Professor Xing Zhang was born in Shanghai, China, in 1963. He received the B.S., M.S., and Ph.D. degrees in electrical engineering and automation from Hefei University of Technology, Hefei, China, in 1984, 1990, and 2003, respectively. Prof. Zhang is currently an IEEE Senior Member and serves as the Director of the National-Local Joint Engineering Laboratory for Renewable Energy Grid Integration Technology at Hefei University of Technology. He is also an Executive Council Member of the China Power Supply Society. From 2008 to 2016, he served as the Vice Dean of the School of Electrical and Automation Engineering at Hefei University of Technology. For more than 20 years, he has led his team in a long-term and fruitful cooperation with Sungrow Power Supply Co., Ltd., resulting in the industrialization of many achievements. His current research interests include photovoltaic generation technologies, wind power generation technologies, and distributed generation systems.

Topic: Hybrid-Mode Control Strategy for Grid-Following and Grid-Forming Inverters in High-Penetration Renewable Energy System

Abstrac:There are two main types of grid-connected modes for grid-connected inverters, namely grid-following (GFL) control and grid-forming (GFM) control. Currently, most grid-connected inverters use the GFL control mode based on grid voltage synchronization. Although the GFL mode can quickly track the maximum power point of photovoltaic systems and respond to grid dispatch commands, it cannot actively support the grid. On the other hand, the GFM mode can achieve synchronization without using the phase-locked loop and can compensate for the missing inertia and damping characteristics of the system while ensuring its own stable operation. However, in the case of high-penetration rates of wind and solar power generation, a single GFL/GFM mode control may face serious challenges in maintaining stable operation due to significant and fluctuating grid impedance at the point of interconnection. This is reflected in the wideband oscillation of grid voltage or grid current. This report analyzes the stability mechanism and characteristics of inverters under the two grid-connected modes, namely the GFL mode and GFM mode, to address this issue. An impedance adaptive dual-mode control strategy is proposed based on this analysis, which ensures the stable operation of a single grid-connected inverter under significant fluctuations in grid impedance. Furthermore, when a single inverter is extended to a multi-inverter system, the two-level stability constraint conditions and the dual-inverter equivalent model of multi-inverter grid-connected systems under both GFL and GFM modes are studied. Based on this, a hybrid-mode operation technique and capacity optimization configuration method for high-penetration renewable energy power generation systems under both GFL and GFM modes are proposed, achieving comprehensive optimization of stability margin and power generation efficiency.