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Electric Propulsion Systems

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Particularly economic, environmentally-friendly, and reliable electric propulsion systems

Wärtsilä has been leading the way to ever more efficient shipping since 1834. Wärtsilä’s extensive portfolio of electric propulsion solutions allows us to select the ideal configuration to meet any vessel’s needs. From high power systems for cruise vessels to low noise systems for research vessels to high redundancy systems for offshore vessels, Wärtsilä has the right solution. And with advances in energy storage systems, we are now able to supply hybrid systems using Wärtsilä’s Energy management systems to increase the vessel’s efficiency.

Electric propulsion systems are particularly economic, environmentally-friendly, and reliable. They are simple to operate and control, and have low levels of noise and vibration.

Benefits at a Glance

Benefits Diesel-Electric Propulsion

Low noise and vibration
Economical operation
Redundant configuration
Flexible use
Excellent dynamic characteristics
Outstanding mains quality
Reduced emissions
High degree of automation
Reduced wear and tear

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Converter topologies

    LCI Converter System

    Frequency converters with line controlled inverters (LCI converters also known as synchro-converters) are designed with a direct current (DC) intermediate circuit, and consist of thyristor rectifiers on the mains side, a thyristor inverter on the motor side, a DC reactor in the intermediate circuit, an excitation converter, and a control system. LCI converters are provided to supply synchronous motors.

    Synchro-converter based systems were also used in Wärtsilä's former shaft alternator system design, with more than 385 units delivered since 1967.

    LCI converter systems have the following advantages:

    • Economic in the high power range
    • Acceleration and braking in both rotational directions (four quadrant operation) without additional measures

    PWM Converter System

    Frequency converters with pulse width modulation (PWM converters) are self-controlled converters designed with a DC voltage intermediate circuit, and comprise (in the DFE solution) a diode rectifier on the mains side, an insulated gate bipolar transistor (IGBT) or integrated gate commutated thyristor inverter (IGCT) on the motor side, DC capacitors in the intermediate circuit, and a control system. For improved mains quality and for reverse power characteristics, the diode rectifier on the mains side is replaced by an IGBT rectifier (active front end AFE design). PWM converters are provided to power either asynchronous or synchronous motors. For synchronous motors, an excitation converter is also provided.

    PWM converter systems have the following advantages:

    • They permit a low level of motor air-gap pulsations, which results in low vibration
    • They allow acceleration and breaking in both rotational directions (four quadrant operation) with an active front end converter or reverse power resistor
    • Compact volume and weight
    • High torque in low speed ranges

    Active Front End (AFE) converters with PWM, instead of a diode rectifier input, offer the following additional benefits and are, therefore, typically used nowadays:

    • No supply transformer for 12-pulse or 24-pulse configurations, no chopper with the control system, or a breaking resistor for reverse power consumption necessary
    • Much better mains quality with THD < 5 % without additional measures
    • More economic operation thanks to better efficiency

    Low Loss Concept

    For certain power system configurations, the patented Wärtsilä “Low Loss Concept” (LLC) can be used. This is designed to remove the need for either a bulky transformer for a DFE drive, or an AFE drive.

    Wärtsilä has devised an ingenious way to overcome this problem by splitting the distribution bus into two sections, and placing the transformer between the two buses = Low Loss Concept (LLC).

    This gives a total reduction in the number of transformers (lower footprint) for installations with more than two drives connected, compared to the DFE solution. Where more than two drives are installed, the advantage of having fewer transformers becomes even more apparent.

    The advantages of this design include:

    • Fewer transformers means less electrical losses in the system, providing lower fuel consumption for any given engine configuration. Volume and space availability in the vessel is also saved thanks to having less installed equipment.
    • Improved system redundancy; as the power distribution is split into 2 x equal top and bottom sections with the drive connected to both, 50 % of the power comes from 1 source with the other 50 % coming from the other. This means that in the case of a failure in one of the switchboards, the drive can continue to operate unaffected, albeit with reduced power.
    • Compared to other systems on the market, a higher redundancy & ERN number can be achieved with the same installed power, or the amount of installed power can be reduced to achieve an equivalent DP plot.
    • Significant savings in space and weight; fewer transformers/converters in the propulsion area; the low voltage system allows a more flexible switchboard room; fewer components saves weight; easier and safer operation; centralised placing enables easy and secure commissioning, operation, control and maintenance; a lower short circuit level; and a total harmonic distortion lower than 5 %.

    Hybrid Energy Storate Systems (ESS)

    Hybrid power systems combine different power sources with energy storage devices. The introduction of the hybrid power system, and its integration with conventional diesel-electric propulsion can offer a significant improvement in efficiency by running the engines at optimal load, and by absorbing many of the load fluctuations through batteries.

    The introduction of Hybrid Power Systems with energy storage is, therefore, a new and attractive means for reducing both fuel consumption and exhaust emissions.

    The Wärtsilä system’s design handles the energy storage capabilities in the form of a battery pack, an hybrid control system, a power transfer system, and an energy storage system. The key element in hybrid type power systems is how to store the energy safely and efficiently. The most available technology at present is batteries. The design and the capacity of an energy storage system will depend on how the system is to be used. Knowledge concerning the actual operational profile of the vessel is therefore important.

    The main objective of the Energy Management System is to control the vessel’s energy flow. Based on the selected operational mode, and whether the batteries are to be operated for peak-shaving or as the main source of power, the EMS has to control the number of engines online, whether the batteries are to be charged or discharged, and the rate of charging and discharging.

