Switching Element Control for Accurate Low-Duty Current Sensing
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Solution Overview
Problem
Existing electronic apparatuses face challenges in accurately measuring current values due to missed detection timings during low conduction ratios of switching elements, leading to inaccurate current measurements.
Innovation Solution
A control device controls the switching element to be in an on-state during a period defined by a detective conduction ratio higher than the target conduction ratio, allowing for accurate measurement of current values using a current sensor signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the switching element is controlled with a low conduction ratio to maintain voltage within target range, then the capacitor voltage is properly regulated, but the on-state period becomes too short to include sampling timing, resulting in inaccurate current measurement
Solution Approach 1:
The controller determines in advance whether the product of switching cycle length and target conduction ratio is smaller than the sampling cycle length. Based on this preliminary determination, it selectively adjusts the conduction ratio to ensure accurate current measurement while maintaining voltage regulation reliability.
Solution Approach 2:
The controller dynamically adjusts the conduction ratio parameter based on the relationship between switching cycle, sampling cycle, and target conduction ratio. When the product of switching cycle and target conduction ratio is insufficient, the controller increases the conduction ratio to ensure the on-state period includes sampling timing, thereby achieving accurate current measurement.
2Measurement precision
If the conduction ratio is increased to ensure sampling occurs during on-state, then current measurement accuracy improves, but the capacitor voltage may exceed the target voltage range
Solution Approach 1:
The controller performs a preliminary check to determine whether increasing the conduction ratio is necessary by comparing the product of switching cycle and target conduction ratio with the sampling cycle length. This preliminary action prevents unnecessary increases in conduction ratio that would cause voltage to exceed the target range.
Solution Approach 2:
The controller selectively adjusts the conduction ratio parameter only when necessary (when the product of switching cycle and target conduction ratio is smaller than sampling cycle length). This conditional parameter change ensures current measurement accuracy is improved only when required, while maintaining capacitor voltage within the target range during normal operation.
Data Source
AI summary
A control device controls a switching element that is connected to a conductor and that executes a switching operation for causing the conductor to switch between conductive and non-conductive states. The control device includes an element controller and a current value measurer. When a target conduction ratio is a positive value lower than 1, the element controller controls the switching element to be in an on-state during a period defined by a switching cycle and a detective conduction ratio than the target conduction ratio and equal to or lower than 1, in at least one cycle that is each the switching cycle. The current value measurer measures a value of direct current flowing in the conductor, based on a detected current value that is digital data generated in every sampling cycle independent from the switching cycle by detection of a current sensor signal output from a current sensor.