Stepper Motor Current Control for Torque Ripple Suppression
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Stepping motors experience rotational vibrations and stop angle errors, particularly in small-scale hybrid and slot magnet types, due to torque fluctuations attributed to reluctance and magnet torque, which conventional methods have not adequately addressed.
Innovation Solution
A stepping motor driver that utilizes a rotational coordinate system to transform phase currents into dp-axis and qp-axis components, applying torque correction waveforms to suppress torque fluctuations, enabling open-loop control and precise driving with reduced vibrations and stop angle errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If sinusoidal current is applied for micro-step driving, then smooth rotation is achieved, but rotational vibrations occur at specific speeds
Solution Approach 1:
The patent changes the current waveform parameters by superimposing harmonic components (particularly 3rd and 5th harmonics) on the fundamental sinusoidal current. This modifies the current waveform shape to counteract the torque fluctuations that cause vibrations at specific rotational speeds, while maintaining the smooth micro-step driving capability.
Solution Approach 2:
The patent applies periodic harmonic current components that are synchronized with the motor's electrical cycles. By introducing these periodic corrections at specific frequencies (3rd and 5th harmonics), the system actively counteracts the periodic torque fluctuations that occur during micro-step operation, eliminating vibrations without disrupting the fundamental smooth rotation.
2Speed
If constant current excitation is applied for stopping, then the motor stops, but stop position deviates from theoretical position
Solution Approach 1:
The patent modifies the current waveform parameters during stopping by incorporating harmonic components into the excitation current. This changes the magnetic field distribution and torque characteristics, allowing the motor to stop at the precise theoretical position rather than deviating due to cogging torque and magnetic asymmetries.
3Device complexity
If simple rotational coordinate system control is used, then construction is simplified, but torque fluctuations remain uncorrected
Solution Approach 1:
The patent changes the current waveform parameters within the existing rotational coordinate system framework by superimposing harmonic components. This approach corrects torque fluctuations without requiring a change to the fundamental control architecture, maintaining simplicity while eliminating harmful torque variations through waveform modification.
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
The solution effectively suppresses rotational vibrations and reduces stop angle errors in stepping motors by correcting torque fluctuations, allowing for precise and stable operation without the need for position or speed feedback.
Implementation Method 1
an inverter that applies a current to a winding of the stepping motor
Data Source
AI summary
A stepping motor driver which drives a stepping motor according to a position angle command includes: a current detector that detects a phase current; an inverter that applies a current to a winding; and a control unit that controls the inverter. The control unit includes: a phase current coordinate transformer that transforms the phase current to generate a dp-axis detection current and a qp-axis detection current; a torque correction command generator that generates a torque correction command according to a torque correction waveform for suppression of torque fluctuation; a torque correction command coordinate transformer that transforms the torque correction command into a dp-axis component and a qp-axis component to generate a dp-axis torque correction component and a qp-axis torque correction component; an adder that superposes the dp-axis torque correction component and the qp-axis torque correction component respectively on a dp-axis fundamental current command and a qp-axis fundamental current command to generate a dp-axis current command and a qp-axis current command; and a control command generator that compares the dp-axis detection current and the qp-axis detection current respectively with the dp-axis current command and the qp-axis current command and applies a control command to the inverter.