Generator output and static capacitor control considering voltage stability for large penetration of photovoltaic power

Transcription

1 International Journal of Smart Grid and Clean Energ Generator output and tatic capacitor control conidering voltage tabilit for large penetration of photovoltaic power Atuhi Enomoto a, Shunuke Aida a*, Shinichi Iwamoto a Satohi Oaki b, Nobuuki Ariohi b, Kimihiko Shimomura b a WASEDA niverit, Okubo Shinjuku-ku, Toko , Japan b CHB Electric Power Compan, Japan Abtract In Japan, the introduction of large capacit of clean energ uch a PV (photovoltaic power generation) i planned to reduce environmental burden. The Japanee government ha et the target of 53 GW of PV b However, large penetration of PV will caue everal problem in power tem. One of thee problem i that voltage value increae with the amount of PV penetration. Thu, we focu our attention on the upper voltage limit for a large penetration of PV in term of voltage tabilit. In thi paper, we conider a mart generator output and tatic capacitor control for the large penetration of PV. For the generator output control we propoe to ue the optimal power flow in term of minimizing bu voltage deviation from the precribed value. Simulation are run uing the IEEJ WEST 10-machine O/V tem model to confirm the validit of the propoed method. Keword: Voltage tabilit, VMPI, generator output control, tatic capacitor control, photovoltaic power 1. Introduction Since power tem load are located further awa from power plant and have become more unevenl ditributed in recent ear, it ha alo become more difficult to maintain voltage tabilit in power tem. Therefore, proper voltage range are determined in order to prevent voltage intabilit and to protect power device. In our previou tudie of a voltage tabilit control cheme, we propoed a voltage tabilit index, the voltage margin proximit index (VMPI), that could eail ield the voltage tabilit margin [1], [2]. In the later tage of the tud, to prevent voltage intabilit phenomena caued b contingenc or voltage collape caued b heav load, we propoed a tatic voltage tabilit preventive control cheme and an emergenc voltage tabilit control cheme both baed on VMPI [3]- [5]. Recentl, however, clean energ uch a photovoltaic power generation (PV) or wind power generation, i penetrating into the Japanee power tem following the enforcement of the Renewable Portfolio Standard (RPS) law and the feed-in tariff (FIT) polic. If a large number of PV penetrate into the power tem, voltage value increae, ince load demand i decreaed due to the active power output of the PV. Epeciall, for decreaing power demand in the pring (Japanee Golden Week) and ummer (Japanee Religiou Holida), it i conidered that the voltage rie will be remarkable. In thi paper, we therefore focu our attention on the upper voltage limit for a large penetration of PV. We propoe a mart generator output and tatic capacitor control for the large penetration of PV. For the generator output control we propoe to ue the optimal power flow in term of minimizing bu voltage deviation from the precribed value. In addition, if voltage value violate the voltage upper limit, we conider tatic capacitor a control equipment againt high voltage, and propoe a tatic capacitor * Manucript received Ma 15, 2013; revied Jul 29, Correponding author Tel.: ; addre: iwamoto.lab.pwr@gmail.com.

2 58 International Journal of Smart Grid and Clean Energ, vol. 3, no. 1, Januar 2014 control method b uing VMPI. Simulation are run uing IEEJ (the Intitute of Electrical Engineer of Japan) WEST 10-machine O/V tem model [6] to confirm the validit of the propoed method. In thi paper, we aume that generator output control mean control of onl active power from generator, and that the power factor of the PV i contant at 1.0. In addition, we focu our attention on a tatic anali of voltage tabilit, and thu dnamic are not conidered here. 2. Voltage Stabilit Index 2.1. Voltage tabilit index VMPI VMPI i an index that evaluate the voltage margin from the operating point to the boundarie of the proper voltage range, epeciall the upper voltage limit. The concept behind VMPI i hown in Fig.1. VMPI i calculated baed on the angle between vector at the upper voltage limit ( ) and at the operating point ( ). VMPI i claified into two tpe; one baed on the voltage pace and the other on the pecified pace. In thi paper, we ue the latter, which i uperior to the former in term of it linearit. VMPI S Fig. 1 Concept behind voltage tabilit index VMPI. The vector at the operating point i pecified b the initial value 2 = [e f P Gen V Gen P Load Q Load ] T. (1) The pecified value at the upper voltage limit i obtained b an optimal power flow (OPF) calculation uing the following formulae. Objective function Minimize f = k c (2) Equalit contraint Generator bue P Gen = k c P Gen, V Gen =V Gen, (3) Load bue P Load = k c P Load, Q Load =k c Q Load (4) Slack bu e = e, f = f (5) Inequalit contraint: Voltage limit V min < V Load < V max (6) Reactive power limit Q Gen min < Q Gen < Q Gen max (7) where e : real part of voltage k c : load multiplier f : imaginar part of voltage V min : lower voltage limit P Gen : active power of generator V max : upper voltage limit V Gen : voltage of generator Q i : reactive power at generator i P Load : active power of load Q Gen_min : lower reactive power limit of generator Q Load : reactive power of load Q Gen_max : upper reactive power limit of generator The pecified vector at the operating point i when it i within the proper voltage range, and i

