Sensorless Motor Drive Rotor Position Detection
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Solution Overview
Problem
Existing sensorless brushless motor drive technologies face challenges in accurately detecting rotor position, especially when the motor is stopped, leading to difficulties in starting and maintaining synchronization, particularly in motors with inadequate phase characteristics control and reduced coil inductance for high-speed performance.
Innovation Solution
A motor drive device that generates a search current and a starting current in a search and start mode, using a pseudo-neutral-point voltage generator and a neutral point difference voltage detector to determine the rotor position, allowing for immediate energization of the appropriate drive phase and enabling torque application without prior position detection, thus enhancing starting reliability and speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If back-EMF voltage detection is used for rotor position detection, then the detection is simple and does not require additional sensors, but the rotor position cannot be detected when the motor is stopped
Solution Approach 1:
The patent applies preliminary action by detecting rotor position before the motor starts using neutral point voltage detection. The system performs initial position detection when the motor is stationary using voltage pulses applied to the motor windings, then transitions to back-EMF detection once the motor is running. This preliminary detection step ensures reliable starting without requiring sensors.
2Reliability
If neutral point voltage detection is used for rotor position detection, then the motor can be started from a stopped position, but the detection reliability is insufficient for motors with reduced coil inductance
Solution Approach 1:
The patent applies dynamics by making the detection method adaptive to motor operating conditions. The system dynamically switches between neutral point voltage detection (when stationary) and back-EMF detection (when running). Additionally, the system adjusts detection parameters based on motor inductance characteristics, enabling reliable operation across different motor types including those with reduced coil inductance for high-speed performance.
3Speed
If the motor is designed with reduced coil inductance for high-speed performance, then the motor speed capability is improved, but the phase characteristics control becomes inadequate affecting detection accuracy
Solution Approach 1:
The patent applies parameter changes by adjusting detection parameters based on motor characteristics. The system modifies detection voltage levels, pulse widths, and switching frequencies to accommodate motors with reduced coil inductance. This enables accurate rotor position detection even in high-speed motors where traditional detection methods fail due to inadequate phase characteristics 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 solution enables quick and reliable starting of the motor by consistently detecting the rotor position, improving the reliability of neutral point difference voltage detection and allowing the motor to start more swiftly, even in low-cost motor drive systems, and operates effectively without the need for back-EMF voltage in the initial position detection process.
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
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 neutral point difference voltage, which is the difference voltage between the neutral point 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.