Flying Capacitor Precharge in Multi-Level DC Converters
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Solution Overview
Problem
Current three-level direct current converters require additional current sources and feedback circuits for precharging flying capacitors, leading to complex structures and high circuit costs.
Innovation Solution
A multi-level direct current converter is designed where the charging loop of a flying capacitor is formed using existing power transistors without additional charging components, employing a voltage follower and resistor configurations to reduce voltage stress on power transistors and simplify the circuit, allowing for efficient precharging without overcharge risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional current sources and feedback circuits are used to precharge the flying capacitor, then the flying capacitor can be properly precharged, but the circuit structure becomes complex and circuit costs increase
Solution Approach 1:
The patent combines the precharging function with the existing power transistor switching operations. The power transistors that are already part of the converter circuit are used to charge the flying capacitor during their normal switching cycles, eliminating the need for separate dedicated precharging components. This merging of functions reduces circuit complexity while maintaining precharging capability.
Solution Approach 2:
The converter circuit serves itself by using its own power transistors and switching operations to precharge the flying capacitor. The normal switching actions of the power transistors inadvertently perform the precharging function, so no external or additional components are needed. The system uses its existing resources to accomplish the precharging task.
2Reliability
If additional current sources and feedback circuits are used to precharge the flying capacitor, then the flying capacitor can be properly precharged, but circuit costs increase
Solution Approach 1:
The patent merges the precharging function with existing power transistor operations, eliminating the need for additional components such as dedicated current sources, feedback circuits, and detection circuits. This reduction in component count directly lowers manufacturing costs while maintaining the necessary precharging capability for reliable converter operation.
3Loss of time
If high charging current is used to precharge the flying capacitor faster, then precharging time is reduced, but voltage stress on power transistors increases
Solution Approach 1:
The patent uses periodic switching actions of the power transistors to charge the flying capacitor in stages rather than attempting to charge it all at once with high current. The capacitor charges incrementally during each switching cycle, which limits the voltage stress on individual transistors while still achieving precharging within an acceptable time frame through repeated cycles.
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 simplifies the structure, reduces circuit costs, and prolongs the service life of power transistors by minimizing voltage stress, while enabling faster precharging through increased charging currents, thus enhancing the applicability and stability of the power supply system.
Implementation Method 1
the voltage follower has a simple structure, an area is reduced
Implementation Method 2
A half input voltage is stored by using a flying capacitor, so that a voltage of a switching node has three level states
Implementation Method 3
a voltage of the source of the first power transistor is (N - 2)/(N - 1) of the input voltage in the entire charging process of the flying capacitor
Data Source
Figure 1
Figure 2a
Figure 2b
AI summary
This application provides a multi-level direct current converter and a power supply system. The multi-level direct current converter includes a direct current conversion unit, a switching unit, a voltage management unit, and a controller. The direct current conversion unit includes a flying capacitor, a first power transistor, and a second power transistor. A first end of the first power transistor is connected to a voltage input end of the multi-level direct current converter, a second end of the first power transistor is connected to a first end of the second power transistor by using the flying capacitor, and a second end of the second power transistor is connected to a reference ground. When detecting that an input voltage of the voltage input end starts to rise from an initial voltage, the controller controls the switching unit to connect the voltage management unit to the first power transistor, to output a preset voltage to the first power transistor by using the voltage management unit; and controls the second power transistor to be conducted, to charge the flying capacitor. According to this application, no additional charging component is required in an entire charging process of the flying capacitor, so that a structure is simple, and circuit costs are low.