Versatile Three-Level FC-NPC Converter With High Fault-Tolerance Capabilities: Switch Fault Detection and Isolation and Safe Postfault Operation

Abstract

This paper deals with a hybrid fault-tolerant converter topology. It is performed through the connection of a classical three-phase three-level Neutral Point Clamped (3L-NPC) converter with a fourth three-level Flying Capacitor (3L-FC) leg. The 3L-FC leg actively balances the 3L-NPC neutral point voltage. For normal operation mode, this paper proposes a mathematical design of the filter needed to connect these two different topologies. Experimentally, and thanks to the already existing decoupling capacitors of the 3L-NPC converter, this filter requires the addition of only one low size inductance. When one fault of the power switch of the 3L-NPC occurs, the paper proposes hardware reconfiguration technique based on only two fuses and one thyristor per leg allows a safe post-fault operation recovery. This is achieved thanks to a simple faultdetection method and a new technique that combines fault leg isolation and corresponding phase post-fault connection to the neutral point. Also, a dedicated FPGA-based control of the reconfigured converter is synthetized to ensure power system availability under fault operation mode. The converter fault-tolerant capabilities are addressed through simulation results and original overall experimental validations of the fault detection and isolation and the post-fault operation steps, carried out on a 15 kW prototype converter.

Reconfiguration of NPC Multilevel Inverters to Mitigate Short Circuit Faults Using Back-to-Back Switches

“…This method has been used in other power electronic circuits [23], [24] and is a potential method for MLIs' recovery. Researchers have successfully achieved maintaining the inverter output waveform in fault-tolerant mode with a forth leg installed in the NPC inverter [25]- [28]. Even though the complexity is increased, the output waveform is effectively maintained after a failure occurs in one phase.…”

“…The ANPC with fault tolerance ability also has the problem of reduced peak output voltage and it is not applicable to various levels besides a 3-level ANPC inverter [22]. Redundant components [23], [24] and forth leg-based methods [25]- [28] are not cost effective since in MLIs, a large number of additional components is required. For the effective method in [29], complex circuitry and additional components are necessary to isolate the failed device or fault current circulation pass.…”

“…Even though the voltage level is decreased, the unbalanced condition caused by the short circuit fault is resolved with very limited additional components. The redundancy strategy and forth leg methods can maintain the same voltage level in the post-reconfigured condition [25]- [28], but many more additional components and complicated control strategies are necessary when compared to the proposed method. The ANPC can achieve balanced phase-to-phase voltage without additional components, but it disables the remaining healthy components in the failed leg which is not cost effective.…”

“…The component-level redundancy (CLR) strategy [23], [24] is not feasible for MLIs since the number of semiconductor devices is very large. The forth-leg-based (FLB) method [25]- [28] has a redundant phase leg, which is not cost effective. The method of utilizing fuses to isolate a faulty device (FUI) [29] has many of add-on components, complex control and extra stress on the remaining healthy devices.…”

FPGA-Based Controller for a Permanent-Magnet Synchronous Motor Drive Based on a Four-Level Active-Clamped DC-AC Converter

“…FPGAs have been employed for implementing diverse control schemes of multilevel converters ( [11][12][13][14][15][16][17][18][19][20][21]), and also for implementing motor-drive controllers ( [17][18][19][20][21][22][23][24][25][26]). References [17][18][19][20][21] propose FPGA-based controllers for multilevel converters operating as motor drives, as it is proposed here.…”