M. Bosworth

Multifunctional megawatt scale medium voltage DC test bed based on modular multilevel converter (MMC) technology

The recent development of modular multilevel converters (MMC) provides new opportunities for medium voltage DC (MVDC) systems for all electric ship design and offshore wind parks. Therefore, the Center for Advanced Power Systems at Florida State University has recently commissioned a new MVDC power-hardware-in-the-loop laboratory rated at 5 MW at DC voltages between 6...24 kV. The new lab features four individual MMCs, each composed of 36 full-bridge cells, and capable of delivering 210 A at 0...6 kV. This paper describes the entire system in detail, including the advanced current and voltage control concepts along with the state of the art digital control hardware. Selected commissioning results demonstrate the performance of the system under dynamic conditions and provide comparison with simulations obtained from a corresponding controller hardware-in-the-loop setup which is also described in the paper.

Multifunctional Megawatt-Scale Medium Voltage DC Test Bed Based on Modular Multilevel Converter Technology

Recent developments in modular multilevel converters (MMCs) provide new opportunities for medium-voltage dc (MVDC) systems for all-electric ship design and offshore wind farms. The Center for Advanced Power Systems at Florida State University has recently commissioned a new MVDC power hardware-in-the-loop laboratory rated at 5 MW at dc voltages from 6 to 24 kV. The new lab features four individual MMCs, each composed of 36 full-bridge cells, capable of delivering 210 A at any voltage in the range of 0–6 kV. This paper describes the entire system in detail, including the advanced current and voltage control concepts along with the state-of-the-art digital control hardware. Selected commissioning results are shown, which demonstrate the performance of the system under dynamic conditions and provide comparison with simulations obtained from a corresponding controller hardware-in-the-loop setup. The results indicate that an MMC-based MVDC system is a strong candidate for the ship power system because of its excellent fault management capability. The setup can be used for the understanding and design of fast fault management schemes in a breakerless MVDC system in the future all-electric ship.

Operation and design considerations of FID at distribution voltages

This paper addresses the theory, construction, and testing of a novel prototype Solid State Fault Isolation Device (SSFID) that serves as an enabling technology for the multi-university, National Science Foundation funded Future Renewable Electrical Energy Distribution and Management (FREEDM) initiative. This initiative focuses on performing the fundamental research and devising breakthrough technologies to aid in the conversion of todays conventional grid to a more flexible and effective Power Electronics Distribution System (PEDS). The SSFID, the device on which this paper focuses, provides high speed (micro-seconds) sectionalizing and re-closing abilities that will support the use and function of other components of the FREEDM system that are being designed and tested by the other universities involved in the initiative. Its functional parameters and requirements are discussed and a prototype design, as well as its testing results, is presented.

Approach to develop ship design evaluation rule-base

The Smart Ship Systems Design (S3D) prototype is a comprehensive engineering and design environment capable of performing concept development and comparison (weights, power demand, speed, range, hull-form etc.), and high level ship system tradeoff studies. This online collaborative design environment is expected to be applied at the early stages of a ship design problem. Currently, the S3D environment contains tools for the development and simulation of the electrical, piping, and mechanical ship systems and the arrangement of the system and is capable of static power flow simulation for all major disciplines. However, the tool does not have a robust capability to evaluate designs using well established engineering guidelines. The research described herein aims to address this gap and this paper presents proposed approaches and outcomes of preliminary studies.

How scattering parameters can benefit the development of all-electric ships

The power distribution system of future all-electric ships is expected to be different from typical terrestrial power distribution systems in a number of areas including grounding schemes and common-mode coupling to the ship hull. Simulation tools currently used to model terrestrial power systems do not take these differences into account. Scattering parameters are suggested to help validating existing models, support the development of specialized models for shipboard power systems, and ultimately facilitate the design of all-electric ships. This paper provides an overview of scattering parameter related activities within the Electric Ship Research and Development Consortium (ESRDC).

