Integration of Large Wind Farms into Electric Grids Dr Mohammad AlZoubi
Introduction
Development
WHAT IS NEXT!! Over the next 12 years, Europe must build new power capacity equal to half the current total.
WIND ENERGY ON LINE
WHAT WE ARE TALKING ABOUT?
Components
Disk Break System
Rotors
From where the problem of integration has been started?
0.66/11kV N
Reactive power requirements. Reactive power requirements. IG Q 1 P 1 P 2 Q 2 Infinite Bus P 3 P 4 consumer Q 3 Q 4 consumer
PFC 0.66/11kV N
FSWT vs VSWT
Wind and grid
Impact of Wind Power on the Angular Stability of a Power System There is no general statement possible. The stability depends on location of wind resources and the problem has to be analyzed individually for each case. The effect of type of generator technology in transit stability is very significant and the DFIG generator presents more performance than a other induction generators
HOWEVER HOWEVER
Single-line diagram of grid connected wind farm with synchronous generators
Single line diagram for HOFA WF
Wind Farms Best wind sites versus Weak Network. This has implications for the variation in network voltage caused by the constant changes in P and Q output of the WF. Despite the variation of wind speed due to wake, the large distances filter these variations. A strong correlation exists between the voltage variations and the stability of the system. Instability can cause the wind farm to shut down
Typical Arrangement of WF
An integrated wind energy conversion system
VOLTAGE INSTABILITY The main cause for voltage stability reduction is the demand of reactive power to the wind generators
Voltage and Torque profiles
F<45.5 45.5<F<46.5 46.5<F<47 47<F<47.5 47.5<F<48.5 48.5<F<49.4 49.4<F<50.6 50.6<F<51.5 51.5<F<51.7 F>51.7 Frequency Hz INSTANTANEOUS 0.35 s 2 s 10 s 1.5 min 11 min permanent 11 min 1.5 min Instantaneous duration The requirement regarding the ability of protection systems to withstand the frequency variations listed in this Table is also applicable to any WF connected to TS through the DS.
Requirements of higher penetration Voltage stability
impact of fault location distance from IG bus on the voltage dip Voltage, [p.u] 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.998 0.997 0.996 0.995 0.994 0.993 0.992 0.991 0.99 0 250 500 750 1000 1250 1500 Fault location distance from IG bus (m) 0.989 250 500 750 1000 1250 1500 Fault location distance from IG, [m] (The fault is on the same feeder connected to IG) (The fault is on different feeder connected to IG)
Voltage drop Fault ride-through recovery profile The wind turbines must be able to continue uninterrupted operation under a transient voltage variation similar to the one illustrated below. 75% voltage drop for 250 ms Transient voltage sag 75% -250 ms 95% -0,5 sec. after fault 95% Seconds Small reduction of Output power (10%)
Voltage Sag Compensation Most WTs are programmed to disconnect themselves from the grid if voltage drops by 30% for 50ms The transmission system operators in many countries require ride-through capability for the wind farms to be integrated into the power network. Solution Power electronics substation or on-board electronics that can help wind farms ride-through faults by generating extra reactive power to hold the line voltage
Behavior at unbalanced grid faults Some grid codes such as the British Grid Code explicitly require that the wind park must ride through unbalanced faults without tripping offline. During such faults, reactive current needs to be injected as well.
Yearly frequency fluctuations histogram for a WF
Key aspects of WT behavior from the electricity industry perspective Starting transients Fluctuations in power output while operating Stopping transients
Sources of starting transients Starting transients arise from the (1) Initial imbalance between mechanical and electrical power flows (2) magnetic inrush phenomenon for IGs. Starting transients can be reduced by soft-start techniques.
Sources of Fluctuations in power output Fluctuations in power output arise from the (1) fluctuations in wind speed and direction (2) fluctuations in terminal voltage or frequency.
Sources of stopping transients Stopping transients arise from the (1) WT disconnection from an electricity NK. (2) Voltage and/or frequency disturbance propagating through the NK which may exceed voltage ratings or expose the rotor to unacceptable accelerating power.
Size and frequency of starting and stopping transients Size of starting and stopping transients of wind farm depends on the (1) Individual WT Size rather than wind farm. Whereas The frequency of starting and stopping transients is a function of the number of WTs in a farm.
STATCOM Solution STATCOM devices are pure power electronic devices made from IGBT, IGCT or GTO based converters to directly generate reactive currents. Compared to SVCs, STATCOMs are faster, smaller, and have better performances at reduced voltages. STATCOMS have the capability to address transient events.
Starting sequence for nine WTs in a 2MW wind farm
Output power of 2 wind farms located 80km apart over a 14-day period
Output power of 2 wind farms located 80km apart over a 3-day period
Prediction Problem
Example time series of online measurement and forecasts of wind power generation in Germany; forecasts with different forecast horizons are shown
Example time series of monitored and forecast power output for Germany
Compensation Schemes 1. Mechanically switched shunt capacitors 2. Static var Compensators (TCR, TCSC) 3. STATCOM 4. Power electronics converters (Inverter/Rectifier-DC link-inverter) Steady State events Transients events The power electronics interface depends on the source characteristics
The problem of harmonics The variable speed WTs are associated with usual problems of harmonic currents and reactive power demand of such equipment. Although of concern it appears that these disadvantages may be overcome especially if 12 pulse conversion equipment is used
WIND FARM CONFIGURATION
WIND FARM CONFIGURATION
Thank you for your patience