Alternator Load Dump Protection via MOS Transistor Control
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Solution Overview
Problem
Conventional alternators face challenges in effectively protecting MOS transistors from damage due to load dump surges, which occur when charging wires are disconnected, leading to transient voltage spikes that can damage electrical loads and alternator components.
Innovation Solution
An alternator design with a bridge circuit comprising switching elements connected in parallel with diodes, a field control section with a capacitor to monitor output voltage and implement a load dump protection mechanism by controlling the switching elements' turn-on and turn-off operations based on threshold voltages, thereby reducing the duration of high voltage exposure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If MOS transistors are turned on simultaneously when output voltage exceeds reference voltage to protect against load dump, then protection operation is executed, but delay time causes energy to increase terminal voltage of capacitance and damage internal circuit components
Solution Approach 1:
The patent applies preliminary action by turning on the MOS transistors in the lower arm before the output voltage reaches its peak during load dump conditions. The control circuit detects the load dump event and activates the protection mechanism proactively, preventing the voltage spike from reaching damaging levels rather than reacting after the voltage has already increased.
Solution Approach 2:
The patent implements dynamic control by adjusting the switching timing of MOS transistors based on real-time detection of load dump conditions. The control circuit dynamically modifies the operation of the bridge circuit components during transient states, optimizing the protection response while minimizing unnecessary voltage increases that would harm internal components.
2Productivity
If MOS transistors are turned off when output voltage decreases to reference voltage to resume rectifying operation, then rectifying operation is restored, but repeated turn-on and turn-off increases power loss and may damage MOS transistors
Solution Approach 1:
The patent applies periodic action by implementing controlled, periodic switching of the MOS transistors during load dump protection. Instead of continuous or frequent switching, the control circuit employs periodic action at optimized intervals, reducing unnecessary switching cycles while maintaining effective protection and minimizing power losses from repeated turn-on and turn-off operations.
Solution Approach 2:
The patent implements parameter changes by dynamically adjusting the reference voltage threshold and switching timing parameters based on the operational state. During load dump protection, the control circuit modifies voltage thresholds and timing parameters to optimize the balance between protection effectiveness and power loss reduction, preventing excessive switching that would damage MOS transistors.
3Reliability
If low pass filter is added to eliminate noise and prevent incorrect operation, then noise is filtered, but device complexity increases
Solution Approach 1:
The patent applies self-service by enabling the control circuit to inherently distinguish between noise and genuine load dump events through intelligent detection algorithms. The control circuit performs self-validation by analyzing voltage change patterns, timing characteristics, and threshold comparisons, eliminating the need for external low pass filters while maintaining reliability in preventing incorrect operations.
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
This design effectively prevents high voltage generation during load dumps, increasing the reliability of the alternator by minimizing power loss and reducing the risk of MOS transistor damage, ensuring prolonged and efficient rectifying operations.
Implementation Method 1
a capacitor (80) connected in parallel to an output terminal of the rectifying module groups (5, 6)
Implementation Method 2
The lower arm is comprised of switching elements (51, 61). Each of the switching elements (51, 61) is connected in parallel to a diode (52, 62). The switching sections receive and rectify a voltage induced by the armature windings.
Implementation Method 3
Each of the switching elements (51, 61) is connected in parallel to a diode (52, 62)
Data Source
AI summary
An alternator has rectifying module groups. The rectifying module groups form a bridge circuit. The rectifying module groups have a load dump protection judgment section for monitoring an output voltage of rectifying module groups. When the monitored output voltage exceeds a first threshold voltage, the load dump protection judgment section provides to a control section an instruction to turn on MOS transistors in a lower arm of the bridge circuit at a time when a predetermined delay time has elapsed. When a second threshold voltage is lower than the first threshold voltage and the monitored output voltage becomes less than the second threshold voltage after the monitored output voltage exceeds the first threshold voltage, the load dump protection judgment section provides to the control circuit an instruction to turn on the MOS transistors in the lower arm after the MOS transistors are turned off during a predetermined time length.