MW-scale power hardware-in-the-loop experiments of rapid power transfers in MVDC naval shipboard power systems

A Medium Voltage DC (MVDC), modular multilevel converter (MMC)-type, MW-scale, power hardware-in-the-loop (PHIL) advanced test facility is being utilized to better understand the impact of fast power transfer between dynamic loads in a notional MVDC shipboard system. In these experiments PHIL simulations demonstrate the transfer of power between two MW-scale, MMC-based loads in a time frame of milliseconds in a 5 kV DC system. The current work also includes the first use of an AC variable voltage source (VVS) as a power source for an MMC. PHIL and controller hardware-in-the-loop (CHIL) test results include a rest-of-system (ROS) simulation of a notional set of ship components. Results will show a distinct aspect to MVDC systems, tolerance to AC side excursions while maintaining the DC bus. Ramp rates that far exceed MIL-STD-1399 are demonstrated in an MMC-based MVDC system architecture. Comparison of CHIL and PHIL results are also presented.

Power balancing in multi-converter systems composed of modular multilevel converters (MMCs)

Multi-converter systems composed of series or parallel connected modular multilevel converters (MMCs) require a means to manage power sharing between the MMCs by balancing the load during operation. Series connected MMCs require proper voltage balancing while parallel connected MMCs require proper current balancing. The paper describes this imbalance phenomenon, illustrates the solution via simulation results, and presents field measurements obtained with a megawatt class medium voltage DC test facility.

Analysis of experimental rapid power transfer and fault performance in DC naval power systems

This paper first puts the challenges from design constraints imposed by mission load requirements on future naval surface combatants into context. Moreover, it provides results from experiments at the three partner universities designed to de-risk emerging medium voltage DC (MVDC) technology based systems and to provide validated models for future systems studies. These experiments are carries out in three recently established test beds all designed for MVDC related work. The investigations specifically targeted two major areas of interest: fault management and rapid power transfer between loads and sources. The results obtained to date reveal valuable insight into both areas.

Considering effects of parasitic coupling to ground in a switching power amplifier

The future naval surface combatant will be an all-electric medium-voltage dc integrated power and energy system; capable of supporting future dynamic loads, such as electric weapons and sensors. This system will be different from typical terrestrial distribution systems in that current carrying conductors are in close proximity to the conductive ship hull structure, and there is no well-defined ‘earth’ ground. Since this system will contain a considerable amount of power electronic devices, adoption of this system will introduce harmonic content and undesirable effects, such as common-mode (ground) current through coupling of the power system and the ships hull. Current research under the Electric Ship Research and Development Consortium aims at development of an analytical framework to characterize and simulate megawatt scale power electronic devices. The 5 MW power hardware-in-the-loop (PHIL) testbed at the Florida State University Center for Advanced Power Systems is used to interface actual power equipment, device(s) under test (DUT), to a real-time simulated environment through power amplifiers and/or actuators. To support future PHIL endeavors, it is necessary to better understand and mitigate impacts of high switching frequencies presented to the DUTs by the amplifiers of the testbed. This paper discusses the 5 MW PHIL testbed focusing on one of the amplifiers. Results from efforts for characterization and mitigation of effects from parasitic coupling to ground are presented.

High speed disconnect switch with piezoelectric actuator for medium voltage direct current grids

With the future adoption of intermittent sources of power generation and the need for dynamic and reconfigurable power systems, a shift in power system design leans towards power electronics based, fault current limited distribution systems. Design requirements for breakers will focus on fast operation to handle dynamic changes, rather than breaking large magnitude fault currents, as in conventional breakers. High-speed disconnect switches are expected to play a vital role in future DC shipboard power systems. Previous work on an NSF funded project resulted in the development of a 200 A, 15 kV fast mechanical disconnect switch for AC applications. This paper explores the use of the same type of technology for DC power systems, describes the differences and identifies the research and development work needed to make the technology fit for shipboard applications.