The use of distributed energy resources is increasingly being pursued as a supplement and an alternative to large conventional central power stations. The specification of a power-electronic interface is subject to requirements related not only to the renewable energy source itself but also to its effects on the power-system operation, especially where the intermittent energy source constitutes a significant part of the total system capacity. In this paper, new trends in power electronics for the integration of wind and photovoltaic (PV) power generators are presented. A review of the appropriate storage-system technology used for the integration of intermittent renewable energy sources is also introduced. Discussions about common and future trends in renewable energy systems based on reliability and maturity of each technology are presented

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Power-Electronic Systems for the Grid Integration of Renewable Energy Sources: A Survey

Due to the stochastic nature of wind, electric power generated by wind turbines is highly erratic and may affect both the power quality and the planning of power systems. Energy Storage Systems (ESSs) may play an important role in wind power applications by controlling wind power plant output and providing ancillary services to the power system and therefore, enabling an increased penetration of wind power in the system. This article deals with the review of several energy storage technologies for wind power applications. The main objectives of the article are the introduction of the operating principles, as well as the presentation of the main characteristics of energy storage technologies suitable for stationary applications, and the definition and discussion of potential ESS applications in wind power, according to an extensive literature review.

A review of energy storage technologies for wind power applications

Energy storage for mitigating the variability of renewable electricity sources: An updated review

Review of energy storage system for wind power integration support

Virtual synchronous generators: A survey and new perspectives

Distributions of stress in force-balanced coils (FBCs) for the superconducting magnetic energy storage (SMES) are analyzed numerically by a finite element method (FEM). Recently, we had developed the FBC concept using the virial theorem, and derived the winding pitch of helical coils as a function of the coil aspect ratio, where the distribution of stress is nearly uniform and working stress is minimized. Coils with the winding pitch were named as FBCs with the virial-limit condition or simply virial-limit coils (VLC), and their excellent characters of stress were confirmed by experiments of a two-layered helical coil which can simulate arbitrary winding pitch numbers. Measurements of distributions of stress on the winding form of the coil proved that a minimum working stress and uniform stress were achieved under the VLC condition. In this paper, stress distributions in FBCs with a monolithic winding form were investigated by FEM, and the results by FEM were compared with the experiments and the analytic solutions of a two-dimensional ideal shell model. Although the shell model could not explain the experimental results, qualitative agreements between FEM and the experiment were obtained.

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FEM analysis of stress distribution in force-balanced coils

A one tenth sized model coil based on the force-balanced coil (FBC) design for 100-MJ class SMES has been designed. This coil is a hand-made coil using NbTi superconductors, and the winding of the model FBC is now in progress. The FBC is a helically wound hybrid coil of toroidal field coils and a solenoid. This coil can minimize the mechanical stress and the required mass of the structure for induced electromagnetic forces. The model FBC with an outer diameter of 0.53 m will have the stored energy of 270 kJ at the maximum magnetic field of 7.0 T. The winding form is made of aluminum alloy and slots are cut on its surface with the shape of the helical winding. From the results of the cooling test with liquid nitrogen, the significant deformations of the winding form have not been observed. The winding of the model coil is carried out without reinforcing materials for the NbTi strand. The in-plane curvature of helical coils causes the winding errors. Then after a slight winding tension is applied to the NbTi strand, each winding is adjusted to be fixed in its place. The experiments will be conducted with liquid helium cooling. The DC power supply for the model FBC can simulate various SMES operations. As a first step, the ramp-rate dependence of the superconducting properties of the model coil will be investigated in order to evaluate the mechanical stress in the helical windings without the reinforcing materials for the NbTi strand.

Development of a One Tenth Sized Model Coil for 100-MJ Class SMES Using Force-Balanced Coil Concept

The objective of this work is to discuss the concept of back-to-back interconnection systems with energy storage, especially with a Superconducting Magnetic Energy Storage (SMES) incorporated into a back-to-back DC link. In this case, each converter of the back-to-back system is used as a power conditioning system for the SMES coils. Since the AC–DC converter can be designed independently of the frequency of the power system, a two-way switch is connected to the AC side of each converter. This two-way switch can select the interconnected power systems. By using the two-way switches, this system can provide the stored energy in the SMES system to each interconnected power system through two AC–DC converters. For instance, lower-cost power of each power network can be stored through two converters during the off-peak hours and made available for dispatch to each power network during periods of demand peak. Then this system increases the reliability of electric power networks and enables the economical operations depending on the power demand. This paper describes the unique operations of the back-to-back interconnection with SMES and discuses the optimal SMES configuration for a 300-MW-class back-to-back interconnection. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(2): 37–43, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20482

Interconnected power systems with superconducting magnetic energy storage

A heterodyne polarimeter which measures the Faraday effect has been under development as a magnetic field sensor for long-pulsed fusion devices. The wavelength of laser beam was chosen to be 850 nm since the radiation-induced loss in optical fibers is significant below 800 nm while the Faraday rotation angle decreases with increasing wavelength. By the use of a distributed Bragg reflector laser diode and a Faraday isolator, excellent stability of phase measurement was attained. The phase resolution was raised to up to 0.02° by the digital complex demodulation and digital bandpass filtering of beat signals. Although the Verdet constant of heavily Tb3+-doped paramagnetic glass is larger than that of ZnSe by about a factor of 1.4, ZnSe is superior to the former in terms of negligible temperature dependence. With a 40-mm-long ZnSe sensing rod, resolutions of the magnetic field strength of about 5 and 2 G were found to be possible with time responses of 1 and 10 ms, respectively.

Fiberoptic heterodyne magnetic field sensor for long-pulsed fusion devices

Force-Balanced Coil (FBC) is a helically wound toroidal coil that can minimize the required mass of its structure by selecting an optimal number of poloidal turns per toroidal turn. A 7-T Force-Balanced Coil (7-T FBC) was designed in order to demonstrate the feasibility of the FBC concept for high field superconducting magnets. The 7-T FBC with an outer diameter of 0.53 m will have 270-kJ stored magnetic energy at maximum magnetic field of 7.0 T. This coil is a hand-made coil using NbTi superconductor. The maximum working stress of the 7-T FBC is lower than the elastic limit of the Cu matrix so that the 7-T FBC can be excited up to the rated magnetic field of 7.0 T without reinforcing materials for the NbTi strand. The winding form is made of aluminum alloy and slots are cut on its surface with the shape of the helical winding with a numerically controlled (NC) lathe. The experiments will be conducted with pool boiling liquid helium cooling in order to measure the quench properties of the 7-T FBC and evaluate the working stresses in the helical windings.

Hiroaki Tsutsui

Papers

FEM analysis of stress distribution in force-balanced coils

Development of a One Tenth Sized Model Coil for 100-MJ Class SMES Using Force-Balanced Coil Concept

Interconnected power systems with superconducting magnetic energy storage

Fiberoptic heterodyne magnetic field sensor for long-pulsed fusion devices

Construction of a 7-T force-balanced helical coil