An analytical technique using the `Newton-Raphson' method is presented to identify the saturated magnetising reactance and the generated frequency of a self-excited induction generator for a given capacitance, speed and load. The technique is shown to be very efficient in analysing such systems under steady state. Computed results are compared with the experimentally obtained values on a laboratory machine, and a reasonable correlation has been observed. Effects of various system parameters on the steady-state performance have been studied, and the results presented provide guidelines for optimum design of such systems.

Analysis of self-excited induction generators

Flywheel Energy Storage System (FESS) is an electromechanical energy storage system which can exchange electrical power with the electric network. It consists of an electrical machine, back-to-back converter, DC link capacitor and a massive disk. Unlike other storage systems such as the Battery Energy Storage System (BESS), FESS is an environmentally-friendly short- or medium-term energy storage system, which has the capability of numerous charge and discharge cycles. These characteristics make the FESS a suitable choice for different applications in the power system such as power quality improvement, power smoothing, renewable energies integration support, stability improvement, etc. This paper presents an overview on the structures and applications of FESS in power system and Microgrid (MG) and also challenges, problems and future works discussed. It can be a driver for development of FESS applications and also recommends suggestions to use its advantages in other areas. Investigation of different studies shows that FESS, as a developing technology, can play an effective role in the operation of the present and future power system and MG.

Review of Flywheel Energy Storage Systems structures and applications in power systems and microgrids

Operational controls are designed to support the integration of wind and solar power within microgrids. An aggregated model of renewable wind and solar power generation forecast is proposed to support the quantification of the operational reserve for day-ahead and real-time scheduling. Then, a droop control for power electronic converters connected to battery storage is developed and tested. Compared with the existing droop controls, it is distinguished in that the droop curves are set as a function of the storage state-of-charge (SOC) and can become asymmetric. The adaptation of the slopes ensures that the power output supports the terminal voltage while at the same keeping the SOC within a target range of desired operational reserve. This is shown to maintain the equilibrium of the microgrid's real-time supply and demand. The controls are implemented for the special case of a dc microgrid that is vertically integrated within a high-rise host building of an urban area. Previously untapped wind and solar power are harvested on the roof and sides of a tower, thereby supporting delivery to electric vehicles on the ground. The microgrid vertically integrates with the host building without creating a large footprint.

DC Microgrid for Wind and Solar Power Integration

Accelerator technical design report for J-PARC

Thanks to the unique advantages such as long life cycles, high power density, minimal environmental impact, and high power quality such as fast response and voltage stability, the flywheel/kinetic energy storage system (FESS) is gaining attention recently. There is noticeable progress made in FESS, especially in utility, large-scale deployment for the electrical grid, and renewable energy applications. This paper gives a review of the recent developments in FESS technologies. Due to the highly interdisciplinary nature of FESSs, we survey different design approaches, choices of subsystems, and the effects on performance, cost, and applications. This review focuses on the state of the art of FESS technologies, especially for those who have been commissioned or prototyped. We also highlighted the opportunities and potential directions for the future development of FESS technologies.

A review of flywheel energy storage systems: state of the art and opportunities.

This paper deals with a pulsed power supply system combining flywheel energy storage system (FESS) and a modular multilevel cascade converter (MMCC) for power compensation in performing rapid excitation of highly inductive and pulsed heavy loads. The FESS system consists of an induction motor with a flywheel to store kinetic energy. Parallelly connected capacitors cause self-excitation phenomena in an induction motor, and it works as an induction generator. Furthermore, the induction generator generates more than twice of electric power of its rated value for a short time. We can apply the proposed FESS to particle accelerators for physics experiments or medical use, and plasma shape and position control in pulsed nuclear fusion devices that require pulsed highpower. In addition, the coils in these applications that generate magnetic fields have large inductances. In plasma control and repetitive operation applications, it is necessary to change current rapidly. We can realize high-speed current control by using the proposed MMCC that can output a voltage higher than the input voltage. By combining the FESS and MMCC, a power supply may be realized with the ability to implement rapid current control while compensating for large power consumption and without significant load disturbance on the power grid.

