Nonlinear Ramp Generator for PWM Transient Response
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Solution Overview
Problem
Traditional PWM control systems exhibit slow transient response and instability due to varying input voltage and output voltage, leading to potential power supply issues and difficulties in maintaining loop stability, especially during changes in power supply or load.
Innovation Solution
A nonlinear ramp generator is introduced to produce a waveform signal with variable slopes, such as log, exponential, or multi-piecewise-linear ramps, which adjusts based on the duty cycle, input voltage, and output voltage, thereby maintaining constant modulation and loop gains, improving the system's transient response and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a traditional linear ramp generator is used in PWM control, then the system structure is simple, but the transient response is slow and the loop stability varies with input voltage changes
Solution Approach 1:
The patent applies the Dynamics principle by transforming the static linear ramp generator into a dynamic nonlinear ramp generator whose slope varies with the duty cycle. The ramp slope is adjusted dynamically based on the relationship between duty cycle and modulation gain, allowing the system to maintain optimal performance across different operating conditions. This dynamic adjustment significantly improves transient response speed while the nonlinear function can be implemented through relatively simple circuit elements.
Solution Approach 2:
The patent applies the Parameter changes principle by changing the ramp voltage parameters (slope) based on the duty cycle. Specifically, the ramp slope is modified as a function of the duty cycle to compensate for the varying modulation gain. When the duty cycle changes, the ramp slope automatically adjusts to maintain a stable loop gain, thereby improving both transient response and loop stability without requiring complex additional components.
2Reliability
If the PWM controller uses a constant slope ramp, then the modulation gain varies with input voltage, but the system is easier to implement
Solution Approach 1:
The patent applies the Feedback principle by using the duty cycle information (which reflects the output voltage status) to feed back and adjust the ramp slope. The nonlinear ramp generator uses the duty cycle as a feedback parameter to automatically adjust the ramp slope, ensuring that the loop gain remains stable despite variations in input voltage. This feedback mechanism improves loop reliability while the feedback path can be implemented through simple voltage-controlled elements.
Solution Approach 2:
The patent applies the Preliminary action principle by pre-establishing the nonlinear relationship between the duty cycle and ramp slope. Instead of reacting to voltage variations after they occur, the system proactively adjusts the ramp slope based on the duty cycle before significant voltage deviations affect the loop stability. This preliminary adjustment ensures that the modulation gain remains stable across different input voltage conditions.
3Speed
If the ramp slope is increased to improve transient response, then the correction speed increases, but the modulation gain becomes more sensitive to input voltage variations
Solution Approach 1:
The patent applies the Dynamics principle by making the ramp slope dynamic rather than fixed. The slope is continuously adjusted based on the duty cycle, allowing the system to have a steeper slope (faster correction) when needed while maintaining appropriate slope values under different operating conditions. This dynamic adaptation resolves the contradiction by allowing fast correction speed only when the duty cycle and input voltage conditions warrant it, thereby maintaining modulation gain stability across the full operating range.
Data Source
AI summary
A pulse-width-modulation (PWM) control system with nonlinear ramp is disclosed. A nonlinear ramp generator generates a nonlinear ramp varied with the duty (Vout/Vin) in a waveform signal, which could be a logarithm ramp, an exponent ramp, a multi-piecewise-linear ramp, a power ramp or a combination of above. The slope of the ramp is not a constant due to the non-linear characteristic. The voltage Vramp will vary with the input voltage Vin, output voltage Vout, and duty (Vout/Vin), therefore it will reduce the influence of the input voltage Vin or output voltage Vout on the modulation gain and loop gain, even to keep the modulation gain and loop gain in constant value. As mentioned-above, the present invention improves the transient response of system, the sensitivity for variation of Vin and Vout, thus it is capable of correcting the output voltage quickly, for supplying a more steady power output.