1 Wind Requirements and Testing for Steady-State Voltage and Frequency Control IEEE PES General Meeting, Boston: July 18, 2016 Steven Saylors, P.E. Senior Specialist Vestas Wind Systems
2 Voltage Control The central wind generation must not produce voltage variation higher than 5% at the connection point in case of partial or full maneuvering, timely or not, the generation complex. (ONS Submodulo 3.6-Section 8.3.1) Voltage Control is performed through reactive power operations from the WTGs and any additional compensation equipment (Capacitor/Reactor Banks, SVC, STATCOM, & OLTC of Substation Transformer) located at the substation. Voltage control can be performed in two different ways: the Slope voltage controller the PI voltage controller.
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4 Voltage Control The voltage controller dynamic response can be tuned according to the Grid Code interconnection requirements from the power off-taker.
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6 Commission Testing From ERCOT Nodal Protocol Section 8 Performance Monitoring July 1, 2015 The Resource Entity shall perform the Automatic Voltage Regulator (AVR) tests and shall supply AVR data as specified in the Operating Guides. The AVR tests must be performed on initial qualification. The AVR tests must be conducted at a time agreed on in advance by the Resource Entity, its QSE, the applicable TSP and ERCOT. Lagging Reactive Testing (a) It is recommended, but not required, that lagging reactive tests be performed when system voltage is within the voltage profile, such as during high load periods {specified using the Summer/Fall voltage profile}. (b) Lagging tests should meet the following performance criteria: (i) Lagging Test 1: Test at or above 95% of the unit s High Sustained Limit (HSL) for at least 15 minutes. IRRs should test at or above 60% of their HSL. Testing acceptance criteria is met if the unit achieved no less than 90% of the unit s most recent CURL. (ii) Lagging Test 2: Test at the unit s HSL for at least one hour. IRRs should test with at least 90% of photovoltaic inverters or wind turbines online. Testing acceptance criteria is met if the unit achieved at least 50% of the units CURL for one hour. Leading Reactive Testing (a) It is recommended, but not required, that leading reactive tests be performed when system voltage is within the voltage profile, such as during low load periods {specified using the Winter/Spring voltage profile}. (b) Leading tests should meet the following performance criteria: (i) Leading Test 1: Test at the unit s normally expected maximum real power output during system light load conditions for at least 15 minutes. IRRs should test at or below 60% of their HSL. Testing acceptance criteria is met if the unit achieved no less than 90% of the unit s original manufacturer reactive curve or most recent CURL.
7 Test 5.3: Voltage Control S.NO Voltage Reference Droop Test 5.3.1 Test 5.3.2 Test 5.3.3 Test 5.3.4 Test 5.3.5 Test 5.3.6 Test 5.3.7 Test 5.3.8 Voltage reference changed to 141.8 kv Voltage reference changed to 140.8 kv Voltage reference changed to 139.8 kv Voltage reference changed to 140.8 kv Voltage reference changed to 142 kv Voltage reference changed to 141 kv Voltage reference changed to 140 kv Voltage reference changed to 141 kv Error within +/-10% tolerance band 4% 4% 4% 4% 8% 8% 8% 8%
8 Frequency Control The role of the frequency control is to make a wind power plant contribute to the system-wide frequency regulation scheme put in place by the TSO. The active power reference to the WTG is reduced by over-frequency or increased by under-frequency events.
P [pu] f [Hz] 9 Frequency (Governor) Response Simulated grid frequency excursions are fed to central plant controller and control response command is then distributed to all turbines operating at the time 51.0 Hz 50.0 Hz 0.9 pu Individual wind turbines respond by pitching blades and/or controlling variable frequency converters to produce aggregated plant response at PCC 0.2 pu
10 Commission Testing From ERCOT Nodal Protocol Section 8(C) Turbine Governor Speed Tests Feb. 11, 2014 INTERMITTENT RENEWABLE RESOURCE (IRR) FREQUENCY RESPONSE TEST PROCEDURE 1. The frequency response function of the Intermittent Renewable Resource (IRR) is tested On-Line at a Load level that allows the IRRs to increase or decrease Load without reaching low operating limits or high operating limits. 2. The test is performed by adding a frequency offset signal that exceeds the Governor Dead-Band value to the measured frequency signal. This should create immediate step change in the measured frequency signal. 3. The test starts at time t 0 when the frequency Dead-Band is exceeded. 4. The MW output signal should be recorded at least every two seconds. 5. The duration of the test is 100 seconds. After 100 seconds, the offset signal should be removed and the IRR should return to pretest power output. 6. The test should be conducted both with positive and negative frequency offsets. 7. The test is considered successful after the signal becomes active if at least 70% of the calculated MW contribution is delivered within 16 seconds and the response is maintained for an additional 30 seconds. 8. Droop shall be set not to exceed 5% with a maximum frequency Dead-Band of +/- 0.017Hz (per BAL-001-TRE-1). 9. IRRs located behind one Point of Interconnection (POI), metered by one ERCOT-Polled Settlement (EPS) Meter, and operated as an integrated Facility may combine IRRs for the purposes of this test.
