A New Pulse Active Width Modulation for Multilevel Converters

An improved SHM‐PWM scheme for three‐phase seven‐level CHB inverter to improve power quality by fulfilling CIGRE WG 36‐05 and EN 50160 and sharing equal power between the H‐bridge cells

“…In literature, several modulation schemes have been proposed for controlling the output voltage waveform quality of multilevel inverters. These can be listed as sinusoidal pulse width modulation (SPWM), space vector modulation, selective harmonic elimination (SHE)‐pulse width modulation (PWM), optimal minimization of THD (OMTHD), optimal PWM (OPWM), and selective harmonic mitigation‐(SHM) PWM . Out of these PWM schemes, SHE‐PWM scheme works on the low‐switching frequency, and it is used to completely eliminate (E‐1) number of specific low‐order harmonics of the output voltage using “E” number of switching instances in each quarter cycle of the output waveform.…”

“…Out of these PWM schemes, SHE‐PWM scheme works on the low‐switching frequency, and it is used to completely eliminate (E‐1) number of specific low‐order harmonics of the output voltage using “E” number of switching instances in each quarter cycle of the output waveform. The major drawback of this scheme is that it only eliminates a limited number of low‐order harmonics while other harmonics (which are not incorporated into the problem) are totally uncontrolled and can attain high magnitudes . Hence, for a specific number of output voltage levels, this scheme requires more number of switching instances to fulfill some power quality standards and to remove more number of low‐order harmonics.…”

“…But it requires more number of switching instances in a quarter period to fulfill some specific power quality standards. Besides that, uneven power distribution between the H‐bridge cells of CHB inverter can occur in the aforesaid SHE‐PWM and SHM‐PWM schemes . This will affect the rating and size of both semiconductor devices and input side isolation transformers.…”

“…The major drawback of this scheme is that it only eliminates a limited number of low-order harmonics while other harmonics (which are not incorporated into the problem) are totally uncontrolled and can attain high magnitudes. [16][17][18][19][20][21][22][23] Hence, for a specific number of output voltage levels, this scheme requires more number of switching instances to fulfill some power quality standards and to remove more number of low-order harmonics. Thus, it results in higher switching losses in power switching devices and reduces the conversion efficiency.…”

“…Besides that, uneven power distribution between the H-bridge cells of CHB inverter can occur in the aforesaid SHE-PWM and SHM-PWM schemes. [16][17][18][19][20][21][22][23][24][25][26][30][31][32][33][34][35][36] This will affect the rating and size of both semiconductor devices and input side isolation transformers. Ghoreishy et al 37 introduced a modified SHM-PWM scheme for a three-phase five-level CHB inverter where variable DC voltage sources have been included as an additional degree of freedom along with the switching angles.…”