Phase Shifted Carrier Modulation technique for Modular Multilevel Inverter

摘要

This paper presents a Phase Shifted Carrier Modulation technique for Modular Multilevel Inverter (MMI). MMI is composed of a number of half bridge units and each unit consists of a floating dc capacitor. Voltage balancing of these floating capacitors is an important issue in MMI. Reverse Polarity (RP) and Bypass Bridge (BB) are the two schemes introduced for capacitor voltage balancing. Both the schemes use an assorting based algorithm with Phase Shifted Carrier Modulation (PSCM). According to this algorithm, one capacitor is chosen within each phase, which complies a prearranged case. The case is associated to the provisional voltage difference within the sub module's capacitor. As a result of which, the minimum charged capacitors are charged, and the maximum charged capacitors are discharged, relying on the direction of transitory power flow. Simulations are carried out using Matlab-Simulink model, and the results show that MMI is effective with the control strategy for balancing the capacitor voltages.