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In hydrogen production, AC‐DC rectifiers must provide a high current and low voltage to the production load. This paper focuses on the efficient performance and elimination of the output ripple in these AC‐DC rectifiers. Unfortunately, efforts to reduce the current ripple often lead to lower efficiency, causing a contradiction. To address this issue, a low‐ripple high‐efficiency AC‐DC rectifier with an auxiliary compensator is proposed in this paper. The proposed rectifier can maximise efficiency while eliminating the current ripple, including the switching ripple and low‐frequency ripple. By incorporating a rectifier‐chopper and a buck circuit with a series‐connected capacitor, the auxiliary compensator, the solution provides an additional flow path for the current ripple at the rectifier output, successfully preventing the ripple from being output to the load. This paper offers a thorough exposition regarding the causative factors and sources of the switching and low‐frequency ripple. Furthermore, a detailed explication of the operating principle of the proposed rectifier system is provided. The losses and costs associated with auxiliary compensators are then analysed for persuasive purposes. Finally, simulation and experimental results verify the feasibility and superiority of the proposed rectifier. [ABSTRACT FROM AUTHOR]

In the case of grid voltage quality problems, the traditional phase‐locked loop (PLL) is hard to detect the accurate grid frequency and phase during the transient response, which will be detrimental to the transient synchronous stability of grid‐connected inverters. This paper proposes a mode switching based transient ride‐through PLL (TRT‐PLL), aiming to improve the transient phase‐locking performance through detection technique and mode switching. The TRT‐PLL incorporates a hybrid filter (HF), a dual‐speed detection module, and a state switch into the traditional synchronous reference frame PLL (SRF‐PLL) structure. The theoretical analysis and paradigm design of TRT‐PLL is presented in detail. Digital simulations and physical experiments are carried out for the comparisons with other existed PLL techniques. The results demonstrate that the satisfied transient performance of the TRT‐PLL has significant advantages, especially in the event of phase jumps. [ABSTRACT FROM AUTHOR]

Voltage source converter (VSC)‐based high‐voltage dc (HVDC) transmission is widely utilised nowadays. However, a VSC‐HVDC connected to a weak ac system still faces the problem of phase‐locked loop (PLL) synchronisation. To tackle this problem, this study proposes a dc voltage synchronisation control (DCSC) based on the power synchronisation control and the power balance equation of the virtual synchronous generator. To analyse the dynamic stability of DCSC, voltage sensitivity indicator (VSI) is used to reflect the voltage fluctuations. Considering the deviations of dc voltage and converter losses, a closed‐loop transfer function of dc voltage is designed. Three important parameters including VSI, virtual damping coefficient and inertia time constant are investigated. The dynamic stability analysis shows DCSC has strong controllability. Then, a three terminals VSC‐MTDC model is simulated in PSCAD/EMTDC. Herein, DCSC is used in one inverter and PLL is used in another inverter. The waveforms obtained by using DCSC are compared with that by using PLL. Simulation results clearly depict that the inverter with DCSC has a normal steady state and a better transient response than using PLL when connected to a strong ac system, also provides better power transfer capability when connected to a weak ac system. [ABSTRACT FROM AUTHOR]

Pumped-storage hydropower plants can contribute to a better integration of intermittent renewable energy and to balance generation and demand in real time by providing rapid response generation. The utilisation of variable-speed pump-turbine units with a doubly fed induction machine is being progressively applied due to its overall efficiency and high level of operating flexibility. This study presents state-of-the-art pumped energy storage system technology and its AC–DC interface topology, modelling, simulation and control analysis. It also provides information on the existing global capacities, technological development, topologies and control strategies of the pumped-storage system. This report also outlines the analysis of dynamic performances of the system. It also attempts to recommend the future works in this area. This study concludes that pumped storage is the most suitable technology for small autonomous island grids and massive energy storage, where the energy efficiency of pumped storage varies in practice. Around the world, the size of the pumped-storage plant mostly lies in the range of a small size to 3060 MW. The back-to-back voltage source converter topology is mostly conducted due to its significant features. Due to its imperative features, the vector control strategy is widely used. The pumped-storage plant is dedicated to power management and stability regulation of grid and isolated power systems. [ABSTRACT FROM AUTHOR]

A hierarchical distributed control method for I–V droop‐controlled‐paralleled DC–DC converters in DC microgrid is proposed. The control structure includes primary, secondary, and tertiary levels. The secondary control level is used to remove the DC voltage deviation and improve the current sharing accuracy. An improved dynamic consensus algorithm is used in the secondary control to calculate the average values of bus voltage and voltage restoration in distributed control. In the tertiary control level, as the main contribution in this study, the system conversion efficiency is enhanced by using the average restoration value obtained in the secondary control level, instead of using the total load current which needs more communication traffic. When the converters are connected to batteries, the method for the state of charge (SoC) management is proposed so that the SoC balance can be guaranteed. The effectiveness of the proposed method is verified by detailed experimental tests based on four 0.7 kW DC–DC converters. [ABSTRACT FROM AUTHOR]