Motor Rotor Angle Estimation Using SOGI Back-EMF Processing
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Solution Overview
Problem
Existing methods for estimating rotor position angles in electric machines suffer from integration errors due to DC offsets in current sampling, leading to reduced precision and efficiency in rotor angle estimation.
Innovation Solution
A method utilizing a second-order generalized integrator (SOGI) to perform a 90-degree phase lag operation on back emf, followed by division with a resonant frequency to obtain stator flux linkage, subtracting inductive magnetic flux, and computing the rotor position angle, thereby eliminating phase angle differences and improving precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a pure integration step is used to compute rotor flux linkage, then the method is simple, but DC offset in current sampling causes integration windup effect and reduces rotor position angle estimation precision
Solution Approach 1:
The patent transforms the integration operation into a differentiation operation by computing the time derivative of the back-EMF signal. This parameter change from integration to differentiation eliminates the integration windup effect caused by DC offset, as differentiation naturally rejects DC components. The rotor flux linkage is obtained by differentiating the back-EMF and then integrating the result, which avoids the accumulation of DC offset errors.
2Measurement precision
If a low-pass filter is used instead of pure integration, then some DC offset effect is reduced, but the filter introduces phase angle lag and cannot completely solve the DC offset problem
Solution Approach 1:
The patent extracts and removes the problematic integration operation that causes windup effect, replacing it with a differentiation-based approach. By taking out the integration step and using differentiation of back-EMF instead, the solution eliminates the root cause of DC offset accumulation while avoiding the need for complex filtering and feedback mechanisms.
3Measurement precision
If a high-pass filter or feedback loop is added to completely solve DC offset, then the DC offset problem is addressed, but the control system becomes more complicated with additional phase angle lag
Solution Approach 1:
The patent inverts the conventional approach by instead of trying to eliminate DC offset through filtering or feedback, it uses differentiation which inherently rejects DC components. This inversion of the problem-solving approach - from attempting to remove DC offset effects to using an operation that naturally ignores DC components - simplifies the system while maintaining precision.
Data Source
AI summary
Disclosed are a method and apparatus for estimating a rotor position angle of an electric machine, an electric machine control system comprising the apparatus, and a computer-readable storage medium. The method comprises obtaining a back emf of a stator of the electric machine; performing a second-order generalized integrator operation on the back emf, to obtain a signal with a phase lag of 90 degrees with respect to the back emf; dividing the phase-lagging signal by a resonant frequency of the back emf to obtain a stator flux linkage of the stator, then subtracting an inductive magnetic flux of the stator from the stator flux linkage to obtain a rotor flux linkage; and computing a rotor position angle based on the rotor flux linkage.