Development of a D-STATCOM prototype based on cascade inverter with isolation transformer for unbalanced load compensation

This paper describes the distribution level static compensator (D-STATCOM) of three-phase three-wire distribution system for unbalanced load compensation. First, a novel transformer-isolated multilevel H-bridges inverter is introduced, which is suitable for large unbalanced load compensation. For solution to improve the power quality at the point of common coupling (PCC), the compensation scheme is proposed with dual d-q transformation and symmetrical components method. In addition, the balancing design method is employed to equalize the phase currents of triangle connection transformer. Then the computer simulation system is built with software PSCAD to test the functions of the D-STATCOM. Finally, the hardware prototype is made based on two H-bridges voltage source inverter with 1700 V/75 A IGBT. The switching frequency of the space vector modulation (SVM) PWM is set at 500 Hz to generate the compensation currents. The DSP and FPGA based system is employed as the controller. Simulation and experimental results are also given to validate the effectiveness of the proposed D-STATCOM