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With the power quality problems of electric railways becoming more and more serious, static VAr compensators (SVCs) have been widely used for power quality management. SVCs can be installed in the low-voltage side of traction substations, the high-voltage side of traction substations or the electric railway power supply side of substations. Different installation positions result in different compensation effects. In this study, characteristics of harmonic and negative sequence currents in the low-voltage and high-voltage sides of traction substations are analysed theoretically. Four schemes with SVCs in different installation positions are proposed. Then based on the measured datum and waveforms, simulation of each scheme is implemented, respectively, using PSCAD/EMTDC software. By comparing the compensation effects of the four schemes, the best SVC installation scheme in the low-voltage side of the traction substation is recommended for the measured traction substation. With SVC, the electric railway will have a less negative effect on the power grid. This study can also be applied to other SVC applications with non-linear loads, such as arc furnaces, rolling mills or electrochemical devices.

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Wide-bandgap (WBG) devices such as Gallium-Nitride (GaN) High Electron Mobility Transistors (HEMTs) have become popular in the power electronics industry as they offer a lower switching loss, higher thermal capability and higher power density than conventional silicon devices. As an attempt of applying WBG devices to the wireless charging technology, this paper adopts two different types of normally-off GaN HEMTs. One adopts the cascode structure provided by Transphorm Inc, operated under 800kHz to charge a battery pack on an electric scooter at 48 V/500W, with the air gap between the transceiver and receiver of ~10cm. The other is enhancement-mode GaN HEMTs provided by GaN Systems Inc, operated at ~6MHz to use one transceiver to charge multiple cell phones @~20W. Both of these chargers have no magnetic cores to reduce the cost and weight. Experimental results show both types of GaN HEMTs significantly increased the charging efficiency over conventional Si devices. Challenges of applying such fast-transition devices are discussed, e.g., common-source inductance and the gate-drive-loop parasitic.

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