This dissertation proposes a novel control methodology for voltage (VPCC) and frequency (ω) control at the Point of Common Coupling (PCC) while controlling the active power (P) and reactive power (Q) output of one as well as multiple Grid-Forming (GFM) Inverters. To achieve the goal of becoming self-operable and flexible, Distributed Energy Resources (DERs)-based inverters should be able to supply the power demand to the load as well as control the voltage and frequency at the PCC irrespective of the ambient conditions—the absence of the grid as well as in the grid-connected system. The dissertation presents a brief review of virtual inertia-based controllers, recently reported in the literature, for parallel-connected inverters in islanded systems. A new control topology, Synchronous Machine Emulator with Embedded Droop Control (SME-EDC) is proposed to control parallel-connected grid-forming as well as grid-connected inverters. This is designed to overcome the challenges in the future modern power grid consisting of large numbers of small-scale Distributed Energy Resources (DERs). It is estimated that the modern power grid will lack adequate grid inertia and will not have stiff grid reference for the DERs to follow using the existing methods like Phase-Locked Loop (PLL). The capabilities of the proposed controller are VPCC and ω control of the inverters, auto-synchronization of the phases of the interfacing inverters without communication and without PLL, black starting the inverters without the presence of the grid, operating in the grid-connected system, controlling P and Q of inverter by droop control, and providing virtual inertia. The control philosophy of the proposed controller is established by rigid PCC voltage control by using capacitor current control. Whereas the auto phase-synchronization is achieved by determining the phase-angle (θP) from the power controlling ω/P droop control. Simulation results from MATLAB/Simulink, and experimental results from the Control Hardware-in-the-Loop (CHIL) testbed and hardware experiment are presented to validate the capabilities of the proposed controller under various grid and load test cases.