What Is Electric Propulsion?

Electric propulsion refers to a propulsion method that uses electric power as the driving force. A ship relies on its own power generation device to obtain electricity to drive the ship's propulsion method. It has been used for more than 160 years.

The ship relies on its own power generation device to obtain electric energy to drive the ship's propulsion method. It has been applied for more than 160 years, so electric propulsion can be regarded as an ancient propulsion method.

In the early 20th century, steam turbines were first applied to ships. Due to the difficulties in manufacturing processes of high-power mechanical reduction gears, many military ships, such as frigates to aircraft carriers, and many large civilian ships such as oil tankers, passenger and cargo ships, etc. Both have adopted electric propulsion and developed various forms of electric propulsion devices. After World War II, with the advancement of science and technology, gear reduction gears that can meet the power requirements of ships have been mass-produced, and the electric propulsion devices under the technical conditions at that time had increased equipment due to the increase in energy conversion links A series of shortcomings such as high cost, low transmission efficiency, and heavy maintenance work, etc. Therefore, the ships use a large number of diesel engines, steam turbines or gas turbines to directly propel. However, due to the special advantages of electric propulsion-extremely superior flexibility, conventional submarines, engineering ships, icebreakers and other special-purpose ships that require good maneuverability, torque characteristics and response characteristics still widely use electric propulsion.

After the 1970s, electronic technology

When developing a candidate architecture for a new ship line type, the first task of the system engineer is to weigh the choice between mechanical propulsion and electric propulsion. If a ship has the following requirements, electric propulsion is a good candidate:

1. Very high guest room load or weapon load is electrical load.

2. The flexibility of major equipment placement should be high.

3. There should be more space for passengers or weapons.

4. Need to reduce vibration and noise.

5, reliability,

The speed control of electric propulsion needs to be continuously adjustable from zero power to full power in both the forward and reverse directions. The speed set value is compared with the actual speed feedback value to generate a speed deviation. The PI torque is used to obtain the propulsion torque value and sent to the frequency conversion device. The speed is adjusted by changing the motor frequency. However, during the adjustment process, the corresponding power should not exceed the maximum propulsion power limit of the available grid.

1. Prevent power outages

Under normal circumstances, propulsion of energy is the main part of the total load of the power station, so it must have the function of automatic load reduction and power failure prevention, and it must be highly coordinated with the power station design and energy management functions. The propulsion controller includes three levels of automatic load shedding in the logic to prevent power outages.

(1) The power management system calculates the maximum load limit from the available grid power. Based on the priority set by the energy allocation or energy management system, the maximum power that can be provided to the thruster is derived.

(2) Load reduction triggered by events. A typical approach is to drive a motor with a digital signal to reduce the load to a preset proportional level and a preset absolute value. This signal may come from the power management system or from the protection / control equipment inside the power distribution panel.

(3) Frequency-triggered load reduction. Measured based on local drive power frequency only. This is generally considered the ultimate protection in logic protection against under-frequency trips due to generator overload.

2. Power propulsion requirements for power stations

The control of the power plant in the electric propulsion system should meet the following requirements:

(1) Power station control shall ensure that there is sufficient power margin in the power grid to meet the needs of safe operation of ships operating under any circumstances.

(2) The generator set running in parallel shall have the control function of frequency and load regulation.

(3) The control of the power plant should be set up so that the failure of the control system will not cause the change of the existing power, that is, when the failure occurs, the generator set should not start or stop.

(4) When the power station is overloaded, it shall have the function of automatically unloading non-critical loads.

(5) The control system of the power station shall ensure the safe distribution of power between propulsion and daily loads. If necessary, offload non-critical loads and / or reduce propulsion power.

(6) When one generator set is not working, the remaining units should be able to supply power to all important equipment and ship's common equipment, while maintaining effective propulsion.

For example, under normal circumstances, two or more generating units are connected in parallel. When one of the generating units suddenly loses power, the remaining units in operation should be sufficient to ensure the uninterrupted operation and effective advancement of important equipment. ^[2]