Comparing Point of Use Power Quality to System Level Power Quality in a Shipboard MVDC Distribution System

The US Navy has specified stringent component based performance criteria for interconnecting electrical system devices into a shipboard distribution system. The performance criteria include power quality and harmonic content at the generation, distribution and load. The distribution system is designed to provide a high level of power quality. At the same time, the end-use loads, especially critical loads, are designed assuming a low level of power quality in the supply system. This study explores the idea of looking at the shipboard power distribution as a system, rather than a collection of individually specified components. This paper reviews the MVDC distribution network as a system, and presents the trade-offs between point of use power quality enhancement filtering, and maintaining a high system-wide level power quality.;The test bench developed for this study is designed in such a way as to allow comparisons to be made between different converter types at the generation, and at the loads. To improve power quality, different topologies of filters are reviewed to determine their effectiveness in improving the power quality both at the generation and load. By reviewing the effect the converter technology and filtering has on the power transmission, system level topology combinations can be determined which provide the best power quality at the loads.;The converter technology types are a driving factor in the results of this study. Disruptions to the normal system operating conditions, such as faults, are applied in the simulation to determine the effect the events have on the converter controls ability to restore the system to a stable operating point. Evaluation of the resulting power at the loads for detrimental effects after the disruptive event is studied to provide more insight on system level topology combinations which improve the power quality at the loads.;Results of the study show that load or generation device placement on the MVDC distribution bus will have an effect on the power quality of neighboring loads, indicating that AC harmonic distortion is transferred through the MVDC bus. The effect of converter PWM frequency on power quality is also studied. Results show that for higher PWM converter frequencies, the percent total harmonic distortion for voltage and current does not necessarily improve. A parallel resonance condition develops on the load bus which increases the percent total harmonic distortion at certain converter PWM frequencies.;Weighing the effects of all the combinations and disruptive events studied, load configurations which provided some amount of AC neutral point grounding, whether through a passive filter or wye-ground transformer on average performed better than configurations which did not.