Test 4: Power Reduction during Frequency Change 11 S.NO Test 4.1 Test 4.2 Test 4.3 Test 4.4 Test 4.5 Test 4.6 Test 4.7 Test 4.8 Test Case Frequency reference stepped from 50 Hz to 50.5 Hz Frequency reference stepped from 50.5 Hz to 51 Hz Frequency reference stepped from 51 Hz to 51.5 Hz Frequency reference stepped from 51.5 Hz to 52 Hz Frequency reference stepped from 52 Hz to 51.5 Hz Frequency reference stepped from 51.5 Hz to 51 Hz Frequency reference stepped from 51 Hz to 50.5 Hz Frequency reference stepped from 50.5 Hz to 50 Hz Error within +/-10% tolerance band
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1 Renewable Energy Resource Requirements for Fault Ride Through and Fault Current Response Dr.-Ing Claudia Rahmann Msc. Ing. Jorge Vega University of Chile
Introduction 2 Grid Code Requirements Transmission system operators (TSO) are responsible for the satisfactory operation of their power systems during normal operation and contingencies TSO set minimum requirements regarding power system performance and define technical requirements that all actors connected to their networks must fulfill Grid code requirements Grid Code Requirements During normal operation During contingencies Fault Ride Through Capability Voltage stability support
FRT 3 Fault Ride Through (FRT) Requirements In a first stage of RER development, the requirements were defined without considering the impacts on power system operation WTs were allowed/forced to be disconnected in case of voltage dips and no contribution to system stability was required Frequency stability problems in countries with high levels of wind power Grid codes have started to include technical requirements regarding the dynamic performance of RER during contingencies Disconnection of RER in case of voltage dips is usually not admitted anymore Grid codes require an uninterrupted operation under fault conditions based on voltage time profiles (FRT capability curves) Unbalanced short-circuits: Possible over-voltages in some of the phases High voltage ride through requirements are sometimes also defined Less common, but present explicitly in some grid codes like South Africa and Germany
FRT 4 FRT-curves and V I q curves Typical voltage time profile (FRT capability curves) V [p. u. ] 1,0 0,8 0,6 0,4 0,2 0 0 0,3 1,0 15 Time [sec] Certain grid codes also impose requirements regarding reactive power response of RER during and after short circuits These requirements are in the form of V I q curves Improvement of system stability Supply 20 100 40 20 20 40 I q In 10 20 30 40 Absorption V Vn
Review 5 Considered countries In total, 11 countries were selected
FRT by country 6 FRT curves for RER Europe 1,0 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 Voltage [p.u.] 0 0 0,15 0,5 1,0 1,5 3 4 5 0,25 15 Time [sec] Germany (TenneT) Denmark (WT) England (WT off-shore) Spain Denmark (PV)
FRT requirements for RER 7 FRT curves for RER America 1,0 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 Voltage [p.u.] 0 0 0,15 0,3 0,5 1,0 1,5 3 4 Mexico Canada (AESO) (WT) 0,65 5 Brazil Canada (Hydro Québec) (WT) Chile 15 Time [sec]
FRT by country 8 FRT curves for RER Others 1,0 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 Voltage [p.u.] 0 0 0,15 0,625 3 4 5 15 Time [sec] China (WT) India (400 kv) (WT) China (PV) South Africa
FRT requirements for RER 9 FRT Requirements for RER Comments Some grid codes require different FRT-curves depending on the voltage level Mexico: the maximum time to ride through a voltage dip is 150 ms only for voltage levels between 69 and 161 kv: For voltage levels of 230 kv the time is 100 ms and for voltage levels of 400 kv is 80 ms India: the maximum time to ride through a voltage dip depends on the voltage level: For 400 kv the time is 100 ms for installations with voltages between 110 kv and 220 kv is 160 ms Other grid codes require different FRT-characteristics depending on the short-circuit type Spain: a less severe profile is required during two-phase short-circuits, with a lowest value of voltage of 0.5 p.u. Voltage in the FRT-curves (or measuring point) not always well specified Spain: voltage at the connection point Chile: phase to ground voltage at the connection point Denmark: voltage at the point of connection (line-to-line voltages for the 50 Hz component) ( PV) and smallest line-to-line voltage for the 50 Hz component ( WT) Significant differences between FRT requirements among the countries
