SMES Device Charged by Renewable Energy Used to Regulate Frequency of Interconnected Power System

Transcription

1 SMES Device Charged by Renewable Energy Ued to Regulate Frequency of Interconnected Power Sytem HONGMEI LI [], ZHENG YAN [], GUOQIN YU [], YI LIN [], KAI NIU [] [] Electrical Engineering Department, Shanghai Jiao Tong Univerity Shanghai, 0040 P. R. CHINA [] Shanghai Municipal Electric Power Company Shanghai, 0005 P. R. CHINA Abtract: - Development and utilization of renewable energy ource (RES) i an important content of global energy development trategy. Being retricted by natural condition, the output characteritic of renewable energy generation i tochatic. If renewable energy generator unit be connected with public grid directly, it will reult in the intability of power grid. In thi paper, apply wind power a an example, uing renewable energy a charge power upply for Superconducting Magnetic Energy Storage (SMES) ytem. SMES device poee ome advantage of high efficiency, fat repone and good capability of exchange active and reactive power independently with power ytem. It i a new idea for developing renewable energy. SMES can regulate output depending on load changing on time, which can tabilize fluctuation of frequency and reduce unneceary power flow among tie line. Simulation reult proved that SMES not only can improve frequency effectively, but alo can reolve the defect of inadequate pinning reerve. Key-Word: - renewable energy, SMES, reerve capacity, primary frequency modulation. Automatic generation control (AGC) Introduction For aving energy and controlling emiion, in 007, the policy of energy conervation power generating and ditribution code (trail) [] wa puhed by State Council General Office of China. During the lat few year, development and utilization of renewable energy ource (RES) i an important content of China energy development trategy too [-3]. Compared with traditional generation technology, RES overcome ome weak of conditional generation technology. It will reinforce practice power grid. It alo provide a new approach to ue RES. So, in [], in the order of every kind of generation unit, wind energy ource, olar energy ource and other renewable energie ource are on the firt place to generate electric power. The ability of primary frequency (PF) regulation of power grid i an important indication of ytem ecurity. If all of generator unit connected with public grid quit their PF device, the elf- Thi work i upported by China Advanced Technology Reearch Project(863 Project Number: 007AA05Z458). adjutment character of whole ytem would become deterioration. In China, the reaon that PF device input rate i very low i a following. Firt, many operation taff do not realize the importance of PF. Secondly, when generator unit throw in PF device, once frequency fluctuate frequently, it will wear out generator unit. Lat, there i not perfect incentive policy about PF regulation, o poitivity of throwing in PF device can not be mobilized. Many PF device were quit or were et big dead-band value to ecape PF regulation [4-5]. Thee meaure attempting to ecape PF regulation will increae burden of generation unit which are aigned to automatic generation control (AGC) ytem. In normal, there are two kind of AGC policie. One policy i baed on uper-hort-term load forecating [6]. The other one i lag control [7]. No matter lead or lag control policy, there mut be diparity on time comparing with diturbance of load happening. So, regulation of generation output alway overhoot or underhoot. Furthermore, if pinning-reerve of local-area i inufficient, it need upport from external area. So, it will reult in not only the increae of burden of tie-line, but alo fee of auxiliary-ervice to be paid. Among all renewable energie, becaue of it economy, wind energy poee the bet propect. ISSN: Iue, Volume 8, December 009

