Coordination Control of Power Flow Controller and Hybrid DC Circuit Breaker in MVDC Distribution Networks

The two main challenges of medium voltage direct current(MVDC)distribution network are the flexible control of power flow(PF)and fault protection.In this paper,the power flow controller(PFC)is introduced to regulate the PF and inhibit the fault current during the DC fault.The coordination strategy of series-parallel PFC(SP-PFC)and hybrid DC circuit breaker(DCCB)is proposed.By regulating the polarity and magnitude of SP-PFC output voltage during the fault,the rising speed of fault current can be suppressed so as to reduce the breaking current of hybrid DCCB.The access mode of SP-PFC to the MVDC distribution network and its topology are analyzed,and the coordination strategy between SP-PFC and hybrid DCCB is investigated.Moreover,the emergency control and bypass control strategies of SP-PFC are developed.On this basis,the mathematical model of SP-PFC in different fault stages is derived.With the equivalent model of SP-PFC,the fault current of the MVDC distribution network can be calculated accurately.A simulation model of the MVDC distribution network containing SP-PFC is established in MATLAB/Simulink.The fault current calculation result is compared with the simulation result,and the effectiveness of the proposed coordination strategy is verified.

Python Supervised Co-simulation for a Day-long Harmonic Evaluation of EV Charging

To accurately simulate electric vehicle DC fast chargers'(DCFCs')harmonic emission,a small time step,i.e.,typically smaller than 10μs,is required owing to switching dynamics.However,in practice,harmonics should be continuously assessed with a long duration,e.g.,a day.A trade-off between accuracy and time efficiency thus exists.To address this issue,a multi-time scale modeling framework of fast-charging stations(FCSs)is proposed.In the presented framework,the DCFCs'input impedance and harmonic current emission in the ideal grid condition,that is,zero grid impedance and no background harmonic voltage,are obtained based on a converter switching model with a small timescale simulation.Since a DCFC's input impedance and harmonic current source are functions of the DCFC's load,the input impedance and harmonic emission at different loads are obtained.Thereafter,they are used in the fast-charging charging station modeling,where the DCFCs are simplified as Norton equivalent circuits.In the station level simulation,a large time step,i.e.,one minute,is used because the DCFCs'operating power can be assumed as a constant over a minute.With this co-simulation,the FCSs'long-term power quality performance can be assessed time-efficiently,without losing much accuracy.