Method and Apparatus for Estimating Rotor Position in a Sensorless Synchronous Motor

Inactive Publication Date: 2010-09-23
ROCKWELL AUTOMATION TECH
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0008]The subject matter disclosed herein describes a simple, robust, and universal position observer for sensorless control of both salient and non-salient pole synchronous machines. The observer may be implemented using an equivalent EMF model of a synchronous machine or, alternately, using a sliding mode controller based on the equivalent EMF model of the synchronous machine. The observer may be used on any type of synchronous machine, including salient or non-salient pole machines su

Problems solved by technology

The mechanical coupling to the shaft of the rotor and the electrical connection to the motor controller result in additional material and installation expense.
The encoder further creates an additional source of failure and subsequent maintenance expense within the system.
The wide variety of synchronous machines, therefore, presents a significant challenge for developing a universal position observer capable of providing an accurate rotor position estimate for each type of synchronous machine.
However, back EMF models for many types of synchronous motors are subject to a fundamental limitation: these motor models are speed dependent.
The drive may erroneously conclude that the motor is operating at zero speed when, in fact, the motor is rotating at a low speed.
Consequently

Method used

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  • Method and Apparatus for Estimating Rotor Position in a Sensorless Synchronous Motor

Examples

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Example

[0038]Referring next to FIGS. 3-5, a first embodiment of the position observer 40 according to the present invention is illustrated. The current feedback (iα and iβ) and voltage signals (vα and vβ), each in the stationary reference frame, are inputs to the position observer 40. The position observer 40 uses a model 44 of a synchronous motor to calculate equivalent EMF values in the stationary reference frame (e′α and e′β) as developed according to equations (1)-(8).

[0039]The model 44 is based on a voltage model of a permanent magnet salient pole synchronous machine in the stationary reference frame, equation (1). Current feedback signals (iα and iβ) and voltage signals (vα and vβ) in the stationary reference frame are input to the position observer 40. These current and voltage signals are used by the EMF model 44, equation (6), to determine the equivalent EMF values (e′α and e′β). The equivalent EMF values are then inputs to block 46 and used to estimate the rotor position, {circum...

Example

[0046]Referring now to FIGS. 6-8, a second embodiment of the position observer 40 according to the present invention is illustrated. The motor current and voltage, each being transformed to the stationary reference frame, are input signals to the position observer 40. The position observer 40 uses a sliding mode model 54 and an equivalent control block 56 to obtain an estimated rotor position, {circumflex over (θ)}.

[0047]Sliding mode control is a non-linear control strategy which attempts to force a dynamic system to operate at a desired operating point using a “bang-bang” type controller. A “bang-bang” type controller compares an input signal against a pre-determined operating point, for example a particular value or plane of operation, and outputs one of two values, for example a zero or a one, based on which side of the operating point the input signal is located. A set of sliding mode equations is developed according to principles of sliding mode control, and the equations are u...

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Abstract

The present invention provides a simple, robust, and universal position observer for use with sensorless synchronous machines. The observer may be implemented using an equivalent EMF model of a synchronous machine or, alternately, using a sliding mode controller based on the equivalent EMF model of the synchronous machine. The observer may be used on any type of synchronous machine, including salient or non-salient pole machines such as a permanent magnet, interior permanent magnet, wound rotor, or reluctance synchronous machine. The observer provides low sensitivity to parameter variations and disturbances or transient conditions in the machine. In addition, no knowledge of speed is required as an input to the observer and an estimated position may be calculated using a subset of the machine parameters.

Description

BACKGROUND OF THE INVENTION[0001]The subject matter disclosed herein relates to control of electric motors and, in particular, to estimating the position of a rotor in a synchronous motor without a position feedback device.[0002]Synchronous motors are electric motors having a magnetic field established in both the rotor and the stator of the motor. The magnetic field in the rotor is typically generated by passing a DC current through slip rings to the winding of the rotor. Alternately, permanent magnets may be mounted on or in the rotor to provide a continuous magnetic field in the rotor. The magnetic field in the stator is typically generated by applying an AC voltage to the winding of the stator at a frequency that matches the frequency of rotation of the magnetic field in the rotor. As a result, knowledge of the position of the rotor is important for high performance control of the synchronous motor.[0003]It is known that high performance control of synchronous motors can be achi...

Claims

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Application Information

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IPC IPC(8): H02P6/18
CPCH02P21/0007H02P21/146H02P21/0042H02P21/18H02P21/26
Inventor LIU, JINGBOROYAK, SEMYONHARBAUGH, MARK M.NONDHAL, THOMAS A.SCHMIDT, PETER B.
Owner ROCKWELL AUTOMATION TECH
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