3 Atuhi Enomoto et al.:generator output and tatic capacitor control conidering voltage tabilit for large penetration 59 when it fall below the upper voltage limit. ing thee propertie, VMPI i defined a follow: VMPI 2.2. VMPI enitivit t 1 co, t 1 co, VMPI enitivit how the variation obtained b witching one of the voltage control device unit. VMPI enitivit VMPI of a voltage control device i repreented b 0 VMPI VMPI VMPI (9) where VMPI 0 i the value of VMPI before the witch and VMPI i the value of VMPI after the witch. Fig. 2 how VMPI variation, that i, VMPI enitivit when the tatic capacitor (bue 6, 7 and 16) are controlled for the IEEJ WEST 10-machine O/V tem model. In Fig. 3, it i etablihed that the behaviour of VMPI i linearl dependent on the amount of control of the tatic capacitor. A imilar linearit i alo found when the other bue are controlled. Becaue there i linearit between VMPI and the control variable of the control device, we can calculate the required control variable b uing VMPI enitivit. (8) 18 1 Fig.2. VMPI enitivit. G G10 G G Fig.3. IEEJ WEST 10-machine O/V tem model. G2 19 G3 20 G4 21 G5 22 G6 23 G7 24 G8 25 G9 26 G2 G3 G4 G5 G6 G7 G8 G9

4 60 International Journal of Smart Grid and Clean Energ, vol. 3, no. 1, Januar Relationhip between VMPI and Penetration of PV We demontrate the relationhip between VMPI and the penetration of PV in order to how the influence on the voltage tabilit when a large number of PV penetrate the power tem model. We ue the IEEJ WEST 10-machine O/V tem model hown in Fig. 3 to run imulation. The aumption of the imulation are a follow. 1) PV i intalled to all load bue, and the power output i proportional to each load demand. 2) Reduction in the generator active power output are the ame a the total power of the PV. 3) The active power output are controlled for all generator, and reduction are proportional to each generator original active power output. In Fig. 4, when the intalled PV are at about 13 [p.u.], VMPI i below zero, and it i confirmed that the voltage value deviate from the proper voltage range of 1.05 [p.u.]. Fig. 4. Variation in VMPI for increaing penetration of PV. 4. Generator Output Control Method Regarding Each Load Bu Voltage (Propoed Method) A tated previoul, if we do not control the tatic capacitor with repect to the voltage, then the voltage value deviate from the proper voltage range when the level of intalled PV reache about 13 [p.u.]. Therefore, if a large number of PV are to be intalled in the power tem, it i poible that the voltage value will deviate from the proper voltage range. Thu, in thi ection, a generator output control method i tated which ue VMPI for a large penetration of PV. In the previou ection, the active power output reduction are proportional to each generator original active power output. However, thi control method i not effective generator output control in term of the voltage tabilit. Therefore, for the generator output control we propoe to ue the optimal power flow in term of minimizing bu voltage deviation from the precribed value. Formulation of minimizing bu voltage deviation OPF Objective function Minimize function = Σ V ref - V Load (10) Equalit contraint Generator bue V Gen =V Gen (11) Load bue P Load =P Load, Q Load = Q Load (12) Slack bu e Slack = e Slack, f Slack = f Slack (13) Inequalit contraint Voltage limit V min < V Load < V max (14) Active power limit P Gen min < P Gen < P Gen max (15) Reactive power limit Q Gen min < Q Gen < Q Gen max (16)

