నైరూప్య

Grid Interconnection of Renewable Energy Sources at the Distribution Level with Power Quality Improvement Features

T.Thillainayaki, P.Shanthi

Renewable energy sources are used in distribution systems using power electronic converters. The high penetration level of renewable energy sources produces power quality issues such as current unbalance, current harmonics etc. This paper provides control strategy for grid interfacing inverters when installed in three phase four wire distribution system. The inverter serves multiple functions, it acts as power converter and also as a shunt active power filter to compensate current unbalance, load current harmonics, load reactive power demand and load neutral current. For this purpose, this paper analyses current controlled four leg voltage source inverter made of insulatedgate bipolar transistor connected to a combination of three phase non linear and single phase linear and non-linear load. The hysteresis controller is used to produce switching pulses. The reference current generation is based on PQ theory. This control strategy allows the combination of grid interfacing inverter and the three phase four wire linear or nonlinear unbalanced load at point of common coupling appears as balanced linear load to the grid. The four leg current controlled voltage source inverter is actively controlled to achieve balanced sinusoidal currents at unity power factor (UPF) even the unbalanced nonlinear load is connected to it. This enables the grid to supply or receive sinusoidal and balanced power at UPF. The grid interfacing inverter has been analyzed under three conditions. i. When RES power is zero, it acts as shunt active power filter. ii. When RES power is less than load power demand, it acts as rectifier. iii. When RES power is greater than load power demand, it injects power to the grid and acts as an inverter. This control concept has been simulated using MATLAB/Simulink.