Superconductive magnetic energy storage

Technical and economic aspects of large scale superconductive magnetic energy storage are discussed. This paper is a review of a program which has been under way at the University of Wisconsin since 1970. Early work between 1970 and 1976 was primarily involved in proving economic and technical feasibility of the concept The present program deals with component development and detailed design ultimately leading to construction of a large superconducting magnet capable of storing 1000–10,000 MWh. The magnet is a single-layered segmented solenoid of approx. 100 m radius. Energy containment is achieved economically by burying the magnet underground in bedrock tunnels. Magnetic loads are transmitted from the conductor to bedrock through glass fiber reinforced composite struts. The conductor consists of a composite of aluminum and NbTi and is designed for full cryogenic stability in 1.8 K superfluid helium. The dewar-conductor assembly will be rippled in a l m radius of curvature to reduce the hoop stress tension. A Graetz bridge is required to convert the d.c. superconducting current into a.c. current in the three-phase power system. Economic analysis indicates that superconductive magnetic energy storage is competitive with alternative large scale storage schemes for units greater than 1000 MWh size.     

Advanced configuration of superconducting magnetic energy storage

\Superconducting Magnetic Energy Storage (SMES) is very promising as a power storage system for load leveling or a power stabilizer. However, the strong electromagnetic force caused by high magnetic field and large current is a serious problem in SMES systems. To cope with this problem, we proposed the concept of Force-Balanced Coil (FBC), which is a helically wound toroidal coil. The FBC can minimize working stresses by selecting an optimal number of poloidal turns. However, the winding of the FBC has a complex three-dimensional shape that can make the manufacturing of the helical windings difficult. To overcome this difficulty, a helical winding machine was developed. From winding tests, the possibility of the coil construction was demonstrated. Moreover, a small helical coil using high temperature superconductors was designed and fabricated in order to estimate the problems of helical winding technique through the experimental results with liquid nitrogen cooling. This paper describes the design condition of the Force-Balanced Coil in order to reduce structure requirements and proposes a solution to the problems of helical winding technique by using experimental devices.     

Application of magnetic energy storage unit as load-frequencystabilizer

Fast-acting energy storage devices can effectively damp electromechanical oscillations in a power system because they provide storage capacity in addition to the kinetic energy of the generator rotor, which can share the sudden changes in power requirement. The effectiveness of small-sized magnetic energy storage (MES) units (both superconducting and normal loss types) for this application is shown, and means of best utilizing the small energy storage capacity of such units to improve the load-frequency dynamics of large power areas are suggested. The proposed method of improving the load frequency control of power systems has the advantage that it does not require the governor or any other part of the power system to perform any sophisticated control action. The control logic suggested for this purpose takes the area control error as its input and uses inductor current deviation feedback. In a power system with a SMES (superconducting MES) unit, the optimal setting of the integrator gain is altered to a higher value. With the suggested control measure, SMES units of 4-6 MJ capacity would suffice in reducing the maximum deviations of frequency and tie-line power flow by about 40% in power areas of 1000-2000 MW capacity     

Application of magnetic energy storage unit as continuous VArcontroller

It is shown that magnetic energy storage units can simultaneously operate as continuous VAr (volt-ampere reactive) controllers while performing the role of load-frequency stabilizers in electrical power systems. This is achieved by operating the converter in the buck-boost mode with a switched capacitor bank placed across its terminals. The P versus Q modulation ranges of the 12-pulse converter depend on the source inductance, secondary voltage of the input transformers, and output current. Once the input transformer is chosen, the Q modulation range depends on the active power transfer and the current through the inductor at any instant of time. The actual reactive power consumption of the converter is varied continuously, depending on the requirements of the power system, while keeping within the Q-modulation range. Switching of the capacitor bank keeps the required Q consumption of the converter within the available range. It is shown that this mode of control improves the overall performance of the power system in P-f and Q-V loops and obviates the use of any additional VAr compensator in the power area where the SMES (superconducting magnetic energy storage) unit is located     

