Hybrid Modular Multilevel Converter With Arm-Interchange Concept for Zero-/Low- Frequency Operation of AC Drives

Abstract

DC-AC Modular Multilevel Converter (MMC) is a promising candidate for high-power AC drive applications. The main challenge of operating the MMC in AC drive applications is its performance during low-frequency conditions, as high voltage ripple is associated with the low-frequency operation, which results in voltage stresses on the involved semiconductor devices. To keep capacitor voltages balanced and bounded in low-frequency operation, different techniques have been proposed in literature, which can be classified into software and hardware approaches. In this paper, a hybrid MMC with arm-interchange concept is proposed to ensure operating successfully during low-frequency conditions. The hybrid MMC consists of two-stages. The first stage is a front-end Integrated Gate Commutated Thyristor (IGCT)-based H-bridge converter, while the second stage is a Full-Bridge Sub-Module (FBSM)-based MMC, where FBSMs is able to generate positive, zero, and negative voltage states. Detailed illustration and design of the hybrid MMC are introduced. Simulation results of the proposed converter are presented to show the effectiveness during low-frequency and normal frequency conditions in AC drive applications. Finally, a scaled-down prototype is employed for experimental validation.

A Detailed Review of MMC Circuit Topologies and Modelling Issues

“…Further optimisation can also be done by mixing different types of cells, resulting in hybrid multilevel converters [55]. Industry and academia have proposed hybrid converter topologies in the last two decades to improve specific aspects of MMC performance such as DC fault blocking capability, footprint, and efficiency [56][57][58][59][60][61]. Hybrid converters are classified into two groups.…”

A Novel Review on Modular Multilevel Converter for Induction Motor Drive Applications

“…The modular multilevel converter with arm interchange control technique [29] is observed in figure 2.…”

Research on Influence Factors and Acceleration Methods of Current Commutation

“…where   For any current commutation process of any topology, simultaneous Eq. 21, (22), (23) and (24), when is(t) is known, if t=t0 exists so that the equations are satisfied at the same time, then the commutation process can be judged as failure.…”

“…The overvoltage when breaking short-circuit current is 2.5 p.u. If the turn-off current capacity is required to be 6 kA, two IGCTs are required to be connected in parallel and then cascaded to 4 levels [22]. According to the data sheet, the voltage drop would be 14 V.…”