On the Influence of the Load Parasitics on the CM Conducted EMI of BLDC Motor Drives

This paper analyzes the influence of the load parasitics on the conducted electromagnetic emissions, especially on their common mode component. The analyses have been performed on a BLDC motor driver, switched with bipolar PWM. According to the final installation of both the electronic module and the load, the prescribed test setup for the electromagnetic interference (EMI) measurements can vary. This modifies the parasitic element values and it can even worsen the emission level, when the load chassis is connected to the reference plane. In this paper, the effect of the load parasitic elements on the conducted emission is analyzed in details, and an equivalent model is derived and verified by simulation. Moreover, such simulations proved that the delay compensation technique can be used to counteract the EMI increase due to the load parasitics.