The wavelet transformation is applied to the high current transformer.The high current transformer elaborated in the paper is mainly applied to the measurement of AC/DC high current.The principle of the transformer is...The wavelet transformation is applied to the high current transformer.The high current transformer elaborated in the paper is mainly applied to the measurement of AC/DC high current.The principle of the transformer is the Hall direct measurement principle.The transformer has the following three characteristics:firstly, the effect of the remnant field of the iron core on the measurement is decreased;secondly,because the temperature compensation is adopted,the transformer has good temperature charactreristic;thirdly,be cause the wavelet transfomation technology is adopted,the transformer has the capacity of good antijanming.展开更多
In line commutated converter based high-voltage direct current(LCC-HVDC)transmission systems,the transformer saturation can induce harmonic instability,which poses a serious threat to the safe operation of the power s...In line commutated converter based high-voltage direct current(LCC-HVDC)transmission systems,the transformer saturation can induce harmonic instability,which poses a serious threat to the safe operation of the power system.However,the nonlinear characteristics of the power grids introduced by the transformer saturation considerably limit the application of the conventional analysis methods.To address the issue,this paper derives a linear model for the transformer saturation caused by the DC current due to the converter modulation.Afterwards,the nonlinear characteristics of power grids with the transformer saturation is described by a complex valued impedance matrix.Based on the derived impedance matrix,the system harmonic stability is analyzed and the mechanism of the transformer saturation induced harmonic instability is revealed.Finally,the sensitivity analysis is conducted to find the key factors that influence the system core saturation instability.The proposed impedance model is verified by the electromagnetic transient simulation,and the simulation results corroborate the effectiveness of the proposed impedance model.Index TermsLine commutated converter based high voltage direct current(LCC-HVDC),transformer saturation,harmonic instability,impedance model.展开更多
This paper proposes a single-ended fault detection scheme for long transmission lines using support vector machine(SVM)for multi-terminal direct current systems based on modular multilevel converter(MMC-MTDC).The sche...This paper proposes a single-ended fault detection scheme for long transmission lines using support vector machine(SVM)for multi-terminal direct current systems based on modular multilevel converter(MMC-MTDC).The scheme overcomes existing detection difficulties in the protection of long transmission lines resulting from high grounding resistance and attenuation,and also avoids the sophisticated process of threshold value selection.The high-frequency components in the measured voltage extracted by a wavelet transform and the amplitude of the zero-mode set of the positive-sequence voltage are the inputs to a trained SVM.The output of the SVM determines the fault type.A model of a four-terminal DC power grid with overhead transmission lines is built in PSCAD/EMTDC.Simulation results of EMTDC confirm that the proposed scheme achieves 100%accuracy in detecting short-circuit faults with high resistance on long transmission lines.The proposed scheme eliminates mal-operation of DC circuit breakers when faced with power order changes or AC-side faults.Its robustness and time delay are also assessed and shown to have no perceptible effect on the speed and accuracy of the detection scheme,thus ensuring its reliability and stability.展开更多