Combination of Flywheel Energy Storage System and Boosting Modular Multilevel Cascade Converter

Stand-alone power systems (SPS) are attracting more and more interest with the global move toward distributed generation (DG). Without strong support from the power grid, they suffer from poor load-following capability at varying loads. A cache power that has fast response and high energy efficiency is demanded. As a solution, this paper provides an AC power technology based on flywheel energy storage. Different from the other DC generation technologies such as electric double layer capacitor (EDLC) or superconducting magnetic energy storage (SMES), the proposed flywheel system generates AC power and therefore can be directly connected to the power line without any power semiconductors. Furthermore, the proposed technology realizes power in/out automatically in response to the frequency/voltage variation of the power line. Therefore, this system has the advantages of robustness, simplicity, and fast response. Besides, by getting rid of power semiconductors, the proposed flywheel system has a good overload capability as high as two to three times. We prove by simulation and experimentation the validity and effectiveness of the proposed technology to provide cache power for stand-alone power systems. © 2013 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Flywheel-based AC cache power for stand-alone power systems

Flywheel energy storage systems are focused as uninterruptible power supplies (UPS) from the viewpoint of environmental friendliness and high durability performance. Using a low-speed and heavy flywheel, and a low-cost squirrel-cage induction motor/generator, two applications are proposed; 1) 11kW voltage sag compensator using a capacitor self-excited induction generator without semiconductor converters; 2) UPS composed of the flywheel system and an engine generator. From some experimental results, an ideal voltage sag compensator and UPS are realized by the low-technology flywheel system.

Development of Voltage Sag Compensator and UPS using a Flywheel Induction Motor and an Engine Generator

Flywheel energy storage systems are good power stabilizers for stand-alone power systems, especially for highly fluctuating load or inrush power demand. In this investigation, a simple setup of a flywheel induction motor device is proposed which is composed of a flywheel and an induction motor directly connected in parallel to the inverter-controlled load. Also, a novel control method to improve the overload capability of the stand-alone power systems is presented by applying frequency control to the load side inverter. Compared to the conventional flywheel energy storage system, the proposed system has the following advantages: 1) simple configuration due to less number of inverters in the proposed system; 2) not only an improved overload capability of the stand-alone power system, but also a decreased capacity of the load-side inverter; 3) simple control and low cost. Although the changes of the flywheelpsilas speed would lead to frequency variations, a survey reveals that a small frequency variation is permitted for quite a lot of industrial machines. The requirement for the frequency variation can be satisfied by a proper capacity design of the flywheel induction motor. A design method to meet the utilitypsilas demand is introduced in this paper. Some experiments are conducted to verify the proposed system and the frequency control method. The experimental results show that the proposed system is easy and practical as an overload improvement method.

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A novel method for improving the overload capability of stand-alone power generating systems based on a flywheel induction motor

The experimental results of an innovative power conversion technology using magnetic energy recovery switch (MERS) in a wind turbine system with a synchronous generator to improve the output power and the efficiency are presented. The MERS can compensate for the reactance voltage of the generator. The output voltage of the system increases and the excitation power of the generator can be significantly reduced. The data indicate a great potential of the new power conversion technology to make the actual wind turbine system compact and to improve the efficiency.

/pdf/application-of-magnetic-energy-recovery-switch-mers-to-3ikkq5j98o.pdf

Shuhei Kato

Papers

Combination of Flywheel Energy Storage System and Boosting Modular Multilevel Cascade Converter

Flywheel-based AC cache power for stand-alone power systems

Development of Voltage Sag Compensator and UPS using a Flywheel Induction Motor and an Engine Generator

A novel method for improving the overload capability of stand-alone power generating systems based on a flywheel induction motor

Application of Magnetic Energy Recovery Switch (MERS) to Improve Output Power of Wind Turbine Generators