Tri-State Cuk Inverter with Power Decoupling for Photovoltaic Applications

This paper proposes modified modulation and control schemes for power decoupling of single-stage single-phase Cuk inverter in continuous conduction mode. Because it has inherent two inductors at the input and output side, the Cuk inverter is able to step up/down the voltage with reduced input and output current ripples. Thus, smaller filtering capacitance, especially at the input side, can be used which increases its suitability for photovoltaic applications. For the maximum power point tracking control, the oscillating even order harmonic components should be eliminated from the inverter's input side otherwise the maximum power cannot be extracted. The inverter's input and output currents will be controlled independently using the proposed modulation scheme and hence even harmonics can be decoupled from the input side's current without adding additional circuitry. In addition, the paper presents a control scheme to generate sinusoidal output grid current while the input current is kept constant with time. The presented systems is verified using MATLAB simulations as well as an experimental prototype controlled by F28335 ezdsp.