Sensorless Brushless Motor Drive Using Back-EMF Zero Crossing
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Solution Overview
Problem
Existing electric drives for brushless motors with permanent magnets require expensive position sensors to maintain optimal operation, leading to high costs and complexity, especially in achieving low noise and energy efficiency.
Innovation Solution
A control method that detects the zero crossing of the counter electromotive force (c.e.m.f.) in a simple and economical manner using a circuit with a resistive-inductive element and a microcontroller, allowing for continuous optimization of the supply voltage to keep the c.e.m.f. and phase current in phase, thereby eliminating the need for expensive sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If expensive position sensors (absolute encoders or Hall effect sensors) are used to detect rotor angular position, then optimal drive performance and low noise are achieved, but system cost and complexity increase
Solution Approach 1:
The patent extracts and eliminates the expensive position sensors (absolute encoders or Hall effect sensors) from the system by using an alternative approach: detecting the zero crossing of the counter electromotive force (c.e.m.f.) through voltage measurements at motor terminals. This allows optimal drive performance to be maintained without the complex and costly sensing equipment.
Solution Approach 2:
The patent introduces an intermediary measurement approach: instead of directly measuring rotor position with sensors, it measures the zero crossing of the c.e.m.f. through voltage measurements at accessible terminals. This intermediary measurement provides the necessary information for optimal control without requiring direct rotor position sensing.
2Device complexity
If sensorless control methods are used to reduce cost, then system cost decreases, but current waveform distortion increases due to zero crossing detection requirements
Solution Approach 1:
The patent applies partial action by measuring voltage at only one motor terminal (rather than all terminals) to detect the zero crossing of the c.e.m.f. This simplified measurement approach is sufficient for control purposes and avoids the need for complex full-wave measurements, thereby reducing cost while minimizing waveform distortion.
Solution Approach 2:
The patent changes the measurement parameter from direct current measurement (which would require current sensors) to voltage measurement at motor terminals. This parameter change enables sensorless control without disturbing the current waveform, as voltage measurement is non-intrusive and does not require current interruption.
3Extent of automation
If current is interrupted to detect zero crossing of c.e.m.f., then sensorless control is enabled, but sinusoidal current waveform is compromised
Solution Approach 1:
The patent uses voltage measurement at motor terminals as an intermediary method to detect the zero crossing of the c.e.m.f. without interrupting the current flow. This intermediary approach provides the necessary detection capability for sensorless control while preserving the continuous sinusoidal current waveform.
Solution Approach 2:
The patent replaces the mechanical/electrical interruption method (stopping current to measure c.e.m.f.) with an electrical measurement method (measuring voltage at terminals). This substitution eliminates the need to interrupt current flow, thereby maintaining waveform quality while enabling sensorless control.
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 reduces the cost and complexity of the drive system while maintaining low noise and energy efficiency, achieving optimal operation without the need for expensive sensors and sophisticated algorithms, thereby minimizing mechanical vibrations and acoustic noise.
Implementation Method 1
a three-phase brushless motor with permanent magnets that generates a sine-wave counter electromotive force (c.e.m.f.)
Data Source
AI summary
An electric drive (1) comprises: a permanent magnet brushless motor (2), a motor (2) power supply bridge (3), a circuit for controlling the power supply bridge (3) according to rotor position and phase currents (IS); the drive (1) comprises a circuit (6) for detecting the zero crossings of the induced counter electromotive force (ES) in the stator windings to determine the position of the rotor and a circuit (25) for indirectly detecting the amplitudes of the phase currents (IS).