Nonlinear PWM Controller for DC-DC Converter Stability
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Solution Overview
Problem
Conventional PWM control systems for DC-to-DC converters face limitations in duty cycle range, leading to suboptimal behavior and instability during large disturbances, and are not well-suited for systems requiring high power efficiency.
Innovation Solution
A nonlinear PWM controller that uses an amplitude determining input signal based on system state variables, allowing for optimal duty cycle determination through methods like dynamic programming, and incorporates state estimation to improve control accuracy and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a linear compensated control loop with large bandwidth is used, then the rejection of output voltage to load current steps is improved and output capacitor size is minimized, but the system becomes unstable for large disturbances due to PWM duty cycle limitations (0%-100%)
Solution Approach 1:
The patent transforms the control approach from linear to nonlinear by changing the mathematical parameters of the controller. Specifically, it uses a nonlinear compensator that can operate effectively across the full duty cycle range (0%-100%), allowing the system to maintain stability for large disturbances while preserving high feedback bandwidth. The nonlinear control law adapts its parameters based on the operating point, enabling optimal performance both near equilibrium and during large transients.
2Ease of operation
If PWM duty cycle is limited to 0%-100%, then the control system operates linearly for small disturbances, but the behavior becomes suboptimal and unstable for large disturbances
Solution Approach 1:
The patent implements a dynamic control strategy where the controller characteristics change based on the operating conditions. The nonlinear compensator dynamically adjusts its behavior - operating in a linear-like manner for small disturbances near the equilibrium point, while transitioning to a nonlinear mode for large disturbances. This dynamic adaptation allows the system to maintain both ease of operation for small signals and reliability for large signals.
3Device complexity
If linear amplifiers are used instead of PWM, then the control is simpler for small disturbances, but the amplitude limitation similar to PWM duty cycle constraints prevents optimal performance for large disturbances
Solution Approach 1:
The patent replaces the traditional linear amplifier mechanism with a nonlinear control system that uses pulse width modulation. Instead of relying on linear amplification with inherent amplitude limitations, the system uses nonlinear switching control where the duty cycle itself becomes the control variable. This substitution allows the system to achieve the full range of control authority (0%-100% duty cycle) while maintaining simplicity through the use of standard PWM circuitry rather than complex linear amplifiers with extended dynamic ranges.
Data Source
AI summary
A switching power supply includes a circuit having at least two reactive components to provide an output voltage and capable of being switched from a first output state to a second output state. A switching component switches the circuit between at least two switching states including the first output state and the second output state. A pulse width modulator receives a duty cycle and drives the switching component to cause switching between two of the at least two switching states. A nonlinear controller component provides a duty cycle to the pulse width modulator. The duty cycle corresponds to at least one predetermined power supply state variable. The nonlinear controller component includes a processor to apply an optimization technique to minimize a predetermined function of the duty cycle and internal states of the power supply and to obtain a relationship between the duty cycle and at least one predetermined state variable.