Comparative study of two stages and single stage topologies for grid-tie photovoltaic generation by PSCAD/EMTDC

This paper presents a comparison study of a typical grid-tie photovoltaic system between two types of topologies: the two stages (boost circuit adds inverter) and the single stage (inverter alone adds a step-up transformer). Some essential models built in this paper include PV array, Boost chopper and grid-tie inverter. The basic characteristics and descriptions of these two topologies are described. Perturb and observe and incremental conductance methods are introduced for MPPT (maximum power point tracking). As key-point, the out loop controller design details for the grid-tie inverter are investigated. The PV array, two system topologies and two MPPT strategies are implemented in PSCAD/EMTDC using its user- defined facility. Simulation results show that the output power of PV array can achieve a stable and accurate MPPT function under ambient conditions change. At the same time, the inverter can maintain a unit power factor by controlling the transferred instantaneous reactive power to zero in the synchronous d-q frame. The simulating results are compared with that of the two stages case in aspects including energy converting efficiency, power quality, and MPPT accuracy. Through this study work, engineers and researchers can obtain an overall comprehension about advantages and disadvantages of these two topologies in designing a PV system.