EC Motor Defect Isolation via Braking Torque Detection
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Solution Overview
Problem
Existing electric motors with semiconductor switches face issues when a defect occurs, leading to short-circuit currents and potential damage to the MOS-FET transistor during disconnection, especially during generator operation, which can hinder vehicle steering.
Innovation Solution
Incorporating a control unit that detects defects via braking torque changes and activates a controllable circuit breaker to disconnect the defective semiconductor switch at zero crossings, utilizing a rotor position sensor to manage the disconnection process and prevent damage to the isolating switch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a relay is used to disconnect the defective semiconductor switch from the stator, then the defective switch can be separated, but sparks occur during disconnection
Solution Approach 1:
The control unit detects the defect in the semiconductor switch and activates the isolating switch before the short-circuit current can cause damage. By performing the isolation action promptly upon defect detection, the system prevents harmful effects while avoiding sparks that would occur with relay-based disconnection.
2Reliability
If a semiconductor switch is used to disconnect the defective semiconductor switch from the stator, then the defective switch can be separated, but the MOS-FET transistor can be destroyed
Solution Approach 1:
The isolating switch acts as an intermediary component between the defective semiconductor switch and the stator. This dedicated isolating switch is designed to handle the disconnection safely, transferring the harmful current away from both the defective switch and the circuit breaker, thus protecting the MOS-FET transistor from destruction.
Solution Approach 2:
The harmful short-circuit current is extracted and diverted through the isolating switch to a safe path. By removing the current from its damaging path and routing it through the isolating switch, the system isolates the defect without exposing the circuit breaker to destructive currents.
3Reliability
If the isolating switch is activated during generator operation, then the defective switch can be disconnected, but the circuit breaker can be destroyed by the phase current
Solution Approach 1:
The control unit continuously monitors the operational state of the electric motor, including detection of generator operation mode. Upon detecting a defect, the control unit determines the appropriate timing for activation of the isolating switch based on real-time feedback about the motor's operational state, ensuring disconnection occurs at an optimal moment that protects the circuit breaker.
Solution Approach 2:
The control unit detects the defect and activates the isolating switch promptly upon identification, before the phase current during generator operation can accumulate enough energy to destroy the circuit breaker. This timely preliminary action prevents the harmful effect while maintaining system functionality.
Data Source
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AI summary
The invention relates to an electronically commutated electric motor. The electric motor has a stator and a rotor, in particular one formed with permanent magnets. The electric motor has a control unit, which is connected on the output side in particular via a power output stage to the stator and is designed to energize the stator so as to produce a rotating magnetic field. The electric motor has a power output stage with semiconductor switches. The power output stage is connected to the stator via at least one controllable switch disconnector. The control unit is designed to detect a defect of a semiconductor switch depending on a braking torque caused by the defect, in particular a change over time in the braking torque, on a rotor of the electric motor, and to activate the switch disconnector so as to disconnect the defective semiconductor switch from the stator.