Simultaneously imposed challenges of highvoltage insulation,high dv/dt,highswitching frequency,fast protection,and thermal management associated with the adoption of 10 kV SiC MOSFET,often pose nearly insurmountable b...Simultaneously imposed challenges of highvoltage insulation,high dv/dt,highswitching frequency,fast protection,and thermal management associated with the adoption of 10 kV SiC MOSFET,often pose nearly insurmountable barriers to potential users,undoubtedly hindering their penetration in mediumvoltage(MV)power conversion.Key novel technologies such as enhanced gatedriver,auxiliary power supply network,PCB planar dcbus,and highdensity inductor are presented,enabling the SiCbased designs in modular MV converters,overcoming aforementioned challenges.However,purely substituting SiC design instead of Sibased ones in modular MV converters,would expectedly yield only limited gains.Therefore,to further elevate SiCbased designs,novel highbandwidth control strategies such as switchingcycle control(SCC)and integrated capacitorblocked transistor(ICBT),as well as highperformance/highbandwidth communication network are developed.All these technologies combined,overcome barriers posed by stateoftheart Si designs and unlock system level benefits such as very high power density,highefficiency,fast dynamic response,unrestricted line frequency operation,and improved power quality,all demonstrated throughout this paper.展开更多
China’s BeiDou Navigation Satellite System(BDS)construction has been completed and the system has been formally commissioned.Most of the Electric Power Systems(EPSs)for MEO satellites were developed by the Shanghai I...China’s BeiDou Navigation Satellite System(BDS)construction has been completed and the system has been formally commissioned.Most of the Electric Power Systems(EPSs)for MEO satellites were developed by the Shanghai Institute of Space Power-sources.The 42 V medium-voltage fully-regulated high-power EPS has been adopted for the first time in medium Earth orbit,with an output power reaching about 3 kW.Compared with the 42 V medium-voltage semi-regulated bus power system used in the Regional Navigation BDS-2 satellite,the EPS of the BDS-3 MEO satellites has increased power by about 80%,adopting many newly developed products such as high-efficient triple junction GaAs solar cells,high-energy-density lithium ion batteries and a high-efficient autonomous power control unit(PCU).Based on the studies on the medium-voltage fully-regulated and high-power EPS technical principles,and the adaptability and reliability of various working modes,the test verifications for the EPS were conducted both on the ground and in orbit.Compared with other global navigation satellite systems such as GPS,Galileo and GLONASS,the EPS of the BDS-3 MEO satellite has a long design life time which is equivalent to that of the GPS and Galileo,but with a larger power supply capability and power ratio,distinguishing its advancement in the field of satellite power technology.展开更多
Medium-voltage distribution systems(MVDSs)mainly consist of a feeder head,lines,distribution transformers,and the equivalent load or power supply interfaced with the distribution transformers.The information of such l...Medium-voltage distribution systems(MVDSs)mainly consist of a feeder head,lines,distribution transformers,and the equivalent load or power supply interfaced with the distribution transformers.The information of such load or power supply can be measured via the three-wattmeter method(THM)and the two-wattmeter method(TWM).The measurements can be used to perform the control of the power supply and simulate the characteristics of the load,so the models of the load and the power supply need to consider the measurement characteristics.Existing research works on three-phase power flow(PF)just consider the measurement characteristics of THM.Hence,the PF equation of the bus measured via TWM is firstly built.Based on conventional measurements,an accurate and general model of the grounded and ungrounded slack bus is proposed.Furthermore,the influence arising from the connection type and angle shift of distribution transformers on the admittance matrix is considered,and thus a general three-phase transformer model is summarized,which is applicable for all the transformers mentioned herein.Finally,Newton's method is adopted to solve the PF calculation,and the performance of the proposed PF model is demonstrated through designed tests.展开更多
Direct current(DC)power grids based on flexible high-voltage DC technology have become a common solution of facilitating the large-scale integration of distributed energy resources(DERs)and the construction of advance...Direct current(DC)power grids based on flexible high-voltage DC technology have become a common solution of facilitating the large-scale integration of distributed energy resources(DERs)and the construction of advanced urban power grids.In this study,a typical topology analysis is performed for an advanced urban medium-voltage DC(MVDC)distribution network with DERs,including wind,photovoltaic,and electrical energy storage elements.Then,a multi-time scale optimal power flow(OPF)strategy is proposed for the MVDC network in different operation modes,including utility grid-connected and off-grid operation modes.In the utility grid-connected operation mode,the day-ahead optimization objective minimizes both the DER power curtailment and the network power loss.In addition,in the off-grid operation mode,the day-ahead optimization objective prioritizes the satisfaction of loads,and the DER power curtailment and the network power loss are minimized.A dynamic weighting method is employed to transform the multi-objective optimization problem into a quadratically constrained quadratic programming(QCQP)problem,which is solvable via standard methods.During intraday scheduling,the optimization objective gives priority to ensure minimum deviation between the actual and predicted values of the state of charge of the battery,and then seeks to minimize the DER power curtailment and the network power loss.Model predictive control(MPC)is used to correct deviations according to the results of ultra short-term load forecasting.Furthermore,an improved particle swarm optimization(PSO)algorithm is applied for global intraday optimization,which effectively increases the convergence rate to obtain solutions.MATLAB simulation results indicate that the proposed optimization strategy is effective and efficient.展开更多
