Inverter is the most important device to utilize the renewable energy sources efficiently. The Sinusoidal Pulse Width Modulation (SPWM) technique is one of the most popular PWM techniques for harmonic reduction of inverters since there are used three sine waves displaced in 1200 phase difference as reference signals for three phase inverter. Nowadays the SPWM switching signal is generated with the help of different FPGAs, microcontrollers and microprocessors. But for these kind of devices it is necessary the programming or coding. This paper represents the SPWM technique for harmonic reduction & shows how to generate SPWM switching signal using different simple Operational-Amplifier (Op-Amp) circuits/analog circuits for three phase pulse width modulated (PWM) voltage source inverter (VSI). All the Op-Amp circuits are simulated and their outputs are shown step by step. This analog circuit (Op-Amp) controlled voltage source inverter is simulated for both standalone load & high voltage sensitive loads/systems like micro-grid system and large industrial machines respectively with transformer & without transformer. The simulation results are shown before and after harmonic reduction using an appropriate passive filter. Furthermore, the paper represents two typical inverter based micro grid system structures where one is with common DC bus & another one is with common AC bus.