A hybrid pulse width modulation(HPWM)strategy using both low and high frequency switching methods is presented for cascaded H-bridge(CHB)and isolated bidirectional DC/DC converter(IBDC)based power electronic transformer. Based on the waveform-synthesis theory and double Fourier integral method

an analytical spectral expression of the HPWM output voltage for 5-level CHB is derived

and a comparison of the output harmonic characteristics between carrier phase-shift(CPS)and HPWM is also provided. The results show that the HPWM voltage contains only fundamental wave and carrier sideband harmonics which means lower switching frequency could be obtained without compromising the total harmonic distortion(THD). To deal with the unbalance of DC voltages under asymmetrical HPWM

a balancing control strategy is implemented

which utilizes a switching function rotation method for the CHB and a voltage feedback-feedforward controller for the IBDC. The proposed method can effectively ensure that each module will work at the same power and DC voltage level. The harmonic analytical method and the proposed control strategy are validated by simulation and experimental results.