A transformerless five level cascaded inverter based single phase photovoltaic system

This paper describes the current control method and the switching scheme of a cascaded five level inverter based grid connected single phase photovoltaic system. For the current control a dual polarised ramptime zero average current error control method is applied, which provides good current regulation, and a narrow ripple current frequency band. Simulation results which demonstrate the method are presented. The redundant inverter states of the five level cascaded inverter allow for a cyclic switching scheme which minimises the switching frequency, equalises stress evenly on all switches and minimises the voltage ripple on the DC capacitors. Simulation and experimental results of a multi carrier PWM voltage controller showing the effectiveness of the switching scheme are presented.