Nonlinear control strategy for current source cascaded H-bridge inverters - An approach considering single-phase DQ components

Current source cascaded H-bridge (CSCHB) inverters can be a good alternative to manage voltage, current and frequency in a medium-voltage load. The power quality achieved by this type of converters and their ability to boost the output voltage without the need of a DC / DC converter in the DC link, have drawn attention to it as a suitable alternative to be used as the interface between DC sources and the grid. However, the converter has some, not so simple, challenges to be solved, mainly in the control of the output voltages when the input currents to each inverter of the system are different. In this paper a non-linear control strategy, able to manage the direct and quadrature (dq) output voltage of each unit in the CSCHB inverter, is proposed. The strategy allows the control of the amplitude and phase angle of the converter's output voltage when it is connected to the grid. Furthermore, the proposed nonlinear scheme ensures a good dynamic response of the controlled variables throughout the entire power range of the system. Simulated results that support the theoretical framework are also presented.