Unified Common Mode Voltage Injection for Multi-Level Converters
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Solution Overview
Problem
Current multi-level power converters require complex computations for common mode voltage injection to balance neutral point current, differing for each converter level due to unique switching functions and states, leading to increased costs and computational complexity.
Innovation Solution
A unified common mode voltage injection method and system that generates CMV signals through min-max calculation or pure third-order harmonic injection, applicable across various converter levels, to modify command signals and reduce total harmonic distortion, while ensuring neutral point current regulation and DC link voltage balancing without exceeding modulation limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If different control strategies are applied for common mode voltage injection in different level converters, then neutral point current balancing is achieved, but control complexity and computational requirements increase
Solution Approach 1:
The patent applies a universal common mode voltage injection strategy that works across different converter levels (3-level, 5-level, 7-level, etc.). Instead of developing separate control strategies for each converter level, the invention uses a single unified approach based on minimizing the absolute value of neutral point current, making the control system adaptable to various converter configurations without increasing complexity
Solution Approach 2:
The patent changes the control parameter from level-specific strategies to a universal parameter: the absolute value of neutral point current. By controlling this single parameter across all converter levels, the system achieves neutral point current balancing without requiring different control algorithms for each converter type, thereby reducing control complexity
2Measurement precision
If level-specific calculation methods are used for neutral point current, then accurate control is achieved, but computational complexity increases
Solution Approach 1:
The patent develops a universal calculation method for neutral point current that applies to all converter levels. The same calculation approach can be used for 3-level, 5-level, 7-level, and other multi-level converters, eliminating the need for multiple level-specific calculation methods and reducing overall computational complexity while maintaining control accuracy
Solution Approach 2:
The patent extracts the essential control objective from complex level-specific methods: minimizing the absolute value of neutral point current. By focusing on this single extracted objective, the invention simplifies the control approach while maintaining effectiveness across different converter configurations
3Reliability
If common mode voltage injection is used to balance neutral point current, then DC capacitor voltage balancing is achieved, but additional control parameters and complexity are introduced
Solution Approach 1:
The patent merges two control objectives into a single unified approach: neutral point current balancing and DC capacitor voltage balancing are both achieved through the same common mode voltage injection strategy. By controlling the absolute value of neutral point current, the system simultaneously achieves both objectives without requiring separate control parameters or strategies
Solution Approach 2:
The unified common mode voltage injection strategy serves multiple functions: it balances neutral point current, balances DC capacitor voltages, and works across different converter levels. This multi-functional approach reduces the need for additional control parameters and simplifies the overall control system
Data Source
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AI summary
A power conversion system includes at least one multi-level power converter and a controller coupled to the at least one multi-level power converter. The controller includes a first CMV injection module (402) and a second CMV injection module (404). The first CMV injection module (402) generates a first CMV signal (406) for modifying at least one voltage command to achieve a first function in association with operation of the power conversion system. The second CMV injection module (404) generates a second CMV signal (406) based at least in part on a three-level CMV limit either for modifying the at least one voltage command or for further modifying the at least one modified voltage command (424) to achieve a second function in association with operation of the power conversion system (100).