Research On Energy Storage System Of Marine Electric Propulsion Based On Super Capacitors

The braking time of the ship electric propulsion system is very short,and it has a huge energy in the process.When the energy is fed back to the DC bus through the inverter,it will cause the voltage pump to very high.If the voltage is too high,it will seriously damage the switch device,and even threaten the safety of the operator.Therefore,this part of the energy must be processed in a timely manner.In the past,the way of consuming energy by resistor was often used to limit the DC bus voltage,which will not only cause the waste of energy,but also cause the serious heat dissipation,and the resistance value can not be quantified.In order to reduce the fluctuation of DC bus voltage,this paper adopts the scheme that the super capacitor and the braking resistor cooperate with each other.Firstly,in this paper,it explains the reason for the selection of super capacitor energy storage are explained by comparing several energy storage methods.Through the study of typical voltage equalizing circuit,in this paper,an improved voltage balancing circuit based on full bridge phase shifting is proposed,which can not only realize the dynamic voltage balancing,but also shorten the time and improve the efficiency.The feasibility of the model is verified by Matlab/Simulink simulation.Secondly,this paper analyzes and studies the ship braking process.The super capacitor system based on module multilevel bidirectional DC-DC converter,not only can make the energy bidirectional flow between the super capacitor energy storage system and the DC bus,but also realizes the voltage balance between the modules,at the same time to stabilize the bus voltage.According to the change of DC bus voltage and the charging level of super capacitor,the energy control strategy is proposed to control the charging and discharging depth of the super capacitor energy storage system,and ensure the safety of the energy storage system.Based on the super capacitor energy storage technology,the overall scheme of ship electric propulsion system was designed,for which reasonable control strategy was formulated.The system is divided into four kinds of operating modes,such as super capacitor energy storage,super capacitor energy release,super capacitor hold mode and resistance energy consumption.The proposed control strategy is verified by Matlab/Simulink platform.Finally,this paper selects three phase asynchronous motor to simulate the ship electric propulsion system,and sets the parameters of the motor.According to the maximum energy generated during the braking process,the energy storage capacity of the system is determined.The simulation model of the whole system is built on the Matlab/Simulink platform.Through the given motor control signals,such as acceleration,loading and braking,the simulation results demonstrate the effectiveness of the scheme and the control strategy of the super capacitor energy storage and resistance energy dissipation,proving the good tracking performance of voltage balance circuit within and between groups.The experimental results prove the rationality of the scheme of super capacitor energy storage and resistance energy dissipation,achieving the desired results.