Mechanisms of the Susceptibility of a Stepper Motor Control System to Narrowband IEMI Injected Through Pulse Signal Lines

Stepper motors, widely used for precise control in robotics and intelligent systems, are vulnerable to intentional electromagnetic interference (IEMI), which can disrupt their operation by affecting motor rotation. This article investigates the mechanisms and characteristics of the electromagnetic susceptibility (EMS) of a stepper motor control system to narrowband IEMI coupled through pulse signal lines. The bulk current injection method was employed, in which continuous wave (CW) and pulse modulation signals were used as the injected narrowband IEMI. The optocoupler (OC) at the drive subsystem interface was identified as the key component affecting the system's EMS, as confirmed through time- and frequency-domain experiments. The differential-mode IEMI activates the light-emitting diode in the OC, causing output logic disturbances that alter the number of driving pulses and ultimately influence the motor speed. Interestingly, at specific interference frequencies, the OC output logic level “1” is disturbed and drops to 0 V, whereas at other frequencies, the logic level “0” is disturbed and rises to 5 V. Under the CW injection, the stepper motor stops, whereas under the PM injection, the motor speed can be manipulated. The relationships between the PM signal parameters and the disturbed motor speed are modeled and experimentally validated. Finally, protection strategies were proposed and validated through experiments.