AC Motor Resistance Calculation for Electric Cars
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Solution Overview
Problem
Existing technologies face challenges in accurately computing the resistance value of an alternating current (AC) motor, especially when it is revolving, as the angular velocity does not reach zero, making it difficult to determine the primary and secondary resistance values.
Innovation Solution
A control device for electric cars is equipped with a power converter, a resistance calculator, and a resistance calculation activator that computes the resistance value based on voltage and current commands, activating the calculator when the AC motor is determined to have stopped revolving, allowing for accurate resistance value calculation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If resistance value is computed when AC motor is revolving, then continuous control is maintained, but measurement precision deteriorates due to complex impedance characteristics
Solution Approach 1:
The system performs resistance value computation in advance when the AC motor is determined to be stopped (angular velocity approximately zero), storing the computed value for subsequent use during motor operation. This preliminary computation avoids the measurement errors that occur when the motor is revolving, while still enabling continuous control through the use of stored values.
2Measurement precision
If angular velocity detection is implemented to determine stopping condition, then resistance computation accuracy is improved, but device complexity increases
Solution Approach 1:
The control device utilizes its own existing angular velocity information (already available for motor control purposes) to determine when the motor has stopped, without requiring additional detection devices. The control device serves dual purposes: both motor control and resistance value computation timing determination.
3Ease of manufacture
If resistance value is computed immediately after activation, then computation timing is simplified, but accuracy deteriorates if motor has not fully stopped
Solution Approach 1:
The system continuously monitors angular velocity and uses this feedback to determine the appropriate timing for resistance value computation. By checking whether the angular velocity is approximately zero at the time of computation request, the system ensures accurate measurements while maintaining relatively simple control logic.
Data Source
AI summary
A resistance calculation activator determines whether or not an electric car is stopped on the basis of a drive command signal and an external signal, and activates a resistance calculator if a powering command is input as the drive command when it is determined that the electric car is stopped. The activated resistance calculator computes, within a resistance calculation period, a resistance value of an AC motor that produces driving force for the electric car, on the basis of a d-axis voltage command value and a d-axis current value supplied to the AC motor.