Estratégia de controle e modos de operação para inversores multifuncionais

Abstract

Natural and climatic conditions impact the photovoltaic generation. Since such pheno-mena have a stochastic characteristic, the resources provided by a photovoltaic generatorconnected to the electrical grid are not dispatchable. In this way, technical challengesrelated to power variations originated at the common connection point are created. Theintegration of batteries in photovoltaic inverters creates multifunctional inverters that al-low the dispatch of renewable resources similar to a conventional generator. Besides, itmakes possible improvements in energy quality, purchase, and sale with the electric grid,power supply for uninterruptable power supply, or supplying remote loads, among otherapplications. The literature addresses these systems. However, there is a gap mainlyabout the bidirectional D.C./D.C converter. Typically, non-isolated topologies are used,often with undesired voltage and current ripple characteristics in the battery. Another is-sue founded in the literature is that the control strategy generally adopted lacks accuracyin tracking the power injected into the electrical grid by the multifunctional inverter. The-refore, this work proposes a multifunctional inverter structure in which the bidirectionalD.C./D.C converter consists of an isolated topology with appropriate characteristics, bothfor the battery side and the D.C. bus side. Since the bidirectional D.C./D.C converterdeals with the different voltage levels of the D.C. bus and the batteries, it is possible to usebatteries with reduced voltage. In addition to the converter structure, a control strategyfor multifunctional inverters capable of tracking a power reference is also proposed. Theproposed multifunctional inverter is capable of operating in different modes: Conventio-nal photovoltaic inverter (mode 1 - grid-tied); programmed dispatch (mode 2 - grid-tied);active and reactive power compensation for local loads (mode 3 - grid-tied); rechargingthe batteries (mode 4 - grid-tied or off-grid) and; uninterrupted power supply (mode 5- off-grid). Experimental and hardware-in-the-loop (HIL) simulation results validate theproposed control structure and describe the features enabled.