As the critical barriers to advanced high-temperature superconducting (HTS) device technologies are overcome, practical HTS devices and systems have been enabled and become available for commercial application. In identifying the applicability of various HTS devices, their operation principles, characteristics, performance, and efficiency are fundamental. Consequently, the corresponding verification of a wide range of HTS devices, especially the HTS power devices and their system technologies, has been comprehensively carried out, and the analytical results are presented in detail towards their practical applications.

The weakness of low voltage ride-through capacity, power oscillations under asymmetrical fault and the instability of the output power are three major difficulties that need to be urgently addressed in the field of doubly fed induction generator (DFIG). To simultaneously deal with these issues, this paper proposes a cost-effective energy storage device-based unified power quality conditioner (ESD-UPQC) to improve the low voltage ride through capability of the DFIG, suppress voltage oscillations under unbalanced faults and regulate DFIG output power during fluctuated wind speed conditions. A comprehensive protection scheme is carried out that the series side converter of the ESD-UPQC is controlled using dual control to suppress the post-fault voltage oscillations under transient conditions, while three advanced control targets are proposed for the parallel side converter aiming at regulating DFIG output power during wind gust, and suppress power oscillations during symmetrical and asymmetrical grid faults. Simulation results attest the feasibility of the proposed controller. The robustness of the proposed ESD-UPQC controller is validated through a series of comparisons based on a lead-acid battery scheme and an ESD-DFIG scheme for power smoothing and LVRT enhancement respectively.

Wind energy is one of the premier renewable energy sources that have gained popularity during the last decade. Among the currently available wind energy conversion systems (WECS), doubly fed induction generator-based technology has been widely employed due to its superior advantageous. The key features of the DFIG-based WECS include its ability to capture more wind energy and support the grid with large reactive power during short disturbance events. On the other hand, DFIG is very sensitive to grid faults which affect its fault ride through (FRT) capability. Furthermore, extreme wind gust even for short durations may lead to the violation of the low voltage ride through (LVRT) threshold limits set by worldwide transmission line operators. This situation cannot be mitigated by the turbine blades pitch controller since the response of the pitch mechanical control is much slower than the rapid dynamic change in the wind speed during short duration of wind gust events. While DFIG FRT capability has been discussed in several papers in the literature, not much attention was given to the mitigation of the effects of extreme wind gust of short duration on the DFIG performance. In this paper, the effect of various levels of wind gust on the performance of a DFIG-based wind energy conversion grid-connected system is investigated and mitigated using a new controller for superconducting magnetic energy storage (SMES) unit. A combination of hysteresis current and fuzzy logic controllers is employed to control the voltage source converter and the DC-DC chopper interfacing the SMES coil with the investigated system. Simulation results reveal the effectiveness of the proposed SMES controller that can be easily implemented within existing as well as new WECS installations.

The limitation of theDC protection device confines the development of MV/LVDC grids. This paper presents a DC dynamic voltage restorer to exploit DC custom power devices for DC distribution networks in principle. It is based on an improved AC/DC dual active bridge and battery energy storage to maintain the voltage profile of sensitive loads in DC networks. The principle of the improved DC-DVR has been analyzed from the perspectives of the range of compensated voltage, current characteristics, and control strategy. Compared with other existing methods, the proposed DC-DVR features a simple structure, an easy control strategy, and the ability to mitigate both voltage sag and swell by injecting forward or reverse voltage. Experiment results demonstrate the correctness of the theoretical analysis and the feasibility of the proposed structure. A case study of DC doubly-fed induction generator (DFIG) interfaced with power grid is carried out, integrated with the proposed DC-DVR to verify the operation principle of the proposed scheme.

AbstractWith regard to the state-of-the-art technologies in the fields of applied superconductivity and electromagnetic devices, research and development highlights are presented. The recent progress and achievement described with principle and technical details include mainly i) applied superconducting materials; ii) superconducting magnets and their applications such as in ITER and Tokamaks; iii) high Tc superconducting (HTS) magnetic levitation and applications; iv) HTS smart grids; v) superconducting and electromagnetic material modelling and characteristics; vi) advanced electromagnetic devices. The applied superconductivity technology and availability are especially focused and verified with the trend of its development prospection.

Wind Turbine Generator (WTG) has become one of the most popular renewable-based power generation that is broadly connected to electricity grids worldwide. Till the year 2019, the total WTGs installed worldwide reached about 650.8GW. The WTG is interfaced to the electricity grid through power electronic converters with a proper control algorithm to facilitate a smooth power delivery as well as maintaining the system voltage and frequency stability during wind intermittency. However, power grids are usually subjected to load expansion which affects the stiffness of the grid and hence its stability. A weak electricity grid exhibits voltage instability that may affect the performance of WTGs and in some cases may lead to serious damages to the wind turbines and the entire system. In this paper, superconducting magnetic energy storage (SMES) technology based on fuzzy logic controller is implemented to effectively resolve this issue and improve the overall performance of WTGs. Hysteresis current and fuzzy logic-based control system is proposed to control the energy exchange between the SMES coil and the investigated system. Results show the effectiveness of the SMES to improve the overall system performance and along with the fault ride-through capability of the doubly-fed induction generator (DFIG).