Sensorless Rotor Position Detection in Permanent-Magnet Motors
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for determining the rotor position in permanent-magnet motors, especially single-phase motors, face challenges such as increased complexity, susceptibility to electromagnetic noise, and reduced electrical power due to the need for Hall-effect sensors or suspension of excitation to detect back EMF transitions.
Innovation Solution
A method employing two schemes to determine rotor position based on current rate changes and voltage equations, allowing for rotor position detection without sensors and maintaining electrical power, using a single winding for both driving and position determination across varying speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a Hall-effect sensor is integrated within the motor to determine rotor position, then rotor position detection accuracy is improved, but device complexity and manufacturing complexity increase
Solution Approach 1:
The patent extracts the rotor position detection function from a separate Hall-effect sensor and implements it through sensorless control algorithms that use existing motor windings and control circuitry. The detection functionality is taken out as a software-based solution rather than a hardware sensor integration.
Solution Approach 2:
The patent makes the motor windings serve dual functions: they both drive the motor and enable rotor position detection through back EMF measurement. The control circuitry performs both motor control and position sensing functions, eliminating the need for dedicated sensor hardware.
2Loss of information
If a Hall-effect sensor is used for rotor position detection, then rotor position information is obtained, but the sensor signal becomes susceptible to electromagnetic noise
Solution Approach 1:
The patent replaces the Hall-effect sensor (a hardware component susceptible to noise) with a software-based detection algorithm that processes voltage and current signals. This substitution eliminates the physical sensor that would be exposed to electromagnetic interference from the motor.
3Measurement precision
If excitation is suspended to detect back EMF transitions for rotor position determination, then rotor position can be detected, but electrical power delivered to the motor is reduced
Solution Approach 1:
The patent uses partial excitation strategies where excitation is applied only to specific windings or for limited time periods sufficient to generate detectable back EMF signals, rather than suspending all excitation. This allows position detection while maintaining adequate power delivery to the motor.
Solution Approach 2:
The patent performs preliminary excitation of windings before the main propulsion phase, using this excitation period to both position the rotor and detect position information. The excitation is timed and controlled to provide detection capability without significantly reducing overall power delivery during the motor's operating cycle.
4Device complexity
If a single-phase motor configuration is used, then device simplicity is improved, but sensorless rotor position determination becomes unfeasible using traditional multi-phase methods
Solution Approach 1:
The patent implements dynamic control strategies for single-phase motors that adapt excitation timing and winding selection based on rotor position and operating conditions. The control system dynamically switches between different excitation patterns to enable position detection and maintain motor operation, making sensorless control feasible for single-phase configurations.
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 simplifies hardware requirements, reduces costs, and maintains high accuracy and power efficiency by switching between schemes based on speed and excitation voltage, effectively addressing the limitations of existing methods.
Implementation Method 1
During rotation, the rotor induces a back EMF in the winding, the magnitude of which depends on the angular position of the rotor.
Implementation Method 2
A permanent-magnet motor will often include a Hall-effect sensor, which outputs a signal indicative of the rotor position.
Data Source
AI summary
A method of determining the position of a rotor of a permanent-magnet motor. The method uses two different schemes to determine the position of the rotor. A first scheme is used when the rotor rotates within a first speed range, by sequentially exciting and freewheeling a winding of the motor, measuring a parameter that depends on the rate of change of current in the winding, and comparing the parameter against a threshold. A second scheme is used when the rotor rotates within a second speed range, by generating a voltage signal that is proportional to the voltage across the winding, generating a further voltage signal that depends on the rate of change of current in the winding, and comparing the two signals.