Summary 10 Characteristics of selected requirements (1) Country Fault duration (ms) Minimum voltage (p.u.) Includes Off-shore? Includes WT PV? Includes V I q requirements? RER (%) Spain 500 0.2 26 Germany *(TenneT) Denmark (Energinet) England * China 150 0 43 250 (PV) 500 (WT) 140 625 (WT) 150 (PV) 0.1 (PV) 0.2 (WT) 0 0.15 (offshore) 0.2 0 45 Ambiguously established 15 30 India 100 0.15 11 South Africa 150 0 5 * Includes FRT requirements for CGU
Summary 11 Characteristics of selected requirements (2) Country Canada (Alberta) Fault duration (ms) Minimum voltage (p.u.) Includes Off-shore? Includes WT PV? Includes V I q requirements? RER (%) 625 0.15 9 Chile 140 0.1 Mexico 150 0 Only required in case of twophase short circuits Ambiguously established Brazil 500 0.2 4 10 1
Voltage Support Requirements for RER 12 Voltage Support Requirements for RER (1) Germany: TenneT requires that RER support grid voltage with additional reactive current during a voltage dip, as shown in the figure. The voltage control must take place within 20 ms after fault recognition by providing a reactive current on the low-voltage side of the RER transformer Supply 20 100 40 20 20 40 I q In 10 20 30 40 Absorption V Vn V Denmark: the wind power plant must have a control function capable of controlling the reactive current component during voltage dips as specified in the figure 20 100 90 40 20 Area A Area C (disconnection) 10 20 30 100 I q In
Voltage Support Requirements for RER 13 Voltage Support Requirements for RER Spain: the wind power plants are required to be able to inject reactive power within 150 ms of grid recovery as shown in the figure South Africa: the RER must supply I q according to the figure (within its technical design limitations) so as to ensure that the RER helps to stabilize the voltage 110 100 90 50 20 V Area A Area B Area E I q In 20 10 20 30 100
Conclusions 14 Outlook (1) Different criteria are applied when defining the requirements for RER within the grid codes RER penetration level and its location in the network, energy policies, network robustness, system characteristics, utility practices, among others Requirements may vary considerable from operator to operator and thus from one country to another Difficulties in their direct comparison Diversity of requirements poses important burdens on RER manufacturers Interpretation of the underlying meaning of the grid code documents, managing the differences in formats (terminology and definitions) Development of hardware and software solutions for the specific requirements of each grid code Diversity of requirements increases the costs of RER
Conclusions 15 Outlook (2) Need of harmonization? Harmonization process has been proposed by Wind Europe (ex EWEA) in a two-step scheme: Structural harmonization Generic grid code format (structure, designations, figures, method of specification, definitions and units) Technical harmonization Standardization from a technical viewpoint is difficult since the requirements depend on the technical characteristics of each power system Structural harmonization in the sense of a generic grid code format should be possible to implement Consistency in the grid codes would assist RER manufacturers to move from market-oriented solutions to universal ones Efforts should be made to move towards this objective
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Requirements for Modeling and Validation of Power System Models for Wind Generation Boston, 18.07.2016 Frank Martin, Siemens Wind Power A/S
2 Why requirements for modeling and validation? Need for (validated) simulation models: Enable system operator to perform grid integration studies Enable WPP developer to perform studies to verify compliance of the WPP with grid code requirements / design WPP equipment...
