June 26, 2023
Improved methodology and characterization for conducted EMI assessment of power electronics
When: 07/14/2023 02:00 PM
Where: Webex Only – https://msstate.webex.com/msstate/j.php?MTID=mfb78c31ee3b5663ac5e78134656c7085
Candidate: Mark Didat
Degree: Doctor of Philosophy in Electrical and Computer Engineering
Dr. Seungdeog Choi,
Dr. Andrew Lemmon,
Dr. Masoud Karimi-Ghartemani,
Dr. Yong Fu.
Electromagnetic Interference (EMI), primarily common mode (CM), is problematic in a wide range of electronic circuits due to its propensity to radiate, particularly in high power applications. It is routine for much effort and resources to be dedicated to its characterization and reduction as EMI compliance is a requirement for most electronic systems and devices, including power electronics. Many well-known factors contribute to a system’s EMI performance including intentional coupling from system components as well as unintentional coupling from parasitics. Sources of intentional coupling may include Y-capacitors intended to mitigate EMI as part of a filter. Unintentional coupling is more elusive and can exist throughout the system in PCB layout, cabling, load construction, and internal to components such as inverter bridges. Lesser-known contributions to EMI performance irregularities can be EMI filter asymmetries, switching asymmetries, line impedance variances, and galvanic coupling from the metrology intended to measure EMI. It is critical to understand these contributors to facilitate designs with optimal EMI performance.
EMI filters are often added to designs with no consideration to asymmetries in construction and component tolerances. This proposal evaluates the impact to CM currents in cases of coupling or leakage inductance imbalances of a CM choke. Similarly, CM currents are also evaluated for cases when EMI filter Y-capacitor imbalances span the components tolerance band. Also analyzed are switching asymmetries in a typical converter topology to understand EMI impact and evaluate potential benefits if intentional asymmetric switching is applied. A practical method is introduced to measure line impedance upstream of devices under test (DUTs) as line impedance variation can impact the performance of EMI filter design. However, few documented practices exist to measure line impedance without specialized instrumentation.
Finally, this work proposes a streamlined method for conducted emissions evaluation employing an oscilloscope, differential voltage probes, and post-processing software implemented in MATLAB. This method eliminates unintended metrology ground coupling that can significantly impact EMI measurements and minimizes risk of instrumentation damage particularly in high power systems.