An Improved CPS-PWM Method for Modular Multilevel Converter

In this paper, an improved carrier phase shifted - pulse width modulation (CPS-PWM) method for half-bridge based modified modular multilevel converter (MMC) is proposed to increase the number of the output voltage levels and so as to reduce harmonics. Compared to the traditional MMC topology, new redundancy sub-modules are added in each bridge arm and the capacitive voltage of the new sub-modules is recursive half of the common. Based on the modified topology of MMC, an improved CPS-PWM control method is proposed by overlaying the pulse trigger signal of each sub-module in each phase, and the base wave component is removed from the superimposed signal, finally, the modulation wave signal is obtained to generating the trigger signal of the new sub-modules. With the proposed method, the number of ac side phase voltage levels increase exponentially. To verify the proposed method, the simulation is performed and the total harmonic distortion of the output voltage current has been reduced obviously from the simulation results.