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A GSA Based Generalised Formulation of SHE-PWM Problem of Multilevel Inverter for Both Equal and Unequal Source Voltages

Sayanti Ray, Pradip Kumar Saha, Goutam Kumar Panda

A generalised formulation of SHE-PWM technique applicable for high power voltage source cascaded multilevel inverter used in constant frequency utility applications has been discussed in this paper. The SHE-PWM scheme features a broad solution space. This paper aims at to eliminate low order dominant harmonics and at the same time maintaining fundamental also. Since SHE equations are non-linear transcendental in nature , to solve these equations a new artificial intelligence technique called Gravitational Search Algorithm has been implemented to find out switching angles with faster and guaranteed convergence. To illustrate the effectiveness of the proposed method, a 3-phase five level voltage source inverter has been considered with six no. of switching per quarter cycle. Since for a 3- phase balanced system all the triplen harmonics are absent in the line, thus in this case with six no of switching per quarter cycle, five dominant non-triplen harmonics (5th to 17th) was possible to eliminate using SHE-PWM technique for both equal and unequal source voltages for a wide range of modulation index and voltage ratio. Then the output voltage THD obtained using this approach is compared with another approach for minimum system voltage THD.