To improve the stability and efficiency of hybrid propulsion systems for ships, a power distribution strategy based on the particle swarm optimization (PSO) threshold for multi-stack fuel cell systems is proposed.

For the hybrid power source system composed of multiple fuel cell stacks and batteries, a fuzzy logic energy management strategy based on the PSO algorithm was designed. By flexibly adjusting the number of fuel cell stacks and their individual output power based on the propulsion system load power and the battery state of charge (SOC), the control threshold of the system was optimized using PSO.

Matlab/Simulink simulation results show that this energy management strategy can quickly meet complex and changing load power requirements, and improve the system efficiency of the hybrid power source. Compared with traditional energy management strategies, the hydrogen consumption of the fuzzy logic-based and PSO threshold-based energy management strategies decreased by 18.96% and 31.48%, respectively.

This intelligent energy management strategy is applicable to multi-stack fuel cell systems in hybrid propulsion ships, and can effectively improve the system efficiency of hybrid power sources and reduce hydrogen consumption.

For a marine 690 Vac bidirectional converter based on a three-level flying capacitor, in order to make it start stably and transition to its normal working state, the flying capacitor must be pre-charged. This paper proposes a pre-charging strategy based on single-tube control which is suitable for three-level flying capacitors.

The on-off of the three-level outer tube is controlled on the basis of the flying capacitor, and efficient and fast pre-charging control is performed.

When this strategy is applied to a 690 Vac bidirectional converter, the pre-charging of the flying capacitor is completed within 1 second in Buck mode and less than 5 seconds in Boost mode. After pre-charging, the voltage of the flying capacitor remains at the value of half of the voltage of the high voltage side, and the voltage of the input side capacitor remains at the value of the input side voltage.

After experimental verification, the proposed pre-charging strategy based on controlling the outer tube of the three-level flying capacitor can be applied to a 690 Vac bidirectional converter device without the need for additional pre-charging power devices, which not only simplifies the topology but also ensures the reliable and fast pre-charging of flying capacitors.