The dynamic characteristic evaluation is an important prerequisite for safe and reliable operation of the mediumvoltage DC integrated power system(MIPS),and the dynamic state estimation is an essential technical appro...The dynamic characteristic evaluation is an important prerequisite for safe and reliable operation of the mediumvoltage DC integrated power system(MIPS),and the dynamic state estimation is an essential technical approach to the evaluation.Unlike the electromechanical transient process in a traditional power system,periodic change in pulse load of the MIPS is an electromagnetic transient process.As the system state suddenly changes in the range of a smaller time constant,it is difficult to estimate the dynamic state due to periodic disturbance.This paper presents a dynamic mathematical model of the MIPS according to the network structure and control strategy,thereby overcoming the restrictions of algebraic variables on the estimation and developing a dynamic state estimation method based on the extended Kalman filter.Using the method of adding fictitious process noise,it is possible to solve the problem that the linearized algorithm of the MIPS model is less reliable when an abrupt change occurs in the pulse load.Therefore,the accuracy of the dynamic state estimation and the stability of the filter can be improved under the periodic disturbance of pulse load.The simulation and experimental results confirm that the proposed model and method are feasible and effective.展开更多
On-shore wind parks are typically connected to the high-voltage(HV)transmission system through a bulk transformer.However,wind generators may be connected directly at a medium-voltage(MV)level,such as a utility-owned ...On-shore wind parks are typically connected to the high-voltage(HV)transmission system through a bulk transformer.However,wind generators may be connected directly at a medium-voltage(MV)level,such as a utility-owned primary distribution network,if the network is capable of sustaining the power flow and ensuring adequate power quality for its users.This paper presents the findings of a comprehensive study on the management of resonance in a utility-owned wind park in Costa Rica.The wind park is connected directly to the MV primary distribution network and has no shunt capacitor for power factor correction.The results demonstrate that such configuration has a higher immunity to resonances,as the total grid equivalent impedance perceived by the wind park is typically dominated by the absent HV/MV transformer and shunt capacitor bank.Moreover,the capacitance provided by the underground feeders of the wind park did not result in natural oscillation frequencies in the range of typical harmonic distortions observed in MV distribution networks that violated power quality standards.展开更多
Due to dynamic interaction between converters, design of control parameters of multi-converters medium-voltage DC (MVDC) power system is much more complicated than of a single-converter situation. Open-loop and closed...Due to dynamic interaction between converters, design of control parameters of multi-converters medium-voltage DC (MVDC) power system is much more complicated than of a single-converter situation. Open-loop and closed-loop transfer functions considering control-loops dynamic interaction between converters are developed, which are suitable for studying influence of control parameters on system stability. With the above transfer functions, a system-level control parameter design proce-dure for dynamic stability (e.g., oscillation frequency and damping factor) of system is proposed. If there are many converters, computational burden of system-level control parameters design procedure will be huge. For this reason, a control parameter sharing method is further proposed in this paper, which is based on dynamic interaction mechanism between converters. In this sharing method, control parameters of equivalent reduced-order model of the system are shared with each converter, so calculation burden of control parameters of system is reduced significantly. Consequently, dynamic stability of the system can be designed by equivalent reduced-order model. Experiments are conduced to validate the system-level control parameter design procedure.展开更多
