A paper written by a research team of Xi'an Jiaotong University (XJTU) won the "Best Paper Award" issued by the Power Electronics Society of the Institute of Electrical and Electronics Engineers (IEEE), the world's largest technical professional organization for the advancement of technology.

Written by the research team led by Professor Liu Jinjun of the XJTU Power Electronics & Renewable Energy Research Center, the paper studied the modeling and analysis methods of microgrid stability based on parallel inverters. It was titled "Small-Signal Modeling and Stability Prediction of Parallel Droop-Controlled Inverters Based on Terminal Characteristics of Individual Inverters".

The thesis was completed under the guidance of Associate Professor Liu Zeng and Professor Liu Jinjun. Doctoral student Wang Shike is the first author, and XJTU is the only corresponding unit. 

Two professors from Virginia Polytechnic Institute and State University also contributed to this research. This project was supported by the National Natural Science Foundation of China and the China Postdoctoral Science Foundation.

A microgrid is an independent power system that includes distributed power sources and loads. It is one of the key technologies to effectively solve the problem of renewable energy generation and improve its utilization rate, which is of great significance for achieving goals of carbon emission peaking and carbon neutrality.

Typical low-frequency oscillation waveforms of a microgrid and the prediction results of the proposed model

As an effective way to access renewable energy, the parallel droop-controlled inverters system is widely used in AC microgrids, but the dynamic interaction between the inverters can easily cause system oscillations and seriously threaten the safe and stable operation of the system.

The thesis proposed fundamental frequency-current port characteristics to characterize the small signal dynamics of the fundamental frequency unique to the droop-controlled inverters.

On this basis, a full-band small-signal model of the parallel droop-controlled inverters system based on port characteristics was constructed, and then a complete system with stable criteria was proposed.

The thesis revealed for the first time that the fundamental frequency dynamic characteristics play an important role in the stability of this type of microgrid system. It also proposed for the first time a method for systematic analysis and prediction of its stability, improving traditional descriptions.

It fundamentally solves the problem that the existing stability criterion based only on the port impedance cannot analyze the low-frequency oscillation of the system caused by fundamental wave dynamics, and lays an important theoretical foundation for the small-signal modeling and stability prediction of parallel droop-controlled inverters.