Control and modulation scheme for a Cascaded H-Bridge multi-level converter in large scale photovoltaic systems

Multi-level Cascaded H-bridge (CHB) converters are ideal for implementing large scale photovoltaic systems. The improved quality of the voltage waveforms, high efficiency and ability to employ multiple Maximum Power Point Tracking (MPPT) algorithms are just some of the advantages. In this paper a three-phase CHB converter supplied with photovoltaic arrays is considered. A control and modulation structure based on Model Predictive Control (MPC) is described. The scheme inherently controls the DC link voltages while also providing the ability to modify any of those voltages to meet MPPT requirements. This avoids the cost and added complexity of extra DC/DC converters that are typically required to keep the DC link voltages uniform. Simulation and experimental results are presented that confirm the correct operation of the proposed approach.