Applications of a Vanadium Redox-flow Battery to Maintain Power Quality

Transcription

1 Applications of a Vanadium Redox-flow Battery to Maintain Power Quality T. Shigematsu, T. Kumamoto, H. Deguchi, and T. Hara Suntitorno Electric Industries, Ltd., Osaka, Japan Abstrucf-The vanadium redox-flow battery (VRB) is a rechargeable battery. The VRB has a quick response time and an outstanding high-rate charge and discharge performance for short time periods. The capacity of the VRB can be easily specified by increasing or decreasing the quantity of electrolyte. By utilizing all these features, the VRB can form an ekective system to maintain power quality, such as a voltage sag compensation system, a stabilizing system for output fluctuations of wind turbines. SEI delivered a VRB to a semiconductor plant as a voltage sag compensation system in April This system normally operates at the rated output of 1.5 MW as a load leveling system. Should a voltage sag occur, it can deliver 3 MW for 1.5 seconds. This VRB has already completely compensated 20 voltage sags. SEI delivered a VRB for the project of The New Energy and Industrial Technology Development Organization (NEDO) in March 2001, and it is nuder evaluation at a WT power plant of Hokkaido Electric Power Company. The VRB's rated output power is 170 kw, and it can be operated up to a maximum power of 275 kw. The VRB has already been found to demonstrate good performance. Index Terms-Vanadium redox-flow battery, Energy storage, Voltage sag, Wind turbine, Power quality I. INTRODUCTION HE vanadium redox-flow battery (VRB) is a T rechargeable battery in which a vanadium solution is used as the electrolyte. Kansai Electric Power Company (KEPCO) and Sumitomo Electric Industries (SEI) have been developing the VRB since [I] [3] The VRB has a quick response time and an outstanding high-rate output performance over short time periods. As an example, a VRB has demonstrated a response time of 350 Us, and at a state of charge (SOC) of 90%, displayed the high-rate output performance of 4.5 times the rated output for one second and three times the rated output for one minute. [2] The capacity of the VRB can be easily specified by increasing or decreasing the quantity of electrolyte. By utilizing all these features, the VRB can be an effective system not only for conventional load leveling applications but also for momentary voltage sag compensation and stabilizing the output fluctuations of wind turbines. In this paper the implementation is described of a VRB in the latter two applications. E. OPERATING PRINCIPLES AND FEATURES OF THE VRB A.. Structure ond Operating Principles of the VRB As shown in Fig. 1, a VRB is comprised of a battery cell section where the battery reaction takes place, positive and negative tanks containing electrolyte, and a pump and piping for circulating the electrolyte from the tanks to the cell. The VRB is connected to an AC system via an AClDC converter. The active material for both the positive and negative electrodes of the VRB is vanadium ions that are dissolved in sulfuric acid and serve as metal ions whose valence number changes. The changes in valence number of the ions (oxidation and reduction reactions) enable the battery to store and discharge electric power. A simplified version of the reaction equation is as follows: Positive electrode: V4' o V5' + e- Negative electrode: V3' o V2' + e- (+: charging, +: discharging) * The left-to-right reaction occurs during charging and the right-to-left reaction occurs during discharging. Fig. 1. Slruclure and principle of a Vanadium Redox Row Ballery(VRB). B. VRB Feotures The VRB offers a wide range of features and can be used in a variety of applications. a) The reaction mechanism is simple (merely changes in valence number) and the recharging-discharging cycle life is extremely long /02/$ IEEE. 1065

