Tim Chiocchio

Notional all-electric ship systems integration thermal simulation and visualization

This work presents a simplified mathematical model for fast visualization and thermal simulation of complex and integrated energy systems that is capable of providing quick responses during system design. The tool allows for the determination of the resulting whole system temperature and relative humidity distribution. For that, the simplified physical model combines principles of classical thermodynamics and heat transfer, resulting in a system of three-dimensional (3D) differential equations that are discretized in space using a 3D cell-centered finite volume scheme. As an example of a complex and integrated system analysis, 3D simulations are performed in order to determine the temperature and relative humidity distributions inside an all-electric ship for a baseline medium voltage direct current power system architecture, under different operating conditions. A relatively coarse mesh was used (9410 volume elements) to obtain converged results for a large computational domain (185m×24m×34m) containing diverse equipment. The largest computational time required for obtaining results was 560 s, that is, less than 10 min. Therefore, after experimental validation for a particular system, it is reasonable to state that the model could be used as an efficient tool for complex and integrated systems thermal design, control and optimization.

AC Loss and Magnetic Shielding Measurements on 2GHTS Inductive Fault Current Limiter Prototype Modules

A new calorimetric measurement set up based on the measurement of nitrogen gas flow rate that results from the liquid nitrogen boil-off was established to measure ac losses in prototype superconducting modules of an inductive fault current limiter (iSFCL). A copper coil, to serve as the primary winding of iSFCL, was used to induce currents in the superconducting modules and drive them to a quench. The set up is suitable for superconducting devices of up to 360 mm in diameter and 400 mm in height. AC losses and magnetic shielding characteristics of the superconducting modules, made from wide second-generation high-temperature superconducting (2GHTS) tapes, were studied. Measurements were carried out at primary currents up to the quench current at frequencies from 10 Hz to 200 Hz. Dependence of primary quench current and ac losses on the frequency were measured. Implications of the extent of ac losses on the operating costs for maintaining liquid nitrogen in a practical iSFCL are discussed. The sudden change in the inductance of the primary coil and the corresponding change in the voltage during a quench of the superconducting modules were demonstrated.

Developing a validated real-time system-level thermal simulation for future all-electric ships

This paper presents a method to perform real-time system-level shipboard thermal simulations. The modeling approach is described in detail as the method is applied to the cooling facilities of the CAPS 5 MW MV laboratory. The derived simulation is studied using standard model validation tools such as factor screening and uncertainty propagation. Error bounds of system response variables are compared to results from experiments on the CAPS cooling facilities published previously. The goal is to provide a first step in the development of real-time system-level thermal simulations suitable for future HIL simulations employed in the engineering of future all-electric ships. It is envisioned that these simulations will be useful for the development and testing of future system-level controls.

Mechanical power-hardware-in-the-loop: Emulation of an aeroderivative twin-shaft turbine engine

This paper presents a method for driving an AC electric motor so that it emulates, at its drive shaft, the steady-state and transient loading and unloading dynamics of an aeroderivative twin-shaft gas turbine engine. This approach allows safe and robust testing of connected equipment, for example an electric generator, without having to install (or risk damage to) an actual gas turbine engine and all of its support systems. The lower inertia constant of an aeroderivative twin-shaft gas turbine relative to a comparably powerful AC motor introduces power, accuracy, and stability limitations in the emulation system. We have studied the performance of the emulation method at reduced scale using two identical 15 kW induction machines on a common shaft in which one machine acts as gas turbine emulation motor and the other one as a generator under test. The speed controller of the vector controlled emulation motor tracks the speed of a real time reference model of an aeroderivative twin-shaft gas turbine engine. Experimental results demonstrate the power and stability limitations that apply to the emulation system.

Finite Element Model of a Superconducting Fault Current Limiter Calibrated by Hardware-in-the-Loop Measurements

A bench top model of an inductive superconducting fault current limiter (iSFCL) has been designed based on wide tape of second generation high temperature superconducting (2GHTS) coated conductor. The tape forms a ring shielding a reduced size ferromagnetic core. The design was optimized using a finite element model, which was calibrated and refined by impedance measurements and power hardware-in-the-loop testing of the bench top iSFCL. The finite-element model was coupled with a lumped element circuit model that simulates the electric power grid. Usefulness of such coupled models for design optimization studies and for reduction of uncertainty in transient simulation models is demonstrated.

Modeling of medium voltage power electronics converters utilizing advanced simulation tools

This paper addresses the steady-state and dynamic modeling of a three-level, neutral-point-clamped (NPC) voltage source converter (VSC) with active front-end (AFE) in a commercial 2.5 MW variable speed motor drive (VSD). The AFE of the modeled VSD adopts the selective harmonic elimination SHE-PWM technique with the optimization of inverter power capacity and power source quality for a wide-range VSD system. The modeling effectively captures the lineside behavior of the VSD driving an induction motor with a simplified model that only considers the AFE in detail. Numerical simulation in the PSCAD/EMTDC simulation package and experimental measurements of the existing physical setup are presented to validate the developed model. The VSC is used as an example to show the model development procedure that could be applied to other VSC and VSD applications. The off-grid operation with variable voltage source (VVS) based on power electronic converter is discussed as means to conduct model validation. Additionally, this paper will briefly discuss how the modeling approach can be used for dynamic parameter extraction.