Sensorless Motor Positioning via Rotor Flux Current Command
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Solution Overview
Problem
Existing methods for determining the position of an electrical machine's drive, especially at low speeds and loads, suffer from large errors due to the current-space vector measurements fluctuating around zero, affecting speed calculations and reliability.
Innovation Solution
A current command is added in the direction of the rotor flux or field within the stator to maintain a sufficient current flow, allowing precise determination of the current-space vector direction and angle, even at low speeds and loads, using a device with two independent channels for position monitoring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If sensorless position determination is used at low speeds and loads, then the system can operate without additional sensors, but the current-space vector amplitude becomes around 0 causing large measurement errors in position and speed
Solution Approach 1:
An additional current command is applied in advance in the direction of the rotor flux or rotor field to ensure sufficient current flow before position determination is performed. This preliminary current application prevents the current-space vector from collapsing to zero, thereby maintaining measurement precision during sensorless operation at low speeds and loads
2Measurement precision
If additional current command is applied in the direction of rotor flux, then the current-space vector direction can be determined precisely at low speeds, but the system complexity increases due to additional control requirements
Solution Approach 1:
The additional current command in the rotor flux direction serves multiple functions simultaneously: it maintains sufficient current-space vector amplitude for accurate position determination, provides field weakening capability, and supports operation across various load conditions. This multi-functionality approach increases measurement precision without proportionally increasing system complexity
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 approach enhances measurement accuracy and reliability by ensuring a stable current flow, reducing errors in position and speed calculations, and enabling safe operation across various load conditions.
Implementation Method 1
measuring the three-phase current of the machine
Implementation Method 2
converting the measured values of this three-phase current to a current-space vector
Implementation Method 3
servomotor with permanent magnet generation of the rotor magnetic field
Data Source
Figure 1
Figure 2A~3B
AI summary
The invention relates to a method for determining the position of the drive of an electric machine (10) such as a motor from the applied current (30, 32, 34), wherein for a secure operation, the position determination of the drive is carried out on two independent paths or channels and subsequently both the measured values are combined and cross-checked for secure mode of operation such as maintaining a safe speed or safe position for the drive, comprising the following method steps: determining the position of the drive in both current channels by measuring the three-phase current to the machine, then converting the measured values for the three-phase current to give a current-space vector, calculating the angle of the current-space vector within an electrical revolution and determining the position of the drive (rotor). According to the invention, a current command, whose field acts in the direction of the rotor flow or rotor field is added within the stator (in the direction of the field weakening) which results in a increase in precision of measurement.