Design and Implementation of a New Nine Level Boost Inverter for Transformerless Grid-Tied PV Application

In this article, a new nine-level inverter that offers four times the input voltage gain is proposed. The configuration is designed based on a switched capacitor (
SC
) along with common ground structure. This inverter could find applications for low voltage PV systems, without using a boost dc/dc converter. Two SC cells are connected in parallel to increase the input PV voltage and enable nine steps in the output voltage. The proposed inverter topology's common ground (
CG
) structure aids in avoiding parasitic capacitance. As a result, it solves the leakage current issue, which plagues transformerless grid-connected PV inverters frequently. This novel inverter can also manage reactive power whether the grid's power factor (
pf
) is lagging or leading. The active and reactive grid power are regulated by a proportional resonant (
PR
) controller. The proposed modulation strategy helps in balancing the voltages of switched capacitors at their base voltage with allowable ripple. Therefore, there is no requirement of extra controller / feedback loop to balance the capacitors’ voltage. The novel inverter has the advantages of highest efficiency, low cost and shows robust performance with quad boost CG facility. However, there is slight increase in voltage, current and VA (volt/amp) stress of some devices, which can be observed in comparison to H bridge and half bridge inverter for the same grid voltage. The proposed inverter's specifications, control approach, thermal modeling, PWM scheme, and loss analysis are discussed in depth along with guidelines for component design. Experimental findings are presented to support the viability and efficacy of the newly proposed inverter.