为加快电力系统数字化转型,保证高压直流输电(high voltage direct current,HVDC)系统高质量安全运行,有必要通过智能技术充分挖掘、提炼HVDC系统日常调控、运维等阶段积累的海量数据和丰富管理经验,从而构建知识图谱辅助工作人员对故...为加快电力系统数字化转型,保证高压直流输电(high voltage direct current,HVDC)系统高质量安全运行,有必要通过智能技术充分挖掘、提炼HVDC系统日常调控、运维等阶段积累的海量数据和丰富管理经验,从而构建知识图谱辅助工作人员对故障进行诊断和处理。提出了一种基于小波变换和深度学习的HVDC系统故障诊断方法。首先,采用小波变换将换流站的故障录波数据(单相接地、相间短路和阀组短路)转换为二维时频图像,并采用数据增强技术来进一步扩充样本数据集。然后,利用ResNet50网络来实现HVDC系统的故障诊断。根据实验结果,所提方法在训练集的分类精度为93%,在测试集的分类精度为82%,证明了该方法的有效性,为HVDC系统的故障诊断提供了一种新的可行性路线。为了进一步验证所提方法,将其与GoogleNet、VGG16、AlexNet、SVM、决策树和KNN等方法进行对比,对比实验结果表明,所提方法在HVDC系统故障诊断中的表现更加出色。展开更多
模块化多电平直流变压器(modular multilevel direct current transformer,MMDCT)为实现电动汽车充放电集群高效稳定并入城市直流配电网提供了一种可行的解决方案,但其启动过程中存在电容充电和变压器励磁涌流造成的冲击电流。为此,提...模块化多电平直流变压器(modular multilevel direct current transformer,MMDCT)为实现电动汽车充放电集群高效稳定并入城市直流配电网提供了一种可行的解决方案,但其启动过程中存在电容充电和变压器励磁涌流造成的冲击电流。为此,提出了一种基于复合频率控制的快速预充电策略,利用直流量和中频量分别独立MMDCT的原边和副边充电。原边充电采用双闭环控制,副边充电采用变步长移相的峰值电流控制,解决了充电速度和冲击电流之间的矛盾。进一步对多种预充电策略的冲击电流进行了量化对比分析。通过仿真验证了所提出预充电策略的有效性和可行性,结果表明,所提出的方法有效控制了冲击电流大小和充电时间。展开更多
具有模块化多电平结构的串联开关直流变压器(direct current transformer, DCT)在使用传统单移相控制时,存在中压侧全桥换流时阀串支路产生电流尖峰的问题,器件承受额外的电流应力。基于该新型DCT的工作原理与电流波形,提出一种基于中...具有模块化多电平结构的串联开关直流变压器(direct current transformer, DCT)在使用传统单移相控制时,存在中压侧全桥换流时阀串支路产生电流尖峰的问题,器件承受额外的电流应力。基于该新型DCT的工作原理与电流波形,提出一种基于中压侧全桥换流移相的阀串支路电流优化调制方法。文中对阀串支路的电流应力进行详细分析,结合电路可靠工作移相角范围,确定中压侧全桥换流移相角最优值的计算方法,从而确立优化控制策略。该优化控制策略独立于原有的功率控制环路运行,不改变DCT功率传输状态,不影响功率的调节控制,易于投入实际应用。仿真与样机实验的结果验证了该优化控制策略降低电流应力的有效性,同时样机实验结果显示效率得到提升。综合原理分析与效果验证可知,该优化控制策略对设备的安全运行与器件选型具有借鉴意义。展开更多
基金ThispaperissupportedbyNationalNatureScienceFoundationofChina (No 60 1760 2 0 )
文摘The wavelet transformation is applied to the high current transformer.The high current transformer elaborated in the paper is mainly applied to the measurement of AC/DC high current.The principle of the transformer is the Hall direct measurement principle.The transformer has the following three characteristics:firstly, the effect of the remnant field of the iron core on the measurement is decreased;secondly,because the temperature compensation is adopted,the transformer has good temperature charactreristic;thirdly,be cause the wavelet transfomation technology is adopted,the transformer has the capacity of good antijanming.
文摘In line commutated converter based high-voltage direct current(LCC-HVDC)transmission systems,the transformer saturation can induce harmonic instability,which poses a serious threat to the safe operation of the power system.However,the nonlinear characteristics of the power grids introduced by the transformer saturation considerably limit the application of the conventional analysis methods.To address the issue,this paper derives a linear model for the transformer saturation caused by the DC current due to the converter modulation.Afterwards,the nonlinear characteristics of power grids with the transformer saturation is described by a complex valued impedance matrix.Based on the derived impedance matrix,the system harmonic stability is analyzed and the mechanism of the transformer saturation induced harmonic instability is revealed.Finally,the sensitivity analysis is conducted to find the key factors that influence the system core saturation instability.The proposed impedance model is verified by the electromagnetic transient simulation,and the simulation results corroborate the effectiveness of the proposed impedance model.Index TermsLine commutated converter based high voltage direct current(LCC-HVDC),transformer saturation,harmonic instability,impedance model.
