Frequency Quality in the Nordic system: Offshore Wind variability, Hydro Power Pump Storage and usage of HVDC Links

Transcription

1 Frequency Quality in the Nordic system: Offshore Wind variability, Hydro Power Pump Storage and usage of HVDC Links by Atsede G. Endegnanew Hossein Farahmand Daniel Huertas-Hernando SINTEF Energy Research DeepWind'213, January 213, Trondheim, Norway 1

2 Introduction Large development of offshore wind power in the North Sea (in 22 : > 35 GW and 23: 96 GW 1 ) Large potential for hydro power generation in Norway with pumped storage (11 GW 2 ) Price difference between system price and water value Pumped storage used during high wind production Investigate the effect of wind power variability (on North sea) and pumped storage on Nordic power system frequency 1 Offshore Wind Power Data, DTU Wind Energy, Twenties, Increasing balance power capacity in Norwegian hydroelectric power stations, TR A7195, Sintef Energy, 212 Offshore wind farms in 22 (red) and 23 (redblack) 2

3 Pumping Vs. Offshore wind production Tonstad & NorGer HVDC cable & German offshore wind 1 Tonstad pumping pattern Offshore wind production DanTysk Offshore wind production NordseeOst Energy (p.u.) hour 3

4 Model description Nordic synchronous power system o Norway, Sweden, Eastern Denmark, and Finland Continental European synchronous system o West Denmark and rest of UCTE Primary control: 6% droop and ±.2 Hz Secondary control: LFC on generators and HVDC links Wind farms and NorGer power flow are modeled as a negative load Initial power flow data are taken from NordPool data from 11 November 21 NorGer flow and pumping data taken from market analysis 4

5 Wind variation Modelled as linear power production change of ΔP within time span of ΔT Average wind speeds above 25 m/s NorGer HVDC link flow changes were also modelled linearly P Storm hits ΔP ΔT t 5

6 HVDC Controller Same basic control topology as the original structure Constant current control mode The central controller has an additional input ΔP o compensate for a given power imbalance o ΔP signal comes from Ramp Following Controller (RFC) 6

7 Ramp Following Controller (RFC) Two inputs: frequency deviation and power flow deviation Gets signal from ACE between two interconnected areas, change in load, change in production or flow on HVDC HVDC cable track changes in wind power production - f f DP max1 C 1* SN TOT SN 1 ΔP g1 R DP min1 DP max DP max2 Px Pref - 1 SN TOT ACE 1sβTl stl DP min ΔP TOT C 2* SN TOT SN 2... DP min2 DP maxn ΔP g2 C n* SN TOT SN n ΔP gn DP minn 7

8 Load Frequency Controller (LFC) Area control error (ACE) shared among several generators Each generator contributes according to its rating - f f DP max1 C 1* SN TOT SN 1 ΔP g1 R DP min1 DP max DP max2 Px Pref - 1 SN TOT ACE 1sβTl stl DP min ΔP TOT C 2* SN TOT SN 2... DP min2 DP maxn ΔP g2 C n* SN TOT SN n ΔP gn DP minn 8

9 LFC controllers LFC in Danmark: ± 9 MW capacity Three largest thermal generators Monitor the German-Danish border flows LFC in Norway ± 375 MW capacity 3 aggregated hydro power plants Monitor the AC-transmission with Sweden and HVDC connections with Denmark 9

10 Simulation Loss of 2 MW offshore wind power generation in western Denmark Power flow variation from Germany to Norway (NorGer): 97 MW 53 MW Initial pumping load at Tonstad: 16 MW Two cases o Case 1: Reduction and stop of pumping (Slow) Active power [MW] Case 1 Case 2 o Case 2: Stop of pumping (Fast) and change to generation Studied result o Nordic frequency 1

11 Results Western Danish power system loses ΔP=2 MW RFC on HVDC links between Nordic and western Danish systems follow the change Frequency deviation in Nordic power system due to LFC in Norway 443 MW variation in power flowing from Germany to Norway Different rate of change in pumping Active power [MW] Active power [MW] DE->NO Case 1 Case Case Frequency deviation [Hz] Active power [MW] Base Case Case 1 Case 2 SK3 SK1&2 SB KS

12 Conclusions Large offshore wind production variations in North Sea will correlate with variable power flows between Continental Europe and Nordic region. RFC control together with LFC in the Nordic region and West Denmark can contribute to power system balance restoration (in the event of large variations in offshore wind generation). RFC will have an impact on the Nordic frequency quality. In addition, the rate of change of pumped storage in hydropower stations will introduce an additional load, which also will affect the Nordic frequency. The relative rate of change in pumping stations with respect to the variations of wind power and flows between the Nordic and Continental Europe system / North Sea will also affect the frequency. Frequency deviations found in this study, assuming realistic wind power and power flows variations and pumping rates, although significant are still within the allowed limits in all the cases studied. Offshore wind variability, pumped storage loads and power flow on the HVDC links connected to the Nordic power system are likely to have significant influence on the Nordic frequency quality in the future. 12

13 Thank You for your attention! Questions? 13

14 Simulation Results (2) Case B => ΔP=2 MW Excess power observed in the Western Danish power system Reversing the power flow on SK3 reduces the steady state imbalance at the German-Danish border Nordic frequency deviation remains within allowed limits Active power [MW] SK3 SK1&2 SB KS SK3,reversed Frequency deviation [Hz] Active power [MW] HVDC control LFC in Denmark LFC in Norway HVDC control, SK3 reversed LFC in Denmark LFC in Norway Active power [MW]