In the quest to harness the full potential of offshore wind power, researchers are delving deep into the intricacies of generator design, seeking to optimize performance and reduce costs. A recent study led by Isaac Rudden from the University of Sheffield’s Electrical Machines & Drives Group has shed new light on the challenges and potential solutions for enhancing the saliency ratio of fractional-slot concentrated-winding (FSCW) generators, a crucial factor for sensorless control in offshore wind turbines.
Offshore wind turbines are increasingly relying on sensorless control to eliminate the need for shaft-mounted sensors, which can be costly and prone to failure. This method estimates rotor position based on the difference between the d- and q-axis inductances, a property known as saliency. However, FSCW generators, which are often used in offshore wind turbines due to their simplicity and robustness, tend to exhibit low saliency ratios, making sensorless control difficult.
“FSCW machines have larger stator teeth, which act like spatial low-pass filters, smoothing out the rotor saliency effects,” explains Rudden. “This makes it challenging to achieve the required saliency ratio for sensorless control.”
The study, published in Energies, investigates methods to improve the saliency ratio of FSCW machines, focusing on 3 MW generators suitable for offshore wind turbines. The researchers explored two main approaches: preserving the conventional machine geometry with minimal modifications, and altering the magnetic circuit.
The findings were clear: significant improvement in the saliency ratio could only be achieved through magnetic circuit modifications, such as adding rotor shoes between the permanent magnets. However, these modifications came with trade-offs, including reduced torque capability and increased rotor eddy current losses.
“While we were able to design machines with saliency ratios of 1.15 and 1.2, these came at the cost of reduced stator power,” Rudden notes. “This would lead to a decrease in annual energy production, making these designs infeasible for commercial use.”
Despite these challenges, the research highlights a promising alternative: a 384s/160p machine with dual star–delta windings. This design has shown a saliency ratio of nearly 1.2 and increased stator power compared to the baseline integer-slot winding machine. This structure could enable sensorless control, making it an attractive option for offshore wind power.
The implications of this research are significant for the energy sector. As offshore wind power continues to grow, the demand for efficient, reliable, and cost-effective generator designs will only increase. This study provides valuable insights into the challenges and potential solutions for enhancing the performance of FSCW generators, paving the way for future developments in the field.
As the energy sector continues to evolve, so too will the technologies that power it. This research is a testament to the ongoing innovation and exploration in the field, driving us towards a more sustainable and efficient future. The work, published in Energies, which translates to ‘Energies’ in English, underscores the importance of continued research and development in the pursuit of optimal generator design for offshore wind power.
