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Dynamic Frequency Support and DC Voltage Regulation Approach for VSC-MTDC Systems

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CSEE Journal of Power and Energy Systems 2023年第2期9卷 645-658页

作者： chongru liu Haoyu liu Siwen Jiang Le Zheng State Key Laboratory for Alternate Electrical Power System with Renewable Energy Sources North China Electric Power UniversityBeijing 102206China

When an additional frequency control is implemented in the voltage source converter-based multi-terminal high voltage direct current(VSC-MTDC)system,the DC grid is capable of responding to a frequency disturbance in the AC system.However,the original additional frequency control may cause the DC voltage to exceed the limit when providing power for a severe frequency disturbance,threatening the security of the DC system.A novel dynamic additional frequency control strategy for the VSC-MTDC system is developed based on the relationship between the DC voltage and the frequency droop coefficient.A dynamic frequency droop coefficient is designed to adaptively adjust the support power of the DC grid,balancing the frequency regulation of the disturbed AC system and the voltage stability of the DC grid.A DC voltage recovery method based on multi-converter cooperation is proposed to cope with the DC voltage deviation caused by the additional frequency control.Simulations validate the advantages and satisfactory performance of the proposed method during power disturbances with different severities and for the process of DC voltage recovery.

关键词： Additional frequency control DC voltage recovery module dynamic frequency droop coefficient VSCMTDC

Data-driven Estimation for a Region of Attraction for Transient Stability Using the Koopman Operator

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CSEE Journal of Power and Energy Systems 2023年第4期9卷 1405-1413页

作者： Le Zheng Xin liu Yanhui Xu Wei Hu chongru liu the School of Electrical and Electronic Engineering North China Electric Power UniversityBeijing 102206China Department of Electrical Engineering Tsinghua UniversityBeijing 100084China

This paper presents a novel Koopman Operator based framework to estimate the region of attraction for power system transient stability analysis.The Koopman eigenfunctions are used to numerically construct a Lyapunov function.Then the level set of the function is utilized to estimate the boundary of the region of attraction.The method provides a systematic method to construct the Lyapunov function with data sampled from the state space,which suits any power system models and is easy to use compared to traditional Lyapunov direct methods.In addition,the constructed Lyapunov function can capture the geometric properties of the region of attraction,thus providing useful information about the instability modes.The method has been verified by a simple illustrative example and three power system models,including a voltage source converter interfaced system to analyze the large signal synchronizing instability induced by the phase lock loop dynamics.The proposed method provides an alternative approach to understanding the geometric properties and estimating the boundary of the region of attraction of power systems in a data driven manner.Index Terms-Koopman operator,lyapunov function,power system transient stability,region of attraction.

关键词： Koopman operator lyapunov function power system transient stability region of attraction.

Mechanism Analysis of Additional Damping Control Strategies for the High-frequency Resonance of MMC Connected to AC Grid

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CSEE Journal of Power and Energy Systems 2023年第3期9卷 1173-1181页

作者： Yanqi Hou chongru liu Yu Wang Wei Kong State Key Laboratory for Alternate Electrical Power System with Renewable Energy Sources North China Electric Power UniversityBeijing 102206China State Grid Economic and Technological Research Institute Co.Ltd. Beijing 102209China State Grid Corporation of China Beijing 100031China

High-frequency resonance can occur when a modular multilevel converter(MMC)is inserted into an AC grid.Additional damping control is a relatively low-cost resonance suppression strategy compared to passive damping strategies.This paper analyzes the influences of a feed-forward voltage filter and feedback current filter for the inner controller for the high-frequency impedance characteristics of the MMC based on a model.Moreover,the mechanism,influencing factors,and limitations of the existing strategy including an additional lowpass filter in the voltage feed-forward stage are investigated.Secondly,a resonance suppression strategy for the inclusion of additional cascaded notch filters in the voltage feed-forward stage is proposed,and its parameter design method and applicable scenarios are analyzed.In addition,this paper analyzes the effects of the inclusion of an additional control in other stages for the inner controller of the MMC.Finally,the correctness of the theoretical analysis and the proposed strategy is verified based on the simulation of an actual project on PSCAD/EMTDC.

