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Dynamic Reactive Power Control for Wind Power Plants Techwindgrid ’09 Grid Integration Seminar Madrid 20/21 April 2009 Ernst Camm Charles Edwards Ken Mattern Stephen Williams ©2009 www.sandc.com Presentation Outline • Introduction to S&C Electric Company • Introduction to Dynamic Reactive Power Control for Wind Power Plants • Inverter Inverter--based Dynamic Compensators • Hybrid Reactive Power Compensators • Power Factor Control Using Hybrid Reactive Power Compensators • Harmonic Resonance And Harmonic Current Injection by WTGs • Summary Introduction to S&C Electric Company • Established in 1911 • Employee Employee--owned company • Headquarters in Chicago, IL USA • 2,100 employees worldwide • Leading provider of products and services for electric power switching, protection, automation, power quality solutions, and engineering services Introduction to S&C Electric Company • Manufacturing & engineering facilities in USA – – – – Chicago, IL Franklin, WI Orlando, FL Alameda, CA • S&C subsidiaries – – – – – S&C Electric Canada Ltd S&C Mexicana, S. de R.L. de C.V. S&C Electric do Brasil Ltda S&C Electric (Suzhou) Co., Ltd S&C Electric Europe Ltd Introduction to Dynamic Reactive Power Control for Wind Power Plants • Grid code reactive power requirements for wind power plants – Vary power factor to meet system operating conditions – Control voltage • Incentives for reactive power production/consumption – Bonus/penalty payments during different demand periods Power Factor Inducti ve Capacit ive <0.95 0.95 to <0.96 0.96 to <0.97 0.97 to <0.98 0.98 to <1.0 1.0 0.98 to <1.0 0.97 to <0.98 0.96 to <0.97 0.95 to <0.96 <0.95 Bonus/Penalty by demand period [% of reference tariff] Peak (Punta) Flat (Llano) Valley (Valle) -4 -3 -2 -1 0 0 0 2 4 6 8 -4 0 0 0 2 4 2 0 0 0 -4 8 6 4 2 0 0 0 -1 -2 -3 -4 Inverter--based Dynamic Compensators Inverter • Voltage source inverter using PWM techniques to synthesize a voltage either greater than or less than the bus where the inverters are connected • Commercial inverterinverter-based dynamic compensators are available in modules of ±1.25 MVAR at 480 V • Short Short--term capabilities of 3.3 MVAR per module (i.e. 264% of the continuous rating) for up to 3 seconds • Capability to swing from full inductive to full capacitive output, or vice versa, in about 2 milliseconds Inverter--based Dynamic Compensators Inverter • Two modules can be connected to a single 2.5 MVA, 0.48/33 kV stepstepup transformer for connection to a 33 kV (or other medium voltage) collector substation • Larger dynamic compensators are comprised of multiple ±2.5 MVAR units with stepstep-up transformers • A single ±1.25 MVAR module can be connected via its own stepstep-up transformer if the total MVAR rating requires an odd number of inverters Hybrid Reactive Power Compensators • Consist of an inverter inverter--based dynamic compensator and one or more mediummedium-voltage mechanically mechanically-switched shunt capacitor banks and reactors • Dynamic compensator can control up to six switched shunt devices (SSDs) – Can be configured to control either voltage, reactive power, or power factor • Dynamic compensator is typically sized such that the largest capacitor or reactor bank does not exceed about 70 to 75% of the rated total dynamic range Hybrid Reactive Power Compensators • Installation for 48 MW wind power plant – ±6.25 MVAR dynamic compensator – two 8 MVAR, 33 kV shunt capacitor banks – one 8 MVAR shunt reactor • Provides reactive power in the range of 0.95 leading (inductive) to 0.95 lagging (capacitive) power factor at the 33 kV POC Power Factor Control Using Hybrid Reactive Power Compensators 100 WPP MW 80 60 MW, MVAR • Hybrid reactive power compensators can be used to dynamically control the power factor at the POC with response times dictated by intentional delays associated with the switching of SSDs • Local collector bus voltage and current sensing and “slow” feedback of voltage and current at the POC through SCADA allows compensator to dynamically control the power factor at a remote POC using a line drop compensation algorithm 40 INVERTER MVAR WPP NET MVAR 20 0 -20 0 1 2 3 4 5 6 Hours 7 8 9 10 11 Harmonic Resonance And Harmonic Current Injection by WTGs • Application review must include review of potential harmonic resonance conditions – Harmonic resonance analysis – Harmonic distortion analysis based on representative “ambient” harmonic levels • In cases where WTGs with power factor correction capacitors are involved, careful attention must also be paid to any potential resonance conditions caused by the WTG capacitors Harmonic Resonance And Harmonic Current Injection by WTGs 100 10 |Z| • If resonance conditions with high local impedances at characteristic harmonic frequencies (i.e. 5th, 7th, 11th, 13th, etc. harmonics) are identified – Capacitor banks in the hybrid reactive compensation system can be converted to harmonic filter banks • If resonance conditions due to WTGs with power factor correction capacitors – Damped C C--type filter commonly used to lower local impedance of the wind power plant over a wide range of frequencies 1 0.1 Low Output High Output Damped 0.01 0 1 2 3 4 5 6 7 8 Harmonic number (n) 9 10 11 12 13 14 Harmonic Resonance And Harmonic Current Injection by WTGs • If utilizing WTGs with DFIG or full full-converter WTGs with appreciable levels of harmonic current injection – Sometimes necessary to apply a highhigh-pass filter to prevent some of the harmonic currents from flowing into the system causing high levels of harmonic voltage and current distortion – If hybrid compensator is applied, one or more of the capacitor banks can be converted to highhigh-pass filters Reactor L Resistor R Capacitor C Summary • Hybrid reactive power compensation systems provide an economical means of meeting typical grid code requirements for power factor and voltage control • The application and associated wind power plant and power system parameters must be carefully reviewed to – Optimize the design of the hybrid reactive power compensator – Identify any potential resonance conditions that may be caused by WTG power factor correction capacitors or collector substation capacitors applied in the hybrid compensator