    Cruise and ferry applications 

    Most modern cruise liners and ferries are designed with converter-fed propulsion systems. These offer numerous advantages in terms of low noise and vibration-free operation, maximized cabin related loading capacity, more economic operation - especially the improved efficiency in partial propulsion power mode, a high degree of reliability, availability and redundancy, lower emission levels, and reduced wear and tear.

    Depending on the required grade of redundancy, and on the operational profile of the vessel, synchro-converter (LCI) or PWM-converter drives with synchronous or induction motors provide well proven and reliable solutions for propulsion systems.

    Seven Seas Voyager neu

    Offshore applications

    The propulsion systems for offshore, pipe and cable laying, as well heavy lift jack-up vessels, need to be designed with excellent dynamic characteristics in order to carry out rapid changes in speed and reversals during manoeuvring and positioning.

    The speed control of the propulsion and thruster motors is realized via frequency converters with pulse-with modulation (PWM) in HV- or LV-technology. The converters are designed (in the standard solution) with a diode rectifier on the mains side, an insulated gate bipolar transistor (IGBT) or an integrated gate commutated thyristor inverter (IGCT) on the motor side, DC- capacitors in the intermediate circuit, and a control system.


    Each PWM-Converter drive is equipped with a Wärtsilä Propulsion drive control panel, which controls and monitors the drive and provides the torque set value via bus connection to the PWM-Converter control. Additionally, actual data including, for example, measured values, alarms, etc., are received from the converter control for continuous data processing, which is then displayed on the 15” touch screen panel mounted in the front door. The Propulsion control panel is also interfaced with the superior ship’s automation, control and monitoring system via a serial data line.

    Special vessels applications

    Propulsion for Research and Survey ships, as well as Fishery Supervision Vessels
    Wärtsilä has delivered the low noise diesel-electric propulsion systems for many research and survey vessels. These propulsion systems are based on the principle of speed controlled DC or AC motors driving the propeller directly or via gears. The most reliable and low noise design is the direct drive.

    Propulsion for Multi-purpose Vessels and Icebreakers
    Multi-purpose vessels and icebreakers require propulsion systems with excellent dynamics to permit the flexible use of the torque speed characteristic, up to high-over torques and propeller standstill.


    With more than 200 installations worldwide, our propulsion systems deliver power for cruise liners and ferries, cable laying vessels, heavy-lift jack-up vessels, research and offshore vessels, and mega yachts – with a combined total of more than 3.000 MW.


      Control System

      The control system of converter-fed propulsion drives is designed for:

      • Four-quadrant operation with reversal of torque and rotational direction, with feedback of the reverse power to the main alternators and to the mains respectively to braking resistors in case of reversing manoeuvre and
      • continuous speed control from 0 to 100 % of the rated speed

      All operational requirements are achieved automatically via the electronic control device. Electronic control is achieved using microprocessor controlled devices, and it also includes the I/O channels necessary for monitoring and alarm functions integrated into the propulsion control system.

      Propulsion Control & Energy Management Systems

      In the Wärtsilä Propulsion Control System, the drives are configured as subordinated consumers for the power system. The propulsion output is automatically reduced if the momentary consumption exceeds the power available from the supplying diesel generator sets. In combination with the power management system, diesel generator sets are started, synchronized, and stopped automatically. In order to retain stable operation of the power plant at all times, the power consumption of the propulsion drives is reduced if:

      • the apparent current of the alternators reaches the nominal value
      • the active power of the diesel alternator set exceeds the nominal value or
      • the speed of the diesel engine decreases below the admissible value

      In the case of manoeuvring or crash stop operations, the reverse power generated by the propulsion motors is fed back to the main alternators and to the mains. In order to retain stable operation of the power plant also during this operation, the reverse power generation of the propulsion drives is reduced if the speed of the diesel engines increases above admissible values.

      Where Hybrid systems are used, the Wärtsilä Energy Management System is used to optimize the power flow in the system, including control of charging and discharging the energy storage and setting the speed of the engines, in addition to the standard functions of the Propulsion Control System and the Power Management System.

      Monitoring Screen Displays

      For local monitoring and auxiliary control of the propulsion system, colour touch screen displays are provided at each propulsion control panel and on the ECR control console with the following mimics and functions:

      • OVERVIEW with a general illustration based on single-line diagrams with the position of the circuit breakers, with values and alarm measuring
      • MOTOR and CONVERTER with a detailed view of the propulsion motors and frequency converters with values and alarm measuring
      • FAULTS with a detailed explanation of the alarm event, the alarm history, and a detailed help function
      • CONTROL with start, stop and speed control by push buttons, acting like a motor potentiometer
      • SET-UP with parameter settings as acceleration ramps, lever characteristic, speed set points, power limitation, and temperature limits, as well as controller settings
      • Display of measured values for failure diagnostics

      Remote Control System

      For remote control of the propulsion drives, a combined speed control and telegraph system can be provided as the command and communication system, designed for sending speed commands from the wheelhouse, bridge wings, engine control room (ECR) or local control consoles to the converter controls. Additionally, operation panels with illuminated push buttons, warning lamps, emergency stop, safety device indications, an overriding device, control transfer facilities, control switches, and speed and power meters can be included.

      • Silver Dawn

        When Silversea’s luxury cruise liner Silver Dawn needed a high-quality, reliable and quiet propulsion system, Fincantieri shipyard turned to Wärtsilä.

        Read more
      • Discovery Princess

        Princess Cruises relies on Wärtsilä’s propulsion system for minimal engine noise and vibrations and ultra-reliable operation on its vessel Discovery Princess.

        Read more


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