5.2.1. Existing PWM Method

Using Min–Max and the third harmonic injection method, the common mode current and voltage are investigated for the three-level NPC inverter. Figure 9a–d depicts the waveforms of CMC using existing Min–Max method, CMV using existing Min–Max method, CMC using the existing third harmonic injection methods, and CMV using the existing third harmonic injection method, respectively.

**Figure 8.** Matlab/Simulation model of the three-phase three-level NPC inverter.

**Figure 9.** Simulation results: (**a**) CMC using existing Min–Max method; (**b**) CMV using existing Min–Max method; (**c**) CMC using the existing third-harmonic injection method; (**d**) CMV using the existing third-harmonic injection method.

The fast Fourier transform (FFT) is conducted for Min–Max and third harmonic injection PWM techniques and it is observed that common mode voltage THD is 14.74% for Min–Max strategy and 11.60% for the third harmonic injection method. In the existing PWM method, the magnitude of the common mode current (rms value) is 1.191 A using the Min–Max and 1.199 A in the case of the third harmonic injection method. This can be reduced further by using Modified PWM Technique.
