As agricultural power equipment evolves toward electrification and intelligence, Permanent Magnet Synchronous Motors (PMSM) have become the ideal drive solution for electric tractors due to their high efficiency, high power density, and precise control. Below are the key design considerations for PMSM in tractors.
|
Feature |
PMSM |
Induction Motor (IM) |
DC Motor |
|
Efficiency |
92%–96% |
85%–90% |
75%–85% |
|
Power Density |
High (compact & lightweight) |
Medium |
Low (requires commutator) |
|
Speed Control |
Excellent (vector control) |
Poor (depends on VFD) |
Good (but needs brushes) |
|
Maintenance |
Maintenance-free |
Low maintenance |
High (brush wear) |
|
Cost |
Higher (rare-earth magnets) |
Low |
Moderate |
Applications:
• Main drive for electric tractors (replacing diesel engines).
• Electrification of PTO (Power Take-Off).
• Hydraulic pump/auxiliary system drives.
Tractors operate under complex conditions, requiring both high torque at low speeds (plowing) and efficient high-speed transport:
• Small tractors (25-50 HP): 20–40 kW pmsm motor, rated torque 150–300 Nm.
• Medium tractors (50-100 HP): 40–75 kW pmsm motor, rated torque 300–600 Nm.
• Large tractors (100+ HP): 75–200 kW pmsm motor, rated torque 600–1500 Nm.
Peak Torque Demand (Short-term Overload):
• Requires 2–3× rated torque during plowing or climbing.
• Field-weakening control is needed to extend high-speed operation.
• Plowing mode: 500–1500 RPM (high torque output).
• Transport mode: 1500–3000 RPM (optimized for efficiency).
• PTO standard speeds: 540/1000 RPM (must be precisely matched).
|
Cooling Solution |
Application |
Pros & Cons |
|
Natural cooling |
Low power (<20 kW) |
Simple, low cost, but limited heat dissipation. |
|
Forced air cooling |
Medium tractors (20–50 kW) |
Requires a fan, increases power consumption. |
|
Liquid cooling |
High power (>50 kW) |
Efficient cooling, suitable for continuous heavy loads. |
Recommendation:
• Liquid + oil dual cooling (for high-power tractors, e.g., 200+ kW).
|
Type |
Characteristics |
Application |
|
Surface-mounted (SPM) |
Simple, low torque ripple, but prone to demagnetization at high speeds. |
Small/medium tractors. |
|
Interior (IPM) |
High demagnetization resistance, wide speed range, robust. |
Large/high-speed tractors. |
Recommendation:
• Interior PM (IPM) (balances high-speed and overload requirements).
• Pole pairs: Typically 4–8 poles (balances speed and torque).
♦ Example: 1000 RPM → 4 poles (33 Hz), 8 poles (66 Hz).
• Stator slots: 36 or 48 slots (reduces cogging torque and noise).
|
Material |
Remanence (Br) |
Coercivity (Hc) |
Cost |
Suitability |
|
NdFeB |
1.0–1.4 T |
800–2000 kA/m |
High |
High-performance tractors. |
|
Ferrite |
0.4–0.5 T |
200–400 kA/m |
Low |
Low-cost light tractors. |
Recommendation:
• NdFeB magnets (high energy density, ideal for high-performance tractors).
Field-Oriented Control (FOC):
• Decouples torque/speed control for fast dynamic response.
• Ideal for instant high-torque demands during plowing.
Direct Torque Control (DTC):
• Sensorless operation, robust but with higher torque ripple.
Encoders (high precision, e.g., 17-bit absolute encoders).
Sensorless control (reduces cost but degrades low-speed performance).
Voltage level: 400V (small/medium), 600V (large electric tractors).
SiC MOSFETs: High-frequency switching for reduced losses.
• Direct drive: Motor connects directly to the drivetrain (eliminates gearbox but requires high-torque motors).
• Hybrid parallel: PMSM + diesel engine (transitional solution).
• Battery capacity:
♦ Pure electric: 100–300 kWh (4–8 hours of operation).
♦ Hybrid: 20–50 kWh (auxiliary power).
• Regenerative braking: Recovers energy during deceleration.
• Protection rating: IP67 (dust/waterproof for harsh farm conditions).
• Vibration resistance: Reinforced bearings and structure (for rough terrain).
John Deere SESAM (pure electric tractor):
• Dual PMSM drive (300 kW total), liquid-cooled.
YTO Electric Tractor (China):
• 120 kW IPM motor, FOC control, 5-hour runtime.
► High-voltage platforms (800V+): Reduces cable weight and improves efficiency.
► Rare-earth-free PM motors: Reduces reliance on NdFeB (e.g., optimized ferrite designs).
► Smart torque distribution: Multi-motor drive + electronic differential (improves field mobility).
|
Key Aspect |
Recommended Solution |
|
Motor type |
Interior PMSM (IPM) |
|
Cooling method |
Liquid cooling (>50 kW) |
|
Control strategy |
FOC + high-precision encoder |
|
Magnet material |
NdFeB |
|
System voltage |
400V–600V |
PMSM in tractors must balance high torque, wide speed range, and harsh-environment durability. Optimizing electromagnetic design, cooling, and control algorithms can significantly enhance the efficiency and reliability of electric tractors.
