DC-link capacitor voltage balancing for inverter safety
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
High-voltage DC-link capacitors in inverters are prone to catastrophic damage and safety hazards due to unbalanced voltage distribution, which can lead to faults like short-circuits, causing potential fires and explosions.
Innovation Solution
A method is implemented where the rectifier stage charges the DC link stage to a low initial voltage level, and a control module determines voltage balance across series-connected capacitors. If balanced, the voltage is increased to a higher level, while unbalanced conditions limit the voltage or raise an alarm, using active rectifier circuits and thyristors to manage the charging process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a single capacitor is used to withstand high DC link voltage (800-900V), then the voltage withstanding capability is improved, but the cost and availability deteriorate
Solution Approach 1:
The patent divides the high voltage DC link capacitor into multiple series-connected capacitors (typically two or more). Each capacitor only needs to withstand a portion of the total voltage (e.g., 400-450V each for an 800-900V system), making them commercially available and cost-effective while collectively providing the required high voltage withstanding capability.
2Strength
If series-connected capacitors are used to achieve high voltage capability, then the voltage withstanding capability is improved, but the risk of unbalanced voltage distribution and catastrophic failure worsens
Solution Approach 1:
The patent implements a preliminary voltage balance check during the start-up phase before the inverter begins normal operation. The control module measures the voltage across each series-connected capacitor and verifies they are balanced (within an acceptable tolerance). Only after successful verification does the system allow full voltage operation, preventing catastrophic failure from unbalanced conditions.
Solution Approach 2:
The control module continuously monitors the voltage distribution across series-connected capacitors and provides feedback control. If unbalance is detected during operation, the system can adjust charging parameters or trigger protective actions to maintain reliability and prevent catastrophic failure.
3Productivity
If the DC link voltage is charged to high level during start-up, then the productivity is improved, but the safety deteriorates due to difficulty in measuring and controlling voltage balance
Solution Approach 1:
The patent performs voltage balance measurement and verification as a preliminary action during the start-up phase, before the inverter begins normal operation. The control module checks whether voltages across series-connected capacitors are balanced within an acceptable tolerance. Only after successful verification does the system proceed to charge the DC link to full operating voltage, ensuring safety while maintaining productivity.
4Reliability
If voltage balance monitoring is implemented, then the reliability is improved, but the device complexity worsens
Solution Approach 1:
The control module performs multiple functions: it monitors voltage balance across series-connected capacitors, controls the charging process during start-up, and provides protective control during normal operation. By consolidating these functions into a single control module rather than adding separate dedicated devices, the patent achieves reliable voltage balance control while minimizing the increase in device complexity.
Data Source
AI summary
The invention provides an inverter system and a method of using said inverter system. A rectifier stage of the inverter system is used to charge a DC link stage to a first voltage level and a control module determines whether voltages over series connected capacitors of the DC link stage are balanced. If those voltages are balanced, the rectifier stage charges the DC link stage to a second voltage level higher than the first voltage level.