Motor Inverter Current Sensor Fault Identification by Test Voltage
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Solution Overview
Problem
Existing electric motor control devices fail to quickly and accurately identify the location of a failed current detecting unit, leading to unnecessary motor shutdowns and maintenance challenges.
Innovation Solution
An electric motor control device that uses a test voltage command to drive the inverter circuit and compares the signal's frequency component in detected current values with a threshold, allowing for rapid identification of failed current detecting units and enabling continued motor operation using normal phases, while generating a failure diagnosis signal independent of current control response time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a failure diagnosis current command value is input into a current controller and a failure is determined based on the voltage command value generated in the current controller, then a failure can be detected, but the determination process requires waiting for the voltage command value to respond to the current command value (longer than response time determined based on current control time constant), and the phase in which current detecting means has failed cannot be determined
Solution Approach 1:
The patent applies preliminary action by performing failure diagnosis before normal current control operations. A test voltage command is applied to the motor during idle periods or startup phases, allowing the system to pre-identify failed current detecting units before actual motor operation begins. This eliminates the need to wait for current control response during critical failure detection moments.
Solution Approach 2:
The patent extracts the failure diagnosis function from the normal current control loop. By separating the diagnostic test (applying test voltage and measuring current) from the operational current control, the system can detect failures independently without being constrained by the current control time constant. The diagnosis is performed as a distinct operation rather than waiting for control loop response.
2Reliability
If a failure is determined based on the magnitude of the voltage command value, then a failure can be detected, but the phase in which current detecting means has failed cannot be determined
Solution Approach 1:
The patent applies segmentation by independently testing each phase (U-phase, V-phase, W-phase) separately. The test voltage is applied to one phase at a time, and the corresponding current detecting unit's output is examined. This segmented approach allows identification of which specific phase has the failed detecting unit, rather than only detecting that a failure exists somewhere in the system.
Solution Approach 2:
The patent applies local quality by examining the specific characteristics of each phase's current detecting unit independently. Each phase is tested with its own test voltage command, and the response is evaluated separately. This localized testing approach preserves information about which specific phase (U, V, or W) has the failure, enabling phase identification rather than just generic failure detection.
3Adaptability or versatility
If the current detecting means in one phase fails, control can be continued by estimating current of the failed phase from information from normal current detecting means of remaining two phases, but the phase of failed current detecting means cannot be determined
Solution Approach 1:
The patent performs failure diagnosis as a preliminary action before normal operation begins. By testing each current detecting unit with test voltage commands during startup or idle periods, the system identifies failed units in advance. This preliminary identification enables the control system to know which phase has failed before switching to estimation mode, preserving failure location information that would otherwise be lost.
Data Source
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AI summary
A control unit 2 of an electric motor control device includes an inverter circuit 6 that supplies power to an electric motor 1, a current control unit 5 that outputs a voltage command value as a drive command of the inverter circuit 6, a current detecting unit 7 that detects current flowing to each phase of the electric motor 1, and a failed phase identifying unit 14 that identifies a location of a failure in the current detecting unit 7. The failed phase identifying unit 14 determines whether or not a magnitude or a phase of a frequency component of the test voltage command included in a detected current value when the inverter circuit 6 is driven with a test voltage command having a frequency higher than a rotational frequency of the electric motor 1 as a drive command is within a predetermined range, and determines that a failure has occurred in a phase that is not within the predetermined range.