Motor Control Unit Protecting Semiconductor Switches from Back-EMF
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Solution Overview
Problem
Existing electric power steering apparatuses face challenges in protecting semiconductor switching devices from damage due to excessive motor back-EMF and regenerative currents when the motor release switch is turned OFF, especially during abnormal operating conditions, leading to potential device destruction without adequate protection mechanisms.
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 the motor back-electromotive force voltage and regenerative currents, and a judging section to turn OFF the semiconductor switching devices when the energy is within a safe operational area, ensuring reliable protection without additional hardware components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the motor release switch is turned OFF to protect semiconductor switching devices from regenerative electric power, then device reliability is improved, but the motor cannot be controlled properly during normal operation
Solution Approach 1:
The control section dynamically changes the operational parameters of the semiconductor switching devices based on real-time monitoring of motor rotational speed and regenerative electric power levels. When parameters exceed safe thresholds, the control section adjusts duty cycles and switching timing to protect devices while maintaining motor control during normal operation.
Solution Approach 2:
The system implements continuous feedback monitoring of motor rotational speed and regenerative electric power. The control section uses this feedback to make real-time decisions about when to activate protection modes by turning OFF semiconductor switching devices, ensuring protection only when necessary and maintaining normal control functionality when conditions are safe.
2Reliability
If additional protection mechanisms are added to prevent device destruction from regenerative electric power, then reliability is improved, but device complexity increases
Solution Approach 1:
The control section is designed to perform multiple functions: normal motor control, monitoring of motor rotational speed, calculation of regenerative electric power, and protection mode activation. By making the control section multi-functional, the patent avoids adding separate dedicated protection hardware, thus improving reliability without significantly increasing device complexity.
Solution Approach 2:
The patent combines the protection functionality with the existing motor control system. The control section integrates monitoring of regenerative electric power and motor rotational speed with the motor control operations, merging protection functions into the control logic rather than adding separate protection circuits.
3Reliability
If the semiconductor switching devices are turned OFF immediately when regenerative electric power is detected, then device protection is improved, but motor control responsiveness deteriorates
Solution Approach 1:
The control section continuously monitors motor rotational speed and calculates regenerative electric power in advance, preparing protection measures before damage occurs. By detecting potential dangerous conditions early and taking preliminary protective actions, the system protects devices without sudden interruptions that would reduce responsiveness.
Solution Approach 2:
The control section dynamically adjusts its protection strategy based on real-time conditions. Instead of immediate OFF switching, it modulates duty cycles and switching patterns adaptively, maintaining motor control responsiveness while providing continuous protection against regenerative electric power damage.
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 the semiconductor switching devices by ensuring they are turned OFF only when the energy is within a safe operational area, preventing device damage and improving the reliability and safety of the electric power steering apparatus.
Implementation Method 1
a motor back-electromotive force voltage (a motor back-EMF) and a regenerative current
Data Source
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AI summary
[Problem] An object of the present invention is to provide a motor control unit that surely and high-reliably performs a protection of a motor release switch that compactly comprises semiconductor switching devices, depending on an abnormal mode and relevant to a temperature, without adding device components, and an electric power steering apparatus equipped with the motor control unit. [Means for solving the problem] The present invention is the motor control unit that is connected to a motor release switch which comprises FETs and is disposed between an inverter and a motor, comprising: 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.