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Ahmad HemamiAhmad Hemami received his BS degree in Mechanical Engineering from the University of Tehran and his PhD in System Dynamics and Control from the Department of Aeronautical and Mechanical Engineering at the University of Salford, UK. Dr Hemami has several years of industrial, academic and research experience. Among his areas of expertise are robotics, control and automation, and wind energy. He has supervised several MS and PhD students, and has served as a consultant for industry. He has over 100 journal and conference publications. He is an adjunct professor at McGill University (Montreal, Canada).

Two Modes of Operation in Back-to-Back Converters for DFIGs, Is It Worthwhile?

Windtech Future Fig 1 Oct 21Advancing from type 1 turbines with a squirrel-cage generator to a doubly fed induction generator (DFIG) was a great step, as it allowed much better wind power grasp. The ability to take part of the generated power from the rotor through power converters made it possible for a wind turbine to benefit from a large proportion of the available, otherwise lost, energy in winds with higher speed. Also, in order to lower the cut-in speed from about 5 to 3–3.5m/s, it was decided to run a turbine at sub-synchronous speed. This called for switching of the roles in the back-to-back converters. This arrangement has been traditionally continued to all the later and larger turbines.
 
By Ahmad Hemami, McGill University, Montreal, Canada

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How Far Will Horizontal Axis Wind Turbines Grow?

Sway Turbine 10MWAfter continuous growth to 12MW (Haliade 12), now the wind turbine manufacturers are targeting 14 to 15MW, and 20MW turbines are expected to be available within a few years. But how far can this continue, thinking about the large mass of the nacelle, the yaw system and all the other components? Will there be any new design entering the race or will the three-bladed horizontal axis wind turbine (HAWT) in its almost standard form continue to be the norm for wind turbines? It can be envisaged that for some time this will remain the norm until a breakthrough happens.
 
By Ahmad Hemami, McGill University, Montreal, Canada

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Are We Going in the Right Direction?

Windtech Future Failure percentageThinking about the time when a major portion of electricity will be provided by wind, solar and other renewable sources, in which power converters play a significant role, the question of power quality pops up. Presently, in many places the amount of generated energy that passes through these converters is very small but now that there is a shift from type 3 turbines (with doubly-fed induction generator, DFIG) to type 4 (direct drive) for the growing offshore turbines, the presence of harmonics lowers the quality of the generated power. In turbines equipped with a DFIG at least 2/3 of the power travels through the stator winding, i.e. there is a clean sinusoidal waveform with no harmonics, but with direct-drive turbines, inevitably all the generated electricity must pass through converters.
 
By Ahmad Hemami, McGill University, Montreal, Canada

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A Design Concept for Future Offshore Wind Turbines

Fig1 Windtech Future May JuneTremendous progress can be observed in wind turbines and their technology development, as demonstrated by the increase in their size and power capture capability. The growth in size, however, cannot be indefinite and eventually reaches a limit, from a practicality viewpoint. All newer generations of current wind turbines from almost all manufacturers in the past 40+ years have been based on improving the previous generation as well as making them larger. This is true except for a few models that could not survive or even could not enter the market, for whatever reason.
 
By Ahmad Hemami, McGill University, Montreal, Canada

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Wind Turbines in 2100

Windtech Future March April 21Predicting the status of wind turbines now for 80 years in the future can be not much different from predicting the future of home computers in 1950 for 2004. You can see the latter in Figure 1 and observe such a prediction to be far from reality.
 
By Ahmad Hemami, McGill University, Montreal, Canada

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Drones or Robots for Blade Repair?

wheel4Recently I have come across the development of a robotic device called BladeBug. It is a legged moving robot for maintenance work on wind turbine blades, specifically for offshore turbines. Suction caps stick to a body for which the robot is to do some work. Congratulations to the people involved in developing the device. There are a lot of challenges to overcome for any new development to achieve the expected capabilities.
 
By Ahmad Hemami, McGill University, Montreal, Canada

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