2 The exploitation of wind energy i development trategic of China and one of meaure ued to regulate the power configuration. Wind energy i characteritic with clean, renewable and low cot. But, the tochatic characteritic of wind power output can not be ignored too. It will reult in the fluctuation of power output. Therefore, if the wind power i connected with power ytem directly in large cale, it will be poible to caue the affect on the peak-load regulation, frequency regulation, power quality, electric network power flow and tranient tability [8-0]. Baed on thee factor howed above, we apply wind energy a an example for analying the practical problem which exit in the wind power upply. Differing with the conventional idea, we propoe that renewable generation unit were not connected to the power grid directly, but applying them a the charge ource upply for torage equipment. Thee torage equipment may be ued a pinning revere of primary frequency regulation and AGC regulation []. In thi paper, wind energy, the renewable energy, i ued a the charge power upply of SMES device, thi application not only provide the charge power upply, but alo may eliminate the direct impact on the power grid while wind generation unit are connected public grid directly. The advantage of quick repone of SMES device may be exploited for regulating the ytem frequency, and that avoiding the exce wearing, imultaneouly, the SMES device may make up deficiency of ytem revere and improve the power quality. The configuration of thi paper i a follow. In Section, we will introduction SMES and dicu technical characteritic of SMES. Action control and power releae characteritic of SMES will be dicued in thi ection too. In Section 3, baed on the feaibility analyi of Section, how SMES device coordinating with frequency modulation unit will be analyzed. Both primary frequency regulation and AGC regulation will be conidered. In Section 4, imulation model will be decribed. In order to conider complexity of interconnected power ytem, triple-area primary and AGC regulation model will be adopted. In the following Section 5 and 6, imulation reult and concluion will be decribed. Introduction of SMES In 975, Superconducting Magnetic Energy torage (SMES) wa dicued in reference [] already. The reference point out, a the cot of foil fuel had increaed and the load factor on electric utilitie had decreaed, the need for efficient, reliable energy torage ytem increaed. With the technical development, mart grid concept wa put forward. Where, how to combine tochatic renewable energy ource with torage device i an important point.. Technical characteritic of SMES High peed development of Flexible AC Tranmiion Sytem (FACTS) make ignificant pole in enhancing the tability, reliability and afety of power ytem. SMES device i energy torage equipment which the energy wa tored in the coil of SMES. Thi technology i an active combination of the FACTS and uperconducting power technology [-6]. SMES exploit the coil manufactured from uperconductor to toring magnetic energy. When power wa tranported, the energy type i not needed to be changed, moreover, the energy converion ha the advantage of high repone peed, high converion efficiency and large pecific capacity (- 0Wh/kg)/pecific power (04-05kW/kg), it i very convenient for tranporting large capacity of energy from SMES device to power grid and power compenation. From the technical viewpoint, SMES device i uncomplicated, beide the vacuum and cooling ytem, the device ha no rotating component. Therefore, SMES device ha the advantage of long ervice lifetime, the intallation location i not retricted. Moreover, the maintain procedure i imple and free-pollution. Nowaday, the -5MJ/MW low temperature of SMES device ha been manufactured a product in the worldwide, 00MJ of SMES device ha be running in the high voltage power ytem, feaibility and technology analyi on 5GWh of SMES device ha been completed. SMES device may atify with thee requirement from voltage tability of tranmiion and ditribution ytem, power compenation, frequency regulation, and that it can improve the tability of power ytem and enhance the tranmiion capacity [7]. Baed on thoe advantage mentioned above, SMES device become an important reearch ubject which many reearcher were interet in. US, Japanee and Ruian have made comprehenive reearch. Adopting US a example, ince 97, ome reearcher found out that the torage equipment of power energy can ufficiently uppre the ocillation of power ytem, which conit of uperconductor inductance coil i characteritic with the high repone peed.. By 98, LASL and BPA (Bonneville Power Adminitration) work together to ISSN: Iue, Volume 8, December 009

