Motor Control Device Power Line Break Detection
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Solution Overview
Problem
Conventional motor control devices face challenges in quickly detecting a break in the power supply line due to noise-induced errors and inability to distinguish between one-phase and two-phase breaks, leading to delayed detection of urgent two-phase breaks.
Innovation Solution
A motor control device that sets a predetermined voltage based on the target low voltage defined by the power supply voltage and PWM duty cycle, allowing for precise detection by comparing low and middle voltages to avoid noise errors and using a counter to differentiate between one-phase and two-phase breaks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the monitoring time is set comparatively long to avoid noise errors, then the measurement precision is improved, but the detection speed deteriorates
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing the relationship between duty ratios and voltage thresholds in a lookup table before operation. During runtime, the break detection unit simply queries this pre-prepared table based on the current duty ratio, avoiding real-time complex calculations and enabling fast detection without prolonged monitoring. This resolves the contradiction by preparing detection criteria in advance, allowing quick comparison with actual voltages.
Solution Approach 2:
The patent implements dynamics by making the voltage threshold dynamic and adaptive to the PWM duty ratio. Instead of using a fixed threshold, the break detection unit dynamically selects the appropriate threshold from the lookup table based on the current duty ratio setting. This allows the detection system to adapt to different operating conditions, maintaining high detection accuracy across varying duty ratios while enabling fast response without extended monitoring periods.
2Device complexity
If a simple voltage comparison method is used, then the device complexity is reduced, but the ability to distinguish between one-phase and two-phase breaks deteriorates
Solution Approach 1:
The patent applies segmentation by dividing the break detection process into distinct functional units: a break detection unit for basic voltage comparison and a break type determination unit for analyzing break patterns. The segmentation of detection criteria into duty ratio-based thresholds allows the system to differentiate between one-phase and two-phase breaks by comparing which specific phase voltages deviate from expected values, thereby maintaining simplicity while enabling comprehensive break type identification.
Solution Approach 2:
The patent implements feedback by continuously monitoring phase voltages, comparing them against duty ratio-dependent thresholds, and using the comparison results to determine break types. The system provides feedback through the counter that tallies the number of detected breaks, and this feedback loop enables the determination unit to distinguish between single and multiple phase breaks based on the pattern and frequency of voltage deviations, all while maintaining relatively simple circuitry.
3Measurement precision
If the threshold value is set high to avoid noise errors, then the measurement precision is improved, but the detection speed deteriorates
Solution Approach 1:
The patent applies parameter changes by making the voltage threshold a variable parameter that changes based on the PWM duty ratio rather than being a fixed high value. The break detection unit selects thresholds from a lookup table that contains pre-calculated values corresponding to different duty ratios. This allows the threshold to be optimized for each operating condition, enabling reliable detection without requiring excessively high thresholds that would slow down the detection response.
Data Source
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AI summary
A microcomputer compares a low voltage LV and a middle voltage MV to a predetermined voltage Vth set at a value in the vicinity of the grounded voltage (0 V) on the basis of detected phase voltages Vu, Vv and Vw, and thus, detects a break in a power supply line.