Truck Electric Drive Motor Current Control for Switching Element Overheating
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Solution Overview
Problem
Electric motor-driven trucks face overheating issues in switching elements due to torque insufficiency, which existing feedback control methods struggle to address efficiently, especially with varying vehicle weights, requiring complex weight measurements or calculations.
Innovation Solution
A control unit in the truck adjusts the current flowing to the electric drive motor based on the accelerator pedal depression amount and rotation speed, limiting the current to a predetermined ratio between 50% and 100% of the maximum value when the rotation speed is zero, thereby preventing overheating without needing vehicle weight measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If feedback control is used to prevent switching element overheating, then switching element temperature is controlled, but response speed is insufficient and temperature exceeds threshold before control activates
Solution Approach 1:
The control unit performs preliminary action by detecting zero rotation speed and proactively limiting the current value to a predetermined ratio (50-100% of maximum) before the switching element temperature can exceed the threshold. This preventive measure eliminates the need for rapid feedback response, as the harmful condition is avoided before it can develop.
2Temperature
If current is forcibly set to zero when temperature exceeds threshold, then switching element overheating is prevented, but torque becomes zero
Solution Approach 1:
The control unit applies preliminary anti-action by limiting the current value to a predetermined ratio (50-100% of maximum) when rotation speed is zero, before the temperature can exceed the threshold. This preemptive current limitation prevents overheating while maintaining sufficient torque generation, avoiding the need to forcibly set current to zero.
3Measurement precision
If vehicle weight is measured or estimated for feedback control, then accurate torque control is achieved, but measurement or estimation needs time and labor or complicated calculations
Solution Approach 1:
The control unit extracts and utilizes the readily available rotation speed signal from the motor control system to determine when current limitation is needed (at zero rotation speed). This eliminates the need to implement separate vehicle weight measurement or estimation systems, significantly reducing system complexity while maintaining effective thermal protection.
4Temperature
If current is limited to predetermined ratio when rotation speed is zero, then switching element overheating is prevented, but torque generation may be reduced
Solution Approach 1:
The control unit implements dynamic current limitation by applying the predetermined ratio (50-100% of maximum current) specifically when rotation speed is zero, and removing the limitation when rotation speed becomes non-zero. This dynamic adjustment maintains sufficient torque during normal operation while preventing overheating during stationary conditions, optimizing both thermal protection and torque generation.
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 prevents overheating of switching elements, reduces the need for complex weight calculations, and maintains torque generation, even under varying load conditions, ensuring reliable operation without forcing the current to zero, thus avoiding torque loss.
Implementation Method 1
an inverter including a plurality of switching elements configured to apply alternating current flow into the electric drive motor
Implementation Method 2
the current continuously flows in one of the plurality of switching elements. The continuous flow of current raises the temperature of the switching element
Data Source
AI summary
When the rotation speed is zero, the current value is specified to monotonically increase with an increase in depression amount of an accelerator pedal in a range of a depression amount from 0% to a predetermined amount P2. The current value is fixed to a limit value Ith irrespective of the depression amount in a range of the depression amount from the predetermined amount P2 to 100%.