Design, Modeling, and Power Electronic Control for Transient Stabilization of Power Grids Using Flywheel Energy Storage Systems

2015-08-01T00:00:00Z (GMT) by Kevin Bachovchin
There is much interest in implementing more wind power plants in future electric energy systems. However, because wind power is unpredictable and difficult to control, large sudden disturbances in wind power generation can cause high deviations in frequency and voltage or even transient instabilities. To address these concerns, one possible solution is to add fast energy storage, such as flywheel energy storage systems. Flywheels can respond faster than conventional generators and could stabilize the system until slower generators can respond. The following approach for transient stabilization using flywheels is proposed. First, the dynamic model for the interconnected system is obtained so that control using the flywheel can be designed and
tested for provable performance. Next, flywheels are placed at each bus with wind generators, which are
the potential disturbance locations. Then, a variable speed drive controller for flywheels is designed
using time-scale separation and nonlinear passivity-based control logic. Switches in the power electronics
interfacing between the flywheel and the rest of the power grid are controlled in order to regulate both the
flywheel speed and the power electronic currents. The controller set points are chosen so that the
flywheel absorbs the wind power disturbance and the rest of the system is minimally affected. Finally,
the power electronics are sized to ensure that the flywheel can handle a certain range of disturbances.
Due to the complex nature of large interconnected power systems, automated methods are
implemented for both the modeling and control of power systems. An automated approach is presented
for symbolically deriving the dynamic model of power systems using the Lagrangian formulation from
classical mechanics, where the model is described in terms of the energy functions of the system.
Another automated method is introduced for symbolically deriving the control law using passivity-based
control, where the control law is derived from desired closed-loop energy functions.
Finally, in the actual implementation of flywheels, one major design challenge is to support the high
speed rotor. A passive magnetic bearing design is presented and the resultant magnetic fields and forces
are computed, demonstrating that stable levitation of the flywheel in all directions is achieved.