An improved hybrid unified power flow controller (IHUPFC) is developed in this paper to control power flow and increase utilization rate of the existing transmission lines. The IHUPFC is composed of an improved "Sen" transformer (IST) and a small capacity UPFC. After a detail introduction of the structure and voltage regulation performance of the IST, this paper derives the capacity relationship between the IST and the UPFC. Then this paper introduces the technology of IHUPFC in power flow regulation and transmission capability improvement. Besides, the advantages of the IHUPFC in performance and structure are analyzed. The IST has simpler structure and larger power flow control area than "Sen" transformer and the IHUPFC provides a continuous active and reactive power flow control. Simulation and experiment studies are used to verify the practicability and superiority of the IHUPFC.

The commercial application of conventional unified power flow controllers (UPFCs) is rare, because of their high installation and operational costs. Sen proposed the “Sen” transformer (ST) that provides similar power flow control functionality as UPFCs, using only a multiwinding transformer and tap changers. However, the ST has output error and response speed issues, due to the discrete characteristics of tap changers. A novel hybrid electromagnetic unified power flow controller (HEUPFC) is proposed. The HEUPFC is composed of a larger capacity ST and a smaller capacity UPFC. The HEUPFC provides economy, flexibility, high reliability, and continuously variable amplitude and phase angle output. The minimum ratio of the magnitude of the series injected voltage from the UPFC is deduced for several center tap cases. The proposed HEUPFC can control the bulk ST power flow with coarse step changes and precise UPFC control, and precisely control active and reactive power flow. Simulation and experimental results were used to verify the practicability of the HEUPFC.

Fast emerging fault current levels in high voltage direct current (HVDC) systems has always been a significant obstacle to building a safer and more reliable grid. Inductive fault current limiters (FCLs), compared with its resistive counterpart, are very effective in restricting the fault rising speed that causes major damage during the whole fault process. In this study, a comprehensive review of the methods used for building inductive type FCLs in HVDC systems is presented. The fault current characteristics of the modern HVDC system is discussed to obtain the basic requirements for the FCL. On the basis of different technological domains, various inductive-type FCL topologies and devices are well categorized and analyzed. After the overall discussion and comparison, representative works, as well as new progress and future prospects, are conveyed in detail. One may find the content of this study helpful as a detailed literature review or a practical technical guidance of this field.

Transmission line sag and voltage are key information to reflect the real-time operation state of power grid. Contactless measurement method has great advantages of no electrical contact, flexibility and mobility, but it is also vulnerable to environmental changes. In this article, a novel overhead transmission line contactless sag and voltage monitoring method is proposed, which only needs a simple potential measurement array and can apply to dynamic conductor measurement. The electrostatic coupling model between the transmission lines and the measuring points is established. The sag and voltage inversion calculation model is proposed and the ill-posed problem is solved. The measurement array and the data acquisition method are designed. The equivalent measurement area (EMA) is determined considering the difference between 3-D model and 2-D model of overhead line. Finally, the effectiveness of the proposed method is verified by single-circuit transmission line simulation and scale-down experiment.

To solve power quality problem in V/V traction power supply system, a novel electrical magnetic hybrid power quality compensation system based on railway power conditioner (RPC) and magnetic static var compensator (MSVC) is proposed in this study. The RPC is only used to transfer active power and suppressing harmonics. The MSVC is used to compensate reactive power and suppress 3rd and 5th harmonic currents. The proposed hybrid compensation system will reduce the capacity as well as the DC‐link voltage of RPC. The principle of negative, reactive and harmonic currents compensation is analysed first. And then, a collaborative control strategy is proposed to make the compensation system have a fast respond speed. At last the simulation and experiment results have verified the proposed structure and its control strategy effectively.

This comprehensive review examines the key role and optimization dispatch of Technical Virtual Power Plants (TVPPs) in the new energy era. This study provides an overview of Virtual Power Plants (VPPs), including their definition, development history, and classification into Technical and Commercial VPPs. It then systematically analyzes optimization methods for TVPPs from five aspects: deterministic optimization, stochastic optimization, robust optimization, and bidding-integrated optimization. For each method, this review presents its mathematical models and solution algorithms. This review highlights the significance of TVPPs in enhancing power system flexibility, improving renewable energy integration, and providing ancillary services. Through methodological classification and comparative analysis, this review aims to provide valuable insights for the design, operation, and management of TVPPs in future power systems.