Modeling and Control of Quasi-Z-Source Inverter for Distributed Generation Applications

TLDR

The voltage‑fed quasi‑Z‑source inverter is favored for PV applications due to its single‑stage buck/boost capability and enhanced reliability. The study aims to model and control the qZSI for distributed generation, proposing a two‑stage constant‑capacitor‑voltage control to overcome modulation index and shoot‑through duty ratio limitations. A small‑signal dynamic model is developed and used to analyze stand‑alone and grid‑connected operation, and a two‑stage constant‑capacitor‑voltage control scheme is implemented. Choosing an appropriate capacitor voltage reference minimizes switching stress, and experiments confirm the theoretical analysis and controller design.

Abstract

The voltage-fed Z-source inverter/quasi-Z-source inverter (qZSI) has been presented suitable for photovoltaic (PV) applications mainly because of its single-stage buck and boost capability and improved reliability. This paper further addresses detailed modeling and control issues of the qZSI used for distributed generation (DG), such as PV or fuel cell power conditioning. The dynamical characteristics of the qZSI network are first investigated by small-signal analysis. Based on the dynamic model, stand-alone operation and grid-connected operation with closed-loop control methods are carried out, which are the two necessary operation modes of DG in distributed power grids. Due to the mutual limitation between the modulation index and shoot-through duty ratio of qZSI, constant capacitor voltage control method is proposed in a two-stage control manner. Minimum switching stress on devices can be achieved by choosing a proper capacitor voltage reference. Experimental results are presented for validation of the theoretical analysis and controller design.