Power conversion in marine environments

Larger ships have a (diesel) generator and their own on-board grid to supply all electric users with power at the right voltage and frequency. Once in port, it is not desirable to deploy this autonomous system for several reasons. Noise and odor nuisance are the most important, but also emissions and costs are reasons to purchase so-called shore power in the port. One problem here is that the quality and specifications of shore power can vary greatly from port to port. Using it 1:1 on the ship is usually not possible. Shore power inverters offer a solution to convert shore power into power suitable for the specific ship.

Developments

Marpower is a company that develops and builds such shore power inverters. Two years ago, the company started developing a new generation that meets the requirements and wishes of today. In addition to the fact that the "installation of today" must be compact and light, there is also the desire to make it scalable and universally applicable, as well as easy to install, low-maintenance and, of course, affordable.

Figure 3 shows the operation schematically: 

On the left, shore power comes in as AC voltage. This is first rectified and then 'chopped' into a square wave that is finally converted by a second transformer to the desired AC voltage for the ship. Hans Zijlstra, commercial director of Elincom: "With regard to the transformers needed, there are many parameters that determine how reliable, efficient and effective the final solution is. Think in basic terms of heat generation and dimensions, but more technically in terms of maintaining sufficient inductance at high currents, parasitic capacity, spreading self-inductance and thus the ability to switch very quickly efficiently when chopping. In the development process it is important to make choices such that an optimum is achieved in this."

Collaboration

To best support Marpower in designing a compact, flexible and universal system without compromising on quality, safety and efficiency, Elincom engaged the German company Block. Block is one of the companies that Elincom represents in the Netherlands and supplies a variety of components to generate a voltage that exactly meets a client's specific requirements. A perfect partner to accurately specify the customer requirement with, make models and simulate them and finally do a lot of testing to arrive at an effective,
efficient and affordable solution. Danny Langbroek, general manager: "In addition to the challenges Hans already mentioned, with every design you also have to deal with production costs. Not every technical solution can be effectively converted into a series product. Furthermore, the technically best material choices for the core material or the winding wire are not always the best price choices either. In that process, we seek the balance, in close consultation with the customer and the factory."

Solutions

One of the choices Marpower made to make the shore power inverter efficient is to use the latest generation of SiC semiconductors. This allows a higher power density to be achieved, but also dictates water cooling. This ultimately results in the possibility of a higher switching frequency of 40 kHz, which allowed the installation to be dozens of times smaller and almost 98% lighter (11 kg for the new inverter compared to 500 kg for a traditional 50 kVA / 50 Hz transformer). Furthermore, much calculation and testing went into determining the correct winding configuration. For the mid-frequency coils used in the shore power inverter, Block chose the first configuration from Figure 4, which was implemented with 30 µm litz wire. All in all, an intensive project in which cooperation between partners, each with their own knowledge, led to a shore power inverter with the right specifications.

Visit Elincom at the WoTS - Booth number 9b049