2 b) The output section (cells) and storage sections (tanks) are independent of each other, making it easier to design the output and storage sections according to the constraints of the application. This feature also adds flexibility lo installation layout by enabling, for example, only the tanks to be installed underground. c) The VRB has an instantaneous response in the order of milliseconds and is capable of high-rate discharge over short periods several times larger than the rated output. Consequently, the VRB is well-suited to absorbing the irregular output fluctuations inherent to renewable energy generation. d) The VRB operates at room temperature and is easy lo maintain. e) There is no emission of COz and the electrolyte is recyclable, making the VRB environmentally friendly. Fig. 2 Battery cubicle containing Cell-Stack of VRB in a semiconductor manufaduring plans IlI. APPLICATION TO POWER QUALITY MAINTENANCE The system also helps reduce electricity costs by utilizing A. Applicatiori to a Momentary Voltage Sag Compensation inexpensive nighttime electric power. Whenever a momentary voltage sag occurs, the battery can deliver the equivalent of twice its rated output, i.e., 3 MW, for 1.5 seconds with negligible delay. System In facilities such as semiconductor manufacturing plants, momentary voltage sags can cause substantial damage such as defective half-finished products and business opportunity losses associated with equipment recovery. Protection Load leveling AC Terminal voltage outnut -r Rated discharge capacity 6,600 V kwh 2) Operating Results The twenty momentary voltage sags that have occurred thus far have all been successfully compensated for by the system. against such damage requires instantaneous high output for extremely short periods of time. A VRB can provide an economical solution that meets these requirements using a suitable instantaneous high-rate output performance and a tank capacity volume matched to the short-period capacity. B. Application to Stabilization of Output Fluctuations of A peak cut function can also be provided if required. In Electricity Generated from Wind Power 2001, SEI delivered a VRB system for use as a momentary Japan is aiming to generate 3,000 MW of electricity from voltage sag compensating system in a semiconductor plant. wind power by the year In the meantime, the effect of wind turbine output fluctuations on power systems is under I) Overview of the Delivered System discussion as a problem that must be dealt with before wind The specifications of the delivered VRB system are shown in Table 1. The external appearance of the equipment is shown in Fig. 2. TABLE 1 SYSTEM SPECIFICATIONS FOR A SEMICONDUCTOR MANUFACTURING PUNTS 1,500 kw power can be introduced. It is believed that combining wind turbines with storage batteries could be an effective solution. Currently the New Energy and Industrial Technology Development Organization (NEDO) has different types of storage batteries installed at wind power generation stations and is conducting verification tests on stabilization of output fluctuations. SEI delivered a VRB with a rated capacity of 170 kw (maximum 275 kw) for this project in March It was installed lo work in combination with a wind turbine (275 kw) at Hokkaido Electric Power Company's Horikappu Wind Power Station, where the tests are being conducted on stabilization of wind turbine output fluctuations. 1) Sumciary of Stabilization Test on Wmd Turbine Output Fluctuatiotu An overview of the system structure is shown in Fig. 3. The system constantly maintains the soundness of the connected to the power system and functions to stabilize equipment by operating with a normal peak cut of 1.5 MW. 1066

3 Purpose : Field test for stabilizing Commissioned Spec. : 170kW x mriizzz loutnu I I Outuu I [ NED0 - IAE - SEI 11 L (The Iiisiil~te Amlied TABLE 2 SYSTEM SPECIFICATIONS FOR APPLICATION TO WIND POWER STATION Parameter Rated Output Specification 170kW during 3 hours (to reduce electrolyte volume by 1 halves) - VRJ3 01/ F-9/E Field -021 E Data Maximum Output 275 kw (to utilize the high- rate output performance) Fig. 3 An overview of Ihe syslem structure for application Io wind power rlalion output fluctuations by absorbing changes in the output of the wind turbine. Wind turbine output fluctuations generally include components ranging from those with relatively long periods to those with very short periods. The battery system has excellent momentary response and is expected to be capable of handling both long- and short-period components. The wind turbine output fluctuations are stabilized using the following method. The actual output of the wind turbine is passed through a low-pass filter having a certain time constant and the output value after the short-period components have been removed is set as the target value for stabilizing. A portion of the output equivalent to the difference between the target value and the actual wind turbine output value is sent lo the battery. 2) Evaluation Conditions of VRB Installed at Hokkaido Electric Power Company s Horikappu Power Plant A summary of the system specifications is shown in Table 2 and the appearance of the system is shown in Fig. 4. Characteristic features of the system include the following: the electrolyte tank is divided into two parts; the system is capable of a 3-hour capacity test; and the system is designed such that tests can be conducted to evaluate the instantaneous high-rate output performance of the VRB in a situation where the inverter output is 275 kw, which is equal to the rated output of the wind turbine and largcr than the rated output of the VRB. 3) Stabilizarioii Test Conrlitiotis a) Stabilization data for time constants of eight minutes, one hour, and eight hours are shown in Figs. 5, 6, and 7. The longer the time constant is, the greater the degree to which the output fluctuations are stabilized. Simultaneously, the output demand on the battery becomes larger and a larger Fig.4 Appcardnce of VRB combimed wilh Horiksppu Wind Power Station of Hokkaido Electric Power Co.,lnc. capacity battery is required b) Stabilization data for a time constant of one hour when operating at 112 capacity (3-hour capacity) is shown in Fig. 8. Although the amount of elecfrolyte has been reduced by one half to achieve a capacity of three hours, the degree of stabilizing exhibits similarly good results. c) Stabilization data (time constant 1 hour) for when the high -rate output characteristics are utilized are shown in Fig. 9. The system responds as a battery without any problems and it has been successfully verified that it can output 275 kw. The data also illustrate that the degree of stabilization is improved accordingly. 1067

