Research On Flexible Switching Technology And Application Of Multi-power Sources Based On Hybrid Switching System

With the development of high-tech industries in China,some important loads have more and more stringent requirements for power quality.Power loss of equipment or bad transient process may cause major economic losses and even threaten the safety of the people.The mainstream solution is to configure a backup power supply or use multiple power supplies.Uninterrupted switching between power supplies is the key to realizing this solution.The technical objectives are to shorten the power-loss time of important loads,while suppressing phenomena such as over-voltage and inrush current caused by operation.Taking electric locomotives powered by multiple power sources as the main application background,this research proposes flexible switching strategies and the basic principles of phase control.Power electronics are introduced into the topology of ordinary vacuum switches,and the two devices work together to complete the task of flexible switching.Based on the analysis of the previous research results of traction power supply system and ordinary three-phase power switching,with multi-power supply as the basic scenario,a flexible switching solution based on the uninterrupted switching strategy is proposed in this paper.The goal of shortening the power supply dead time to less than 1/4 cycle(5 ms)and ensuring continuous power supply for lower-level equipment is proposed.The switching transient over-voltage and inrush current are effectively suppressed.The implementation of this strategy is proposed,which is composed of the power electronics unit(PEU)and a vacuum switch(VS)to form the hybrid switch.The reliable operation of the system is ensured through the VS fracture to prevent problems caused by faults such as false triggering,breakdown or short-circuit of the PEU.Moreover,the mechanical contacts undertake the task of steady-state current,which effectively avoids the heat dissipation problem of PEU during long-term current flow.PEU can accurately switch at the target points and execute the uninterrupted switching strategies,which provides a sufficient time window for the mechanical switch,and ensures the effective completion of flexible switching.As the theoretical study on the flexible switching of multiple power sources,combined with the typical application of single-phase dual power supply switching,a practical topology for electric locomotives with uninterrupted power supply used in the railway auto-passing neutral section is proposed in this paper.Flexible switching strategies for various neutral sections and different driving directions have been formulated.The ideal target phase points of each unit of the hybrid switching system with asymmetric structure is analyzed.The saturation characteristics of the main transformer of the locomotive and the opening/closing characteristics of the mechanical switches are fully utilized,thereby providing the practical and feasible closing windows for the mechanical switches.Combining the load status analysis,the influence of the arcing and pre-breakdown characteristics of the vacuum switch on the switching process and the correction effect,the action sequence and system reliability under the fault state are demonstrated.The coupling simulation model of locomotive,switch and traction grid is established.According to the actual system parameters,the phase control switching processes under different neutral sections,different loads,and different phases are simulated.The influence of power electronics auxiliary circuits is discussed.The effectiveness of the flexible automatic switching system and strategy used in the railway auto-passing neutral section is proved theoretically.In order to realize the experimental description of the flexible switching of multiple power sources in the uninterruptible power supply system,a flexible switching test platform is designed in combination with the simulation model.In order to solve the time scatter problem caused by the deployment of electric locomotives in areas with large latitude span and large temperature difference between day and night,a displacement-current double closed-loop phase controller is designed to stabilize the closing time.An embedded hardware system based on flexible switching strategy and closed-loop control has been developed.The experimental equipment is built,and the experimental parameters are reasonably designed.The experiments of flexible switching between the two power supply arms are carried out on the electric locomotive running in the forward/reverse direction.Comparing the simulation and experimental results,the over-voltage and inrush current have been proved to be effectively suppressed.The dead time of the power supply is reduced to less than 5 ms.In addition,this test platform can also verify the breaking performance of vacuum switches and PEU IGBTs under rated conditions.In order to further improve the multi-power flexible switching strategy and expand the application field,based on the above research,this paper applies the flexible switching strategy to the three-phase main-standby power switching solution of the data center.The topology of the three-phase hybrid flexible transfer switch has been designed.When the main power supply loses voltage,under-voltage or over-voltage,the switching strategy is analyzed.The switching process between light load and heavy load is simulated and analyzed.The current commutation between the vacuum switch and its parallel branch is the key technology for the successful operation of the hybrid switch.Through the theoretical analysis of the current commutation and the equivalent experiment with the large-capacity current source test platform,the limit time required to ensure the successfully completion of the current commutation is obtained.The equivalent commutation experiment with the current source is carried out,and the limit time is obtained,which further perfects the flexible phase-control switching theory of multiple power sources based on the hybrid switch.