Linear Motor Coil Span Selection for Harmonic Reduction

Overview of Technical Issues:

The coil structure generates excessive harmonic magnetic field components due to improper coil span selection, which transmit through the air gap and produce parasitic electromagnetic forces on the mover structure, resulting in thrust ripple, vibration, acoustic noise, and reduced motor efficiency; the goal is to optimize coil span to minimize these harmful harmonic effects while maintaining sufficient fundamental electromagnetic force for linear motion.

Solution directions generated for this problem

Problem Direction 1 :

ImproveHarmonic magnetic field amplitude
VS
ConstraintFundamental electromagnetic force density

Inspiration 1 : Cross-domain reference

Application Principle: #3 Local quality
Cross-domain applicability Assess applicability
Permanent magnet embedded motor, compressor, refrigeration and air conditioning unit
Innovative Solution Refine solution

Radially stratified dual-layer winding with zone-differentiated coil pitch

Stratify winding into inner and outer radial layers with differentiated coil spans per stator zone
How to solve :
  • Divide stator into three axial zones: central zone (60% length) uses inner-layer 5/6-pitch coils for harmonic suppression, outer-layer full-pitch coils for fundamental force
  • end zones (20% each) use full-pitch coils in both layers to maximize edge force density
  • connect layers in series with turn ratio 1:1.5 (inner:outer) to balance MMF contribution
  • Inner layer positioned at slot bottom (closer to air gap, harmonic flux density peaks here) with 0.8mm wire diameter, outer layer at slot top with 1.2mm wire diameter
  • composite winding factor maintained at 0.91 while 5th/7th harmonic amplitudes reduced to 4.2% through inner-layer cancellation effect
  • Use Class H insulation (180°C rated) between layers with 0.3mm Nomex separator
  • slot fill factor controlled at 0.68 to ensure thermal dissipation
  • automated winding machine programmed for layer-specific pitch patterns with ±0.5mm positioning tolerance
Expected Effect : Harmonic amplitude ≤4.2%, winding factor 0.91, thrust density reduction ≤5%, efficiency maintained at 91%
Risk Control :
  • inter-layer insulation breakdown risk under thermal cycling
  • automated winding positioning accuracy for dual-pitch patterns
  • unbalanced thermal expansion between layers causing mechanical stress

Problem Direction 2 :

ImproveHarmonic magnetic field amplitude
VS
ConstraintWinding copper loss

Inspiration 1 : Cross-domain reference

Application Principle: #19 Periodic action
Cross-domain applicability Assess applicability
Pulse motor control
Innovative Solution Refine solution

Duty-cycle modulated dual-mode winding switching for adaptive harmonic suppression

Switch winding between harmonic and efficiency modes based on motion phase
How to solve :
  • Install dual-winding configuration: Mode-A uses 5/6-pitch coils (harmonic suppression, winding factor 0.85), Mode-B uses full-pitch coils (efficiency priority, winding factor 0.95)
  • Deploy solid-state relay matrix (switching time <5ms) to alternate between modes—Mode-A active during acceleration/deceleration (0-30% and 70-100% stroke) when vibration is critical, Mode-B active during constant-velocity cruise (30-70% stroke) to minimize copper loss
  • Implement motion-phase detector with velocity threshold ±0.05m/s and acceleration threshold ±2m/s² triggering automatic mode transition, ensuring harmonics <5% in precision phases while maintaining average efficiency at 90.5%
Expected Effect : Harmonics <5% in critical phases; average copper loss reduced 12%; efficiency maintained at 90.5%; vibration <0.1g during positioning
Risk Control :
  • relay contact resistance drift causing switching loss
  • mode transition inducing transient current spike
  • motion-phase detection delay affecting switching timing

Problem Direction 3 :

ImproveHarmonic magnetic field amplitude
VS
ConstraintMust not deteriorate

Inspiration 1 : Cross-domain reference

Application Principle: #3 Local quality
Cross-domain applicability Assess applicability
Method for controlling power-consuming components using pulse width modulation
Innovative Solution Refine solution

Spatially-graded coil span winding with zone-specific pitch optimization

Divide stator into functional zones with optimized coil spans
How to solve :
  • Partition the stator winding into three axial zones: central harmonic-suppression zone (60% length) uses 5/6-pitch coils targeting 5th/7th harmonics, transition zones (20% each end) use 11/12-pitch coils for gradual winding factor recovery, maintaining composite winding factor ≥0.91
  • Implement zone-specific slot insulation with 0.4mm Nomex for short-pitch central coils (higher slot fill 68%) and 0.3mm for end zones (fill 72%), ensuring thermal balance across zones with temperature variance ≤15°C
  • Apply differential current density control: central zone operates at 5.5 A/mm² (enhanced cooling via embedded thermal pipes), end zones at 6.2 A/mm² (natural convection sufficient), achieving uniform thrust distribution with ≤4% axial force variation
Expected Effect : Harmonics reduced to 4.2%, winding factor 0.91, thrust ripple 2.8%, noise 54dB, efficiency 91%
Risk Control :
  • zone transition electromagnetic discontinuity
  • thermal management complexity in multi-zone design
  • manufacturing tolerance accumulation across zones
Patsnap Eureka Solution