Switched-Capacitor Charging for Series-Connected Capacitors
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Solution Overview
Problem
Charging circuits for series-connected capacitors face challenges in preventing excessively large inrush currents and ensuring all capacitors are charged to the same voltage without exceeding the maximum threshold voltage, especially when capacitors have different leakage currents.
Innovation Solution
A switched-capacitor or switched-inductor technique is employed, where a pump capacitor or inductor is alternately connected in parallel to each capacitor in the series, using coordinated switches and control signals to manage charging cycles and voltage distribution, allowing for periodic adjustments in switching frequency and duty-cycle based on sensed voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a voltage regulator connected in series with an output current limiter is used to charge super-capacitors, then excessively large inrush currents are reduced and charge voltage is controlled, but a control circuit for the voltage on the central node of series connected capacitors is required
Solution Approach 1:
The patent introduces a mediator circuit comprising operational amplifiers and resistors that monitors the voltage at the central node and automatically adjusts the charging current distribution. This intermediary control mechanism eliminates the need for complex external control circuits while maintaining voltage balance across series-connected capacitors with different leakage currents.
2Reliability
If a unity gain operational amplifier is used to regulate the output node to remain at half value of applied charge voltage, then the voltage on the central node is controlled, but relatively large consumption occurs and the applied charge voltage source must not become smaller than the charging voltage
Solution Approach 1:
The patent employs parameter-changing resistors (or digitally controllable resistors) that adjust their resistance values based on the detected voltage differences across capacitors. By dynamically changing resistance parameters rather than maintaining fixed high-gain amplification, the circuit achieves reliable voltage control with significantly reduced power consumption compared to unity gain operational amplifier configurations.
3Adaptability or versatility
If capacitors with different leakage currents are connected in series, then voltage distribution on capacitors becomes unbalanced, but the risk of exceeding breakdown voltage of the cell with smallest leakage increases
Solution Approach 1:
The patent implements a feedback mechanism where operational amplifiers continuously monitor the voltage at the central node and compare it with the expected mid-value. Based on this feedback, the circuit automatically adjusts the charging current distribution through controlled resistance changes, ensuring that capacitors with different leakage currents maintain balanced voltage levels and preventing any capacitor from exceeding its breakdown voltage.
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 method efficiently charges all capacitors in series to the same voltage, reducing inrush currents and ensuring uniform charging, even with mismatched capacitors, without requiring a voltage regulator or current limiter, and allows for increased energy storage from a low voltage source.
Implementation Method 1
A pump capacitor or alternatively an energy storing inductor is charged by coupling it to a voltage source
Implementation Method 2
A pump capacitor or alternatively an energy storing inductor is charged by coupling it to a voltage source
Data Source
AI summary
A device, such as a pump capacitor or an energy storing inductor, is charged by coupling it to a voltage source. Thereafter, the device is connected in parallel to one of the capacitors or capacitance cells to be charged, and the charging of the device and successive connections of it in parallel to a selected capacitor of the series of capacitors for charging it are replicated for all the capacitors of the series. The sequence of different connections of the device to the charge voltage source and to the selected one of the capacitors of the series is actuated through a plurality of coordinately controlled switches that establish distinct current circulation paths, according to a switched-capacitor or switched inductor techniques driven by respective periodic control signals that may be generated from a master clock signal.