Motor Driver EMI: How PWM Switching Creates Electromagnetic Noise

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Pulse-width modulation is widely used in motor drives because it efficiently controls voltage, current, torque, and speed. However, the fast switching transitions that give PWM its high efficiency also generate a broad electromagnetic noise spectrum. As a result, a motor inverter acts as a repetitive high-frequency excitation source that couples energy through power cables, motor windings, and chassis structures. The spectrum's envelope depends strongly on rise and fall times, as well as on the switching devices, duty cycle, and modulation scheme. Differential-mode noise arises from rapidly changing currents in power loops, while common-mode noise couples through parasitic capacitance to the chassis and surrounding structures.

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