In this paper, the effects and mitigation strategies of pulsed loads on medium voltage DC (MVDC) electric ships are explored. Particularly, the effect of high-powered pulsed loads on generator frequency stability are examined. As a method to stabilize a generator which has been made unstable by high-powered pulsed loads, it is proposed to temporarily extract energy from the propulsion system using regenerative propeller braking. The damping effects on generator speed oscillation of this method of control are examined. The impacts on propeller and ship speed are also presented.
The models of multi-zone electric ship is important to the development of ship operational capability and performance. However, there is not one best model type that can fit all the needs of the engineering process. High-fidelity models are needed to act as a digital twin to the system hardware for testing and validation purposes. However, a highly detailed digital model of a MVDC does not enable insight and development of analytical control and optimization algorithms. This paper presents a reduced order model (ROM) of a notional four-zone medium voltage ship. This ROM can be written in a closed-form analytical expression that is appropriate for analysis and high-level supervisory control synthesis.
The U.S. Navy is investing in the development of new technologies that broaden warship capabilities and maintain U.S. naval superiority. Specifically, Naval Sea Systems Command (NAVSEA) is supporting the development of power systems technologies that enable the Navy to realise an all-electric warship. A challenge to fielding an all-electric power system architecture includes minimising the size of energy storage systems (ESS) while maintaining the response times necessary to support potential pulsed loads. This work explores the trade-off between energy storage size requirements (i.e. mass) and performance (i.e. peak power, energy storage, and control bandwidth) in the context of a power system architecture that meets the needs of the U.S. Navy. In this work, the simulated time domain responses of a representative power system were evaluated under different loading conditions and control parameters, and the results were considered in conjunction with sizing constraints of and estimated specific power and energy densities of various storage technologies. The simulation scenarios were based on representative operational vignettes, and a Ragone plot was used to illustrate the intersection of potential energy storage sizing with the energy and power density requirements of the system. Furthermore, the energy storage control bandwidth requirements were evaluated by simulation for different loading scenarios. Two approaches were taken to design an ESS: one based only on time domain power and energy requirements from simulation and another based on bandwidth (specific frequency) limitations of various technologies.
This paper presents a control design methodology that addresses high penetration of variable generation or renewable energy sources and loads for networked AC /DC microgrid systems as an islanded subsystem or as part of larger electric power grid systems. High performance microgrid systems that contain large amounts of stochastic sources and loads is a major goal for the future of electric power systems. Alternatively, methods for controlling and analyzing AC/ DC microgrid systems will provide an understanding into the tradeoffs that can be made during the design phase. This method develops both a control design methodology and realizable hierarchical controllers that are based on the Hamiltonian Surface Shaping and Power Flow Control (HSSPFC) methodology that regulates renewable energy sources, varying loads and identifies energy storage requirements for a networked AC/DC microgrid system. Both static and dynamic stability conditions are derived. A renewable energy scenario is considered for a networked three DC microgrids tied into an AC ringbus configuration. Numerical simulation results are presented.
Wilson, David G.; Glover, Steven F.; Cook, Marvin A.; Weaver, Wayne W.; Robinett, Rush D.; Young, Joseph Y.; Borraccinia, Joe B.; Ferrese, Frank F.; Amy, John A.; Markel, Stephen M.; McCoy, Tim J.
Several technical power system architectures are being evaluated for the Navy's next generation all-electric warship. One concept being considered includes a scheme to power both port and starboard busses from a single generator with dual-windings. This approach offers redundancy and reduces the effects of prime mover light loading, but it inherently couples the two busses through the common generator. In this work, dynamic issues of galvanic and electro-mechanical coupling of power systems through a single dual-wound generator are discussed. Previous works focused on harmonics and galvanic coupling. Herein, focus is placed on average-value modeling of the galvanic coupling and on evaluation for fault response. Conclusions are presented from analysis, simulation, and experimental results.
In most distributed power electronic systems, the transmission line effects associated with cabling are neglected due to the expectation that cables are sufficiently short to be modeled as a lumped parameter model. However, as converter switching speeds and control bandwidth increase, especially in large distributed power electronic based systems, the transmission line effects may become an important consideration when establishing margins of stability. In this work, immittance based stability analysis is applied to power electronic systems with long cables between source and load converter. In particular, the Energy Systems Analysis Consortium (ESAC) method is utilized to compute limits on cable length so as to maintain prescribed stability margins. Simulation results are presented in support of the approach.