Synchronous Motor Inverter Control for Rotor Angle Offset Correction
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Solution Overview
Problem
Existing methods for detecting offset errors in rotation angle sensors of permanent magnet synchronous motors face challenges in accuracy, particularly at low rotational speeds due to motor temperature effects, and struggle with calibrating d-axis voltage and q-axis current zero determination.
Innovation Solution
A power conversion device with an inverter and a magnetic pole position correction unit that calculates the actual and ideal current phases during a three-phase short circuit, allowing for precise correction of the rotor's magnetic pole position based on the difference between these phases, considering the rotor's rotational speed and stator temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If only d-axis voltage is applied in rotor stopped state to search for zero q-axis current, then the method is simple to implement, but calibration of Vd magnitude and energization time is difficult and accuracy is insufficient
Solution Approach 1:
The patent changes the operating parameters from static (rotor stopped) to dynamic (rotor rotating), and applies both d-axis and q-axis voltages simultaneously rather than sequentially. This parameter change enables more accurate offset error detection by utilizing the back-EMF generated during rotation, which provides additional information for calibration without requiring complex manual adjustment of Vd magnitude and energization time.
2Ease of manufacture
If offset error is calculated based on phase current difference in short-circuited motor end, then the method is straightforward, but error caused by motor temperature particularly stator temperature is large at low rotational speeds
Solution Approach 1:
The patent performs offset error detection during normal motor operation before temperature-induced errors significantly affect the measurement. By detecting the current phase during rotation and comparing it with the ideal current phase calculated from motor parameters, the system captures the offset error before thermal effects accumulate, thereby improving accuracy at low speeds where temperature variations are more problematic.
Solution Approach 2:
The patent introduces the ideal current phase as an intermediary reference that is calculated based on motor parameters and rotational speed. This intermediary allows comparison with the actual current phase to extract the offset error, providing a temperature-compensated reference that remains accurate even when stator temperature varies, thus resolving the temperature sensitivity issue.
3Ease of operation
If rotation angle sensor is attached to rotor, then magnetic pole position information can be acquired for torque control, but attachment errors cause angle errors and torque deviation from command value
Solution Approach 1:
The patent implements a feedback mechanism where the detected current phase during motor operation is continuously compared with the ideal current phase. The difference (offset error) is fed back to correct the magnetic pole position information from the rotation angle sensor, thereby compensating for attachment errors and improving torque control accuracy without requiring reattachment or manual calibration of the sensor.
Data Source
AI summary
A power conversion device includes: an inverter that converts a DC voltage into an AC voltage and drives a synchronous motor; and a magnetic pole position correction unit that corrects an error in a magnetic pole position of a rotor from a rotation angle sensor of the synchronous motor. The magnetic pole position correction unit includes an actual current phase calculation unit that calculates a current phase from a current when three-phase lines are short-circuited during rotation of the synchronous motor and an ideal current phase calculation unit that calculates an ideal current phase based on a rotational speed of the rotor and a temperature of a stator, and corrects the magnetic pole position from a difference between outputs of the actual current phase calculation unit and the ideal current phase calculation unit.