With the rapid development of the direct current(DC)distribution network,DC voltage measurement technology is increasingly important to ensure safe operation in the distribution network.The measurement accuracy of the...With the rapid development of the direct current(DC)distribution network,DC voltage measurement technology is increasingly important to ensure safe operation in the distribution network.The measurement accuracy of the traditional sensor based on resistance dividers decreases over time because the resistors age due to temperature and electromagnetic radiation.To address this problem,a novel type of medium-voltage DC voltage sensor with self-correction ability is presented in this paper.A resistor with large R_(H)is connected in series with RK and R_(G),i.e.two precise resistors with low resistance,to transform the measured medium voltage into low voltage.Among these three resistors in the divider,R_(H)connects with the measured medium DC line,while R_(G)connects with the ground.An electronic switch,K,is paralleled with RK,the precise resistor at the middle position.Generally,the state of the electronic switch is off,and the current flows through RK.Medium DC voltage can be measured according to the voltage on R_(G)with the divider ratio.When the sensor needs self-correction,the electronic switch will be controlled by FPGA(Field Programmable Gate Array)to turn it off and on;therefore,two values of low voltage can be obtained using time-sharing sampling.Two equations can be built according to the divider principle,and R_(H)in the divider can be evaluated by solving the equations.As a result,the measurement error caused by the change in R_(H)can be avoided.Finally,the medium-voltage DC sensor developed in this paper has been tested at the Institute of High Voltage,Wuhan,China.The experimental results show that the sensor can perform self-correction without manual operation,and the sensor’s accuracy can reach 0.12%.Sensors with a self-calibration function can realize long-term high-precision measurement without manual maintenance,showing a good application prospect.展开更多
From flexible interconnection among feeders to hybrid alternating current(AC) and direct current(DC)distribution structures of future smart distribution systems medium-voltage DC distribution centers with flexibly int...From flexible interconnection among feeders to hybrid alternating current(AC) and direct current(DC)distribution structures of future smart distribution systems medium-voltage DC distribution centers with flexibly interlinked multiple microgrids(MGs) will have wide applications on the demand side. A generic coordinated control framework based on a distributed cooperation scheme is proposed for such DC centers, as opposed to centralized control structures. A novel unified control only using local measurements is proposed for these interlinking converters. During normal power disturbances, automatic coordinated power control and mutual support among sub-systems can be realized, thereby improving DC voltage and AC frequency stability to enable multiple MGs to be treated as a real unified cluster. Moreover, with this method, interlinking converters can realize seamless transition in power dispatching mode, common DC bus voltage control mode, and MG support mode without communication and control system switching. A simplified dynamic model has been developed to verify the proposed control strategy. This work is expected to provide a new solution for flexible interconnection and operational control of large-scale MG clusters.展开更多
The share of voltage source converter(VSC)technology is increasing in conventional power systems,and it is penetrating into specific transportation systems such as electric vehicles,railways,and ships.Researchers are ...The share of voltage source converter(VSC)technology is increasing in conventional power systems,and it is penetrating into specific transportation systems such as electric vehicles,railways,and ships.Researchers are identifying feasible methods to improve the performance of railway electrification systems(RESs)by utilizing VSC-based medium-voltage direct current(MVDC)railways.The continuous motion of electric trains makes the catenary resistance a variable quantity,as compared to the traction substation(TSS),and affects the currentsharing behavior of the system.A modified droop control technique is proposed in this paper for VSC-based MVDC RES to provide more effective current-sharing while maintaining catenary voltages above the minimum allowable limit.The droop coefficient is selected through an exponential function based on the ratio between the concerned TSS current and the system average current.This enables small adjustments of droop values in less concerning marginal current deviations,and provides higher droop adjustments for large current deviations.Meanwhile,the catenary voltages are regulated by considering the voltage data at the midpoint between two TSSs,which experiences the lowest voltages owing to the larger distance from the TSSs.The proposed techniques are validated via simulations and experiments.展开更多
Innovative advancement in power electronics is reshaping the conventional high-voltage transmission systems and has also opened a new paradigm for researchers to consider its benefits in the railway electrification sy...Innovative advancement in power electronics is reshaping the conventional high-voltage transmission systems and has also opened a new paradigm for researchers to consider its benefits in the railway electrification system(RES).In this regard,the medium-voltage direct current RES(MVDC-RES)is a key area of interest nowadays.In this paper,a secondary energy source(SES)consisting of renewable energies(REs)and energy storage systems(ESSs)is proposed to solve the issues of catenary voltage regulation,rail potential,and stray current in the MVDC-RES.Some of the major integration topologies of the SES are analyzed for MVDC-RES and the most effective one is proposed and implemented.The voltage at the point of connection(PoC)of the SES is used as a reference for controlling different operation modes of REs and ESSs.Moreover,feedforward control is used at the ESS converter to attain the quick response from the batteries for the desired operation.The proposed scheme improves the catenary voltage,and reduces the rail potential and stray current.Besides,the scheme provides higher energy density and reduces line losses.Simulation results are provided to validate the operation modes and advantages of the proposed scheme.展开更多
基金conducted under ARPA-e from DOE with the award number DE-AR0000892.
