Research and Development of the Utility Scale, Tocardo T4 Tidal Turbine

QED Naval and Tocardo turbines have successfully deployed a small scale tidal energy device. Their Gen 01
Subhub device has three generators and is designed for community scale projects (150 kW - 300 kW total), but
the ambition is to develop industrial scale (300 kW - 1.25 MW total), and utility scale (2 MW - 4 MW total).
The utility scale device is expected to have multiple generators, each with a rated power of approximately 1 MW.
This project concerns the development of this generator.
Tocardo's experience is in Permanent Magnet Synchronous Machines (PMSMs), which matches the wider
alignment of the wind and tidal industry. These machines are typically directly driven, and as such need to
develop high torques (so-called torque engines). Given the torque of a PMSM is linked to the current in stator
windings, thermal limits are usually the cause of torque limits in an electrical machine. As such, a machine that
could deliver greater thermal performance would be able to develop a higher maximum torque, which for this
application may be able to improve energy capture before field weakening at higher flow rates.
As such Tocardo has done preliminary design work for a so-called "open-core nacelle" topology, see Fig. 1. This
would replace the solid rotor shaft with a pipe, allowing sea water to flow freely through the turbine. This would
create an extra surface for cooling, improving the thermal performance without the need for flooding the nacelle,
or the installation of active cooling of the components. Both of the latter present operational challenges, which
in the tidal sector is something to be avoided.
As such, the aim of this project is to assess the design of the electrical machine within such a topology, and to
assess the effectiveness of the open-core nacelle topology through the use of thermal modelling. The aim is that
at the conclusion of the project a design for a MW scale tidal turbine will have been created. Depending on the
outcomes of the modelling this design may feature the open-core nacelle concept or may be a more conventional
PMSM optimised for the tidal environment. Finally, over the course of the project design tools and processes
will be assessed with the aim of improving Tocardo's design capabilities.