Motor Control Device Resolver Offset Correction
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Solution Overview
Problem
Existing motor control systems face challenges in achieving high precision due to errors caused by manufacturing precision, assembly errors, and signal processing delays in resolver-based systems, leading to inaccuracies in torque control and phase alignment, especially when friction and load are present.
Innovation Solution
A motor control method that measures current command values during constant velocity operation and calculates a correction value to adjust the motor's rotation position, allowing for precise control even with detected rotation position deviations, by flowing a constant d-axis current and minimizing q-axis current flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a resolver-based angle detector is used to detect rotor rotation angle, then the motor control system can be implemented, but manufacturing precision errors and assembly errors cause deviation between the angle detector and synchronous motor rotation positions
Solution Approach 1:
The patent applies preliminary action by performing offset error correction before normal motor operation. The system rotates the motor in a field-weakening control region, measures current command values, calculates offset errors, and corrects the detection signal beforehand. This ensures that when the motor operates normally, the angle detection is already corrected for manufacturing and assembly errors, achieving high precision without requiring perfect initial alignment
Solution Approach 2:
The patent replaces mechanical alignment adjustment with an electrical correction system. Instead of physically adjusting the resolver alignment to match the synchronous motor rotation positions, the system uses electrical signal processing to calculate and apply offset corrections. This substitution allows for easier manufacturing and assembly while maintaining high detection precision through software-based compensation
2Ease of operation
If offset error correction is performed using voltage command values, then correction can be implemented, but noise from PWM driving affects the command voltage and reduces precision
Solution Approach 1:
The patent extracts the offset error calculation from the noisy voltage command signal and instead uses current command values. By taking out the correction basis from the PWM-affected voltage domain to the current domain, the system eliminates the noise interference while maintaining the ability to perform offset correction. The current command values provide a cleaner signal for accurate offset error calculation
3Measurement precision
If the motor is operated in a field-weakening control region to measure current command values for offset correction, then high-precision correction can be achieved, but the motor must be rotated at high speed which consumes more energy
Solution Approach 1:
The patent applies partial action by performing the offset correction measurement only during a brief initialization or calibration phase, rather than continuously during normal operation. The field-weakening region measurement is done partially - just enough to obtain the necessary current command values for correction - and then the system returns to normal operation. This excessive action (high-speed rotation) is limited to the correction phase only, minimizing overall energy consumption while achieving high precision
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 approach enables high-precision motor control by correcting for errors caused by resolver inaccuracies and signal delays, maintaining control accuracy despite friction and load influences, and reducing the impact of noise from PWM driving.
Implementation Method 1
The resolver causes a magnetic field by applying a sinusoidal signal (Esin(ωt) (where E is an amplitude of a sinusoidal wave and ω is an excitation frequency)) to the rotor coil. In the magnetic field, a voltage (KEsin(ωt)×sin(θ), KEsin(ωt)×cos(θ)) has a phase difference between two stator coils orthogonal to each other is produced in the two stator coils.
Data Source
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AI summary
This motor control device generates a voltage command value from a current command value and performs feedback control by means of a detected current flowing through a motor. The motor control device is provided with: a speed control unit that causes the motor to rotate at a set speed, and performs speed control of the motor on the basis of a speed command value that causes the flow of a d-axis current that is a set amount of current; a current measurement unit that measures a current command value that is on the basis of the output of the speed control unit when the motor is rotated at the set speed and the set amount of d-axis current is flowing; and a correction value calculation unit that calculates a correction value for the rotational position of the motor on the basis of the measured current command value.