文摘This paper proposes a single-ended fault detection scheme for long transmission lines using support vector machine(SVM)for multi-terminal direct current systems based on modular multilevel converter(MMC-MTDC).The scheme overcomes existing detection difficulties in the protection of long transmission lines resulting from high grounding resistance and attenuation,and also avoids the sophisticated process of threshold value selection.The high-frequency components in the measured voltage extracted by a wavelet transform and the amplitude of the zero-mode set of the positive-sequence voltage are the inputs to a trained SVM.The output of the SVM determines the fault type.A model of a four-terminal DC power grid with overhead transmission lines is built in PSCAD/EMTDC.Simulation results of EMTDC confirm that the proposed scheme achieves 100%accuracy in detecting short-circuit faults with high resistance on long transmission lines.The proposed scheme eliminates mal-operation of DC circuit breakers when faced with power order changes or AC-side faults.Its robustness and time delay are also assessed and shown to have no perceptible effect on the speed and accuracy of the detection scheme,thus ensuring its reliability and stability.
文摘为加快电力系统数字化转型,保证高压直流输电(high voltage direct current,HVDC)系统高质量安全运行,有必要通过智能技术充分挖掘、提炼HVDC系统日常调控、运维等阶段积累的海量数据和丰富管理经验,从而构建知识图谱辅助工作人员对故障进行诊断和处理。提出了一种基于小波变换和深度学习的HVDC系统故障诊断方法。首先,采用小波变换将换流站的故障录波数据(单相接地、相间短路和阀组短路)转换为二维时频图像,并采用数据增强技术来进一步扩充样本数据集。然后,利用ResNet50网络来实现HVDC系统的故障诊断。根据实验结果,所提方法在训练集的分类精度为93%,在测试集的分类精度为82%,证明了该方法的有效性,为HVDC系统的故障诊断提供了一种新的可行性路线。为了进一步验证所提方法,将其与GoogleNet、VGG16、AlexNet、SVM、决策树和KNN等方法进行对比,对比实验结果表明,所提方法在HVDC系统故障诊断中的表现更加出色。
文摘模块化多电平直流变压器(modular multilevel direct current transformer,MMDCT)为实现电动汽车充放电集群高效稳定并入城市直流配电网提供了一种可行的解决方案,但其启动过程中存在电容充电和变压器励磁涌流造成的冲击电流。为此,提出了一种基于复合频率控制的快速预充电策略,利用直流量和中频量分别独立MMDCT的原边和副边充电。原边充电采用双闭环控制,副边充电采用变步长移相的峰值电流控制,解决了充电速度和冲击电流之间的矛盾。进一步对多种预充电策略的冲击电流进行了量化对比分析。通过仿真验证了所提出预充电策略的有效性和可行性,结果表明,所提出的方法有效控制了冲击电流大小和充电时间。
文摘具有模块化多电平结构的串联开关直流变压器(direct current transformer, DCT)在使用传统单移相控制时,存在中压侧全桥换流时阀串支路产生电流尖峰的问题,器件承受额外的电流应力。基于该新型DCT的工作原理与电流波形,提出一种基于中压侧全桥换流移相的阀串支路电流优化调制方法。文中对阀串支路的电流应力进行详细分析,结合电路可靠工作移相角范围,确定中压侧全桥换流移相角最优值的计算方法,从而确立优化控制策略。该优化控制策略独立于原有的功率控制环路运行,不改变DCT功率传输状态,不影响功率的调节控制,易于投入实际应用。仿真与样机实验的结果验证了该优化控制策略降低电流应力的有效性,同时样机实验结果显示效率得到提升。综合原理分析与效果验证可知,该优化控制策略对设备的安全运行与器件选型具有借鉴意义。
