Three-Level Converter Soft-Start for Flying Capacitor Precharge
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Solution Overview
Problem
Three-level converters with flying capacitors face overvoltage risks during starting if the flying capacitor is not pre-charged, and existing solutions either require complex and costly dynamic charging circuits or introduce unbalanced bus voltage with passive devices.
Innovation Solution
A three-level converting circuit with soft-start circuits and relays that sequentially charge capacitors and flying capacitors, using relays and resistors to manage voltage thresholds and prevent overvoltage, allowing for safe and efficient pre-charging of capacitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a charging circuit is added to pre-charge the flying capacitor, then the overvoltage risk of switch devices is reduced, but the circuit becomes more complicated and costly
Solution Approach 1:
The patent combines the charging function with the existing soft-start circuit, merging two functions into one existing circuit structure. This avoids adding a separate charging circuit while still achieving the pre-charging of the flying capacitor, thus reducing circuit complexity and cost while maintaining overvoltage protection.
Solution Approach 2:
The soft-start circuit is designed to serve multiple functions: both soft-start control and flying capacitor charging. By making the soft-start circuit multi-functional, the patent eliminates the need for a dedicated charging circuit, thereby simplifying the overall circuit structure while ensuring reliable overvoltage protection.
2Reliability
If passive devices are added to the main circuit to solve overvoltage, then the switch device overvoltage risk is reduced, but bus voltage becomes unbalanced
Solution Approach 1:
The patent employs feedback control through control signals that monitor the flying capacitor voltage and adjust the switching states accordingly. This feedback mechanism ensures that the flying capacitor is properly charged while maintaining bus voltage balance, avoiding the need for passive devices that would disrupt voltage equilibrium.
Solution Approach 2:
The patent uses dynamic switching control where the switching states are adjusted in real-time based on the charging status of the flying capacitor. This dynamic approach allows the circuit to adaptively maintain bus voltage balance while providing overvoltage protection, unlike static passive devices that would cause voltage imbalance.
3Device complexity
If the flying capacitor is not pre-charged during starting, then the circuit structure remains simple, but switch devices risk overvoltage
Solution Approach 1:
The patent implements preliminary action by using the soft-start circuit to charge the flying capacitor before the main switching operations begin. This pre-charging action is performed during the soft-start phase, ensuring that the flying capacitor is ready to prevent overvoltage before the converter enters normal operation, thus maintaining both circuit simplicity and reliability.
Data Source
AI summary
A three-level converting circuit, and a starting method and electronic equipment thereof. The circuit includes: a first voltage source; a first soft-start circuit; a first capacitor; a first switch, a second switch, a third switch and a fourth switch sequentially connected in series; a flying capacitor; a second soft-start circuit; a second voltage source and a second capacitor. The three-level converting circuit can pre-charge the flying capacitor, the first capacitor and the second capacitor when executing the starting method thereof, thereby preventing the over-voltage damage of the switches.