Aircraft Starter Generator Using Segmented Exciter and MOSFET Bridge
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Solution Overview
Problem
Conventional aircraft starter generator systems face challenges in efficiently controlling wide band gap devices for consistent power generation, particularly at low speeds where synchronous machine-based exciters struggle to generate sufficient power for starting the engine.
Innovation Solution
A MOSFET-based bridge configuration with an inverter/converter/controller system using Space Vector Pulse Width Modulation (SVPWM) and reverse conduction based inactive rectification, along with a dual functional exciter stator that configures into AC and DC windings to provide necessary excitation currents in both start and generate modes, and sensorless rotor position estimation methods for accurate power switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If synchronous machine-based exciters are used in conventional starter generator systems, then the system structure is simplified, but the excitation power is insufficient at low speeds for starting the engine
Solution Approach 1:
The exciter is divided into two independent systems: a permanent magnet generator (PMG) providing excitation power during engine starting, and a synchronous exciter that operates after engine start. This segmentation allows each subsystem to be optimized for its specific function, with the PMG delivering high power at low speeds without the limitations of synchronous machines.
Solution Approach 2:
The permanent magnet generator acts as an intermediary system that bridges the power gap during engine starting. It provides the necessary excitation power when the synchronous exciter cannot operate effectively at low speeds, enabling successful engine start before transitioning to normal synchronous excitation operation.
2Loss of energy
If wide band gap devices are used in the inverter/converter, then switching losses and conduction losses are reduced, but control complexity increases to achieve consistent efficiency
Solution Approach 1:
The control system dynamically adapts its strategy based on operating conditions. SVPWM is used during engine starting when high power delivery is needed, while reverse conduction based inactive rectification is employed during power generation to minimize losses. This dynamic adaptation allows the system to maintain high efficiency across different operating modes without requiring overly complex control logic for each specific condition.
Solution Approach 2:
The control approach changes parameters based on operating mode: using active switching control (SVPWM) during starting and passive reverse conduction during generation. This parameter change strategy simplifies the overall control complexity by having distinct, well-defined control modes rather than requiring a single complex control algorithm to handle all conditions.
3Power
If a three electric machine set with permanent magnet generator is used, then excitation power and torque density are improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The permanent magnet generator is designed with multi-functionality to reduce overall system complexity. It serves as the excitation source during engine starting and can also contribute to power generation. This universal design approach justifies the addition of the third machine by providing multiple benefits across different operating phases, offsetting the increased device complexity.
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 solution enables efficient and reliable power conversion in both start and generate modes, minimizing losses and maintaining high efficiency across the entire speed range of the aircraft engine, with improved torque density and power generation capabilities.
Implementation Method 1
reverse conduction based inactive rectification
Implementation Method 2
Space Vector Pulse Width Modulation (SVPWM)
Implementation Method 3
utilize the aircraft engine after it has started in a generate mode, to thereby provide electrical energy
Implementation Method 4
a permanent magnet generator
Data Source
AI summary
An aircraft starting and generating system includes a starter/generator that includes a main machine, an exciter, and a permanent magnet generator. The system also includes an inverter/converter/controller that is connected to the starter/generator and that generates AC power to drive the starter/generator in a start mode for starting a prime mover of the aircraft, and that converts AC power, obtained from the starter/generator after the prime mover have been started, to DC power in a generate mode of the. A load-leveling unit (LLU) is selectively coupled with a DC power output from the starter/generator and has an inverter/converter/controller (ICC) with an LLU metal oxide semiconductor field effect transistor (MOSFET)-based bridge configuration that supplies DC power to the DC power output in a supply mode, and that receives DC power from the DC power output, in a receive mode. A LLU bridge gate driver is configured to drive the LLU MOSFET-based bridge during a supply mode and a receive mode using bi-polar pulse width modulation (PWM).