The modular multilevel converter(MMC)operation mechanism and the numerical method of loss calculation are reviewed. Based on PLECS under carrier phase shifted sinusoidal pulse width modulation(CPS-SPWM)

the sub-module loss characteristics are analyzed

including different voltage balancing methods and circulating current suppression methods. Regardless of the status of the converter working performance

the comparison shows that

with the voltage balancing method of energy balance and circulating current suppression method of three phase decoupled second harmonic circulation current suppression

the loss distribution consistency of MMC is higher and the loss rate lower. The loss consistency of different working conditions is similar. Finally

the loss consistency of nearest level control(NLC)is compared with that of CPS-SPWM

and it is shown that with CPS-SPWM the sub-module loss consistency is better. This work is supported by National Natural Science Foundation of China(No.51277065)and National High Technology Research and Development Program of China(863 Program)(No. 2012AA050401).