Multilevel Converter Common Mode Voltage Reduction via Switching State Selection
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Solution Overview
Problem
Multilevel power converters face issues with common mode voltage, which can lead to unacceptable voltage levels in power conversion systems, particularly in motor drives and other applications where efficient power utilization is crucial.
Innovation Solution
The implementation of a controller that provides switching control signals to multilevel rectifier and inverter stages to selectively employ subsets of switching states that minimize common mode voltage contributions, allowing for complete or partial cancellation of these voltages, thereby enhancing the applicability of multilevel converters while maintaining cost and performance advantages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If all possible switching states are utilized in typical space vector modulation scheme, then output power utilization is maximized, but common mode voltage becomes unacceptable
Solution Approach 1:
The patent extracts and eliminates specific switching states from the complete set of possible switching states. By removing only those states that generate high common mode voltage while retaining states that provide adequate power utilization, the system achieves a balance between energy efficiency and common mode voltage reduction.
Solution Approach 2:
The patent changes the modulation parameters by selectively employing subsets of switching states with different common mode voltage characteristics. Through space vector modulation techniques, the controller adjusts which switching states are activated based on the desired output while maintaining common mode voltage within acceptable limits.
2Object-affected harmful factors
If switching states are selected to minimize common mode voltage contribution, then common mode voltage is reduced, but power utilization efficiency decreases
Solution Approach 1:
The patent applies partial action by using only a subset of the complete switching state repertoire. Instead of completely restricting switching states to minimal common mode voltage options, the system selectively employs intermediate subsets that provide sufficient power utilization while adequately controlling common mode voltage.
3Power
If multilevel converter architecture is implemented, then output voltage capability is enhanced, but system complexity increases
Solution Approach 1:
The patent segments the converter into multiple levels (e.g., five-level, seven-level configurations) using series connections of voltage sources and switching networks. This segmentation enables generation of multiple discrete output voltage levels, enhancing output voltage capability while distributing the complexity across modular stages.
Solution Approach 2:
The patent implements nested multilevel topologies where smaller voltage conversion stages are embedded within larger system architecture. For example, nested neutral point clamped converters or cascaded H-bridge configurations nest multiple voltage levels within a unified control framework, achieving high output voltage capability through hierarchical structuring.
Data Source
AI summary
Multilevel converters and space vector modulation operating methods are presented in which fewer than all possible switching states are employed for space vector modulation of rectifier and inverter circuits to promote common mode voltage contribution cancellation or reduction therebetween and by using subsets of possible space vector modulation switching states associated with minimal positive or negative common mode voltages and in some cases using virtual vectors which have zero common mode voltages to eliminate the 3rd order harmonic components in common mode voltage as well as to reduce common mode voltage affects associated with multilevel inverter stages.