The Doubly Fed Induction Machine as an Aero Generator

Abstract

Modern aircraft require a robust and reliable supply of electrical power to drive a growing number of high power electrical loads. Generators are driven by a mechanical offtake from the variable speed gas turbine, while a constant frequency AC network is preferred. Here doubly-fed induction machines are advantageous since they can be controlled, through a fractionally rated converter, to decouple electrical frequency from the mechanical drive speed, making control of the network frequency possible. However, the converter must be suitably rated, according to drive speed range, electrical voltage and frequency regulation, and power requirements. This paper develops and validates a simulation model of the doubly-fed induction generator system, which is applied to find the power flow through the machine's stator and rotor connections over a wide mechanical speed range in order to size the converter. A field orientated control scheme is implemented, to provide standalone voltage and frequency regulation across a drive range of ±40% synchronous speed, on a purpose-built 6.6kW hardware test platform. Based on the mechanical speed range of an aero gas turbine and the identified converter sizing, the suitability of a doubly-fed induction generator for aero applications is appraised. It is shown that a converter rated at 18% of full system rating can be used to meet the aircraft electrical specifications, and offer a potential improvement in aircraft performance, with no additional mechanical components.

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

“…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.…”

Electrical Machines and Power Electronics For Starter-Generators in More Electric Aircrafts: A Technology Review

“…Several machine technologies have been proposed for S/G applications [7], [20], including permanent magnet machines (PMMs) [21], [22], induction machines (IMs) [23]- [25], switched reluctance machines (SRMs) [26]- [29] and brushless wound-field synchronous machines (WFSMs) [30]. Fig.…”

“…A relatively large air gap (due to vibration) causes a significant stator current to sustain the magnetizing flux. Earlier investigations have shown the feasibility of the doubly-fed induction machine (DFIM) as an aero-generator [23]. It was primarily related to the replacement of the hydraulic constant speed drive (CSD), allowing variable speed for the engine.…”

“…With an inverter at 18% of the full system rating, it could achieve this target, with no mechanical components. However, it would generally require an excitation system for the rotor based on brushes and slip rings, considering that brushless configurations [23] are based on more complex control algorithms.…”

Experimental investigation of a Doubly-Excited Flux-Switching Machine for aircraft DC power generation

“…• No use of slip rings and brushes • DC generation using a diode bridge rectifier The most common electrical machines proposed in literature for this application are induction, switched reluctance and Permanent Magnet (PM) machines [8]. The advantages of an induction machine are well described in [9] and [10], however, it requires complex power electronics in generator mode and is considered unlikely to have the power density of its rivals [2]. The Switched Reluctance machine is characterized by an intrinsic high fault tolerance and high ruggedness due to its simple rotor construction [1], [11].…”