Active Bridge Rectifier Overvoltage Protection for Motor Vehicle Load Dump
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Solution Overview
Problem
Active bridge rectifiers in motor vehicle electrical systems face challenges in managing overvoltages during load shedding, as conventional protection strategies like short-circuiting phases are not robust enough to handle sudden voltage changes, leading to potential damage from oscillating voltages between threshold values.
Innovation Solution
A method that operates a motor vehicle electrical system with an active bridge rectifier, switching between rectifier and short-circuit modes, using filtered control signals and varying switching times to manage voltage thresholds, extending short-circuit mode duration when a cable break is detected, and reducing switching time when necessary to minimize transistor load and power loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional passive bridge rectifiers with Zener diodes are used for overvoltage protection, then robustness against overvoltages is improved, but power losses increase and efficiency decreases
Solution Approach 1:
The patent transitions from passive Zener diode clamping to active switching elements (MOSFETs/IGBTs) that can dynamically control the clamping voltage and timing. The control unit adjusts switching parameters based on detected overvoltage conditions, enabling efficient energy management while maintaining protection. This parameter change allows the system to achieve both robustness and efficiency by actively managing the protection mechanism rather than passively dissipating energy.
2Loss of energy
If active bridge rectifiers with MOSFETs are used to reduce power losses, then efficiency is improved, but robustness against overvoltages during load shedding deteriorates
Solution Approach 1:
The patent implements a control unit that continuously monitors the DC voltage at the rectifier output and detects overvoltage conditions during load shedding. When an overvoltage is detected, the control unit activates the switching elements to clamp the voltage, then deactivates them when voltage returns to normal. This feedback-based active control provides robust protection while maintaining the efficiency benefits of active rectifiers, resolving the contradiction between efficiency and robustness.
Solution Approach 2:
The system dynamically switches between different operating states: normal rectification mode, overvoltage clamping mode, and idle mode. The switching elements are activated only when needed for protection, rather than remaining continuously active or passive. This dynamic operation maintains efficiency during normal operation while providing robust protection during transient overvoltage events, resolving the contradiction between power loss and reliability.
3Reliability
If phase short-circuiting is used to protect against overvoltages, then overvoltage protection is improved, but voltage oscillation between threshold values increases causing instability
Solution Approach 1:
The control unit detects overvoltage conditions and activates the clamping function before the voltage can oscillate between threshold values. By responding quickly to detected overvoltage and maintaining clamping until voltage stabilizes below the threshold, the system prevents the formation of voltage oscillations. This preliminary protective action ensures both overvoltage protection and voltage stability, resolving the contradiction between protection and stability.
4Reliability
If switching elements are activated frequently to manage voltage thresholds, then overvoltage protection is improved, but switching losses and transistor load increase
Solution Approach 1:
The control unit activates the switching elements only for the minimum necessary duration to clamp the voltage during overvoltage events, rather than continuous activation. The switching elements are turned on when overvoltage is detected and turned off when voltage stabilizes, providing partial action only when needed. This approach maintains effective protection while minimizing switching losses and transistor stress, resolving the contradiction between protection and energy loss.
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 reduces overvoltages and power losses by differentiating between load shedding due to consumer disconnection and cable breaks, ensuring robust protection against voltage peaks and maintaining system stability during load shedding events.
Implementation Method 1
the excess energy can be converted into heat
Implementation Method 2
evaluation of the output voltage present at the DC voltage connections of the active bridge rectifier
Data Source
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AI summary
The invention relates to a method for operating an on-board power supply of a motor vehicle, said on-board power supply having an electrical motor that can be operated in a power-generating manner and a bridge rectifier that is connected to the electrical motor via phase connections, and which power supply can be operated in a rectifier operating mode and in a short circuit operating mode. After the bridge rectifier has been operated at least once in a short circuit operating mode in a first method phase, the method comprises, inter alia, the step of determining, on the basis of at least one characteristic of a signal indicating a drop in voltage between the DC voltage connections of the bridge rectifier, whether the signal of the upper threshold value has been exceeded as a result of a cable breakaway at at least one of the DC voltage connections. In the above-mentioned case, in a second method phase, the bridge rectifier is subsequently operated in the short circuit operating mode for an extended period of time, and/or, in the second method phase, a control signal having a second switching time greater than that in the first method phase is used, in order to control the active switching elements. The invention also relates to means for carrying out a corresponding method.