Motor Current Monitoring via Synchronous Averaging
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Solution Overview
Problem
Condition monitoring of electromechanical systems using casing-mounted vibration transducers is hindered by transmission path effects, environmental noise sensitivity, and the need for precise mounting, which can lead to missed indicators of machine condition and increased complexity, especially in hostile environments.
Innovation Solution
The method involves synchronizing and resampling electric motor current and voltage signals with angular displacement of the shaft, creating a synchronous average that reduces noise and periodic components, allowing for accurate condition monitoring even with lower resolution transducers and non-constant angular velocities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If casing-mounted vibration transducers are used for condition monitoring, then vibration signals can be measured, but transmission path effects attenuate subtle vibration details and reduce measurement precision
Solution Approach 1:
The patent extracts the vibration sensing function from the mechanical casing-mounted transducer and relocates it to the electrical domain by measuring current signals directly at the motor terminals. This eliminates the transmission path through the casing and bearing caps, directly capturing vibration-induced current modulations without mechanical attenuation.
Solution Approach 2:
The patent replaces the mechanical vibration measurement system (accelerometers mounted on casing) with an electrical measurement system (current sensors measuring motor phase currents). The mechanical vibration information is converted into electrical current modulations, substituting mechanical sensing with electrical sensing to avoid transmission path losses.
2Stability of the object's composition
If casing-mounted vibration transducers are permanently fixed to the structure, then consistent measurement positions are maintained, but special mounting arrangements are required and device complexity increases
Solution Approach 1:
The patent eliminates the mechanical mounting system entirely by measuring electrical current signals at the motor terminals rather than mounting physical transducers on the casing. The current sensors are connected electrically to the motor windings, requiring no mechanical attachment to the structure and thus eliminating mounting complexity.
Solution Approach 2:
The patent uses the existing motor windings and current measurement infrastructure for dual purposes: both for normal motor control/operation monitoring and for vibration condition monitoring. The same current sensors and electrical connections serve both functions, eliminating the need for separate dedicated vibration sensing infrastructure.
3Loss of information
If multiple unidirectional vibration transducers are used to obtain sufficient information for confident condition assessment, then measurement completeness improves, but device complexity and cost increase
Solution Approach 1:
The patent measures current modulations in all three motor phase windings simultaneously, capturing vibration information from multiple spatial locations through the electrical domain. By analyzing the current signals in each phase, the system obtains comprehensive vibration information without needing multiple physical transducers mounted at different locations on the casing.
Solution Approach 2:
The patent replaces the need for multiple mechanical transducers with a single electrical measurement system that monitors current signals. The electrical current measurements inherently contain vibration information from the entire motor structure, eliminating the need for multiple spatially distributed mechanical sensors.
4Reliability
If casing-mounted vibration transducers are used in hostile environments, then vibration monitoring can be performed, but transducer performance degrades over time due to environmental effects
Solution Approach 1:
The patent replaces mechanical vibration transducers that are susceptible to environmental degradation (temperature, humidity, contamination) with electrical current measurements. The current sensors operate in the electrical domain and are not directly exposed to the harsh mechanical and thermal environment that degrades mechanical transducers, thereby extending operational lifespan in hostile conditions.
Solution Approach 2:
The patent uses the motor windings and current path as an intermediary medium to sense vibrations. Instead of placing sensors directly in the hostile environment on the casing, the measurement is performed through the electrical current that flows through the motor windings, which are protected from the harshest environmental conditions and provide a stable measurement interface.
Data Source
AI summary
A method, apparatus and computer program for monitoring the condition of electromechanical systems in which electrical rotating machinery is used. The method includes measuring current and/or voltage signals, measuring an angular position of a rotating shaft of interest of the electromechanical systems or estimating the value of discrete angular position of a rotating shaft, synchronizing the current and/or voltage signals to the scaled angular displacement of the rotating shaft, dividing the synchronous electrical signals into intervals corresponding to each completed rotation of the rotating shaft, averaging a number of intervals of synchronous electrical signals to obtain an average synchronous electrical signal, extracting characteristic data of the magnitude from the values of the average synchronous electrical signal, and comparing the extracted characteristic data with a threshold limit to alarm the user when the limit is exceeded.