Energy Harvesting Comparison and Analysis in 1000V and 1500V Grid-Connected PV Systems

Different architectures of 1000VDC and 1500VDC grid-connected PV systems for different AC grid voltage levels are compared in this paper with respect to energy harvesting during one year period. One stage architecture is compared with two two-stage concepts already presented in literature and industry - "mini-boost" and "string-optimizer". An idea of mini-boost considers a booster rated for a portion of the nominal power that operates only in the cases when MPP voltage is lower than minimum allowed DC bus. Otherwise it is by-passed and the inverter operates as in one-stage architecture. Another concept, "string-optimizer" can be considered as a buck-boost topology that controls DC bus voltage at the minimum value. In this way range of energy harvesting operation is increased and performances of the inverter are improved. However, buck-boost topology is less efficient than a boost and, additionally in this case, it needs to be rated for the full system power. All the analysis and comparison is based on comprehensive PV panel and converter loss models, real enviromental conditions measurements and real and commercially available circuit components. Experimental verification of the employed models is provided by the measurements conducted on 22kW grid-tied solar inverter.