An Effective dq-based Control Technique for a Grid-Connected Single-Phase PUC5 Inverter

Abstract

This paper presents a simple yet robust dq-frame current control strategy for a single-phase 5-level Packed U-Cell (PUC5) inverter, targeting efficient and reliable integration of renewable energy (RE) sources into the grid. The proposed approach exploits the inherent self-balancing characteristics of the PUC5 topology, thereby eliminating the need for capacitor voltage sensors or active balancing circuits. This leads to a simplified hardware structure and reduced overall system complexity and cost. A conventional PI-based dq controller is employed to regulate the injected grid current, ensuring decoupled control of active and reactive powers. Extensive simulations in MATLAB/Simulink demonstrate that the system maintains a unity power factor and achieves low total harmonic distortion (THD) using a basic L-type filter. Moreover, one of the key outcomes is the natural and stable self-balancing of the flying capacitor voltage, which consistently maintains its voltage around half the DC link voltage with low ripples, even under dynamic changes in current reference and DC input voltage. These results confirm the PUC5-controller solution’s reliability and suitability (compelling alternative to more complex multilevel converter architectures) for grid-connected applications.