A quantum leap in marine technology
To be historically accurate, shaft generators came into the picture as a way to optimize vessel energy efficiency. Despite the most recent reversal in fuel price development, the long-term aim is to seek ways to reduce a vessel’s consumption. Additionally, the enforcement and strengthening of the pollution prevention standards according to MARPOL are driving the need to reduce emissions and make marine technology greener. Regardless of the starting point, shaft generators are undoubtedly the right solution.
Fortunately for us, there is still one overlooked area that makes this technology even more interesting. To start, let’s list some requirements taken from a classification society: THD less than 8%, operating frequency in a steady state within +/- 5%, and the voltage variations allowed in a transient state of -15% to +20%. Although these requirements are generally achievable with even a rather basic frequency converter, it is only possible with heavy filtering.
In contrast, The Switch’s state-of-the-art 4Q converter with vector control can easily reach a THD of less than 3%, extremely precise frequency control and a voltage transient dip of 0%.
When a vessel’s electrical power is entirely produced by gensets, the control and stability of grid become a mechanical issue. Hence, when comparing the electrical dynamics, an advanced converter will see impedance instead of inertia and available electrical torque instead of fuel injection. Clearly, we can raise the bar when it comes to the grid quality.
Let’s not forget that frequency converters have not come to replace gensets yet. Every industry is ultimately conservative. Thus, despite aiming for better solutions, the goal also is to minimize risk.
In a distributed vessel grid, we find two types of electrical sources: one or more synchronous generator gensets and one or more frequency converters working in parallel. Yet one classic problem still remains: load share.
Yes, The Switch frequency converters now also handle the droop control of vessel grids. Being able to fully control the load share among all sourcing branches is such a positive step that we now also have an extra degree of freedom to balance a perfect trade-off between redundancy and efficiency. Think about the reliability improvement when converters can keep gensets running with minimum fuel consumption while still being ready to enter if something goes wrong.
We can safely say that marine technology has taken a quantum leap forwards by giving more responsibility to power electronics.
It took quite a while for power converters to come about. But now that they are here, there’s still work to be done to help this application move more mainstream. In the end, grid quality and shaft generator solutions are inherently related. And power electronics give us powerful tools to continuously develop new and more energy-efficient solutions for vessels to navigate the seas.
José Galvez
Product Manager, Converters