| Urban rail transit can effectively alleviate the problem of urban traffic congestion,and it has developed rapidly in recent years.Traditional urban rail transit power supply systems mostly use diode rectifier unit,which have the problems of waste of regenerative braking energy and large fluctuations in catenary voltage.The flywheel energy storage systems(FESS)can effectively recover the regenerative braking energy and stabilize the catenary voltage.However,there are few researches on the control strategies of the flywheel energy storage systems.In this thesis,comprehensively considered the energy conservation,voltage stabilization and energy management of the flywheel energy storage systems,and designed a control strategy of the single-flywheel energy storage systems.In order to solve the problem of small capacity of the single-flywheel energy storage systems,the flywheel energy storage arrays(FESA)were adopted and two different FESA control strategies were proposed.The correctness of the control strategies proposed in this thesis were verified based on the simulation platform and experimental platform of FESA.Firstly,a model of urban rail transit power supply systems with FESS was established.The operating characteristics of the traditional urban rail transit power supply systems were analyzed,and the equivalent circuit models of the traction substations and urban rail trains were established.The structure and principle of the FESS were described and the mathematical model of the FESS was established.A simulation platform for the FESS of urban rail transit was built,which provided theoretical foundations for the subsequent researches.Secondly,a control strategy for single-flywheel energy storage systems was designed.It mainly included two parts: permanent magnet synchronous motor(PMSM)control for FESS and energy management for FESS.In order to reduce the loss of the FESS and ensure the output power at high speed,PMSM adopted maximum torque current ratio control in the non-flux-weakening operating regions and adopted current leading angle flux weakening control in the flux-weakening operating regions.Comprehensively considering the requirements of energy conservation and voltage stabilization and energy management of FESS,a single-flywheel energy storage systems control strategy based on multi-voltage thresholds was designed.The energy-release mode improved the energy conservation and voltage stabilization performance of the FESS,and the flywheel speed was controlled within a reasonable range by SOC management module.Then,the control strategies of FESA were proposed.Due to the small capacity of the single-flywheel energy storage systems,it’s difficult to meet the energy absorption demand of train regenerative braking,so the FESA were adopted in this thesis.For the cooperative control of the FESA,two control strategies based on speed-error regulation control and the "voltage-speed-current" three closed-loop control were respectively proposed.The energy management and speed balance of the FESA were realized and the performance of the two control strategies was compared through simulation.Finally,an experimental platform was built for experimental verification.A 1MW FESA experimental platform composed of three 333 k W flywheel energy storage units was built.The control strategy of 1MW FESA was verified by using PWM converter to simulate the traction and braking condition of urban rail train.The experimental results verified the effectiveness of the FESA control strategy proposed in this thesis. |
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