Brushless Doubly Fed Starter Generator DC Excitation
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Solution Overview
Problem
Conventional brushless starter generators face challenges in supplying short circuit current due to the inherent design of induction machines, where excitation collapses when a short circuit is applied, making them less effective compared to wound field machines.
Innovation Solution
A brushless doubly fed induction generator is designed with a rotor and stator configuration that includes power windings and control windings, where direct current is supplied to the control windings to produce a magnetic flux, enabling the rotor to generate alternating current in power windings, even at varying shaft speeds, and allowing for the supply of short circuit current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a standard induction machine is used for a brushless starter generator, then the machine is less expensive, less complicated and less heavy compared to wound field machines, but the excitation collapses when a short circuit is applied, making it difficult to supply short circuit current
Solution Approach 1:
The stator windings are segmented into two independent sets: control windings connected to a DC power source for excitation, and power windings connected to the load. This segmentation allows the control windings to maintain magnetic flux during short circuits while the power windings handle current supply, resolving the contradiction between simplicity and short circuit capability
Solution Approach 2:
A DC power source is introduced as an intermediary element to provide excitation current to the control windings. This intermediary ensures continuous magnetic flux maintenance during short circuit conditions, enabling the induction machine to supply short circuit current without compromising its inherently simple structure
2Adaptability or versatility
If direct current is supplied to control windings to produce magnetic flux, then the rotor can generate alternating current in power windings at varying shaft speeds, but the device complexity increases compared to conventional induction machines
Solution Approach 1:
The control windings serve multiple functions: they establish the magnetic flux necessary for induction and can operate with varying shaft speeds. By making the control winding system multi-functional, the patent achieves variable speed adaptability without proportionally increasing overall device complexity
Solution Approach 2:
The patent changes the excitation parameter from AC to DC, and introduces independent control over the magnetic flux. This parameter change enables the system to maintain functionality across varying shaft speeds by adjusting DC excitation levels, achieving versatility while managing complexity through controlled parameter variation
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides a simpler, cost-effective, and efficient induction machine capable of supplying short circuit current, competing with wound field machines in the market, particularly suitable for smaller aircraft applications.
Implementation Method 1
The control windings are electrically connected to a power source, which provides direct current as excitation current to the control windings, thereby producing a magnetic flux
Implementation Method 2
The rotor moves through the magnetic flux, thereby generating an alternating current in the power windings as an output current
Data Source
AI summary
A doubly fed brushless induction starter generator includes a stator and a rotor, which are separated by an air gap. The stator includes stator winding slots, each of which includes a first layer of power windings, a second layer of power windings, and a third layer of control windings, which include 2-pole single-phase windings. The control windings are arranged in the stator winding slots between the air gap and the first and second layers of power windings. Direct current is delivered to control windings in the generator as an excitation current to thereby produce a magnetic flux, through which the stator is moved to produce and alternating current in the power windings as an output current. The output current can be delivered to an electrical load, such as an electrical component on an aircraft.