Synthetic Inertia from Wind Turbine Generation

Transcription

1 Synthetic Inertia from Wind Turbine Generation Midwest Reliability Organization 2017 Fall Reliability Conference St. Paul, MN October 25, 2017 Sr Grid Interfaces Engineer Schenectady, NY USA

2 Synthetic Inertia from Wind Turbine Generation October 25, 2017 Confidential. Not to be copied, reproduced, or distributed without prior approval. CAUTION CONCERNING FORWARD-LOOKING STATEMENTS: This document contains "forward-looking statements" that is, statements related to future events that by their nature address matters that are, to different degrees, uncertain. For details on the uncertainties that may cause our actual future results to be materially different than those expressed in our forward-looking statements, see as well as our annual reports on Form 10-K and quarterly reports on Form 10-Q. We do not undertake to update our forward-looking statements. This document also includes certain forward-looking projected financial information that is based on current estimates and forecasts. Actual results could differ materially. to total riskweighted assets.] NON-GAAP FINANCIAL MEASURES: In this document, we sometimes use information derived from consolidated financial data but not presented in our financial statements prepared in accordance with U.S. generally accepted accounting principles (GAAP). Certain of these data are considered non-gaap financial measures under the U.S. Securities and Exchange Commission rules. These non-gaap financial measures supplement our GAAP disclosures and should not be considered an alternative to the GAAP measure. The reasons we use these non-gaap financial measures and the reconciliations to their most directly comparable GAAP financial measures are posted to the investor relations section of our website at [We use non-gaap financial measures including the following: Operating earnings and EPS, which is earnings from continuing operations excluding nonservice-related pension costs of our principal pension plans. GE Industrial operating & Verticals earnings and EPS, which is operating earnings of our industrial businesses and the GE Capital businesses that we expect to retain. GE Industrial & Verticals revenues, which is revenue of our industrial businesses and the GE Capital businesses that we expect to retain. Industrial segment organic revenue, which is the sum of revenue from all of our industrial segments less the effects of acquisitions/dispositions and currency exchange. Industrial segment organic operating profit, which is the sum of segment profit from all of our industrial segments less the effects of acquisitions/dispositions and currency exchange. Industrial cash flows from operating activities (Industrial CFOA), which is GE s cash flow from operating activities excluding dividends received from GE Capital. Capital ending net investment (ENI), excluding liquidity, which is a measure we use to measure the size of our Capital segment. GE Capital Tier 1 Common ratio estimate is a ratio of equity

3 Why? System Needs Large Grids with significant penetration of wind (and solar PV) power Modern variable speed wind turbine generators do not contribute to system inertia System inertia declines as wind generation displaces synchronous generators (which are de committed) Result is deeper, faster frequency excursions for system disturbances Increased risk of under frequency load shedding (UFLS) and cascading outages October 25, 2017 St. Paul, MN 3

4 A little history The preceding slide was used in 2009, for initial marketing of this concept. Many of us thought We ll use the turbine s inertia to help counteract the decline in synchronous inertia! We can use control to synthesize inertia, through the power electronics. Synthetic Inertia seems like a good name (or is it?).more on this later. October 25, 2017 St. Paul, MN 4

5 (Initial) Control Concept Use controls to extract stored inertial energy Provide incremental arresting energy (meaning kw s) during the first 10 seconds of grid events. Allow time for governors and other controls to act Target incremental energy similar to that provided by a synchronous turbine generator with inertia (H constant) of 3.5 pu sec. Focus on functional behavior and grid response: do NOT try to exactly replicate synchronous machine behavior Goal: Have the best impact on frequency nadir for the available power and energy October 25, 2017 St. Paul, MN

6 Conventional Synchronous Machine Inertial Response October 25, 2017 St. Paul, MN 6

7 Constraints Not possible to increase wind speed Avoid stall (slowing wind turbine reduces aerodynamic lift) Must respect WTG component mechanical & electrical ratings Maintain stability of controls.and Warnings Not all settings are good for each application Be aware of tradeoffs in performance (especially during the recovery period.) Faster isn t necessarily better How low can you go (pre trigger power)? October 25, 2017 St. Paul, MN 7

8 How does it work? Basic components of a Double fed Asynchronous Wind Turbine Generator: 3 AC Windings Electrical Power Delivered to Grid Machine Terminals Wind f net P stator f rotor P rotor P rotor F rotor P conv F network Wind Turbine Wound-Rotor Generator Converter October 25, 2017 St. Paul, MN 8

9 How does it work? (part 2) Basic machine equations for all rotating machines Mechanical Torque, T m J d dt T a T m T e Electrical Torque, T e H 1 2 J ω VA 2 mo base Basic Notation: J is the inertia of the entire drive train in physical units H is the inertia constant it is scaled to the size of the machine. A typical synchronous turbine generator has an H of about 3.5 MWsec/MW. H Kinetic Energy Stored in the VA base Rotor (Watt - sec) October 25, 2017 St. Paul, MN 9

10 How does it work? (part 3) Mechanical Torque, T m Electrical Torque, T e In steady state, torques must be balanced When electrical torque is greater than mechanical torque, the rotation slows, extracting stored inertial energy from the rotating mass October 25, 2017 St. Paul, MN 10

11 What s different? Mechanical Power Electrical Power Synchronous Generator Governor Response / Fuel Flow Control Machine Angle (d q Axis) / Passive Wind Turbine* Pitch Control / Uncontrolled Wind Speed Converter Control / Active Inertial Response Inherent / Uncontrolled By Control Action * Variable speed, pitch controlled WTGs October 25, 2017 St. Paul, MN 11

