Sensorless Brushless Motor Drive Using Terminal Difference Voltage Detection
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Solution Overview
Problem
Existing sensorless drive technologies for brushless motors face challenges in accurately detecting the rotor position, especially when the motor is stopped, leading to issues like rotor reversal and synchronization loss, particularly in motors with inadequate phase characteristics control and those without a neutral point terminal.
Innovation Solution
A motor drive device and method that generates a search pulse to detect the rotor position using a terminal difference voltage, which represents the difference between the motor terminal voltage and a pseudo-neutral-point voltage, allowing for reliable and quick starting of the motor without requiring a rotor position sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sensorless drive technology is used to eliminate rotor position sensors, then cost and reliability are improved, but rotor position detection accuracy deteriorates when the motor is stopped
Solution Approach 1:
The patent introduces an intermediary signal processing mechanism that uses terminal difference voltage as a mediator to detect rotor position. By calculating the difference voltage between motor terminals and using phase detection circuits to identify the phase with maximum voltage, the system can determine rotor position without direct sensor input, thus resolving the contradiction between sensorless operation and detection accuracy.
Solution Approach 2:
The patent replaces the mechanical/physical rotor position sensor with an electrical measurement system. Instead of using physical sensors to detect rotor position, the system substitutes electrical voltage measurement and signal processing to achieve the same function, eliminating the need for physical sensors while maintaining detection capability.
2Adaptability or versatility
If rotor position is detected using back-EMF voltage, then sensorless operation is achieved, but detection fails when the rotor is not turning
Solution Approach 1:
The patent applies preliminary action by using terminal difference voltage measurement during the startup phase before the motor begins rotation. This preliminary detection method works when the rotor is stationary or at low speed, providing rotor position information before back-EMF becomes available, thus enabling smooth transition to back-EMF-based sensorless control.
Solution Approach 2:
The patent changes the detection parameter from back-EMF voltage (which requires motion) to terminal difference voltage (which works at standstill). By switching the detection method based on motor operating state, the system maintains adaptability across all speed ranges while eliminating the limitation of back-EMF-based detection at zero speed.
3Productivity
If conventional rotor position detection methods are used, then starting can be achieved, but rotor reversal and synchronization loss occur due to inaccurate position detection
Solution Approach 1:
The patent implements feedback by continuously monitoring terminal difference voltage and using this information to adjust and refine rotor position estimation. The detected phase information feeds back to the control system to ensure accurate torque application, preventing rotor reversal and synchronization loss during the critical starting phase.
Solution Approach 2:
The patent applies dynamics by adapting the detection method to the motor's operating state. The system dynamically switches between terminal difference voltage detection (for startup and low speed) and back-EMF detection (for higher speeds), ensuring optimal performance and reliability across the entire operating range while maintaining starting capability.
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 solution enables reliable and rapid starting of brushless motors by accurately detecting the rotor position over a wider electrical angle range, improving noise resistance and reducing the likelihood of rotor reversal and synchronization loss.
Implementation Method 1
Sensorless drive technologies generally detect the rotor position by reading the back electromotive force (back-EMF) voltage produced in the stator winding when the rotor is turning.
Implementation Method 2
a terminal difference voltage detector operable to detect a terminal difference voltage denoting the difference between the N-phase motor terminal voltage and the pseudo-neutral-point voltage
Data Source
AI summary
Problems with accuracy reading position detection signal peaks and minute phase differences in the detection current make motor drive control easily susceptible to differences in motor characteristics. The rotor position is determined based on whether or not a terminal difference voltage, which is the difference voltage between the motor terminal voltage and the pseudo-neutral-point voltage when the motor phases are selectively energized, exceeds a specific threshold value. The phase energized to start the motor is determined based on this determination and the motor is energized accordingly to start. Instead of switching directly from the search step at the initial rotor position to the back-EMF voltage mode, a search and start mode that creates initial rotor speed sufficient to start the motor is executed before entering the back-EMF voltage mode.