The power system is dependent on control of power and voltage for its stability and reliability. Voltage Source Converter (VSC) technology has the advantage of being able to almost instantly change its working point within its capability limit. Due to this advantage, VSC can be used to support the system to maintain active power or output voltage constant during load variation. To achieve this, Proportional Integral (PI) controllers are used for its simplicity and robustness. In this paper mathematical model for Voltage Source Converter is developed. PI based controllers are developed for constant DC voltage as well as constant DC power for load variation. In addition to analysis of the mathematical model of the VSC, the controller performance analysis is also carried out for Two and Three level converter. The results are compared in terms of the THD and the controller parameters. Simulation is carried out in MATLAB/SIMULINK environment.