Active Converter Overvoltage Protection via Dynamic Clamping
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Solution Overview
Problem
Active converters in motor vehicle electrical systems face challenges in managing overvoltages during load shedding events, such as cable breaks, due to insufficient clamping capabilities of current valves like field-effect transistors, leading to continuous oscillation between active rectification and phase short circuits, which cannot be effectively terminated.
Innovation Solution
Implementing a method that determines whether the electrical machine is de-energized by monitoring voltage clamp activation and phase current thresholds, allowing for the cessation of phase short circuits and switching back to regular rectification, using controllable current valves and clamp circuits to manage overvoltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If active converters are used instead of passive converters, then power losses in normal operation are reduced, but the ability to clamp overvoltages is insufficient
Solution Approach 1:
The patent implements a dynamic control strategy that switches between different operating modes (active rectification, voltage clamping, phase short-circuiting) based on real-time system conditions. The control unit continuously monitors voltage levels and automatically transitions between protection modes, making the converter adaptive rather than static. This resolves the contradiction by maintaining low losses during normal operation while dynamically activating protection mechanisms only when overvoltage conditions occur.
Solution Approach 2:
The patent changes the operational parameters of the current valves based on system conditions. During normal operation, the converter operates with standard rectification parameters. When overvoltage is detected, the control unit changes parameters by activating clamping circuits and executing phase short-circuit sequences, thereby altering the electrical characteristics to provide protection. This parameter transformation allows the system to maintain efficiency normally while gaining protection capability when needed.
2Reliability
If phase short circuits are continuously activated to protect against overvoltages, then overvoltage damage is prevented, but the system oscillates between rectification and short circuit modes without stable termination
Solution Approach 1:
The patent implements a feedback control mechanism where the control unit continuously monitors the DC voltage level and the state of the electrical machine. The feedback loop determines when to activate protection modes and when to return to normal rectification. By using voltage threshold comparisons and monitoring the decay of excitation current, the system receives continuous information about system state, enabling stable decision-making rather than oscillation. The feedback ensures that phase short-circuiting is terminated appropriately when overvoltage conditions resolve.
Solution Approach 2:
The patent employs periodic evaluation of system conditions to determine whether to maintain or terminate protection modes. The control unit periodically checks voltage levels, current states, and machine excitation conditions at defined intervals. This periodic assessment allows the system to rhythmically transition between modes in a controlled manner, preventing continuous oscillation by introducing deliberate evaluation points where the system can stabilize its decision to remain in or exit protection mode.
3Ease of operation
If the electrical machine continues to supply energy after a cable break, then consumers can be supplied by the battery, but overvoltages can damage the power electronics
Solution Approach 1:
The patent introduces clamping circuits as intermediary protective elements between the electrical machine and the power electronics. These clamping circuits act as mediators that safely handle the excess energy from the electrical machine when a cable break occurs. The clamping circuits provide a controlled path for the generated overvoltage, preventing it from reaching and damaging the power electronics while allowing the electrical machine to continue operating and supplying consumers through the battery.
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 enables quicker transition to regular rectification and prevents repetitive cycles of rectification and phase short circuits, effectively managing overvoltages and ensuring stable operation after a cable break.
Implementation Method 1
Each of the controllable current valves of one of the two converter branches has a clamp circuit assigned to it, which is set up to activate a voltage clamp from a first point in time, from which a voltage potential present at a first DC voltage connection or a voltage present between the first and the second DC voltage connection increases to a predetermined first threshold value, and to keep the voltage clamp activated as long as the voltage potential does not fall below the first threshold value
Implementation Method 2
Converters of various designs operated as rectifiers can be used to feed direct current networks from three-phase sources, in particular motor vehicle on-board networks by three-phase generators
Data Source
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AI summary
In an active converter (102) which is connected to an electrical machine (101), in which clamping circuits for activating voltage clamping after a first time are provided, and which is also set up to activate a load shedding reaction only if activation conditions are present after a second time, the activation conditions comprise the fact that it is determined that the voltage clamping is still activated at the second time and/or a voltage potential has not yet fallen below the first threshold value and/or a value which indicates a current flowing through at least one phase connection (U-Y) is above a third threshold value.