Dr. Zainan Li
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Academic Career Length
6Years (2021-Present)
(Calculated once Scilit publication data is synced: current year − year of first publication + 1)
Representative Publications
View All Publications2 November 2021 in IEEE Transactions on Power Delivery
Journal Article
To improve the consumption of renewable energy and to meet complex load demands. A model of a multi-terminal flexible DC distribution network with multiple overhead branch lines is constructed. Aiming at frequent non-permanent faults of overhead lines, a fast pilot protection scheme is proposed to cover the whole fault process. Using the hybrid DC circuit breaker (HDCCB) action as the boundary mark, the fast pilot protection can be divided into two phases: post-fault and fault restart. The first phase highlights rapidity, sending a trip command to HDCCB within 1-2 ms after the fault. The second stage emphasizes reliability, and points out that the data of the whole fault process should be fully utilized, and to fully excavate the characteristics of fault current. A multi-time scale and multi-criteria fusion protection scheme is proposed, which can effectively improve the reliability of fault area identification. Finally, a corresponding model was built based on PSCAD, a large number of simulation tests and robustness analysis proved that the proposed fast pilot protection scheme is feasible.
12 July 2024 in IEEE Transactions on Industrial Electronics
Journal Article
In a modular multilevel converter (MMC), the dc side fault current is characterized by a fast-rising rate and high peak values. To address this problem, an adaptive current-limiting control (ACLC) method, which is based on the bridge arm current, has been proposed. A dynamic ACLC model, aiming to suppress the fault current, has been constructed by introducing of a bypass ratio that reduces the dc voltage. This model incorporates the bridge arm current as a critical variable, giving a linearized current limit suppression curve for adaptive bypass ratio output. Additionally, the ac/dc coupling mechanism within the converter has been thoroughly analyzed. The influence of the ACLC on the ac side current has been examined, providing a theoretical basis for the upper limit of the bypass ratio constraint in both strong and weak ac systems. A half-bridge high-voltage direct current transmission technology based on the modular multilevel converter (HB-MMC-HVDC) network model was built in the real-time digital simulator to test the proposed ACLC method. The results show that the proposed ACLC method reduces the peak current values by 12.33% and 34.52% under strong ac and weak ac systems, respectively, compared with other fault current-limiting (FCL) methods, and has a better current-limiting effect.
14 July 2024 in International Journal of Electrical Power & Energy Systems
Journal Article
KJKe Jia
Ke JiaKYKunpeng Yao
Kunpeng Yao
ZLZiyi Liu
Ziyi Liu
TZTianxin Zhang
Tianxin Zhang
Zainan LiTBTianshu Bi
Tianshu Bi
24 September 2023 in International Journal of Electrical Power & Energy Systems
Journal Article
Zainan LiKJKe Jia
Ke JiaJSJunlei Sun
Junlei Sun
HLHaolin Liu
Haolin Liu
ZLZiyi Liu
Ziyi Liu
TBTianshu Bi
Tianshu Bi
25 August 2025 in IEEE Transactions on Power Electronics
Journal Article
Integrating renewable energy sources into a bipolar modular multilevel converter (MMC) via a common ac bus can lead to an increase in ac in-feed current during a single pole-to-ground fault, resulting in bridge arm overcurrent and a blocking risk for the MMC. To address this problem, an adaptive current limiting control (ACLC) that accounts for the ac in-feed current boosting effect is proposed. First, a dynamic model of ac in-feed current rise in a faulty MMC is developed to analyze the mechanism of bridge arm current increase. The capacitor discharge between the bipolar MMCs is identified as the root cause of the bridge arm overcurrent. Then, the dynamic ACLC model is built for the bipolar MMC to reduce the ac in-feed current by differentially adjusting the number of inserted submodules in each MMC in the bipolar MMC. Finally, the proposed ACLC is validated through real-time simulation, showing a 43.66% reduction in peak bridge arm current to avoid the risk of MMC blocking and superior current-limiting performance compared to other methods.
9 October 2025 in IEEE Transactions on Industrial Electronics
Journal Article
In a modular multilevel converter-based multiterminal high-voltage direct current (MMC-HVdc) system, unbalanced active power (UAP) between converters is easily induced after ac/dc faults, resulting in severe dc transient overvoltage. To solve this problem, a postfault dc transient overvoltage control is proposed. The generation mechanism of UAP among multiterminal MMCs is analyzed, and the coupling model linking UAP to dc overvoltage is established, revealing a positive correlation between the peak voltage and UAP amplitude. Within the MMC region connected to the wind farm (WF), the proposed method achieves optimal allocation of UAP to suppress the overvoltage peak by dynamically coordinating multiple power units in accordance with the time sequence. Specifically, the submodule capacitor voltage boosting capability in the MMC serves as temporary energy storage, and UAP is redistributed between the WF and the DBR based on the energy equal area criterion. The real-time digital tests show that the proposed method reduces the peak transient overvoltage by over 9.1%, stabilizing at 1.0 p.u. and exhibits superior voltage control capability compared to other methods. Additionally, it minimizes reliance on the DBR, reducing DBR capacity and head dissipation by more than 25% and 25.58%, respectively, thereby enhancing the safety of the MMC-HVdc system.
About Me
Li Zainan, Ph.D., Assistant Researcher of Chongqing University. Graduated from North China Electric Power University. Mainly engaged in research on control and protection of flexible DC transmission/distribution. As the first author/co-author, he has published 14 SCI/EI-indexed papers in TIE, TPEL, TPD, IJEPES, China Journal of Electrical Engineering, and Power System Automation. He has also obtained 5 invention patents. He is a reviewer for international authoritative journals such as IEEE, TIE, TSE, TPD, and JESTPE. He has received the second prize at the national grid and provincial levels and the gold medal at the Geneva International Invention Exhibition.
Representative achievements in the past five years:
[1] Z. Li, K. Jia, T. Bi, et al. "Adaptive Current Limit Control for Half-Bridge MMC-HVDC Single Pole-to-Ground Fault. " in IEEE Transactions on Power Electronics, vol. 41, no. 2, pp. 2452-2462, Feb 2026.
[2] Z. Li, K. Jia*, T. Bi and J. Li. "ACLC Control in Half-Bridge MMC for DC Fault" in IEEE Transactions on Industrial Electronics, vol. 72, no. 1, pp. 516-524, Jan 2025.
[3] Z. Li*, J. Duan, W. Lu and Wei. Yang. "A fast pilot protection for DC distribution networks considering the whole fault process." in IEEE Transactions on Power Delivery, vol. 37, no. 4, pp. 3121-3132, Aug 2022.
[4] Z. Li, K. Jia, T. Bi, et al. "Postfault DC Transient Overvoltage Control for Multiterminal MMC-HVDC System. " in IEEE Transactions on Industrial Electronics, 2025, Early Access.