Inverter Overheating Prevention via Speed Limiting
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Solution Overview
Problem
Conventional electric vehicles fail to adequately prevent overheating of the inverter when the cooler that cools it experiences abnormalities, leading to insufficient load factor limitation and potential overheating.
Innovation Solution
An electronic control unit sets a vehicle speed limit where the induced voltage from the motor equals the input voltage to the inverter, controlling the motor to operate within this range during cooler abnormalities, thereby executing field-weakening control to prevent temperature increases in the inverter elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the motor operates at high rotational speed, then the vehicle speed increases, but the induced voltage exceeds the input voltage causing field-weakening control execution and inverter element temperature increase
Solution Approach 1:
The electronic control unit preliminarily determines a vehicle speed limit based on the relationship between induced voltage and input voltage before abnormality occurs. When cooler abnormality is detected, this pre-determined speed limit is immediately applied to prevent the induced voltage from exceeding the input voltage, thereby avoiding field-weakening control and inverter overheating.
Solution Approach 2:
The system changes the operational parameter (vehicle speed limit) based on the state of the cooler. By adjusting the vehicle speed limit according to the cooler's abnormality status, the system ensures that the induced voltage remains within acceptable ranges, preventing inverter element temperature increase while still allowing motor operation.
2Temperature
If conventional load factor limitation is applied, then the inverter element temperature is controlled under normal conditions, but the limitation is insufficient when cooler abnormality occurs at high rotational speeds
Solution Approach 1:
The vehicle speed limit is dynamically adjusted based on real-time detection of cooler abnormality. Under normal conditions, the motor can operate without speed restrictions. When cooler abnormality is detected, the system dynamically imposes a speed limit to prevent inverter overheating, thereby adapting the operational constraints to the actual system state.
Solution Approach 2:
The electronic control unit continuously monitors the cooler's operation status and provides feedback to adjust the vehicle speed limit. This feedback mechanism ensures that when cooler abnormality is detected, the system responds by limiting the vehicle speed to prevent inverter element temperature increase, creating a closed-loop control system.
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
This approach effectively suppresses overheating of the inverter elements by ensuring the induced voltage does not exceed the input voltage, even during cooler malfunctions, thus maintaining the inverter's performance and preventing overheating.
Implementation Method 1
When the motor rotates at a relatively high rotational speed, an induced voltage generated by the motor (also referred to as a counter-electromotive voltage) becomes higher than the DC voltage input to the inverter
Implementation Method 2
a cooler that cools the inverter
Data Source
AI summary
An electric vehicle includes a motor, an inverter, a battery, a cooler configured to cool the inverter, and an electronic control unit. The electronic control unit is configured to execute following when abnormality occurs to the cooler: i) set a vehicle speed, at which an induced voltage by the motor becomes at most equal to an input voltage that is input to the inverter from the battery side, as vehicle speed limit, and ii) control the motor such that the electric vehicle travels within a range of the vehicle speed limit.