Flying Capacitor Pre-Charge in Multi-Level Power Converters
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Solution Overview
Problem
Existing power converters face challenges in efficiently managing startup stress on flying capacitors, leading to increased switch stress during cold starts, which can affect performance and reliability.
Innovation Solution
A multi-level power converter with a pre-charge unit that includes charging circuits, sensing amplifiers, and comparators to sense and control the charging of flying capacitors based on output voltage thresholds, reducing startup stress by pre-charging the capacitors to a predetermined fraction of the output voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the power converter starts up without pre-charging the flying capacitor, then the circuit can start immediately, but the switches experience excessive stress and potential failure
Solution Approach 1:
The patent applies preliminary action by pre-charging the flying capacitor before the main power conversion operation begins. The pre-charge unit charges the flying capacitor to a predetermined fraction of the output voltage during a start-up cycle, ensuring that when the switches operate normally, the voltage stress on them is reduced. This preliminary charging action prevents excessive stress on switches during startup while maintaining circuit reliability.
2Reliability
If the pre-charge unit charges the flying capacitor to full output voltage, then switch stress is minimized, but charging time and energy loss increase
Solution Approach 1:
The patent applies partial action by charging the flying capacitor only to a predetermined fraction of the output voltage (not 100% of full voltage) during the pre-charge phase. This partial charging is sufficient to reduce switch stress to acceptable levels while avoiding the excessive charging time and energy loss that would occur if the capacitor were charged to full output voltage. The fraction is carefully selected to balance reliability improvement with acceptable start-up time.
3Device complexity
If the flying capacitor voltage is not monitored during pre-charge, then the control circuit is simpler, but the capacitor may be overcharged causing switch stress
Solution Approach 1:
The patent applies feedback by incorporating a sensing amplifier that continuously monitors the flying capacitor voltage during the pre-charge cycle. The sensing amplifier compares the flying capacitor voltage to a reference voltage (predetermined fraction of output voltage) and provides feedback to the pre-charge unit. When the flying capacitor reaches the target voltage level, the feedback signal stops the pre-charge operation, preventing overcharging and ensuring switch protection without requiring complex control circuitry.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces startup stress on switches, enhancing the reliability and efficiency of the power converter by ensuring balanced voltage distribution across capacitors, thereby improving overall performance.
Implementation Method 1
a pre-charge unit connected to the flying capacitor and the output terminal and configured to pre-charge the flying capacitor based on a voltage at the output terminal during a start-up cycle of the multi-level power converter
Implementation Method 2
a sensing amplifier connected to the first node and the second node to sense a flying capacitor voltage of the flying capacitor
Implementation Method 3
a comparator configured to generate a disable signal to disable the charging circuit responsive to the flying capacitor voltage being at least a predetermined fraction of a voltage at the output terminal
Data Source
AI summary
According to some embodiments, a multi-level power converter, includes an output terminal, a reference terminal, an inductor, a flying capacitor, a first switching stage including a first switch connected to the output terminal and connected to the flying capacitor at a first node, and a second switch connected to the flying capacitor at a second node and connected to the reference terminal, a second switching stage including a third switch connected to the first node and the inductor, and a fourth switch connected to the inductor and the second node, and a pre-charge unit connected to the flying capacitor and the output terminal and configured to pre-charge the flying capacitor based on a voltage at the output terminal during a start-up cycle of the multi-level power converter.