Brushless Motor Sinusoidal Control With Hall-Based Rotor Prediction
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Solution Overview
Problem
Sinusoidal-drive brushless motors face challenges in reducing magnetic sound due to distorted sine-wave phase currents caused by varying inductance and resistance values, and high control frequencies, which increase costs with the use of expensive elements like high-performance microcomputers and resolvers.
Innovation Solution
A method that uses a control system with a microcomputer-based motor control device, including a rotor position estimation processing unit, speed estimation processing unit, and speed instruction unit, to apply a pseudo sine-wave voltage with an advance angle, reducing distortion and noise without expensive components, by adjusting the PWM duty-value and using an open-loop control method with dq-three phase conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If sinusoidal drive is used to reduce motor noise, then magnetic sound is reduced, but phase current distortion occurs due to varying inductance and resistance values
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing the relationship between rotor position and inductance/resistance values in lookup tables before motor operation. During sinusoidal drive, the control system retrieves these pre-computed values based on current rotor position to determine the appropriate sine wave voltage amplitude, thereby compensating for varying inductance and resistance without real-time calculation delays or waveform distortion.
2Manufacturing precision
If vector control with resolver and current sensor is used to reduce phase current distortion, then waveform accuracy is improved, but device cost increases
Solution Approach 1:
The patent extracts and eliminates the need for expensive current sensors and resolvers by using only Hall sensor information combined with pre-stored inductance and resistance data. The control system retrieves inductance and resistance values from lookup tables based on rotor position, removing the requirement for additional costly components while maintaining waveform accuracy.
Solution Approach 2:
The patent replaces expensive, high-precision components (resolvers and current sensors) with cheaper alternatives (Hall sensors and pre-stored data tables). This substitution uses low-cost components to achieve the same control objective, reducing overall system cost while maintaining adequate performance for sinusoidal drive applications.
3Productivity
If high rotation speed with low rated current is used in motor applications, then productivity is improved, but sine wave distortion increases due to high control frequency
Solution Approach 1:
The patent applies preliminary action by pre-calculating sine wave voltage values for all possible rotor positions and storing them in lookup tables before high-speed operation. During motor operation at high speeds, the control system simply retrieves pre-computed values based on rotor position from Hall sensors, eliminating the need for real-time sine wave generation and calculation, thereby maintaining waveform accuracy even at high control frequencies.
Solution Approach 2:
The patent implements dynamic adaptation by storing multiple sets of inductance and resistance values corresponding to different rotor positions and operating conditions in lookup tables. The control system dynamically selects the appropriate parameter set based on current rotor position and operating state, enabling accurate sinusoidal control across varying speeds and loads without waveform distortion.
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 effectively lowers the distortion rate of phase currents and motor magnetic sound, enabling low-noise brushless motors at reduced costs, even in high-rotation speed applications with low-rated currents, by accurately maintaining rotation speed and minimizing waveform distortion.
Implementation Method 1
a plurality of magnetic sensors outputting magnetic pole position detection signals according to a change of a magnetic pole position accompanying rotation of the rotor are arranged at opposite positions to the rotor, the magnetic pole position of the rotor is detected based on change and arrangement position of each magnetic pole position detection signal of the magnetic sensors
Implementation Method 2
a sinusoidal drive in which a stator coil voltage is changed into a sine wave
Implementation Method 3
by adjusting the PWM duty-value
Data Source
Figure 1
Figure 2
Figure 3(a)~3(b)
AI summary
In an elapsed time of a sensor edge period (electric angle 60 degrees), the position of a rotor for the next sensor edge period (electric angle 60 degrees) is predicted, and a sine-wave voltage drive is carried out. Meanwhile, a speed control process is performed to correct a difference between a target rotation speed and an actual rotation speed. Moreover, an advance angle process that advances an angle of an applying voltage relative to a rotor rotation position is carried out so that a phase of phase current is ahead of an induced voltage. The speed control process enables smooth continuation of control even when sensor signals are switched, thereby curbing distortion of phase-current waveform. The advance angle process increases a peak value of phase current and a motor electromotive force, reduces changes of current relative to a change in supplied voltage, and curbs distortion of phase-current waveform.