Analysis of Multiaxis Current Controller for Power System Friendly Front-End Converter Employing Two-Level and Three-Level Topologies

It is highly essential to develop a control technique that can be applied to conventional two-level as well as high-power multilevel front-end converters (FECs). Multiaxis current controlled, unity power factor (PF), regenerative FEC is described in this article. Current error space phasor is controlled by multiaxis current monitoring and its movement is confined within the prescribed hexagonal boundary. It is shown that the needed information on sector change detection can be derived from instantaneous values of supply voltages for the two-level FECs. However, similar approach cannot be extended for three-level FECs. Hence, sector change detection technique employing additional outer hysteresis band is proposed. With the help of experimental results, for steady state and dynamic conditions of FEC, it is demonstrated that the proposed current-controlled technique is equally applicable to two-level and three-level FECs. A three-level flying capacitor topology is considered, where voltage balancing of flying capacitors is guaranteed by effective utilization of redundant switching states. Results clearly depict the power system friendly nature of the presented scheme, i.e., unity PF, low total-harmonic distortion in supply current, good load and line regulations, and capacitor voltage balancing with regenerative capability of the converter. All the schemes are implemented on OPAL-RT hardware-in-loop platform.