To ensure their sound and continuous operation to the greatest extent,VSC-based DC girds have extremely stringent requirements for transmission line relay protection.In terms of guaranteeing their reliability,accurate...To ensure their sound and continuous operation to the greatest extent,VSC-based DC girds have extremely stringent requirements for transmission line relay protection.In terms of guaranteeing their reliability,accurate identification of lightning strikes on DC transmission lines is one of the urgent key problems to be solved.An effective ultra-high-speed identification scheme of lightning strikes suitable for the VSC-based DC grid is proposed in this paper.First,an 1-mode reverse voltage traveling wave(RVTW)is constructed applying the pole-mode transformation theory.Next,fault traveling wave propagation characteristics along the DC transmission line are analyzed in depth utilizing Peterson's law.Then,differences of time-frequency electromagnetic transient characteristics of 1-mode RVTWs between disturbances and faults caused by lightning strikes are distinguished in detail by means of the classical wavelet transformation multi-resolution analysis theory.Finally,extensive simulations are carried out to evaluate the performance of the proposed identification scheme,and by which its excellent rapidity,reliability and robustness are validated.Index Terms-Lightning-strike identification,Multi-resolution analysis,Relay protection,Traveling-wave protection,VsC-based DC grid,Wavelet transformation.展开更多
Multi-terminal voltage sourced converter(VSC)-based high voltage direct current (HVDC) system composes of a number of VSCs connected to an HVDC grid (or dc grid).The dc grid is often configured by cable interconnectio...Multi-terminal voltage sourced converter(VSC)-based high voltage direct current (HVDC) system composes of a number of VSCs connected to an HVDC grid (or dc grid).The dc grid is often configured by cable interconnections between converter stations,thus imposing resonance issues affecting harmonic interaction in the system.Based on the harmonic transfer characteristics of VSC and HVDC systems,the appearance and the interaction of inter-harmonics in the multi-terminal VSC-based HVDC system are analyzed.Simulation models are built and implemented using SimPowerSystems in MATLAB.The simulation results show that,a series of inter-harmonics are produced and tend to be dominant in low-frequency range.Especially in the dc grid,the inter-harmonic transfer can be magnified due to inter-harmonic resonances.The complex resonance issues in the dc grid are investigated in combination with interaction through the VSC,it is beneficial to harmonic filter designs as well as other harmonic mitigation methods.展开更多
Large-scale renewable energy transmission via thevoltage source converter (VSC) based high-voltage direct current(HVDC) is a crucial development direction for constructing anew-typed power system in China. However, re...Large-scale renewable energy transmission via thevoltage source converter (VSC) based high-voltage direct current(HVDC) is a crucial development direction for constructing anew-typed power system in China. However, renewable energy ischaracterized by volatility, intermittency, and randomness. Whenthe sending-end modular multilevel converter (MMC) cannotadapt to the rapid fluctuations in renewable energy output, itsenergy balance will be disrupted by the active power differencebetween the AC and DC sides, causing issues such as widebandoscillations and exacerbated circulating currents. To solve theproblem mentioned above, a novel energy balance-based controlmethod for MMCs connected to wind farms is proposed in thispaper, enabling the MMC to effectively adapt to fluctuationsin renewable energy output and naturally maintain circulatingcurrent at a relatively low level. Firstly, the evolution principleillustrating topology decomposition and reconfiguration of theMMC is revealed. Secondly, the control method for AC internalvoltage is proposed, which combines the energy balance betweenthe half MMCs and voltage amplitude support. Thirdly, the DCinternal voltage is defined, and its control method is proposedbased on the MMC’s overall energy balance. Then, independentcontrol of each bridge arm is achieved by integrating the energybalance of the bridge arms with both the AC and DC internalvoltages. Finally, an electromagnetic transient simulation modelis built with PSCAD/EMTDC, and the efficacy and practicalityof the proposed method are demonstrated through extensivesimulation experiments.展开更多
基金supported by the National Natural Science Foundation of China(No.52277075)the State Key Laboratory of Advanced Power Transmission Technology(Grant No.GEIRI-SKL-2020-012).
文摘To ensure their sound and continuous operation to the greatest extent,VSC-based DC girds have extremely stringent requirements for transmission line relay protection.In terms of guaranteeing their reliability,accurate identification of lightning strikes on DC transmission lines is one of the urgent key problems to be solved.An effective ultra-high-speed identification scheme of lightning strikes suitable for the VSC-based DC grid is proposed in this paper.First,an 1-mode reverse voltage traveling wave(RVTW)is constructed applying the pole-mode transformation theory.Next,fault traveling wave propagation characteristics along the DC transmission line are analyzed in depth utilizing Peterson's law.Then,differences of time-frequency electromagnetic transient characteristics of 1-mode RVTWs between disturbances and faults caused by lightning strikes are distinguished in detail by means of the classical wavelet transformation multi-resolution analysis theory.Finally,extensive simulations are carried out to evaluate the performance of the proposed identification scheme,and by which its excellent rapidity,reliability and robustness are validated.Index Terms-Lightning-strike identification,Multi-resolution analysis,Relay protection,Traveling-wave protection,VsC-based DC grid,Wavelet transformation.
基金supported by"111"Project of China(No.B08013)National Natural Science Foundation of China(No.51177044)
文摘Multi-terminal voltage sourced converter(VSC)-based high voltage direct current (HVDC) system composes of a number of VSCs connected to an HVDC grid (or dc grid).The dc grid is often configured by cable interconnections between converter stations,thus imposing resonance issues affecting harmonic interaction in the system.Based on the harmonic transfer characteristics of VSC and HVDC systems,the appearance and the interaction of inter-harmonics in the multi-terminal VSC-based HVDC system are analyzed.Simulation models are built and implemented using SimPowerSystems in MATLAB.The simulation results show that,a series of inter-harmonics are produced and tend to be dominant in low-frequency range.Especially in the dc grid,the inter-harmonic transfer can be magnified due to inter-harmonic resonances.The complex resonance issues in the dc grid are investigated in combination with interaction through the VSC,it is beneficial to harmonic filter designs as well as other harmonic mitigation methods.
基金supported by the National NaturalScience Foundation of China (No. 52277075), and Postgraduate ScientificResearch Innovation Project of Changsha University of Science & Technology(No. CSLGCX23062).
文摘Large-scale renewable energy transmission via thevoltage source converter (VSC) based high-voltage direct current(HVDC) is a crucial development direction for constructing anew-typed power system in China. However, renewable energy ischaracterized by volatility, intermittency, and randomness. Whenthe sending-end modular multilevel converter (MMC) cannotadapt to the rapid fluctuations in renewable energy output, itsenergy balance will be disrupted by the active power differencebetween the AC and DC sides, causing issues such as widebandoscillations and exacerbated circulating currents. To solve theproblem mentioned above, a novel energy balance-based controlmethod for MMCs connected to wind farms is proposed in thispaper, enabling the MMC to effectively adapt to fluctuationsin renewable energy output and naturally maintain circulatingcurrent at a relatively low level. Firstly, the evolution principleillustrating topology decomposition and reconfiguration of theMMC is revealed. Secondly, the control method for AC internalvoltage is proposed, which combines the energy balance betweenthe half MMCs and voltage amplitude support. Thirdly, the DCinternal voltage is defined, and its control method is proposedbased on the MMC’s overall energy balance. Then, independentcontrol of each bridge arm is achieved by integrating the energybalance of the bridge arms with both the AC and DC internalvoltages. Finally, an electromagnetic transient simulation modelis built with PSCAD/EMTDC, and the efficacy and practicalityof the proposed method are demonstrated through extensivesimulation experiments.
