Active Rectifier Reactive Current Injection for Lower DC Link Voltage
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Solution Overview
Problem
Aerospace power systems face challenges with high power frequencies, leading to increased voltage drops and limited options for high-voltage components, resulting in high switching losses, costs, and lead times for semiconductor devices, which are exacerbated by the need for high DC link voltages in active rectifiers.
Innovation Solution
A power generation system that includes a variable frequency generator and a current injector with a controller to provide an injection current with both real and reactive components, maintaining a power factor of at least 0.9, which reduces the modulation index of the DC link voltage without increasing the voltage, thereby mitigating over-modulation and the need for high-voltage components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If active rectification is used in aerospace power systems with high frequency (up to 800Hz), then AC to DC conversion is achieved, but voltage drop across rectifier inductance increases significantly
Solution Approach 1:
The patent changes the operating parameters by limiting the DC link voltage to 700V or below, which fundamentally alters the rectification operation mode. This parameter change allows the system to operate at high frequencies without experiencing excessive voltage drops, as the lower voltage level reduces the proportional impact of inductive losses.
2Loss of energy
If DC link voltage is increased to compensate for voltage drop at high frequency, then power conversion efficiency improves, but higher voltage power switches and capacitors are required
Solution Approach 1:
The patent applies parameter changes by deliberately constraining the DC link voltage to 700V or below, which resolves the contradiction by showing that high frequency operation can be maintained without requiring high voltage components. This parameter constraint prevents the need for expensive high-voltage switches and capacitors while managing switching losses through alternative means.
Solution Approach 2:
The patent employs dynamic control strategies to manage the rectification process at high frequencies with limited voltage headroom. By dynamically adjusting operating parameters and using advanced control algorithms, the system optimizes performance within the 700V constraint, preventing excessive voltage drops and switching losses without requiring higher voltage ratings.
3Power
If higher voltage switching devices are used to handle increased DC link voltage, then power handling capability improves, but cost and lead time increase significantly
Solution Approach 1:
The patent resolves this contradiction by changing the voltage parameter constraint to 700V or below, which allows the use of lower voltage, lower cost switching devices with shorter lead times. The power handling capability is maintained through optimized control strategies and efficient use of the available voltage headroom, eliminating the need for expensive high-voltage components.
4Strength
If reactive current injection is applied to reduce DC link voltage, then modulation index is reduced and component stress decreases, but power factor must be maintained above 0.9
Solution Approach 1:
The patent applies parameter changes by injecting reactive current to reduce the DC link voltage to 700V or below, which reduces the modulation index and component stress. The power factor control is managed through coordinated control of the reactive current injection, ensuring it remains above 0.9 while achieving the voltage reduction benefit.
Data Source
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AI summary
A power generation system includes a generator (110) configured to output alternating current (AC) power, an active rectifier (120) configured to receive the AC power from the generator (110), convert the AC power to direct current (DC) power, and output the DC power. A current injector (130) is connected to the active rectifier (120) and is configured to provide an injection current to power flowing through the active rectifier (120). The injection current includes a reactive component.