Design development of brushless doubly fed machines

Brushless doubly fed machines (BDFMs) are gaining research interest globally as they offer a practical and reliable alternative to doubly fed induction generators (DFIGs), especially in remote areas like offshore wind sites. For his PhD research, Dr Olubamiwa tackled other aspects concerning the design of BDFMs. He presented an exhaustive review of BDFM design illustrating the evolution of BDFMs and providing context behind contemporary designs; an innovative methodology for the design of BDFMs was also developed. A systematic design evaluation approach was highlighted which helps ensure optimised BDFM designs comply with wind turbine grid code requirements. The design evaluation method was also shown to provide an analytical framework for comparing DFIGs and BDFMs and determining suitable pole pair combinations for BDFMs. Dr Ore Olubamiwa explains that:

“The most common generators used in onshore wind turbines are DFIGs. However, DFIGs use slip rings and brushes that tend to fail quite often. Offshore wind sites are gaining traction in the wind energy industry, but they typically have low accessibility. The incessant slip ring and brush issues complicate DFIG usage in offshore sites, as the lack of accessibility increases the operational and maintenance costs. An interesting research direction in solving this problem is the use of BDFMs instead of DFIGs. BDFMs have better reliability compared to DFIGs due to the absence of slip rings and brushes. BDFMs share very similar advantages to DFIGs, in that they don’t use a fully rated converter, and have a wide speed range and power factor control. BDFMs are capable of synchronous torque operations just as in DFIGs. and also have superior low-voltage ride-through characteristics compared to DFIGs. However, BDFMs have a complex machine structure, and their operations are relatively complicated.”

Dr Oreoluwa Olubamiwa with Dr Nathie Gule and Professor Maarten Kamper of the Department of Electrical and Electronic Engineering, Stellenbosch University, presented in their published article, a coupled circuit model of BDFMs with nested loop and cage+NL rotors, which uses the winding function theory. With this robust model, a quick method for determining suitable rotor topologies for specific BDFM applications was demonstrated. Critical information necessary for BDFM rotor design is also rapidly accessible using the model.

Figure 1: Brushless doubly fed machine prototype

You can find more information in the following published research papers:

  1. O.I. Olubamiwa, N. Gule, and M.J. Kamper, “Coupled circuit analysis of the brushless doubly fed machine using the winding function theory,” IET Electric Power Applications, vol. 14, pp.1558-1569(11), September 2020.
  1. O.I. Olubamiwa, N. Gule, “A Review of the Advancements in the Design of Brushless Doubly Fed Machines”, Energies, vol. 15, no.3, pp 725, January 2022.
  1. O.I. Olubamiwa and N. Gule, “Prioritizing power factor in power density assessments of doubly fed induction generator alternatives,” in 2020 International Symposium on Power Electronics, Electrical Drives, Automation and Motion (SPEEDAM), June 2020, pp. 47-52.
  1. O.I. Olubamiwa and N. Gule, “Design and optimization of a cage + nested loops rotor BDFM,” in 2020 International Conference on Electrical Machines (ICEM), vol. 1, August 2020, pp. 1868-1874.

Leave a Reply

Your email address will not be published. Required fields are marked *