SMPS Digital Control Feed-Forward Compensation for Voltage Transients
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Solution Overview
Problem
Existing switched mode power supply (SMPS) control units face challenges with long computation times, increased power consumption, noise introduction due to quantization, and inherent delays causing transients, especially when dealing with input voltage transients and light loads.
Innovation Solution
A digital control unit with a coarse, low-computation feed forward compensation process that rapidly responds to input voltage transients by performing arithmetic shift operations for initial adjustments and subsequent accurate calculations, reducing the impact of transients on output voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a traditional feedback compensator is used to control duty cycle, then output voltage stability is improved, but response speed to input voltage transients deteriorates
Solution Approach 1:
The feed-forward compensator performs preliminary action by detecting input voltage transients before they significantly affect the output voltage and proactively adjusting the duty cycle. The transient detector monitors Vin and triggers early compensation, while the coarse adjustment module provides immediate duty cycle modification based on the detected transient, preventing large output voltage deviations before they occur.
Solution Approach 2:
The compensation system is segmented into distinct functional modules: a transient detector for monitoring input voltage, a coarse adjustment module for immediate duty cycle modification, and an accurate adjustment module for precise output voltage regulation. This segmentation allows each module to specialize in specific tasks, with the coarse module handling rapid transient response and the accurate module ensuring steady-state precision.
2Measurement precision
If accurate voltage feed-forward compensation is performed, then response accuracy to input voltage transients is improved, but computation time increases
Solution Approach 1:
The feed-forward compensation is segmented into two stages: coarse adjustment and accurate adjustment. The coarse adjustment module provides immediate, computationally simple compensation using basic calculations, while the accurate adjustment module performs more precise calculations. This temporal segmentation allows the system to first respond quickly to transients and then refine the compensation accuracy.
Solution Approach 2:
The compensation operates in periodic phases: first the coarse adjustment is applied immediately upon transient detection, then the accurate adjustment is computed and applied in subsequent cycles. This periodic action pattern allows the system to balance speed and accuracy by alternating between rapid initial compensation and more computationally intensive refinement.
3Device complexity
If only feedback compensation is used, then system complexity is reduced, but output voltage transient magnitude increases
Solution Approach 1:
The feed-forward compensator performs preliminary action by detecting input voltage transients and adjusting the duty cycle before the transients can cause large output voltage deviations. The transient detector continuously monitors Vin and triggers compensation proactively, reducing the magnitude of output voltage transients before they fully develop.
Solution Approach 2:
The feed-forward compensator acts as an intermediary between the input voltage and the duty cycle control. It processes the input voltage transient information and generates compensatory duty cycle adjustments that are combined with the feedback control signal, thereby mediating the effect of input transients on the output voltage.
4Ease of manufacture
If ADC quantization is used for input voltage measurement, then measurement is simplified, but noise is introduced causing spurious transients
Solution Approach 1:
The coarse adjustment and accurate adjustment modules work together to combine the benefits of simple and precise measurements. The coarse module uses simplified quantized ADC data for rapid initial compensation, while the accurate module refines the measurement and compensation. This merging allows the system to tolerate quantization noise in the initial stage while achieving accurate final compensation.
Data Source
AI summary
A digital control unit generates a control signal to control a duty cycle of a switched mode power supply such that a faster response to an input voltage transient is achieved. The digital control unit comprises a feedback compensator, a feed forward compensator, a transient detector, and a controller. The transient detector receives a signal indicative of the input voltage of the switched mode power supply and detects transients on the received signal. The feedback compensator receives a signal indicative of the output voltage of the switched mode power supply and adjusts the control signal. The feed forward compensator receives a signal indicative of the input voltage of the switched mode power supply, performs a relatively fast, but coarse, adjustment of the control signal, and then performs a more accurate, but relatively slow, adjustment of the control signal.