3 building the 30MJ/0MW of SMES ytem, thi ytem uppreed the low frequency of 0.35Hz pontaneou ocillation on the 500 kv, double-loop line of 500kM from the North-Wet Region in the Pacific Ocean to the South Galifornia [8]. In China, reearching on low temperature uperconducting technology began at the lat 950. In recent 40 year, a number of tudying work have etablihed the bai of uperconductor material and technology. Tinghua Univerity and Electrician Intitute of China have developed corporately the controllable torage equipment of 0kJ/5 kw uperconductor. Thi device can enure the total harmonic wave ditortion at about 9% from the total output of AC current [9]. 35kJ/7 kw of direct-cooling high temperature SMES pecimen had been developed corporately by Technology Univerity of Huazhong and many companie. Moreover, dynamic imulation tet wa implemented on the ample. Tet reult howed that SMES device can retrain the power ocillation caued from the hort-circuit fault and improve the tability of power ytem effectively [0].. Action control and power releae characteritic of SMES Numerou tudying how that the tranform efficiency of SMES up to above 96%, the releae peed of power i fat, and commonly everal ten milliecond be needed only. Baed on the demand of large power ytem, we can control the trigger angle for implementing the control of active and/or reactive power from the SMES for large power ytem, and that can control the active or reactive power eparately. From thi viewpoint, SMES device can be conidered a a FACTS device which can exchange active or reactive power with power ytem. Setting the reaonable control law, the tability of power ytem can be improved effectively. The paive tability of power ytem wa changed a the initiative tability. The AC/DC converter device of controllable SMES device ha voltage-type and current-type. Main circuit tructure of current-type converter can be equivalent to a controllable current ource. Amplitude and phae angle of Output current can be regulated by changing the modulation ratio of pule width modulation (PWM) and trigger angle of witch component, o active and reactive power regulation can be implemented in four quadrant conveniently [3]. Comparing to voltage-type converter, the current-type converter poee more capacity to provide reactive power, o the voltage fluctuation on SMES device wa decreaed effectively. Moreover, it i feaible to implement multi-bridge parallel in high power application cae. Voltage-type converter wa applied widely, and can be ued to compenating the bu-bar voltage []. The reference [] how that when applying current-type converter of multipule, the voltage fluctuation of uperconductor coil can be retricted, at the ame time, the power lo wa decreaed uccefully, o the current-type converter i the optimal choice for high power of SMES device. During dicharging, whether voltage-type or current-type converter, they can continue to upply power for ome certain time, o the tability of power output i aured..3 Charging power ource of SMES device Thi paper preent applying the wind energy a the charging power ource of SMES device for making up a deficiency of pinning reerve of primary and econdary frequency regulation. When the SMES device wa intalled at the bubar of outlet of wind farm, it i convenient to regulate the frequency of power ytem quickly. Beide, like the wind farm, the large-ized of SMES device may alo be intalled at the bubar of outlet of the pumping water tored energy plant, heat power plant, garbage power plant and tidal power tation. When the generating capacity i intable or exce, may charge the SMES device, a well a avoiding the direct impact. While the ytem tability and power quality needed to be improved, the SMES device may play important pole. 3 SMES device coordinate with frequency modulation unit Mentioned above, SMES device may regulate active and reactive power eparately by controlling the trigger angle. When the range of dead-band of governor i overlarge, the unit can t to join into primary frequency regulation. However, when the unit operate with full load, ISSN: Iue, Volume 8, December 009

4 the unit will lot the capacity of frequency modulation. At thi condition, ytem frequency modulation can be implemented by exploring the advantage of quick tranform of SMES device, injecting or aborbing power what may be ued to make up a deficiency of the inadequate pinning reerve. 3. SMES device coordinate with the primary frequency regulation When the SMES device act for coordinating with the unit of primary frequency regulation, the bet way i to intalling the SMES device at the bu-bar ide of unit needed to coordinate. Becaue of the SMES device act time, the order of milliecond, i le than the act time of unit of primary frequency regulation, the act time of frequency regulation may be decreaed. At the ame time, when the unit are lack of capacity of primary frequency regulation, SMES device may be ued a the pinning reerve. To aiding primary frequency regulation, the frequency bia wa ued a the act criterion. For example, when the frequency bia i more than the act value of dead band of primary frequency regulation, SMES device may be witched on for exchange power with ytem. While the frequency bia i le than the etting value of dead band, the SMES device would be quit. applying the SMES device to replace partial AGC unit, not only the ahead-control of SMES device may be implemented, at the ame time, power unbalance may be improved on time. SMES device can beforehand adjut active output by receiving uper-hort-term load forecat alone. Baed on AGC unit condition which SEMS device cooperate with, SMES device can upply the inadequate of pinning reerve.. When applied in lag-control, ACE can be ued a the action ignal of SMES. 4 Decription of imulation model In thi paper, imulation model of primary frequency modulation and AGC modulation wa baed on typical tipple-area interconnection power ytem, a howed in Fig.. 3. SMES device coordinate with AGC Not only the performance of frequency regulation of the thermal unit i different from hydro unit, but alo the great difference occur among thermal unit. At the ame time, when the AGC with different behaviour were put into operation, it i difficult to reach to ynchronization adjutment, o the adjutment effect i not ideal. Specially, while thermal unit act frequently, the cot and unit wear will rie. Lead-control of AGC can be implemented by applying uper-hort-term load forecat to calculate the bia of generation plan and ditribute the plan on AGC unit which adjutment peed i low. Ahead-control period commonly i 5 minute. Lag-control period of AGC i only everal ten of econd, o the conflict i not caued from control time. If Fig. typical 3 area ytem model Thi paper applie the SIMULINK to imulation. For qualitative analyi, the imulation model can be implified, o the nonlinear factor of uint ramp control (URC) and upper and lower limit of generation rate control (GRC) aren t involved in thi imulation model. The dead-band loop ISSN: Iue, Volume 8, December 009

