Reducing electromagnetic interference in a grid tied single phase power inverter

Abstract

As the demand for a more robust and reliable electrical grid continues to grow, the United States Navy is determined to find effective energy solutions. The use of energy management systems (EMS) and uninterruptible power systems (UPS) can be seen both ashore and afloat. Most UPS and EMS are comprised of power inverters. These inverters must comply with the military standards for conducted emissions. In this thesis, two different modulation strategies, bipolar and unipolar, are explored. The primary goal is to understand the effects each modulation strategy has on the conducted electromagnetic interference (EMI) and then try to eliminate that EMI in the common and differential mode paths. In order to accomplish this, a laboratory experiment on an EMS using both modulation strategies was performed. The EMS was in grid-connected mode. Once the differential and common mode currents and voltages were obtained, Simulink was used to model the laboratory EMS. Once there was confidence in the model's ability to predict the laboratory behavior, a line impedance stabilization network (LISN) was added to the design. Comparing the LISN voltage to the MIL-STD showed that the current model was not within limits. The addition of a passive filter proved to minimize the conducted EMI for a single-phase grid-tied inverter.