Brushless DC Motor Torque Ripple Reduction via Position-Dependent Current Correction
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Solution Overview
Problem
Brushless DC motors experience significant torque ripple due to magnetization processes and mechanical inaccuracies, which are particularly problematic in high-precision applications like robot joints, and existing methods either require more phases or components, increasing cost and complexity, or only partially reduce ripple.
Innovation Solution
A method using a motor control unit with a data memory for storing angle-of-rotation-dependent correction data, where phase currents are determined and filtered to generate reference current data, which are then applied to control currents to eliminate or reduce torque ripple, incorporating a position predictor controller for speed-dependent adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If three-phase winding is used in brushless DC motors, then the motor structure remains simple and cost-effective, but torque ripple occurs due to magnetization processes and mechanical inaccuracies
Solution Approach 1:
The patent applies parameter changes by modifying the control current parameters through position-dependent correction values stored in memory. Instead of changing the physical motor structure, the invention adjusts the electrical control parameters (current magnitude and phase) based on rotor position to compensate for torque ripple caused by the fixed three-phase winding configuration.
Solution Approach 2:
The patent implements feedback by using a position sensor to detect rotor angle and using this information to retrieve appropriate correction values from memory. The control system continuously adjusts the control current based on the detected position feedback, creating a closed-loop system that compensates for torque ripple in real-time while maintaining the simple three-phase structure.
2Object-generated harmful factors
If motors with higher number of phases are used, then torque fluctuations are reduced, but manufacturing effort and costs increase significantly
Solution Approach 1:
The patent creates a virtual multi-phase effect by copying and superimposing control currents with position-dependent correction values onto the basic three-phase winding. Instead of physically adding more phases, the invention synthesizes the effect of higher-phase motors through controlled current injection into the existing three-phase structure, achieving torque ripple reduction without increased manufacturing complexity.
Solution Approach 2:
The invention changes the control current parameters dynamically based on rotor position to simulate the behavior of higher-phase motors. By adjusting current magnitude, phase, and timing according to stored correction data, the system achieves the torque smoothness characteristics of multi-phase motors while maintaining the simple three-phase physical winding structure.
3Object-generated harmful factors
If ironless rotors with self-supporting coils are used, then torque ripple is reduced, but it cannot be completely avoided and manufacturing complexity increases
Solution Approach 1:
The patent uses position feedback from a sensor to continuously monitor rotor angle and retrieve appropriate correction values from memory. This closed-loop control adjusts the control current in real-time to compensate for torque ripple, achieving complete ripple elimination without modifying the rotor structure or using complex ironless designs.
Solution Approach 2:
The invention replaces mechanical solutions (ironless rotors, special rotor structures) with an electronic control solution. Instead of modifying the physical rotor to reduce torque ripple, the patent uses electronic correction of control currents based on position feedback, substituting a complex mechanical design with a simpler controlled system that achieves the same effect.
4Object-generated harmful factors
If electronic correction with position-dependent data from memory is applied, then torque ripple is reduced across all rotational positions, but additional components and processing are required
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing correction values in memory during the design phase. Instead of computing corrections in real-time during operation, the system retrieves pre-computed position-dependent correction data from memory, reducing the computational burden during runtime while achieving comprehensive torque ripple compensation across all rotor positions.
Solution Approach 2:
The invention replaces complex real-time computational mechanics with a simpler memory retrieval system. By substituting on-the-fly calculations with pre-stored correction data lookup based on position feedback, the system achieves torque ripple compensation with minimal processing requirements, reducing control system complexity while maintaining effective correction across all rotational positions.
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 compensates for torque ripple in simple designs across nearly all rotational positions, ensuring smooth operation with constant torque, suitable for high-precision applications like robots, and can be applied to both new and installed motors, including gears and mechanical components.
Implementation Method 1
brushless DC motors, which are basically designed as three-phase synchronous machines with excitation by permanent magnets. The rotating magnetic field of the three-phase winding causes the permanently excited rotor to move.
Implementation Method 2
with a position sensor on the rotor of the motor for detecting the instantaneous relative or absolute position of the rotor
Data Source
Figure 1a~1b
Figure 2
Figure 3
AI summary
A method and arrangement for reducing the torque ripple of a brushless DC motor having a stator, a rotor, and a motor control unit, via which motor control unit the motor is controlled in a polyphase manner, having a data memory for storing rotational angle-dependent correction data of the control current of the motor, which are impressed on the instantaneous values for controlling the motor. In a first step, for each position of the rotor, the phase currents holding the rotor in this position are determined and are used to derive reference current data, which is stored in a table of the data memory together with the respective position data of the rotor, determined by the position sensor. In a second step, during continuous operation of the motor, the position-dependent reference current data stored in the data memory is combined with the control current of the motor.