Investigation of harmonic distortion in multi-pulse rectifiers for large capacitive charging applications

The United States Navy's future fleet of vessels will deploy an increasing number of high power electrical loads that will operate in a transient nature. As the electrical requirements increase, the efficiency of power conversion will become more important than ever before. Converting AC power to DC power can be very inefficient due to the generation of harmonics that are injected into the power system during conversion. Previous work has shown that the magnitude of the harmonics generated can be reduced significantly when multipulse rectifiers are implemented. These types of rectifiers work through splitting the three-phase input into additional phases so that the output ripple and distortion can be reduced. Higher numbers of phases result in improvement in power quality but come with added costs and complexity. Previous work in the literature has evaluated these types of converters into purely resistive or slightly inductive loads but not into highly capacitive loads, similar to those the Navy has plans to utilize. The work presented here investigates the harmonic content of multi-pulse rectifiers when used to charge large capacitive loads. Six, twelve, eighteen, and twenty-four pulse rectifiers have been simulated using Simulink® to predict how higher pulse numbers reduce the injection of harmonic distortion. Model validation will be carried out using a hardware implementation of each rectifier at the 1 kW level using a three-phase motor-generator source. Preliminary results from the simulations will be presented here.