FAULT-TOLERANT STRATEGY FOR A DELTA-CHB-BASED STATCOM IN THE OVERMODULATION REGION

The cascaded H-bridge (CHB) is a popular topology for Static Synchronous Compensator (STATCOM) applications. Since this converter is composed of tens/hundreds of components, concerns related to reliability are inherent in the design of this converter. Generally, redundant cells are used, increasing “Manuscript received 05/05/2020; first revision 08/04/2020; accepted for publication 09/14/2020, by recommendation of Editor Demercil de Souza Oliveira Jr. http://dx.doi.org/10.18618/REP.2020.4.0029” the cost of STATCOM. Indeed, there is a potential for fault-tolerant operation when the overmodulation region is considered. This work explores the inherent redundancy of the delta-CHB in the overmodulation region. Initially, an analytical expression for the boundary between the linear region and overmodulation is determined and validated for different operating conditions. Then, the fault-tolerant is evaluated in a simulation environment, considering a case study of a 17 MVA/13.8 kV delta-CHB STATCOM composed of 24 cells per arm. Symmetric and asymmetric failures are addressed. The results indicate that the converter is capable of operating at rated conditions after 4 faults distributed in the three converter arms (5.5 % redundancy factor) without exceeding the recommended harmonic distortion values.