Impact of superconductive magnetic energy storage on electric powertransmission

The authors demonstrate that a superconductive magnetic energy storage (SMES) system can provide a significant positive impact on electric power transmission. By using SMES, transmission-line loadings during heavy load hours can be reduced if the SMES system is located near the major load. Transmission losses as well as the fuel cost for the losses over a 24 hr period can also be decreased. An SMES scheme, the SMES-DC link, is introduced for energy storage and control of power flow. The operation of this scheme and the benefits it provides are described     

Improvement of synchronous generator damping throughsuperconducting magnetic energy storage systems

Stabilization of a synchronous generator through control of firing angle of the power converters in superconducting magnetic energy storage (SMES) systems is considered. An optimum strategy of the firing angle control is designed so as to eliminate the transients in minimum time. A nonlinear model of a synchronous generator, its governor and exciter systems, and an SMES system connected to the generator terminal is considered. The optimum firing angle control is derived retaining the nonlinearities of the system dynamics. Digital simulation results indicate that the proposed strategy controls the slowly growing as well as first swing instabilities very effectively     

Operation principle and applications of multiterminalsuperconductive magnetic energy storage systems

The basic operation principle of a multiterminal superconductive magnetic energy storage (MSMES) system is introduced. The motivation for developing the MSMES systems is to combine and maximize the flexibility benefits provided by energy storage and the controllability benefits provided by power electronic systems. A MSMES system can be used simultaneously as an energy storage device and a power flow control device. This attribute enables MSMES systems to perform some unique functions in electric power systems. Potential applications of MSMES systems and their impact on solving the problems faced by power systems today are discussed     

Enhancing the utilization of photovoltaic power generation bysuperconductive magnetic energy storage

The authors demonstrate that a superconductive magnetic energy storage (SMES) system can enhance large-scale utilization of photovoltaic (PV) generation. Results show that power output from a SMES system can be used to smooth out PV power fluctuations so that the combined PV/SMES output is dispatchable and free from fluctuations. Power generated from PV arrays is shown to be fully utilized under different weather conditions, and PV penetration is increased to significant levels without adversely affecting the power system. Coupled with PV generation, a SMES system is even more effective in performing diurnal load leveling. A coordinated PV/SMES operation scheme is proposed, and its demonstration under different weather conditions is discussed     

Application of superconducting magnetic energy storage in electrical power and energy systems: a review

Superconducting magnetic energy storage (SMES) is known to be an excellent high‐efficient energy storage device. This article is focussed on various potential applications of the SMES technology in electrical power and energy systems. SMES device founds various applications, such as in microgrids, plug‐in hybrid electrical vehicles, renewable energy sources that include wind energy and photovoltaic systems, low‐voltage direct current power system, medium‐voltage direct current and alternating current power systems, fuel cell technologies and battery energy storage systems. An extensive bibliography is presented on these applications of SMES. Also, some conclusive remarks in terms of future perspective are presented. Also, the present ongoing developments and constructions are also discussed. This study provides a basic guideline to investigate further technological development and new applications of SMES, and thus benefits the readers, researchers, engineers and academicians who deal with the research works in the area of SMES. Copyright © 2017 John Wiley & Sons, Ltd.     

Application of superconductive magnetic energy storage in anasynchronous link between power systems

The concept that superconductive magnetic energy storage (SMES) can be incorporated into a back-to-back DC link is introduced. With an SMES-DC link, an SMES system can be shared between several neighboring power systems. This results in better economics for SMES usage for each participating power system. In addition to SMES operation, an SMES-DC link also allows asynchronous connection and interchange of power between the interconnected systems. It is demonstrated that an SMES-DC link can achieve significant economic benefits over pure power interchange or SMES operation alone. The basic principle of an SMES-DC link, which is able to interconnect any number of neighboring power systems with a single SMES unit, and various interconnected system operation modes are presented. A battery-DC link is discussed and compared with the SMES-DC link     

