Green Propulsion (Electric Hybrid)

Green Propulsion for environmental friendly propulsion of ships



Praxis Automation Technology BV has extended the Mega-Guard product range with a new concept for Green Propulsion in order to show our commitment to environmental friendly propulsion of ships. We provide a total in-house developed and manufactured electric and hybrid propulsion solution for shipowners and shipyards who care about the environment and on-board safety. 


The following applications are covered by Mega-Guard Green Propulsion:


  • Full electric: Battery power and electric motor
  • Diesel electric: Generator power and electric motor
  • Serial hybrid: Battery plus generator power and electric motor
  • Parallel hybrid: Battery plus generator power. Shaft driven by electric motor and/or combustion engine


The backbone of Mega-Guard Green Propulsion is the energy distribution with an highly efficient DC Bus and communication between the different Green Propulsion products with redundant Ethernet.

As for all Mega-Guard products, Mega-Guard Green Propulsion is supported by a worldwide service network and comes with a guaranteed availability of spare parts and support of 20 years as a minimum. All Mega-Guard products are designed to the highest standards of safety and are class approved by all major classification societies.

Mega-Guard Green Propulsion can be further extended with other Mega-Guard products such as Heading Control, Dynamic Positioning and  Control, Alarm and Monitoring systems. 




Green Propulsion product summary

The Mega-Guard Green Propulsion product line is built-up with the following main products:



GreenPod is a highly efficient steerable thruster covering propulsion applications from 100kW to 2.2MW. Two versions are available: an electric motor mounted 'under water' in line with propeller shaft and a version with a so called L drive with electric motor mounted inside hull on top of the thruster. GreenPod contains a permanent magnet high efficiency electric motor to support a green environment. Up to two electric steering motors provide 360 degrees steering functionality of GreenPod. 



GreenBattery is a safe, highly efficient and modular energy storage system with relatively low weight and small volume. Each GreenBattery has a capacity of 80kWh and a nominal DC Bus voltage  of 832VDC. Multiple GreenBatteries can be mounted in parallel to realize energy storage systems ranging from 80kWh to 4MWh. Each GreenBattery includes a Master BMS and DC Bus contactor. Various safety devices are built into  GreenBattery. In the unlikely event of a battery cell explosion, it does not propagate to other cells (no thermal runaway) and it is contained inside the battery housing in order to guarantee a safe energy storage system without pollution to the  surrounding environment of GreenBattery.   





GreenMachine and GreenPower

GreenMachine is a highly efficient permanent magnet electrical machine for propulsion and electric power generation. Low speed versions of GreenMachine are available for direct mounting to a propeller shaft without gearboxes. Medium and  high speed versions are available for connecting to third party thrusters and gearboxes (parallel hybrid). GreenPower consists of a variable speed combustion engine connected to a GreenMachine acting as electric generator. In this way a highly efficient and light weight electric power generator plant is realized to further support a green environment.




GreenInverter covers applications for electric motor and generator drive and includes battery charging with GreenPower generator sets or with shore power. In addition, a GreenInverter AC is available for AC grid generation to support hotel load. GreenInverter is available in power ranges from 100kW to 2.2MW. GreenInverter is connected to the DC Bus with a nominal voltage of 832VDC. A DC Bus contactor and other safety devices are built into each GreenInverter.







GreenPCS propulsion control system fully automates the remote control from bridge of the GreenPod or GreenMachine propulsors. In case of parallel hybrid applications; the combustion propulsion engine is controlled as well and automatic change over from electric propulsion motor (low power) to combustion propulsion engine (high power) is fully supported.  The GreenPCS propulsion control system also provides steering functions with the application of GreenPod and third party steerable thrusters.






DC Bus

The DC Bus interconnects all GreenInverters and GreenBatteries which are installed at different locations. DC Bus Distribution Cabinets include cable connections for all DC Bus cables and the cables are protected for short circuit by DC Bus fuses inside the cabinets.  DC Bus tie breakers are able to separate port and starboard side propulsion and power generation in case of abnormalities.









