随着电网换相型高压直流输电(line commutated converter based high voltage direct current,LCC-HVDC)技术的广泛应用,交直流混联电网的谐波交互问题愈加复杂,建立LCC-HVDC小信号模型是分析换流器交直流谐波耦合特性的重要手段。为此...随着电网换相型高压直流输电(line commutated converter based high voltage direct current,LCC-HVDC)技术的广泛应用,交直流混联电网的谐波交互问题愈加复杂,建立LCC-HVDC小信号模型是分析换流器交直流谐波耦合特性的重要手段。为此,基于谐波状态空间理论(harmonic state space, HSS)建立双端12脉动LCC-HVDC小信号模型,不仅考虑了LCC谐波传递特性,还考虑了换流变压器联结方式、控制链路延时等因素的影响。采用模块化思想分别建立各子系统谐波状态空间模型,通过接口矩阵连接为整体,使得LCC的谐波状态空间建模在易于扩展的同时,提高了精确度。最后,给出交直流谐波传递的具体表达式,并通过PSCAD仿真验证模型的准确性。所建模型不仅为后续扩展或接入更为复杂的系统奠定了基础,还可应用于双端LCC系统谐波交互稳定性评估和系统参数优化设计。展开更多
针对柔性直流输电系统(voltage source converter based high voltage direct current transmission,VSC-HVDC)控制参数设计过程中存在的鲁棒性差、依赖已知电路参数、工程设计经验化等问题,提出一种基于马尔科夫转换场(Markov transiti...针对柔性直流输电系统(voltage source converter based high voltage direct current transmission,VSC-HVDC)控制参数设计过程中存在的鲁棒性差、依赖已知电路参数、工程设计经验化等问题,提出一种基于马尔科夫转换场(Markov transition field,MTF)与深度确定性策略梯度算法(deep deterministic policy gradient,DDPG)结合的鲁棒性强、不依赖电路参数特性以及可视化的VSC-HVDC控制参数优化设计方法。首先,采用马尔科夫转换场将电路功率、电压等一维时序波形数据转换为二维马尔科夫转换场域图像并使用马尔科夫转换场损失函数(Markov transition field loss,MTFL)判断二维转换域图的数据波动性;其次,将MTFL损失函数与DDPG算法相结合,综合利用MTFL损失函数对系统输出时序数据动态特性评价能力更强的优点和DDPG算法泛化性能优秀的特点,实现VSC-HVDC系统控制参数优化;最后,通过MATLAB模拟和实验结果验证该方法的有效性。展开更多
柔性直流电网的故障检测与保护研究是当前电力领域的关键技术。直流电网发生故障时,故障电流迅速上升导致电网系统设备损坏且稳定性下降,因此对故障保护系统的快速性和可靠性要求极高。通过比较线路上限流电感电压值在故障前后的变化,...柔性直流电网的故障检测与保护研究是当前电力领域的关键技术。直流电网发生故障时,故障电流迅速上升导致电网系统设备损坏且稳定性下降,因此对故障保护系统的快速性和可靠性要求极高。通过比较线路上限流电感电压值在故障前后的变化,提出一种利用限流电感两端电压比值实现线路故障识别的方法。在PSCAD/EMTDC仿真平台建立四端模块化多电平换流器型柔性直流输电(modular multilevel converter high voltage direct current,MMC-HVDC)电网模型,对所提出的方法进行故障启动、类型识别和极线选择验证。在故障被正确识别后,相应的直流断路器(DC circuit breaker,DCCB)能够正确动作并隔离故障。此外,还对系统的性能指标以及故障过渡电阻值、故障后系统的噪声、故障距离和通信误差方面因素进行可行性分析。研究结果表明,所提出的故障保护方案能够准确识别并且快速隔离故障,从而保障电网安全稳定运行。展开更多
This paper focus on the Modeling and Calculation of DC current distribution in AC power grid induced under HVDC Ground-Return-Mode. Applying complex image method and boundary element method, a new field-circuit coupli...This paper focus on the Modeling and Calculation of DC current distribution in AC power grid induced under HVDC Ground-Return-Mode. Applying complex image method and boundary element method, a new field-circuit coupling model was set up. Based on the calculation result with complex image method, this paper derived the modification factor for induced earth potential from practical measurement, which increased the accuracy of calculation. The modification method is helpful for evaluation on the effect of means used for blocking the dc-bias current in transformer neutral and also useful for the forecast of the DC current distribution when the power grid is in different line connection mode. The DC distribution character in Guangdong power grid is shown and suggestion is proposed that the mitigation of dc-bias should start from those substations whose earth-potential is highest.展开更多