Application of superconducting magnetic energy storage unit toimprove the damping of synchronous generator

A systematic approach to the design of a controller for superconducting magnetic energy storage (SMES) units to improve the dynamic stability of a power system is presented. The scheme employs a proportional-integral (PI) controller to enhance the damping of the electromechanical mode oscillation of synchronous generators. The parameters of the PI controller are determined by the pole assignment method based on modal control theory. Eigenvalue analysis and nonlinear computer simulations show that SMES with the PI controller can greatly improve the damping of the system under various operating conditions. Although the PI controller is designed for a special load condition, it can also provide good damping under other load conditions     

Energy conservation and environmental benefits that may be realizedfrom superconducting magnetic energy storage

The energy conservation and environmental benefits of superconducting magnetic energy storage (SMES) are described. Since SMES can uncouple generation from load, it can shift generation around, thereby changing the operational characteristics of the system. The technology has the capability of reducing fuel consumption, which can in turn reduce emissions. In a regional setting it can potentially shift emissions both in volumes and in physical areas to avoid problem situations. With its capability to strategically shift generation and significantly affect emissions and air quality it can `stretch' clean energy generation options. With these attributes, SMES can be recognized as an energy and environmental management technology and tool     

Design, performance, and cost characteristics of high temperaturesuperconducting magnetic energy storage

A conceptual design for superconducting magnetic energy storage (SMES) using oxide superconductors with higher critical temperature than metallic superconductors has been analyzed for design features, refrigeration requirements, and estimated costs of major components. The study covered the energy storage range from 2 to 200 MWh at power levels from 4 to 400 MW. A SMES that uses high temperature superconductors (HTS) and operates at high magnetic field (e.g. 10 T), can be more compact than a comparable, conventional low-temperature device at lower field. The refrigeration power required for a higher temperature unit (20 to 77 K) will be less by 60% to 90%. The improvement in energy efficiency is significant for small units, but less important for large ones. The material cost for HTS units is dominated by the cost of superconductor, so that the total cost of an HTS system will be comparable to a low temperature system only if the superconductor price in $/ampere-meter is made comparable by increasing current density or decreasing wire cost     

An optimization technique of robust load frequency stabilizer for superconducting magnetic energy storage

As an interconnected power system is subjected to rapid load disturbances with changing frequencies in the vicinity of the inter-area oscillation mode, a system frequency may be heavily disturbed and oscillate. Under the circumstances, the stabilizing effect of the conventional load frequency control (LFC), i.e. a governor, cannot be expected. To compensate for such load disturbances and stabilize frequency oscillations, the active power controlled by superconducting magnetic energy storage (SMES) can be applied. In this paper, a new optimization technique of a robust load frequency stabilizer equipped with SMES is presented. To enhance the robustness of the load frequency stabilizer against system uncertainties such as various load changes, system parameters variations etc., the multiplicative uncertainty is included in the system modeling. As a result, the robust stability of the stabilized system can be easily guaranteed in terms of the multiplicative stability margin (MSM). The configuration of the load frequency stabilizer is practically based on a second order lead/lag compensator with a single feedback input. The control parameters are automatically optimized by a tabu search algorithm, so that the desired damping ratio of the target inter-area mode and the best MSM are achieved. The simulation study exhibits the high robustness of the load frequency stabilizer against uncertainties. Moreover, a SMES unit requires small power capacity for frequency stabilization.     

当前储能市场和储能经济性分析

储能在未来电网以及可再生能源的应用中将起到至关重要的作用.它的应用范围涉及发电、传输、分配乃至终端用户.本文简要分析并总结了储能市场的经济性,重点阐述了储能应用的主要瓶颈问题——成本.通过分析与计算,确定了储能产品的目标成本,并且以材料创新及以历史上光伏产业规模效应的经验曲线为参考分析了能够降低储能成本的可行途径.储能应用市场将为传统能源结构带来根本性的变化,给社会经济带来巨大的福利,它的应用势在必行.但是,要实现储能的大规模应用还有诸多艰巨的任务与挑战,其中最重要的是要降低储能系统的成本,而实现这个目标需要多方面的共同努力.     

