The utility model discloses a multistage dc -to -ac converter controlling means implements on -off control to forming the on -off control signal that is generated by PWM control for the dc -to -ac converter utilization of multilevel hierarchy, regularly has the phase difference to each grade messenger's switch, obtains the output of heterogeneousization, its characterized in that possesses the phase difference operation part of the phase difference operation of carrying out [ DELTA t=TS K ], and wherein T be the PWM counting value that the control of above -mentioned PWM was used, and S be the progression of above -mentioned dc -to -ac converter, and DELTA t be above -mentioned phase difference, and K is the coefficient above 1, and the switch of each grade of messenger's the aforesaid regularly has the phase difference (DELTA t) that above -mentioned phase difference operation part calculated.
