Overview of the development of marine electric propulsion
Ship electric propulsion is not a new term. This term appeared in 1838 and has a history of more than 160 years. Ship electric propulsion develops with the continuous progress of the ship and shipping industry and the electrical and power electronic technology. In the early 20th century, AC and DC electric propulsion systems have been used in ships. Looking back at the development of electric propulsion, there are roughly the following stages:
- Test period
At the end of the 19th century, Germany and Russia first began to test the application of electric propulsion using batteries as energy. After that, the first generation of electric propulsion was put into use in 1920, and the effect was obvious on small passenger ships across the Atlantic. This period lasted from the birth of electric boats to the beginning of the 20th century. During this period, most of the electric propulsion was powered by batteries, and DC motors were used as propulsion motors, and the power was below 75kW.
- Wide application period
In the 1920s and 1930s, although the technology of high-power steam turbines as the prime mover of ships was mature, due to the lack of mechanical processing level and capability, high-power ships from civil freighters, passenger ships, oil tankers to aircraft carriers mostly used electricity. Advance. Electric propulsion has been widely used in the popular period. In addition to special engineering ships such as submarines and icebreakers, the United States alone has 226 frigates and 488 civilian ships that use electric propulsion. The “New Mexico” electric propulsion battleship built by the United States uses steam turbines to generate electricity, and the total shaft power propelled by asynchronous motors has reached 4000-22000k W.
- Make full use of electric propulsion for a long period of time
In the late 1940s, due to the advancement of machining technology, especially the improvement of the processing capacity of gear transmissions, steam turbines and diesel engines became large-scaled, and the mass production capacity was also improved. However, the electric propulsion at that time was due to technical conditions. Restrictions, the device is large, heavy, low efficiency, and high cost, which severely limits its wide application. Therefore, most surface ships are propelled by steam turbines, diesel engines, gas turbines and various combined power plants.
In the 1950s, electric propulsion was mainly an adjustable-speed “generator-motor” DC system, and the speed regulation was realized by the variable resistance of the motor’s excitation circuit.
In the 1960s, semiconductor technology can ensure that the excitation is controlled by the thyristor system, which promotes the development of electric propulsion systems. In the mid-1960s, AC electric propulsion with variable pitch appeared.
In the 1970s, electric propulsion was characterized by the use of high-current semiconductor components to transfer the current of the three-phase AC generator used for the work of the ship’s general power grid to the electric propulsion device. However, the ship’s DC propulsion motor has a commutator and an electric Brushes have many shortcomings in use, such as sparks during heavy load and reverse rotation, commutator wear, brush burnout, electromagnetic interference, and maintenance difficulties. As the frequency conversion technology is still new under the conditions at the time, the available AC propulsion devices cannot provide the necessary capacity. The AC commutator motor has the same shortcomings as the DC variable speed system.
- A period of vigorous development
After the 1980s, the AC propulsion system that adjusts the speed of the propulsion motor by changing the current frequency and voltage supplied to the motor replaced the DC propulsion system, and various propulsion schemes realized by inverters and frequency converters have been widely used. The use of more compact and lighter AC propulsion motors-synchronous motors and asynchronous motors can enable the system to obtain higher frequencies and greatly simplify equipment maintenance. The following two systems using modern AC converter technology have been widely used:
(1) A system with a direct frequency converter and a quiet synchronous propulsion motor, suitable for 1~40MW power use;
(2) A system with a frequency converter with an intermediate DC link and an asynchronous propulsion motor. The motor speed range is 800 ~1500r/min, and it has a deceleration transmission device connected to the propulsion shaft. This type of propulsion device is suitable for 7~8MW Power usage.
In the late 20th century, the continuous improvement of power electronic device manufacturing technology and continuous improvement of control technology have greatly promoted the application level of commercial ship electric propulsion technology, and greatly improved the effective power level of the electric propulsion system. Electric propulsion has appeared in the application field of civil ships. With the unprecedented development and prosperity, the application scope of electric power merchant ships is expanding day by day.
In addition, the ship’s propulsion structure ranges from a single engine such as gas turbine, diesel engine or nuclear power to a variety of prime movers; the power level ranges from 100 kilowatts to tens of megawatts; the propulsion mode is more diversified, such as uses Extensive pod-style propulsion. Due to the use of control technologies such as pulse width modulation and cyclic frequency conversion, the control of the propulsion motor in electric propulsion is more reliable, and the power quality of various equipment on the ship is guaranteed. The above-mentioned series of changes make electric propulsion the development trend of ship propulsion technology.