Variable Frequency Control for Peak Current Mode Power Converters
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Solution Overview
Problem
In power conversion apparatuses with drive switches, existing control methods fail to maximize the on-operation period relative to the switching period, leading to insufficient output voltage when input voltage is low, even with peak current mode control.
Innovation Solution
A control apparatus that includes a current control unit, a switching determining unit, and a frequency switching unit, which adjusts the switching frequency of the drive switch based on the output of a comparator to maximize the on-operation period relative to the switching period, allowing for peak current mode control and expanding the output voltage range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the switching frequency is increased to improve the output voltage response speed, then the output voltage can reach command voltage faster, but the on-operation period ratio cannot be maximized when input voltage is low
Solution Approach 1:
The patent applies dynamics by making the switching frequency variable rather than fixed. The frequency switching unit dynamically adjusts the switching frequency between a first frequency and a second frequency based on real-time detection of comparator output inversion status, allowing the system to optimize between response speed and on-operation period ratio under different operating conditions.
Solution Approach 2:
The patent changes the switching frequency parameter adaptively. When the comparator output does not invert during the on-operation period, the system switches to a lower frequency to maximize the on-operation period ratio. This parameter change enables the system to overcome the limitation of insufficient output voltage at low input voltages while maintaining good response characteristics.
2Duration of action of moving object
If the on-operation period is increased to maximize the time ratio, then the output voltage can reach higher levels, but the switching frequency must be decreased
Solution Approach 1:
The system dynamically adjusts the switching frequency based on whether the comparator output inverts during the on-operation period. This dynamic adjustment allows the on-operation period to be extended when needed (by lowering frequency) while maintaining higher frequencies for faster response when conditions permit, resolving the contradiction between duration and speed.
Solution Approach 2:
The patent uses feedback from the comparator output inversion detection to control the frequency switching. The switching determining unit monitors whether inversion occurs during the on-operation period and provides feedback to the frequency switching unit, which adjusts the switching frequency accordingly. This closed-loop feedback mechanism enables automatic optimization of the on-operation period ratio without manual intervention.
3Measurement precision
If peak current mode control is used to control the drive switch, then the current control precision is improved, but the determination of maximum time ratio state becomes complex
Solution Approach 1:
The patent simplifies the determination of maximum time ratio state by using feedback from the comparator output inversion status. Instead of complex calculations or multiple sensors, the system simply detects whether the comparator output inverts during the on-operation period. This feedback-based approach maintains peak current mode control precision while significantly reducing control system complexity.
Solution Approach 2:
The comparator inherently provides the information needed to determine the maximum time ratio state through its output inversion status. The system leverages the existing comparator function to simultaneously perform current comparison and maximum time ratio detection, eliminating the need for separate determination mechanisms and reducing overall system complexity.
Data Source
AI summary
A control apparatus performs peak current mode control in which a drive switch is turned off when output of a comparator is inverted during an on-operation period determined by a basic signal. The comparator inverts the output when a reactor current increases to a command current. The control apparatus determines that a switching frequency of the drive switch is required to be switched when the output of the comparator is detected to have not become inverted during the single switching period while the peak current mode control is being performed. The control apparatus sets the switching frequency to a first frequency when the switching determining unit determines that the switching frequency is not required to be switched, and switches the switching frequency from the first frequency to a second frequency lower than the first frequency when the switching determining unit determines that the switching frequency is required to be switched.