DC-DC Converter Controller Using Capacitor Charge Balance
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Solution Overview
Problem
Existing DC-DC converters face challenges in achieving optimal dynamic response to load current steps, particularly in minimizing voltage overshoot and undershoot, due to limitations in switching frequency, output capacitance, and inductance, which affect efficiency and stability.
Innovation Solution
A control method and controller for DC-DC converters that exploit capacitor charge balance principles to minimize output voltage deviation by adjusting duty cycles and using a controlled current source to manage inductor current, allowing for rapid recovery and minimal voltage fluctuations during load changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If switching frequency is increased to improve dynamic response, then recovery time is reduced, but efficiency decreases and design complexity increases
Solution Approach 1:
The controller predicts the required inductor current change using a double integrator circuit that calculates the area between reference and actual inductor currents. This preliminary calculation enables the controller to proactively adjust the duty cycle before significant voltage deviation occurs, achieving fast recovery without requiring excessively high switching frequency that would reduce efficiency.
2Stability of the object's composition
If output capacitance is increased to maintain output voltage during load current change, then voltage deviation is reduced, but the converter becomes bulky and expensive
Solution Approach 1:
The controller continuously monitors the actual inductor current and compares it with the reference inductor current. This feedback mechanism enables real-time detection of current deviations and automatic adjustment of the duty cycle through the double integrator, maintaining output voltage stability without requiring oversized output capacitors.
3Loss of time
If output inductance is reduced to improve dynamic response, then recovery time is reduced, but output voltage ripple increases and efficiency decreases
Solution Approach 1:
The controller dynamically changes the duty cycle parameter based on the calculated area between reference and actual inductor currents. This parameter adjustment enables the converter to achieve fast transient response without requiring reduction of the output inductance, thereby avoiding increased voltage ripple and maintaining efficiency.
Data Source
AI summary
The invention relates to a control method and a controller for a DC-DC converter, such as a synchronous Buck converter, which exploits the principle of capacitor charge balance to allow the converter to recover from a positive and/or negative load current step in the shortest achievable time, with the lowest possible voltage undershoot/overshoot. The control method may be implemented by either an analog or a digital circuit. The controller may be integrated with existing controller schemes (such as voltage-mode controllers) to provide superior dynamic performance during large-signal transient conditions while providing stable operation during steady state conditions. The invention also relates to a method and a modification of a DC-DC converter topology that comprises connecting a controlled current source between an input terminal and an output terminal of the DC-DC converter; detecting a load current step to a new load current; modifying a duty cycle of the DC-DC converter; and modifying current through a parallel output capacitor of the DC-DC converter by controlling current of the current source. The methods and circuits provided herein are applicable to Buck converters and Buck-derived converters such as forward, push-pull, half-bridge, and full-bridge converters.