Sensorless Motor Control Using Duty-Based Zero-Cross Correction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional sensorless motor control techniques struggle to maintain stability at low rotation ranges due to deviations in induced voltage detection, leading to inaccurate zero-cross point detection and difficulties in performing stable sensorless control.
Innovation Solution
A motor control device that includes a drive circuit, a first voltage detection unit, and a control unit. The control unit detects a zero-cross point by intersecting a detected terminal voltage with a zero-cross determination level and corrects the voltage value by multiplying it with a coefficient inversely proportional to the output duty ratio, especially at low duty ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If sensorless control is performed at low duty ratio, then energy consumption is reduced, but detection value of induced voltage deviates from theoretical voltage value due to hardware response delay
Solution Approach 1:
The patent changes the parameter of voltage detection by introducing a correction coefficient that is calculated based on the duty ratio. When the duty ratio is below a threshold, the correction coefficient compensates for the hardware response delay effect, adjusting the detected voltage value to match the theoretical value. This allows accurate voltage detection at low duty ratios while maintaining energy efficiency.
2Device complexity
If conventional sensorless control is used at low rotation range, then device complexity is reduced, but zero-cross point detection timing deviates from ideal timing
Solution Approach 1:
The patent implements a feedback mechanism where the detected terminal voltage is compared with the zero-cross determination level, and the correction coefficient is adjusted based on the duty ratio feedback. This feedback loop ensures that the zero-cross point detection timing remains accurate even at low rotation ranges, without adding significant complexity to the control system.
3Device complexity
If voltage detection is performed without correction at low duty ratio, then device complexity is reduced, but sensorless control stability deteriorates
Solution Approach 1:
The patent applies preliminary action by pre-calculating the correction coefficient based on the duty ratio before performing voltage detection. This preliminary correction ensures that the voltage detection results are accurate from the start, preventing control instability without requiring complex real-time adjustments or additional hardware.
Data Source
AI summary
A control device for a three-phase motor includes a drive circuit that converts DC power supply voltage into three-phase AC voltage and supplies the three-phase AC voltage to the three-phase motor, a first voltage detection unit that detects terminal voltage of three phases of the three-phase motor, and a control unit that detects a point at which a first voltage value, which is a detection value of the terminal voltage, intersects a predetermined zero-cross determination level as a zero-cross point, and controls the drive circuit based on a detection result of the zero-cross point. The control unit corrects the first voltage value by multiplying the first voltage value by a first coefficient inversely proportional to an output duty ratio with respect to the three-phase motor in a case where the output duty ratio is equal to or less than a predetermined threshold.