Shore-to-ship (S2S) power supply systems provide an effective approach to achieving the decarbonization of maritime transport. These systems require the use of voltage source converters (VSCs) operating in grid-forming (GFM) mode to ensure stable microgrid operation during connection and islanded transitions. As a method to synchronize the GFM converter with the ship generators, the international standard IEC/IEEE 80005-2:2016 recommends the usage of droop values established by the ship prior to connection with the shore. However, various techniques exist for designing the power control loop (PCL), and the implementation of droop values differs among these methods. This paper presents a comparative analysis of a traditional droop controller, a virtual synchronous generator (VSG), specifically, a synchronverter, and a virtual oscillator controller (VOC), when the same droop values are applied to all. Simulation results demonstrate that the droop controller and the synchronverter yield nearly identical responses. In contrast, the VOC exhibits variable equivalent droop gains as a function of the output voltage, leading to distinct dynamic behavior.

Shore-to-ship (S2S) power supply systems play a key role in the decarbonization of the maritime transport. These systems require the use of voltage source converters (VSCs) operating in grid-forming (GFM) mode. GFM converters must handle significant load impedance variations, primarily resulting from fluctuations in the power consumption of docked vessels. Moreover, the power demand of ships such as cruises and container vessels can reach several MW or even tens of MW, further complicating the integration of S2S connections in ports. Therefore, the design of a robust and high-performance GFM controller is essential. This paper proposes a single-loop voltage controller, designed using state-space control theory, for the operation of GFM converters in S2S applications. The proposed controller achieves accurate voltage tracking, fast transient response, and complete disturbance rejection at both the positive-and negative-sequence components of the fundamental frequency, due to its zero output impedance. In addition, the controller exhibits a favorable sensitivity function and wide stability margin. These features enable compliance with international standards for S2S connections.

The reduction of emissions, noise and fuel consumption costs that ships incur while berthing is driving investment in the electrification of port power supply systems. Current regulations, such as the IEC/IEEE 80005, require vessels to shut down their onboard generators and connect to shore power for as long as practicable during port stays. The method of supplying electrical energy to ships from shore power stations is known in the shipping industry as cold ironing. The shore-to-ship grid consists of a 60/50-Hz ac-voltage bus, rated from 1 kV to 15 kV for medium-voltage systems, and up to 1 kV for low-voltage systems. These grids can be supported by multiple grid-forming (GFM) power converters connected in parallel. These converters must interface with the ship’s power plant both when the onboard generators are running and after they are shut down. In such conditions, the converters often supply different types of loads and experience variable loading configurations depending on the type and size of the vessel. The parallel connection of GFM converters, combined with the variable impedance of the ship’s power plant can affect the stability of the shore-to-ship power connection. It is fundamental that each GFM converter sees at its output an impedance that is at least equal to the minimum impedance required to ensure stability. This article focuses ensuring stability in shore-to-ship connections through a comprehensive design of the voltage and droop controllers, in combination with virtual impedance (VI). The VI helps prevent instabilities when GFM converters are connected in parallel, regardless of the impedance seen from their output terminals.