Unified CMV Injection for Multi-Level Converter Voltage Balancing
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Solution Overview
Problem
Conventional power conversion systems, particularly multi-level converters, face challenges in efficiently controlling neutral point voltage balancing and reducing total harmonic distortion (THD) due to the use of different control strategies, which can lead to harmonic signal creation and stress on switching devices.
Innovation Solution
A unified common mode voltage injection algorithm and method are implemented in a power conversion system, using a unified CMV injection module to modify voltage commands and balance DC link voltages, thereby reducing THD and minimizing voltage stress on capacitors through strategic switching patterns and CMV signal injection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If different control strategies are employed for regulating output voltage and balancing DC link voltages, then the power converter can meet operational requirements, but the system complexity increases and may create harmonic signals
Solution Approach 1:
The patent combines multiple control functions (output voltage regulation, DC link voltage balancing, and common mode voltage injection) into a unified control strategy. The common mode voltage injection is integrated with the existing control loops, allowing simultaneous achievement of THD reduction and DC link voltage balancing through a single coordinated control mechanism rather than separate independent controls
Solution Approach 2:
The common mode voltage injection mechanism serves multiple functions simultaneously: it reduces output voltage THD, balances DC link capacitor voltages, and minimizes switching device stress. This multi-functional approach eliminates the need for separate dedicated control systems for each function, thereby reducing overall system complexity while maintaining operational reliability
2Object-generated harmful factors
If conventional separate control strategies are used for THD reduction and DC voltage balancing, then each function can be addressed, but harmonic signals may be created and switching devices experience stress
Solution Approach 1:
The patent utilizes the common mode voltage injection technique to convert what would normally be harmful harmonic distortions into beneficial effects. By injecting a carefully controlled common mode voltage, the system actively compensates for harmonic components in the output voltage, thereby reducing THD. Simultaneously, this injection helps balance the DC link capacitor voltages and reduces stress on switching devices, turning a potential source of harm into a protective mechanism
3Productivity
If multiple independent control strategies are implemented, then various operational requirements can be met, but the overall system efficiency decreases
Solution Approach 1:
The patent merges multiple control functions into a unified common mode voltage injection framework that simultaneously handles output voltage regulation, DC link voltage balancing, and harmonic mitigation. This integration reduces the computational burden and coordination overhead associated with multiple independent control loops, thereby improving power conversion efficiency while maintaining comprehensive operational control
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 (422) 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 (408) based at least in part on a local limit either for modifying the at least one voltage command (422) 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.