A Brushless Hybrid Excited Starter-Generator With Independent Excitation Flux Circuit for Aircraft AC Power Generation

To improve the power density and efficiency of starter-generators (SGs) for aircraft ac power systems, a hybrid excited SG (HESG) with an independent excitation flux circuit is presented in this article. Thanks to the Halbach-array permanent magnet (PM) arrangement, isolated PM, and electrical excited (EE) rotor magnetic paths, this topology is capable of handling strong overload capability and high efficiency. Then, the principle of flux regulation is revealed based on the magnetic equivalent circuit (MEC) and 3-D finite element analysis (3-D-FEA). Then, the key parameters, such as PM thickness, PM segments, PM rotor length, and EE rotor offset distance, are determined to improve the air-gap flux density and power density, and to reduce back EMF harmonic components. Furthermore, the electromagnetic performance of the proposed HESG is investigated, including the no-load flux density distribution, voltage regulation, on-load output and regulating characteristics, loss, as well as efficiency. It is demonstrated that the proposed HESG efficiency can achieve 95.8%. Finally, a 60 kVA prototype is manufactured and tested to verify the FE-predicted results.