Voltage Control Tuning of a Single-Phase Grid-Connected 3L qZS-Based Inverter for PV Application

This paper proposes a control tuning method to regulate the average dc-link voltage from a symmetrical quasi-Z-source (qZS) topology connected to a single-phase three-level (3L) neutral-point-clamped (NPC) multilevel inverter. A case study of a single-phase grid-connected photovoltaic (PV) system and its control methods are analyzed. An ac small-signal model from a 3L qZS topology was proposed and applied for selecting a suitable operational point of a feedback control system based on initial design requirements and analytical equations. The proposed method does not directly adjust the shoot-through duty cycle that could be determined by an external MPPT algorithm. It is based on the power flow control between grid-utility and PV array. Simulation results obtained from a PSCAD/EMTDC model to different controller settings are discussed. Considering its simplicity, the proposed voltage control tuning method for a single-phase 3L qZS-based NPC inverter PV grid-connected systems could be extended to other topologies (like three-phase applications).