Wind Turbine vs. Wind Power Plant modeling and validation Wind Turbine Wind Turbine Generator Converter 0.69 /33 kv WTG Trafo 33 kv Busbar 132/400 kv 400/16 kv Fault Ride Through Wind Turbine Generator Converter 0.69 /33 kv WTG Trafo 33 kv Busbar 33 kv Busbar 33/132 kv Park Trafo 132 kv Busbar 132 kv PCC Power Station Power Quality Harmonics Wind Turbine Generator Converter 0.69 /33 kv WTG Trafo 33 kv Busbar HPPP 132/50 kv 50/10 kv 10/0.4 kv Flicker Control Features Consumer PQ Capability P(f) Function Protection
Wind Turbine vs. Wind Power Plant modeling and validation Wind Turbine Generator Converter 0.69 /33 kv WTG Trafo 33 kv Busbar Wind Power Plant 132/400 kv 400/16 kv Wind Turbine Generator Converter 0.69 /33 kv WTG Trafo 33 kv Busbar 33 kv Busbar 33/132 kv Park Trafo 132 kv Busbar 132 kv PCC Power Station Active Power Response Wind Turbine Generator Converter 0.69 /33 kv WTG Trafo 33 kv Busbar HPPP 132/50 kv 50/10 kv 10/0.4 kv Ramp rates Frequency Control Consumer LFSM FSM V, Q, PF Control WPP features
5 Requirements for simulation models / studies TenneT Offshore [1] (Source: TenneT TSO GmbH) NGET Grid Code[2] (Source: National Grid ) Commission Regulation (EU) NC RfG [3] (Source: European Commission) Hydro Quebec [4] (Source: Hydro Quebec) TCC High-Voltage [5] (Source: VDE)
6 Requirements for simulation models / studies Grid Code TenneT Offshore Scope (studies) Time step? RMS vs. EMT Validation and accuracy Blackbox vs. open model + both o - Generic model vs. manufacturer specific? Tool dependency NETOMAC, PSCAD NGET + RMS o - no ENTSO-E NC RfG Hydro Quebec TCC High- Voltage) o Both + Both o o - no + PSS/E, EMTP- RV o RMS + - no
7 Electrical simulation models Simulation models are available: Generic WT and WPP controller models WECC IEC 61400-27-1 (CD) Manufacturer specific WT and WPP controller models in relevant simulation tools RMS e.g. PSS/E, DIgSILENT Power Factory,... EMT e.g. PSCAD, EMTP-RV,... Models for other type of studies (e.g. harmonics)
8 Electrical simulation models necessary investigations / studies Steady state investigations e.g. load flow, loading of cables and transformers, voltage drop, reactive power capability Dynamic stability investigations e.g. verify if WPP stays connected and support the grid during UVRT as well as OVRT situations Short Circuit Studies and protection design Harmonics analysis and stability Transient investigations e.g insulation coordination, detailed transient studies
Requirements for model validation - example FRT SWT-3.0 / 3.2 MW DD 2000 tests SWT-4.0 MW 2200 tests SWT-6.0 MW DD 900 test
10 Requirements for model validation - example FRT Requirements and guidelines for model validation: Grid codes (generic) WECC IEC 61400-27-2 (approach without success criteria) FGW TR4 (approach and success criteria, FRT) PVVC (approach and success criteria, FRT)
Requirements for model validation - example FRT (IEC 61400-27-2) 11 No individual values for the error in the standard (Source: IEC 61400-27)
Reactive Power [Mvar] +Ve Sequence Voltage [pu] Active Power [MW] Reactive Current [ka] Active Current [ka] D3 Platform Model Validation Grid Modeling 4 3 2 1 0 Measured Simulation -1 0 1 2 3 4 5 6 7 8 9 10 4 3 2 1 0 Measured Simulation -1 0 1 2 3 4 5 6 7 8 9 10 0.8 0.7 0.6 0.5 0.4 4 3 2 1 0-1 Measured Simulation -2 0 1 2 3 4 5 6 7 8 9 10 0.3 2 0.2 0.1 Measured Simulation 0 0 1 2 3 4 5 6 7 8 9 10 1.5 1 0.5 0 Measured Simulation -0.5 0 1 2 3 4 5 6 7 8 9 10
LV Side +Ve Sq. Voltage [kv] Reactive Power [MVAr] MV Side +Ve Sq. Voltage [kv] Active Power [MW] Reactive Current [ka] Active Current [ka] D3 Platform Model Validation Playback 4 3 Measured Simulation 2 1 0-1 0 1 2 3 4 5 6 7 8 9 10 Time [s] 4 3 Measured LV Simulation ref 2 1 0-1 0 1 2 3 4 5 6 7 8 9 10 Time [s] 12 10 8 6 4 2 Measured Simulation 0 0 1 2 3 4 5 6 7 8 9 10 4 3 2 1 0-1 Measured Simulation -2 0 1 2 3 4 5 6 7 8 9 10 0.8 0.6 0.4 2 1.5 1 0.5 Measured Simulation 0.2 Measured Simulation 0 0 1 2 3 4 5 6 7 8 9 10 0-0.5 0 1 2 3 4 5 6 7 8 9 10 Time [s]
Requirements for model validation other than FRT Model validation focus on FRT Other aspects: Reactive Power Control function and features Harmonics... Model validation for EMT models
Frequency [Hz] Active Power [MW] Wind Power Plant Frequency Control Model Validation 50.6 120 50.4 100 50.2 80 50 60 49.8 40 49.6 20 49.4 49.2 0 100 200 300 400 500 0 Measured Simulation -20 0 100 200 300 400 500
Points for Discussion Models for what kind of studies Validation requirements mostly unclear (e.g. tolerances, EMT model) Will an generic model (IEC 61400-27-1 / -2) be used
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Further information: Frank Martin Siemens Wind Power A/S Grid Connection Elektrovej 325 DK-2800 Kgs. Lyngby Denmark Mobile: +45 3037-5363 frank.martin@siemens.com
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