Motor Control Device Torque Limiting for Overheating Prevention
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Solution Overview
Problem
Existing motor control systems for electric vehicles fail to accurately limit drive torque when a motor is in a locked state, leading to potential overheating and damage, as the current limitation is not adaptive to varying cooling mechanisms and ambient temperatures.
Innovation Solution
A motor control device that dynamically limits current output from the inverter to the motor based on the cooling mechanism's state, using temperature sensors to adjust torque limitation values and prevent overheating by setting motor and inverter continuous energizable torque limits according to cooling water temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If drive torque limitation is performed assuming normal ambient temperature, then motor and inverter are protected from overheating, but current output is excessively limited even when cooling mechanism is sufficient
Solution Approach 1:
The patent applies dynamics by making the drive torque limitation value variable rather than fixed. The control device dynamically adjusts the limitation value based on real-time cooling water temperature feedback. When cooling is sufficient (low temperature), higher current can be permitted; when cooling is inadequate (high temperature), current is restricted. This dynamic adaptation resolves the contradiction between protection and productivity by optimizing the limitation strategy according to actual thermal conditions.
Solution Approach 2:
The patent changes the parameter of drive torque limitation value from a constant assumption-based value to a variable determined by cooling water temperature. By establishing a relationship between cooling water temperature and appropriate limitation values, the system adapts the protection level to actual cooling capacity, allowing maximum current output when cooling is effective while maintaining safety when cooling is insufficient.
2Reliability
If drive torque is decreased to prevent thermal destruction at normal ambient temperature, then coil and switching element are protected, but motor performance is excessively restricted when adequately cooled
Solution Approach 1:
The patent implements feedback by continuously monitoring cooling water temperature and using this information to adjust the drive torque limitation value. The control device establishes a feedback loop where cooling water temperature serves as the input signal and the drive torque limitation value is the output that gets adjusted. This feedback mechanism ensures that protection levels are matched to actual cooling performance, preventing both overheating damage and unnecessary performance restriction.
Solution Approach 2:
The patent changes the parameter of drive torque limitation from a fixed value based on normal ambient temperature assumptions to a variable parameter determined by actual cooling water temperature. By creating a mapping between cooling water temperature ranges and appropriate torque limitation values, the system optimizes motor output while maintaining protection, allowing full power when cooling is adequate and reducing power only when thermal conditions require it.
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
Effectively prevents motor and inverter overheating by appropriately limiting current output according to the cooling mechanism's state, ensuring safe operation across different temperature conditions.
Implementation Method 1
a cooling mechanism that cools at least one of the motor and the inverter
Data Source
AI summary
To appropriately limit a current output from an inverter to a motor according to a state of a cooling mechanism that cools the motor and the inverter. A motor control unit includes a current command unit configured to calculate current command values (Id*, Iq*) for determining a current to be output to a motor on the basis of an input torque command, a motor lock determination unit configured to determine whether the motor is in a locked state on the basis of a motor rotation speed Nrpm indicating a rotation state of the motor, and a torque command limitation unit configured to limit the current to be output to the motor by limiting the torque command on the basis of a cooling water temperature Tc indicating a state of the cooling mechanism in a case where the motor lock determination unit determines that the motor is in the locked state.