Modular photovoltaic based static synchronous compensator (PV-STATCOM) is extensively applied to either supply or consume reactive AC power to electricity network. However, the absence of mechanical rotating mass in voltage source converters (VSC) restricts their contribution in regulating voltage fluctuations or sufficient fast inertial frequency response. In this paper, a virtual inertia based control methodology over the dc-link voltage is applied to accommodate a smooth transient frequency response and a feed forward term based on the oscillations of the active power is appended to cater for the unbalanced grid voltage condition. This combination presents a package which provides seamless inertial energy response and straight power supply in the impact of an unbalanced grid condition. This control methodology has been verified using the Hardware-in-the-loop (HiL) technique in Matlab/Simulink and Xilinx System Generation environment. The real-time co-simulation results prove the veracity of this control scheme.