Abstract
An inductive wireless power transfer system is proposed as a power supply for an on-line monitoring system for an overhead catenary. Because of the high voltage (25 kVrms) applied to the catenary, galvanic isolation was required to supply power to the attached monitoring system. The proposed wireless power system was able to transmit 50 W over a distance of 60 cm at 6.78 MHz. Design methodologies for the transmitter and the receiver coils, 6.78-MHz GaN-based full-bridge inverter, and rectifier are proposed in this paper. Pareto optimality, a multi-objective optimization technique, was used to determine optimal solutions in terms of efficiency and copper usage. A 100-W, 6.78-MHz full-bridge inverter was developed using 100 V, 35 A, E-HEMT GaN MOSFETs. Because of the high operating frequency, two factors were considered in the design of the full-bridge inverter, (1) close placement of the gate driver and the switch to minimize parasitic inductance and the resulting fluctuation of the drive signal and (2) effective heat dissipation from the switches and gate drivers for a high power rating. In addition, a full-wave rectifier was built using Schottky barrier diodes with a reverse recovery time of a few tens of nano-seconds. The developed wireless power system was experimentally evaluated. The measured coil-to-coil efficiency was 77%, and the measured efficiencies of the inverter and the rectifier were 92% and 93%, respectively. The overall system efficiency was 57% for a transfer of 47 W. Finally, the dependences of the efficiency on the distance, operating frequency, and load were evaluated.
Highlights
Applications of inductive wireless power transfer (WPT) technology have transitioned from W level biomedical devices to MW level transportation systems [1,2,3,4,5,6,7,8]
∗ ww ∗achieved tt proposed methodology, a 95% coil-to-coil efficiency at a distance of 30 cm and 3.74-MHz where, ωω0 is the operating frequency of the system, M is the mutual inductance between the transmitter and the receiver, RR1 and RR2 are the equivalent series resistances (ESRs) of the transmitter and the receiver coils, respectively, RRLL is the load resistance of the system, ρρ is the density of the copper, ll, ww and t are the total length, width, and the thickness of the coil trace, respectively
Mass (m) = ρ ∗ l ∗ w ∗ t where, ω0 is the operating frequency of the system, M is the mutual inductance between the transmitter and the receiver, R1 and R2 are the equivalent series resistances (ESRs) of the transmitter and the receiver coils, respectively, R L is the load resistance of the system, ρ is the density of the copper, l, w and t are the total length, width, and the thickness of the coil trace, respectively
Summary
Applications of inductive wireless power transfer (WPT) technology have transitioned from W level biomedical devices to MW level transportation systems [1,2,3,4,5,6,7,8]. Application that the WPT system is useful as a power supply: an on-line monitoring system for a high-voltage catenary (see Figure 1a) [9]. Because of the high-voltage (25 kVrms ) of the catenary, the monitoring system cannot obtain power from a low-voltage grid (110 Vrms or 220 Vrms ) without having a sufficient insulation or isolation gap. 25-kVrms overhead wire and ground is 25 cm (30-cm isolation distance is recommended). This is the reason that the lengths of the insulators used for 25-kVrms catenaries are longer than 30 cm (60 cm or longer insulators are common). It is converted to a 6.78-MHz AC voltage and supplied to the transmitter (TX) coil using a GaN-based H-bridge inverter.
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