Integration of a bi-directional DC–DC converter model into a real-time system simulation of a shipboard medium voltage DC system
Introduction
Recently, direct current (dc) power distribution technology has been investigated in many studies as a promising candidate for future power systems [1], [2], [3]. The major changes in power technologies have resulted from the development of power electronic technologies. While current dc power converters are not yet comparable to ac transformers in terms of efficiency and reliability, the additional functionalities and compactness may offset these disadvantages in some applications. Considering the fact that most power electronic loads need dc power for end use or dc power interfaces, dc distribution systems are considered advantageous for both low and medium power level distribution. Moreover, since power converters can execute multiple functions including active flow control and power quality improvement concurrently, they can provide flexibility in power system control and management.
This research is targeting dc power systems in electric ships, specifically a notional U.S. Navy Medium Voltage DC (MVDC) shipboard power system. Since shipboard power systems have limited resources in limited space, its control objectives are more rigorous and strategic than terrestrial power systems with regard to protections, restoration, reliability, survivability, and so on [4], [5]. The purpose of the study is to develop a notional MVDC power system for next-generation integrated electric ship. Since the MVDC system contains a lot of components such as turbine generators, power converters, energy storages, and critical loads (radar, pulsed loads, and motor drives), the major task of the Electric Ship Research and Development Consortium (ESRDC) and FSU/CAPS is to implement the whole MVDC system into a real-time simulation model considering hardware-in-the-loop (HIL) test. Therefore, the final product of the whole project is the real-time simulation model in the RTDS (Real-Time Digital Simulator™) environment. From this point of view, the goal of the work presented in this paper is to augment the simulation model of a notional MVDC system, developed by the ESRDC as illustrated in Fig. 1, with realistic bi-directional dc/dc converter models. With the availability of such a model in a large scale simulation model, this research subsequently focuses on improving energy efficiency of the MVDC system using bidirectional dc/dc converters.
The configuration of the developed bi-directional dc/dc converter model is depicted in Fig. 2, originally proposed by Wang et al. [6], because it has the following important features required by shipboard power systems: (1) galvanic isolation between two voltage levels through a high frequency transformer, (2) full-bridge converters on both sides for high power application, (3) current-fed converter on the low voltage side and voltage-fed converter on the high voltage side, and (4) active clamping circuit on the low voltage side for zero-voltage switching. Compared to other configurations such as those employing voltage-fed converters on both sides [7], this configuration can smooth the power transfer due to the inductor and allow the independent control of the two converters in each operating mode.
This paper presents the controller design procedures of the bi-directional dc/dc converter. In Section 2, the small-signal average models of the converter for buck mode and boost mode are derived. The small-signal average models can provide useful tools for evaluating control performance such as pole locations and stability margins. Section 3 describes controller design process of the bi-directional dc/dc converter. An intelligent optimum search algorithm referred to as Particle Swarm Optimization (PSO) is applied to optimize the controllers. Finally, the control performance is verified via frequency-domain analysis and real-time simulations of the developed large-scale shipboard MVDC system in Section 4.
Section snippets
Basic principle
The bi-directional dc/dc converter has two operating modes – buck and boost mode. In buck mode, electric power is transferred from the high voltage side to the low voltage side. To this end, the cross-connected switch pairs in the voltage-fed converter such as (S5, S6) and (S7, S8) should be switched in turn as shown in Fig. 3(a) where D and Ts represent the steady-state duty cycle and the switching period, respectively. During the on-time of either pair of switches, which lasts for D·Ts,
Control principle
The small-signal control-to-output transfer function Gvd(s) of the buck-mode converter can be obtained from the circuit equations of Fig. 4(a) as
The small-signal transfer function Gid(s) of the boost-mode converter can be obtained from Fig. 4(b) by applying superposition theory aswhere RHV is the equivalent resistance of load and line in the MVDC side.
Note that the small-signal transfer
Control performance
The optimal control parameters for buck mode found by the PSO are Kp = 6.5, Ki = 2083.6. Fig. 8 shows the bode plot of the bi-directional dc/dc converter in buck-mode using the small-signal transfer function such as (14), (16). The compensated system has infinite gain margin and 33.1° phase margin, which is stable. All poles of the small-signal model are in LHP such as −320.5, and −777.3 ± 2483.6i. Therefore, it can be verified that the closed-loop system is stable and has good steady-state
Conclusions
A bi-directional dc/dc converter model has been implemented to a large-scale real-time simulation model of a notional MVDC shipboard power system. The small-signal average models of a bi-directional dc/dc converter are derived for designing controller and evaluating the performance and stability of the power converters. The controller design for the bi-directional dc/dc converter is complicated because of non-minimum phase zero and uncertain operations of the critical loads in the MVDC system.
