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Traditional means for implementing the switching of the power switches in multilevel converters is subharmonic pulse width modulation (SHPWM) or triangulation approach involving a comparison between a target reference waveform and several high-frequency carrier waveforms where all the power switches usually work at high switching frequency. The asymmetric modulation method (AMM) which is derived from hybrid modulation method is illustrated. The contribution of asymmetric modulation is to provide a general method of finding the locus of the output stepped-wave for the hybrid modulation method. This study also provides an illustration of the `Mathematic expression of modulation process` of SHPWM and AMM where it is easy to see how the two techniques are related, and the output expression of the AMM method can be easily obtained from the general N-level double-Fourier output expressions of SHPWM where cumbersome mathematical work has been avoided. Through the analysis of modulation process for SHPWM and AMM, results show that the AMM is an improved version of SHPWM method with optimised switching combination. Theoretical analysis, simulation and experimental results are provided to validate the feasibility of the proposed analysis method.