This paper presents a numerical study of the current self-excited oscillations during the opening of high voltage direct current(HVDC) metallic return transfer breaker(MRTB).The switching arc is simulated using the ma...This paper presents a numerical study of the current self-excited oscillations during the opening of high voltage direct current(HVDC) metallic return transfer breaker(MRTB).The switching arc is simulated using the magneto-hydrodynamics(MHD) theory coupled with the electric circuit variation.The simulation is proved accurate in simulating the current oscillation and the commutation process in MRTB by the good agreement between the calculated results and the experimental results,which are obtained on a MRTB prototype designed to break about 5 kA of DC current.Both kinds of the results show that the current oscillation starts at about 16.5 ms and the total arc time is about 24 ms with a commutation capacitor bank of 72 μF and an inductor of 173 μH.With a further analyze on how circuit parameters influence arc current oscillations,this study helps to improve the current interruption capability of MRTB.展开更多
The ground level ion current density produced by corona discharge in high voltage direct current(HVDC)transmission lines can reflect the operation status of the lines,but the distorted electric field at the edge of th...The ground level ion current density produced by corona discharge in high voltage direct current(HVDC)transmission lines can reflect the operation status of the lines,but the distorted electric field at the edge of the Wilson plate seriously affects the measurement results of ion current density.In order to measure the ground level ion current density accurately and directly,a new reduced scale wire-plate experimental device in which the Wilson plate is flush with the grounding plate is designed.The influence of protective annulus width and the height of the Wilson plate from the grounding plate on ground level ion current density are studied.In addition,the differences between the micro-current galvanometer method and the sampling resistance method in the measurement of ion current density are compared.Finally,the ground level ion current density distributions of unipolar and bipolar HVDC transmission lines are measured.The results show that the edge effect of the Wilson plate can be neglected when the width of protective annulus is less than 2 mm,and the ion current density is nonlinear with the height of the Wilson plate from the grounding plate.Moreover,the internal resistance of the digital voltmeter seriously affects the measurement results and it is necessary to correct the results.Finally,at the same applied voltage,the ground level ion current density in the negative conductor region is higher than that in the positive conductor region.展开更多
随着中国交直流混联电网的快速发展,弱送端系统特征日益显著,构网型与跟网型变流器混合送出模式电压支撑优势显著,但直流故障受扰过程中系统功率动态交互过程尚不明晰。为此,首先分析常规跟网型变流器经基于电网换相换流器的高压直流输...随着中国交直流混联电网的快速发展,弱送端系统特征日益显著,构网型与跟网型变流器混合送出模式电压支撑优势显著,但直流故障受扰过程中系统功率动态交互过程尚不明晰。为此,首先分析常规跟网型变流器经基于电网换相换流器的高压直流输电(line commutated converter based high voltage direct current,LCC-HVDC)送出系统的局限性,阐明电压弱支撑下其在换相失败(commutation failure,CF)后易出现功率振荡,从而加深故障程度,导致后续换相失败的发生;其次,理论分析常规构网型变流器电流分配系数调控极限对应的电气量相量关系,揭示换相失败过程中构网型变流器存在电流限幅控制延迟退出的情况,进而造成暂态过电压抑制效果欠佳甚至进一步导致后续换相失败的发生。最后,提出换相失败时间尺度下的改进电流限幅故障穿越控制,并基于PSCAD/EMTDC平台,验证相关理论分析及控制策略的正确性和有效性。展开更多
