A Multi-functional Four-leg Grid Connected Compensator

There has been a growing demand on using an active power filter (APF) for grid-connected converter systems based on non-conventional energy sources such as solar, wind and fuel-cells. In addition to power quality conditioning, the APF can also be used for bi-directional active power exchange with the three phase four wire grid and therefore acts as a multifunctional compensator. This paper presents a four-leg, shunt multi-functional grid-connected power quality compensator. The compensator reference currents are generated using the well known instantaneous p-q-r theory. A simple modification in the conventional theory to eliminate the neutral current from the three-phase four-wire power system is proposed. A digital controller is used to implement dead-beat current control. The outputs of the digital current controller are used as reference voltages for a 3D space-vector modulator (3D-SVM). A new approach for PWM waveform generation in 3D-SVM is proposed. The PWM is implemented on a floating point DSP. All the intermediate steps are discussed from the view point of implementation on DSP-FPGA platform. The multi-functional compensator is analysed and simulated for the most practical conditions at the power system and the simulation results are presented.