AC Motor Control Device Thermal Protection via Compensated Temperature
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Solution Overview
Problem
Existing control methods for AC rotating electric machines fail to reliably prevent breakdown due to excessive heat, as they often lead to currents flowing after the set temperature is reached, potentially exceeding it and causing damage to switching elements and the machine.
Innovation Solution
A control device with a temperature detection unit, a temperature compensation unit, and a torque limiting unit that calculates a compensated temperature higher than the detected temperature to adjust the torque command value, ensuring the AC rotating electric machine operates within safe thermal limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the torque command value is corrected using the detected temperature of the switching element, then the temperature control is simplified, but the switching element may still exceed the set temperature due to excessive current flow
Solution Approach 1:
The control device calculates a compensated temperature that is higher than the actual detected temperature in advance. This preliminary action allows the torque command value to be corrected based on a conservative temperature estimate, ensuring that current is reduced before the actual temperature reaches the set temperature, thereby preventing overheating while maintaining simple control logic
Solution Approach 2:
By using a compensated temperature higher than the actual temperature for torque command correction, the system applies a preliminary anti-action that prevents excessive current flow before it can cause dangerous temperature rise. This conservative approach ensures that even with simplified control, the switching element temperature remains below the set temperature
2Power
If the inductive voltage increases with angular speed, then the power generation capability improves, but the both-end voltage of the DC power source reaches the limit value
Solution Approach 1:
The control device dynamically adjusts the torque command value based on the compensated temperature calculation, which accounts for the relationship between angular speed and inductive voltage. This dynamic control allows the system to maintain optimal power generation capability while preventing the DC power source voltage from exceeding its limit by reducing current when necessary
Data Source
AI summary
Provided is a control device for an AC rotating electric machine, which includes: a temperature detection unit configured to detect a temperature of a protection unit provided in an object to be protected when a current is supplied from a power conversion circuit including a switching element to the AC rotating electric machine and output, as a detected temperature, one of the temperature and a temperature of the object to be protected that is estimated from the temperature; a temperature compensation unit configured to calculate, through use of the detected temperature output from the temperature detection unit, a compensated temperature equal to or higher than the detected temperature; and a torque limiting unit configured to limit, through use of the compensated temperature calculated by the temperature compensation unit, a torque command value input thereto.