直驱风电场耦合到电网换相换流器高压直流输电(line-commutated-converter based high voltage direct current,LCC-HVDC)交流母线的应用场景增多,LCC-HVDC调制产生的次同步间谐波激励系统固有模态产生的强迫次同步振荡(forced subsynch...直驱风电场耦合到电网换相换流器高压直流输电(line-commutated-converter based high voltage direct current,LCC-HVDC)交流母线的应用场景增多,LCC-HVDC调制产生的次同步间谐波激励系统固有模态产生的强迫次同步振荡(forced subsynchronous oscillation,FSSO)问题日益明显。针对这一问题,文章首先推导LCC-HVDC调制产生的间谐波扰动期间FSSO的时域表达式,提出了该系统次同步间谐波激发耦合风电场FSSO的机理。根据FSSO机理,提出了缓解FSSO的参数优化目标:第一,提升被激励次同步模态的阻尼;第二,使被激励次同步模态的振荡频率尽可能远离间谐波的频率范围;第三,要兼顾故障穿越的动态特性。然后,识别了与耦合系统模态阻尼特性及振荡频率的风电系统控制参数,提出了综合考虑模态阻尼、模态振荡频率与间谐波频率的偏离程度以及风电场故障穿越性能的缓解FSSO的风电场参数优化策略。最后,通过PSCAD/EMTDC时域仿真搭建系统模型,验证了理论分析的正确性和缓解FSSO参数优化策略的有效性。展开更多
文摘随着电网换相型高压直流输电(line commutated converter based high voltage direct current,LCC-HVDC)技术的广泛应用,交直流混联电网的谐波交互问题愈加复杂,建立LCC-HVDC小信号模型是分析换流器交直流谐波耦合特性的重要手段。为此,基于谐波状态空间理论(harmonic state space, HSS)建立双端12脉动LCC-HVDC小信号模型,不仅考虑了LCC谐波传递特性,还考虑了换流变压器联结方式、控制链路延时等因素的影响。采用模块化思想分别建立各子系统谐波状态空间模型,通过接口矩阵连接为整体,使得LCC的谐波状态空间建模在易于扩展的同时,提高了精确度。最后,给出交直流谐波传递的具体表达式,并通过PSCAD仿真验证模型的准确性。所建模型不仅为后续扩展或接入更为复杂的系统奠定了基础,还可应用于双端LCC系统谐波交互稳定性评估和系统参数优化设计。
文摘针对柔性直流输电系统(voltage source converter based high voltage direct current transmission,VSC-HVDC)控制参数设计过程中存在的鲁棒性差、依赖已知电路参数、工程设计经验化等问题,提出一种基于马尔科夫转换场(Markov transition field,MTF)与深度确定性策略梯度算法(deep deterministic policy gradient,DDPG)结合的鲁棒性强、不依赖电路参数特性以及可视化的VSC-HVDC控制参数优化设计方法。首先,采用马尔科夫转换场将电路功率、电压等一维时序波形数据转换为二维马尔科夫转换场域图像并使用马尔科夫转换场损失函数(Markov transition field loss,MTFL)判断二维转换域图的数据波动性;其次,将MTFL损失函数与DDPG算法相结合,综合利用MTFL损失函数对系统输出时序数据动态特性评价能力更强的优点和DDPG算法泛化性能优秀的特点,实现VSC-HVDC系统控制参数优化;最后,通过MATLAB模拟和实验结果验证该方法的有效性。
文摘柔性直流电网的故障检测与保护研究是当前电力领域的关键技术。直流电网发生故障时,故障电流迅速上升导致电网系统设备损坏且稳定性下降,因此对故障保护系统的快速性和可靠性要求极高。通过比较线路上限流电感电压值在故障前后的变化,提出一种利用限流电感两端电压比值实现线路故障识别的方法。在PSCAD/EMTDC仿真平台建立四端模块化多电平换流器型柔性直流输电(modular multilevel converter high voltage direct current,MMC-HVDC)电网模型,对所提出的方法进行故障启动、类型识别和极线选择验证。在故障被正确识别后,相应的直流断路器(DC circuit breaker,DCCB)能够正确动作并隔离故障。此外,还对系统的性能指标以及故障过渡电阻值、故障后系统的噪声、故障距离和通信误差方面因素进行可行性分析。研究结果表明,所提出的故障保护方案能够准确识别并且快速隔离故障,从而保障电网安全稳定运行。
文摘This paper focus on the Modeling and Calculation of DC current distribution in AC power grid induced under HVDC Ground-Return-Mode. Applying complex image method and boundary element method, a new field-circuit coupling model was set up. Based on the calculation result with complex image method, this paper derived the modification factor for induced earth potential from practical measurement, which increased the accuracy of calculation. The modification method is helpful for evaluation on the effect of means used for blocking the dc-bias current in transformer neutral and also useful for the forecast of the DC current distribution when the power grid is in different line connection mode. The DC distribution character in Guangdong power grid is shown and suggestion is proposed that the mitigation of dc-bias should start from those substations whose earth-potential is highest.
