Implications of the DC Voltage Control Strategy on the Dynamic Behavior of CIGRE-UK Spring Conference and Technical Visit 14-15 March 2012. Multi-terminal HVDC following a Converter Outage F. Gonzalez-Longatt 1,2 , J. Roldan 3 M. Burgos-Payán 3 , V. Terzija 4 1 Coventry University 2 Venezuelan Wind Energy Association 3 Universidad de Sevilla 4 The University of Manchester Francisco M. Gonzalez-Longatt, www.fglongatt.org.ve 1
I. Outline I. Introduction II. Control Strategies for MTDC Networks Operation (i) Inner-Fast Current Controller, (ii) DC Voltage Controller, (iii) AC Voltage Controller, (iv) Active Power Controller, (v) Reactive Power Controller. CIGRE-UK Spring Conference and Technical Visit 14-15 March 2012. III. DC Voltage Control: Methods (i) Direct Voltage-Droop Method (ii) Voltage-Margin Method IV. Simulations and Results (i) Case I : Sudden load increase, (ii) Case II : One Converter Outage V. Conclusions Francisco M. Gonzalez-Longatt, www.fglongatt.org.ve 2
I. Introduction (1/2) • The EU and the G8 Heads of Government committed their countries in 2009 to an 80 % reduction in Green House Gas emissions by 2050. • International consensus to reach this target requires the EU to achieve a CIGRE-UK Spring Conference and Technical Visit 14-15 March 2012. 'nearly zero-carbon power supply ‘. • Supergrid is the name of this future electricity system that will enable Europe to undertake a once-off transition to sustainability. • Multi-terminal HVDC (MTDC) using Voltage Source Converter (VSC) is the most appropriate technology to enable the concept of Supergrid. Francisco M. Gonzalez-Longatt, www.fglongatt.org.ve 3
I. Introduction (2/2) • The power injections ( P i ) in a DC grid Scotland Shore Line (5GW) are controlled by the converters. Denmark Shore Line (3.5GW) • On a MTDC grid as Supergrid, the England Shore Line power flow into, or out of, each (24GW) NorNed2 NorNed converter can be dynamically changed (7GQ Interface Capacity) without any reconfiguration of the HVDC grid. CIGRE-UK Spring Conference and Technical Visit 14-15 March 2012. • Although Supergrid should allow the full control of active power on all converters, several control challenges arise from this condition. • The purpose of this paper is to analyze the potential implications of the DC Voltage Control Strategy on the dynamic behavior of Multi- terminal HVDC following a Converter Outage . Francisco M. Gonzalez-Longatt, www.fglongatt.org.ve 4
II. Control Strategies for MTDC (1/3) Schematic representation of MTDC control system hierarchy P g 1 The master control optimizes the overall performance of the MTDC by regulating the DC side voltage. It is provided with the minimum set of functions necessary P l 1 for coordinated operation of the terminals in the DC circuit, U V dc i , CIGRE-UK Spring Conference and Technical Visit 14-15 March 2012. i.e. start and stop, minimization of losses, oscillation damping i and power flow reversal, black start, AC frequency and AC P P voltage support. i dc i , VSC n dc P l i , P , g i The terminal controllers determine the behavior of the converter at the system bus. They are designed for the main functions for controlling: active power ( P ), reactive power ( Q ), AC and the Time DC voltage ( V ac , U dc ) Scale Francisco M. Gonzalez-Longatt, www.fglongatt.org.ve 5
II. Control Strategies for MTDC (2/3) V U ac Ctrl , dc Ctrl , P Q Terminal Controller Ctrl Ctrl P Q ref ref P Q * * i i d q V U CIGRE-UK Spring Conference and Technical Visit 14-15 March 2012. ac ref , dc ref , U V dc ac Terminal Controllers are based on locals actions and measurements . Wide-area measurement and control can improve the system performance. Francisco M. Gonzalez-Longatt, www.fglongatt.org.ve 6
