Switched Converter Adaptive Load Current Feedforward Control
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Solution Overview
Problem
Boost converters face constraints in achievable closed-loop bandwidth due to the presence of right-half-plane zeros (RHPZ), leading to prolonged load-transient response and impaired dynamic performance.
Innovation Solution
Implementing an adaptive load current sensing and feedforward control loop, where the load current is continuously measured and used to generate a feedforward control signal, adjusted by adaptation circuitry and a variable gain amplifier, to enhance dynamic response and mitigate the effects of RHPZ.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If classical peak current mode control is used, then the converter is simple to implement, but the closed-loop bandwidth is limited due to right-half-plane zeros
Solution Approach 1:
The patent measures load current in advance and uses it to generate a feedforward control signal before the load transient fully impacts the output. This preliminary action allows the controller to anticipate and respond to load changes more quickly, effectively increasing the closed-loop bandwidth without requiring complex compensation networks that would limit bandwidth.
Solution Approach 2:
The patent introduces an intermediary feedforward control path that processes load current measurements separately from the main feedback loop. This intermediary path generates control signals that are combined with the classical peak current mode control signals, allowing the system to achieve higher bandwidth while maintaining the simplicity of the original control structure.
2Speed
If the closed-loop bandwidth is increased to improve dynamic response, then the load-transient response improves, but stability is compromised due to right-half-plane zeros
Solution Approach 1:
By measuring load current in advance and generating feedforward control signals before the transient occurs, the system can respond to load changes more quickly without waiting for the feedback loop to detect the output voltage deviation. This preliminary action improves dynamic response while maintaining stability because the feedforward path does not introduce additional phase lag in the feedback loop.
Solution Approach 2:
The patent combines feedforward control based on load current measurement with the classical feedback mechanism. The feedback loop continues to provide stability assurance by correcting any residual errors, while the feedforward path provides the fast initial response. This combination allows the system to achieve both fast dynamic response and maintained stability.
3Speed
If load current is measured continuously and used for feedforward control, then the response to load transients is faster, but the device complexity increases
Solution Approach 1:
The patent introduces an intermediary feedforward control path that processes load current measurements separately from the main feedback loop. This intermediary path generates control signals that are combined with the classical peak current mode control signals, allowing the system to achieve higher bandwidth while maintaining the simplicity of the original control structure.
Solution Approach 2:
The patent utilizes existing circuit parameters and nodes (such as the load current measurement point) to generate the feedforward control signal without requiring entirely new measurement circuits. By repurposing existing signals and components, the implementation complexity is minimized while still achieving faster load-transient response.
Data Source
AI summary
A switched voltage converter may be controlled with load current feedforward control loop in addition to an output voltage feedback loop. The converter includes a first switch device that is controlled to open and close at a selected switching rate with a selected duty cycle. The first switch device is coupled in series with an inductor and conducts current through the inductor while the first switch is closed. A second switch device conducts current from the inductor to an output capacitor and to load while the first switch is open to produce an output voltage and a resulting load current through the load. The load current is measured in a continuous manner and a load current feedforward control signal is generated that is representative of the load current. The switch rate and/or duty cycle of the first switch is adjusted in response to the load current feedforward control signal.