AC Motor Torque Estimation via Angle-Adaptive Sampling
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Solution Overview
Problem
Existing alternating-current motor control systems using rectangular wave voltage control face challenges in maintaining control responsiveness and stability due to distortion components in motor current, which are exacerbated by filtering processes that increase the load on the electronic control unit and lead to torque fluctuations, especially at low rotation speeds.
Innovation Solution
The system incorporates a torque estimating portion that samples phase currents at varying electrical angles based on rotation speed, allowing for angle interruptions between switching interruptions to remove distortion without filtering, thereby improving estimation accuracy and reducing torque fluctuations while maintaining a simple structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a filtering process is applied to remove distortion components from motor current, then measurement precision of torque estimation is improved, but device complexity and processing load increase
Solution Approach 1:
The patent extracts only the necessary current samples at specific electrical angles (0°, 60°, 120°, etc.) where distortion components are minimized, rather than processing all current samples through a filter. This selective extraction achieves torque estimation accuracy without requiring complex filtering structures.
Solution Approach 2:
The patent performs preliminary selection of optimal sampling angles before torque estimation. By pre-determining that current samples at 0°, 60°, 120°, etc. electrical angles contain minimal distortion, the system prepares the cleanest possible data for torque calculation in advance, avoiding the need for post-sampling filtering.
2Measurement precision
If filtering process time constant is increased to remove distortion, then measurement precision is improved, but response speed decreases
Solution Approach 1:
Instead of using a filter with a time constant that delays the response, the patent directly extracts current samples at electrical angles where distortion is naturally minimal (0°, 60°, 120°, etc.). This extraction approach provides accurate torque estimation without introducing the time delay inherent in filtering operations.
3Measurement precision
If sampling frequency is increased to improve torque estimation accuracy, then measurement precision is improved, but use of energy and processing load increase
Solution Approach 1:
The patent applies partial sampling by selecting only specific current samples at critical electrical angles (0°, 60°, 120°, etc.) rather than processing all available current data. This partial action provides sufficient torque estimation accuracy while significantly reducing the processing energy required by the ECU.
Solution Approach 2:
The sampling strategy serves multiple functions simultaneously: it identifies distortion-free current samples for accurate torque estimation, reduces processing load on the ECU, and maintains control responsiveness. This multi-functional approach eliminates the need for separate high-frequency sampling and filtering systems.
4Power
If rectangular wave voltage control is used to increase modulation factor, then power output is improved, but harmful factors increase due to current distortion
Solution Approach 1:
The patent converts the harmful effect of rectangular wave voltage-induced current distortion into a beneficial sampling strategy. By identifying that distortion is minimal at specific electrical angles (0°, 60°, 120°, etc.), the system uses these same angles for torque estimation, effectively turning the distortion pattern into a useful characteristic for accurate measurement.
Data Source
AI summary
When a rectangular wave voltage control mode is selected, a control apparatus estimates the output torque of an alternating-current motor based on the outputs of a current sensor and a rotation angle sensor, and executes torque feedback control by adjusting the phase of rectangular wave voltage based on the difference between the torque estimated value and a torque command value. The control apparatus executes a switching interruption that outputs a control command to a switching element of an inverter every 60 degrees of electrical angle, and executes an angle interruption that samples the phase currents of the alternating-current motor based on the output of the current sensor and converts those phase currents into a d-axis current and a q-axis current every predetermined electrical angle that is set beforehand. The control apparatus for the alternating-current motor then sets the predetermined electrical angle such that the number of angle interruptions between switching interruptions varies according to the rotation speed of the alternating-current motor.