A control scheme in the dq reference frame for Hexverter-based systems

A control approach developed in the α β0 reference frame must be able to track control signals which are sinusoidal functions of time. Therefore, designing these compensators is not a straightforward task. Alternatively, a control scheme elaborated in dq reference frame offers the possibility to track dc control signals. It also allows the design of compensators with simpler structures and low dynamic orders. The purpose of this work is to propose a control scheme in the dq reference frame for Hexverter-based systems. Considering the Hexverter's operating principle and its characteristic waveforms, a frequency decoupled branch current control model in the dq reference frame is synthesized. It can be considered as an extension of the control model developed for the two-level voltage source inverter. A feature of the proposed control is to allow independent regulation of the Hexverter's active and reactive power flows. The former control is then integrated to a modulator and a voltage balancing algorithm when the Hexverter-based system is functioning as an intertie. The effectiveness of the characterized system is validated via a detailed PSCAD/EMTDC computer simulation.