关键词： Additional damping control strategy additional cascaded notch filters additional low-pass filter modular multilevel converter(MMC) high-frequency resonance

Analysis on Local and Concurrent Commutation Failure of Multi-infeed HVDC Considering Inter-converter Interaction

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Journal of Modern Power Systems and Clean Energy 2022年第4期10卷 1050-1059页

作者： Bilawal Rehman chongru liu Huan Li Chuang Fu Wei Wei State Key Laboratory for Alternate Electrical Power System with Renewable Energy Sources North China Electric Power UniversityBeijing 102206China Department of Electrical Engineering Technology National Skills University IslamabadIslamabad45710Pakistan State Key Laboratory of HVDC Electric Power Research InstituteChina Southern Power GridGuangzhou 510663China

This paper provides a comprehensive analysis of local and concurrent commutation failure(CF)of multi-infeed high-voltage direct current(HVDC)system considering multi-infeed interaction factor(MIIF).The literature indicates that the local CF is not influenced by MIIF,whereas this paper concludes that both the local CF and concurrent CF are influenced by MIIF.The ability of remote converter to work under reduced reactive power enables its feature to support local converter via inter-connection link.The MIIF measures the strength of electrical connectivity between converters.Higher MIIF gives a clearer path to remote converter to support local converter,but at the same time,it provides an easy path to local converter to disturb remote converter under local fault.The presence of nearby converter increases the local commutation failure immunity index(CFII)while reducing concurrent CFII.Higher MIIF causes reactive power support to flow from remote converter to local converter,which reduces the chances of CF.A mathematical approximation to calculate the increase in local CFII for multi-infeed HVDC configurations is also proposed.A power flow approach is used to model the relation between MIIF and reactive power support from remote end.The local and concurrent CFIIs are found to be inverse to each other over MIIF;therefore,it is recommended that there is an optimal value of MIIF for all converters in close electric proximity to maintain CFII at a certain level.The numerical results of established model are compared with PSCAD/EMTDC simulations.The simulation results show the details of the influence of MIIF on local CF and concurrent CF of multi-infeed HVDC,which validates the analysis presented.

关键词： Commutation failure(CF) multi-infeed highvoltage direct current(HVDC)system multi-infeed interaction factor commutation failure immunity index(CFII)

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基于虚拟阻抗补偿的PMSG恒导纳建模方法

中国电机工程学报 2024年第6期44卷 2362-2373,I0024页

作者：史一博刘崇茹新能源电力系统国家重点实验室(华北电力大学) 北京市昌平区102206

永磁直驱风力发电系统结构复杂、节点数多,在进行电磁暂态实时仿真时,若采用传统建模方法会因系统导纳矩阵计算过于复杂导致仿真规模严重受限。该文提出一种基于虚拟阻抗补偿的永磁同步发电机(permanent magnet synchronous generator,P... 详细信息

永磁直驱风力发电系统结构复杂、节点数多,在进行电磁暂态实时仿真时,若采用传统建模方法会因系统导纳矩阵计算过于复杂导致仿真规模严重受限。该文提出一种基于虚拟阻抗补偿的永磁同步发电机(permanent magnet synchronous generator,PMSG)恒导纳建模方法,该方法基于传统发电机模型,通过在转子上补偿虚拟阻抗的方式使发电机导纳矩阵固定,并以暂态误差最小为目标,对阻抗参数进行优化设计;再通过结合换流器的伴随离散电路模型,可建立PMSG完整恒导纳模型并进行电磁暂态仿真,能够节省大量的计算资源。仿真试验证明,该模型具有较高的仿真精度,并且可以用于FPGA等离散化硬件仿真平台上,具有良好的适用性。

关键词：恒导纳模型虚拟阻抗补偿永磁同步电机

Steady‐state power operation region of a modular multilevel converter connecting to an AC grid

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High Voltage 2021年第6期6卷 1009-1023页

作者： Jiecong Wang chongru liu Udaya DAnnakkage Xiao Li Chenbo Su State Key Lab.for Alternate Electrical Power System with Renewable Energy Sources North China Electric Power UniversityBeijingChina University of Manitoba WinnipegCanada

The modular multilevel converter(MMC)has become a widely used topology for voltage source converter-based high‐voltage direct current transmission projects.To calculate the power operation region of an MMC directly and efficiently,we propose a novel steady‐state phasor model of the MMC.The model is expressed as an equivalent capacitance in series with a voltage source,where parameters are independent of alternating current(AC)electrical quantity.Based on the model,we propose an open‐loop approach to determine the operation region boundary of MMC by calculating the envelopes of the P-Q curves.The effect of MMC parameters,the circulating current control,and the short‐circuit ratio of the AC grid to the power operation region can be determined by the size and position of the power operation region.The proposed approach and analysis results were verified by an MMC/AC simulation model built in PSCAD/EMTDC.

