Power Converter Current Sensor Diagnosis With Two-Phase Sensing
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Solution Overview
Problem
Existing power conversion devices require AC current sensors in all three phases to accurately diagnose failures, increasing manufacturing costs and potentially failing to detect issues under certain motor operation conditions.
Innovation Solution
A power conversion device with AC current sensors in only two phases, utilizing a first and second diagnosis unit that switch determination methods based on motor operation conditions, allowing accurate failure detection by converting voltage and current values into a two-phase orthogonal coordinate system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If AC current sensors are installed in all three phases to enable accurate failure diagnosis, then diagnostic reliability is improved, but manufacturing cost increases
Solution Approach 1:
The invention extracts the third phase current sensor from the system by calculating its value through coordinate transformation. Instead of installing sensors in all three phases, the system uses two-phase sensors combined with Clarke transformation and failure diagnosis algorithms to achieve the same diagnostic reliability, thereby reducing component quantity and manufacturing cost.
Solution Approach 2:
The invention introduces coordinate transformation (Clarke transformation) as an intermediary mathematical tool to convert two-phase current measurements into equivalent three-phase current information. This intermediary process enables accurate failure diagnosis without requiring physical sensors in all three phases, resolving the contradiction between diagnostic reliability and manufacturing cost.
2Ease of manufacture
If AC current sensors are installed in only two phases to reduce cost, then manufacturing cost decreases, but diagnostic accuracy under certain operation conditions deteriorates
Solution Approach 1:
The invention changes the parameter representation from direct three-phase current measurements to transformed two-phase current measurements using Clarke transformation. By changing the coordinate system and using differential calculations based on voltage commands and transformed current values, the system maintains diagnostic accuracy across various operation conditions while using fewer sensors.
Solution Approach 2:
The invention implements feedback mechanisms where the system continuously monitors the relationship between voltage commands and transformed current values. By using feedback control and comparing expected versus actual values in the transformed coordinate system, the system achieves reliable failure detection even with only two-phase sensors, preventing diagnostic accuracy deterioration.
3Difficulty of detecting and measuring
If diagnosis method based on voltage and current deviation is used, then diagnostic capability is improved, but reliability under low deviation conditions deteriorates
Solution Approach 1:
The invention moves the diagnosis from the time domain to the frequency domain through coordinate transformation (Clarke transformation to dq coordinates). By transforming the diagnosis to another dimensional space, the system can detect failures through spectral analysis and pattern recognition that are not dependent on voltage-current deviation magnitude, thereby maintaining reliability under low deviation conditions while improving overall diagnostic capability.
Data Source
AI summary
A power conversion device that converts DC power into three-phase AC power and outputs the three-phase AC power includes: an AC current sensor that detects two-phase current values among three-phase AC currents generated by the three-phase AC power; a target current calculation unit that calculates a target current based on a target torque; a voltage command calculation unit that calculates a voltage command value based on the target current and a detection value of the AC current sensor; and an AC current sensor diagnosis unit that determines abnormality of the AC current sensor based on a detection value of the AC current sensor. The AC current sensor diagnosis unit includes: a first diagnosis unit that determines the abnormality based on a two-phase voltage command value obtained by converting the voltage command value into a value in a two-phase orthogonal coordinate system with any output phase as a reference; and a second diagnosis unit that determines the abnormality based on a two-phase current detection value obtained by converting a detection value of the AC current sensor into a value in the two-phase orthogonal coordinate system. The AC current sensor diagnosis unit performs switching of determination between the determination of the abnormality by the first diagnosis unit and the determination of the abnormality by the second diagnosis unit corresponding to an operation condition of the power conversion device.