Rectifier Input Short-Circuit Over-Voltage Protection
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Solution Overview
Problem
Electric machines, such as alternators and motors, face damage from over voltage conditions, particularly in critical applications like aircraft systems, where existing protection methods are inadequate.
Innovation Solution
A multi-phase alternating current generating electric machine system with a rectifier, low side and high side switching devices, a voltage sensing device, and a power control unit that short-circuits the rectifier input when the output voltage reaches a threshold and synchronizes removal with zero-crossing of phase current to prevent over-voltage damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If over voltage protection is implemented by short-circuiting the rectifier input, then the electric machine is protected from over voltage damage, but transient voltage spikes and switching surges may occur causing additional harm
Solution Approach 1:
The control system continuously monitors the output voltage of the rectifier and prepares to activate the short-circuit protection path before over-voltage damage can occur. When the voltage reaches a predetermined threshold, the protection mechanism is already in place to immediately divert the current, preventing both over-voltage damage and minimizing transient spikes by using pre-positioned switching devices.
Solution Approach 2:
The patent introduces an intermediary protection circuit with switching devices (transistors or thyristors) that act as a mediator between the rectifier input and the electric machine. This intermediary path provides a controlled short-circuit route that bypasses the rectifier during over-voltage conditions, eliminating direct switching surges while still protecting the machine. The intermediary switching devices are specifically designed to handle the transition smoothly without creating harmful transients.
2Device complexity
If simple voltage threshold switching is used, then the control system is simple, but it cannot prevent transient-free switching and may cause damage
Solution Approach 1:
The control system employs feedback by continuously monitoring the output voltage of the rectifier and using this information to control the switching devices. The feedback loop compares the actual voltage with a predetermined threshold and adjusts the switching state accordingly. This feedback mechanism enables the system to achieve transient-free switching while maintaining relatively simple control logic, as the switching decisions are automatically made based on real-time voltage measurements without complex algorithms.
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 system effectively limits the rectified DC output voltage, preventing damage from over-voltage conditions and ensuring transient-free switching, thus protecting the electric machine from voltage-related failures.
Implementation Method 1
a voltage sensing device operatively connected to an output of the rectifier for sensing an output voltage of the rectifier
Implementation Method 2
generating a signal that switches the low side switching devices to an on state when the output voltage of the rectifier reaches a threshold voltage
Implementation Method 3
at least one current sensing device operatively connected to the phases of the multi-phase alternating current generating electric machine
Data Source
AI summary
A system and method for protecting an electrical power generation system from an over-voltage. The output voltage of a multi-phase rectifier, operatively connected between the output terminals of an electric machine and a load, is monitored. The input of the multi-phase rectifier is short-circuited upon detection that the output voltage has reached a threshold voltage. Removal of the short-circuiting of the input of the multi-phase rectifier is synchronized with a substantially zero-crossing of phase current flowing through switching devices in the rectifier once the output voltage is no longer above the threshold voltage.