DC Link Capacitor Isolation for Aircraft Fault Current Protection
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Solution Overview
Problem
The challenge of managing high fault currents resulting from the discharge of DC link capacitors in electrical power systems, particularly in electric and hybrid-electric aircraft, which can exceed component ratings and cause damage due to the collapse of voltage across the capacitor.
Innovation Solution
Incorporating a power semiconductor switch in series with the DC link capacitor and a control unit that responds to faults by opening the switch to prevent capacitor discharge, utilizing hardware-implemented control mechanisms and specific semiconductor devices like depletion-mode MOSFETs or JFETs, and employing a control unit with a potential divider and comparator to manage the switch state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a DC link capacitor is used to maintain smooth DC output waveform, then power quality is improved, but fault current magnitude increases due to capacitor discharge
Solution Approach 1:
The patent extracts the harmful discharge path from the system by introducing a series switch between the DC link capacitor and the DC electrical network. This switch isolates the capacitor during faults, preventing the discharge current from flowing into the network while preserving the capacitor's voltage-smoothing function during normal operation.
Solution Approach 2:
The series switch acts as an intermediary element between the DC link capacitor and the DC electrical network. It mediates the connection by being normally closed to allow capacitor discharge for smoothing, but can open to block harmful fault currents while still permitting the capacitor to maintain voltage stability during normal conditions.
2Reliability
If traditional protection methods are used (turning on all transistors or adding parallel diode), then component protection is improved, but device complexity increases
Solution Approach 1:
The patent removes the need for complex protection circuits by extracting the protection function into a simple series switch with basic control logic. Instead of requiring all transistors to turn on or adding parallel diodes, the solution uses a single series switch that opens to block fault current, significantly reducing the complexity of the protection mechanism.
3Object-affected harmful factors
If series switch is added to prevent capacitor discharge, then fault current is reduced, but device complexity increases
Solution Approach 1:
The series switch serves multiple functions: it enables the DC link capacitor to provide voltage smoothing during normal operation by being closed, and it provides fault current protection by opening during faults. This multi-functionality justifies the addition of the switch while delivering both smoothing and protection benefits from a single component.
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
Effectively prevents damage to power converters by isolating the DC link capacitor during faults, ensuring faster response times and reducing component size and mass through targeted discharge management.
Implementation Method 1
a DC link capacitor connected between the first and second DC output terminals
Data Source
AI summary
An electrical power system and an aircraft including an electrical power system are provided. The electrical power system includes: an electrical power source; a DC electrical network; a power converter including at least one input terminal and first and second DC output terminals, the at least one input terminal connected to the electrical power source, the first and second DC output terminals connected to the DC electrical network; a DC link capacitor connected between the first and second DC output terminals; a power semiconductor switch connected in series with the DC link capacitor between the first and second DC output terminals; and a control unit configured to respond to a fault in the DC electrical network by opening the power semiconductor switch, whereby discharge of the DC link capacitor is prevented.