This paper presents a performance comparison between a conventional Proportional-Integral (PI) controller and a nonlinear PI (NLPI) controller for three parallel-connected voltage source inverters operating in an islanded microgrid under both uniform and non-uniform delay conditions. Time delays in parallel inverter systems significantly affect transient stability, damping characteristics, voltage regulation, and power-sharing performance. The presence of uniform and non-uniform delays can introduce oscillations, degrade dynamic response, and weaken overall system stability. Two delay scenarios are investigated to analyze these effects: (i) a uniform delay of 50μs applied to all inverters, and (ii) non-uniform delays of 50μs, 60μs, and 70μs applied individually. Under these operating conditions, the conventional PI controller demonstrates noticeable oscillatory transients, higher overshoot, and slower settling behavior. To improve robustness and dynamic performance, a nonlinear PI control approach is implemented while maintaining a simple control structure. Simulation results demonstrate that the NLPI controller provides improved damping, reduced overshoot, and faster settling time under both uniform and non-uniform delay conditions. These results confirm that the nonlinear PI controller enhances the robustness and stability of parallel inverter systems operating under practical delay variations.