5 where Atuhi Enomoto et al.:generator output and tatic capacitor control conidering voltage tabilit for large penetration 61 V ref : reference voltage V min : lower voltage limit V Load : voltage at load V max : upper voltage limit e : real part of voltage P Gen : active power of generator f : imaginar part of voltage Q Gen : reactive power of generator P Gen : active power of generator P Gen_min : lower active power limit of generator V Gen : voltage of generator P Gen_max : upper active power limit of generator P Load : active power of load Q Gen_min : lower reactive power limit of generator Q Load : reactive power of load Q Gen_max : upper reactive power limit of generator Alo, it i conidered that the voltage value violate the voltage upper limit onl uing the generator output control. Therefore, we control the tatic capacitor if the voltage value deviate from the voltage upper limit. In thi paper, the flowchart of PV penetration i hown in Fig. 5. At firt, we intall 1 [p.u.] PV and determine the generator output b calculating the OPF. Then, we meaure the voltage value at each load bu. If an of the bu voltage value are above 1.03 [p.u.] (for example), we have to perform voltage control. If all the load bu voltage value are below 1.03 [p.u.], we can intall PV up to 30 [p.u.], which i the target value. Fig. 6 how a flowchart of tatic capacitor control. In Fig. 6, if an of the load bu voltage value are above 1.03 [p.u.], we calculate the VMPI enitivit and make a bu number ranking in decending order of VMPI enitivit. Finall, we reduce, b 0.05 [p.u.], the tatic capacitor intalled at the bu with the highet ranking. Fig. 5. Flowchart of PV penetration. Fig. 6. Flowchart of the tatic capacitor control. 5. Simulation In thi ection, a imulation i run to confirm the validit of the propoed method. In thi imulation, the IEEJ WEST 10-machine O/V tem model i ued. Aumption in imulation are a follow. 1) PV i intalled at all load bue, and the power output i proportional to each load demand. 2) The total generator active power output are equal to the total PV power output. 3) All generator are controlled and the reduction are proportional to generator original active power output. 4) Control device are onl the tatic capacitor intalled at the load bue.

6 Voltage [p.u.] VMPI[deg] 62 International Journal of Smart Grid and Clean Energ, vol. 3, no. 1, Januar 2014 Fig. 7 how the relationhip between VMPI and the penetration of PV when the propoed method are carried out and Fig. 8 how the voltage value at each load bu after voltage control ha been carried out when the intalled PV are at 30 [p.u.]. If we do not control the voltage, PV can be intalled onl to a maximum of 13 [p.u.]. But, b uing the propoed method, we can intall PV up to 30 [p.u.], which i our target. And Fig. 7 and Fig. 8 how the voltage value at each load bu after voltage control ha been carried out. It i confirmed that the load bu voltage are within the proper voltage range. Alo, Table 1 how the amount of each generator output control until 30 [p.u.] of PV are intalled ever 5 [p.u.]. Table 2 how the tatic capacitor intalled on each bu, which are ued for voltage control until 30 [p.u.] of PV are intalled. Method1 i that all generator are controlled and reduction are proportional to each generator original active power output. Method2 i that all generator are controlled b propoed method. It wa confirmed that amount of the tatic capacitor control i le than the method1 when we determine the generator output uing the propoed method Fig.7 Variation of VMPI for penetration of PV Fig.8 Voltage value after the control Table 1: Amount of generator control Penetration of PV[p.u.] Load Bu No. Generator 5[p.u.] 10[p.u.] 15[p.u.] 20[p.u.] 25[p.u.] 30[p.u.] G G G G G G G G G G

7 Atuhi Enomoto et al.:generator output and tatic capacitor control conidering voltage tabilit for large penetration 63 Table 2: Amount of tatic capacitor control 6. Concluion Bu No. Initial value [p.u.] Amount of control [p.u.] (Method 1) Amount of control [p.u.] (Method 2) Recentl, clean energ uch a PV ha attracted attention becaue of the threat poed b eriou environmental and energ problem. Thu, in thi paper, we have focued our attention on wide-cale penetration of PV, with an emphai on upper voltage limit conideration, and have hown the relationhip between VMPI and PV penetration. Moreover, we have propoed a mart control method b uing the optimal power flow in term of minimizing bu voltage deviation from the precribed value for a large penetration of PV. Finall, to verif the effectivene of the propoed method, we have run imulation uing the IEEJ WEST 10 machine O/V tem model. A a reult, it i confirmed that load bu voltage are within the proper voltage range in a mall amount of tatic capacitor control b uing the propoed method. Reference [1] Kataoka Y, Watanabe M, Iwamoto S. A new voltage tabilit index conidering voltage limit. In: Proc. of IEEE PES PSCE '06, 2006: [2] Tamura Y, Sakemoto K, Taama Y. Voltage intabilit proximit index (VIPI) baed on multiple load flow olution in illconditioned power tem. In: Proc. of the 27th IEEE Conference on Diciion and Control, 1988: [3] Kataoka Y, Watanabe M, Iwamoto S. Voltage tabilit preventive control uing VMPI enitivitie. Preented at: IEEJ Proceeding of the 18th Annual Conference of Power & Energ Societ, 2006 (in Japanee). [4] Sakaeda S, Watanabe M, Iwamoto S. Fat voltage tabilit preventive control uing ellipe-approximate P-V curve. Preented at: 2008 IEEE PES General Meeting, [5] Tanaka H, Tokumitu K, Iwamoto S, Kobaahi R, Hirano D, Takeuchi A. Development of the emergenc voltage control cheme uing VMPI. Preented at: 2009 IEEE PES General Meeting, [6] Standing Special Committee of Power Stem Model Standardization. Standard Model of Power Stem. Technical Report of IEE of Japan, No.754, 1999.