This document proposes a sensor-less motor starting technique for grid-connected small wind turbines. It describes operating the generator as a motor using grid power to rapidly accelerate the turbine rotor up to its optimal tip speed ratio. This allows the turbine to reach maximum power coefficient faster and extract more energy from the wind. Simulation results show that the proposed technique reduces starting time compared to aerodynamic starting alone and increases the overall energy captured by the turbine.

1. Sensor-less Motor Starting of Grid Connected Small Wind
Turbine
Mohamed Aner mfaaner@ucalgary.ca
Ahmed Ali ahmedtawoos@yahoo.com
Edwin Nowicki enowicki@ucalgary.ca
David Wood dhwood@ucalgary.ca
International Conference on Recent Advances in Energy
and Power Systems, RAEPS 2012

2. 1. Introduction
2. Proposed System
3. Wind Turbine Description
4. Proposed Control Technique.
5. Backward operation of VSMC
6. Simulation
7. Conclusion
Outline:Outline:

3. 1.1. IntroductionIntroduction
• Small wind turbine takes longer time for starting due to the lake of pitch adjustment.
• When the turbine starts under the aerodynamic torque, it takes turbine takes 13 sec to reach it optimal tip
speed ration at rated wind speed while at cut-in wind speed it take around 45 sec. for 5kW wind turbine.
• Due to the intermittence of the wind, the wind turbine system needs to increase the conversion efficiency
to extract the max. possible energy.
• If the turbine can reach faster to its optimal speed, the turbine can extract more energy especially at higher
power rating.
• small wind turbines are being grid connected which can use grid power for rapid acceleration in order to
reach to the optimal tip speed ratio fast.

4. Starting of 5 kW wind turbineStarting of 5 kW wind turbine

5. 2.2. Proposed SystemProposed System

6. 3.3. Wind Turbine DescriptionWind Turbine Description
6 5 4 3 2
6 5 4 3 2 1 0
3
0.5
=
=
= + + + + + +
m P
p T
T
P AC U
C C
C a a a a a a a
ρ
λ
λ λ λ λ λ λ
4.4. Proposed Control TechniqueProposed Control Technique
• According to the dynamic equation of the turbine rotor , the rotor can be accelerated if the
generator is operated as a motor.
• The turbine rotor can operate near its optimal tip speed ratio if the generator torque
matches the aerodynamic torque
a gT T J d dt B− = Ω + Ω

7. 4.1 Motoring Mode4.1 Motoring Mode
• When wind turbine starts, the turbine speed has to be increased to establish operation at
maximum power coefficient , The turbine speed can be quickly increased, if the
aerodynamic torque is assisted by operating the generator as a motor using grid power
and the bidirectional power flow feature of the VSMC.
• In order to reach the maximum acceleration, the generator torque is set to its rated value
by injecting the rated quadrature current component to the generator in the positive
direction according.
1.5 ( )= −e m qT P Iλ

8. 4.2 MPPT Mode4.2 MPPT Mode
• When the turbine reaches to 60% of optimal tip speed ratio λopt, the MPPT control
takes over to maintain operating around λopt.
=
Ω
mvir
mvir
P
T
max
3
0.5=mvir P virP AC Uρ
vir
opt
RU
λ
Ω=
• Rotor speed can be estimated from the space vector angle of the generator voltage
( )2 /3 2 /32
3
−
∠Θ = + +J J
a b cSV V V e V eπ π

9. 5.5. Backward operation of VSMCBackward operation of VSMC
 VSMC Control:VSMC Control:
 Rectifier stage control aspects:Rectifier stage control aspects:
 Switching frequency Fs should be higher than Fo and Fi.
 Only two switches should be turned on at the same time “one from upper and the
other from lower switches” to insure current continuity.
 The rectifier should be switched at zero current.
 The switching should provide a max DC link voltage.
 The switching should provide a unity input displacement power factor “DPF”.

10. Control Technique LayoutControl Technique Layout

11. Modulation of Input PhasesModulation of Input Phases
( )ic
ic
md
md
θ
θ
π
β
α
sin
3
sin
=






−=

12. ( )
)(1
sin
3
sin
βα
β
α
θ
θπ
ddd
md
md
o +−=
=






−=
Inverter stage controlInverter stage control

13. 6. Simulation results
Starting at 10 m/s

14. Starting at 4 m/s

15. Starting time Versus Wind Speed

16. Energy Gain due to Motor Starting

17. 17
7. Conclusion7. Conclusion
• The proposed control technique allows faster starting.
• The proposed motor starting control technique produce more energy than
aerodynamic starting
• The proposed Control technique has significant increase in conversion efficiency
• The proposed starting technique can start the turbine at any wind speed even below
the cut-in wind speed.