II. Control Strategies for MTDC (3/3) i i Q P max max K K P Q i Q , i P , * * K K i i ref ref , p P , d p Q q s s i i Q Controller P Controller max max V U ac Ctrl , dc Ctrl , P Q Terminal Controller Ctrl Ctrl P Q CIGRE-UK Spring Conference and Technical Visit 14-15 March 2012. ref ref P Q * * i i q d V U ac ref , dc ref , U V dc ac i i U V max max dc ref , ac K K i Vac , i Udc , * U V * K K i i dc ac ref , p Vac , p Udc , q d v s s d K i i V ac Controller * U dc Controller i i id , v K max d ref , d max p id , s i L d i L q K i iq , * i K v q ref , p iq , q s v I dq Controller q Francisco M. Gonzalez-Longatt, www.fglongatt.org.ve 7
III. DC VOLTAGE CONTROL (i) Voltage Margin Method (VMM) (ii) Voltage-Droop Method (VDM) U U dc ,A dc ,A Lower limit CIGRE-UK Spring Conference and Technical Visit 14-15 March 2012. U Rectifier Inverter dc Initial operating point a “a” U Slope m c U , dc ref dc “b” b U ref Upper limit P P a P A A P P P P ref upper upper lower lower b P ref When U dc drops the slack converter When the active power is to be transmitted station (VSC A ) will increase the active from Terminal B to Terminal A ( P A <0, P B >0), the voltage margin ( U dc ) is power injection in the DC grid P A until a new equilibrium point. subtracted from the DC reference voltage for Terminal A. Francisco M. Gonzalez-Longatt, www.fglongatt.org.ve 8
IV. Simulations and Results (1/2) • The dynamic behavior of AC/DC Test System is analyzed based on time-domain simulations. DigSILENT PowerFactory TM v14.0.525.1. CIGRE-UK Spring Conference and Technical Visit 14-15 March 2012. DC Test System: VSC MTDC system. AC Test System: of Stagg and El-Abiad. • Case I : The effect of sudden load increases on power flows and transient response in the AC/DC Test System. • Case II : The effects of a converter outage on the dynamic response are also analyzed. Francisco M. Gonzalez-Longatt, www.fglongatt.org.ve 9
IV. Simulations and Results (2/2) • An sequential solution algorithm is used for the AC/DC power flow solution. DIgSILENT Lake Main External Grid 45/15 40/5 North 1-3 1-3 3-4 3-4 DIgSILENT Bus 3 99.50 1.00 135.98.. 36.08 -34.93 45.00 22.26 -22.21 40.00 -3.94 18.55 85.82 .. 14.89 -16.73 15.00 1.66 -3.48 5.00 18.55 0.00 0.00 0.85 38.87 38.87 22.64 22.64 INVERTER -19.62 Bus 1 Bus 3 Bus 4 0.00 106.00 99.50 99.20 1.06 1.00 0.99 0.00 -3.94 -4.31 99.90 -13.78 -17.43 -0.36 CIGRE-UK Spring Conference and Technical Visit 14-15 March 2012. VSC 37 VSC 37 Multi-Terminal HVDC System 70.93 0.06 -0.26 -1.26 Bus 7 119.03 14.37 17.88 3.70 149.70 2-3 2-3 1.00 0.00 -28.94 9.33 2-4 2-4 45 45 0.00 0.00 1-2 1-2 29.00 4.67 7-8 7-8 6-7 6-7 -97.14 13.90 17.62 0.36 6-8 6-8 -69.02 -3.69 -3.15 -3.65 119.03 14.37 17.88 3.70 29.82 28.09 -27.00 -9.24 Bus 2 Bus 5 0.00 0.00 0.00 0.00 100.00 98.94 29.00 27.32 27.32 4.67 1.00 0.99 -2.44 -4.20 40.00 20.00 25.62 -25.36 60.00 Bus 6 Bus 8 -106.69 10.00 -0.83 -1.35 10.00 154.22 148.24 113.94 25.64 25.64 1.03 0.99 VSC 26 VSC 26 VSC 58 VSC 58 2-5 2-5 0.00 0.00 G 57.90 -36.23 South Elm ~ 0.00 0.00 G2 20/10 60/40 -60.00 35.00 35.00 RECTIFIER -60.00 INVERTER Stagg and El-Abiad Test System Project: fglongatt 40.00 5.00 5.00 fglongatt 40.00 Graphic: AC Power Networ DC Voltage Control on Multi-Terminal HVDC Bus 2 Bus 5 100.00 98.94 Juan Manuel Roldan Date: 01/01/2012 1.00 0.99 Francisco M. Gonzalez-Longatt, PhD -2.44 -4.20 PowerFactory 14.0.525 Annex: VSC Multi-Terminal HVDC System Project: fglongatt Graphic: DC Power Netwo DC Voltage Control Dynamic Case Date: 01/01/2012 Francisco M. Gonzalez-Longatt, PhD PowerFactory 14.0.525 Annex: • That solution is used as initial conditions for the dynamic simluations. Francisco M. Gonzalez-Longatt, www.fglongatt.org.ve 10
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