Model-Free Predictive Current Control of a 3-φ Grid-Connected Neutral-Point-Clamped Transformerless Inverter

Abstract

Utility grid-tied photovoltaic (PV) installations are becoming a typical component of the current electrical energy grid. The adoption of transformerless inverters has recently changed the topology of these systems. Despite being small, inexpensive, and effective, transformerless inverters have a recurring leakage current issue. Numerous studies are being conducted to improve its performance and bring the leakage current down to acceptable levels. The studies propose three tracks for addressing the leakage current problem of transformerless PV systems: the control technique, the inverter modulation, and the inverter topology. This study applies the model-free predictive control (MFPC) technique to a grid-connected NPC 3-φ transformerless converter powered by a PV panel. An LCL filter connects the transformerless inverter to the grid. The system model considers the grid filter components and the internal impedance of the utility grid. The proposed system’s discrete model is established before describing the MFPC controller’s algorithm. The suggested system is simulated in MATLAB using the MFPC and a standard PI current controller with SVPWM modulation. According to the simulation’s findings, the MFPC controller performs best regarding current spectrum, THD, and earth leakage current. Additionally, MFPC-based systems are more efficient than those that use PI controllers.

Small-Signal Model of the NPC + GCC Multilevel Transformerless Inverter in Single-Phase Photovoltaic Power Systems

“…Due to its cost and simplicity, the NPC is the most widely used topology in low-power systems. Moreover, the use of the midpoint of the input voltage leads to additional benefits in the leakage-current-to-ground reduction [1,[21][22][23][24].…”