A circuit-oriented approach for the analysis of pulse width modulation (PWM) three phase inverter is presented in order to run unbalanced loads in low nonlinear effects as harmonics. This method uses the identification of a six switch nonlinear device, which consists of only the active and passive switches in three phase inverter. When operating characteristics of the MOSFET switch are determined according to step-sinus pulse width modulation method, an average equivalent inverter model can be formed. After that, SSPWM technique is used to drive unbalanced loads in order to compare with common pulse width modulation (PWM) running unstable loads. First, the inverter load of resistive (R) and inductive (L) are performed at the MATLAB Simulink so that by PWM technique could be shown the reducing effect of the harmonic on loads. After that, the system is implemented by real elements as MOSFETs, PIC17F877A, PC 817 phototransitors.