Reactive Current Injection in Aerospace Active Rectifiers
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Solution Overview
Problem
Aerospace power systems face challenges with high power frequency rectification due to increased voltage drop and limited options for high-voltage components, leading to high DC link voltage requirements, increased switching losses, and elevated costs, especially when semiconductor switch voltage ratings exceed 1200V.
Innovation Solution
A power generation system incorporating a variable frequency generator with an active rectifier and a current injector that provides an injection current with both real and reactive components, controlled by a controller using lookup tables or equations to maintain a power factor of at least 0.9, reducing the modulation index in the DC link voltage without increasing the DC link voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If active rectification is used in aerospace power systems with high power frequency (up to 800 Hz), then AC to DC conversion is achieved, but voltage drop across rectifier inductance increases significantly
Solution Approach 1:
The patent changes the electrical parameters by injecting a reactive current component that shifts the power factor from unity to a leading power factor (0.85-0.95). This parameter change in the operating conditions allows the system to compensate for the increased inductive voltage drop at high frequencies, effectively reducing the net voltage drop across the rectifier inductance.
2Power
If higher voltage power switches and capacitors are used to accommodate high DC link voltage, then the rectifier can handle high power frequency operation, but component choices are limited and cost increases significantly
Solution Approach 1:
By injecting reactive current to create a leading power factor condition, the patent effectively reduces the DC link voltage requirement. This allows the system to use lower voltage rated components (1200V or below) that have better availability and lower cost, while still handling the same power level at high frequency through the compensated voltage relationship.
Solution Approach 2:
The patent converts the typically harmful effect of inductive voltage drop at high frequency into a beneficial control mechanism. By intentionally operating with a leading power factor, the system uses the reactive current injection to counteract the inductive drop, turning what would be a loss into a means of voltage regulation and component rating reduction.
3Power
If semiconductor switch voltage rating exceeds 1200V, then the rectifier can accommodate higher DC link voltage requirements, but switching losses increase significantly
Solution Approach 1:
The patent changes the operating parameters by maintaining DC link voltage at or below 700V through reactive current injection. This parameter control ensures that lower voltage rated switches (with lower switching losses) can be used, while the leading power factor operation compensates for the reduced voltage headroom by adjusting the current waveform to account for inductive drops.
4Ease of manufacture
If DC link voltage is limited to at most 700V to reduce losses and cost, then component cost and switching losses are reduced, but the rectifier must operate at high power factor with compensation
Solution Approach 1:
The patent implements a feedback control system where the controller continuously monitors the operating conditions and adjusts the reactive current injection magnitude and phase accordingly. This feedback mechanism maintains the leading power factor operation dynamically, automatically compensating for changes in load, frequency, or inductance to keep DC link voltage within the desired 700V limit while managing the increased control complexity.
Data Source
AI summary
A power generation system includes a generator configured to output alternating current (AC) power, an active rectifier configured to receive the AC power from the generator, convert the AC power to direct current (DC) power, and output the DC power. A current injector is connected to the active rectifier and is configured to provide an injection current to power flowing through the active rectifier. The injection current includes a reactive component.