12 How does it work? (part 4) Mechanical Torque is a function of: (1) Wind Speed (2) Blade Pitch (3) Blade Speed ( ά Rotor Speed) Electrical Torque is a function of: (1) Converter Control (2) Commands from Turbine Control Synthetic inertia uses controls to increase electric power during the initial stages of a significant downward frequency event October 25, 2017 St. Paul, MN 12

13 What happens during a grid event? 1) Disturbance (e.g., generator trip) initiates grid frequency decline 2) Controls detect significant frequency drop 3) Instructs WTG controls to increase electrical power 4) Additional electric power delivered to the grid 5) Rate and depth of grid frequency excursion improves 6) WTG slows as energy extracted from inertia; lift drops 7) Other grid controls, especially governors, engage to restore grid frequency towards nominal 8) Controls release increased power instruction 9) WTG electric power drops, to allow recovery of rotational inertial energy and energy lost to temporarily reduced lift 10) Transient event ends with grid restored October 25, 2017 St. Paul, MN 13

14 Control Overview... a possible approach Terminal Frequency Reference Frequency Frequency Deadband Limiter - Error Power Turbine Washout Washout Shaping Controls + To Converter Controls Generator Power Order Advantage of this approach: it is highly flexible, allowing controls to be customized to the maximum benefit of the host grid. October 25, 2017 St. Paul, MN 14

15 Example: 14GW, mostly hydro system, for trip of a large generator MW Synchronous Machine 1000 MW Wind without WindINERTIA 1000 MW Wind with Simple WindINERTIA Model (Rated Wind Speed) Wind Plant POI Bus Frequency (Hz) With WindINERTIA frequency excursion is ~21% better Reference Case Without WindINERTIA frequency excursion is ~4% worse 0 10 Time (Seconds) Minimum frequency is the critical performance concern for reliability October 25, 2017 St. Paul, MN 15

16 Example: (cont.) MW Synchronous Machine 1000 MW Wind without WindINERTIA 1000 MW Wind with Simple WindINERTIA (Wind Speed above Rated) 1000 MW Wind with Simple WindINERTIA Model (Rated Wind Speed) Wind Plant POI Bus Frequency ( With WindINERTIA frequency excursion is ~21-23% better Range of possible recovery characterisics Time (Seconds) Performance is a function of wind and other conditions: not perfectly deterministic like synchronous machine inertial response October 25, 2017 St. Paul, MN 16

17 Big System Example: Frequency Control on Wind Plants Source: Western Wind & Solar Integration Study Phase 3 Frequency Response and Transient Stability 40% of wind plants (e.g., new ones) had these controls, for a total of 300 MW initial curtailment out of 27GW production. October 25, 2017 St. Paul, MN 17

18 Field Tests: Approach and Constraints Not possible to drive grid frequency Controls driven with an external frequency signal (very similar to frequency of previous example) Performance a function of wind speed (also, not possible to hold wind speed constant during tests) Since WTG must respect other controls Turbulence & drivetrain and tower loads management affect performance of individual WTGs at any particular instant Exact performance of single WTG for a single test is not too meaningful Aggregate behavior of interest to grid October 25, 2017 St. Paul, MN 18

19 Field Tests: Results Power (kw) m/s Avg Meas 10 m/s Avg Meas 14 m/s Avg Meas Time (Seconds) Test count: 8 m/s - 19 tests 10 m/s 19 tests 14 m/s 52 tests October 25, 2017 St. Paul, MN 19

20 Simulations Power (kw) m/s Avg Meas 10 m/s Avg Meas 14 m/s Avg Meas 8 m/s PSLF 10 m/s PSLF 14 m/s PSLF Time (Seconds) Simulations capture key aspects of observed field performance. October 25, 2017 St. Paul, MN 20

21 So..What s New? Pre-trigger Activation Time Boost Level Boost Period Recovery & Reset Period Source: IESO (Ontario) Performance Validation document Issue 7.0 dated June 7, 2017 Deadband October 25, 2017 St. Paul, MN 21

22 A Change in Terminology? Inertial control responds to frequency drops only in second time frame: Uses inertial energy from rotating wind turbine to supply power to system Requires energy recovery from system to return wind turbines to nominal speed Is more This responsive is Fast Frequency at higher Response, wind speeds NOT System Inertial Response. In the language of NERC Essential Reliability Services: Governor control responds: To both frequency drops and increases In 5-60 second time frame This Requires is either curtailment Fast Frequency to be able Response, to increase or power Primary Frequency Response In the language (depending of NERC on aggressiveness Essential Reliability of the control) Services: Suggested term (?): Inertia-based Fast Frequency Control (IBFFR)" October 25, 2017 St. Paul, MN 22

23 Summary and Conclusion Need and demand for inertial response from WTGs has been growing, and GE has offered this feature to meet this need since Other OEMs are offering other inertia based controls. Diverse approaches are being offered (and developed) today. Fundamental physical differences in WTGs mean that inertial behavior is not identical to synchronous machines. Probably better termed a Fast Frequency Response (FFR) rather than surrogate synchronous inertia. Emerging grid codes are starting to require FFR; the codes must recognize physical reality, constraints, and tradeoffs. Final thought: Difference between can and should. October 25, 2017 St. Paul, MN 23

24 Thanks October 25, 2017 St. Paul, MN 24

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