Improvement of energy harvesting capability in grid-connected photovoltaic micro-inverters

In this paper, a multi-stage micro-inverter system depending on a dual neutral point clamped (D-NPC) inverter is developed for low power photovoltaic (PV) applications. The primary objectives of this study are determined as improving the performance of the proposed D-NPC inverter-based micro-inverter and its controller to ensure better system reliability and promote the overall efficiency. In comparison with conventional systems, the designed system provides many advantages: (1) utilization of lower rating switching components, (2) reduced switching frequency and voltage stress, (3) reduced the size of filter components, (4) higher efficiency, and (5) lower total harmonic distortion (THD). The weighted efficiency of the system is remarkably increased by the value of 2.15% compared to the conventional micro-inverter and reached 93.73%. Furthermore, the THD value of the output current is measured below 3% for the proposed system with the small size of passive filtering elements. Further, dynamic grid support and anti-islanding detection capabilities are provided through the utilized controller structure to fulfill grid codes. Consequently, obtained results demonstrate that the improved system can be a considerable candidate for photovoltaic micro-inverter applications in terms of weighted efficiency, output current THD, and reasonable cost.