Improved Transformerless Grid-Tied PV Inverter Effectively Operating at Twice the Switching Frequency With Constant CMV and Reactive Power Capability

Abstract

In this article, an improved single-phase transformerless inverter is presented, which obviates the leakage current issue to a great extent. The proposed solution uses the dc-bypass (H6 type) topology with a diode clamp circuit, operated by a modified unipolar pulse-width modulation (PWM) scheme. An advantage of reduced switching losses comes with the use of the modified unipolar PWM, which produces effective double switching frequency at the inverter output. Due to the PWM strategy and diode clamp circuit, the common-mode voltage (CMV) of the inverter is constant throughout the operation. Consequently, the ground leakage current is negligible even in the presence of high parasitic capacitance of photovoltaic (PV) panels. Further, the other desirable features of the grid-tied inverters, such as reactive power injection for grid stability and low-voltage ride through (LVRT) are not compromised with the proposed scheme. A combination of high efficiency, constant CMV (and hence, negligible leakage current) and reactive power feeding capability with low component count stand the proposed system out among the existing transformerless grid-tied systems. The design and working principle of the proposed system are discussed and analyzed in detail. Simulation and experiment results are included to validate the proposed solution and its merits.