5 5 /R SMES STEP K/S -Kk In Out deadband governor 0.3+ prime mover p- /R 5 T3 T 3.4 SMES - k STEP - k3 K/S -Kk InOut deadband governor 0.3+ prime mover p- 0+ T 3.4 a - a3-3.4 T3 - k3 5 /R3 SMES3 STEP3 a3 - p-3 K/S -Kk3 InOut deadband governor prime mover3 T T3 Fig. triple-area model of primary frequency regulation and AGC regulation ISSN: Iue, Volume 8, December 009

6 wa only conidered [3]. The other parameter etting can be een from Fig. and Table.. Among them, k, k 3 repreent the tie-line direction of area with area and 3 repectively. AGC regulation part wa marked in dahed border of Fig.. Table. Sytem parameter for the triple-area model T 0.08 g T 0.3 t T p R K p 0.4Hz/pu 0Hz/pu T ij k - ij a - ij k 0.3 i Dead-band 0.033Hz 4. Effect from SMES device on primary frequency regulation Secondary frequency regulation mainly wa ued to adjuting the load of lowly change, pecially, it i applicable to control forecat load: certainty load. But primary frequency modulation i a quick regulation proce of imple feedback loop of generation unit to load change. It wa only tarted up while econdary frequency regulation wa too late to regulate the high-peed change of load. So a to underline the primary contradiction, the affect of econdary frequency regulation wan t conidered in the analyi of primary frequency regulation. When SMES device wa intalled in power ytem, power flow of tie-line and frequency change curve were howed in Fig.3. Among them, curve repreent the affect from primary frequency regulation only under the condition without SEMS device. Curve how when SMES device wa intalled in the area of load diturbance, repone time i 30m after load diturbing happening. In fact, thi condition i an ideal time of SMES device action. Curve 3 repreent that SMES device wa intalled in the area of load diturbance, but the repone time i 4 after load diturbing. During imulation, load diturbance value of 0.0 p.u i uppoed, at the ame time, 0.0p.u of power output will be upplied by SMES device. The parameter of thi ytem are taken from [4]. The relevant parameter are given in Table. 5 Simulation reult 5. Effect from SMES device on primary frequency regulation Secondary frequency regulation mainly wa ued to adjuting the load of lowly change, pecially, it i applicable to control forecat load: certainty load. But primary frequency modulation i a quick regulation proce of imple feedback loop of generation unit to load change. It wa only tarted up while econdary frequency regulation wa too late to regulate the high-peed change of load. So a to underline the primary contradiction, the affect of econdary frequency regulation wan t conidered in the analyi of primary frequency regulation. When SMES device wa intalled in power ytem, power flow of tie-line and frequency change curve were howed in Fig.3. Among them, curve repreent the affect from primary frequency regulation only under the condition without SEMS device. Curve how when SMES device wa intalled in the area of load diturbance, repone time i 30m after load diturbing, in fact, thi condition i an idea time of SMES device action. Curve 3 repreent that SMES device wa intalled in the area of load diturbance, but the repone time i 4 after load diturbing. During imulation, uppoing a load diturbance of 0.0p.u, 0.0p.u of power output from SMES device. Curve given in Fig.3 (a) howing SMES device i ueful for further modification of frequency bia, a een from curve howed in Fig.3 (a). A known from comparing curve and of Fig.3 (a), when SMES device act at 30m after load diturbing, SMES device action ISSN: Iue, Volume 8, December 009

7 not only i ueful for quick recovery of frequency, but alo ueful for retricting frequency fluctuation. Fig.3 (b) how the condition of power flow change of tie-line, curve repreent it i benefit to reducing power flow among tie-line, when SMES device quickly act at the time of load diturbance. At the ame time, power upport from outer-area wa reduced effectively. Table lit the imulation reult. There i the average value of frequency bia and tie-line change while only primary frequency regulation device coordinate with SMES device. Curve, that i, if SMES device act after load diturbance happened 30m, the reult i optimal (a) 0 T() (a) T() (b) 0 T() Fig.3 Primary frequency regulation tatu while SMES device intalled Table Average of frequency bia and tie-line change baed on primary frequency and SMES regulation f (pu) ptie (pu) Curve Curve Curve (b) T() Fig.4 AGC regulation tatu while SMES device intalled Table 3 Average of frequency bia and tie-line change baed on AGC and SMES regulation f (pu) ptie (pu) Curve Curve ISSN: Iue, Volume 8, December 009

