Stall Detection for Multiphase Motors via Current Difference Analysis
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Solution Overview
Problem
Existing methods for stall detection in synchronous multiphase motors driven in sinusoidal mode face challenges, such as decreased motor power and noisy torque ripples due to the need for a floating phase to measure back electromotive force (BEMF), and are unreliable for low-speed motors with low-BEMF levels.
Innovation Solution
A method and circuit that measure phase currents and their differences at regular intervals during sinusoidal micro-stepping, generating a stall detection signal by analyzing these differences and comparing them to a threshold value, without requiring a floating phase or position sensors, and dynamically adjusting the threshold based on average motor current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If BEMF voltage is measured using a floating phase, then stall detection is enabled, but motor power decreases and torque ripples increase
Solution Approach 1:
The patent extracts the stall detection function from the traditional BEMF measurement method using a floating phase. Instead of dedicating one phase to BEMF measurement (which reduces motor power), the invention extracts only the necessary current difference information from all phases operating normally, eliminating the need for a floating phase while maintaining stall detection capability.
Solution Approach 2:
The patent makes all phases multi-functional: they simultaneously contribute to motor power generation and provide stall detection information. By measuring current in all phases and calculating differences, the system achieves both propulsion and monitoring functions without requiring a dedicated floating phase, thus improving overall system efficiency.
2Reliability
If BEMF voltage is measured using a floating phase, then stall detection is enabled, but noisy torque ripples occur
Solution Approach 1:
The patent extracts stall detection information from the difference between phase currents rather than from BEMF measurements taken during a floating phase interval. This extraction method from normal operating currents eliminates the disruptive floating phase operation that causes torque ripples, while still providing reliable stall detection through current difference analysis.
3Reliability
If current increase method is used for stall detection, then stall detection is possible, but it fails for low-speed motors with low-BEMF level
Solution Approach 1:
The patent changes the detection parameter from absolute current increase (which is too small at low speeds) to current difference between phases. By measuring the difference between phase currents rather than absolute current changes, the system becomes sensitive enough to detect stall conditions even in low-speed motors with low BEMF levels, significantly improving adaptability across different motor operating conditions.
Data Source
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AI summary
A method for detecting stall of a multiphase motor operated in a sinusoidal micro-stepped mode. The method comprises: a) measuring (210) at least one phase current and/or measuring (210) the sum of all phase currents at regular time intervals synchronous with the micro-steps, b) calculating (220) the difference between the measured phase current at a first moment and the measured phase current of the same phase at a previous moment and/or the difference between the measured sum of all phase currents at a first moment and the measured sum of all phase currents at a previous synchronous moment, c) analyzing (230) the series of obtained current differences so as to generate a stall detection signal.