Multilevel Converter Precharge Circuit Reduces Switch Voltage Rating
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Solution Overview
Problem
In multilevel converters with flying capacitors, the lack of initial charge during startup necessitates higher voltage-rated switching devices, increasing die area and losses, which diminishes the efficiency benefits of these converters.
Innovation Solution
A pre-conditioning method biases switching nodes to a fraction of the input voltage during startup, gradually charging the flying capacitor, allowing all switching devices to be rated for a lower voltage, eliminating the need for higher voltage-rated devices and reducing losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If higher voltage-rated switching devices are used during startup, then the converter can handle the full input voltage, but the die area and losses increase
Solution Approach 1:
The patent applies preliminary action by pre-charging the flying capacitor to a fraction of the input voltage (e.g., half) before normal operation begins. This preliminary charging action ensures that during startup, the voltage across switching devices remains limited to this fraction rather than the full input voltage, allowing the use of lower voltage-rated devices with smaller die areas and reduced switching losses while maintaining reliable operation
2Reliability
If higher voltage-rated switching devices are used during startup, then the converter can handle the full input voltage, but the die area increases
Solution Approach 1:
The patent applies preliminary action by pre-charging the flying capacitor to a fraction of the input voltage (e.g., half) before normal operation begins. This preliminary charging action ensures that during startup, the voltage across switching devices remains limited to this fraction rather than the full input voltage, allowing the use of lower voltage-rated devices with smaller die areas while maintaining reliable operation
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
This approach enables the use of lower voltage-rated devices across the board, minimizing die area, switching losses, and overall costs while maintaining high efficiency.
Implementation Method 1
A precharge circuit is coupled to a flying capacitor. The precharge circuit is configured to initially bias the switch nodes to a fraction of an input voltage when the input voltage is initially applied to an input voltage terminal of the multilevel voltage converter. The precharge circuit is then configured to gradually precharge the flying capacitor to a flying capacitor operating voltage that is approximately equal to the bias voltage
Data Source
AI summary
A method for operating a multi-level converter is disclosed. A multi-level converter is provided with a plurality of switches connected in series and a flying capacitor connected to switch nodes of the plurality of switches. The switch nodes are biased initially to a fraction of an input voltage when the input voltage is initially applied to the plurality of switches. The flying capacitor is then precharged to a flying capacitor operating voltage. The multi-level converter is then operated after the flying capacitor is precharged by activating control signals to the plurality of switches. Diversion of precharge current by the plurality of switches may be performed while the flying capacitor is being precharged.