Sensorless PMSM Initial Position Estimation Using Counter Torque
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Solution Overview
Problem
The accuracy of initial position estimation in sensorless-type permanent magnet synchronous motors is compromised due to displacement of the magnetic pole position, particularly in inner-rotor motors with lower inertia, leading to inaccurate rotor positioning and potential mechanical issues during operation.
Innovation Solution
A control device for a permanent magnet synchronous motor that applies a pulse train with specific voltage pulses to search for the initial magnetic pole position, including a first pulse and a second pulse generating torque opposite to the first pulse's direction, to minimize rotor displacement and enhance estimation accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage is applied to the winding for initial position estimation, then the magnetic pole position can be estimated, but the rotor may rotate due to generated torque, deteriorating estimation accuracy
Solution Approach 1:
The patent applies preliminary anti-action by generating a counter torque before the rotor can rotate significantly. When voltage is applied to estimate the magnetic pole position, a counter voltage is simultaneously applied to generate a counter torque that prevents rotor rotation. This anticipatory counter-action eliminates the displacement that would otherwise occur during the measurement process, thereby maintaining both measurement accuracy and position stability.
2Speed
If the rotor inertia is reduced (inner-rotor motor design), then the motor responds faster, but the rotor rotates more easily during voltage application, worsening position estimation accuracy
Solution Approach 1:
The patent addresses this contradiction by applying preliminary anti-action through counter torque generation. The low-inertia inner-rotor design provides fast response speed, while the simultaneously applied counter torque prevents the rotor from rotating during voltage application for position estimation. This ensures that the magnetic pole position remains stable during measurement, thereby maintaining estimation accuracy despite the reduced inertia.
3Measurement precision
If multiple voltage applications are performed at different angle positions, then the magnetic pole position can be determined by comparing current values, but cumulative rotor displacement occurs, further deteriorating estimation accuracy
Solution Approach 1:
The patent applies preliminary anti-action by generating counter torque during each voltage application in the sequence. This prevents cumulative rotor displacement that would otherwise occur during multiple measurements. By maintaining the rotor position stable throughout the entire estimation process, the patent enables accurate magnetic pole position determination without requiring excessive time for correction or re-measurement.
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
The proposed solution effectively reduces magnetic pole position displacement and improves the accuracy of initial position estimation, ensuring precise rotor positioning and stable motor operation, even in inner-rotor motors with low inertia.
Implementation Method 1
a Permanent Magnet Synchronous Motor (PMSM) includes a stator including a winding (armature) and a rotor using a permanent magnet and flows an alternating current to the winding to generate a rotating magnetic field
Implementation Method 2
the voltage is applied to the winding so as to generate a magnetic field for each of n angle positions
Implementation Method 3
the rotor rotates in synchronization with the rotating magnetic field
Data Source
AI summary
A control device of a permanent magnet synchronous motor that is a control device of a sensorless-type permanent magnet synchronous motor in which a rotor using a permanent magnet rotates by a rotating magnetic field caused by a current flowing in an armature includes: a driver that applies a voltage to the armature and drives the rotor; an initial position estimator that estimates an initial position which is a magnetic pole position of the rotor that is stopped; and a controller that controls the driver so as to apply a pulse train including a voltage pulse for searching the initial position for each of n angle positions dividing a search range of an electrical angle of 360 degrees to the armature, wherein the pulse train includes a first pulse and a second pulse.