A protection system using a multi-agent concept for power distribution networks is proposed.Every digital over current relay(OCR)is developed as an agent by adding its own intelligence,self-tuning and communication ab...A protection system using a multi-agent concept for power distribution networks is proposed.Every digital over current relay(OCR)is developed as an agent by adding its own intelligence,self-tuning and communication ability.The main advantage of the multi-agent concept is that a group of agents work together to achieve a global goal which is beyond the ability of each individual agent.In order to cope with frequent changes in the network operation condition and faults,an OCR agent,proposed in this paper,is able to detect a fault or a change in the network and find its optimal parameters for protection in an autonomous manner considering information of the whole network obtained by communication between other agents.Through this kind of coordination and information exchanges,not only a local but also a global protective scheme is completed.Simulations in a simple distribution network show the effectiveness of the proposed protection system.展开更多
The interaction between grid-connected inverters and the grid may cause stability issues,and compromise the reliable operation of the inverters.This study investigates the stability of a three-level neutral point clam...The interaction between grid-connected inverters and the grid may cause stability issues,and compromise the reliable operation of the inverters.This study investigates the stability of a three-level neutral point clamped(NPC)inverter connected to the grid using impedance-based methods.Because the impedance model of a three-phase three-level NPC inverter has not yet been reported,this study fills the literature gap by analyzing the influence of three-level DC-side neutral point control on the impedance characteristics.By fully considering the DC bus dynamics and DC voltage control loop,and the current loop and phase-locked loop(PLL),the admittance model of a three-phase three-level NPC inverter is established and verified by simulation.Additionally,in the stability analysis of a threelevel NPC inverter grid-connected system,the frequency coupling introduced by the PLL and DC bus dynamics is included with the help of an established admittance model.The stability of the grid-connected system under different grid short circuit ratios(SCR)and operating power levels is analyzed according to the Nyquist stability criterion.The experimental results revealed that the established impedance model of the three-phase three-level NPC inverter can properly represent the stability of this system.展开更多
文摘A protection system using a multi-agent concept for power distribution networks is proposed.Every digital over current relay(OCR)is developed as an agent by adding its own intelligence,self-tuning and communication ability.The main advantage of the multi-agent concept is that a group of agents work together to achieve a global goal which is beyond the ability of each individual agent.In order to cope with frequent changes in the network operation condition and faults,an OCR agent,proposed in this paper,is able to detect a fault or a change in the network and find its optimal parameters for protection in an autonomous manner considering information of the whole network obtained by communication between other agents.Through this kind of coordination and information exchanges,not only a local but also a global protective scheme is completed.Simulations in a simple distribution network show the effectiveness of the proposed protection system.
基金This work was supported in part by the National Natural Science Key Foundation of China under Grant 51937001the Natural Science Foundation Key Project of Chongqing Province under Grant cstc2019jcyj-zdxmX0005National Grid Project under Grant 5200-201958248A-0-0-00.
文摘The interaction between grid-connected inverters and the grid may cause stability issues,and compromise the reliable operation of the inverters.This study investigates the stability of a three-level neutral point clamped(NPC)inverter connected to the grid using impedance-based methods.Because the impedance model of a three-phase three-level NPC inverter has not yet been reported,this study fills the literature gap by analyzing the influence of three-level DC-side neutral point control on the impedance characteristics.By fully considering the DC bus dynamics and DC voltage control loop,and the current loop and phase-locked loop(PLL),the admittance model of a three-phase three-level NPC inverter is established and verified by simulation.Additionally,in the stability analysis of a threelevel NPC inverter grid-connected system,the frequency coupling introduced by the PLL and DC bus dynamics is included with the help of an established admittance model.The stability of the grid-connected system under different grid short circuit ratios(SCR)and operating power levels is analyzed according to the Nyquist stability criterion.The experimental results revealed that the established impedance model of the three-phase three-level NPC inverter can properly represent the stability of this system.
