Conventional band-pass filter (BPF)-based damper is commonly employed to damp the vibrations in the drive train caused by turbulent winds. However, for the case of grid disturbances or faults resultant torsional vibrations, the performance of the BPF-based damper can be compromised because of the potential low-frequency vibration modes from grid side. To overcome this shortcoming, low-pass filter (LPF)-based torsional damper was proposed in this study. The theoretical analysis of the two torsional damper was assessed in frequency domain. Performance comparison of the two dampers was conducted through simulations and the proposed LPF-based torsional damper outperformed the conventional one in the presence of unexpected low-frequency vibrations. Results also showed that retuning the BPF by decreasing the quality factor can restore the intended performance of torsional damper.

This paper describes two methods for the short-circuit protection of the LLC resonant converter. One of them uses the voltage across the capacitor and the other uses the voltage across the inductor of the resonant tank. These voltages can be processed (integrated or differentiated) to recover the resonant tank current. The two circuits illustrated in the described methods make it possible to develop a robust LLC converter design and to avoid using lossy current measurement elements, such as a shunt resistor or current transformer. The methods also allow measuring resonant tank current without breaking high-current paths and connecting the measuring circuit in parallel with the inductor or capacitor of the resonant tank. Practical implementations of these indirect current measurements have been experimentally tested for the short-circuit protection of the 1600 W LLC converter.

Q-switched and mode-locked erbium-doped fibre lasers (EDFLs) are demonstrated by using non-conductive graphene oxide (GO) paper as a saturable absorber (SA). A stable and self-starting Q-switched operation was achieved at 1534.4 nm by using a 0.8 m long erbium-doped fibre (EDF) as a gain medium. The pulse repetition rate changed from 14.3 to 31.5 kHz, whereas the corresponding pulse width decreased from 32.8 to 13.8 µs as the pump power increased from 22 to 50.5 mW. A narrow spacing dual-wavelength Q-switched EDFL could also be realised by including a photonics crystal fibre and a tunable Bragg filter in the setup. It can operate at a maximum repetition rate of 31 kHz, with a pulse duration of 7.04 µs and pulse energy of 2.8 nJ. Another GOSA was used to realise mode-locked EDFL in a different cavity consisting of a 1.6 m long EDF in conjunction with 1480 nm pumping. The laser generated a soliton pulse train with a repetition rate of 15.62 MHz and pulse width of 870 fs. It is observed that the proposed fibre lasers have a low pulsing threshold pump power as well as a low damage threshold.