IV th International Conference on Advances in Energy
Indian Institute of Technology Bombay, Mumbai
LVRT for Wind Power System
[Paper Code: 254]
Ishwari S Tank2
of Electrical Engineering, IIT Bombay
2Dept. of E&TC Engineering, SITRC
Scope of Presentation
• Wind Energy Conversion System
• LVRT requirements
• System Characteristics: SCR
• Validation of LVRT
• Behavior of WECS should be similar to that of conventional power plants.
• Grid code(IWGC) has been revised.
LVRT (Low Voltage Ride Through) : wind farm connected to 66kV and
above should fulfill LVRT requirements.
Power contained in Wind:
P = ½ ρ A v3 Watts
The power extracted from Wind:
P = ½ ρ A v3Cp
P= ½ ρ A v30.59 Watts
Where, Cp= Power coefficient
Cp v/s TSR
• Power coefficient (Cp) indicates the aerodynamic efficiency.
• Ratio of extracted power to the power contained in wind.
• Maximum power coefficient occurs at a specific TSR.
• Wind turbine is connected to SCIG through a shaft and gearbox.
• This topology represents a fixed-speed wind turbine system.
• Variable speed operation.
• Generator is connected to the grid through full converters.
• This allows the control to maximize performance.
• Variable speed Topology.
• Stator is directly connected to grid.
• Rotor connected to grid through converters.
Effects of voltage sag on Different WTG
• Effects on SCIG:
Generator gets demagnetized and speeds up.
• Effects on DFIG:
The generator gets demagnetized and speeds up and converters may fail
due to current limitations of the converters.
• Effects on PMSG:
Generator speeds up and converters may fail due to current limitations of
During sag condition, the WTG should:
Remain connected to the grid and stay operational.
Support the system during fault condition by injecting reactive power.
• Wind farms connected to 66kV and above can be disconnected if the operating point
falls below the line in figure.
• Vf =15% of Nominal System voltage
• Vpf = Minimum voltages mentioned in IWGC.
The fault clearing time for various system nominal voltage levels:
• Grid, can be modeled as a voltage source in series with impedance ZGRID:
SCC = Vbase2/|Zbase|
SCR = SCC/Sbase
• Short Circuit Ratio (SCR) = 20 (as per German grid code) or 6 (as per IWGC).
Solutions for LVRT
• Chopper resistor.
• Energy Storage System: Battery bank, Super capacitor etc.
• Excess energy can be stored in turbine- rotor inertia.
• Non-MPPT operation.
Control scheme: Normal condition
• Generator side control:
Controls speed of generator.
Generator operated at maximum power point with the help of
modified Hill Climb Search.
• Grid side control:
Maintains DC-link voltage constant.
Controls flow of active and reactive power.
Control scheme: Fault condition
• DC-link chopper resistor:
Maintains DC-link voltage constant.
Active power dissipated in the form of heat through chopper resistor.
• Grid side converter control:
Reduces active and reactive power to zero.
• Generator side control:
Generator is not affected by grid fault.
Continues to produce expected power.
Graph 1: Wind Speed
Graph 4: Electromagnetic and
Graph 2: Generator Speed
Graph 3: Generator Current
Graph 5: Generated Power
Graph 6: Grid Voltage
Graph 7: Grid Current
Graph 8: Grid Active Power
Graph 9: Grid Reactive Power
Graph 10: DC-Link Voltage
Graph 11: Transformer Secondary Voltage
• LVRT requirement is a major leap in the integration of Wind Power System
with the grid.
• We can implement the LVRT requirement combining 2 or 3 technologies.
• Control can be modified to implement reactive power compensation and
support the grid during fault condition.
• Not only the LVRT requirement but we should consider other grid
connectivity issues as well.
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