Abstract
Cascaded H-bridge converter (CHB) is a multilevel topology that is a well-suited solution for multiple applications such as flexible ac transmission systems or motor drives. This paper is focused on a CHB where the cells present an aging mismatch. This can be caused by the maintenance operation which forces the replacement of some damaged cells of the converter with new or repaired ones. In this paper, a new improved approach of the active thermal control (ATC) of the CHB using discontinuous pulsewidth modulation (PWM) (D-PWM) is presented. The D-PWM technique is used to reduce the power losses of one cell reducing its average temperature in order to increase its remaining lifetime. However, the combination of D-PWM with traditional phase-shifted PWM (PS-PWM) introduces high harmonic distortion in the output voltage of the CHB converter at twice the carrier frequency. A detailed harmonic distortion analysis of the CHB output voltage when the D-PWM based ATC is active is presented. From this analysis, a modification of the traditional PS-PWM is derived to eliminate the harmonic distortion at twice the carrier frequency. Experimental results show how the ATC using D-PWM is achieved whereas the harmonic distortion around twice the carrier frequency is eliminated.
Highlights
Nowadays, multilevel converter is a mature technology which has been developed since decades [1]
Reducing as much as possible the maintenance costs is a key factor of commercial power converters
The active thermal control methods applied to CHB usually introduce harmonic distortion at low frequency which is a drawback in terms of output waveforms degraded quality and corresponding extra filtering costs
Summary
Multilevel converter is a mature technology which has been developed since decades [1]. Like pumps, fans, power quality applications and in renewable energy integration [2], [3] Among this family, a popular multilevel topology is the cascaded H-bridge converter (CHB) which is shown in Fig. 1 and particularized for a three-cell CHB. The basic power cell is the H-bridge, it is possible to find in the literature other power cells like NPC or T-type [5] Among other advantages, this topology is very popular because is able to achieve very high nominal output voltages with a large number of voltage levels providing a high modularity and natural fault-tolerant capability. As it is well-known, PS-PWM method presents some advantages when it is applied to a CHB converter. The substituted power cells present a different cumulated aging compared with the others, and after a long-term operation, a non-negligible damage mismatch can be found among the cells [19]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
