Control and protection strategy for a three-phase single-stage boost type grid-connected current source inverter for PV applications

Renewable or Sustainable Energy (SE) sources such as photovoltaic (PV) cells usually generate variable power. Hence power electronic circuits are used to extract maximum power from these sources at all times. Further, Grid-integration demands tight technical standards to be met. Hence novel power electronic converter topologies are used to bring down the level of harmonics while interfacing the SE sources with the utility of fixed grid voltage. These two functions can be performed using two separate power conversion stages. But this would reduce the overall efficiency and reliability of the system. Hence, it is desirable to use a single power electronic conversion stage to perform both the functions. This paper evaluates a single stage power electronic converter topology capable of boosting the variable dc voltage towards the ac mains. The chosen topology, a Current Source Inverter (CSI), is used as an interface between the PV source and the utility. The paper discusses the principle of operation, control and protection strategy used for this topology. Experimental results of the Grid-Connected (GC) Current Source Inverter (CSI) based PV system using real time Digital Signal Processor dSPACE are also presented. Finally three phase sinusoidal currents are injected into the grid at unity power factor (UPF).