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| Grid-Forming Vector Current Control of Ship Shore Converter |
| Cheng Peng1, Wang Xiaorui1, Liu Qihui2, Zhang Hui3, Yang Shengxiang3 |
1. Institute of Energy Power Innovation North China Electric Power University Beijing 102206 China;
2. School of Electrical and Electronic Engineering North China Electric Power University Beijing 102206 China;
3. Ningbo Beilun Third Container Terminal Co. Ltd Ningbo 315800 China |
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Abstract As the available power supply for ships in seaports, the shore converter can replace the synchronous generator with heavy diesel, resulting in less NOx, SOx, and other pollutants. The pre- synchronization method is employed for the continuous power supply between the ship generator and the shore converter. However, due to the inrush connecting current produced by the undesired phase angle difference, the shore source fails to replace the ship source. This paper develops the grid-forming vector current control for the shore converter.
The proposed control strategy is implemented in the synchronous reference frame of the ship power system determined by the phase-locked loop. The commanded current reference of the shore converter is produced by the voltage amplitude-frequency control loop, and the modulated converter voltage is obtained by the current control loop. With the pulse-width modulation, the seamless self-synchronization between the ship and the shore is achieved with the parallel connection and the voltage forming. On the one hand, the phase-locked loop is employed instead of the active power-frequency synchronization loop, which can generate the phase angle for the frame transformation and voltage modulation without power provision. The pre-synchronization for the quasi-synchronization with the voltage modulation and the parallel connection is avoided. On the other hand, the commanded current reference is generated from the measured voltage amplitude and frequency of the ship power system. This approach can provide the desired active and reactive power to maintain non-steady errors of the voltage amplitude and frequency during the load transfer and islanded supply. Consequently, the grid-forming capability of the ship power system is achieved.
Then, a mathematical model of the grid-forming vector current control is established. Accordingly, the system stability, voltage tracking capability, and sensitivity against load variations are analyzed. With the larger equivalent bandwidth coefficient of the grid-forming vector current control, higher voltage tracking capability and minor sensitivity against load variations are achieved while maintaining a sufficient stability margin.
Finally, hardware-in-loop tests are conducted in conditions of the shore-ship connection, shipload transfer, islanded power supply capability with load variations, and voltage amplitude and frequency regulation of the grid-forming vector current control. The proposed grid-forming vector current control achieves a seamless connection between the ship power system and the shore converter without pre-synchronization while maintaining the voltage amplitude and frequency stability of the ship power system.
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Received: 31 July 2023
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2024, Vol. 39 
