After more than 3 years of research, the FST (Flexible Smart Transformer) project has been successfully completed. Funded by the Grid 2030 innovation programme, the project has consisted in the development of a wireless power transfer module with a high capacity of isolation between the primary and the secondary side, allowing the development of new applications.
The FST project consists of the development of a new multi-purpose device with additional advantages compared to very high voltage power converters. Firstly, it proposes a magnetic coupling through a dielectric medium instead of a closed ferrite core in the high-frequency transformer stage. This modification reduces the weight significantly, gives intra-modularity and scalability to the system, and achieves a simple design of the very high voltage isolation. Secondly, the use of SiC (silicon carbide) technology helps to reduce the volume of the entire system. All these features help to drastically reduce maintenance and transportation costs.
On the other hand, it is expected to contribute to the decisive transformation of the current transmission grid paradigm to meet the challenges of decarbonisation of society. In fact, this innovation contributes to remove traditional insulations such as mineral oil, which means a significant reduction of pollutants. This new insulation method also allows for a significant volume reduction, which will contribute to a better integration from an environmental impact point of view.
Some of the potential applications are: Solid State Transformers (SST); AC/AC Converters; HV Flexible AC Transmission Systems (FACT); High Voltage Energy Storage Systems (ESS); HVDC Links; HV DC/DC; Unified Power Flow Controllers (UPFC) and Offshore Wind Farms.
The particularity of this development lies in the fact that it is designed for use in high-voltage transmission grids (230kV and 400kV in Spain) as a unified power flow controller (UPFC). This uniqueness poses two fundamental challenges, which have been tackled throughout the execution of the project:
- The device has had to be designed (based on a patent registered at the Spanish Patent and Trademark Office, reference number ES3462.6) in order to be connected to very high voltage networks. This challenge has been fixed using an inductive coupling in order to transfer power, solving the isolation problems presented by traditional dry transformers. On the other hand, the design has also considered achieving high voltage values by means of serialisation and parallelisation of several modules. This is possible because the system works with floating voltage references.
- The usual design of these devices is unidirectional, due to the nature of inductive power transfer applications (always from the grid to the load). Nevertheless, the FST module allows a bidirectional power transfer. This key feature enables an effective control of power flows within the network.
Both challenges have been successfully overcome, resulting in a module capable of overcoming these two technological barriers. The technical specifications of this device are listed in the following table:
A test bench has also been successfully executed to check the operating characteristics of the device, where it has been possible to evaluate the correct performance of the module.
The manufacturing of an UPFC based on the technology developed in the FST project will provide an ideal power electronics solution for the decarbonisation of the energy sector demanded by the current energy transition, achieving a substantial improvement in several aspects:
- Controllability of the electrical grid, as it will allow leading power flows, as well as controlling voltage levels, thus facilitating the penetration of renewable energies.
- Stability of the power grid, allowing the integration of additional impedance to avoid inter-area oscillations.
- Cost reduction, achieving a more efficient grid by means of power flow control, reducing transport costs as it is a totally modular system, reducing maintenance costs, etc.
- Environmental, as it is a cleaner equipment, with no need for coolant, thus eliminating the risk of contamination by waste.