Acknowledgements
This work was supported in part by the MKE (The Ministry of Knowledge Economy), Korea, under the ITRC(Information Technology Research Center) support program supervised by the IITA(Institute for Information Technology Advancement) (IITA-2009-C1090-0904-0002) and the new faculty research program 2010 of Kookmin University.
Il-Yop Chung received his B.S., M.S., and Ph.D. degrees in electrical engineering from Seoul National University, Seoul, Korea, in 1999, 2001, and 2005, respectively. He was a Postdoctoral Associate at Virginia Polytechnic Institute and State University, Blacksburg, VA, from 2005 to 2007. He was also a Visiting Researcher at ABB US Corporate Research Center, Raleigh, NC in 2007. From 2007 to 2010, he worked for the Center for Advanced Power Systems (CAPS) at Florida State University,
References (20)
- et al.
Real-time digital simulation and experimental verification of a D-STATCOM interfaced with a digital controller
Elect. Power Energy Syst.
(2004) - et al.
DC distribution for industrial systems: opportunities and challenges
IEEE Trans. Ind. Appl.
(2003) - et al.
Efficiency analysis of low and medium voltage DC distribution systems
- et al.
DC power distribution for server farms
(2007) Integrated shipboard power and automation control challenge problem
- et al.
Next generation integrated power system-NGIPS technology development roadmap ser 05D/349
(2007) - et al.
Operation principles of bidirectional full-bridge DC/DC converter with unified soft-switching scheme and soft-starting capability
IEEE APEC
(2000) - et al.
A bidirectional DC–DC convereter for an energy storage system with galvanic isolation
IEEE Trans. Power Electron.
(2007) - et al.
A soft-switching active-clamp scheme for isolated full-bridge boost converter
IEEE APEC
(2004) - et al.
Fundamentals of Power Electronics
(2001)
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Il-Yop Chung received his B.S., M.S., and Ph.D. degrees in electrical engineering from Seoul National University, Seoul, Korea, in 1999, 2001, and 2005, respectively. He was a Postdoctoral Associate at Virginia Polytechnic Institute and State University, Blacksburg, VA, from 2005 to 2007. He was also a Visiting Researcher at ABB US Corporate Research Center, Raleigh, NC in 2007. From 2007 to 2010, he worked for the Center for Advanced Power Systems (CAPS) at Florida State University, Tallahassee, FL as a Postdoctoral Associate and Assistant Scholar Scientist. Currently, he is a Full-time Lecturer at Kookmin University, Seoul, Korea. His research interests are power quality, distributed energy resources, renewable energy, and shipboard power systems.
Wenxin Liu received his Ph.D. degree in Electrical Engineering from Missouri University of Science and Technology (formerly University of Missouri-Rolla), Rolla, MO in 2005. He received his B.S. and M.S. degrees from Northeastern University, China in 1996 and 2000, respectively. From 2005 to 2009, he was an Assistant Scholar Scientist with the Center for Advanced Power Systems (CAPS) at Florida State University, Tallahassee, FL. He is currently an Assistant Professor with the Klipsch School of Electrical and Computer Engineering at New Mexico State University, Las Cruces, NM. His current research interests include neural network control, swarm intelligence, control and optimization of microgrid, and renewable energy.
Karl Schoder is an Assistant Scholar Scientist with the Center for Advanced Power Systems at Florida State University. He received his Ph.D. degree in Electrical Engineering from West Virginia University in 2002. His research interests include modeling, simulation, control and reconfiguration of electric power systems. He is an active member of the IEEE and IEEE-PES.
David A. Cartes received the Ph.D. degree in engineering science from Dartmouth College, Hanover, NH. He is an Associate Professor of the Department of the Mechanical Engineering at Florida State University (FSU), Tallahassee, FL from January 2001. He heads the Power Controls Lab at the Center for Advanced Power Systems. He is also the director of the Institute for Energy Systems, Economics and Sustainability (IESES) at FSU. His research interests include distributed control and reconfigurable systems, real-time system identification, and adaptive control. In 1994, he completed a 20-year U.S. Navy career with experience in operation, conversion, overhaul, and repair of complex marine propulsion systems. He is a member of the American Society of Naval Engineers.