Energy storage systems with multilevel converters play an important role in modern electric power systems with large-scale renewable energy integration.This paper proposes a reverse-blocking modular multilevel convert...Energy storage systems with multilevel converters play an important role in modern electric power systems with large-scale renewable energy integration.This paper proposes a reverse-blocking modular multilevel converter for a battery energy storage system(RB-MMCBESS). Besides integrating distributed low-voltage batteries to medium or high voltage grids, with the inherited advantages of traditional MMCs, the RB-MMC-BESS also provides improved DC fault handling capability. This paper analyzes such a new converter configuration and its operating principles. Control algorithms are developed for AC side power control and the balancing of battery state of charge. The blocking mechanism to manage a DC pole-topole fault analyzed in depth. Comprehensive simulation results validate both the feasibility of the RB-MMC-BESS topology and the effectiveness of the control and fault handling strategies.展开更多
In view of the DC fault current isolation deficiency for the conventional half-bridge sub-module(HBSM)based modular multilevel converter(MMC),this paper presents an improved MMC topology.Both quasi reverse blocking su...In view of the DC fault current isolation deficiency for the conventional half-bridge sub-module(HBSM)based modular multilevel converter(MMC),this paper presents an improved MMC topology.Both quasi reverse blocking submodules(QRBSMs)and current limit modules(CLMs)are employed to improve the DC fault handling capability for HVDC applications.This paper analyzes such a new converter configuration and operation principles.Then the DC pole-to-pole short circuit fault is taken into consideration for further study,as well as the fault current blocking mechanism and quantitative relationship between system electrical stress and key parameters.To validate the feasibility of the proposed topology and fault protection theory,extensive simulation results are demonstrated.It is concluded that the QRB-MMC can effectively block the fault current under DC fault condition.In addition,CLMs play an important role in further accelerating fault current attenuation.Moreover,QRB-MMC employs the original control and modulation strategies under normal operation conditions;thus,it further reduces the complexity of industry design.展开更多
The common-mode current is an important indicator with transformerless photovoltaic inverters.However,up to now,there is not an accurate method to predict common-mode current in the inverter design process,resulting f...The common-mode current is an important indicator with transformerless photovoltaic inverters.However,up to now,there is not an accurate method to predict common-mode current in the inverter design process,resulting from inappropriate device selection or exceeded the expected common-mode current.In order to solve this problem,this paper proposes an accurate common-mode current prediction method based on graph theory for transformerless photovoltaic inverters.In this paper,the mathematic model of the common-mode current is derived using graph theory analysis method in the full-bridge topology,and it is used to predict common-mode current.The validity and correctness of the proposed prediction method are validated by simulation and experiment.The oscillation frequency and amplitude can be predicted by the proposed common-mode prediction method,whereas the traditional common-mode analysis method cannot.This paper provides a novel way to predict and analyze common-mode current in the transformerless photovoltaic inverters.展开更多
基金supported by the State Key Laboratory of Large Electric Drive System and Equipment Technology(No.SKLLDJ042016005)the National Key Research and Development Program of China(No.2016YFE0131700)the National Natural Science Foundation of China(No.51577010)
文摘Energy storage systems with multilevel converters play an important role in modern electric power systems with large-scale renewable energy integration.This paper proposes a reverse-blocking modular multilevel converter for a battery energy storage system(RB-MMCBESS). Besides integrating distributed low-voltage batteries to medium or high voltage grids, with the inherited advantages of traditional MMCs, the RB-MMC-BESS also provides improved DC fault handling capability. This paper analyzes such a new converter configuration and its operating principles. Control algorithms are developed for AC side power control and the balancing of battery state of charge. The blocking mechanism to manage a DC pole-topole fault analyzed in depth. Comprehensive simulation results validate both the feasibility of the RB-MMC-BESS topology and the effectiveness of the control and fault handling strategies.
基金supported in part by the State Key Laboratory of Large Electric Drive System and Equipment Technology(No.SKLLDJ042016005)in part by Open Fund of State Key Laboratory of Operation and Control of Renewable Energy&Storage Systemsin part by the National Key Research and Development Program of China(2016YFE0131700).
文摘In view of the DC fault current isolation deficiency for the conventional half-bridge sub-module(HBSM)based modular multilevel converter(MMC),this paper presents an improved MMC topology.Both quasi reverse blocking submodules(QRBSMs)and current limit modules(CLMs)are employed to improve the DC fault handling capability for HVDC applications.This paper analyzes such a new converter configuration and operation principles.Then the DC pole-to-pole short circuit fault is taken into consideration for further study,as well as the fault current blocking mechanism and quantitative relationship between system electrical stress and key parameters.To validate the feasibility of the proposed topology and fault protection theory,extensive simulation results are demonstrated.It is concluded that the QRB-MMC can effectively block the fault current under DC fault condition.In addition,CLMs play an important role in further accelerating fault current attenuation.Moreover,QRB-MMC employs the original control and modulation strategies under normal operation conditions;thus,it further reduces the complexity of industry design.
基金This work was supported by the National Natural Science Foundation of China under Grant 51577010the Fundamental Research Funds for the Central Universities under Grant 2017JBM054the Natural Science Foundation of Guangdong Province under Grant 1714060000016.
文摘The common-mode current is an important indicator with transformerless photovoltaic inverters.However,up to now,there is not an accurate method to predict common-mode current in the inverter design process,resulting from inappropriate device selection or exceeded the expected common-mode current.In order to solve this problem,this paper proposes an accurate common-mode current prediction method based on graph theory for transformerless photovoltaic inverters.In this paper,the mathematic model of the common-mode current is derived using graph theory analysis method in the full-bridge topology,and it is used to predict common-mode current.The validity and correctness of the proposed prediction method are validated by simulation and experiment.The oscillation frequency and amplitude can be predicted by the proposed common-mode prediction method,whereas the traditional common-mode analysis method cannot.This paper provides a novel way to predict and analyze common-mode current in the transformerless photovoltaic inverters.
