Performance Assessment of Three-Phase NPC-Based Grid Integrated Single-Stage Solar PV System With Reduced DC Bus Capacitor

Abstract

This work proposes an effective reduction in the capacitor size of the DC-bus of a conventional three-phase neutral point clamped (NPC) inverter-based grid integrated single-stage solar photovoltaic (PV) system. This has been done by implementing a metallized polypropylene film DC-bus capacitor instead of an electrolytic capacitor. As an outcome, this enhances the system's long-term reliability, reduces cost, and increases the system's life expectancy. The unbalance in capacitor voltage due to a small DC-bus capacitor is also identified. As a solution, a carrier-based modified modulation strategy is implemented to improve the dynamic response of neutral-point voltage. A single-stage solar PV array is utilized in this paper. An optimal power extraction (OPE) scheme is adopted to extract solar PV power. The DC-bus voltage overshoot issue that arises during the change in irradiation is resolved, and minimal oscillations are observed. The implemented scheme allows the feeding of the extracted power to the three-phase grid via the NPC converter, which in turn diminishes the total harmonic distortion (THD) of the grid. The PI controller minimizes the voltage and current error. The system performance is observed using a MATLAB version simulation model and authenticated through the experimental results obtained from the laboratory prototype.