Green EMS

GreenEMS energy management system allows for automatic energy source selection and control  from either the GreenBattery energy banks or GreenPower generator sets. In addition, the energy management system controls the charging of GreenBatteries either by GreenPower generator sets or by shore power.


Applications Green Propulsion

Advantages of electric propulsion

There are two main reasons to change to electric propulsion: zero emissions during electric propulsion and fuel efficiency. Fuel efficiency can be increased with electric propulsion when there is a large difference in operating hours at e.g. cruise speed and maximum speed (or power). The  reason for this is that the combustion engine is running only at optimal efficiency when fully loaded; at all other operating points efficiency drops. Electric propulsion when combined with combustion engines realizes that the combustion engine is running at optimal efficiency most of the time, by using the spare power for charging battery packs and/or by switching off one or more combustion engines depending on load requirement. In addition, electric motor propulsion, especially when combined with steerable thrusters, gives a much better maneuverability when compared to combustion propelled vessels as the RPM can be easily controlled from zero to maximum. Some ship applications also require strongly reduced noise emission and this can be realized with the GreenPod steerable thruster as the electric motor is mounted 'under water' for optimum noise reduction.

The Mega-Guard Green Propulsion product line covers various propulsion applications which can be summarized as follows:


Full electric propulsion

The full electric propulsion uses an electric motor to drive the propeller shaft. Electric power is coming from battery banks and charging is done through shore power. Combustion engines are not installed. With large batteries you can  have long periods of electric propulsion and the AC grid for hotel load is generated from the battery bank too. The highly efficient GreenPod steerable thruster perfectly fits into full electric applications.








Serial hybrid propulsion

The serial hybrid also uses an electric motor to drive the propeller shaft.  Electric power is coming from battery banks or, when battery bank is empty, from a combustion generator set. Charging of the battery bank is done through the combustion generator set or by shore charging. With large batteries you can have long periods of electric propulsion without the need for combustion engines to run as the AC grid for hotel load is generated from the battery bank too. The highly efficient GreenPod steerable thruster perfectly fits into full electric applications.









Parallel hybrid propulsion

The parallel hybrid  propulsion system uses both a combustion engine and an electric motor to drive the propeller shaft. In fact, the combustion engine and the electric motor are mounted in parallel. 
Parallel mounting is generally done in one of two ways:

  • The propeller shaft from the combustion engine is split in two parts and the electric motor is mounted in between the two shaft parts. This means that the electric motor is mounted in-line with the propeller shaft. The electric motor has also to carry the usually much higher load from the combustion engine. The highly efficient permanent magnet electric motor with hollow shaft fits this purpose.
  • The electric motor is mounted on an additional input of the gear box which is mounted in between the combustion engine and the propeller shaft.

Parallel hybrid propulsion allows you to drive the propeller shaft by either the electric motor or the combustion engine or by both (boost mode). In case the vessel is propelled by combustion engine, the electric motor acts like a generator which can be used for charging the battery banks.

In case there is a big difference in between operating hours at cruising speed compared with operating hours at maximum speed/power it makes sense to install a parallel hybrid system. The relatively small electric motor can propel the vessel at cruise speed for longer periods. When maximum speed/power is required, the large combustion engine takes over the propulsion and the electric motor is used as generator for charging the batteries. The parallel hybrid has
built-in redundancy as the shaft can be driven by either the electric motor or the combustion engine. The highly efficient GreenMachine perfectly fits into parallel hybrid applications. 


Diesel-electric propulsion

A diesel-electric propulsion system uses generator sets to generate electric power for the electric propulsion motors. The generator sets consist of a combustion engine, which could be gas or diesel, and is connected
directly to an electrical generator. The electric propulsion motor is connected directly to the propeller shaft. The diesel electric system usually has multiple generator sets and multiple electric motors connected to a common electrical DC bus. The highly efficient GreenPod steerable thruster and the GreenMachine electric generator fit perfectly into diesel-electric applications. Note that there is no electric storage of energy in a diesel electric propulsion application.







