Field-Oriented Motor Current Control With Rotor Offset Compensation
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Solution Overview
Problem
Inaccuracies in determining the rotor position offset angle in field-oriented current control of electric motors lead to significant performance and efficiency losses.
Innovation Solution
A method using a field-weakening controller to correct setpoint values of motor currents by adjusting the rotor position offset angle, ensuring the motor voltage does not exceed a maximum voltage, thereby optimizing efficiency and performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a calibration method is used to determine the rotor position offset angle, then the rotor position can be determined, but the determination accuracy is limited and causes performance loss
Solution Approach 1:
The patent applies preliminary action by performing a calibration procedure before normal motor operation to determine an initial rotor position offset angle. This calibration is done once beforehand, and then during field-weakening operation, a compensation value is added to this pre-determined angle to correct for inaccuracies. The preliminary calibration establishes a baseline that is then refined during operation.
Solution Approach 2:
The patent changes the parameter of rotor position offset angle by introducing a compensation value that is added to the initially calibrated angle. This parameter change allows the system to adjust the effective rotor position angle during field-weakening operation, compensating for calibration inaccuracies and improving motor performance without requiring a completely new calibration method.
2Productivity
If field-weakening control is activated by changing the rotor position offset angle, then setpoint values are automatically corrected, but this may cause instability in the base speed range
Solution Approach 1:
The patent applies dynamics by making the field-weakening control activation conditional on the degree of modulation of the motor voltage. The compensation value is only added to the rotor position offset angle when the degree of modulation is at least approximately maximum, meaning the control strategy dynamically adapts to the operating conditions. This prevents instability in the base speed range while enabling efficiency optimization at high voltage utilization.
Solution Approach 2:
The patent uses feedback by monitoring the degree of modulation of the motor voltage to determine when to activate the field-weakening control. The system continuously checks whether the motor voltage is at least approximately at the maximum voltage level, and only then activates the compensation mechanism. This feedback ensures stable operation in the base speed range while enabling performance optimization when operating near voltage limits.
3Productivity
If the rotor position offset angle is adjusted to optimize efficiency, then performance improves at maximum voltage, but the motor voltage may exceed the maximum voltage limit
Solution Approach 1:
The patent introduces a compensation value as an intermediary element between the calibrated rotor position offset angle and the actual angle used for control. This compensation value acts as a mediator that adjusts the effective angle to optimize efficiency while the field-weakening controller simultaneously adjusts setpoint values to ensure the motor voltage does not exceed the maximum limit. The intermediary compensation enables efficiency optimization without directly causing voltage violation.
Solution Approach 2:
The patent employs feedback through the field-weakening controller that monitors motor voltage levels and automatically corrects setpoint values when the voltage would otherwise exceed the maximum limit. This feedback mechanism allows the system to use the compensated rotor position angle for efficiency optimization while preventing harmful voltage excursions by real-time adjustment of control setpoints.
Data Source
AI summary
A method for field-oriented current control of motor currents of an electric motor is provided. The motor voltage is limited by a maximum voltage. A field-weakening controller corrects setpoint values of reference variables for the current control when a motor voltage exceeding the maximum voltage is required to control the motor currents to the setpoint values. A calibration value of a rotor position offset angle between a rotor of the electric motor and a position sensor system configured to determine a rotor position of the rotor is learned by a calibration of the position sensor system and stored. Furthermore, a value of the rotor position offset angle, used for the determination of the setpoint values in operation of the electric motor using a motor voltage which is at least approximately the maximum voltage, is changed in relation to the calibration value by a change value.