A UAV motor does not operate under perfectly sinusoidal electrical conditions. Its electronic speed controller (ESC) regulates power through switching, producing current waveforms that can affect electromagnetic losses.

This creates a challenge for motor designers. Electrical steel may show low core loss under standard laboratory tests, yet the finished stator can behave differently once it is installed in an ESC-driven motor.

Key Takeaways

ESC switching and current harmonics can contribute to additional electromagnetic losses in UAV motors.
Standard electrical steel core-loss data helps compare materials, but it does not directly predict finished-motor losses.
Motor manufacturers need to consider actual excitation conditions when evaluating NGOES for high-frequency applications.

Why ESC Drive Conditions Matter

In a BLDC motor, fundamental electrical frequency is related to mechanical speed and rotor pole count. However, the current waveform also affects magnetic losses.

Depending on the ESC control method and operating conditions, phase currents may contain low-order harmonics and PWM switching ripple. These components can produce additional magnetic flux variations and stator core losses.

A 2026 study published in Actuators, Integrated Performance Prediction Method for Drone Propulsion BLDC Motor Considering Square Wave Current and Mechanical Losses, examined how actual BLDC drive current characteristics and mechanical losses affect motor performance prediction.

The researchers combined inverter simulation, electromagnetic finite-element analysis, and a mechanical loss model. Including the mechanical loss model reduced the input power prediction error from 26.61% to 2.62% and the efficiency prediction error from 36.27 percentage points to 2.55 percentage points at one tested operating point.

The study did not explicitly model PWM-induced losses, which the researchers identified as an area for future work.

Fundamental Frequency vs PWM Switching Frequency

PWM switching frequency is set by the ESC control system, independently of the motor's fundamental electrical frequency.

Fundamental frequency describes the main magnetic field variation, while PWM switching introduces higher-frequency voltage components that can produce current ripple and additional magnetic losses.

Increasing PWM switching frequency does not automatically increase stator core loss. Depending on the motor's inductance and control strategy, higher switching frequencies can reduce current ripple. The resulting iron loss must be evaluated from the actual excitation waveform.

How Harmonics Affect Stator Core Loss

1793668940639-How ESC Harmonics Affect Stator Core Loss.webp

Illustration comparing sinusoidal and PWM harmonic waveforms and their effects on UAV motor stator core loss

Standard electrical steel core-loss tests use specified magnetic flux densities and frequencies, typically under sinusoidal excitation.

In an ESC-driven UAV motor, current harmonics and PWM-related ripple can alter the magnetic flux waveform, introducing loss components that standard sinusoidal tests do not fully capture.

Research on high-power-density UAV propulsion motors has examined how PWM switching frequency and current harmonics affect core loss, AC copper loss, and motor efficiency.

The researchers found that increasing phase inductance helped suppress current harmonics and reduce ripple-related losses.

How Harmonic Flux Creates Additional Core Loss

Harmonic flux components can produce additional magnetization cycles and eddy currents within the stator laminations.

The resulting losses depend on the amplitude and frequency of the harmonic flux components, as well as their distribution through the stator.

For example, high-frequency flux variations near stator teeth may contribute to localized heating even when the fundamental operating frequency remains unchanged.

Core Loss Is Only Part of Motor Loss

UAV motor losses extend beyond the electrical steel core. Winding resistance produces copper loss, while bearing friction and windage contribute to mechanical losses. Permanent magnets and other conductive rotor components can also experience eddy-current losses.

Reducing stator iron loss therefore does not necessarily produce an equivalent reduction in total motor loss.

Why UAV Operating Conditions Matter

A UAV propulsion motor may operate at different speed and load points during hovering, climbing, and maneuvering.

Changes in speed and load alter motor current and magnetic loading, while the ESC control response can change the current waveform.

Evaluating only a single rated operating point can miss losses that become important elsewhere in the UAV flight profile.

What Electrical Steel Test Data Can Tell Motor Designers

Published electrical steel core-loss data provides a basis for comparing NGOES grades under specified test conditions. Loss measurements at frequencies and magnetic flux densities relevant to UAV motor operation can support a more application-specific assessment.

1793668944458-Electrical Steel Core Loss Test Data for UAV Motors.webp

Electrical steel laminations with illustrative core-loss curves across different frequencies for UAV motor material evaluation

These measurements can support electromagnetic simulation and material screening before prototype testing. Motor-level analysis can then account for the expected excitation waveform and stator geometry.

Cutting stress and lamination insulation can further influence finished-core losses.

Working With an Electrical Steel Manufacturer

HWHG manufactures non-grain-oriented electrical steel coils using controlled cold rolling, annealing, and coating processes. Its production facilities include six-stand tandem rolling mills and high-temperature annealing equipment.

For UAV motor manufacturers, HWHG can provide relevant material specifications and magnetic test data for NGOES selection. Buyers can also use Mill Test Certificates (MTCs) and HWHG's online certificate verification service to check material documentation and traceability.

These records support material evaluation, while additional harmonic-related losses must be assessed under the motor's actual ESC operating conditions.

1780384596857-HWHG Electrical Steel Label.webp

Concept illustration of HWHG non-grain-oriented electrical steel coil with a sample Mill Test Certificate and online verification interface

Conclusion

ESC current harmonics and PWM ripple can introduce additional stator losses in UAV motors. Evaluating these effects alongside material core-loss data provides a more complete basis for NGOES selection.

UAV Motor Core Loss: How ESC Harmonics Affect Electrical Steel Performance

Electrical Steel for Servo Motors: Magnetic Requirements and Stator Core Performance

Drone Motor Efficiency: How Stator Core Loss Affects Heat and Performance

Outrunner vs Inrunner Drone Motors: Design, Torque, and Stator Differences

Send Your Drawing or Specs, Get a Fast Material Quote