4 ... -,.... O:M 2:M 403 6:M 8:M l0:m 12W W 1800 M03 2' Tlme Fig. 5 Stahililalion data for lime conslants of 8 minuter : 2001/05/18 (VRBl70kWl6h a1 Hokkaido Eledric Power Company's Hariksppu WT Power Planl) 5w g 400 d g 3m discharge' 0 charge t ~ -la, -m -3@n om s m 800 roo0 12:w,400 16:m 18:w w om Tlmc Fig. 6 Stahilizalian data for lime conslants of 1 houm: 2001/05/22 (VRB170kW/6h SI Hokkaido EIeclric Power Compmy'r Horikappu \yt Power Planl) + m B dlrrhsrge 0 charge -1 di, 00 t U -MO 50 E! a :O :m 003 The Fig. 7 Stabilization ddld lor lime UlnStdnls 01 8 hours : 2001/04/06 (VRB170kW/hh at Hokkaido Electric Power Company's Horikappu WT Powcr Planl) P 1068

5 - 005 V 50 boo i:bb 4:L i:oo ioioo iiibo icoo is:oo igoo itoo ziloo U:oo Time Fig. 8 Stabiliration data for lime conslanls of 1 hours when operating at ti2 capacity: (VRB:l70kWl3h al Hokkaido Electric Power Company's Horikappu W Power Plant) sm S 4m Y dsm s. g 203 im discharge $ 0 charge c I m " a 0 50 z -3m om zm +m em em tom izm iwn ism inm mm 2zm om $ Time Fig. 9 Slabiliialion dala for lime conslanl~ of 1 hours rhen the high -rale output caracteristics itre ulilized: 2001/11/26(VRB:275kW al Hakkaido Electric Power Company's Horikappu W Power Plant) 4) Observations The response of the VRB, which also includes an inverter, is on the order of a millisecond. The results of this study are believed to demonstrate that the system achieves stabilization that is consistent with the original aim. The degree of stabilization and the required battery capacity vary greatly depending on the time constant. The required degree of stabilization should be determined in response to the economical factors of the battery system and the system control requirements. Regarding wind turbine output stabilization applications, it is speculated that the required battery capacity can ultimately be reduced to approximately 20% of the rated output of the wind turbine by utilizing the instantaneous high-output performance of the VRB. The authors wish to study this possibility further. N. CONCLUSIONS As a result of environmental problems and deregulation of the electric power industry, a variety of distributed power sources, among them wind power, will be introduced into future electric power systems. It is expected that electric power storage technology will become a key technology in electric power systems for ensuring supply reliability and maintaining power quality. The VRB has unique characteristics not seen in other batteries and it is believed that these characteristics can be utilized in a wide variety of applications in addition to those discussed in this paper. We have reached the practical application stage, and will need to focus development work on reducing cost and improving practical applicability. 1069

6 V. REFERENCES [l] N. Tokuda, Y. Miki, H. Arai, K. Yamamoto, K. Eniura, K. Motoi, T. Shinzato, and T. Kanno, Vanadium Redox Flow Battery System for Use in Office Buildings, in Electric Energy Storage Association Technologies, Sep Hiroshige DEGUCHI was born on Nov He received M.S. degrees in Electrical Engineering from Tokyo University, Tokyo, Japan in Since 1991 he has been an Engineer of Sumitorno Electric Industries and is currently Assistant Manager of [2] T. Kaizuka and T. Sasaki. Evaluation of Control Energy Storage System Maintaining Electric Power Quality by use of Development Group. He is in charge Rechargeable Battery System, in IEEE Power of the development of Redox Flow Engineering Society Winter Meeting, Battery. Mr.Deguchi is a member of [3] M. Miyake, and N. Tokuda, Vanadium Redox Flow the Institute of Electrical Engineers Battery for a Variety of Applications, in IEEE Power of Japan. Engineering Society Summer Meeting, VI. BIOGRAPHIES Toshio SHIGEMATSU was born on Dec He received M.S.degrees in Applied Physics from Osaka University, Osaka, Japan in Since 1982 he has been an Engineer - of Sumitomo Electric Industries and is currently assistant General Manager of Energy Storage System Development Group. He is in charge of the development of Redox Flow Battery. MrShigematsu is a member of the Institute of Electrical Engineers of Japan. Takushi HAM was bo1 n on Sep He received M.S. degrees in Electrical Engineering from Okayama University, Okayama, Japan in Since 1974 he has been an Engineer of Sumitomo Electric Industries and is currently General Manager of Energy Storage System Development Group. MI. Hara is a member of the Institute of Electrical Engineers of Japan. Takahiro KUMAMOTO was born on Nov He received B.S. degrees in Electrical Engineering from Osaka City University, Osaka, Japan in Since 1992 he has been an Engineer of Sumitorno Electric Industries and --.. is currently member of Energy Storage System Development Group. He is in charge of the development of Redox Flow battery. 1070