Self-Commutating Switched Reluctance Generator for Aerospace
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Solution Overview
Problem
Switched reluctance generators face inefficiencies and reliability issues in aerospace applications due to complex control requirements and sensor dependency, leading to increased size, weight, and reduced reliability compared to permanent magnet alternators.
Innovation Solution
A self-commutating switched reluctance generator with variable flux and independent winding control, utilizing peak flux only under transient conditions, and employing stored timing data to optimize energization and reduce power losses, eliminating the need for complex timing functions and sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a switched reluctance generator uses complex control systems with shaft encoders and microprocessors to provide timing data for current flow control, then the generator can achieve precise control of power output, but the system reliability decreases and device complexity increases
Solution Approach 1:
The SRG controller uses self-commutating control where the controller monitors its own output voltage and uses zero-crossing detection to automatically determine when to switch excitation windings, eliminating the need for external timing signals from shaft encoders or resolvers. The controller stores timing data from previous cycles and uses it to predict optimal excitation timing, making the system self-sufficient and highly reliable without complex external sensors.
2Reliability
If a permanent magnet alternator operates at fixed current to ensure safe short circuit operation, then the system is simple and robust, but the generator efficiency is limited to maximum 50% and power must be fixed during design
Solution Approach 1:
The SRG controller dynamically adjusts the excitation current and timing based on real-time monitoring of output voltage and load conditions. Unlike fixed current PMA operation, the SRG controller varies the excitation current magnitude and duration cycle-by-cycle to optimize power transfer efficiency while maintaining safe operating limits during short circuits. This dynamic control enables efficiency exceeding 50% while preserving system robustness.
Solution Approach 2:
The controller changes multiple parameters including excitation current magnitude, excitation timing duration, and switching frequency based on operating conditions. By adjusting these parameters dynamically, the SRG achieves optimal efficiency across varying load conditions while maintaining the ability to safely handle short circuit currents, overcoming the fixed parameter limitation of traditional PMA designs.
3Loss of energy
If a switched reluctance generator uses variable flux with peak flux only under transient conditions, then the power losses are reduced and efficiency is enhanced, but the control complexity increases
Solution Approach 1:
The controller automatically implements variable flux operation by monitoring output voltage and using stored timing data to determine optimal excitation duration. During steady-state operation, the controller limits excitation to reduce losses, while automatically increasing excitation duration and magnitude during transient conditions or load changes to maintain voltage regulation. This self-adjusting behavior reduces power losses without requiring complex external control systems.
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
This approach enhances efficiency and reliability by reducing power losses and eliminating the need for complex control systems, achieving higher integrity and fault tolerance suitable for aerospace applications.
Implementation Method 1
A switched reluctance (SR) motor or generator consists of a number of windings designed to create flux paths within the machine that change in length, or reluctance, as the machine moves or rotates
Implementation Method 2
The magnetic concept of 'reluctance' represents the difficulty that flux has in completing a complete circuit. Most energy in the machine is stored in these reluctance elements and it is the change in reluctance (effectively length) of these flux paths that drives the energy conversion process from mechanical to electrical within a SR machine
Data Source
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AI summary
The present Invention provides a switched reluctance generator and devices and methods for the control of such a generator. It Is particularly concerned with generators and controls which can operate in an aerospace environment. The generator may have: a rotor having a plurality of rotor poles; a stator having a plurality of stator poles; and a controller, wherein: either said plurality of rotor poles or said plurality of stator poles each have windings to which current can he supplied to energise said poles and from which current can be drawn to a load; and the controller is arranged to: periodically excite each of the windings In turn to a pre-determined level of current; measure the current generated in each winding; cease the excitation when the current generated in each winding exceeds the excitation current; and direct the generated current in each winding to the load. The generator may thereby avoid the need to determine the position of the rotor poles relative to the stator poles to provide the commutation of the generator. The generator can thereby be made self-commutating without the use of complex sensors or microprocessors, which significantly improves Its reliability and certifiability.