Single-Carrier Modulation for 9-Level Neutral Point Clamped Inverters in Three Phase Transformerless Photovoltaic Systems

SIRIVURI VANI; P.GURUVULA NAIDU; B.SRINIVASA RAO

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25-Mar-23

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Single-Carrier Modulation for 9-Level Neutral Point Clamped Inverters in Three Phase Transformerless Photovoltaic Systems

Author(s):

SIRIVURI VANI , AITAM Engineering College, Tekkali, Andhra Pradesh.; P.GURUVULA NAIDU, AITAM Engineering College, Tekkali, Andhra Pradesh; B.SRINIVASA RAO, AITAM Engineering College, Tekkali, Andhra Pradesh

Keywords:

Neutral point clamped inverter, transformerless photovoltaic system, common mode voltage, pulse width modulation

Abstract:

In this photovoltaic based three phase nine level neutral point clamped inverter is proposed. When no transformer is used in a grid-connected photovoltaic (PV) system, a galvanic connection between the grid and the PV array exists. In these conditions, dangerous leakage currents (common-mode currents) can appear through the stray capacitance between the PV array and the ground. In order to avoid these leakage currents, different inverter topologies that generate no varying common-mode voltages, such as the half-bridge and the) full-bridge topologies, have been proposed. In transformerless systems, the PV module parasitic capacitance can introduce leakage currents in which the amplitude depends on the converter topology, on the pulse width modulation, and on the resonant circuit comprised by the system components. There is a strong trend in the photovoltaic inverter technology to use transformerless topologies in order to acquire higher efficiencies combining with very low ground leakage current. While safety requirements in transformerless systems can be met by means of external elements, leakage currents and the injection of dc into the grid must be guaranteed topologically or by the inverter’s control system. Modulation strategy is one of the most important issues for three-level neutral-point-clamped inverters in three-phase transformerless photovoltaic systems. It has a very simple structure, and the common-mode voltages can be kept constant with no need of complex space-vector modulation or multicarrier pulse width modulation. Based on the common-mode voltage model, modulation techniques are proposed to eliminate the leakage current in transformerless PV systems without requiring any modiﬁcation on the converter. The simulation results are obtained using MATLAB/SIMULINK software.