Nonlinear Voltage-Mode Control for Wide-Input Power Converters
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Solution Overview
Problem
Conventional voltage-mode control of power converters experiences reduced control loop bandwidth and poor load transient response due to input voltage variations, leading to large output voltage ripple, especially at lower input voltages, and requires hardware-intensive solutions like current-mode control or input voltage feedforward control.
Innovation Solution
A power converter controller that includes an analog-to-digital converter to generate a digital representation of the feedback signal, a nonlinear gain block to transform the signal using a nonlinear function, and a switch control block to adjust the on-time of the primary-side switch, thereby maintaining a high small-signal control-to-output DC gain across a wide range of input voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional voltage-mode control is used, then the control loop bandwidth is reduced at lower input voltages, but the hardware complexity remains low
Solution Approach 1:
The patent applies parameter changes by transforming the feedback signal through a nonlinear function that compensates for input voltage variations. The transformation function adjusts the feedback signal based on the duty cycle, maintaining consistent control loop bandwidth across different input voltages. This digital parameter transformation resolves the contradiction by improving control loop speed without adding hardware complexity.
Solution Approach 2:
The patent substitutes hardware-intensive current-mode control with a digital signal processing approach. Instead of using current sensors, comparators, and additional analog circuitry, the invention uses a digital nonlinear transformation of the voltage feedback signal to achieve the same control loop bandwidth improvement, thereby reducing hardware complexity while maintaining or improving control performance.
2Speed
If current-mode control is used to eliminate input voltage variation effects, then control loop bandwidth is improved, but hardware complexity and power consumption increase
Solution Approach 1:
The patent replaces current-mode control hardware with a digital voltage-mode control approach. Instead of using current sensors, operational amplifiers, and comparator circuits required for current-mode control, the invention uses a digital microcontroller to perform nonlinear transformation on the voltage feedback signal. This substitution eliminates the need for additional analog hardware while achieving the same control performance.
Solution Approach 2:
The patent creates a digital copy or representation of the feedback signal and processes it through software-based nonlinear transformation. Rather than physically measuring current and processing it through analog circuits, the system copies the voltage feedback signal and applies mathematical transformation algorithms, achieving current-mode control effectiveness through digital signal processing instead of hardware.
3Speed
If input voltage feedforward control is used, then control loop bandwidth is improved, but hardware complexity increases due to additional voltage sensing
Solution Approach 1:
The patent extracts the essential control function from complex hardware circuits and implements it through digital signal processing. Instead of adding feedforward voltage sensing hardware and processing circuits, the invention extracts the control bandwidth improvement function and implements it through software-based nonlinear transformation of the existing feedback signal, eliminating the need for additional voltage sensing hardware.
Solution Approach 2:
The patent makes the digital microcontroller perform multiple functions: it processes the feedback signal, applies nonlinear transformation, and generates control signals. This universal digital approach replaces dedicated analog circuits for feedforward control, allowing the same hardware to achieve control loop bandwidth improvement without additional voltage sensing hardware.
4Speed
If voltage-mode control is designed for high input voltage operation, then control loop bandwidth is maintained at high voltages, but output voltage ripple increases at low input voltages
Solution Approach 1:
The patent applies dynamics by making the feedback signal transformation adaptive to input voltage conditions. The nonlinear transformation function dynamically adjusts the feedback signal based on the duty cycle, which varies with input voltage. This dynamic adjustment maintains consistent control loop bandwidth across all input voltages, preventing the increase in output voltage ripple that occurs with fixed-bandwidth designs at low input voltages.
Data Source
AI summary
A power converter controller includes an analog to digital converter (ADC) to generate a digital representation of a feedback signal of a power converter, the feedback signal being received from a compensator of the power converter and being based on an output voltage of the power converter. A nonlinear gain block of the power converter controller receives the digital representation of the feedback signal and generates a transformed digital representation of the feedback signal using a nonlinear function. A switch control block of the power converter controller controls an on-time of a primary-side switch of the power converter based on the transformed digital representation of the feedback signal.