A New Nine-Level Highly Efficient Boost Inverter for Transformerless Grid-Connected PV Application

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Abstract
Transformerless grid-connected multi-level PV (photovoltaic) inverter has the major concern of leakage current and buck behavior of output voltage, hence not suitable for low voltage PV applications. A new 9L4x (nine-level quad boost) highly efficient inverter based on the SC (switched capacitor) with a CG (common ground) configuration has been proposed in this paper, which provides four times the gain of input voltage. Hence, this inverter is preferable for low voltage PV applications without any boost dc/dc converter intermediate stage. The inverter is designed in such a way that total conducting switches for different level generation is minimum. This technique helps to increase the efficiency of the inverter. Two SC cells are utilized to step-up the input PV voltage and facilitate nine steps in output voltage. The common grounding feature of the proposed inverter topology helps mitigate the leakage current. Additionally, this new inverter can handle reactive power during the grid’s lagging/leading pf (power factor) condition. To regulate the active and reactive grid power, a PR (proportional resonant) controller is designed. The proposed modulation strategy balances the voltages of switched capacitors at their base voltage with allowable ripple. The inverter circuit details, control strategy, PWM (pulse width modulation) scheme, thermal modeling, and loss analysis with component design guidelines are described in detail. Experimental results are presented to validate the effectiveness and feasibility of this proposed inverter.

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