Active Bridge Rectifier Overvoltage Protection via Voltage Filtering
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Solution Overview
Problem
Active bridge rectifiers in vehicle electrical systems face challenges during load shedding, where repetitive phase short circuits lead to heavy loading and potential damage of switching elements, as conventional protection strategies are insufficient in managing voltage oscillations between upper and lower threshold values.
Innovation Solution
The implementation of a vehicle electrical system with an active bridge rectifier and a control device that filters the DC voltage signal and adapts the comparator thresholds to prevent high-frequency repetitive switching, using filters like RC or SC filters, and adjusting thresholds to avoid frequent activations and deactivations of phase short circuits, thereby reducing the load on switching elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional passive bridge rectifiers with Zener diodes are used for overvoltage protection, then robust overvoltage clamping is achieved, but power losses increase and adaptability decreases
Solution Approach 1:
The patent transitions from passive Zener diodes with fixed clamping characteristics to active switching elements (MOSFETs, IGBTs) with controllable switching characteristics. The switching elements can be dynamically controlled to provide overvoltage protection only when necessary, reducing continuous power losses while maintaining protection robustness through adaptive parameter adjustment.
Solution Approach 2:
The patent replaces the mechanical/passive clamping action of Zener diodes with an active electronic control system. The control device monitors voltage conditions and actively switches protection elements on or off based on real-time system state, substituting passive mechanical clamping with active electronic control to reduce energy losses.
2Loss of energy
If active bridge rectifiers with controlled switching elements are used, then power losses decrease and adaptability increases, but overvoltage protection robustness deteriorates
Solution Approach 1:
The patent introduces a control device as an intermediary between the switching elements and the overvoltage protection function. This control device monitors system conditions and coordinates the switching elements to provide both efficient power conversion and robust overvoltage protection, bridging the gap between the two conflicting requirements.
Solution Approach 2:
The patent designs the active bridge rectifier system to perform multiple functions: efficient power conversion during normal operation and robust overvoltage protection during fault conditions. The switching elements and control device are configured to adaptively switch between these functions, making the system universally capable of handling both operational modes effectively.
3Reliability
If phase short circuits are implemented for load shedding protection, then overvoltage damage is prevented, but switching elements experience heavy loading and potential damage
Solution Approach 1:
The patent implements dynamic control of phase short circuits based on real-time voltage monitoring. The control device activates short circuits only when overvoltage thresholds are exceeded and deactivates them when voltage returns to normal, creating a dynamic response that prevents overvoltage damage while minimizing unnecessary stress on switching elements during normal operation.
Solution Approach 2:
The patent employs feedback control where the control device continuously monitors output voltage and adjusts switching element states accordingly. When voltage exceeds thresholds, feedback triggers short circuit activation; when voltage returns to normal, feedback triggers deactivation. This closed-loop feedback mechanism ensures protection is provided only when necessary, reducing cumulative stress on switching elements.
4Stability of the object's composition
If hysteresis control with upper and lower threshold values is used for load shedding, then output voltage oscillation is controlled, but frequent switching operations occur causing heavy load on switching elements
Solution Approach 1:
The patent implements preliminary filtering of the detected DC voltage value before it is used for control decisions. By filtering the voltage signal in advance, the control device receives a smoothed voltage profile that reduces high-frequency variations, thereby preventing spurious switching operations while maintaining effective hysteresis control for voltage stability.
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 approach reduces the stress on active switching elements, allowing them to be smaller and cheaper, while preventing undesired frequent switching operations, thus enhancing the reliability and efficiency of the electrical system during load shedding events.
Implementation Method 1
the filter circuitry is set up to filter a detected value for the DC voltage
Implementation Method 2
the at least one control device is set up to convert an AC voltage output by the electrical machine into a DC voltage by driving active switching elements of the bridge rectifier
Implementation Method 3
an electrical machine, an active bridge rectifier and at least one control device, wherein the at least one control device is set up to convert an AC voltage output by the electrical machine
Data Source
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AI summary
The invention relates to a motor-vehicle electrical system, comprising an electric machine, an active bridge rectifier, and at least one control device, wherein the at least one control device is designed to convert an alternating voltage output by the electric machine at a number of phase connections into a direct voltage by controlling active switching elements of the bridge rectifier, and wherein means (71) are provided, which are designed to trigger a short circuit of at least two of the phase connections as soon as a signal characterizing the direct voltage exceeds an upper threshold value and to remove the short circuit as soon as the signal characterizing the direct voltage falls below a lower threshold value thereafter. Evaluating means are provided, which are designed to record a value of the direct voltage, to filter the recorded value, and to provide the filtered value as the signal characterizing the direct voltage.