| The braking process of the ship contains a huge energy. In the ship electric propulsion system driven by uncontrollable AC-DC-AC voltage source type converter, if such huge energy feedback to the DC bus, it will cause the DC bus voltage pump to very high. More seriously, it may damage to the power electronic device in the frequency converter, having a threat to the safety of system and person. Currently, the way of consuming energy by the braking resistor was often used to limit the DC bus voltage. But it has the shortcomings of the low efficiency,serious heat dissipation and so on. The scheme was taken in this paper that the super capacitor energy storage as the first choice and the braking resistance to consume energy as the backup for controlling the DC bus voltage in a certain range.Firstly, the energy storage mechanism and equivalent circuit of super capacitors were introduced and studied. A theoretical study was proceeded on the charge and discharge characteristics of super capacitor, and then the design method of super capacitor energy storage array was introduced. Through the research on a variety of typical super capacitor voltage equalizing circuit,a novel dynamic voltage-balancing circuit based on soft-switching technology was presented in this paper, enhancing the circuit efficiency and equalizing the voltages fast at the same time.Secondly, an in-depth analysis and research was launched on the braking process of ship electric propulsion system. The Buck-Boost type (or current reversible) DC/DC converter was selected, which can realize two-way flow of energy between the super capacitor energy storage device and the DC bus. The overall structure of ship electric propulsion system based on super capacitor energy storage was designed, for which the control requirement was put forward. The system was divided into four operating modes of super capacitor energy storage mode, super capacitor energy release model, super capacitor hold mode and the braking resistance energy consumption mode. The reasonable coordination control strategy for super capacitor energy storage module and braking resistor energy dissipation circuit was worked out.Finally, by calculating the regenerative energy of the ship braking process, the super capacitor energy storage scale was determined. Then the designed overall structure and the control strategy of system was modeled and realized in MATLAB/Simulink. The conditions such as ship braking, acceleration and sudden load were simulated and studied. The comparison of experimental results shows, the presented scheme that the super capacitor energy storage as the first choice and the braking resistance to consume energy as the backup,and its control strategy is correct and effective. At the same time, simulation of the novel voltage-balancing circuit in the process of ship braking, acceleration and sudden load was carried on,verifying the good tracking performance of voltage equalizing. And the experimental result shows high practical value of the voltage equalizing circuit. |
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