Switched-Capacitor Converter Pre-Charging Control
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Solution Overview
Problem
Switched-capacitor converters experience high stress on switch devices and components due to inrush current during startup, which is not effectively managed by conventional methods that either slow down the startup process or fail to pre-charge capacitors efficiently.
Innovation Solution
A controller is used to pre-charge capacitors during startup by adjusting the gate-to-source voltage of switch devices and implementing PWM control to limit inrush current, allowing for simultaneous charging of multiple capacitors and reducing the on-state resistance of switch devices, thereby minimizing stress on components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a shunt resistor is placed in series with the switched-capacitor converter input to reduce inrush current, then the stress on switch devices is reduced, but the startup process becomes very slow
Solution Approach 1:
The patent applies preliminary action by pre-charging the capacitors before the main switching operation begins. The controller activates switch devices in a specific sequence during a pre-charge phase, charging capacitors C1-C4 to their steady-state values before normal operation starts. This preliminary charging action eliminates the need for a slow shunt resistor during startup, as capacitors are already charged when full power operation begins.
Solution Approach 2:
The patent segments the startup process into distinct phases: a pre-charge phase where capacitors are charged sequentially through specific switch device combinations, and a normal operation phase. This segmentation allows the system to prepare capacitors in advance using controlled switching patterns, avoiding the need for continuous slow charging through a shunt resistor throughout the entire startup period.
2Device complexity
If conventional startup methods are used without capacitor pre-charging, then the circuit structure remains simple, but large inrush current causes high stress on switch devices and components
Solution Approach 1:
The patent makes the switch devices multi-functional by using them for both capacitor pre-charging during startup and normal switching operation. The same switch devices (Q1-Q6) that operate during regular converter function are also used to control the pre-charge sequence. This eliminates the need for separate pre-charge circuitry, maintaining simple circuit structure while providing comprehensive protection against inrush current stress.
Solution Approach 2:
The switched-capacitor converter performs its own pre-charging function using its internal switch devices and capacitor network, without requiring external pre-charge circuitry. The controller manages the self-service pre-charge sequence by activating switch devices in a specific pattern, allowing the converter to prepare itself for operation using its own components, thus avoiding additional complexity.
3Reliability
If capacitors are pre-charged to steady-state values during startup, then inrush current is minimized and component stress is reduced, but the control complexity increases
Solution Approach 1:
The patent implements periodic action through a structured pre-charge sequence that operates in repeating cycles during startup. The controller activates switch devices in a specific periodic pattern, turning them on and off in sequence to charge capacitors progressively. This periodic switching pattern systematically charges each capacitor to its target voltage level, providing controlled pre-charging without requiring complex continuous control algorithms.
Solution Approach 2:
The patent employs feedback mechanisms where the controller monitors the charging state of capacitors and adjusts switch device activation accordingly. The controller detects when capacitors have reached their steady-state values and transitions from pre-charge mode to normal operation mode. This feedback-based control ensures capacitors are charged to the correct voltages without overcharging, managing control complexity through adaptive switching based on actual capacitor states.
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 enables a faster transition from startup to regular operation with reduced stress on switch devices and other components, optimizing capacitor pre-charging and minimizing inrush current, thus enhancing the efficiency and reliability of switched-capacitor converters.
Implementation Method 1
Each leg of a switched-capacitor converter includes a capacitor, and a switch device is connected to each leg for controlling charging of the capacitors
Implementation Method 2
A controller is used to pre-charge capacitors during startup by adjusting the gate-to-source voltage of switch devices
Data Source
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AI summary
A switched-capacitor converter includes a rectifier at the output, a plurality of legs coupled between the input and the rectifier, and a controller. Each leg of the switched-capacitor converter includes a capacitor, and a switch device is connected to each leg. A first group of the legs is coupled to a first branch of the rectifier, and a second group of the legs is coupled to a second branch of the rectifier. The controller alternates switching of the first and second groups of legs after startup, to transfer energy from the input to the output during a first part of each switching cycle via the first group of legs and to ground during a second part of each switching cycle via the second group of legs. The controller or a current limited source provides for precharging of at least one of the capacitors during startup.