To counteract a potential reduction in grid stability caused by a rapidly growing share of intermittent renewable energy sources within our electrical grids, large scale deployment of energy storage will become indispensable. Pumped hydro storage is widely regarded as the most cost-effective option for this. However, its application is traditionally limited to certain topographic features. Expanding its operating range to low-head scenarios could unlock the potential of widespread deployment in regions where so far it has not yet been feasible. This review aims at giving a multi-disciplinary insight on technologies that are applicable for low-head (2-30 m) pumped hydro storage, in terms of design, grid integration, control, and modelling. A general overview and the historical development of pumped hydro storage are presented and trends for further innovation and a shift towards application in low-head scenarios are identified. Key drivers for future deployment and the technological and economic challenges to do so are discussed. Based on these challenges, technologies in the field of pumped hydro storage are reviewed and specifically analysed regarding their fitness for low-head application. This is done for pump and turbine design and configuration, electric machines and control, as well as modelling. Further aspects regarding grid integration are discussed. Among conventional machines, it is found that, for high-flow low-head application, axial flow pump-turbines with variable speed drives are the most suitable. Machines such as Archimedes screws, counter-rotating and rotary positive displacement reversible pump-turbines have potential to emerge as innovative solutions. Coupled axial flux permanent magnet synchronous motor-generators are the most promising electric machines. To ensure grid stability, grid-forming control alongside bulk energy storage with capabilities of providing synthetic inertia next to other ancillary services are required. 

Low-head pumped hydro storage: A review of applicable technologies for design, grid integration, control and modelling

Assessment and control of wind turbine by support vector machines

Wind and wave energy are the main forms of offshore energy. In this study, a new joint wind and wave energy (JWWE) power conversion system, which simultaneously features wind power generation and wave power generation, is investigated. In the JWWE power generation system, a dual-stator linear and rotary permanent magnet generator (DSLRPMG) is employed to directly convert the wind and wave energy. The topology and operating principles of the power generation system are analysed, and the rectifier topology with two three-phase bridge converter is introduced for the JWWE power generation system. On the basis of the vector control method, the mathematical model of the DSLRPMG is deduced. The virtual flux direct power control method without any AC voltage sensors is applied for the power generation system. A new decoupling control method including flux decoupling and power decoupling is proposed and analysed. Meanwhile, an experimental setup is constructed, and the experiments are done. Both the simulation and experimental results show the validity and correctness of the control strategy.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-epa.2019.0719

Decoupling control of a dual-stator linear and rotary permanent magnet generator for offshore joint wind and wave energy conversion system

The main share in the annual electricity generation wind farms provides during periods when the wind speed exceeds 8 m/s. Therefore, when designing a synchronous generator of wind power plants, it is necessary to provide maximum efficiency for rotor speeds corresponding to such values of wind speed. In generators of wind turbines or micro hydroelectric power stations, it is advisable not to observe the known ratio of the equality of constant and variable losses. The ratio ensures the maximum efficiency in the nominal regime. To increase the energy efficiency of the installation, the generator should be specifically designed. Thus, the maximum efficiency point of the generator is shifted to the zone of maximum loads and rotation frequencies - to the right of the nominal point.

Energy Efficiency of the Wind Power Generator

Power generation of small wind turbine: Under high-speed operation

Design, modeling and simulation of variable speed Axial Flux Permanent Magnet Wind Generator

Wind energy systems with permanent magnet generators, especially axial flux permanent magnet generators (AFPMG), have been quite popularly studied and employed recently. However, a known shortcoming of such systems is that they can operate efficiently only in a very limited range of wind speeds, which corresponds to about 70 to 110% of the rated speed of the generator employed and the energy available outside of this wind speed bracket is not accessed at all, and in fact, wasted. Moreover, the absence of any means of excitation control to maintain a regulated output voltage under varying speed conditions calls for expensive power converters. This study presents a novel methodology to obtain a constant output voltage from an AFPMG under varying wind conditions, through the integration of field poles and their control, along with modifications in stator winding. This significantly enhances the power extraction capability of the system over a much wider operational range (corresponding to 25–125% of the rated speed) while eliminating the requirement of a DC–DC converter to maintain constant output voltage. The details of the design of the constant voltage AFPMG and the results establishing the effectiveness of the methodology have also been presented.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-rpg.2016.0384

Manik Singh

Papers

Design, modeling and simulation of variable speed Axial Flux Permanent Magnet Wind Generator

Design of a novel field controlled constant voltage axial flux permanent magnet generator for enhanced wind power extraction