Multilevel inverter using cascaded 3-phase transformers with common-arm configuration

In multilevel inverter development for 3-phase applications, total number of transformer in the circuit can be reduced by using of cascaded 3-phase transformer circuit instead of single-phase transformer circuit. In the scheme, total number of switching components in the circuit is still a drawback to achieve lower cost and smaller size of the inverter compared with conventional multilevel inverter. This paper includes a challenging method to reduce total switching components in the multilevel inverter by adopting common-arm structure.The proposed inverter has been operated by two control schemes, Newton–Raphson and Equal-area method. After theoretical and experimental comparison of the methods, we found that Newton–Raphson method is useful to eliminate a specific harmonic order. However, the method has a shortcoming in real time operation which is performed by iterative calculation of the nonlinear equations. With Equal-area method, we can easily find the switching angles by calculating a trigonometric function. It can sufficiently minimize Total Harmonic Distortion (THD) of output voltage in real time operation of Digital Signal Processor (DSP).

► It is a challenging method to reduce total switching components in the multilevel inverter by adopting common-arm structure.
► The proposed inverter has been operated by two control schemes, Newton–Raphson and Equal-area method.
► We found that with Equal-area method, we can easily find the switching angles by calculating a trigonometric function.