Microgrids are being developed as a building block for future smart grid system.Key issues for the control and operation of microgrid include integration technologies and energy management schemes.This paper presents ...Microgrids are being developed as a building block for future smart grid system.Key issues for the control and operation of microgrid include integration technologies and energy management schemes.This paper presents an overview of grid integration and energy management strategies of microgrids.It covers a review of power electronics interface topologies for different types of distributed generation(DG)units in a microgrid,a discussion of energy management strategies,as well as the DG interfacing converter control schemes.Considering the intermittent nature of many renewable energy based DG units,the ancillary services of DGs using the available interfacing converter rating are also discussed in the paper.展开更多
In the present scenario,modular multilevel converters(MMCs)are considered to be one of the most promising and effective topologies in the family of high-power converters because of their modular design and good scalab...In the present scenario,modular multilevel converters(MMCs)are considered to be one of the most promising and effective topologies in the family of high-power converters because of their modular design and good scalability;MMCs are extensively used in high-voltage and high-power applications.Based on their unique advantages,MMCs have attracted increasing attention from academic circles over the past years.Several studies have focused on different aspects of MMCs,including submodule topologies,modeling schemes,modulation strategies,control schemes for voltage balancing and circulating currents,fault diagnoses,and fault-tolerant control strategies.To summarize the current research status of MMCs,all the aforementioned research issues with representative research approaches,results and characteristics are systematically overviewed.In the final section,the current research status of MMCs and their future trends are emphasized.展开更多
Modular multilevel converters(MMCs)have been one of the most broadly used multilevel converter topologies in industrial applications,particularly in medium-voltage motor drives and high-voltage dc power conversion sys...Modular multilevel converters(MMCs)have been one of the most broadly used multilevel converter topologies in industrial applications,particularly in medium-voltage motor drives and high-voltage dc power conversion systems.However,due to the utilization of large amount of semiconductor devices,the reliability of MMCs becomes one of the severe challenges constraining their further development and applications.In this paper,common electrical faults of the MMC have been summarized and analyzed,including open-circuit switching faults,short-circuit switching faults,dc-bus short-circuit faults,and single line-to-ground faults on the ac side.A thorough and comprehensive review of the existing online fault diagnostic methods has been conducted.In addition,fault-tolerant operation strategies for such various fault scenarios in MMCs have been presented.All the fault diagnosis and fault-tolerant operation strategies are comparatively evaluated,which aims to provide a state-of-the-art reference on the MMC reliability for future research and industrial applications.展开更多
An online partial discharge(PD) measurement performed on a high voltage direct current(HVDC) wall bushing successfully identified the presence of internal discharges.The wall bushing is a sulfur hexafluoride gas-insul...An online partial discharge(PD) measurement performed on a high voltage direct current(HVDC) wall bushing successfully identified the presence of internal discharges.The wall bushing is a sulfur hexafluoride gas-insulated bushing,rated for 500 kV dc and terminated on a thyristor-controlled HVDC converter bridge.The measurement of PD within the HVDC station environment is particularly challenging due to the high levels of electromagnetic noise caused by thyristor switching events and external air-corona from the neighboring high-voltage equipment.An additional challenge is the""mixed"voltage stress on the bushing insulation,which has both ac and dc high-voltage components.There are also fast transients during the firing of thyristors in the HVDC conversion process that cause added stress to the insulation.As a result,the analysis and interpretation of PD data for HVDC equipment is more complex;PD pulses may occur in response to the ac,dc,or switching transient voltage stresses.In this paper,an online PD measurement strategy for noise filtering and isolation of PD sources within the bushing are discussed.The PD measurement data is plotted on a phase-resolved diagram where the line supply power cord voltage was used as a reference. The phase-resolved diagram appears to suggest that the fast transients,caused during switching,trigger some PD events.Measurements were also performed with the aid of a modern PD measurement instrument having noise separation capabilities.The findings from the online PD measurements are verified with physical evidence,found after the bushing was removed from service,suggested internal PD had occurred inside the bushing.展开更多
The modular multilevel converter(MMC)is now the most attractive topology for medium and high voltage power conversion applications with several advantages over the traditional voltage source converter(VSC).However,due...The modular multilevel converter(MMC)is now the most attractive topology for medium and high voltage power conversion applications with several advantages over the traditional voltage source converter(VSC).However,due to a large number of sub-modules(SMs)in the MMC,system reliability is a big challenge in its practical application,where each SM may be considered as a potential point of failure.In this paper,a reliability evaluation based on the Markov model is proposed for the MMC.The failure rates of the power electronic devices and SMs are firstly analyzed.Then,the Markov model and the state transition equation of the system are built in detail.A general reliability evaluation function is established,in which the mean time to failure and reliability evaluation of the MMC with redundant SMs are also discussed.Finally,a practical direct current(DC)distribution example for reliability evaluation is analyzed,and the results verify that the reliability evaluation based on the Markov model could provide a useful reference for project design.展开更多
文摘Microgrids are being developed as a building block for future smart grid system.Key issues for the control and operation of microgrid include integration technologies and energy management schemes.This paper presents an overview of grid integration and energy management strategies of microgrids.It covers a review of power electronics interface topologies for different types of distributed generation(DG)units in a microgrid,a discussion of energy management strategies,as well as the DG interfacing converter control schemes.Considering the intermittent nature of many renewable energy based DG units,the ancillary services of DGs using the available interfacing converter rating are also discussed in the paper.
