Rotor Position Detection via Phase Current Inductance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for determining the rotor position in permanent-magnet motors, especially at low speeds, are unreliable due to susceptibility to electromagnetic noise and complexity in design, and often require costly Hall-effect sensors or rely on back EMF transitions that are difficult to detect.
Innovation Solution
A method that uses changes in inductance of the phase winding to determine rotor position by exciting and freewheeling the phase winding, measuring parameters such as phase current magnitude or time intervals, and comparing them against a saturation threshold unique to each motor, which is sensitive to temperature changes, allowing for reliable position determination without relying on back EMF.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a Hall-effect sensor is integrated within the motor to determine rotor position, then the rotor position can be determined, but the design and manufacture of the motor becomes complicated and costs increase
Solution Approach 1:
The invention extracts the rotor position detection function from the mechanical structure by using electrical measurements (phase current during excitation and freewheeling periods) to infer position, eliminating the need for physical Hall-effect sensors integrated into the motor
Solution Approach 2:
The motor's own electrical characteristics (inductance variations affecting phase current) are used to determine rotor position, allowing the motor to self-diagnose its state without external sensing components
2Measurement precision
If a Hall-effect sensor is used to determine rotor position, then position information is obtained, but the sensor signal becomes susceptible to electromagnetic noise
Solution Approach 1:
The invention replaces the Hall-effect sensor's magnetic field detection method with an electrical measurement method that monitors phase current characteristics, which are less susceptible to electromagnetic noise interference
3Device complexity
If back EMF transitions are used to determine rotor position, then sensorless operation is achieved, but the method cannot reliably determine position at low speeds
Solution Approach 1:
The invention changes the measurement parameter from back EMF (which is speed-dependent) to phase current during excitation and freewheeling (which reflects inductance changes independent of speed), enabling reliable low-speed and standstill position detection
Solution Approach 2:
The system performs preliminary excitation of the phase winding before commutation to actively probe the inductance state, allowing position determination without relying on the motor's natural back EMF generation
4Ease of operation
If a fixed saturation threshold is used to determine rotor position, then the determination process is simplified, but temperature variations cause inaccurate position determination
Solution Approach 1:
The invention makes the saturation threshold dynamic by adjusting it according to temperature conditions, allowing the system to maintain accurate position determination across varying thermal environments while preserving the simplicity of threshold-based detection
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 enables reliable rotor position determination at low speeds and reduces component costs by eliminating the need for expensive sensors, while being less prone to noise and temperature variations, ensuring accurate commutation of phase windings.
Implementation Method 1
transitions in the polarity of the back EMF induced in a phase winding may be used to determine the rotor position
Implementation Method 2
the method makes use of the changes in the inductance of the phase winding that arise as the rotor rotates from one aligned position to the next aligned position
Data Source
AI summary
A method of determining the position of a rotor of a brushless permanent-magnet motor is provided. The phase winding is freewheeled when a phase current exceeds an upper threshold. The method further includes measuring a parameter that corresponds to either: (i) the magnitude of the phase current during or at the end of freewheeling when the phase winding is freewheeled for the fixed period of time, or (ii) the time interval between the start and end of freewheeling or the start and end of excitation when the phase winding is freewheeled until the phase current falls below the lower threshold. The measured parameter is then used to define a saturation threshold. The phase winding is subsequently excited and freewheeled in the same manner, and the parameter is measured again. The method then compares the measured parameter against the saturation threshold, and determines that the rotor is at a predetermined position.