GreenPod steerable electric thruster


GreenPod steerable electric thruster is designed as a highly efficient fit and forget propulsor that additionally saves  a lot of engine room space. In fact, due to its low height GreenPod can be mounted in almost any location.

Two versions are available:


  • Pod with electric motor mounted 'under water' in line with propeller shaft.
  • L drive with electric motor mounted inside hull on top of the L shaped propeller shaft.


GreenPods are available in sizes in between 100kW and 2.2MW. The highly efficient permanent magnet electric motor increases efficiency to support a green environment.

Up to two electric steering motors are mounted on top of GreenPod for reliable and fail safe steering. GreenPod electric propulsion motor is controlled by GreenInverter and the steering motors are controlled
by a low power version of GreenInverter. These GreenInverters can be mounted on top of GreenPod for simplified and trouble free installation. GreenInverters are connected directly to DC Bus and to Ethernet communication lines. 

Three different propeller configurations can be supplied:


  • Pushing : standard configuration up to 12.5 knots
  • Dual : propeller contra rotating propellers for speeds above 12.5 knots
  • Nozzle : to increase efficiency at speeds below 5 knots to realize highest bollard pull

















GreenMachine and GreenPower


GreenMachine is a highly efficient permanent magnet electrical macine for propulsion and electric power generation. 

GreenMachine is available in RPM ranges in between 266  (low speed direct drive of propeller shaft) and 3600 (high speed generator set). GreenMachine can be either flange or bracket mounted. In addition, customer can choose between hollow shaft or solid shaft on one side or on both sides of the machine. In case of parallel hybrid applications, the low speed GreenMachine can be connected to the propeller shaft on one side and the other side can be connected to the output shaft of gearbox.

GreenPower is built-up with a light weight and high speed diesel engine connected directly to a highly efficient GreenMachine electric generator. In this way a very compact and efficient generator set is realized. GreenPower can be built-up with diesel engines from Hyundai, Volvo, Steyr and Cummins. Flange mounting connections, vibration damping plates and other specifications can easily be adapted to accommodate other combustion engines.

GreenMachine and GreenPower are cooled by water cooling (50% water/50% glycol). Each GreenMachine and GreenPower is controlled by a GreenInverter which is connected to DC Bus of nominal 832VDC.















GreenBattery electric energy storage

GreenBattery is a highly efficient and modular energy storage system with relatively low weight and small volume. Each GreenBattery has a capacity of 80kWh and a nominal DC Bus voltage of 832VDC. Multiple GreenBatteries  can be mounted in parallel to realize energy storage systems ranging from 80kWh to 4MWh.

Each GreenBattery is built up with 8 individual batteries and a Master BMS. The Master BMS contains a 5”TFT touch operator panel with controller and includes a DC Bus contactor and heat exchanger. All external connections are made available on the Master BMS.

Various safety devices are built-in for preventing thermal runaway. In the unlikely event of a battery cell explosion, it is contained inside the battery housing in order to guarantee a safe energy storage system without pollution to the surrounding environment of GreenBattery. Each battery is totally enclosed and GreenBattery includes a pressure based safety release which should be vented to the outside environment.

GreenBattery is liquid cooled by seawater or water/ glycol and a built-in controller regulates battery temperature in between 20 and 40 degrC. GreenBattery can be placed in any room with the ambient temperature up to 55 degrC. GreenBattery does not heat-up the room. 






























Battery management 

The batteries are built up with Lithium NCA technology battery cells which have considerable lower weight and higher power density when compared to other battery chemistries. In addition the applied Panasonic battery cells have a long

 track record and are widely used in electric cars. Each battery has 12 temperature measurements and a built-in BMS (Battery Management System) which communicates with the Main BMS. The Main BMS 5”TFT touch operator panel 

contains redundant Ethernet ports for communication to GreenInverters for charging/discharging and GreenEMS for energy management. GreenBattery fulfils the latest class requirements and a risk based assessment is made for
every project and approved by class. GreenBattery is supplied in two different mechanical lay-outs: a vertical one for space  saving and a horizontal one with a lower center of gravity.








