Angle Offset Estimation for Permanent-Magnet Synchronous Motors
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Solution Overview
Problem
Existing methods for determining the angle offset of an angle sensor in permanent-magnet synchronous motors, such as those used in elevator systems, are inefficient and require the motor to turn freely or specific motor configurations, which are not always feasible, especially after mechanical installation is complete.
Innovation Solution
A two-stage method where an initial angle offset is determined through a short-circuit test by inducing stator currents and then fine-tuned by controlling motor torque to maintain zero speed, allowing the estimation of the angle offset without requiring the motor to turn freely or knowing motor parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a DC current is applied to the motor to determine the angle offset, then the offset can be determined from the difference between the applied current angle and measured angle, but the motor must be able to turn freely which is problematic after mechanical installation
Solution Approach 1:
The patent replaces the mechanical DC current alignment method with an electrical signal injection method. Instead of applying DC current and mechanically aligning the motor, the system injects test signals into the motor windings and determines the angle offset from the current response. This substitution eliminates the need for mechanical freedom while achieving the same measurement objective through electrical means.
Solution Approach 2:
The patent changes the operational parameters from DC current application to AC signal injection at specific frequencies. By using signal injection with varying frequencies and analyzing the current response magnitude and phase, the system can determine the angle offset without requiring the motor to be mechanically free to turn, thus adapting to installed conditions.
2Measurement precision
If voltage stimulus is injected to determine rotor orientation from current response, then the actual rotor orientation can be determined, but the motor must be magnetically asymmetric (salient) with changing phase inductances
Solution Approach 1:
The patent employs feedback by continuously monitoring the current response to injected voltage signals and using this information to iteratively refine the angle offset estimation. The system injects test signals, measures the current response, compares it with expected responses at different rotor positions, and adjusts the estimated angle offset accordingly until convergence is achieved. This feedback mechanism enables accurate rotor orientation determination without requiring magnetic asymmetry.
Solution Approach 2:
The patent uses periodic signal injection at multiple frequencies to excite the motor windings and elicit current responses that reveal rotor position information. By injecting periodic test signals and analyzing the frequency-domain characteristics of the current response, the system can determine the angle offset for both salient and non-salient motors, thus eliminating the magnetic asymmetry requirement.
3Productivity
If the motor is coupled to a load, then the system is ready for operation, but existing angle offset determination methods cannot be applied because they require free motor rotation
Solution Approach 1:
The patent performs angle offset determination as a preliminary action during the commissioning phase before full operational load is applied. The system uses the frequency converter to inject test signals into the motor windings while the motor is stationary or rotating at low speed with minimal load, allowing accurate angle offset measurement. Once the angle offset is determined, the motor can be fully coupled to its operational load, thus resolving the contradiction between system readiness and measurement capability.
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 method allows for accurate and efficient estimation of the angle offset, minimizing movement and not requiring prior knowledge of motor parameters, making it suitable for systems already coupled to a load.
Implementation Method 1
A first stage comprises short-circuiting phases of a stator of the motor to one another. Releasing the brake causes the axle to turn, and stator currents are induced.
Data Source
Figure 1~2
AI summary
The present disclosure describes a two-stage method for estimating an angle offset of an angle sensor in a system comprising a permanent-magnet synchronous motor. An initial value for the estimated angle offset is first determined with a short-circuit test. Next, a torque of the motor may be controlled so that the motor is maintained at a zero speed. Minor adjustments are made to the value of the angle offset to find a minimum magnitude of stator current. A value at which the stator current is at its minimum is used as a final angle offset.