Embedded Switched Z-Source Multilevel Inverter for Grid Interfaced Photovoltaic Systems

Abstract

The modeling and the implementation of the embedded switched z-source type cascaded multilevel inverter for photovoltaic (PV) interfaced applications have been presented. With the ability to draw continuous current with an inherent filtering capability, the embedded switched z-source type inverter provides a single-stage conversion with a high output gain which makes it suitable for PV arrays with a low voltage rating. By applying a modular cascading method with a reduced number of H-bridge the multilevel inverter (MLI) is designed for a series-parallel connected PV array. It is controlled using the basic multicarrier PWM technique and synchronized with the grid. With the derived design equations for each mode, its stability has been analyzed and compared for different duty cycles. The developed MLI connected with a PV array has been simulated with the idea of reducing the impact of partial shading by using shorter series of strings, providing a high gain conversion with lower stress across the components. A prototype of the MLI has been tested to give a power rating of 2 kW and the results from both the simulation and the hardware have been discussed.

Keywords

• bridge circuits
• dc-ac power converters
• power grid
• pulse width modulation
• solar energy