Generator Motor Phase Short Circuit Control
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Solution Overview
Problem
In electrical machines with active bridge rectifiers, sudden load changes lead to voltage peaks due to the slow dissipation of the excitation field, causing stress and premature failure of control valves, especially during de-excitation periods, where phase short circuits result in significant power losses and inefficiencies.
Innovation Solution
A method that synchronizes the initiation and cancellation of phase short circuits with the natural frequency of the electrical machine, using controllable flow valves to control the switching frequency, thereby reducing the load on these valves and minimizing power losses by coordinating switching operations with the natural oscillations of the system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If phase short circuits are used to prevent voltage peaks during load shedding, then voltage stability is improved, but power losses increase and control valves experience excessive stress
Solution Approach 1:
The patent applies periodic action by synchronizing the initiation and elimination of phase short circuits with the natural frequency oscillations of the electrical machine. Instead of continuous or arbitrary switching, the control unit triggers phase short circuits only during specific phases of the natural oscillation cycle, thereby achieving voltage stabilization while minimizing the duration and frequency of corrective actions, thus reducing power losses and valve stress.
2Reliability
If phase short circuits are initiated frequently to maintain voltage stability, then voltage control is improved, but control valve lifespan decreases due to excessive stress
Solution Approach 1:
The control unit synchronizes switching operations with the natural frequency oscillations of the electrical machine, initiating and eliminating phase short circuits only during appropriate phases of the oscillation cycle. This periodic synchronization reduces the frequency of switching operations compared to continuous or frequent corrective actions, thereby decreasing mechanical and electrical stress on control valves and extending their operational lifespan while maintaining effective voltage control.
3Speed
If the excitation field dissipation is accelerated to respond quickly to load changes, then response speed is improved, but system stability deteriorates due to oscillations
Solution Approach 1:
The patent utilizes the natural frequency oscillations (vibrations) of the electrical machine as a basis for control timing. By synchronizing phase short circuit operations with these inherent oscillations, the system leverages the existing dynamic behavior rather than fighting against it, allowing for faster response to load changes while maintaining stability through resonance-based timing rather than aggressive excitation field manipulation.
4Reliability
If continuous monitoring and frequent switching are used to maintain voltage stability, then voltage regulation is improved, but system complexity increases
Solution Approach 1:
The control unit utilizes the naturally occurring frequency oscillations of the electrical machine itself as the timing reference for switching operations. Instead of requiring complex external synchronization signals or artificial timing mechanisms, the system serves itself by using its own inherent dynamic characteristics to guide the control strategy, thereby simplifying the overall system architecture while maintaining effective voltage regulation.
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 significantly shortens the de-excitation period, reduces power losses in the control valves, and enhances the robustness of the system by performing switching operations during low phase current times, thus preventing excessive stress and prolonging the lifespan of the system components.
Implementation Method 1
an at least generator-operable electric motor (1) with an active bridge rectifier (2)
Implementation Method 2
The semiconductor valves are switched on by providing a corresponding control voltage at their gate connection (activation), as a result of which the drain-source path of the semiconductor valves becomes conductive or has a low resistance. Accordingly, the semiconductor valves are switched off in that the provision of the control voltage is terminated and the drain-source path thus becomes non-conductive or has a high resistance.
Implementation Method 3
one way of preventing voltage peaks in the vehicle electrical system in the event of load shedding is to switch on the current valves of the upper or lower rectifier branch (i.e. all high-side or all low-side current valves) in all half-bridges. In this way, the electrical machine is short-circuited internally
Data Source
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AI summary
The invention relates to a method (100) for controlling an at least generator-operable, multi-phase electric motor (1), the phase connections thereof (U–Y) being connected in an active rectifier bridge (2) to a first direct current connection (B-) respectively by means of first current valves (UL - YL) which can be controlled and which can be activated and deactivated, and to a second direct current connection (B+) by means of second current valves (UH–YH). Said method consists of, when the electric motor (1) is operated by a generator, after the occurrence of a load shedding, initiating and canceling multiple phase short circuits of the phase connections (U–Y) by means of the first current valves (UL–YL). According to the invention, a variable characterising an individual frequency of the electric motor (1) and the first current valves (UL - YL) are controlled to a switching frequency for introducing and interrupting the phase short-circuits, based on the variable characterizing the individual frequency of electric motor (1).