Switched Reluctance Motor Torque Ripple Control
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Solution Overview
Problem
Switched reluctance motors (SR motors) experience significant torque fluctuation and excessive output torque due to magnetic saturation and varying current conditions, particularly at high temperatures and low battery voltages, leading to potential mechanical damage to driven loads.
Innovation Solution
The SR motor design features concavities and convexities alternately formed on rotor or stator teeth, with deeper concavities on the edge side where teeth first approach and shallower concavities as the facing area increases, to control the air gap and magnetic resistance, thereby suppressing torque fluctuation and ensuring consistent torque output across varying current conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a large current is given to the coil, then the output torque increases, but torque fluctuation becomes large due to magnetic saturation
Solution Approach 1:
The invention applies local quality by creating non-uniform air gaps through concavities and convexities on rotor tooth surfaces. The air gap length varies locally along the rotor tooth, being smaller at certain positions and larger at others, which modifies the magnetic flux distribution and inductance characteristics to suppress torque fluctuation while maintaining high output torque capability
Solution Approach 2:
The concavities and convexities are pre-formed on the rotor tooth surfaces before operation. This preliminary structural modification ensures that the air gap and magnetic resistance are optimized in advance to prevent excessive torque fluctuation when large current is applied, rather than attempting to control it during operation
2Reliability
If a small current is given to the coil, then torque fluctuation is suppressed, but the output torque falls off as the facing area increases
Solution Approach 1:
By creating localized variations in air gap length through concavities and convexities, the invention ensures that even when small current is applied, the magnetic flux distribution remains optimized to maintain adequate output torque across the entire rotor rotation range, preventing torque fall-off
3Reliability
If the SR motor is designed to generate necessary torque under worst condition (high temperature×low voltage), then excessive output torque is generated under best condition (low temperature×high voltage)
Solution Approach 1:
The concavities and convexities are pre-formed on the rotor tooth surfaces to establish optimized magnetic circuit characteristics in advance. This preliminary structural modification ensures that torque output is naturally regulated across all operating conditions, preventing excessive torque generation under best conditions while ensuring adequate torque under worst conditions
Solution Approach 2:
The invention changes the physical parameters of the magnetic circuit by modifying the air gap length through concavities and convexities. This parameter modification alters the inductance characteristics and magnetic resistance, thereby regulating the torque-output curve to prevent excessive torque while maintaining reliability across varying temperature and voltage conditions
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 design effectively reduces maximum torque generation at high currents, prevents excessive output torque, and increases minimum torque generation at low currents, minimizing torque ripple and protecting driven loads from mechanical damage.
Implementation Method 1
a coil 22 for generating a magnetic force; When a current is given to the coil 22, the coil 22 produces magnetic poles of which polarities are opposite to each other
Implementation Method 2
Rotation force is given to the rotor 11 by a pair of the rotor teeth 24 among the plurality of the rotor teeth magnetically attracted by a pair of the stator teeth 23
Implementation Method 3
the output torque (T) of the SR motor varies depending on the current (T) flowing though the coil and the changing rate of inductance (dL/dθ)
Implementation Method 4
the changing rate of inductance (dL/dθ) lowers due to magnetic saturation as a facing area between the stator tooth and rotor tooth increases
Data Source
AI summary
A plurality of concavities and convexities is provided on tips of all rotor teeth 24 of the SR motor 5. Depths of the concave portions α are deep on an edge side where a stator tooth 23 and rotor tooth 24 first approach and are shallow as a facing area between the stator tooth 23 and rotor tooth 24 increases. Therefore, magnetic resistance between the stator tooth 23 and rotor tooth 24 becomes high at an early stage of the stator tooth 23 and rotor tooth 24 facing each other and becomes low as the facing area between the stator tooth 23 and rotor tooth 24 increases. As a result, torque fluctuation can be suppressed at a time of a large current and a minimum generation torque can be increased at a time of a small current.