AC/DC System Dynamics Under AC Power System Faulted Conditions

Transcription

1 AC/DC System Dynamics Under AC ower System Faulted Conditions A sensitivity on DC Voltage Control parameters Mario Ndreko Delft University of Technology, Fulty of EEMCS, Intelligent Electrical ower Grids, Delft, the Netherlands m.ndreko@tudelft.nl

2 Contents kground Model of the VSCased MTDC grid Control of the DC voltage in the MTDC grid Test system and results Conclusions

3 3 roblem kground What is the combined ACDC system dynamic response under AC power system faulted conditions? AC ower System Multiterminal DC grid 9 3 AC ower System How does DC voltage control parameters influence the ACDC system dynamics? What is the influence of the DC grid topology on these intertions between the AC and the DC system? meshed Radial topology

4 VSCHVDC System DC Chopper VSC i q Outer Controllers i q U U U s U s C Inner Controller kp Ki s ωl ωl kp Ki s R ch Σ = abc Σ d u c, ~ WM pulses modulator u c, abc dq R u c, abc q u c, i abc abc i d L dq i q 3 u s, abc LL s Outer Controllers Inner Controllers WM Switching modules

5 5 Model of the MTDC Grid Detailed switch model includes small time constants which involves high computational costs Simplifications are necessary when modeling AC and DC systems for stability studies The models should be simple enough for system stability studies but should not neglect the DC circuit dynamics

6 Model of the MTDC Grid Simplified model of the converter: Quasi steady state model Assuming an infinite band width of the inner controller we neglect the inner controller dynamics The tive and reretive current erences as given by the outer controller are directly used in the dq xy transformation The output current is also limited by means of control AC and DC side are coupled by the relation of the power balance I pr j Us e U s U s Q Q Isource jx pr ix cos sin id i y sin cos i q I source xy i q i q VSC I pr Current Limiter s I U U s jx I pr dq id pr I i ji pr x y i y i x Outer Controllers DC cable model C U s U U s, Case where inner controller and phase retor are included xy i q i q Current Limiter dq Inner Controller and phase Retor model * i q I pr * d u s q u s

7 7 Model of the MTDC Grid Model of the DC cables ( n) I (3) U ( ) () U n U () I dx Ax u dt Newton Raphson DC grid system power flow for initialization of state spe model (Lossless converter) (3) I () U x U U U I I I n m br br br u I I I n () I T T x( m n)

8 8 Control of the DC voltage In a MTDC grid it is crucial to control the DC voltage at controllable levels both during normal operation and faulted conditions ower In the DC grid ower Out of the DC Grid C Multiterminal DC grid

9 9 Control of the DC voltage The most common method of DC voltage control in a MTDC is the power based droop control DC Voltage Droop Controller U k p _ droop k p_ k s i_ max min Active current component of the VSCHVDC Rectifier U Inverter U s, U A s ower based DC voltage droop control A

10 Test System: Results IEEE 39bus test system in SS/E Quasisteady state model of the converter Standard type model of wind turbines Standard th order generator model with control MW Multiterminal DC grid MW convenional generation = 5. MW onshore wind generation = MW offshore wind generation = 8 MW Total load = 77. MW

11 ch [MW] Test System: Results Radial connection AC Terminal Voltage Converter Active ower Meshed DC grid Radial DC grid L3, L5, L5, L, L3=km L, L =km L5, L, L3 =km NE system DC Terminal Voltage us 3 us 3 DC terminal 3 DC terminal 33 DC terminal VSC 3 VSC 3 Onshore Converters DC Chopper VSC 3 VSC 3

12 Degrees ch [MW] Test System: Results Effect of the fault in the MTDC connected remote AC system Converter Active ower VSC DC Terminal Voltage G Rotor angle deviation DC terminal Onshore Converters DC Chopper 5 VSC Meshed DC grid Radial DC grid L3, L5, L5, L, L3=km L, L =km L5, L, L3 =km NE system

13 Degrees () () ( ) 3 Test System : Results Sensitivity of the DC voltage droop control parameters (radial connection) U U U Inverter A slope k p Converter Active ower VSC 3 Kp=5 Kp= Converter Active ower VSC 3.5 Dissipated ower chopper Dissipated ower chopper 3 A 5.5 U U U Inverter A Converter Active ower VSC Dissipated ower chopper 33 A Deviation from st.st valie of rotor angle for G 5 5

14 Degrees Degrees Test System: Results Sensitivity of the DC grid topology (meshed and radial MTDC) AC Terminal Voltage VSC Active ower VSC 3 Angle deviation from steady state of generators in Seven Generator System G Meshed MTDC G Radial MTDC Active ower VSC Radial MTDC Meshed MTDC Active ower VSC Angle deviation from steady state of generators in Seven Generator System G Meshed MTDC G Radial MTDC

15 5 Summary Under AC side disturbances it is more the DC voltage droop control parameters which influence the AC/DC system intertions and less the topology of the MTDC grid itself The higher is the proportional gain of the DC voltage droop controller, the larger is the tive power overshoot that appears and the disturbance added to the asynchronously HVDC connected power system There is a tradeoff between the choice of the DC voltage droop controller and the Chopper in terms of power dissipated In the case of ancillary services provided by the MTDC grid, the intertions between the DC voltage droop controller and the dedicated control loops should be extensively studied

16 Thank you!!

17 7 References [] M.Ndreko, A. A. van der Meer, M. Gibescu and M.A.M.M van deer Meijden, «Impt of DC Voltage Control arameters on AC/DC System Dynamics Under Faulted Conditions,» σε IEEE ower Energy Society GM,. [] M.Ndreko, A.van der Meer, M. Gibescu,. Rawn and M.A.M.M van der Meijden, «Damping ower System Oscillations by VSCased HVDC Networks: A North Sea Grid Case Study,» Wind Energy Integration in Large ower Systems workshop, London, Oct. 3, 3. [3] M. Ndreko, A. A. van der Meer, J. os, M. Gibescu, K. Jansen and M.A.A.M van der Meijden, Transient Stability Analysis of an Onshore ower System With MultiTerminal Offshore VSCHVDC: A Case study for The Netherlands.IEEE ES General Meeting, July 3, Vancouver C.