zones and maximum power can be harvested due to independent control of these zones. Using the proposed nonlinear controller, the DC-DC converters, usually used for maximum power point tracking, can be omitted. Moreover, exchanging the reactive power with the grid can be controlled at PCC