High Step-up Converter with Transformerless Inverter for PV-Grid connected Power System

Photovoltaic(PV) systems are expected to play an important role in future energy production. An asymmetrical interleaved high step-up converter is used to get high step up gain to step up the input energy which is obtained from PV panel without operating at an extreme duty ratio. The traditional inverter which is used to convert the converter output energy from DC to AC, contains a line frequency or a high frequency transformer between the inverter and Grid. Due to this isolation transformer, the efficiency of the system is reduced and also it increases the cost and size. In order to overcome these difficulties the efficient solution is to remove the isolation transformer, which may leads to appear of Common Mode(CM) ground leakage current on the parasitic capacitor between the PV panels and ground. The common mode current reduces the efficiency of power conversion stage and affects the quality of grid current. To eliminate this CM leakage current, virtual DC bus is proposed in this project. By connecting the grid neutral line directly to the negative pole of the DC bus, the stray capacitance between the PV panels and the ground is bypassed. The CM ground leakage current can be suppressed completely. This topology will be modulated by using unipolar SPWM technique to reduce the output current ripple and harmonics. IndexTerms—High Step-up,photovoltaic system,voltage multiplier module,transformerlessinverter,common mode current, unipolar SPWM,virtual DC bus,switched capacitor.