基金Project supported by National Natural Science Foundation of China （51007072, 51177124）, Doctoral Foundation of Ministry of Education of China （20110201130006, 20110201120069）, New Century Excellent Talents Program from Ministry of Education of China.
文摘This paper presents a numerical study of the current self-excited oscillations during the opening of high voltage direct current(HVDC) metallic return transfer breaker(MRTB).The switching arc is simulated using the magneto-hydrodynamics(MHD) theory coupled with the electric circuit variation.The simulation is proved accurate in simulating the current oscillation and the commutation process in MRTB by the good agreement between the calculated results and the experimental results,which are obtained on a MRTB prototype designed to break about 5 kA of DC current.Both kinds of the results show that the current oscillation starts at about 16.5 ms and the total arc time is about 24 ms with a commutation capacitor bank of 72 μF and an inductor of 173 μH.With a further analyze on how circuit parameters influence arc current oscillations,this study helps to improve the current interruption capability of MRTB.
基金supported by National Natural Science Foundation of China(Nos.51877027,51877028)State Key Laboratory of Electrical Insulation and Power Equipment(EIPE18206).
文摘The ground level ion current density produced by corona discharge in high voltage direct current(HVDC)transmission lines can reflect the operation status of the lines,but the distorted electric field at the edge of the Wilson plate seriously affects the measurement results of ion current density.In order to measure the ground level ion current density accurately and directly,a new reduced scale wire-plate experimental device in which the Wilson plate is flush with the grounding plate is designed.The influence of protective annulus width and the height of the Wilson plate from the grounding plate on ground level ion current density are studied.In addition,the differences between the micro-current galvanometer method and the sampling resistance method in the measurement of ion current density are compared.Finally,the ground level ion current density distributions of unipolar and bipolar HVDC transmission lines are measured.The results show that the edge effect of the Wilson plate can be neglected when the width of protective annulus is less than 2 mm,and the ion current density is nonlinear with the height of the Wilson plate from the grounding plate.Moreover,the internal resistance of the digital voltmeter seriously affects the measurement results and it is necessary to correct the results.Finally,at the same applied voltage,the ground level ion current density in the negative conductor region is higher than that in the positive conductor region.
文摘随着中国交直流混联电网的快速发展,弱送端系统特征日益显著,构网型与跟网型变流器混合送出模式电压支撑优势显著,但直流故障受扰过程中系统功率动态交互过程尚不明晰。为此,首先分析常规跟网型变流器经基于电网换相换流器的高压直流输电(line commutated converter based high voltage direct current,LCC-HVDC)送出系统的局限性,阐明电压弱支撑下其在换相失败(commutation failure,CF)后易出现功率振荡,从而加深故障程度,导致后续换相失败的发生;其次,理论分析常规构网型变流器电流分配系数调控极限对应的电气量相量关系,揭示换相失败过程中构网型变流器存在电流限幅控制延迟退出的情况,进而造成暂态过电压抑制效果欠佳甚至进一步导致后续换相失败的发生。最后,提出换相失败时间尺度下的改进电流限幅故障穿越控制,并基于PSCAD/EMTDC平台,验证相关理论分析及控制策略的正确性和有效性。
文摘直驱风电场耦合到电网换相换流器高压直流输电(line-commutated-converter based high voltage direct current,LCC-HVDC)交流母线的应用场景增多,LCC-HVDC调制产生的次同步间谐波激励系统固有模态产生的强迫次同步振荡(forced subsynchronous oscillation,FSSO)问题日益明显。针对这一问题,文章首先推导LCC-HVDC调制产生的间谐波扰动期间FSSO的时域表达式,提出了该系统次同步间谐波激发耦合风电场FSSO的机理。根据FSSO机理,提出了缓解FSSO的参数优化目标:第一,提升被激励次同步模态的阻尼;第二,使被激励次同步模态的振荡频率尽可能远离间谐波的频率范围;第三,要兼顾故障穿越的动态特性。然后,识别了与耦合系统模态阻尼特性及振荡频率的风电系统控制参数,提出了综合考虑模态阻尼、模态振荡频率与间谐波频率的偏离程度以及风电场故障穿越性能的缓解FSSO的风电场参数优化策略。最后,通过PSCAD/EMTDC时域仿真搭建系统模型,验证了理论分析的正确性和缓解FSSO参数优化策略的有效性。
