Three-Phase Inverter Active Voltage Balance Control
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Solution Overview
Problem
Three-phase three-level inverters without transformers face issues of common mode leakage current and voltage imbalance, leading to harmonic distortion and faulty ground fault protection, which degrade the AC power output and increase the total harmonic distortion (THD) in the signal.
Innovation Solution
A three-phase three-level inverter with active voltage balance control, utilizing a controller to select a subset of switching states that reduce common mode voltage, and by substituting non-adjacent small vectors for adjacent small vectors to balance the common mode voltage and capacitor voltages, thereby minimizing leakage current and harmonic distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of stationary object
If transformer is removed from the power system, then size and expense are reduced, but common mode leakage current increases
Solution Approach 1:
The patent introduces a control mechanism that acts as an intermediary to manage the inverter's switching states. This controller monitors and adjusts the switching sequences to actively balance the neutral point voltage, thereby mitigating the harmful leakage current effect without requiring a physical transformer intermediary.
Solution Approach 2:
The patent changes the operational parameters of the inverter by selectively substituting switching states. Specifically, it replaces certain adjacent small vector switching states with non-adjacent small vector switching states, which alters the voltage balance dynamics and reduces common mode leakage current while maintaining power conversion functionality.
2Device complexity
If NPC inverter configuration is used, then component count and cost are reduced, but voltage imbalance increases
Solution Approach 1:
The patent implements a dynamic control strategy where the inverter's switching states are continuously adjusted based on real-time voltage balance requirements. The controller dynamically selects and substitutes switching sequences to maintain neutral point voltage stability, transforming the static voltage balance problem into a dynamically controlled solution.
Solution Approach 2:
The patent changes the operational parameters of the inverter by selectively substituting switching states. Specifically, it replaces certain adjacent small vector switching states with non-adjacent small vector switching states, which alters the voltage balance dynamics and reduces common mode leakage current while maintaining power conversion functionality.
3Ease of operation
If traditional switching states are used, then control simplicity is maintained, but harmonic distortion increases
Solution Approach 1:
The patent changes the operational parameters of the inverter by selectively substituting switching states. Specifically, it replaces certain adjacent small vector switching states with non-adjacent small vector switching states, which alters the voltage balance dynamics and reduces common mode leakage current while maintaining power conversion functionality.
Solution Approach 2:
The patent implements an active voltage balance control mechanism that monitors the neutral point voltage and adjusts switching states accordingly. This feedback-based approach ensures that voltage imbalance is continuously corrected, reducing harmonic distortion while maintaining relatively simple control through systematic switching state substitution.
Data Source
AI summary
A system and methods for active voltage balance of capacitors connected to a DC power source and to a three-phase three-level inverter, implemented by a controller comprising a space vector diagram is disclosed.