Brushless Motor Torque Ripple Reduction via Harmonic Current Correction
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Solution Overview
Problem
Existing brushless motor control methods for magnet assistance-type reluctance motors face high CPU processing loads due to complex calculations required for torque ripple reduction, making it difficult to implement effectively, especially in applications like electric power steering where current values change frequently.
Innovation Solution
A method that calculates and superimposes first and second higher harmonic wave components onto the fundamental-wave current using correction maps to reduce torque ripple, allowing the CPU to reference stored relations between phase currents and correction parameters, thereby reducing the computational load and maintaining torque ripple within acceptable limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If complex calculation methods are used to reduce torque ripple, then torque ripple reduction effect is improved, but CPU processing load increases
Solution Approach 1:
The patent pre-calculates and stores correction values in a lookup table before operation. During motor control, the system only needs to retrieve pre-computed correction values based on current operating conditions, avoiding complex real-time calculations while maintaining torque ripple reduction effectiveness
Solution Approach 2:
The patent creates a simplified model by storing correction data in a lookup table that replicates the results of complex calculations. This table serves as a pre-computed copy of the correction information, allowing fast retrieval without repeating the original complex calculation process during motor control operation
2Manufacturing precision
If real-time torque ripple correction is implemented, then torque ripple is reduced, but computational complexity increases
Solution Approach 1:
Correction values are pre-calculated and stored in a lookup table before motor operation. During real-time control, the system retrieves these pre-computed values based on current operating parameters, achieving torque ripple correction without real-time complex calculations
Solution Approach 2:
The patent uses a lookup table structure that provides inexpensive, fast access to correction data. Instead of performing expensive real-time calculations, the system retrieves pre-computed correction values from the table, significantly reducing computational complexity during motor 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 approach significantly reduces the CPU load required for controlling torque ripples in brushless motors, enabling effective torque ripple reduction without the need for high-performance CPUs, thus improving system efficiency and lowering costs, particularly in electric power steering systems.
Implementation Method 1
the rotor is rotated by magnet torque that is caused by magnetic attraction force of the permanent magnet
Implementation Method 2
reluctance torque that is based on a difference in inductance between magnetic paths
Data Source
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AI summary
A control device 50 that drives and controls a brushless motor 3 of a four-pole 24-slot configuration includes: a base current calculation section 52 that calculates fundamental-wave current indicating a winding current value associated with maximum torque control; a correction component calculation section 59 that calculates 12th-order first higher harmonic wave component Bsin12(θ+β) to cancel a torque ripple of magnet torque, and 12th-order second higher harmonic wave component Asin12(θ+α) to cancel a torque ripple of reluctance torque, based on a phase current value detected by a current sensor 64; a correction map 58 in which relation between phase current and parameters A, B, α, and β of the both higher harmonic wave components is stored; and a current correction section 60 that corrects supply current by superimposing each 12th-order higher harmonic wave component on the fundamental-wave current in order to create current command values Id' and Iq'.