Four-Switch Three-Phase Static VAR Compensator with Capacitor Voltage Offset Suppression

Fault tolerant capability as well as cost reduction of Four-Switch Three-Phase (FSTP) converter in comparison with its traditional Six-Switch Three-Phase (SSTP) counterpart, has attracted lots of attention in last decade. Despite its versatile features, it suffers from some intrinsic problems. Voltage offset of DC link capacitors along with superimposed second harmonic voltage ripple on capacitors voltage are major issues with FSTP. In this paper an Adaptive Space Vector Modulation (SVM) is proposed for a Static VAR compensator which guaranties the balanced current injection to the grid, even though, the DC voltage ripple is existing. Besides, as the DC link Capacitors are floating in Static VAR compensators, unequal voltage division on them is the next concern. These issues are also tackled by sensing the capacitors voltage and made modification on reference voltages which is fed to the modulator. Time domain simulation in Matlab/Simulink is undertaken to evaluate the efficacy of the proposed method.