关键词： PSCAD/EMTDC operation power

HVDC送端系统振荡引发受端换相失败的机理分析

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电工技术学报 2024年第9期39卷 2743-2754页

作者：郑乐吴晶徐衍会孙英云刘崇茹华北电力大学电气与电子工程学院北京102206

高压直流输电系统送、受端存在电气耦合及两端的控制配合,因此,送端振荡可通过系统控制逻辑、电气量及控制量变化等影响受端系统的运行状态,增加了受端换相失败的风险。现有工作主要研究了送端大扰动引发受端换相失败的现象与机理,通过... 详细信息

高压直流输电系统送、受端存在电气耦合及两端的控制配合,因此,送端振荡可通过系统控制逻辑、电气量及控制量变化等影响受端系统的运行状态,增加了受端换相失败的风险。现有工作主要研究了送端大扰动引发受端换相失败的现象与机理,通过对标准直流系统进行小信号分析,发现直流系统中存在低频频段的固有振荡频率,一旦交流系统发生相近频段的振荡,将可能诱发直流系统共振。在此基础上,首先分析共振引起系统电气量以及控制量的波动对换相失败的影响,通过HVDC的准稳态方程分析共振后直流电流上升导致关断角下降,进而引发首次换相失败的机理;然后从两端的控制系统出发,研究逆变侧控制切换引发后续换相失败的机理;最后对CIGRE直流输电标准测试系统进行验证,并结合换相失败发生机理对换相失败的抑制策略进行了初步讨论。

关键词：高压直流输电送端振荡受端换相失败机理分析

基于锂离子电池电化学机理特性的电气等值模型研究

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中国电机工程学报 2024年第10期44卷 3916-3926,I0014页

作者：赵冬梅裴建楠刘崇茹徐辰宇宋晨铭华北电力大学电气与电子工程学院北京市昌平区102206

为更准确地表征低倍率充放电工况下电池内外部的动态状况,该文根据锂离子电池电化学原理推导出一种机理电气等值模型,明确机理电气等值模型相关电气元件参数的计算方法,揭示其与锂离子电池电化学参数之间的关联。所提机理电气等值模型... 详细信息

为更准确地表征低倍率充放电工况下电池内外部的动态状况,该文根据锂离子电池电化学原理推导出一种机理电气等值模型,明确机理电气等值模型相关电气元件参数的计算方法,揭示其与锂离子电池电化学参数之间的关联。所提机理电气等值模型兼具锂离子电化学模型的精度以及常规经验等效电路模型在储能控制参数整定、大规模储能电站等效建模方面便捷性的优势,更适用于新型电力系统场景下的储能电站建模、仿真、参数整定及安全监测。

关键词：锂离子电池机理电气等值模型锂离子电池电化学模型经验等效电路模型大规模储能电站

考虑频率耦合特性的D-PMSG复数域阻抗建模及其特征分析

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电力系统自动化 2024年第10期48卷 118-128页

作者：苏晨博刘崇茹王瑾媛郝琪董浩云华北电力大学电气与电子工程学院北京市102206

阻抗分析法因其简单有效被广泛用于含电力电子变换器的互联系统稳定性研究。然而,采用传统方法对频域序阻抗建模时,需通过非线性变换(Park变换及其反变换)进行坐标系转换,这会导致不同周期分量的卷积运算及相应的频移,其过程较为烦琐。... 详细信息

阻抗分析法因其简单有效被广泛用于含电力电子变换器的互联系统稳定性研究。然而,采用传统方法对频域序阻抗建模时,需通过非线性变换(Park变换及其反变换)进行坐标系转换,这会导致不同周期分量的卷积运算及相应的频移,其过程较为烦琐。针对上述问题,基于复向量时域微分算子,提出了永磁直驱同步发电机(D-PMSG)等效阻抗建模方法。该方法在时域周期系统稳定运行轨迹的邻域内直接进行小信号线性化,并采用指数旋转因子灵活反映系统受扰后的时变特性,结合时域微分算子等效表征互联系统控制环节的动态特性,避免了频域阻抗建模时坐标系的反复变换,大幅降低了解析建模的复杂度。此外,所提方法能够更加清晰地阐释互联系统受到扰动时D-PMSG并网逆变器产生频率耦合现象的物理意义;同时,能够说明基频电压初始相位对耦合分量相频特性的影响。最后,利用仿真验证了所提算法的有效性。

关键词：复向量阻抗建模永磁直驱同步发电机(D-PMSG) 频率耦合系统稳定性分析