文摘Simultaneously imposed challenges of highvoltage insulation,high dv/dt,highswitching frequency,fast protection,and thermal management associated with the adoption of 10 kV SiC MOSFET,often pose nearly insurmountable barriers to potential users,undoubtedly hindering their penetration in mediumvoltage(MV)power conversion.Key novel technologies such as enhanced gatedriver,auxiliary power supply network,PCB planar dcbus,and highdensity inductor are presented,enabling the SiCbased designs in modular MV converters,overcoming aforementioned challenges.However,purely substituting SiC design instead of Sibased ones in modular MV converters,would expectedly yield only limited gains.Therefore,to further elevate SiCbased designs,novel highbandwidth control strategies such as switchingcycle control(SCC)and integrated capacitorblocked transistor(ICBT),as well as highperformance/highbandwidth communication network are developed.All these technologies combined,overcome barriers posed by stateoftheart Si designs and unlock system level benefits such as very high power density,highefficiency,fast dynamic response,unrestricted line frequency operation,and improved power quality,all demonstrated throughout this paper.
文摘China’s BeiDou Navigation Satellite System(BDS)construction has been completed and the system has been formally commissioned.Most of the Electric Power Systems(EPSs)for MEO satellites were developed by the Shanghai Institute of Space Power-sources.The 42 V medium-voltage fully-regulated high-power EPS has been adopted for the first time in medium Earth orbit,with an output power reaching about 3 kW.Compared with the 42 V medium-voltage semi-regulated bus power system used in the Regional Navigation BDS-2 satellite,the EPS of the BDS-3 MEO satellites has increased power by about 80%,adopting many newly developed products such as high-efficient triple junction GaAs solar cells,high-energy-density lithium ion batteries and a high-efficient autonomous power control unit(PCU).Based on the studies on the medium-voltage fully-regulated and high-power EPS technical principles,and the adaptability and reliability of various working modes,the test verifications for the EPS were conducted both on the ground and in orbit.Compared with other global navigation satellite systems such as GPS,Galileo and GLONASS,the EPS of the BDS-3 MEO satellite has a long design life time which is equivalent to that of the GPS and Galileo,but with a larger power supply capability and power ratio,distinguishing its advancement in the field of satellite power technology.
基金supported in part by the National Natural Science Foundation of China(No.52177071).
文摘Medium-voltage distribution systems(MVDSs)mainly consist of a feeder head,lines,distribution transformers,and the equivalent load or power supply interfaced with the distribution transformers.The information of such load or power supply can be measured via the three-wattmeter method(THM)and the two-wattmeter method(TWM).The measurements can be used to perform the control of the power supply and simulate the characteristics of the load,so the models of the load and the power supply need to consider the measurement characteristics.Existing research works on three-phase power flow(PF)just consider the measurement characteristics of THM.Hence,the PF equation of the bus measured via TWM is firstly built.Based on conventional measurements,an accurate and general model of the grounded and ungrounded slack bus is proposed.Furthermore,the influence arising from the connection type and angle shift of distribution transformers on the admittance matrix is considered,and thus a general three-phase transformer model is summarized,which is applicable for all the transformers mentioned herein.Finally,Newton's method is adopted to solve the PF calculation,and the performance of the proposed PF model is demonstrated through designed tests.
基金supported by Fundamental Research Funds for the Central Universities(No.2019JBM057).
