Motor Control Unit Protects Semiconductors from Regenerative Power
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Solution Overview
Problem
Existing electric power steering apparatuses fail to reliably protect semiconductor switching devices from damage due to excessive motor back-EMF and regenerative currents during abnormal operations, such as system failures or motor rotation, without adding hardware components or performing optimal control based on abnormal modes.
Innovation Solution
A motor control unit that includes a control section to detect sensor states and motor rotational speed, an energy calculating section to determine safe operation areas, and a judging section to turn OFF or ON semiconductor switching devices based on detected energy levels and abnormality modes, ensuring protection by managing regenerative currents and temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the motor control unit turns OFF the motor release switch immediately when an abnormality is detected, then the semiconductor switching devices are protected from damage, but the motor cannot be stopped safely when rotating by external force due to regenerative electric power causing switching loss
Solution Approach 1:
The control unit performs preliminary action by turning OFF the motor release switch before the regenerative electric power causes excessive switching loss. The control unit calculates the regenerative electric power based on motor back-EMF voltage and regenerative current, and proactively switches off the FETs when the calculated power exceeds a predetermined threshold, preventing damage before it occurs.
Solution Approach 2:
The control unit implements feedback control by continuously monitoring motor rotational speed, calculating motor back-EMF voltage, measuring regenerative current, and computing regenerative electric power. Based on this real-time feedback, the control unit dynamically decides whether to keep the motor release switch ON or OFF, ensuring optimal protection while allowing motor operation within safe parameters.
2Productivity
If the motor control unit allows continuous operation to maintain steering assist function, then productivity is maintained, but the semiconductor switching devices are exposed to damage risk from excessive regenerative electric power
Solution Approach 1:
The control unit applies dynamic control by continuously adjusting the motor release switch state based on real-time regenerative electric power calculations. The switch remains ON when regenerative power is within safe limits, allowing continuous steering assist operation, and switches OFF when regenerative power exceeds the threshold, preventing device damage. This dynamic adaptation resolves the contradiction between maintaining productivity and ensuring reliability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The motor control unit effectively protects semiconductor switching devices by ensuring they are turned OFF within safe operation areas, preventing damage and improving the reliability and safety of the electric power steering apparatus without adding new components.
Implementation Method 1
a motor back-electromotive force voltage (a motor back-EMF) and a regenerative current
Data Source
AI summary
A motor control unit that is connected to a motor release switch which includes FETs and is disposed between an inverter and a motor, including: a control section to detect an assist state of the inverter, to turn-ON or turn-OFF a control of the inverter based on a detection result and to detect whether abnormality is existed or not; a motor rotational speed detecting section to detect a motor rotational speed; an energy calculating section to calculate an energy based on the motor rotational speed; a judging section to turn-OFF all of the FETs of the motor release switch when the energy is within an area of safety operation; and a state detecting section to detect whether abnormality is existed or not based on information from an abnormality detecting section that detects abnormality of the sensors and the inverter, wherein the control section turns-ON the control of the inverter when the state detecting section does not detect abnormality and turns-OFF the control of the inverter when the state detecting section detects abnormality.