Harmonic Filters For Electronic Drive Systems Targeting Aircraft Applications

Abstract: Climate change pressures fossil-driven vehicles into electrification to sustain a healthy planet and environment for its inhabitants. Air traffic contributes to the ongoing climate crisis, and electric aircraft is taking its toll on the avionics market. The electrification of aircraft is complex and requires specialists and researchers to engage in the subject to haste the process of electric aircraft becoming commercial.  The electrification of aircraft comes with challenges in electromagnetic compatibility (EMC). Part of the aim of this study was to get a broad view of what EMC problems electric aircraft are facing. The leading purpose was to understand electric drive with brushless DC (BLDC) motors and to design and construct an active cancellation filter (ACF) for reducing harmonic noise in electric propulsion systems. A literature study including recent research on EMC issues onboard, outside of, and within the system of electric aircraft deepened the view of the specifications and limits in the electronic design of the airplane. The literature study also covered electric propulsion using BLDC motors and ACF topologies for suppressing harmonics originating from the power inverter in the electric propulsion system.  Measurements on a Cypress motor kit with a BLDC motor showed ringings on the motor phase voltages. The parasitic drain-source capacitances in the MOSFETs of the motor inverter caused the ringings, and damping resistors managed to overcome the ringings in simulations and when measured. However, adding damping resistors line-to-line on the motor phase was determined to be ineffective, but the knowledge of the ringings and how to manage them will become relevant for future work. This study proposed an ACF and a hybrid filter for attenuating harmonics caused by a square wave. The proposed hybrid filter was the ACF filter with an LC filter added to it. Simulations showed that the ACF suppresses harmonics up to 2 MHz, and the hybrid filter had no impact. The measured results showed that the ACF and hybrid filter suppress harmonics up to 10 MHz, and beyond 10 MHz, the filters stop the attenuation of harmonics. The purpose of the hybrid filter was to eliminate harmonics in the higher frequency band, where the performance of the ACF started to lack. However, the hybrid filter showed no influence on the ACF performance, which might have been due to software issues with the Fourier transform.  Although the filters did attenuate harmonics from the voltage pulse source, it could not be stated whether the ACF and hybrid filter topology will perform the same when applied to the drive system of an electric aircraft. Future work will determine how the filters perform on the Cypress motor kit, and eventually, with electric aircraft.