Motor-Driven Compressor Switching Element Thermal Management
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Solution Overview
Problem
Motor-driven compressors experience unnecessary operation suspensions due to overheating protection control when the DC voltage applied to switching elements is low, leading to incorrect temperature readings and premature shutdowns.
Innovation Solution
A control unit is implemented in the motor-driven compressor that executes a suspension control and field weakening control, with two temperature thresholds: a first threshold set for high DC voltage and a second threshold higher than the first, allowing the compressor to operate safely even at low DC voltages by switching between these thresholds during field weakening control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If field weakening control is activated to reduce counter electromotive force and increase rotation speed at low DC voltage, then the rotation speed of the electric motor increases, but the temperature detected by the temperature detector rises excessively due to increased current supply, causing unnecessary operation suspensions
Solution Approach 1:
The patent applies dynamics by making the temperature threshold dynamic rather than fixed. The control unit switches between a first temperature threshold (when field weakening control is not active) and a second temperature threshold (when field weakening control is active). This dynamic adjustment allows the system to accommodate the temporary temperature rise caused by field weakening control while maintaining reliable operation protection.
Solution Approach 2:
The patent changes the parameter of temperature threshold based on the operating condition (whether field weakening control is active). By switching between two different temperature threshold values, the system adapts to the changed thermal conditions during field weakening control, preventing false overheating detections while maintaining protection functionality.
2Device complexity
If a fixed temperature threshold is used for overheating protection, then the control system is simple, but the temperature threshold is inaccurate at low DC voltages, causing premature shutdowns
Solution Approach 1:
The patent transitions from a static fixed temperature threshold to a dynamic threshold system that automatically switches between two values based on the activation state of field weakening control. This maintains relatively simple control logic while significantly improving the accuracy of overheating protection under different operating conditions.
3Speed
If the amount of current supplied to the electric motor is increased for field weakening control, then the counter electromotive force is reduced and rotation speed increases, but the heat transmitted from the circuit board to the temperature detector increases, raising the detected temperature
Solution Approach 1:
The patent dynamically adjusts the temperature threshold upward when field weakening control is active, accounting for the additional heat transmitted to the temperature detector from the circuit board. This allows the system to tolerate the temporary temperature increase caused by high current supply during field weakening control without triggering false overheating shutdowns.
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 solution limits unnecessary operation suspensions by accurately managing temperature thresholds, ensuring the compressor operates reliably even at low DC voltages, maintaining high torque and increased rotation speed while preventing overheating.
Implementation Method 1
The switching elements perform switching operations so that the motor driver converts DC voltage of a battery (DC power supply) to AC drive voltage
Implementation Method 2
In the electric motor, the rotation produced by the electric motor generates magnetic flux that generates counter electromotive force
Implementation Method 3
The switching elements generate heat when performing switching operations
Implementation Method 4
The field weakening control reduces the counter electromotive force by supplying the electric motor with current from the motor driver to weaken the magnetic flux generated by the rotation of the electric motor
Data Source
AI summary
A motor-driven compressor includes an electric motor driven by a motor driver, which includes a switching element that converts DC voltage from a battery to AC voltage. A control unit controls the switching operation of the switching element. A temperature detector detects the temperature of the switching element. The control unit suspends the switching operation of the switching element when the temperature detected by the temperature detector rises to a temperature threshold. The temperature threshold includes a first temperature threshold, corresponding to a withstand temperature of the switching element, and a second temperature threshold, which is higher than the first temperature threshold. The control unit switches the temperature threshold from the first temperature threshold to the second temperature threshold when the control unit activates a field weakening control that reduces counter electromotive force generated by the electric motor.