Selective harmonic elimination for cascaded H-bridge rectifiers based on indirect control

In this paper, a selective harmonic elimination pulsewidth modulation (SHE-PWM) method is introduced for multilevel cascaded H-bridge rectifiers. The indirect control strategy is utilized for control of the multilevel rectifier, where it does not need any current sensor and the system reliability increases by this way. Using the proposed control strategy and the modulation technique, a controllable power factor with nearly sinusoidal ac current waveform is generated. All dc link voltages are regulated to a constant reference voltage, even if the attached loads consume various amounts of power. In the proposed strategy, four major non-triplen harmonics are completely eliminated, and the maximum switching frequency is limited to 150Hz. To verify the validity and effectiveness of the proposed control strategy, several simulations are carried out on a 7-level cascaded H-bridge rectifier in PSCAD/EMTDC environment.