Sensorless Rotor Position Estimation at Standstill via Extended Flux
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Solution Overview
Problem
Existing methods for sensorless rotor position detection in dynamoelectric machines, such as those described in U.S. Patent No. 7,072,790, are inadequate for low-speed or standstill operations, leading to inefficiencies and reliability issues.
Innovation Solution
A system that estimates rotor angular position and velocity by measuring AC currents and potentials across stator windings, transforming them into a stationary frame, and processing these signals to derive extended rotor flux values, which are then used in a phase lock loop to determine the rotor's position and velocity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If sensorless rotor position detection methods (back EMF, signal injection, or flux-based methods) are used to eliminate mechanical shaft sensors, then device complexity and cost are reduced, but measurement precision deteriorates at low speeds or standstill conditions
Solution Approach 1:
The patent transforms the rotor position detection problem from the rotating reference frame to a stationary reference frame, fundamentally changing the parameter space in which measurements are made. This transformation enables the use of extended rotor flux components that are observable in the stationary frame, particularly at low speeds where traditional methods fail. The mathematical transformation of voltage and current equations into the stationary frame reveals new measurable parameters (extended flux components) that provide reliable position information regardless of rotor speed.
2Reliability
If traditional flux-based rotor position detection is used, then it works well at high speeds, but reliability deteriorates at low speeds or standstill due to insufficient flux signal
Solution Approach 1:
The patent introduces a new dimensional perspective by transforming from the rotating d-q reference frame to the stationary alpha-beta reference frame. This dimensional change reveals extended flux components (lambda_alpha and lambda_beta) that exist in the stationary frame and contain position information that is accessible even when the rotor is stationary or moving slowly. The extended flux concept adds a new dimension to flux observation that is independent of rotor speed.
3Device complexity
If back EMF method is used for rotor position detection, then it is simple to implement, but measurement precision deteriorates at low speeds due to insufficient back EMF signal magnitude
Solution Approach 1:
The patent uses extended rotor flux as an intermediary quantity that bridges the gap between measurable stator voltages/currents and rotor position information. The extended flux components serve as intermediate signals that contain encoded position information and can be extracted through mathematical processing in the stationary frame. This intermediary approach allows position detection without directly measuring weak back EMF signals at low speeds.
Data Source
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AI summary
A method and system for estimating an angular position and an angular velocity of a rotor in a dynamoelectric machine (12) measures an AC current (28) and a potential (26) for each of a plurality of windings coupled to a stator of the dynamoelectric machine, transforms the measured currents and potentials to a stationary frame (α-β) to produce transformed currents and transformed potentials, and processes the transformed currents and transformed potentials to produce a first intermediate signal and a second intermediate signal. The first intermediate signal and the second intermediate signal are cross-coupled and processed (Fig. 3) to obtain a first extended rotor flux value and a second extended rotor flux value. The first extended rotor flux value arid the second extended rotor flux value are applied to a phase lock loop (Fig. 4) to derive an estimated rotor angular position and an estimated rotor angular velocity for the dynamoelectric machine.