Wide-Bandgap Device Enabled Multilevel Converters With Simplified Structures and Capacitor Voltage Balancing Capability

Abstract

This paper aims to point out and demonstrate the opportunities enabled by wide-bandgap (WBG) devices for multilevel converters, contributing to the international technology roadmap for WBG power semiconductors (ITRW). The emergence of silicon carbide (SiC) and gallium nitride (GaN) devices offers new opportunities to push the boundaries of power converter performances. Featuring high single-device blocking voltage and ultra-low switching loss, WBG devices can enable a group of multilevel converters with simplified structures and a higher number of levels to be practically implemented in applications with various power levels. This paper highlights how the use of WBG devices can reduce the number of required devices in the simplified multilevel topologies, how the capacitor voltage balance can be achieved with the newly proposed redundant level modulation (RLM) enabled by the ultra-low switching loss of WBG devices and how the switching frequency and efficiency can be improved with WBG multilevel converters. A 1.2 kV/100 kW, three-phase demonstrator implemented with a simplified four-level active neutral point clamped (ANPC) structure and commercial SiC power modules is studied to show the opportunities brought by WBG devices for multilevel converters. A voltage balancing scheme based on the RLM and a power loss analysis are presented for this configuration.

A 1200V DC-link Hybrid Si/SiC Four-level ANPC Inverter with Balanced Loss Distribution, $dv/dt$ and Cost

“…As analyzed in [2], [16], considering a 1200 V dc-link voltage, S1 and S3 in this topology both block and switch at 400V, while S2 blocks up to a static 800 V and switches still at 400 V. In other words, the worst-case for S2 starts from blocking a 400 V followed by a 400 V switching, which brings the voltage across S2 to 800 V. Therefore, 1700V power modules are selected for S2 to leave a +112% margin (with reference to the 800 V static blocking voltage). Power modules for S1 and S3 are rated at 1200V to leave a +200% margin (with reference to 400 V switching voltage).…”

“…This uneven loss distribution is undesirable in multilevel converters as established in [5]- [11], which poses challenges in the thermal design and limits the converter performance. Moreover, because over 60% of the power loss is concentrated on the primary (outer) modules in the all-SiC+4L-ANPC configuration as reported in [2], only 20% loss on each of the secondary (inner) modules appears to question the meaningfulness and necessity of employing the costly SiC devices for all of them. Additionally, the all-SiC solution also brings other disadvantages such as the high dv/dt issues due to the fast switching of SiC devices which can lead to EMI issues, insulation stress and motor terminal overvoltage [12].…”

“…Towards these targets, propulsion inverters have been evolving by employing emerging technologies such as Silicon Carbide (SiC) devices and multilevel topologies. [2] reported a novel solution employing all-Silicon-Carbide (all-SiC) and four-level active neutral point clamped (4L-ANPC) topology [3], [4], which employs mature 1200/1700V SiC halfbridge modules to realize an efficient power conversion with a 1200V dc-link voltage. However, [2], [4] revealed that the power loss distribution among devices in this configuration is significantly uneven, which is the inherent property of the 4L-ANPC topology.…”

“…[2] reported a novel solution employing all-Silicon-Carbide (all-SiC) and four-level active neutral point clamped (4L-ANPC) topology [3], [4], which employs mature 1200/1700V SiC halfbridge modules to realize an efficient power conversion with a 1200V dc-link voltage. However, [2], [4] revealed that the power loss distribution among devices in this configuration is significantly uneven, which is the inherent property of the 4L-ANPC topology. This uneven loss distribution is undesirable in multilevel converters as established in [5]- [11], which poses challenges in the thermal design and limits the converter performance.…”

Linear Control Compensator for a Variable-Transformer in Wide-Voltage Power Converters

“…Several alternatives have been proposed being the multilevel converters one of the most popular. This solution is characterized by the ability to turn off and on power cells to supply and vary either voltage or current [3]. However, when the variations required are wide, more cells and control signals are required, making the converter implementation complex.…”