Multilevel Power Converter With Negative Voltage Limiting
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Solution Overview
Problem
Multilevel power converters experience temporary high negative voltages due to oscillations in DC voltage, particularly when direct-current transmission links consist of different conductor types, leading to potential module overload and increased costs when addressing these issues with additional modules or bipolar modules.
Innovation Solution
A multilevel power converter assembly with a voltage limiting device that limits only negative voltages, allowing modules of one type to output either one polarity or zero voltage, while modules of another type can output both polarities or zero, with the voltage limiting device connected in parallel to the second type of modules to manage undesired negative voltages without affecting positive voltages during normal operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the number of modules is increased to cope with negative voltages, then the multilevel power converter can withstand higher voltages without module overload, but the complexity and cost of the system increases
Solution Approach 1:
The voltage limiting function is segmented from the main power conversion function. Instead of requiring all modules to handle negative voltages, a separate voltage limiting device is introduced that only activates when negative voltages occur, allowing the main modules to remain simpler in design.
Solution Approach 2:
A voltage limiting device acts as an intermediary component between the multilevel power converter and the negative voltage conditions. This mediator absorbs the stress of negative voltages through controlled breakdown, protecting the main converter modules from overload while maintaining their original design complexity.
2Adaptability or versatility
If bipolar modules are used to handle negative voltages, then the power converter can operate with both positive and negative voltages, but the cost increases
Solution Approach 1:
Instead of making all modules bipolar (handling both polarities), the voltage limiting device provides the negative voltage handling capability locally and only when needed. The main modules can remain as simpler unipolar modules designed for positive voltage operation, reducing manufacturing costs while maintaining the ability to handle negative voltages through the limiting device.
3Power
If the voltage limiting device limits only negative voltages, then normal positive voltage operation is maintained without limitation, but the device must selectively respond to different polarities
Solution Approach 1:
The voltage limiting device utilizes the harmful negative voltage condition to trigger its protective function. The breakdown characteristic of the limiting device is specifically exploited to activate only when negative voltages exceed a certain threshold, converting the harmful negative voltage into a triggering signal for protection while leaving positive voltage operation completely unaffected.
Data Source
AI summary
An assembly having a multilevel power converter, which has at least one phase module, wherein the phase module has a plurality of modules, each with a first electrical module terminal and a second electrical module terminal. The plurality of modules includes modules of a first type, which are able to output a voltage of only one polarity or zero voltage at their first electrical module terminal and their second electrical module terminal. The plurality of modules includes modules of a second type, which are able to output a voltage of one polarity, a voltage of opposite polarity or zero voltage at their first electrical module terminal and their second electrical module terminal. Depending on the polarity of a voltage across the modules of the second type, a voltage limiting device limits the voltage.