A static synchronous compensator (STACOM) is shunt Flexible AC Transmission Systems (FACTS) device used in distribution system to mitigate the reactive power dynamically as well as to improve the power quality in Transmission network. This paper will show the design of a STATCOM for three phase three wire system to mitigate the reactive power using constant decoupled current control method. It is difficult and time consuming process for conventional method to tune the PI controller parameters of STATCOM. In order to tune the PI controller parameters properly two recent optimization techniques has been developed, one is Differential Search algorithm (DSA) and another one is Wind Driven optimization (WDO) which are used in this paper. The aim is to be minimize the integral square error for both outer voltage controller and inner current controller simultaneously. To calculate the PI gain by DSA and WDO technique will be demonstrate and show the improvement of convergence speed, reduction of error, the overshoot in capacitor voltage and other circuit parameters. The results are compared with hit and trial method, which are shown that the DSA algorithm based PI controller tuning method giving more optimized results.