GreenInverter high power inverter


GreenInverter is designed to be installed close to the device to be controlled for distributed DC Bus applications. However, centralized installation of GreenInverter is supported as well.  GreenInverter is built-up with two  controllers: a dedicated Digital Signal Processor for four quadrant motor and generator control functions and a Control Processor with four Ethernet ports for programming PLC functions in accordance with IEC61131 standard.
GreenInverter is equipped with a local operator panel consisting of a 5"TFT touch display and an emergency stop switch. Most relevant parameters such as power, current and voltage are continuously displayed on the 5"TFT.

GreenInverter is also available for following:

  • DC/DC conversion :GreenInverter DC/DC
  • AC grid generation :GreenInverter AC


These GreenInverters are based upon the standard GreenInverter and extended with magnetics. In addition, a low power GreenInverter LP is available for e.g. steering motor and bow thruster.





GreenInverter covers applications for electric motor and generator drive and includes battery charging with GreenPower generator sets or shore power as well. GreenInverter is built-up in a modular way, supporting applications from 100kW to 2.2MW. GreenInverter is a four quadrant controller with active front end technology. Motor operation changes into generator operation as soon as a motor is driven by propeller (brake energy) or combustion engine (parallel hybrid). The generated energy is used for GreenBattery charging. GreenInverter includes independent safety systems such as Safe Torque Off on AC side and DC Bus contactor on DC side. The contactor also supports pre-charging and discharging in order to safely connect and disconnect GreenInverter from DC Bus. GreenInverter is optimized for DC Bus voltages in between 650VDC and 975VDC and a nominal current up to 450A. This results in a rated power range from 350kW to 500kW. Multiple GreenInverters can be paralleled to increase the power up to 2.2MW. GreenInverter is IP67 protected and can be bulkhead mounted.






GreenEMS and GreenPCS


Energy Management

GreenEMS energy management system allows for automatic energy source selection from either the GreenBattery energy banks or GreenPower generator sets. In addition, the energy management system controls the charging of GreenBatteries either by GreenPower or by shore power. 

GreenEMS includes a 5”TFT touch operator panel on which all data regarding consumers (GreenPod's, GreenBattery charging and hotel load) and producers
(GreenPower generator sets and GreenBatteries discharging) are available. Mode selection pushbuttons are available as well on GreenEMS 5”TFT touch operator panel.

GreenEMS contains a project specific control strategy in order to control the consumers and producers. GreenEMS communicates to GreenInverter, GreenBattery and GreenPCS through redundant Ethernet communication ports to monitor and command these devices. As all  Green products are built-up from the same technology, a transparent and trouble free control strategy can be implemented in standard IEC61131 language.



Propulsion Control System


GreenPCS propulsion control system fully automates remote control from the bridge of GreenPod or GreenMachine propulsors. In case of parallel hybrid applications, the combustion propulsion engine is controlled as well and automatic change over from electric propulsion motor (low power) to combustion propulsion engine (high power) is fully supported. The GreenPCS propulsion control system provides steering functions with the application of GreenPod and third party steerable thrusters. The GreenPod azimuth lever includes two 2.5”TFT display panels and operator  pushbuttons for mode selection. They can be supplied including electrical shaft for synchronous operation. GreenPCS can also be applied for thrusters without steering function. In this case, typically a GreenPCS dual lever with two 2.5”TFT displays and two rows of operator pushbuttons is supplied to independently operate the port and starboard side GreenMachine. 

GreenPCS operator modes are adapted for every application. An example functionality is given below with two GreenPod steerable thrusters:

  • Individual mode
  • Combined mode
  • Autopilot mode with Mega-Guard HCS
  • DP auto mode with Mega-Guard DP
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Praxis Automation Technology
Zijldijk 24A,
2352 AB Leiderdorp
The Netherlands

+31 (0)71 5255 353

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