Three-Phase Motor Drive Methods for Torque Ripple Reduction
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Solution Overview
Problem
Three-phase motors experience torque ripples during back electromotive force (BEMF) detection, leading to reduced efficiency, increased noise, and wear due to the temporary non-energization of phases, which affects the accuracy of rotor position detection and motor control.
Innovation Solution
The method involves using sinusoidal and non-sinusoidal drive functions to modulate the phases of a star-connected three-phase motor, specifically employing a cosine drive function during BEMF detection to minimize torque ripple by adjusting the modulation ratio and phase energization periods, thereby reducing the impact of torque ripples.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a phase is temporarily non-energized for BEMF detection, then rotor position detection accuracy is improved, but torque ripples increase causing reduced efficiency and increased noise
Solution Approach 1:
The patent applies parameter changes by switching the drive function from sinusoidal to non-sinusoidal (cosine-based) during BEMF detection periods. This changes the electrical parameters (voltage waveform shape, modulation ratio) to minimize torque ripple while enabling accurate BEMF measurement during the non-energized phase window.
Solution Approach 2:
The patent implements periodic action by alternating between sinusoidal drive mode (for normal operation) and non-sinusoidal drive mode (for BEMF detection). The system periodically switches phases to non-energized states at specific intervals to perform BEMF detection, creating a rhythmic pattern of energization and detection that maintains both torque smoothness and detection accuracy.
2Measurement precision
If a phase is temporarily non-energized for BEMF detection, then rotor position detection accuracy is improved, but motor efficiency decreases due to torque ripples
Solution Approach 1:
The patent changes operational parameters by using non-sinusoidal drive functions with adjusted modulation ratios during BEMF detection. This parameter adjustment reduces the magnitude of torque ripples and minimizes energy loss, thereby maintaining higher motor efficiency while still achieving accurate rotor position detection through the non-energized phase periods.
3Object-generated harmful factors
If sinusoidal drive function is used during BEMF detection, then smooth torque production is maintained, but rotor position detection accuracy deteriorates
Solution Approach 1:
The patent uses periodic action by switching between sinusoidal drive (for torque smoothness) and non-sinusoidal drive (for detection accuracy) in a time-multiplexed manner. During normal operation, sinusoidal drive maintains smooth torque, while during scheduled detection windows, the system switches to non-sinusoidal drive to enable accurate BEMF-based rotor position detection.
Solution Approach 2:
The patent applies dynamics by making the drive function adaptive and time-varying. The control system dynamically switches between different drive functions (sinusoidal and non-sinusoidal) based on the operational phase and detection requirements, optimizing both torque smoothness and detection accuracy at different time intervals rather than using a fixed drive mode.
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 improves motor efficiency, reduces noise and wear, and maintains accurate rotor position detection by minimizing torque ripples across a full 360-degree rotation, enhancing the overall performance and lifespan of the motor.
Implementation Method 1
detecting a first back electromotive force (BEMF) voltage of the first phase
Data Source
AI summary
A method of driving a three-phase motor includes, while a first phase is energized, driving a second phase using a first drive function which is sinusoidal. The first phase is switched to a non-energized state and a back electromotive force (BEMF) voltage of the first phase is detected. For at least a portion of a time when the first phase is non-energized the driving of the second phase depends on the output of a second drive function different from the first drive function. The second drive function may be non-sinusoidal and may be a cosine function. The second drive function may drive the second phase when the output of the second drive function is a modulation ratio less than 1. When the output of the second drive function is a modulation ratio greater than or equal to 1 the second phase may be driven to a modulation ratio of 1.