Motor Drive Closed-Loop Fault Detection in EPS FET Circuits
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Solution Overview
Problem
Existing motor control devices in electric power steering systems cannot detect secondary failures where both upper and lower FETs in the motor drive circuit and the motor cutoff FET have a short-circuit failure, forming a closed-loop circuit, which can lead to dangerous steering conditions.
Innovation Solution
A motor control device with an arithmetic processing unit that monitors phase voltages and currents to accurately detect primary and secondary failures, including short-circuit failures in upper and lower FETs and motor cutoff FETs, and adjusts assist force application accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If current detection methods are used to detect FET failures, then primary failures (short-circuit failures of upper or lower FETs) can be detected, but secondary failures (simultaneous short-circuit failures of both upper and lower FETs forming a closed-loop circuit) cannot be detected
Solution Approach 1:
The control unit proactively applies a test voltage to the motor before normal operation to detect potential secondary failures in advance. By performing this preliminary detection, the system can identify closed-loop circuit conditions that would otherwise remain undetected during normal operation, preventing dangerous steering conditions from developing
Solution Approach 2:
The system implements a feedback mechanism where the control unit monitors the voltage applied to the motor and compares it against expected values. When the detected voltage deviates from the expected range (indicating a secondary failure), the system provides feedback to stop assist force application, thereby maintaining safety through continuous monitoring and response
2Reliability
If a two-system motor drive circuit is used to detect coil winding failures, then single system failures can be detected and the motor can continue operating with one system, but secondary failures involving both motor drive circuit FETs and cutoff FETs cannot be detected
Solution Approach 1:
The control unit acts as an intermediary that performs additional voltage application and detection functions beyond the standard motor control. This intermediary detection mechanism specifically targets the closed-loop circuit condition by measuring voltage across the motor terminals, enabling detection of secondary failures that the redundant motor drive circuits alone cannot identify
Solution Approach 2:
The control unit applies a test voltage to the motor before normal operation to detect potential secondary failures in advance. By performing this preliminary detection, the system can identify closed-loop circuit conditions that would otherwise remain undetected during normal operation, preventing dangerous steering conditions from developing
3Device complexity
If simple current detection is implemented for safety, then the system remains simple and cost-effective, but it cannot detect the dangerous closed-loop circuit condition formed by simultaneous FET failures
Solution Approach 1:
The control unit is designed to perform multiple functions: normal motor control, current detection, voltage application, and secondary failure detection. By making the control unit multi-functional, the system achieves enhanced safety capabilities without adding separate dedicated hardware systems, thereby maintaining relative simplicity while improving reliability
Solution Approach 2:
The system implements a feedback mechanism where the control unit monitors the voltage applied to the motor and compares it against expected values. When the detected voltage deviates from the expected range (indicating a secondary failure), the system provides feedback to stop assist force application, thereby maintaining safety through continuous monitoring and response
Data Source
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AI summary
A closed-loop circuit is detected based on a short-circuit failure of a motor control switching element of a motor drive circuit and a cutoff switching element. A motor control device including a motor, a motor drive circuit (10a) that is connected to a power supply device and the motor and controls the output of the motor, and a processing unit for detecting a closed-loop circuit formed by the motor and the motor drive circuit (10a) based on a short-circuit failure of switching elements arranged in the motor drive circuit (10a).