光储联合系统中储能电站的能量管理

为提高储能设备利用率,实现储能电站能量的合理管理,以浙江地区某光伏电站配置的MW级储能电站示范工程为背景,针对现有单应用模式下储能装置容量和功率存在富余的特点,文章提出了一种平抑波动和分时电价相结合的储能装置控制方案。根据光伏出力特点,在光伏波动较强时进行光伏波动平抑,在光伏出力较弱时,根据储能装置剩余容量(state of charge,SOC)的实际情况,结合当地负荷变化曲线,实施分时电价策略。仿真实验表明,该控制方案维持储能设备SOC在合理范围的前提下,能及时平抑白天光伏的波动。同时在一定程度上实现了对负荷的削峰填谷,提高了储能设备利用率,实现了储能电站能量的合理管理,为项目后续示范应用提供了理论依据与技术支撑。     

Compressed air-brine energy storage

Compressed air-brine energy storage (CABES) is similar to ordinary compressed air energy storage (CAES). However, in CABES, the heat of compression of the air is stored via a surface-type heat exchanger in water or, preferably, concentrated brine contained in an unpressurized reservoir. Furthermore, the brine is stratified into a hot, lower density, upper layer and a cold, higher density, lower layer, thus eliminating half the needed reservoir volume. In the energy delivery phase the hot brine heats the compressed air prior to its expansion through an expander/generator to recover the stored electric energy. Calculations on a three-stage CABES plant indicate that:

• 1.(1) the overall electric efficiency is at least 67%;
• 2.(2) the energy storage density of the brine is 0.016 m³ per electric kWh delivered from storage;
• 3.(3) the required unit heat transfer surface is 0.27 m² per electric kWh;
• 4.(4) the contribution of the reservoir and heat exchanger costs to the cost of electric energy delivered from storage is not excessive.

     

节能的地下含水层蓄热(冷)器

分析了地下含水层蓄热（冷）的特点，阐述了使用含水层蓄热（冷）的系统节能和环保的重要意义，介绍了一些欧洲应用实例。     

On generation-integrated energy storage

Generation-integrated energy storage (GIES) systems store energy at some point along the transformation between the primary energy form and electricity. Instances exist already in natural hydro power, biomass generation, wave power, and concentrated solar power. GIES systems have been proposed for wind, nuclear power and they arise naturally in photocatalysis systems that are in development. GIES systems can compare very favourably in both performance and total cost against equivalent non-integrated systems comprising both generation and storage. Despite this, they have not hitherto been recognised as a discrete class of systems. Consequently policy decisions affecting development or demonstration projects and policy approaches concerning low-carbon generation are not fully informed. This paper highlights that policy structures exist militating against the development and introduction of GIES systems-probably to the detriment of overall system good.     

Enhancement of transient stability of an industrial cogeneration system with superconducting magnetic energy storage unit

This paper has developed the coordination of load shedding scheme and superconducting magnetic energy storage (SMES) unit to enhance the transient stability of a large industry cogeneration facility. The load-shedding scheme and the tie line tripping strategy by using the frequency relays have been designed to prevent the power system from collapse when an external fault of utility power system occurs. An actual external fault case and a simulated internal fault case have been selected to verify the accuracy of the load shedding scheme by executing the transient stability analysis. To improve the frequency and voltage responses, an SMES unit with various control modes has been installed in the cogeneration system. The sensitivity analysis of the SMES unit with different parameters is applied to achieve better system responses. Besides, an SMES unit with active power deviation as feedback signal is also considered to improve the electric power fluctuation of the study plant with rolling mills. It is found that the SMES system will enhance the electric power quality and minimize the economic losses of the cogeneration facility due to unnecessary load shedding.