Tanzo Nitta

Technical and Cost Evaluation on SMES for Electric Power Compensation

RASMES (Research Association of Superconducting Magnetic Energy Storage) in Japan developed a road map of SMES for fluctuating electric power compensation of renewable energy systems. Based on the progress of large superconducting coils, the technical status is already established to develop the several MWh class SMES for frequency control, load fluctuation compensation, and generation fluctuation compensation. With integrated operations of several dispersed SMES systems, it is expected that the 100 MWh class SMES for load fluctuation leveling (peak cut) can be introduced in the period of 2020-30, and the first 1 GWh class SMES for daily load leveling can be installed in the period of 2030-40. From the results of Japanese national projects, experimental device developments and SMES design studies, if the output power of SMES is 100 MW, the target cost of SMES can be evaluated with 2000 USD/kW of the unit cost per output power (the unit cost per kW).

Improvement of Power System Stability by Use of Superconducting Fault Current Limiter With ZnO Device and Resistor in Parallel

Superconducting fault current limiters (SCFCLs) are expected to improve the reliability and stability of power systems. SCFCLs can be classified into R-types (resistive) and L-types (inductive) by the fault current limiting impedance. An L-type FCL is more effective in suppressing the voltage drop during a fault. On the other hand, a R-type FCL is more effective in consuming the acceleration energy of generators at the fault. Both functions lead to the improvement of the transient stability of the power system. We have proposed and fabricated the FCL unit, which is expected to have both functions. It consists of an inductive superconducting fault current limiter with a resistor and a ZnO device in parallel. In this paper, the simulation analysis on one machine and an infinite bus transmission system including the proposed FCL unit was carried out. EMTP (electro-magnetic transients program) was used in order to analyze the power system characteristics of the FCL unit. A rotor angle of the generator and a critical fault clearing time were analyzed to evaluate the effects of the FCL unit on the improvement of the transient stability of the model power system. A contribution share of the voltage drop suppression and the acceleration energy consumption to the improvement of the power system stability were clarified with various conditions, such as, generator output and fault clearing time.

Experimental study on sudden-short-circuit characteristic of synchronous generator with SCFCL

Superconducting fault current limiters (SCFCLs) are expected to improve the reliability of power systems. An SCFCL of a transformer type with adjustable trigger current level was proposed. Three SCFCLs of this type for 3-phase AC power source were designed and made. The trigger current level of each trial SCFCL can be adjusted to equal value, and the SCFCLs can be used as a 3-phase SCFCL. As preliminary tests, sudden-short circuit tests with a 20 kVA synchronous generator are carried out. Limiting tests of the 3-phase SCFCL at fault are carried out with the synchronous generator. The effect of 3-phase SCFCL and the characteristics of the synchronous generator are studied experimentally.

Power charging and discharging characteristics of SMES connected to artificial transmission line

To consider the characteristics of SMES and to investigate problems on the operations of SMES in power systems, we carried out some experiments on an experimental network. In the network, a small superconducting magnet is connected to a small synchronous generator through a double thyristorized converter and transformers. The generator is connected to the regional power system through artifitial transmission lines, AC power into or out of SMES and reactive power are controlled. Furthermore, a computer simulation program is made for the experimental system. The results of the simulation are compared with those of the experiments. For the experiments and the simulation, the harmonics current-flow, power-flow, characteristics of the generator and so on, are discussed.

Combined power supply method for micro grid by use of several types of distributed power generation systems

A power control method to compensate power fluctuation of the load in the microgrid systems is proposed and discussed. Active power responses of several kinds of distributed power generation systems (DGs) such as gas engine, micro gas turbine, etc., energy storage system, and load fluctuation of a site have been measured. Based on the measurements, combination control method for several kinds of DGs and an energy storage system has been made and experiments have been carried out by use of small scale micro grid model system. It is shown that the load fluctuation has been compensated by the proposed method

Design methods and integrated control for microgrid

The authors have been carrying out a preliminary study on the design of microgrid. Designing microgrid includes selection and capacity determination of power supply devices according to their response characteristics, efficiency and initial cost, and development of methods for integrated control to maintain power quality and efficiency. Both design and control methods depend on conditions of loads, for which microgrid is installed. In this paper, design methods of microgrid, such as power demand analysis, response characteristics measurement of power sources and fuel efficiency measurement of engine-generators, and integrated control methods for power sources are proposed, along with experimental results for a prototype of microgrid.

Design and Manufacture of Superconducting Generator with High-Response Excitation

Superconducting generators have numerous advantages, one being their capability of improving the stability of power systems because they enable the selection of lower synchronous impedances. This advantage can be increased by adoption of high-response excitation.

State of charge control for energy storage by use of cascade control system for microgrid

The hybrid control system, which is a combination of cascade control and local control, is proposed as a method to compensate power fluctuations caused by load and renewable energy sources in a microgrid using distributed power generation systems(DGs). When energy storage system(ESS) such as EDLC is used in the microgrid to compensate power fluctuations, its state of charge(SoC) should be controlled. In this paper, a new method to control ESSs SoC which would enable power compensation with less energy capacity and with less effect to the compensation result is proposed. This method uses the feature of the cascade control that faster DGs reference is dependent on slower DGs output. The new method is implemented on EDLC in the model microgrid and its effectivity is verified by a simulation and a experiment. The result of the simulation and experiment is also reported in the paper.

Energy capacity reduction of energy storage system in microgrid by use of heat pump: Characteristic study by use of actual machine

The installation of renewable energy sources based generators such as photovoltaic cells and wind turbines require energy storage systems(ESSs) to control power fluctuation. ESSs, however, are quite expensive. In order to reduce the necessary capacity of ESSs for microgrid applications, the control of heat pumps is researched. In this research, basic characteristic of a heat pumps power consumption is measured experimentally by use of heat pump chiller unit used in real building. Using the measured characteristic, a method to reduce the energy capacity of ESS is proposed and studied. The capacity reduction of ESS that can be achieved by use of heat pump control and the effect of control on temperature were calculated using simulations.

Power System Characteristics of the SCFCL in Parallel With a Resistor in Series With a ZnO Device

Superconducting fault current limiters (SCFCLs) are expected to improve the reliability and stability of power systems. The 3-phase FCL system, which consists of 3 superconducting fault current limiters of transformer type in parallel with a resistor in series with a ZnO device, was proposed and its small model was designed and made. In a power system the FCL system is expected to limit the peak of the fault current inductively and also to consume the acceleration energy of the generators by means resistive component. The power system characteristics of the proposed FCL system was experimentally investigated by use of the model FCL and a laboratory scale power system simulator. The FCL system switches its impedance from inductive type (L-type) to inductive+resistive type (L + R-type) in a cycle due to the ZnO device. The peak of the fault current was limited in the L-type time interval and the energy was consumed in L + R-type interval. The proposed FCL system limited the fault current at the simulated fault and successfully recovered the stand-by mode in the model power system. At the same time, the energy consumption in the resistor reduced the accelerating energy of the generator and then improves the power system transient stability.