Three-Level Inverter Phase Legs for Turbine Engine Starters
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Solution Overview
Problem
Conventional start inverters for electric engine starters in aircraft engines experience high ripple currents due to sub-transient reactance, leading to larger component requirements and inefficiencies.
Innovation Solution
A three-level inverter system with a pulse width modulator using carrier waves, reference waves, and command signal generators to reduce ripple current by applying phase disposition or phase opposite disposition modulation techniques, effectively converting DC power into AC power with minimized ripple.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional two-level inverter phase legs are used, then the inverter can provide sufficient power, but high ripple current is generated due to sub-transient reactance requiring larger components
Solution Approach 1:
The inverter phase legs are segmented into three-level configurations instead of conventional two-level designs. This segmentation divides the voltage output into three distinct levels (positive DC bus, zero reference, and negative DC bus), which reduces the rate of change of voltage (dv/dt) and consequently reduces ripple current generation while maintaining power output capability.
Solution Approach 2:
The patent transitions from a two-level voltage output structure to a three-level voltage output structure, adding an additional dimension to the voltage hierarchy. This dimensional change introduces a midpoint reference level between the positive and negative DC buses, enabling reduced ripple current through more gradual voltage transitions.
2Reliability
If solid-state switching devices are sized to accommodate high ripple current, then reliable operation is achieved, but component size and system complexity increase
Solution Approach 1:
By segmenting the inverter into three-level phase legs, the current ripple amplitude is reduced, which allows solid-state switching devices to be sized for lower current ratings while maintaining reliability. This segmentation effectively distributes the stress on components, enabling smaller device sizes.
Solution Approach 2:
The patent changes the voltage level parameter from two-level to three-level operation, which fundamentally alters the current waveform characteristics. This parameter change reduces the peak ripple current magnitude, allowing for smaller component sizing while preserving reliable operation under normal operating conditions.
3Object-generated harmful factors
If three-level inverter phase legs are used, then ripple current is reduced, but inverter structure complexity increases
Solution Approach 1:
While three-level phase legs do increase structural complexity compared to two-level designs, the segmentation into standardized modular units with consistent topology across phases allows for systematic implementation. The repeated modular structure mitigates some of the complexity increase through design standardization.
Solution Approach 2:
The patent converts the potential harm of increased structural complexity into a benefit by demonstrating that the three-level configuration, despite its added complexity, delivers significant reductions in ripple current that justify the structural investment. The complexity is transformed into a means of achieving superior electrical performance.
4Force
If peak current is increased to maximize torque, then starter-generator torque is maximized, but ripple current increases requiring larger components
Solution Approach 1:
By transitioning to three-level inverter phase legs, the patent adds a dimensional advantage in voltage control that allows peak current to be increased for maximum torque while the three-level structure simultaneously suppresses ripple current through its inherent voltage transition characteristics, resolving the trade-off between torque and ripple.
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 reduces peak current ripple, allowing for equivalent peak fundamental current flow, thereby maximizing torque provided to the starter-generator while minimizing component size and improving efficiency.
Implementation Method 1
A three-level inverter system with a pulse width modulator using carrier waves, reference waves, and command signal generators to reduce ripple current by applying phase disposition or phase opposite disposition modulation techniques
Data Source
AI summary
A start inverter for an electric engine start scheme includes an inverter phase leg with solid-state switches and a pulse width modulator operatively connected to the solid-state switches of the inverter phase leg. The pulse width modulator provides command signals to the solid-state switches of the inverter phase leg to invert direct current into alternating current with less ripple than a start inverter with two solid-state switches per phase leg.