Auxiliary-Assisted DC-DC Converter Control for Faster Load Transients
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Solution Overview
Problem
Current DC-DC converters face challenges in achieving fast transient response, particularly in automotive applications, due to the constraints imposed by the auxiliary inductor current slew rate, which is limited by the output voltage, necessitating large and costly decoupling capacitors.
Innovation Solution
A controller is introduced that operates a main converter and an auxiliary converter at different frequencies, with the main converter controlling the voltage at the auxiliary output, thereby relaxing the physical limits of the auxiliary LC filter and improving transient response. This includes adaptive-voltage-positioning control to dynamically adjust slew rates based on load currents, allowing for reduced capacitance and current requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the auxiliary inductor current slew rate is increased to improve transient response, then the transient response is improved, but the output voltage constraint limits the achievable slew rate
Solution Approach 1:
The patent implements dynamic control of the auxiliary inductor current slew rate through a current source that can be independently regulated. The slew rate is no longer fixed by the output voltage constraint but can be dynamically adjusted based on transient requirements, allowing the system to adapt to different transient conditions while maintaining fast response capability.
Solution Approach 2:
The patent changes the controlling parameter for the auxiliary inductor current from being voltage-limited to being current-source-limited. By introducing a controlled current source with adjustable slew rate parameters, the system can achieve higher and more flexible current slew rates that are not constrained by the output voltage, thereby improving transient response.
2Reliability
If large decoupling capacitors are used to meet transient requirements, then transient response is improved, but cost and volume increase
Solution Approach 1:
The patent replaces the passive mechanical approach of using large decoupling capacitors with an active control system. The controlled current source in the auxiliary converter actively manages transient current delivery, substituting the need for large energy-storage capacitors with a dynamically controlled current generation mechanism, thereby reducing capacitor volume while maintaining transient performance.
Solution Approach 2:
The auxiliary converter acts as an intermediary between the main power stage and the output load. It provides a controlled current path that supplements or replaces the traditional decoupling capacitor function, enabling transient response improvement without requiring large output capacitors.
3Speed
If the auxiliary converter operates at high frequency to improve transient response, then transient response is improved, but control complexity increases
Solution Approach 1:
The patent segments the control functions between the main converter and auxiliary converter. The main converter operates at a lower frequency for steady-state power delivery, while the auxiliary converter operates at a higher frequency specifically for transient response. This functional segmentation allows each converter to be optimized for its specific role without requiring the entire system to operate at high frequency, managing complexity through division of labor.
Data Source
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AI summary
A method, power converter and controller are disclosed for controlling a power converter having a main converter connected between a first input voltage and a ground and having a main output at an output terminal, an auxiliary converter connected between a second input voltage and the ground and having an auxiliary output, an output capacitor connected between the main output terminal and a ground, and an auxiliary capacitor connected between the auxiliary output and the main output terminal; and a controller; the method comprising: operating the main converter at a first frequency, operating the auxiliary converter at a second frequency; controlling the main converter to control the voltage at the auxiliary output; and controlling the auxiliary converter to control the voltage at the main output.