Inverter Current Sensing with Duty-Ratio Offset Hold Logic
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Solution Overview
Problem
Existing current detection systems struggle to accurately detect offset current during PWM control in multiphase inverters, leading to errors in current control and potentially causing torque ripples in electric power steering systems.
Innovation Solution
A current detection device that includes a current detection unit, a correction value calculation unit, and a correction unit. The correction value calculation unit calculates an offset correction value based on current detection values during the switching element's off period and updates this value. The correction unit then uses this offset correction value to correct current detection values during the switching element's on period, with specific conditions for updating the offset correction value based on duty ratio limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If offset current detection is performed during PWM control by detecting current through switching element, then current control accuracy should be improved, but offset current cannot be accurately detected when duty ratio is at extreme values (0% or 100%)
Solution Approach 1:
The system performs preliminary detection of offset current during periods when the switching element is OFF, before the actual PWM control period begins. This allows the offset current to be detected and corrected in advance, avoiding the problem of inaccurate detection during extreme duty ratio conditions. The correction value is calculated and stored beforehand, then applied during the control period to ensure accurate current control.
2Measurement precision
If correction value is continuously updated during PWM control, then current control accuracy is improved, but system complexity and computational load increase
Solution Approach 1:
The system updates the offset current correction value periodically during specific phases of PWM control (when switching element is OFF), rather than continuously during the entire control cycle. This periodic update approach maintains current control accuracy while reducing computational load and simplifying the control system architecture. The correction value is updated at appropriate intervals and held constant during periods when it cannot be accurately measured.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enables accurate detection of offset current during PWM control, thereby improving the accuracy of current control and reducing torque ripples in electric power steering systems.
Implementation Method 1
a current detection unit configured to detect current flowing through a switching element of one arm of either an upper-side arm or a lower-side arm of a multiphase inverter on which PWM control is executed, based on a voltage drop of a resistor element connected in series to the switching element
Data Source
AI summary
A current detection device includes a current detection unit configured to detect current flowing through a switching element of a lower-side arm; a correction value calculation unit configured to calculate an offset correction value, based on a detection value of the current detected by the current detection unit in a period during which the switching element off during PWM control, and to hold and update the calculated offset correction value; and a correction unit configured to correct, by the offset correction value held by the correction value calculation unit, the detection value of the current detected by the current detection unit in a period during which the switching element is on. The correction value calculation unit is configured to not update the offset correction value in a case where a duty ratio of the PWM control is equal to or less than a duty ratio lower limit value.