Iterative Average Current Mode Control for Multi-Mode DC-DC Converters
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Solution Overview
Problem
Multi-mode DC-DC converters face issues with output voltage ringing during mode transitions due to interactions between voltage and current control loops, which can reduce voltage loop bandwidth and exacerbate ringing problems, especially when switching between buck, boost, and buck-boost modes.
Innovation Solution
The implementation of an iterative average current mode control, where the output voltage of the error amplifier is proportional to the output current, with a compensation method that remains the same across modes, reduces output voltage ringing by avoiding subharmonic oscillations and maintaining higher switching frequency operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional voltage and current control loops are used in multi-mode DC-DC converters, then the converter can operate in buck, boost, and buck-boost modes, but output voltage ringing occurs during mode transitions due to interactions between control loops
Solution Approach 1:
The patent extracts the current control loop from the traditional voltage control structure and implements it as a separate iterative average current mode control loop. This separation prevents the harmful interactions between voltage and current loops that cause output voltage ringing during mode transitions, while maintaining the ability to operate in multiple modes.
Solution Approach 2:
The patent changes the control parameter from traditional peak current mode to iterative average current mode. By using average current sensing and control, the system achieves smoother transitions between modes and eliminates the subharmonic oscillations and ringing that occur with peak current mode control during mode changes.
2Speed
If voltage loop bandwidth is increased to improve response, then transient response improves, but output voltage ringing is exacerbated during mode transitions
Solution Approach 1:
The patent implements iterative average current mode feedback control that uses information from previous switching cycles to adjust the current control. This feedback mechanism provides damping during mode transitions, allowing for faster transient response without exacerbating output voltage ringing, as the iterative feedback compensates for the increased bandwidth effects.
3Productivity
If peak current mode control is used, then switching frequency can be increased, but subharmonic oscillations occur during mode transitions causing voltage ringing
Solution Approach 1:
The patent replaces the peak current mode control mechanism with iterative average current mode control. This substitution eliminates the subharmonic oscillation mechanism inherent in peak current mode control during mode transitions, allowing high switching frequency operation without the harmful oscillations and ringing that would otherwise occur.
Data Source
AI summary
A multi-mode converter using iterative average current mode pulse width modulation (PWM) control is provided. The converter may include a current sense amplifier configured to output a current sense signal over a present switching cycle based on an inductor current through an inductor, a voltage error amplifier configured to output an error voltage based on a difference between a reference voltage and an output voltage, and a PWM controller. The PWM controller may include an error voltage modifier circuit configured to selectively output the error voltage or a modified error voltage based on a mode signal, and an iterative average current control circuit configured to generate a PWM signal based on the output from the error voltage modifier circuit, the current sense signal over the present switching cycle and a current sense signal over a previous switching cycle that precedes the present switching cycle.