Induction Machine Current Sensor Diagnosis via Phase Short-Circuit
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Solution Overview
Problem
Current methods for diagnosing current sensors in n-phase induction machines with n-1 sensors are inefficient, as they cannot accurately determine which sensor is defective and do not allow for recalibration, leading to potential hazards due to incorrect torque generation and increased costs.
Innovation Solution
A method involving short-circuiting the n phases of the induction machine for a short period to measure time profiles of n-1 short-circuit currents, comparing these with target values to identify errors such as offset, amplification discrepancies, short circuits, and demagnetization, allowing for sensor recalibration and defect detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If n-1 current sensors are used for regulation, then device complexity and costs are reduced, but the ability to diagnose sensor errors and perform recalibration is insufficient
Solution Approach 1:
The patent implements periodic short-circuit tests during machine operation to diagnose current sensor errors. The control unit periodically switches to a short-circuit operating state where all phases are short-circuited, measures the resulting currents with the n-1 sensors, and compares them against expected values. This periodic diagnostic action enables reliable error detection and recalibration capability without adding permanent diagnostic hardware, thus maintaining low device complexity while improving reliability.
Solution Approach 2:
The system uses its own operational characteristics during short-circuit states to perform self-diagnosis of current sensors. By measuring the short-circuit currents that naturally flow when phases are shorted and comparing these against calculated reference values, the system serves its own diagnostic needs using existing sensors and control logic, eliminating the need for separate diagnostic sensors or external testing equipment.
2Reliability
If additional current sensors are added to monitor all phases, then sensor error detection capability is improved, but device complexity and costs increase
Solution Approach 1:
Instead of continuously monitoring all phases with additional sensors, the system periodically switches to a short-circuit state to perform diagnostic measurements. This periodic action allows the n-1 existing sensors to serve dual purposes: normal regulation during operation and diagnostic measurement during short-circuit states, thereby achieving reliable error detection without adding permanent diagnostic hardware.
Solution Approach 2:
The existing n-1 current sensors are made multi-functional by using them both for normal phase current measurement during regulation and for diagnostic measurement during periodic short-circuit states. This universal usage of existing sensors eliminates the need for dedicated diagnostic sensors, reducing device complexity while maintaining reliable error detection capability.
3Measurement precision
If short-circuit operation is used for diagnosis, then sensor error detection precision is improved, but machine operation is interrupted
Solution Approach 1:
The diagnostic short-circuit operation is implemented as a brief periodic interruption rather than a continuous state. The control unit quickly switches to short-circuit mode for measurement, then immediately returns to normal operational mode. This approach maintains continuity of useful action by minimizing interruption duration while still achieving precise sensor error detection through the diagnostic measurement window.
Solution Approach 2:
The diagnostic process is executed as a rapid skip through the short-circuit state - the system quickly transitions to short-circuit mode, performs the necessary current measurements for diagnosis, and immediately transitions back to normal operation. This rushing through the diagnostic state minimizes productivity impact while still achieving the measurement precision needed for accurate sensor error detection.
Data Source
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AI summary
The invention relates to a method for diagnosing current sensors (S1, S2) of an n-phase induction machine (M) having n-1 current sensors, wherein the n phases (U, V, W) of the induction machine are short-circuited for a brief period of time during normal operation of the induction machine, and the time progressions of the n-1 currents are measured by the n-1 current sensors during short-circuit operation. The actual values of the time progressions of the n-1 measured short-circuit currents are compared to corresponding prescribed target values for the n-1 short-circuit currents. A potential fault state of one or more current sensors is determined from the comparison.