Alternative for wired shore connection for charging – What solution are there?

What is available alternatives for charging based on wired shore connection? This article is written by Suraj Timilsina, research assistent with UiT in Narvik summer 2019.

Introduction

Electric vehicle (EV) charging stations are the infrastructure that supplies electrical energy for recharging of EVs like electric cars, electric bike and other plugin hybrids. EV charging stations has been stationed throughout the globe and have different modes of charging varying from simple plug-in to wireless and fast charging.

However , that is not true in case of electric maritime vessels and electric aircraft. Especially in case of charging technology for electric maritime vessels, the charging mode is still mostly primitive and limited to a simple plug-in type. Several researches are going underway in order to develop and commercialize charging technology for electrical propulsion of maritime vehicles.

Cable and plug based charging

The most commonly used charging mode for electric vehicles is wired charging that utilizes different standards such as CHAdeMO, CCS and Type 2 plug. In maritime applications, Figure 1 shows a commonly used shore wired charging installation based on industrial 400 V outlets.

Figure 1 – Shore connection using 400 V industrial plugs at a port

The charging process involves a connection from the AC grid or external source, to the vehicle with ac/dc converter and battery arrangement. Connection between charging station and vessel is aided through standard power cables. This charging method is most suitable for pier where the smaller  vessel will stay parked for longer. Due to its lower costs (production, installation and operation) these are the more commonly found chargers. Also, due to these lower costs it is usually much cheaper to charge at AC chargers, making them more popular for general day to day charging.

It is also possible to utilize electric vehicle standards for maritime applications. RAICHO-I is one of such small vessel that employs wired charging using CHAdeMO. Its battery capacity is 18KWh and about 80% battery is charged within 30 min.

Issues regarding wired charging

  • Periodic maintenance and repair of hardware
  • Poor weather protection (Ice and snow problem)
  • Proper insulation should be maintained
  • Cable connecting shore and ship necessary
  • Different standards for charging depending upon manufacturing

Pantograph tower charging

Unlike shore wired charging , pantograph tower charging mode is more of a integrated system for docking and charging of ferries. It is usually used for charging larger vessel with higher power capacity. This mode of charging implements comparative larger structure (pantograph tower) than wired shore charging station.

Consequently following docking of the vessel, the charging system is activated by the mean of onboard control system. When the ferry becomes ready in its docking position alongside the pantograph tower, the pantograph connects to the onboard unit and starts charging batteries. The charging system employs mechanism to compensate any movement of the ferry due to tidal swinging as shown in Figure 2.

Figure 2 – Pantograph tower

FerryCHARGER

The FerryCHARGER system manufactured by Stemmann-Technik from Germany is used in around 90% of the docking operations for the ferry Ampere, operating between Lavik and Oppedal. It takes less than seven seconds to establish contact with the ferry. The initial charging power of 1,250 A (AC – alternating current) at the start of the operation, is increased to 1,650 A by the system.

The centre piece of the FerryCHARGER towers is the charging pantograph. Its working range is 3,000 mm in the vertical and 300 mm in the horizontal direction. The movement of the ship (rolling, yamming, pitching, 5° each) is compensated automatically. Furthermore, a remote maintenance system is integrated allowing access to the complete control system, including camera monitoring of on-board or external workplaces. The charging level is generally separated into low voltage and medium voltage level. The size of battery and time for charging determined which charging level is preferred.

  • Low voltage                : 1600 A, 0.6/1 kV     or   3000 A, 0.6/1 kV
  • Medium voltage         : 300 A, 6/10(12) kV  or    600 A, 6/10(12) kV

Figure 3 – Pantograph connection to the vessel

Automatic Plug-in system (APS)

Automatic plug-in systems charges electric vessels without the need of human intervention. Integrated with optimal mooring system, APS has potential to revolutionize the E-charging sector. It provides charging solution for variety of electrical vessel including electrical and hybrid vessel like ferry.

Some of the significant features of Automatic plug-in system APS are:

  • Short charging time
  • Accommodate variety of vessels
  • Safe operation due to electrical interlock
  • Limited infrastructure cost
  • Robust design reduces maintenance cost
  • Integration with mooring system

CAVOTEC is one of the leading company with a patented Automatic plug-in system and have variety of implementation based on APS.  Its combination of MoorMaster system with APS ensures automated mooring and charging.

Figure 4 – Cavotec plug-in system

DC charging instead of AC

The batteries onboard vessel is charged using DC (Direct current) but the supply from the grid is AC (Alternating current). An AC charging point/shore charging station supplies the vessel’s onboard charger, which in turn converts the AC power to DC allowing the battery to be charged. The size of the onboard charging device is constrained by the space inside the vessel, where any reduction in volume is positive. Considering the onboard converter to be small, the amount of power that they are able to deliver to the battery is typically low.

Even with development of much more compact devices replacing big and heavy transformer, it still requires a separate space in the vessel and capacity of the vessel limits the size of charger components. Especially in case of small vessel with very small charging period (20-30 minute) AC charging is not practical. DC charging is preferred out of several merits such as:

  • DC fast charging bypasses the onboard charging devices
  • Direct supply of power and safety of vessel
  • DC charging is external and thereby not constrained by size or cost
  • Smart charging enabling adjustment of charging level to suit battery status

Charging solution for small vessels

Different vessels of varying battery capacity have varying charging solutions. For example, small vessels with battery capacity within range of 1000 kWh and short charging time prefers fast DC charging solutions, whereas use of AC charging would be impractical in this case. As the capacity and size of vessel increases, manual connection of wired shore charging may not be optimal choice anymore. More advanced and effective way of charging is required, such as:

  • An hydraulic arm with x, y and z axis control with flexible socket head can be implemented as one of alternative charging solution. A fully automated charging system without any need of human intervention aided by precise arrangement of position and other sensors. The communication system enabling control of system aboard the vessel and intelligent charging along with information on battery status.
  • An arrangement of electromagnetic interlocking between shore-side (aided by simple automated hydraulic system) and ship-side power inlet. Other features being human intervention-free fully automated charging solution.

Resources

  1. http://www.stemmann.com/en/products/charging_systems/ferrycharger
  2. CAVOTEC Automatic plug-in system and Moor-Master

 

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