Siddharth B. Pratap

Utilization of Optimal Control Law to Size Grid-Level Flywheel Energy Storage

This paper presents a method for sizing grid-level flywheel energy storage systems using optimal control. This method allows the loss dynamics of the flywheel system to be incorporated into the sizing procedure, and allows data-driven trade studies to be performed which trade peak grid power requirements and flywheel storage capacity. A demonstration of the sizing methodology will be illustrated through a case study based on home consumption and solar generation data collected from the largest smart grid in Austin, Texas, USA.

A compulsator driven rapid-fire EM gun

A compulsator-driven railgun is an attractive alternative to the homopolar generator-inductor-switch configuration, especially for repetitive duty. A conceptual design of a rapid-fire EM-gun system is presented. The generator is sized to accelerate a 0.08-kg projectile to 2 to 3 km/s at a 60 pulse-per-second repetition rate. Initial design parameters are discussed, and example current and velocity waveforms are given. The generator is discharged at the proper phase angle to provide a current zero just as the projectile exits the muzzle of the railgun.

Reduced-Order Dynamic Model of Permanent Magnet and HTSC Interaction in an Axisymmetric Frame

This paper presents a reduced order model for a permanent magnet (PM) and high-temperature superconductor (HTSC) in an axisymmetric frame. This model is formulated as a bond-graph to aid integration into system models for applications such as lift bearings, where the nonlinear force-displacement interactions are important for stability analysis and control design. The reduced-order model is based on the mechanical and electromagnetic interaction between a PM and bulk HTSC. Performance of the proposed reduced-order model is compared to finite element method (FEM) analysis and experimental tests to confirm the static and transient performance.

3-D Transient Modeling of Bulk High-Temperature Superconducting Material in Passive Magnetic Bearing Applications

Bulk high-temperature superconductors are being considered for use in several engineering applications, including passive magnetic bearings. These bearings, apart from being passive, i.e., inherently stable, also offer the promise of lower bearing losses; thus, they are being considered for use with flywheels for energy storage in applications related to frequency regulation and for correcting forecasting errors associated with renewable energy sources. The effort presented in this paper was undertaken to characterize the performance of these bearings such as longitudinal and transverse stiffness and loss characteristics. To this end, a finite-element method (FEM) using the T- Ω potentials was used for the formulation. The results of the FEM were verified with experiments. These experiments are described. This FEM tool was also used to guide the development of a reduced-order model, which could run faster and, therefore, could be used in larger system simulations. Some discussions about the run time on a desktop PC are also presented.

Lumped-Parameter Model to Describe Dynamic Translational Interaction for High-Temperature Superconducting Bearings

This paper discusses a lumped parameter modeling methodology to describe the dynamic vertical and translational force interaction between a bulk superconductor and levitated permanent magnet (PM). The model is formulated to be easily incorporated into larger rigid body system models to aid design of superconducting bearings for flywheel energy storage applications. The proposed modeling technique will significantly reduce the computational expense in order to shorten the design cycle process. The validity of the proposed lumped parameter model is demonstrated by comparing results from finite-element method analysis and measurements of the force displacement interaction between a PM and a bulk high-temperature superconductor.

Assessment of losses in the field coil of the compulsator under dynamic conditions

Air core compensated pulsed alternators are being developed as compact power supplies for tactical electromagnetic gun systems. The field coil of the compensated pulsed alternator is a critical component that establishes the excitation magnetic field. Since the machine is air cored, the number of ampere-turns required from the field coil are significant. The rotating nature of the field coil requires that it be light so it can be supported under centrifugal loads. This implies that the current density in the field coil conductors is quite large. Charging the field coil too fast also results in transient losses due to proximity and skin effects. These must be accounted for in the design and simulation of these machines. During the discharge into the load, transient currents flow in the armature winding. These currents produce magnetic fields that interact with the field coils and produce additional losses. This calculation is complicated by the fact that there is relative motion between the conductors. This paper describes a two-dimensional numerical analysis that has been conducted to evaluate the losses in the field coil under these two dynamic conditions.

Transient eddy current distribution in the shield of the passively compensated compulsator-air-core machines

The eddy current distribution in the shield of an air-core passively compensated pulsed alternator (compulsator) is discussed. The action of the shield reduces the inductance of the armature winding considerably, thus enabling it to deliver high-power pulse to low-impedance loads. By virtue of its function, the shield is stressed mechanically as well as thermally. An analytical solution of the 2-D diffusion and convective diffusion equations is obtained. The solution is obtained by the extraction of the poles and corresponding residues of the transformed equations. The theory was developed specifically for the shield of an air-core compulsator, which is a single-phase alternator. By using superposition, the results can also be applied to determine the transient eddy current distribution in the shield of superconducting synchronous generators. >

Dynamic Performance of Lumped Parameter Model for Superconducting Levitation

This paper presents modeling and validation testing of the 3-D lumped parameter translational model, which describes the dynamics of a levitated permanent magnet over an array of bulk high-temperature superconductors. Previous model development and verification focused on measuring the static force-displacement curve of a magnet over a single-grain bulk superconductor. The methodology presented in this paper uses multiple multigrain yttrium barium copper oxide superconducting bricks, which is more relevant to actual bearing and magnetic levitation designs, and a larger cylindrical permanent magnet. The dynamic step input response of the system is evaluated. These tests show that, with proper consideration of brick and grain boundaries, the lumped parameter method can be used to describe the dynamic behavior and local translational stiffness of a levitated permanent-magnet assembly.