# Phd defence by Jing Yuan

## Time

29.10.2020 kl. 13.00 - 16.00

## Description

Jing Yuan, Department of Energy Technology, will defend the thesis "Impedance Source Converters for Renewable Energy Systems"

### TITLE

Impedance Source Converters for Renewable Energy Systems

### PHD DEFENDANT

Jing Yuan

### SUPERVISOR

Professor Frede Blaabjerg

### CO-SUPERVISOR

Associate Professor Yongheng Yang

### MODERATOR

Associate Professor Pooya Davari

### OPPONENTS

Associate Professor Erik Schaltz, Dept. of Energy Technology, Aalborg University (Chairman)

Professor Fei Gao, University of Technology of Belfort-Montbeliard

Associate Professor Chi-Seng Lam, University of Macau

### ABSTRACT

Impedance-source networks are promising power conversion stages due to their performance in terms of flexible step-up/down conversion ratios, and high reliability with the shoot-through protection. Accordingly, significant efforts have been made to advance the impedance source converters through topological innovations, but there are still many limitations, which hinder their further applications in renewable energy systems.

In general, the impedance source networks can be integrated into the traditional voltage-source inverter, which makes it a single-stage solution with boost capabilities. Alternatively, they can be applied as the first-stage DC-DC converter in the two-stage power conversion solutions. However, such impedance source networks, have several disadvantages, e.g., a low voltage gain, a discontinuous input current, a narrow adjustable control range, and high voltage stresses across the components. If these problems cannot be effectively addressed, they will degrade the performance of the impedance source networks. Thus, the solutions to the above limitations are demanded. Additionally, although many efforts have been made to improve the performance of the impedance source networks through novel topologies, the design and optimization of the impedance source networks have not been fully addressed yet. Seen from the design perspective, the performance of the impedance source networks can be further enhanced. Therefore, it is necessary to demonstrate special design considerations and a systematic

design procedure for impedance source networks. With the above and in order to improve the integration of renewable energy systems with impedance source networks, this Ph.D. project was carried out to develop novel impedance source networks for high-efficiency and high-reliability DC-AC and DC-DC power conversion systems. Throughout this project, several impedance source networks are proposed, which can be employed in DC-AC and DC-DC conversion systems. Compared with traditional impedance source networks, the proposed inverters based on the non-magnetic-coupled impedance networks can achieve a continuous input current, lower voltage stresses, and fault-tolerant operations.

In addition, modified magnetic-coupled-based impedance source DC-DC converters are proposed, which feature a continuous input current, trans-inverse capability, and a wide adjustable duty cycle range. Especially, the possible DC current saturation in the core is addressed by the configuration of the proposed magnetic-coupled-based topologies. To demonstrate the performance

of the proposed topologies, benchmarking studies of the proposed topologies against several selected prior-art topologies in terms of voltage stress, input current ripple, component count, duty cycle control range. Lab-scale prototypes have also been built to validate the performance.

Furthermore, a systematic design method for impedance source networks was introduced in this Ph.D. project. Several specific design considerations in terms of topology, modulation strategy, switching frequency, and practical layout are explored. Additionally, the basic design principle is provided for capacitors and inductors, which are widely used in impedance-source converters. Moreover, the design procedure is demonstrated on a quasi-Zsource network design. An optimal design of the coupled inductors with different winding structures is also provided.

The contributions of this Ph.D. project have been presented in five journal papers and four conference papers.

### The defence will be in english - all are welcome

Streaming info tbd.

### Host

Department of Energy Technology

### Address

PontoppidanstrÃ¦de 105, Room 3.115