Eduard Muljadi National Renewable Energy Laboratory Golden CO eduard.muljadi@nrel

1. New Challenges in High Penetration Renewable Energy Sources Eduard Muljadi National Renewable Energy Laboratory Golden CO  eduard.muljadi@nrel.gov Missouri S&T University October 12, 2009Rolla, MO

2. Conventional vs. Wind Power Plant Other Conv. Generator Load Load GSU Xfmr Prime Mover Large Synchronous Generator • Research needs for wind plant: • Collector system optimization • Reactive power management • Voltage regulation at POI and each turbine • AC vs. DC; OH vs. UG; offshore vs. in land collector systems. • Predictive maintenance. • Wind plant model vs. WTG model.

3. Single or multiple large (100 MW) generators. Prime mover: steam, combustion engine – non-renewable fuel affected by fuel cost, politics, and pollution restrictions. Controllability: adjustable up to max limit and down to min limit. Predictability: preplanned generation based on load forecasting, influenced by human operation based on optimum operation (scheduled operation). Located relatively close to the load center. Generator: synchronous generator Fixed speed – no slip: flux is controlled via exciter winding. Flux and rotor rotate synchronously. Power Generation Conventional Power Plant

4. Power Generation Wind Power Plant • Many (hundreds) of wind turbines (1 MW – 5 MW each) • Prime mover: wind (wind turbine) –renewable (free, natural, pollution free) • Controllability: curtailment • Predictability: wind variability based on wind forecasting, influenced more by nature (wind) than human, based on maximizing energy production (unscheduled operation). • Located at wind resource, it may be far from the load center. • Generator: Four different types (fixed speed, variable slip, variable speed, full converter) – non synchronous generation • Type 3 & 4: variable speed with flux oriented controller (FOC) via power converter. Rotor does not have to rotate synchronously.

5. Single or multiple large (100 MW) generators. Prime mover: steam, combustion engine – non-renewable fuel affected by fuel cost, politics, and pollution restrictions. Controllability: adjustable up to max limit and down to min limit. Predictability: preplanned generation based on load forecasting, influenced by human operation based on optimum operation (scheduled operation). Located relatively close to the load center. Generator: synchronous generator Fixed speed – no slip: flux is controlled via exciter winding. Flux and rotor rotate synchronously. Power Generation Conventional vs Wind Power Plant • Many (hundreds) of wind turbines (1 MW – 5 MW each) • Prime mover: wind (wind turbine) –renewable (free, natural, pollution free) • Controllability: curtailment • Predictability: wind variability based on wind forecasting, influenced more by nature (wind) than human, based on maximizing energy production (unscheduled operation). • Located at wind resource, it may be far from the load center. • Generator: Four different types (fixed speed, variable slip, variable speed, full converter) – non synchronous generation • Type 3 & 4: variable speed with flux oriented controller (FOC) via power converter. Rotor does not have to rotate synchronously.

6. Four basic topologies based on grid interface: Type 1 – conventional induction generator Type 2 – wound-rotor induction generator with variable rotor resistance Type 3 – doubly-fed induction generator Type 4 – full converter interface Power Generation Types of Wind Turbine Generator Type 1 Type 2 Type 3 Type 4 Plant Feeders ac dc generator to to dc ac full power

7. Research needs: Needs a light weight, high efficiency, high power, low rpm, direct drive generator and the corresponding power converter, suitable for harsh environment (offshore). Smarter control strategies to reduce the loads, increase energy yield, and capable of riding through voltage transients and producing high power quality under normal conditions. New types of power converters: high power, high efficiency, and good grid interface capability. Power Generation Types of Wind Turbine Generator Type 1 Type 2 Type 3 Type 4 Plant Feeders ac dc generator to to dc ac full power

8. Real and Reactive Power Balance (to keep frequency and voltage constant) Adjustable Loads Inductive Load Induction Motors/Generators Variable Loads Base Loads Line Inductance Power Losses Freq UP Voltage UP Static Compensation Real Power Reactive Power Storage Freq Down Voltage Down Base Generators Line Capacitance Reserves Adjustable Generators (conventional Gen, RE) Variable Generators (RE) Switched Capacitors Synchronous Generators/ Condensers

9. Wind Power Generator VAR Compensation to help regulate voltage Other generators Output Variability • Research needs: • Reactive power management • Fast acting generation reserves • Aggregation impacts on power smoothing • Ramp up/down impacts • Storage • Forecast storage (Load Center) VR Power delivered unaffected by wind variability Voltage and Freq unaffected by wind variability Output power to compensate wind variability Low Wind Penetration Level Output power due to wind variability time time time time Output power due to wind variability Other generators High Wind Penetration Level Output power to compensate wind variability Power delivered can be affected by wind variability Voltage and Freq can be affected by wind variability time time time time

