Fly Capacitor Pre-Charging Circuit for M-Level Converter Startup
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Multi-level converter cells face challenges in pre-charging fly capacitors to a target voltage at startup, which is essential for enabling operational mode switching and ensuring that driver circuits for power transistors are adequately powered.
Innovation Solution
The proposed solution involves operating the M-level converter cell in a boost mode to repeatedly transfer charge from a battery to fly capacitors until they reach the target voltage. This is achieved by controlling the power FETs in a specific configuration, including setting the outermost low-side power FET to a current-limiting reduced gate drive mode, toggling the innermost low-side power FET to charge the fly capacitors, and ensuring all high-side power FETs are initially off.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional pre-charging circuits are used for multi-level converter cells, then the circuit structure becomes complex and bulky, but the pre-charging function can be achieved
Solution Approach 1:
The patent makes the existing power FETs and inductor serve dual functions: they operate as standard power switching components during normal converter operation, and simultaneously function as pre-charging components by controlling specific FETs to charge fly capacitors from the battery. This eliminates the need for separate pre-charging circuitry while ensuring reliable pre-charging of all fly capacitors to required voltage levels
Solution Approach 2:
The converter cell uses its own internal components (power FETs and inductor) to perform the pre-charging function without requiring external or dedicated pre-charging circuitry. By selectively activating specific FETs in a controlled sequence, the system charges its own fly capacitors using its existing hardware, thereby simplifying the overall circuit structure
2Productivity
If fly capacitors are pre-charged using traditional methods, then adequate voltage is achieved, but the pre-charging process is slow and inefficient
Solution Approach 1:
The patent employs periodic toggling of the innermost low-side power FET to charge the fly capacitors in repeated cycles. This periodic switching action rapidly transfers charge from the battery through the inductor to the fly capacitors, achieving full pre-charging much faster than traditional continuous or linear charging methods would allow
3Ease of operation
If all power FETs are controlled in normal switching mode at startup, then operational mode switching can proceed, but driver circuits may not be adequately powered due to uncharged fly capacitors
Solution Approach 1:
The patent performs preliminary pre-charging of all fly capacitors to their required voltage levels before enabling normal operational mode switching of the converter. By controlling specific power FETs to charge the capacitors first, the system ensures that driver circuits will have adequate power supply when normal operation begins, preventing startup failures or unreliable 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 allows for efficient and compact pre-charging of fly capacitors, ensuring that the M-level converter cell can commence normal switching operations once all capacitors are fully pre-charged to their respective target voltage levels.
Implementation Method 1
an inductor L coupled to a battery B... repeatedly transfer charge from the battery to fly capacitors
Data Source
AI summary
Effective, efficient, and compact circuits and corresponding methods that enable startup of a multi-level (M-level) converter cell to ensure that driver circuits for power transistors are adequately powered in order to be able to switch the power transistors ON and OFF, and to ensure that all fly capacitors are pre-charged to a target voltage level before enabling operational mode switching of the M-level converter cell. Embodiments utilize the power available from a battery connected to an M-level converter cell and operate a converter cell in a boost mode to repeatedly transfer charge from the battery to one or more fly capacitors until a respective target voltage is reached for each fly capacitor.