Medium Voltage DC Shipboard Power System Research Articles

Energy flow control and sizing of a hybrid battery/supercapacitor storage in MVDC shipboard power systems

The propulsion system of a medium-voltage dc (MVDC) ship is subject to large thrust/torque variations due to interactions of the ship and the propeller with sea waves. These variations induce steep power fluctuations on the MVDC bus, adversely impacting the stability, efficiency and power quality. Hybrid energy storage system (HESS) is a promising solution for mitigating these power fluctuations. Dictating the energy that the HESS components must deliver/absorb, the energy management strategy (EMS) impacts the size/capacity of the energy storage system (ESS). Based on this consideration, sizing and EMS of a battery/supercapacitor (SC) HESS are jointly optimised by using a deep reinforcement learning-based method. The proposed method splits the power between the HESS components such that while the operational constraints are satisfied, energy storage size and losses are minimised. Its features are adaptability to varying sea states, real-time implementation feasibility, while obviating the requirement for knowledge of the ship propulsion power profile. The efficacy of the joint sizing/EMS on reducing the ESS size is validated by comparing the sizes when battery-only, SC-only and HESS are employed in the MVDC shipboard power system. Real-time implementation feasibility and adaptability to various ship propulsion power profiles is confirmed through real-time simulations.

A novel approach for real-time implementation of MVDC shipboard power system reconfiguration

In a Shipboard Power System (SPS), faulty components are separated from the rest of the system after the occurrence of faults. In this situation, it is important to quickly restore the power supply to the affected parts of the SPS and reconfigure the system to improve its reliability and ensure safe and satisfactory operation of the system. Similar to terrestrial power systems, onboard post-fault reconfiguration aims to ensure the maximum delivery power/service to the system’s loads following a fault. In this paper, in order to deal with the reconfiguration problem during the fault situations in Medium Voltage DC (MVDC) SPS, a real-time Simulated Annealing (SA)-based reconfiguration technique is designed and implemented in the Real-Time Digital Simulator (RTDS). To validate the proposed approach, two MVDC SPS models including four and six zonal loads are used to simulate several fault scenarios. The simulation results demonstrate the effectiveness of the proposed approach to reconfigure the system under different fault situations in the real-time operation of the SPS.

Fuzzy Logic Based Energy Storage Management System for MVDC Power System of All Electric Ship

In this paper, for supporting the medium voltage dc (MVDC) shipboard power system, an energy storage management (ESM) system based on fuzzy logic (FL) has been proposed and its performance with a proportional-integral (PI) control based ESM system is compared. In order to support the peak demand and pulsed load, a hybrid energy storage system incorporating high energy density storage (battery) and high power density storage (supercapacitor) is proposed. For energy transfer among the energy storages and the MVDC system, bidirectional dc–dc converters with dual active bridge (DAB) configuration are used. With the change of the bus voltage and load power demand, the ESM systems provide instantaneous reference powers for charging or discharging of the battery and supercapacitor. The reference powers for the battery and supercapacitor are sent to the respective controllers of the DAB converters. Two power sharing strategies are designed to share power among multiple energy storages. The MVDC shipboard power system with the generators, loads, battery, and supercapacitor with DAB converters are modeled in SimPowerSystems. Simulation results are used to make a comparison of performances of the FL and PI controller based ESM systems. Finally, controller hardware-in-the-loop based experimental results are added to demonstrate the effectiveness of the controller.

A Sliding-Mode Duty-Ratio Controller for DC/DC Buck Converters With Constant Power Loads

Incorporating a medium-voltage dc (MVDC) integrated power system is a goal for future surface combatants and submarines. In an MVDC shipboard power system, dc/dc converters are commonly employed to supply constant power to electric loads. These constant power loads have a characteristic of negative incremental impedance, which may cause system instability during disturbances if the system is not properly controlled. This paper proposes a sliding-mode duty-ratio controller (SMDC) for dc/dc buck converters with constant power loads. The proposed SMDC is able to stabilize the dc power systems over the entire operating range in the presence of significant variations in the load power and input voltage. The proposed SMDC is validated by both simulation studies in MATLAB/Simulink and experiments for stabilizing a dc/dc buck converter with constant power loads. Simulation studies for an MVDC shipboard power system with constant power loads for different operating conditions with significant variations in the load power and supply voltage are also provided to further demonstrate the effectiveness of the proposed SMDC.

A co-simulation method as an enabler for joint analysis and design of MAS-based electrical power protection and communication

Multi-agent system (MAS) protection is under investigation as a potential method for distributed control in modern electrical power systems. The coordination of the MAS is based on local measurements available to each agent’s site as well as on the information exchanged between agents over the communication network. Hence, the communication network should be considered to be a main factor in determining overall system performance. Numerical simulation is a fundamental tool of the design process. Existing electric power simulation tools can satisfactorily model traditional power systems where power and communication are considered to be decoupled and MAS are not present. Similarly, the simulation tools for communication systems have been developed independently from the application, particularly power system scenarios, so they are decoupled from the actual use of the information. If the loop between communication and power is closed and the coupling is strong, as in MAS-controlled power systems, such a simulation environment may yield unrealistic results. Aiming at filling this gap, this paper proposes a co-simulation solution for power systems, communication networks, and MAS, based on the extended capability of the co-simulation platform called VPNET. VPNET consists of three parts: Virtual Test Bed for time domain simulation of power systems, OPNET for the simulation of communication networks, and the Co-simulation Coordinator for data exchange and time synchronization between the other two simulators. The Co-simulation Coordinator has been exploited for MAS integration, as the rules of each agent are defined in the modules provided by the Co-simulation Coordinator. The proposed extended co-simulation platform is tested in the analysis of the performance of the MAS-based protection schemes of a medium-voltage DC shipboard power system. Numerical simulations have been performed for communication testing and protection testing. In the communication test, the network parameters (bandwidth and transmission time) are analyzed to evaluate the performance of the communication network under various conditions; in particular, links failure. The MAS-based protection system was then tested under various operating conditions of the communication network (latency and links failure). From the simulation results it can be seen that the designed MAS protection can handle these conditions successfully. Particularly in the link failure conditions, this co-simulation platform could simulate the re-routing process of the communication network and lead to correct protection performance, which is impossible with individual simulators alone. These simulation results show the utility of VPNET in exploring the design trade-offs between protection strategies and communication in the design phase.

Integration of a bi-directional DC–DC converter model into a real-time system simulation of a shipboard medium voltage DC system

A bi-directional dc/dc converter model is investigated for a notional Medium Voltage DC (MVDC) shipboard power system to improve energy flexibility and deal with peak energy demand in shipboard power system. Surplus energy in the MVDC system during light load condition can be captured by energy storages distributed in local load zones through the bi-directional dc/dc converters and then can be used during heavy load condition or black starting of the MVDC system. In this paper, the derivation process of the small-signal average models of the isolated-type bi-directional dc/dc converter is presented for controller design. This paper also presents the controller optimization process using intelligent optimal searching algorithm, Particle Swarm Optimization, for optimizing dynamic and steady-state control performance of a bi-directional dc/dc converter. The control performance of the proposed controller is evaluated using frequency-domain analysis and time-domain simulation of the large-scale notional MVDC shipboard power system using the Real-Time Digital Simulator.