Silicon (Si) insulated-gate bipolar transistors are widely used in railway traction converters. In the near future, silicon carbide (SiC) technology will push the limits of switching devices in three directions: higher blocking voltage, higher operating temperature, and higher switching speeds. The first silicon carbide (SiC) MOSFET modules are available on the market and look promising. Although they are still limited in breakdown voltage, these wide-bandgap components should improve traction-chain efficiency. Particularly, a significant reduction in the switching losses is expected which should lead to improvements in power-weight ratios. Nevertheless, because of the high switching speed and the high current levels required by traction applications, the implementation of these new modules is critical. An original method is proposed to compare, in terms of stray inductance, several dc bus-bar designs. To evaluate the potential of these new devices, a first set of measurements, based on a single-pulse test-bench, was obtained. The switching behavior of SiC devices was well understood at turn-off and turn-on. To complete this work, the authors use an opposition method to compare Si-IGBT and SiC-MOSFET modules in voltage source inverter operation. For this purpose, a second test-bench, allowing electrical and thermal measurements, was developed. Experimental results confirm the theoretical loss-calculation of the single-pulse tests and the correct operation of up to three modules directly connected in parallel. This analysis provides guidelines for a full SiC inverter design, and prospects for developments in traction applications are presented.

Today, in Electric Railways, the old DC supply systems are reaching their limits. To improve their efficiency and increase railroad traffic, a new DC Electrification has recently been proposed at 9-kV. It is now necessary to prepare the migration of infrastructure and rolling stock, using Power-Electronic-Transformers (PETs), for adaptation to this voltage level. For this application, high efficiency and reduced volume are essential. This paper clearly demonstrates that it is now possible to achieve compact, high-power, isolated DC-DC converters using 3.3-kV SiC-MOSFET power modules with high efficiency. After a preliminary study based on simulations, the paper focuses on characterization and implementation of elementary isolated DC-DC converters. The proposed topology is a series-resonant converter rated for a nominal power of 300-kW at 1.8-kV. First, laboratory testing using an “opposition-method” is used to evaluate the elementary converters up to their nominal power using both electrical and thermal measurements to accurately determine losses and efficiency. At the nominal output power, an efficiency of 98.93% is obtained. This is quite remarkable for an isolated DC-DC converter operating under 1.8-kV with a switching frequency of 15-kHz. Finally, two elementary isolated DC/DC converters are associated in ISOP configuration (Input Seriesed/Output Paralleled) in order to achieve a 3-kV/1.5-kV PET with a nominal power of 600-kW as a prelude to the final 9-kV/1.5-kV power conversion.

Silicon (Si) insulated-gate bipolar transistors (IGBTs) are widely used in power converters. Silicon carbide (SiC) technology will push the limits of switching devices in three directions: higher blocking voltage, higher operating temperature, and higher switching speed. The first SiC-metal-oxide-semiconductor field-effect transistor (MOSFET) half-bridge modules (SiC HBM) are now commercially available and look promising. Although they are still limited in breakdown voltage, these components should, for instance, improve traction-chain efficiencies. In particular, a significant reduction in switching losses is to be expected which should lead to improvements in power-to-weight ratios-of particular interest for rolling-stock. Nevertheless, because of the high switching speed and the high current levels required by traction applications, the implementation of these modules is critical. In this paper, the authors investigate the parallel connection of SiC HBM with a focus on traction equipment. The key points are underlined and an original approach is proposed to design the bus-bar and the gate-drive circuit. Experimental results performed on an opposition method test bench, valid the correct operation of three SiC modules in parallel.

Currently, in electric railways, the old dc supply systems are reaching their limits. In several European railway networks, due to the line-voltage drops between substations, there are several sectors where traffic can no longer increase and where locomotives cannot operate at their nominal ratings. To improve the power capacity, a medium voltage dc (MVdc) three-wire supply system with voltage boosters based on imbricated cell multilevel choppers (ICMC) was proposed. In order to increase efficiency, the authors evaluate the potential of new SiC-mosfets in this topology. An opposition method test bench using two ICMCs was built with 1.7-kV/300-A half-bridge modules. The design of the multilevel converters takes into account the constraints related to high switching frequency operation (up to 50 kHz). Thanks to the opposition method, losses in ICMCs can be determined by electrical and thermal measurements with good accuracy. Finally, solutions with SiC-mosfets and Si-insulated gate bipolar transistors are compared in terms of efficiency.

Silicon (Si) IGBTs are widely used in railway traction converters. In the near future, Silicon Carbide (SiC) technology will push the limits of switching devices in three directions: higher blocking voltage, higher operating temperature and higher switching speed. The first SiC MOSFET modules are available on the market and look promising. Although they are still limited in breakdown voltage, these wideband-gap components should improve traction-chain efficiency. Particularly, a significant reduction in the switching losses is expected which should lead to improvements in power-weight ratios. Nevertheless, because of the high switching speed and the high current levels required by traction applications, the implementation of these new modules is critical. In this paper, the authors focus on the parallel connection of Dual-SiC MOSFET modules. The key points are underlined and an original approach is proposed to design the bus-bar and the gate drive circuit. Experimental results performed on an Opposition Method test-bench, valid the good operation of three Dual-SiC MOSFET modules in parallel.

The 25-kV/50-Hz ac single-phase supply is a widely used railway system in France with a length of 9,698 km. Overhead lines are supplied by substations drawing power from two phases of a three-phase utility. They behave as nonlinear and time-varying loads and represent one of the most important sources of voltage unbalance for the electricity-transmission network. In the case of weak networks, railway operators are required to install compensation systems in substations to satisfy utility regulations and to avoid penalties regarding voltage unbalance and reactive power consumption. The limits are established by the energy provider with a view to guaranteeing an acceptable power quality to other customers.