文摘Direct current(DC)power grids based on flexible high-voltage DC technology have become a common solution of facilitating the large-scale integration of distributed energy resources(DERs)and the construction of advanced urban power grids.In this study,a typical topology analysis is performed for an advanced urban medium-voltage DC(MVDC)distribution network with DERs,including wind,photovoltaic,and electrical energy storage elements.Then,a multi-time scale optimal power flow(OPF)strategy is proposed for the MVDC network in different operation modes,including utility grid-connected and off-grid operation modes.In the utility grid-connected operation mode,the day-ahead optimization objective minimizes both the DER power curtailment and the network power loss.In addition,in the off-grid operation mode,the day-ahead optimization objective prioritizes the satisfaction of loads,and the DER power curtailment and the network power loss are minimized.A dynamic weighting method is employed to transform the multi-objective optimization problem into a quadratically constrained quadratic programming(QCQP)problem,which is solvable via standard methods.During intraday scheduling,the optimization objective gives priority to ensure minimum deviation between the actual and predicted values of the state of charge of the battery,and then seeks to minimize the DER power curtailment and the network power loss.Model predictive control(MPC)is used to correct deviations according to the results of ultra short-term load forecasting.Furthermore,an improved particle swarm optimization(PSO)algorithm is applied for global intraday optimization,which effectively increases the convergence rate to obtain solutions.MATLAB simulation results indicate that the proposed optimization strategy is effective and efficient.
基金supported by the National Key Basic Research Program of China(973 Program)(No.613294)the Natural Science Foundation of China(No.51877211)
文摘The dynamic characteristic evaluation is an important prerequisite for safe and reliable operation of the mediumvoltage DC integrated power system(MIPS),and the dynamic state estimation is an essential technical approach to the evaluation.Unlike the electromechanical transient process in a traditional power system,periodic change in pulse load of the MIPS is an electromagnetic transient process.As the system state suddenly changes in the range of a smaller time constant,it is difficult to estimate the dynamic state due to periodic disturbance.This paper presents a dynamic mathematical model of the MIPS according to the network structure and control strategy,thereby overcoming the restrictions of algebraic variables on the estimation and developing a dynamic state estimation method based on the extended Kalman filter.Using the method of adding fictitious process noise,it is possible to solve the problem that the linearized algorithm of the MIPS model is less reliable when an abrupt change occurs in the pulse load.Therefore,the accuracy of the dynamic state estimation and the stability of the filter can be improved under the periodic disturbance of pulse load.The simulation and experimental results confirm that the proposed model and method are feasible and effective.
基金supported in part by TotalEnergies EP Brasil through the ANP regulatory incentive for R&DIin part by the National Council for Scientific and Technological Development under Grant#306921/2019-7。
文摘On-shore wind parks are typically connected to the high-voltage(HV)transmission system through a bulk transformer.However,wind generators may be connected directly at a medium-voltage(MV)level,such as a utility-owned primary distribution network,if the network is capable of sustaining the power flow and ensuring adequate power quality for its users.This paper presents the findings of a comprehensive study on the management of resonance in a utility-owned wind park in Costa Rica.The wind park is connected directly to the MV primary distribution network and has no shunt capacitor for power factor correction.The results demonstrate that such configuration has a higher immunity to resonances,as the total grid equivalent impedance perceived by the wind park is typically dominated by the absent HV/MV transformer and shunt capacitor bank.Moreover,the capacitance provided by the underground feeders of the wind park did not result in natural oscillation frequencies in the range of typical harmonic distortions observed in MV distribution networks that violated power quality standards.
基金supported in part by the National Key Research and Development Program of China under Grant 2020YFB1506800in part by the China Postdoctoral Science Foundation under Grant 2021M692378in part by the National Natural Science Foundation of China under Grant 51977142.
文摘Due to dynamic interaction between converters, design of control parameters of multi-converters medium-voltage DC (MVDC) power system is much more complicated than of a single-converter situation. Open-loop and closed-loop transfer functions considering control-loops dynamic interaction between converters are developed, which are suitable for studying influence of control parameters on system stability. With the above transfer functions, a system-level control parameter design proce-dure for dynamic stability (e.g., oscillation frequency and damping factor) of system is proposed. If there are many converters, computational burden of system-level control parameters design procedure will be huge. For this reason, a control parameter sharing method is further proposed in this paper, which is based on dynamic interaction mechanism between converters. In this sharing method, control parameters of equivalent reduced-order model of the system are shared with each converter, so calculation burden of control parameters of system is reduced significantly. Consequently, dynamic stability of the system can be designed by equivalent reduced-order model. Experiments are conduced to validate the system-level control parameter design procedure.
基金supported by the National Key Research and Development Program of China(2018YFB0904702).
