Alva Industries‘ saturation-free FiberPrinted™ motors offer superior torque capabilities and can exceed the peak torque performance of iron-cored motors.
This is due to conventional electric motors using cores made of ferromagnetic materials to support windings and enhance magnetic flux density and energy density.
Saturation occurs in these ferromagnetic materials when an increase in the applied external magnetic field, H, no longer significantly increases the magnetization, causing the total magnetic flux density, B, to begin leveling off.
This is depicted in the magnetization curve (B-H curve) of a material, where the curve bends to the right (Fig. 1). The saturation limit is reached at point [B2, H2], although the curve starts leveling off earlier, around point [B1, H1].
Fig. 1. B-H curve
Laminated electrical steel sheets used in motor cores are also made from ferromagnetic materials, which means they experience saturation. Different steel grades will saturate at different levels of H and B, as shown in Fig. 2.
Fig. 2. B-H curves of different steel types.
The relationship between H and B is given by B = μH, where μ is magnetic permeability. As you move along the B-H curve, μ changes as shown in Fig. 3. At higher values of H, magnetic permeability decreases toward the permeability of free space, such as a vacuum or air.
Fig. 3. Variation of B and μ with increase of H.
In electric motors, the external magnetic field H is generated by currents flowing through the copper coils, making H proportional to the current. Once saturation occurs, further increases in current cause H to rise proportionally, while the steel’s permeability, μ, diminishes to the extent that the steel’s magnetic properties resemble that of air.
In practical terms, the teeth bearing the highest currents at any given moment can go into full saturation, represented by the red regions in Fig. 4, and in magnetic terms, these areas effectively ‘disappear’ as paths for conducting magnetic flux.
Fig. 4. Saturation of iron teeth.
The performance of a motor is partly defined by its ability to convert input current into output torque. The linearity of the current-to-torque relationship is a critical performance metric because motors are easier to control when torque increases linearly with current across the entire operational range.
As input current rises, traditional iron-cored motors may saturate, limiting their ability to provide adequate torque. In contrast, slotless motors can continue to deliver increasing torque proportional to the current within practical limits (Fig. 5).
Fig. 5. Torque vs current with and without the magnetic saturation.
Due to this feature, conventional slotless motors can achieve comparable or even higher peak torques (for brief durations of a few seconds) than traditional iron-cored motors under similar conditions.
Alva Industries’ FiberPrinted™ motors, which feature a higher copper fill factor and optimized winding geometry compared to conventional slotless motors, demonstrate higher torque capability and can outperform iron-cored motors in peak torque scenarios.
Modeling indicates that even at currents as high as 10 times the rated amount, the back iron in FiberPrinted™ motors does not reach significant saturation levels. Therefore, under typical operating conditions, Alva motors can effectively be considered ‘saturation-free.’
