A new switching algorithm in Back to Back CHB Multilevel converters with the advantage of eliminating isolation stage

Back to Back CHB Multilevel converters have been widely considered in high power applications; however, there are certain drawbacks which restrict the use of these structures. In this paper, a new switching algorithm is introduced for a back to back cascaded H-bridge (CHB) converter with the ability to regulate the DC bus voltages to a reference value and produce a low frequency output voltage. The main purpose of this novel switching algorithm is to eliminate the need for an isolation stage between the H-bridge cells. The proposed back to back converter can connect directly to MV levels and correct the input power factor, even if the output load is non-linear. In order to limit the switching loss, a maximum switching frequency of 3kHz has been chosen for the line side converter; furthermore, to eliminate a specific harmonic component, the load side converter is modulated through the selective harmonic elimination method. Using the predictive current control method for the rectifier, the input current is programmed to be sinusoidal and in phase with the input voltage; in addition, the current distortion is kept below 5% at maximum power consumption. The validity and effectiveness of the proposed method is verified through simulations on a 5-level back to back converter in the MATLAB/SIMULINK environment.