Electric Vehicle Torque Limiting for Induced Voltage Control
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Solution Overview
Problem
Electric vehicles experience unintentional deceleration and stability issues due to regenerative torque generation when the inverter fails, causing induced voltage from the motor generator to exceed battery voltage, leading to current flow into the battery.
Innovation Solution
An electronic control unit (ECU) is implemented to restrict the torque requested by the driver, limiting the induced voltage by controlling the motor generator's rotation number, ensuring the induced voltage remains below the battery voltage, thereby preventing regenerative torque and maintaining vehicle stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the inverter controls the rotation number of the motor generator to limit the induced voltage when battery voltage is low, then the induced voltage becomes lower than the battery voltage, but when a trouble occurs in the inverter, the induced voltage cannot be limited and current flows into the battery causing regenerative torque
Solution Approach 1:
The control device performs preliminary action by limiting the requested torque before the inverter failure can cause harmful effects. When the battery voltage is low, the control device proactively restricts the torque request to prevent the induced voltage from exceeding the battery voltage, even though the inverter might fail. This preliminary restriction ensures that even if the inverter cannot control the motor generator rotation, the induced voltage remains below the battery voltage threshold, preventing current flow into the battery and avoiding unintended deceleration.
2Speed
If the inverter allows the motor generator to rotate at high speed for vehicle travel, then the vehicle can move efficiently, but the induced voltage may exceed the battery voltage causing current to flow into the battery
Solution Approach 1:
The control device applies parameter changes by dynamically adjusting the requested torque parameter based on the battery voltage level. When the battery voltage is low, the control device changes the torque parameter to a restricted value that prevents the induced voltage from exceeding the battery voltage, regardless of the vehicle speed. This parameter adjustment ensures that the motor generator operates in a safe voltage range while still allowing the vehicle to travel, thereby maintaining both speed and reliability.
3Loss of information
If the control device notifies the driver of performance changes when battery voltage is reduced, then the driver can adjust driving behavior, but the induced voltage may still exceed battery voltage causing regenerative torque
Solution Approach 1:
The control device acts as an intermediary between the driver's torque request and the motor generator operation. Instead of directly transmitting the driver's full torque request to the motor generator, the control device mediates by restricting the requested torque when the battery voltage is low. This intermediary action prevents the induced voltage from exceeding the battery voltage while still allowing the vehicle to operate. The control device thus protects the system from harmful regenerative torque while maintaining driver awareness through performance change notifications.
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 ECU effectively prevents unintentional deceleration by ensuring the induced voltage from the motor generator does not exceed the battery voltage, even if the inverter fails, thus maintaining vehicle stability and preventing regenerative torque during high-speed travel.
Implementation Method 1
when the vehicle travels to rotate the motor generator, an induced voltage is developed by the motor generator
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
An electric vehicle (1) includes: a motor (6) configured to be driven by electric power supplied from a battery (7); a limit control unit (10) configured to calculate a limit rate for limiting a requested torque requested for the electric vehicle (1) so that an induced voltage developed by the motor (6) is equal to or lower than a voltage of the battery (7); a drive torque calculation unit (10) configured to calculate a drive torque for traveling the electric vehicle (1) based on the requested torque and the limit rate.