Energy Balancing Control and Stability Analysis of Hybrid Modular Multilevel Converter During DC Fault Ride Through
Chen Canfeng1, Jiao Jiancheng1, Li Mengwei1, Zuo Anguo2, Zhang Kai1
1. Power Electronics and Energy Management Key Laboratory Ministry of Education of China School of Electrical and Electronic Engineering Huazhong University of Science and Technology Wuhan 430074 China; 2. Changchun Rail Transit Group Co. Ltd Changchun 130000 China
Abstract：The DC fault ride-through (DC-FRT) of the hybrid modular multilevel converter (H-MMC) is an effective means to cope with DC short-circuit faults in flexible DC grids, and the DC voltage collapse during DC-FRT makes the DC-side energy-balancing control (EBC) ineffective. The absence of EBC will hinder the rapid recovery of the internal characteristics of the H-MMC during the DC-FRT, thereby affecting the DC-FRT characteristics and restart of the H-MMC. To ensure the energy balancing of the H-MMC during DC-FRT, an AC-side EBC of H-MMC in αβz coordinate is proposed, which can optimize the FRT characteristics of H-MMC. To investigate the problem of poor stability in the application of the AC-side EBC, a small-signal model (SSM) of the H-MMC considering the AC-side EBC is constructed. The capacitor energy harmonic stability problem faced by the AC-side EBC is elucidated through the SSM. Based on stability analysis, suggestions for parameter selection of the AC-side EBC are proposed to ensure stability and dynamic performance during DC-FRT. Firstly, the AC-side EBC under the αβz coordinate for H-MMC DC fault ride-through is proposed based on the instantaneous power theory. The αβz-axis capacitor energy and reactive power of the H-MMC are controlled separately through the dq-axis components of the positive and negative sequence AC currents. Secondly, the system stability is discussed through small-signal modeling. The impact of capacitor energy harmonics on AC-side EBC is taken into account. Through participation factor and eigenvalue analysis, the reasons for the poor stability of AC-side EBC is attributed to the coupling effect generated by the fundamental and second harmonic components of capacitor energy through AC-side EBC. Through parameter sensitivity analysis, it is found that the dynamic response time τER of EBC, the bandwidth of the notch filter, and the PQ operating points have an impact on the stability of AC-side EBC, and the dynamic performance of AC-side EBC will be greatly limited. Based on stability analysis, several recommendations are proposed for the AC-side EBC: (1) The notch filter bandwidth should be set between 5 Hz and 15 Hz. (2) The τER of the αβ-axis controller and the z-axis controller should be selected separately. The τER of the αβ-axis controller should meet the stability requirements, while the τER of the z-axis can be selected based on dynamic performance requirements. (3) When the DC voltage is 0, the stability of the αβ-axis parameter design does not need to be considered. However, during the process of DC voltage recovery, the stability issues also need to be addressed. It is also suggested to adopt the proposed AC-side EBC in αβz coordinates, as the parameters of the AC-side EBC in ABC coordinates cannot be designed separately. The conclusions and recommendations are verified through simulations and experiments. It is indicated that the dynamic performance and stability of the AC-side EBC can be achieved simultaneously when the above recommendations are adopted, and the DC-FRT characteristics of H-MMC can be significantly improved. The following conclusions can be drawn: (1) The proposed AC-side EBC can achieve rapid recovery of the internal characteristics of the H-MMC during DC-FRT, significantly optimizing the DC-FRT characteristics of the H-MMC. (2) The AC-side EBC exhibits significant parameter stability issues, which arise from the coupling generated by capacitor energy harmonic through the AC-side EBC. (3) This stability issue can be avoided through the reasonable selection of AC-side EBC parameters, ensuring that the AC-side EBC maintains stability and dynamic performance during both normal operation and DC-FRT scenarios.
陈灿锋, 焦健成, 李孟伟, 左安国, 张凯. 混合型模块化多电平变换器直流故障穿越过程能量平衡控制及其稳定性分析[J]. 电工技术学报, 2025, 40(18): 6040-6056.
Chen Canfeng, Jiao Jiancheng, Li Mengwei, Zuo Anguo, Zhang Kai. Energy Balancing Control and Stability Analysis of Hybrid Modular Multilevel Converter During DC Fault Ride Through. Transactions of China Electrotechnical Society, 2025, 40(18): 6040-6056.
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