Multiphase Motor Inverter ON Failure Detection via Phase Current Estimation
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Solution Overview
Problem
In multi-phase motor driving devices for electrical power steering, the existing failure detection methods cannot reliably detect the 'ON failure' of switching elements on the lower side of the inverter circuit, as the current flowing to these elements is not detectable during the intended sampling periods due to the configuration of shunt resistors and switching element operations.
Innovation Solution
The detection timing of the current flowing to the shunt resistor is shifted from the OFF period to the ON period of the upper switching element, allowing for the detection of abnormal currents that indicate an 'ON failure' in the lower switching element, and current values are estimated based on currents from other phases to determine the presence of such failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the shunt resistor is connected to the lower switching element and current sampling is performed during the OFF period of the upper switching element, then the phase current detection is enabled, but the ON failure of the lower switching element cannot be detected
Solution Approach 1:
The patent applies preliminary action by performing current sampling during the OFF period of the upper switching element (which is the normal operating condition), and then using the relationship between phases to detect abnormalities. The control unit samples the current during normal operation and compares it with expected values to detect ON failures of lower switching elements before they cause motor drive failures.
Solution Approach 2:
The patent uses the shunt resistor as an intermediary element to detect current flow indirectly. By measuring the voltage across the shunt resistor during the OFF period of the upper switching element, the system can infer the state of the lower switching element. The control unit acts as another intermediary, comparing the detected current with expected values to determine failures.
2Reliability
If the detection timing is shifted to the ON period of the upper switching element, then the ON failure of the lower switching element can be detected, but the normal phase current detection timing is changed
Solution Approach 1:
The patent implements periodic action by alternating between two detection modes: during normal operation, current sampling is performed during the OFF period of the upper switching element for phase current detection; for failure detection, sampling is performed during the ON period. This periodic switching between detection timings allows the system to maintain both normal operation monitoring and failure detection capabilities without permanent disruption.
3Reliability
If additional detection circuits are added to detect lower switching element failures, then the failure detection capability is improved, but the device complexity increases
Solution Approach 1:
The patent applies universality by making the existing current detection circuit perform multiple functions: it detects both normal phase currents during the OFF period of upper switching elements and detects ON failures of lower switching elements during the ON period. The control unit is programmed to switch between detection modes, eliminating the need for separate dedicated failure detection circuits and reducing overall system complexity.
Data Source
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AI summary
This invention provides a multiphase motor driving device capable of detecting ON failure of switching elements (Q2, Q4, Q6) on the lower side in an inverter circuit (3). The detection timing of the current flowing to a shunt resistor (Ru) of a U-phase is shifted from an OFF period to an ON period of a switching element Q1 on an upper side in the U-phase, and whether or not ON failure occurred in the switching element Q2 on the lower side is determined based on the current flowing to the shunt resistor (Ru) of the U-phase in the ON period. If the detection timing is simply shifted, the U-phase current that is necessary under normal circumstances may not be detected in the ON period of the switching element Q2 on the lower side, and thus the current value of the U-phase current is estimated based on the currents flowing to the shunt resistors (Rv, Rw) of the other two phases (V-phase, W-phase).