10. Transmission Constraints • Research needs: • Short term storage – stability improvement. • Long term storage – economic/peak-shaving. • Large-scale transmission optimized planning. • HV Power Electronics (FACTS devices). • Smart Grid, DSM, Deferrable Load, LAARS, PHEV • Forecast Thermal Limit (thin wire) Wind Power Generator Storage Wind Power Generator (Load Center) Stability Limit (high impedance long distance weak-grid) Storage Output power to the load Stored power in the storage Storage (Energy Time Shifter) Output power Powered by the storage Powered by the plant time time time Output power due to wind variability Output power curtailed No-Storage, Curtailment (Energy Wasted) Curtailment time time

11. Nature of Load Wind plant can only regulate down (curtailment). Generation following/scheduling is based on wind forecast. • Research needs: • Aggregation of ACE control • Reserve sharing among balancing areas • Load Acting as Resource (ERCOT) • Improve accuracy of wind forecast • Look ahead control strategy. Economic Dispatch Spinning/Non Spinning Reserves Sub-hour scheduling Spinning Reserves

12. Wind Power Plant Output Data Annual Hourly Average Summer Peaking Spring Peaking Peak Shift California Region Midwest Region Research needs: Adapt the characteristics the load (DSM) to the local source Understand the regional behavior of wind pattern and other RE Sources. Multiple types of RE sources in parallel mode.

13. Possible shift by Demand Side Management Possible shift by Storage or Parallel Operation with other RES Matching Wind and Load • Research Needs: • Demand Side Management • Power and information flow (in the same wire or wireless) • Hybrid appliances (gas/electric) activated by electricity pricing. • Price incentives for helping the grid maintain frequency. • Energy Storage • Short term storage for stability of the power system • Distributed storage close to the load or end use reduces round trip loss, encourages mass production of storage at smaller sizes, thus lowers the manufacturing cost. • Buy low, sell high based on the signal LMP or spot pricing. • Parallel Operation with other RES • Generation profile from PV and CSP tends to occur during the day when the price of electricity is high. Thus, higher COE may be offset by the LMP. • Wind and sunlight are two different sources with different time constants. Total output variation may smooth out the total output.

14. Price Triggered Load Storage Activation • Wind generation is intermittent and varies during the day and it can cause local congestions. • Transmission congestions can lead to unequal pricing and vulnerable power system operations. • Congestion triggers different in prices at different sites throughout the day. • Research Needs: • Economic incentive for V2G or G2V (as energy commodity or spinning reserve) based on transmitted pricing signal over wired/wireless communication. • Demand side management for customers to get paid to turn on/off the loads to help increasing stability margin. • Smart devices, smart grid, wireless communication will allow the automation to take place during the day. • Potential market for customers capable of adjustable VAR production. 6:20PM 1:20PM 2:20PM 6:45PM 6:50PM 7:00PM

15. Wind Power Plant Operation Normal Operation One Day of Output Variation Cumulative vs. Local Ramping Rates Cumulative Ramping Down 0.4 GW/Hr Localized Ramping Down 5.25 GW/Hr • Research needs: • Spinning or non spinning reserves • Parallel operation with other RE sources • Long-term energy storage to shift the output and get a better price of electricity. • Research needs: • Fast acting reserve • Coordination with nearby wind power plants • Short-term energy storage to shape the ramp rates.

16. Voltage Ride Through (during transient events) • Wind power plant should be able to stay on-line under transient faults/disturbances. • The voltage should tolerate 0 p.u. for 15 msec (9 cycles). • The wind power plant should be able to regulate the power factor between 0.95 leading/lagging. • The wind power plant should have a SCADA system to allow remote access and monitoring. • Research Needs: • Wind plant added value for VAR regulation even when the wind plant is off line. • Wide Area Monitoring, Protection and Control. • Wind plant coordination with surrounding other plants. • WTG with integrated storage.

17. Power Quality (Voltage and Frequency) and Energy Management Voltage variations can be minimized by adjustable VAR compensation. Frequency variations can be minimized by fast acting spinning reserves and storage (short term) Load-Wind matching can be improved by including other RE resources (CSP, PV, Geo, Hydro, Bio), cleaner and cheaper conventional power plants, DSM, and storage (long term: CAES, PHEV, Fuel Cell – H2, Battery, Flywheel). The forecast error can be minimized by shorter scheduling periods, coordinated nationwide wind measurements, and better forecasting methods. Transmission constraints and curtailment can be minimized by improvements on the transmission lines (FACTS devices, Series/Parallel Capacitors, additional lines, dynamic ratings, storage). Summary

18. Phasor Measurement Unit (PMU) deployment allows the wind power plant to be monitored more precisely during normal and transient operation. The stability margin can be measured more accurately, and remedial action scheme can be deployed at the correct time confidently, thus blackout and outage can be prevented. Wide Area Monitoring, Protection, and Control (WAMPAC) can help monitor the surrounding power system relative to the stability limit and anticipate the next coordinated control action to protect the wind plant ahead of potential/impending disturbances in the vicinity. Use of smart grid, modern control, high speed data communication, and power system intelligence allow the system operates in autopilot and reduces the burden on operators to manage normal operation but allows special intervention in critical events. High penetration RE sources may force us to follow a new paradigm (AC vs. DC, centralized vs. distributed, constant f vs. 60 Hz, synchronized vs. floating/island networks, instant delivery vs. stored energy) Summary