Control of a 19 level cascaded H-bridge multilevel converter photovoltaic system

Multilevel Cascaded H-Bridge (CHB) converters have attractive features for the implementation of large scale photovoltaic systems. They can be directly connected to high voltages and the multilevel voltage synthesis reduces the harmonic distortion introduced. In addition, they have individual DC links ideal for connecting photovoltaic arrays. Existing high performance voltage balancing techniques can also be adapted to integrate Maximum Power Point Tracking (MPPT). This paper considers a 19 level three-phase CHB converter with photovoltaic arrays supplying power. The structure and control of the system is presented, which shows that the DC link voltages can be individually controlled according to MPPT demands, negating the need for DC/DC converters. The system also maintains balanced output currents for power transfer to the grid. Simulation and experimental results are presented that validate the operation of the system.