Motor Drive Overcurrent Threshold Adjustment for Current Stability
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Solution Overview
Problem
In motor drive control devices, the ΔΣADC method for converting motor current detection values into digital signals is slow, leading to instability when motor load increases rapidly, causing the motor current to exceed target values.
Innovation Solution
A semiconductor device with an A/D converter, overcurrent determination unit, drive control signal generation unit, and overcurrent threshold setting unit dynamically adjusts the overcurrent threshold based on conversion results to prevent current exceeding target values, using a ΔΣ modulation type A/D conversion circuit for real-time control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a ΔΣ modulation type A/D conversion circuit is used to convert motor current detection values, then the effective value of motor current can be obtained for stable constant current control, but the conversion time is relatively long (several tens of ms) causing the system to respond slowly to rapid load changes
Solution Approach 1:
The patent segments the current detection and control functions into two parts: a fast overcurrent protection function that operates independently using simple threshold comparison, and a slower constant current control function that uses the ΔΣADC for accurate effective value measurement. This segmentation allows each function to operate at its optimal speed without interfering with the other.
Solution Approach 2:
The overcurrent protection function performs preliminary action by continuously monitoring the instantaneous current and triggering protective measures before the slower ΔΣADC can detect and respond to overcurrent conditions. This preliminary protection mechanism prevents damage while the main control system processes data at its normal slower rate.
2Reliability
If the overcurrent threshold is set too low to prevent overcurrent, then protection is improved, but false overcurrent detection occurs during normal operation causing unnecessary control interruptions
Solution Approach 1:
The patent applies different quality requirements to different parts of the control system: the overcurrent protection function uses a simple, fixed threshold with high sensitivity for immediate protection, while the constant current control uses a dynamic, adaptive threshold that adjusts based on operating conditions. This local differentiation allows each function to optimize its threshold strategy without compromising the other.
Solution Approach 2:
The constant current control threshold is made dynamic by continuously adjusting it based on the target current and actual operating conditions, while the overcurrent protection threshold remains static and fixed. This dynamic adaptation allows the system to distinguish between normal transient current increases and actual overcurrent faults.
3Reliability
If the overcurrent threshold is dynamically adjusted based on conversion results, then false detection is reduced, but the control system complexity increases
Solution Approach 1:
The patent extracts the complex threshold adjustment logic into a separate overcurrent protection module that operates independently from the main constant current control loop. This modular extraction simplifies the overall system architecture by isolating the dynamic threshold adjustment functionality, making it easier to implement and maintain without affecting the core control algorithm.
Data Source
AI summary
A semiconductor device has an A/D converter configured to convert an analog signal representing a current flowing in a control target into a digital signal, an overcurrent determination unit configured to, based on the analog signal, determine that an overcurrent has occurred in the control target when the current flowing in the control target has exceeded an overcurrent threshold, and determine that the overcurrent has not occurred in the control target when the current flowing in the control target has not exceeded the overcurrent threshold, a drive control signal generation unit configured to generate a drive control signal for controlling driving of the control target so that the current flowing in the control target is equal to a target current, based on a conversion result of the A/D converter, and generate the drive control signal to reduce the current flowing in the control target when the overcurrent determination unit determines that the overcurrent has occurred, and an overcurrent threshold setting unit configured to set the overcurrent threshold based on the conversion result of the A/D converter and the target current.