8 5. Effect from SMES device on econdary frequency regulation When applying SMES device to upplementing partial regulation capacity of AGC, change curve of tie-line and ytem frequency were howed in Fig.4 and 5. In Fig.4, curve repreent the cae when the AGC unit wa thrown in only, curve decript that cae when all unit joint into AGC action, moreover, baed on the value of load forecat, the output regulation value of SMES device wa 0.0 p.u, the SMES device wa intalled in output-end of generator of load diturb area. i.e, regulation value of ahead-load forecat ditributed to thi AGC unit wa complemented by SMES device. From Fig.4 and table 3 we can ee, while SMES device coordinate with AGC, SMES will be benefit to frequency and tie-line recovery quickly Fig 5 provide that comparion reult of ahead and lag-control. Among them, curve preent the 0.0p.u active power output provided by SMES device baing on uperhort time load forecat. After one period (4), the load rie to 0.0p.u, curve how that AGC unit action only, SMES device doen t act. Curve 3 wa obtained baing on the ize of ACE, applying lag-control of SMES device, i.e, SMES device act at one period (4) behind diturb appearance. It i may be een from the imulation reult of Fig. 5 (a), under thi condition of uper-hort time load forecat and lag-control of ACE, the action of SMES device may reduce frequency fluctuation effectively, peeding up the frequency recovery to allowed arrange. From Fig. 5 (b) we can obtain that aheadcontrol i benefit to reduce tie-line power flow. Lag-control will increae burden of tie-line. So, ahead-control baed on uper-hort time load forecat will benefit to recover frequency fluctuation and to reduce tie-line power flow. Table 4 lit the average value of frequency bia and tie-line power flow change on three kind of control mode. Thee value can be ued to prove that ahead-control i optimal control method. Frequencu bia p.u) Tie-line changing p.u) T() T() (a) (b) Fig.5 comparing SMES-in-advanced control with SMES-in-lag control Table 4 ahead-control comparing with lagcontrol baed on SMES controlling f (pu) ptie (pu) Curve E Curve Curve Concluion Baing on all analyi and imulation mentioned above, following reult can be ummarized: ) If renewable energy wa tored and ued a the upply ource of SMES device, not only the direction impule on power ytem may be avoided, but alo may be ued a ytem reervation, o it can play active pole for tability of power grid. ) Applying SMES device to frequency regulation, not only frequency fluctuation can be reduced, but alo the ytem tability wa improved. At the ame time, decreaing the power flow ISSN: Iue, Volume 8, December 009

