(b)Fig. 10. RMS value (a) Source voltage (b) load voltage
During VCM operation DSTATCOM no longer compensates for current related PQ problems as observed in fig. 11(b) from 0.2 to 0.45seconds. Now, when the unbalance in the system vanishes, the DSTATCOM again switches back to CCM operation and further tries compensate current related PQ problems.
5. CONCLUSION
In this paper, using hysteresis current control strategy, operation of DSTATCOM is carried out to maintain source current sinusoidal and in phase with the source voltage (CCM). Moreover a novel concept of single phase SRF theory is used to mitigate voltage unbalance in a three phase four wire system and so to maintain load voltage at 1 p.u. (VCM). Further, a novel concept of Dual Functional DSTATCOM is proposed so that single DSTATCOM can be utilized to mitigate both current and voltage related PQ problems by switching of DSTATCOM between Current Controlled Mode (CCM) and Voltage Controlled Mode (VCM). The simulation is performed under MATLAB/Simulink environment and results show the effectiveness of the proposed algorithm.