Fault-Tolerant Control and Isolation Method for NPC-Based AFEC Using Series-Connected 10kV SiC MOSFETs

Abstract

Power Conditioning Systems (PCS) based on three-level converters with series-connected 10kV SiC MOSFETs have gained popularity for medium voltage applications with the increase in distributed energy sources. With the use of Silicon Carbide (SiC), a wide bandgap semiconductor composed of Silicon (Si) and Carbon (C), MOSFET increases in power electronics application due to higher switching frequency operations. A high switching frequency such as 10 kHz or more leads to a reduction in magnetic components' size and the PCS structure's size. Therefore, the smaller, modular, and lightweight PCS can be attained for micro-grid integration, EV charging, or high inertia-dominated power grid applications. The three-level NPC (3L-NPC) inverter using series-connected 10kV SiC MOSFET is a suitable topology for coupling the PCS with the medium-voltage utility grid. The converter's pole sustainability increases with the two series-connected switches, yet the switches are still sensitive and prone to malfunction under various environmental and mechanical causes. Therefore, a meticulous fault isolation and coordination design may be necessary for the front-end converter for possible switch faults in the converter poles. A well-designed fault-tolerant controller may sustain the converter operation under fault conditions while protecting the healthy parts of the converter. Besides, it minimizes the harmful effects of fault on the grid side and increases the system availability. This paper analyzes short and open circuit switch faults that might occur in the PCS. Accordingly, a fault-tolerant method and a fault isolation method are proposed. The proposed methods are verified with Saber™ and the Real-Time Digital Simulator simulation platforms.

Overvoltage Protection of Series-Connected 10kV SiC MOSFETs Following Switch Failures in MV 3L-NPC Converter for Safe Fault Isolation and Shutdown

“…The AC switch comprises two 15 kV SiC MOSFETs and anti-parallel SiC JBS diodes for current regulation, with two 10kV series-connected 15kV SiC MOSFETs serving as a backup to prevent bidirectional current flow in case of primary relay failure [35]. Upstream, a CEF-type fuse rated at 6A and 17.5 kV provides secondary protection [35]. Furthermore, within the PCS, a Metal Oxide Varistor (MOV) safeguards against overvoltage [48]- [49].…”

“…It can detect open switch and short circuit failures within 10µs, which is faster than DC bias and midpoint voltage diagnosis [34]. However, the turn-on switch failure across a single SiC MOSFET in a series-connection cannot be detected instantly using the desat detection [35].…”

“…The turn-on failure across M 11 causes overvoltage during turn-off across series-connected M 12 [35]. The active clamp at the gate terminal turns-on M 12 , thus creating a dead short circuit, which is identified by desat detection [35].…”

“…The turn-on failure across M 11 causes overvoltage during turn-off across series-connected M 12 [35]. The active clamp at the gate terminal turns-on M 12 , thus creating a dead short circuit, which is identified by desat detection [35]. The active clamp has been demonstrated for clamping turn-off voltage after short circuit failure in series-connected 10kV SiC MOS-FETs [36].…”

Voltage Balancing of Series-Connected SiC mosfets With Adaptive-Impedance Self-Powered Gate Drivers

“…Comparatively, although passive VB strategies like using snubbers result in higher loss compared with the above active VB strategies, they are still widely applied in industrial applications thanks to their better reliability and robustness without any closed-loop controlling complexity [18]. Although some novel topologies and energy recycling approaches are put forward to reduce the loss of snubbers, they are still not attractive due to the complex structure, dedicated modulation and limited applicability [19]- [25].…”