The Benefits of SiC <sc>mosfet</sc>s in a T-Type Inverter for Grid-Tie Applications

Abstract

It is well known that multilevel converters can offer significant benefits in terms of harmonic performance and reduced switching losses compared to their two-level counterparts. However, for lower voltage applications the Neutral-Point-Clamped (NPC) inverter suffers from relatively large semiconductor conduction losses because the output current always flows through two switching devices. In contrast, the T-Type multilevel inverter has less conduction losses because only a single outer loop switching device is required to connect the converter output to the upper and lower DC buses, albeit at the expense of increased switching losses since these outer switches must now block the full DC link voltage. Silicon Carbide (SiC) MOSFET devices potentially offer substantial advantage in this context with their lower switching losses, but the benefit of replacing all switching devices in a T-Type inverter with SiC MOSFETs is not so clear-cut. This paper now explores this issue by presenting a detailed comparison of the use of Si and SiC devices for a three-level T-Type inverter operating in grid-tie applications. The study uses datasheet values, switching loss measurements and calibrated heat sink thermal measurements to precisely compare semiconductor losses for these two alternatives for a T-Type inverter operating at or near unity power factor. The results show that replacing only the DC bus connection switches with SiC devices significantly reduces the semiconductor losses, allowing either the converter power level or the switching frequency to be significantly increased for the same device losses. Hence the use of SiC MOSFETS for T-Type inverters can be seen to be an attractive and potentially cost effective alternative, since only two switching devices per phase leg need to be upgraded.

Improved Space Vector Modulation for Neutral-Point Balancing Control in Hybrid-Switch-Based T-Type Neutral-Point-Clamped Inverters With Loss and Common-Mode Voltage Reduction

“…To reduce the system complexity as well as improve the output THD performance, M 1 , M 4 , Q 2 , Q 3 , D 2 and D 3 in hybrid structure 1 are selected to operate, and the new structure is shown in Fig. 3 [21]. The hybrid structure 2 utilizes Si IGBT and SiC Schottky diode as clamping leg switches and SiC SiC MOSFET: Si IGBT:…”

“…3. T-type inverter with hybrid switch structure 2 [21]. the clamping leg, neutral point balancing (NPB) [22]- [25] and the common-mode voltage (CMV) performance.…”

“…For switching loss reduction [21] and NPB [22]- [25] in 3 phase 3-L TNPC inverter with hybrid switch combination, SVM 1 with NPB [23], SVM 2 with NPB [24], and improved SVM 2 with NPB are compared, and 1st sector of the space vector modulation hexagon is given as an example. The nearest three space vector (NTSV) [26] and discontinuous pulse width modulation (DPWM) [27] are adopted to track the reference vector and further reduce the switching loss.…”

A High-Power-Density Single-Phase Rectifier Based on Three-Level Neutral-Point Clamped Circuits

“…Along with the development of semiconductor technology, new Wide Band Gap (WBG) semiconductor devices such as SiC devices have gradually come into view [10][11][12][13][14]. SiC devices enjoy a higher bandgap energy, a higher critical electric field, a higher saturation velocity, and superior thermal conductivity directly in comparison with Si devices, which means SiC devices have lower switching loss and no reverse recovery.…”

Analytical and Simulation Fair Comparison of Three Level Si IGBT Based NPC Topologies and Two Level SiC MOSFET Based Topology for High Speed Drives

“…Furthermore, the T-NPC inverters incorporate additional advantages such as lower conduction losses when compared with the NPC inverter, being the better choice for low voltage applications [12,13].Most of the state-of-the-art comparisons between the SiC metal-oxide-semiconductor field-effect transistor (MOSFET) and Si IGBT based inverters are done on the device level or in 2L VSIs [14,15] or hybrid topologies such as the H8 inverter [16]. Recently, also some multilevel Si IGBT based, SiC MOSFET based, or gallium nitride (GaN) based topologies have been compared, such as the single phase T-type inverter [17,18], advanced inverter topologies [19], or the single phase two stage decoupled active neutral point clamped (NPC) converter [20]. Generally, inverters with GaN and SiC MOSFET devices have shown benefits when compared to their Si counterparts such as lower losses, high efficiency at high frequency applications, reduced volume of the heat sink and output filter, etc.A similar comparison was introduced in [21], where the 2L SiC inverter was compared with the 3L NPC inverter in terms of overvoltages and power losses, having the same output current total harmonic distortion (THD) and the same output voltage capabilities.…”