文摘With the rapid development of the direct current(DC)distribution network,DC voltage measurement technology is increasingly important to ensure safe operation in the distribution network.The measurement accuracy of the traditional sensor based on resistance dividers decreases over time because the resistors age due to temperature and electromagnetic radiation.To address this problem,a novel type of medium-voltage DC voltage sensor with self-correction ability is presented in this paper.A resistor with large R_(H)is connected in series with RK and R_(G),i.e.two precise resistors with low resistance,to transform the measured medium voltage into low voltage.Among these three resistors in the divider,R_(H)connects with the measured medium DC line,while R_(G)connects with the ground.An electronic switch,K,is paralleled with RK,the precise resistor at the middle position.Generally,the state of the electronic switch is off,and the current flows through RK.Medium DC voltage can be measured according to the voltage on R_(G)with the divider ratio.When the sensor needs self-correction,the electronic switch will be controlled by FPGA(Field Programmable Gate Array)to turn it off and on;therefore,two values of low voltage can be obtained using time-sharing sampling.Two equations can be built according to the divider principle,and R_(H)in the divider can be evaluated by solving the equations.As a result,the measurement error caused by the change in R_(H)can be avoided.Finally,the medium-voltage DC sensor developed in this paper has been tested at the Institute of High Voltage,Wuhan,China.The experimental results show that the sensor can perform self-correction without manual operation,and the sensor’s accuracy can reach 0.12%.Sensors with a self-calibration function can realize long-term high-precision measurement without manual maintenance,showing a good application prospect.
基金supported by National NaturalScience Foundation of China (No. 51507109, No. 51707128)Science and Technology Project of China Southern Power Grid (No. GZKJQQ00000417)
文摘From flexible interconnection among feeders to hybrid alternating current(AC) and direct current(DC)distribution structures of future smart distribution systems medium-voltage DC distribution centers with flexibly interlinked multiple microgrids(MGs) will have wide applications on the demand side. A generic coordinated control framework based on a distributed cooperation scheme is proposed for such DC centers, as opposed to centralized control structures. A novel unified control only using local measurements is proposed for these interlinking converters. During normal power disturbances, automatic coordinated power control and mutual support among sub-systems can be realized, thereby improving DC voltage and AC frequency stability to enable multiple MGs to be treated as a real unified cluster. Moreover, with this method, interlinking converters can realize seamless transition in power dispatching mode, common DC bus voltage control mode, and MG support mode without communication and control system switching. A simplified dynamic model has been developed to verify the proposed control strategy. This work is expected to provide a new solution for flexible interconnection and operational control of large-scale MG clusters.
基金partly supported by‘‘the Open Project of National Rail Transit Electrification and Automation Engineering Technique Research Center’’(No.NEEC-2017-A03)partly supported by‘‘the Fundamental Research Funds for the Central Universities’’(No.2682017CX041).
文摘The share of voltage source converter(VSC)technology is increasing in conventional power systems,and it is penetrating into specific transportation systems such as electric vehicles,railways,and ships.Researchers are identifying feasible methods to improve the performance of railway electrification systems(RESs)by utilizing VSC-based medium-voltage direct current(MVDC)railways.The continuous motion of electric trains makes the catenary resistance a variable quantity,as compared to the traction substation(TSS),and affects the currentsharing behavior of the system.A modified droop control technique is proposed in this paper for VSC-based MVDC RES to provide more effective current-sharing while maintaining catenary voltages above the minimum allowable limit.The droop coefficient is selected through an exponential function based on the ratio between the concerned TSS current and the system average current.This enables small adjustments of droop values in less concerning marginal current deviations,and provides higher droop adjustments for large current deviations.Meanwhile,the catenary voltages are regulated by considering the voltage data at the midpoint between two TSSs,which experiences the lowest voltages owing to the larger distance from the TSSs.The proposed techniques are validated via simulations and experiments.
文摘Innovative advancement in power electronics is reshaping the conventional high-voltage transmission systems and has also opened a new paradigm for researchers to consider its benefits in the railway electrification system(RES).In this regard,the medium-voltage direct current RES(MVDC-RES)is a key area of interest nowadays.In this paper,a secondary energy source(SES)consisting of renewable energies(REs)and energy storage systems(ESSs)is proposed to solve the issues of catenary voltage regulation,rail potential,and stray current in the MVDC-RES.Some of the major integration topologies of the SES are analyzed for MVDC-RES and the most effective one is proposed and implemented.The voltage at the point of connection(PoC)of the SES is used as a reference for controlling different operation modes of REs and ESSs.Moreover,feedforward control is used at the ESS converter to attain the quick response from the batteries for the desired operation.The proposed scheme improves the catenary voltage,and reduces the rail potential and stray current.Besides,the scheme provides higher energy density and reduces line losses.Simulation results are provided to validate the operation modes and advantages of the proposed scheme.
