Fault-Tolerant Operation of 3-Phase 7-Level CHBMLI with Modified Neutral Point Shift Method
Nihal C. Khaire, Madhuri A. Chaudhari, Rohit Kumar
Abstract
Multilevel inverters(MLI) are now widely used in industrial and domestic applications. The multilevel inverter improves the voltage quality compared with the conventional inverter. However, due to the presence of more components, MLI is less reliable. Even fault in a single switch could lead to unbalance of output line voltages. This paper discusses the fault-tolerant operation of Cascaded H - Bridge (CHB) Multilevel Inverter with modified neutral point shift (NPS) technique. If there is a fault in any cells of CHB, it is bypassed and then the NPS technique is implemented to tolerate the fault. Bypassing the faulty cellto isolateit that will not contribute to theoutput; hence it can be later removed for maintenance. It allows the operation to be continued rather than completely shutting down the operation. But after NPS implementation the voltage is balanced but less than that of a healthy system. This paper presents a modified NPS technique, which maintains MLI output voltages at pre-fault conditions. In this paper, fault-tolerant control technique is presented with its mathematical modeling. This modeling is implemented in MATLAB/Simulink for 3-phase CHB. Faults at various cells are created to verify the performance of the system.