Challenges and Opportunities for Wound Field Synchronous Generators in Future More Electric Aircraft

Abstract

Electrical machines and drives keep moving away from traditional technologies such as brushed machines and wound field machines towards lighter, 'easier to maintain' machines. A very interesting aspect is that certain transport applications, especially the aerospace industry, still favour the classical wound field machine for its main generating system such as the Boeing 787.This paper focuses on investigating this particular trend by presenting a detailed overview of historical power generation systems on aircraft. This paper compares the current state of the art of wound field machines with other generator families. The results of this analysis are then projected into the needs of the electrical power generation and distribution system on aircraft. While power density is a major objective for any aerospace application, however the extra benefits associated with wound field systems are still essential in modern aircraft.The paper then focuses on the main challenges for improving power density of wound field machines. Recommendations, opportunities and improvements related to wound field machines are discussed. In conclusion, if robust designs for higher speed wound field generators were consolidated, it would be very probable that these classical machines might still be implemented on future MEA platforms.

High-Power Machines and Starter-Generator Topologies for More Electric Aircraft: A Technology Outlook

“…The different designs can be calculated in terms of GOD (using rated P and n) and then be categorized onto different GOD levels of performance (complexity of design), e.g., 1E5, 3E5, 5E5, 5.7E5 and 1E6 [21].…”

“…(DOL) arrangement has been extensively employed for more than 60 years [21], and it has been used in commercial solutions like Airbus A340 and Boeing B777 [58]. However, the constant speed drive (CSD) is a complicated, large and heavy system (i.e., input speed with heavy mechanical gearboxes), and performs with poor generation efficiency and inferior trustworthiness [3], [39].…”

“…The 'variable-speed variable-frequency' (VSVF) system has recently been captivating interest (i.e., "frequency-wild AC system"), where the first commercially available largescale implementation of this category is employing four 120/150 kVA VF generators in the Airbus A380 platform. Moreover, VSVF technology is also found in Boeing B787 [21]. Recently, a 'variable-voltage' bus strategy has been proposed to enhance the power management [62].…”

“…A multitude of machine technologies have been suggested for high-power machines or S/G applications [32], [67], including 1) wound-field synchronous machines (WFSMs) [21], [68], 2) permanent magnet machines (PMMs) [69], [70], 3) induction machines (IMs) [71]- [73], and 4) reluctance machines (RMs) [74]- [77]. regarding the electrical machine families are the focus for Sections IV and V. Since IMs, PMMs and RMs demands active PEC at the stator-side, all of them will automatically include S/G functionality, they will be treated as an S/G hereafter.…”

“…In MEA systems, the electric power is secondary [20], meaning that all propulsion power is directly originating from fuel engines (without electrical conversion). While Boeing 787 still favour classical wound-field synchronous machine (WFSM) generator technology [21] for secondary electric power, the E-Fan X project employed the PMM as its main generator [1], contributing to primary electric power as well. This highlights the fact that there is still an ongoing debate on the most suitable machine topologies.…”