The traditional three-level PWM modulation is
shown in Fig 1 (b), the phase contrast of driving signal is
180o so there must be a phase-shift disposal in the driving
circuit. In one period, every transistor switch needs on-off
actuation so power losses are added on. An improved
three-level PWM modulation is proposed to throw off the
phase-shift circuit and to decrease the open-close actuation
times. The principle of this modulation is shown in Fig 3.