9 among tie-line. So avoiding the increae of power exchange caued from non-concioune. 3) Adopting renewable energy to charge torage energy device, will give an new reearch ubject of mart grid. 4) It i poible to caue further line blocking due to different intallation location of SMES device. It i alo poible to reducing the power flow among tie-line. Thee problem are worthy of further tudying. Reference: [] [] Fu Shuti, Wang Haining. On Coordination of Energy Saving and Reduction of Pollution Policy with Electricity Market Reform in China [J]. Automation of Electric Power Sytem, Vol. 3, No. 6, 008, pp. 3-34, 75. [3] Wang Chao, Zhang Xiaoming, Tang Maolin, Zhu Qingdai. Real-time Dipatching Optimization Model for Energy-aving and Emiion-reduction Generation in Sichuan Grid [J]. Automation of Electric Power Sytem, Vol. 3, No. 4, 008, pp [4] Zhao Ting, Dai Yi-ping, Gao Lin. Influence of Primary Frequency Control Ability Ditribution on Power Sytem Security and Stability [J]. Electric Power, Vol.39, No.5, 006, pp. 8-. [5] Duan Nan, Li Guoheng, Wang Yuhan. Reearch on Primary Frequency Modulation Function Operating on Large Foil-fuel Power Plan [J]. North China Electric Power, Vol.003, pp. -4. [6] Gao Zonghe, Ding Qia, Wen Bojian et al. AGC-in-advance Baed on Super-hort-term Load Forecating [J]. Automation of Electric Power Sytem, Vol.4, No., 000, pp [7] Chau Jieying. Study on the Real-time Optimal Dipatch in Deregulated Environment [D] 005, Tinghua Univerity. [8] Zhu Zuoyun, Suen Jiangang, Bi Yuliang. The Impact of Wind Power Generation on Shanghai Power Network [J]. Ditribution & Utilization, Vol.4, No.4, 007, pp [9] Shang Jincheng, Zhou Jieying, Cheng man. Coordination Theory of Electric Power Sytem Optimal Dipatch Conidering Security and Economic. Automation of Electric Power Sytem, Vol.3, No.6, 007, pp [0] Mohd. Haan Ali, Minwon Park, In-Keun Yu, Tohiaki Murata, Junji Tamura. Improvement of Wind Generator Stability by Fuzzy Logic- Controlled SMES [J]. Proceeding of International Conference on Electrical Machine and Sytem, Seoul. Korea., 007. [] Gao Fuying, Gao Xiang, Jia Yanbing et al. Dicuion on Application of Diturbance Control Standard in Eat China Power Grid [J]. Automation of Electric Power Sytem, Vol. 3, No., 007, pp [] William V. Haenzahl. Will Superconducting Magnetic energy Storage Be Ued on Electric Utility Sytem? [J]. IEEE Tranaction on Magntic, Vol. MAG-, No., 975, pp [3] W. Haenzahl. Superconducting Magnetic Energy Storage [J]. IEEE Tranaction on Magnetic, Vol. 5, No., 989, pp [4] Li Jun. The Study on Key Iue of Current Source Converter for Super-conducting Magnetic Energy Storage Sytem [D]. Zhejiang Univerity [5] Byung M. Han, George G. Karady. A New Power-Conditioning Sytem for Superconducting Magnetic Energy Storage [J]. IEEE Tranactiong Energy Converion, Vol. 8, No., 993, pp [6] Li Jun, K. W. E. Cheng, D. Sutanto, Dehong Xu. A Multimodule Hybrid Converter for High-Temperature Superconducting Magnetic Energy Storage Sytem (HT-SMES) [J]. IEEE Tranaction on Power Delivery, Vol. 0, No., 005, pp [7] Zhang Wenliang, Qiu Ming, Lai Xiaokang. Application of Energy Storage Technologie in Power Grid [J]. Power Sytem Technology, Vol.3, No.7, 008, pp. -9. [8] Han Chong, Li Yan, Yu Jiang et al. Application Development of SMES in Electric Power Sytem Part One: General Review [J]. Automation of Electric Power Sytem, 00, pp [9] Jiang Xiaohua, Chu Xu, Wu Xuezhi, et al. A 0kJ/5kW SMES Sytem[J]. Automation of Electric Power Sytem, Vol. 8, No. 4, 004, pp [0] Shi Jing, Tang Yuejin, Zhou Yuheng et al. 35Kj/7kW Conduction-coled High T c Superconducting Magnet Storage [J]. Automation of Electric Power Sytem, Vol. 30, No., 006, pp [] Huang Xiaohua, Li Xuebin, Zhang Zhifeng et al. Experimental Reearch of Voltage Sourch Inverter for SMES [J]. Relay, Vol. 36, No. 3, 006, pp [] I. J. Igleia, J. Acero. Comparative Study and Simulation of Optimal Converter Topologie ISSN: Iue, Volume 8, December 009

10 for SMES Sytem [J]. IEEE Tranaction on applied uperconductivity, Vol. 5, No., 995, pp [3] Li Hongmei, Yan Zheng. Application of Q- learning Approach with Prior Knowledge to Non-linear AGC Sytem [J]. Automation of Electric Power Sytem, Vol. 3, No. 3, 008, pp , 99. [4] T.P. Imthia Ahamed, P.S. Nagendra Rao, P.S. Satry. A Reinforcement Learning Approach to Automatic Generation Control [J]. Electric power ytem reearch, Vol. 6, 00, pp Appendix Table 5 Nomenclature SMES Superconducting Magnetic Energy Storage AGC Automatic generation control RES Renewable Energy Source PF primary frequency BPA Bonneville Power Adminitration FACTS Flexible AC Tranmiion Sytem URC Uint Ramp Control GRC Generation Rate Control PWM pule width modulation ISSN: Iue, Volume 8, December 009