Sensorless Brushless Motor Drive Mode Switching
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Solution Overview
Problem
In sensorless driving of brushless motors, switching from rectangular wave drive to sign wave drive often results in loss of synchronism or torque drop due to unknown rotor angle, which deteriorates controllability.
Innovation Solution
A sensorless driving apparatus and method that includes a first drive unit for rectangular waves, a second drive unit for sign waves, and a switching unit that switches from the first drive unit to the second when the rotor angle reaches a predetermined angle, allowing for precise position information detection and improved control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If switching from rectangular wave drive to sign wave drive is performed based on rotation speed within a switching cycle, then drive mode transition is achieved, but rotor angle becomes unknown causing loss of synchronism and torque drop
Solution Approach 1:
The patent applies preliminary action by determining the rotor angle at the timing of switching from rectangular wave drive to sign wave drive before the actual switching occurs. This allows the control unit to prepare the appropriate drive signals in advance, ensuring that the sign wave drive starts with known angle information, thereby preventing loss of synchronism and torque drop while maintaining reliable operation during drive mode transition
2Productivity
If switching from rectangular wave drive to sign wave drive is performed at high rotation speed, then drive performance is improved, but position information in shorter angular cycle becomes unavailable causing controllability deterioration
Solution Approach 1:
The patent uses feedback by continuously monitoring rotation speed and using it to determine rotor angle position during the transition from rectangular wave drive to sign wave drive. The control unit receives rotation speed information, processes it to calculate the appropriate rotor angle, and uses this feedback to generate accurate drive signals for sign wave operation, maintaining controllability even at high rotation speeds where position information becomes more critical
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 suppresses loss of synchronism and torque drop by ensuring the rotor angle is known at the time of switching, enabling high-precision drive control and stable rotation speed management, particularly in applications like oil pumps.
Implementation Method 1
it is possible to obtain angle information of the rotor from an induced voltage produced by rotation of the rotor (in other words, speed-induced voltage)
Implementation Method 2
it is possible to obtain angle information of the rotor from a voltage of a non-energized phase induced by application of pulse-shaped voltage to an energized phase (in other words, transformer-induced voltage)
Data Source
AI summary
The present relates to a sensorless driving apparatus and a sensorless driving method for a brushless motor. In a state that the brushless motor is driven by rectangular waves, when the driving apparatus detects that a rotation speed of the brushless motor becomes higher than a predetermined speed and thereafter it detects that an angle of a rotor of the brushless motor becomes a predetermined angle, the driving apparatus switches the drive from rectangular wave drive to sign wave drive. The driving apparatus sets as the predetermined angle an angle at which energizing mode is switched in the rectangular wave drive or an angle at which a motor torque is at a peak value in the rectangular wave drive.