Brushless PM Motor Rotor Positioning via Back-EMF Zero Crossing
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Solution Overview
Problem
Brushless permanent magnet motors face challenges in determining rotor position without Hall-effect sensors, as existing sensorless schemes either complicate the design or reduce electrical power efficiency, and hardware-based solutions are costly.
Innovation Solution
A method that calculates the phase of back EMF using measured phase current and voltage, determines zero-crossing points, and aligns the rotor position, enabling efficient operation across a wider power range without the need for hardware, using software-based calculations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Hall-effect sensors are used to determine rotor position, then measurement precision is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent extracts the rotor position detection function from physical Hall-effect sensors and implements it through software-based back EMF analysis. By calculating the phase of back EMF from measured voltage and current, the system determines zero-crossing points that indicate rotor position, eliminating the need for additional sensor hardware while maintaining measurement capability
Solution Approach 2:
The patent replaces the mechanical/electrical Hall-effect sensor system with a computational approach. Instead of using physical sensors to directly measure rotor position, the system uses software algorithms to analyze electrical signals (voltage and current) already present in the motor circuit, substituting hardware-based detection with software-based calculation
2Device complexity
If sensorless schemes suspend excitation to determine rotor position, then device complexity is reduced, but power efficiency deteriorates
Solution Approach 1:
The patent applies partial action by determining rotor position at specific zero-crossing points of the back EMF waveform rather than continuously monitoring throughout the entire excitation cycle. This selective measurement approach provides sufficient position information for commutation while minimizing the impact on power delivery, avoiding the need to suspend excitation entirely
3Measurement precision
If complex hardware arrangements are used for sensorless control, then measurement precision is maintained, but device complexity increases
Solution Approach 1:
The patent enables the motor's existing electrical circuitry to serve dual purposes: both driving the motor and providing the signals needed for rotor position detection. The voltage and current measurements taken for normal motor control are reused to calculate back EMF phase and determine rotor position, allowing the system to self-diagnose its state without requiring separate detection hardware
Solution Approach 2:
The patent makes the existing voltage and current measurement circuits universal, using them both for motor control and for rotor position detection. The same sensors and processing circuits that monitor motor operation for commutation purposes also extract rotor position information through back EMF phase calculation, eliminating the need for dedicated position sensing hardware
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 allows accurate determination of rotor position at zero-crossing points, both within and outside excitation periods, enhancing operational efficiency and reducing system costs by eliminating the need for complex hardware.
Implementation Method 1
measuring voltage applied to the phase winding of the motor during excitation of the phase winding, calculating a phase of back EMF induced in the phase winding using the measured phase current and the measured voltage
Data Source
AI summary
A method of determining a position of a rotor of a brushless permanent magnet motor includes measuring phase current flowing through a phase winding of the motor during excitation of the phase winding, and measuring voltage applied to the phase winding of the motor during excitation of the phase winding. The method includes calculating a phase of back EMF induced in the phase winding using the measured phase current and the measured voltage. The method includes determining a zero-crossing point of the back EMF induced in the phase winding using the calculated phase of back EMF induced in the phase winding. The method includes determining an aligned position of the rotor of the brushless permanent magnet motor when the back EMF induced in the phase winding is at the zero-crossing point.