Power Management of Wind Turbines presented by: Barry Rawn MASc Candidate University of Toronto Wind Power Generation Symposium- February 20th, 2004 SF pm
motivation modelling control potential Power Management of Wind Turbines
motivation
Improving the flexibility and power quality provided by wind generation can enable the spread of wind power.
motivation what are the main differences between conventional generators and wind turbines?
motivation The power available in the wind varies on several time- scales. This could impact: -power planning -power quality I.
motivation Wind turbines are systems having nonlinear dynamics and oscillatory modes. This can affect considerations of grid stability where controlled wind turbines are present. II.
motivation Modern turbines run at variable speeds and interface to the grid through power electronic converters. An exploration can be made of the extent to which a controlled turbine can act as a more stable-looking generator.
modelling
λ The blades of a turbine transfer momentum from the wind like the wings of an aircraft. The character of the flow depends on an effective angle of attack -blades
modelling Aerodynamic stall has two important effects: -dictates an optimal power extraction -defines a division between two dynamical regimes STABLE UNSTABLE SLOW FAST hub speed torque power -blades
modelling irregular wind field forces system both periodically and randomly disturbance at the blade passing frequency may occur due to: ● tower shadow ● wind shear ● rotational sampling -spinning blades
modelling blade passing frequency present in spectrum of blade forces, but not in spectrum of wind averaging force signals associated with rotor angle reveals periodic components less significant for variable speed systems -spinning blades
modelling flexible structure has many mechanical modes of oscillation these must be considered in structural designs -mechanical modes
modelling for control and power system studies, capturing the two main inertias and their flexible coupling is sufficient -mechanical modes
modelling
control
● several degrees of freedom available to control energy flow within the system ● power in must balance power out
control ● different strategies exist
control Tony Turbine Greg Grid
control Tony Turbine uses control freedom to: - optimize power extraction - minimize torsional oscillations
control Greg Grid Left with responsibility to balance power Can partially influence how power is delivered to the grid
control Tony Turbine feeds Greg Grid a power that's best for the wind turbine, and Greg accommodates.
control ● control tasks are decoupled in some sense ● influence on grid is a shared responsibility between both Tony Turbine and Greg Grid
control let's consider a different division of tasks: one based on energy management
control Fast Freida Cool Clara
control Fast Freida maintains power balance and minimizes torsional oscillations using energy from the turbine
control Cool Clara sets a smooth power extraction, and reacts to grid changes appropriately using full freedom
control Cool Clara requests a power that is least harmful to the grid. Fast Freida conveys it and attempts to contain wind disturbances.
control The success of such a control scheme places trust in two main assumptions.
control Fast Freida has to trust that Cool Clara will always demand a power that is achievable.
control Cool Clara has to trust that Fast Freida will manage the capacitor voltage within tolerances, and limit mechanical resonance
control appropriate control design makes both assumptions valid
control
potential
Assuming such control could be practically realized, this methodology: ● further reduces potentially troublesome influence of wind variation ● frees the converter interface to make the system appear more robust over short time scales ● allows the possibility of shifting between optimal and conservative power extraction, based on grid conditions
potential Future investigation would further characterize the properties of such a controlled system. Examples include: ● controls based on inference of hub energy could eliminate need for accurate wind speed measurement and reduce stall recovery incidents ● some potential may exist for a kind of dispatchability of energy on short time scales between turbines in a wind farm
thanks! presented by: Barry Rawn MASc Candidate University of Toronto Power Management of Wind Turbines