# Research and Development of Inland Green and Smart Ship Technologies in China
## 3 Current Inland Green and Smart Ship Technology in China
### Green Ship Technology
#### 3.2.2 Direct Current (DC) Networking  
Inland ships generally have a short cruising range, which provides favorable conditions for electrification. Compared with the traditional alternating current (AC) networking electric propulsion system, direct current (DC) networking electric propulsion systems are an emerging electric propulsion technology that have significant advantages in terms of energy conservation, cost, weight, and system complexity [32]. First, a DC microgrid fault analysis model was established considering the active response and transient characteristics of the converter, and a fault location method of the DC microgrid was developed under the active response of the converter. The mechanism of the elastic recovery of the ship's DC grid voltage under large disturbances was revealed, and an optimized control method provided an effective solution for resolving DC network faults.  
Next, targeting the assessment of electrical equipment reliability in the Yangtze River Green Smart Ship DC Network, and based on the operation and maintenance data accumulated during the operation, an electrical equipment condition monitoring database was constructed [33]. Through comprehensive data source acquisition, combined with high-performance data processing and analysis, multi-source information fusion technology was used to monitor the states of the electrical equipment and to diagnose fault states. A scientific decision-making and maintenance information reference was provided for the management and control of inland ship DC network electrical equipment and to reduce potential safety hazards. The assessment methods of electrical equipment were also studied to improve the safety and reliability of the DC network.  
Further, the variable-frequency speed regulation characteristics of the generator sets in the DC grid system were studied to ensure that the oil/gas ran along the optimal consumption curves, thereby minimizing system energy consumption and emissions and maximizing operational efficiency. The use of battery energy storage was also assessed. Considering the speed regulation characteristics of the multi-source, multi-load, and multi-scenario generator set, the optimal configuration of the DC grid batteries w studied to improve overall efficiency and to propose battery capacity and configuration specifications. Reliable and efficient operation of the power converter for the DC system was evaluated and a smart charging control method was developed, resulting in improved efficiency of the smart charge/discharge controller to achieve further energy-savings [34]. A theoretical basis for calculating the efficiency of the DC network system of river and sea ships was established and guidance and specifications for the optimized design of the system were provided. Finally, using the hierarchical control strategy of the ship's DC network energy management system based on the droop characteristics, a stable control strategy for power interactive oscillations when multiple units are connected in parallel, and an active damping control strategy for improving the damping characteristics of constant-power loads, a DC network energy management system was developed and implemented for the ship. In practical engineering applications, the ships used in this system can adopt various forms such as diesel electric hybrid, gasoline electric hybrid, and pure electric.