基金Supported by the Science and Technology Program of State Grid Corporation of China(5100-201999330A-0-0-00)。
文摘In the present scenario,modular multilevel converters(MMCs)are considered to be one of the most promising and effective topologies in the family of high-power converters because of their modular design and good scalability;MMCs are extensively used in high-voltage and high-power applications.Based on their unique advantages,MMCs have attracted increasing attention from academic circles over the past years.Several studies have focused on different aspects of MMCs,including submodule topologies,modeling schemes,modulation strategies,control schemes for voltage balancing and circulating currents,fault diagnoses,and fault-tolerant control strategies.To summarize the current research status of MMCs,all the aforementioned research issues with representative research approaches,results and characteristics are systematically overviewed.In the final section,the current research status of MMCs and their future trends are emphasized.
文摘Modular multilevel converters(MMCs)have been one of the most broadly used multilevel converter topologies in industrial applications,particularly in medium-voltage motor drives and high-voltage dc power conversion systems.However,due to the utilization of large amount of semiconductor devices,the reliability of MMCs becomes one of the severe challenges constraining their further development and applications.In this paper,common electrical faults of the MMC have been summarized and analyzed,including open-circuit switching faults,short-circuit switching faults,dc-bus short-circuit faults,and single line-to-ground faults on the ac side.A thorough and comprehensive review of the existing online fault diagnostic methods has been conducted.In addition,fault-tolerant operation strategies for such various fault scenarios in MMCs have been presented.All the fault diagnosis and fault-tolerant operation strategies are comparatively evaluated,which aims to provide a state-of-the-art reference on the MMC reliability for future research and industrial applications.
基金Manitoba Hydro for funding and supporting this research
文摘An online partial discharge(PD) measurement performed on a high voltage direct current(HVDC) wall bushing successfully identified the presence of internal discharges.The wall bushing is a sulfur hexafluoride gas-insulated bushing,rated for 500 kV dc and terminated on a thyristor-controlled HVDC converter bridge.The measurement of PD within the HVDC station environment is particularly challenging due to the high levels of electromagnetic noise caused by thyristor switching events and external air-corona from the neighboring high-voltage equipment.An additional challenge is the""mixed"voltage stress on the bushing insulation,which has both ac and dc high-voltage components.There are also fast transients during the firing of thyristors in the HVDC conversion process that cause added stress to the insulation.As a result,the analysis and interpretation of PD data for HVDC equipment is more complex;PD pulses may occur in response to the ac,dc,or switching transient voltage stresses.In this paper,an online PD measurement strategy for noise filtering and isolation of PD sources within the bushing are discussed.The PD measurement data is plotted on a phase-resolved diagram where the line supply power cord voltage was used as a reference. The phase-resolved diagram appears to suggest that the fast transients,caused during switching,trigger some PD events.Measurements were also performed with the aid of a modern PD measurement instrument having noise separation capabilities.The findings from the online PD measurements are verified with physical evidence,found after the bushing was removed from service,suggested internal PD had occurred inside the bushing.
基金supported by the National Natural Science Foundation of China(No.51607084)the National Key Research and Development Program of China(No.2017YFB0903504)+2 种基金Jiangsu Electric Power Company Project(No.J2018076)State Grid Technology Project(No.5210EF17002B)the State Key Laboratory of Smart Grid Protection and Control.
文摘The modular multilevel converter(MMC)is now the most attractive topology for medium and high voltage power conversion applications with several advantages over the traditional voltage source converter(VSC).However,due to a large number of sub-modules(SMs)in the MMC,system reliability is a big challenge in its practical application,where each SM may be considered as a potential point of failure.In this paper,a reliability evaluation based on the Markov model is proposed for the MMC.The failure rates of the power electronic devices and SMs are firstly analyzed.Then,the Markov model and the state transition equation of the system are built in detail.A general reliability evaluation function is established,in which the mean time to failure and reliability evaluation of the MMC with redundant SMs are also discussed.Finally,a practical direct current(DC)distribution example for reliability evaluation is analyzed,and the results verify that the reliability evaluation based on the Markov model could provide a useful reference for project design.
