Investigation of the control scheme of a single phase Cascade H-Bridge multilevel converter capable for grid interconnection of a PV park along with reactive power regulation and maximum power point tracking

This paper investigates the control scheme of a multilevel cascade single phase converter -consisted of two cell cascaded full-bridge converters-, where the modified p-q theory with ramp comparison has been applied for the proper single-phase interconnection of a 5 kW photovoltaic park with the grid. With the proposed method the converter is able to generate a five level ac-voltage, to utilize maximum power point tracking operation and achieve both active power control of the grid connected photovoltaic park system along with reactive power control for the correction of the reactive power of the load. The switching pattern of the topology -where IGBTs can be used as switches- is realized with the use of the ramp comparison method and two PI controllers. In addition, this pattern has been implemented taking into consideration the two-cell cascaded full-bridge multilevel converter of the topology. On the other hand, the PI controllers have been selected based on the requirements of the system, while the control strategy was built taking into account the maximum power point tracking. Finally, for the dimensioning of the converter suitable waveforms are presented - based on the derivation of appropriate mathematical equations.