DC Bus System Research Articles

Fault analysis for DC Bus-integrated energy storage system, electric vehicle supply equipment, and photo voltaic systems

Reliable access to cost-effective electricity is the backbone of the U.S. economy, and energy storage is an integral element of the power system with high penetration of Distributed energy resources (DERs). Investment in energy storage is essential for keeping pace with the increasing demands for electricity arising from continued growth in U.S. productivity, continued expansion of national cultural imperatives (e.g., emergence of the distributed grid and electric vehicles), and the projected increase in DERs. This research is on the forefront of this transition with fault analysis execute for a real system to be implemented in New York City at a Utility substation. The project seeks to pair a grid-connected battery energy storage system (BESS), solar photovoltaic (PV) system, and an electric vehicle charging system (EVCS) on a common DC bus. A transient model has been developed and different fault scenarios (i.e., high-impedance and low-impedance faults) have been simulated, at various points of the system for several durations. The objective of this study is to determine the requirements for electrical protection equipment, i.e., DC Circuit Breakers (DCCBs) in terms of capacity and fault clearing time that can ensure stable operation of the DC bus system while meeting the utility and IEEE requirements for system stability. The results showed that fast-response DCCBs is a key element for the system. Solid-State DC breakers with ultra-high speed must be deployed for prompt detection/isolation of faults. Actual ratings of converters and allied equipment need to be considered before the finalization of ratings and specification of protection equipment.

Protection Coordination Strategy for the Distributed Electric Aircraft Propulsion Systems

The current trend in distributed electric aircraft propulsion systems is to utilize the DC bus system at higher voltage levels than conventional aircraft systems. With Boeing and Airbus utilizing the +/−270 V bipolar DC bus system, the research on high-voltage systems is increasing gradually, with voltage levels ranging from 1 to 10 kV systems or +/−0.5 to +/−5 kV DC bus systems. These voltage levels present considerable challenges to the distributed electric aircraft propulsion systems. In addition to partial discharge effects, there are other challenges, particularly the challenge associated with effectively limiting short-circuit fault currents due to the low cable impedance of the distribution system. The cable impedance is a significant factor that determines the fault current during fault conditions. Due to the low impedance, there is a sharp increase in fault current, necessitating an enhanced protection strategy, which ensures that the system is adequately protected. This paper introduces a coordinated protection strategy specifically designed for distributed electric aircraft propulsion systems to mitigate or prevent short-circuit faults. The proposed algorithm utilizes an I2t-based strategy and the current-limiting-based strategy to protect the system from short-circuit faults and overload conditions. Redundant backup protection is also included in the algorithm in case the circuit breaker fails to operate.

Power Layout Design of a GaN HEMTs-Based High Power High-Efficiency Three Level ANPC Inverter for 800 V DC Bus System

Power Layout Design of a GaN HEMTs-Based High Power High-Efficiency Three Level ANPC Inverter for 800 V DC Bus System

Multi-Agent-Based Controller for Microgrids: An Overview and Case Study

A microgrid can be defined as a grid of interconnected distributed energy resources, loads and energy storage systems. In microgrid systems containing renewable energy resources, the coordinated operation of distributed generation units is important to ensure the stability of the microgrid. A microgrid needs a successful control scheme to achieve its design goals. Undesirable situations such as distorted voltage profile and frequency fluctuations are significantly reduced by installing the appropriate hardware such as energy storage systems, and control strategies. The multi-agent system is one of the approaches used to control microgrids. The application of multi-agent systems in electric power systems is becoming popular because of their inherent benefits such as autonomy, responsiveness, and social ability. This study provides an overview of the agent concept and multi-agent systems, as well as reviews of recent research studies on multi-agent systems’ application in microgrid control systems. In addition, a multi-agent-based controller and energy management system design is proposed for the DC microgrid in the study. The designed microgrid is composed of a photovoltaic system consisting of 30 series-connected PV modules, a wind turbine, a synchronous generator, a battery-based energy storage system, critical and non-critical DC loads, the grid and the control system. The microgrid is controlled by the designed multi-agent-based controller. The proposed multi-agent-based controller has a distributed generation agent, battery agent, load agent and grid agent. The roles of each agent and communication among the agents are designed properly and coordinated to achieve control goals, which basically are the DC bus voltage quality and system stability. The designed microgrid and proposed multi-agent-based controller are tested for two different scenarios, and the performance of the controller has been verified with MATLAB/Simulink simulations. The simulation results show that the proposed controller provides constant DC voltage for any operation condition. Additionally, the system stability is ensured with the proposed controller for variable renewable generation and variable load conditions.

Design-oriented DC-side stability analysis of VSC-HVDC systems based on dominant frequency analysis

This paper derives analytical DC-side stabilizing conditions of voltage-source-converter-based high voltage DC (VSC-HVDC) links for control design. The case of a single modular multilevel converter (MMC) connected to an infinite DC bus system is first explored to determine the frequency of the dominant mode (dominant frequency) in the DC link. Then, the small-signal model of a generic two-terminal HVDC system is formulated. Since stability discrimination only focuses on the behaviors of the dominant mode, nondominant modes are collapsed in a way that leaves their dynamic properties nearby the dominant frequency intact. Accordingly, concise DC-side stabilizing conditions based on key parameters of physical systems and controllers can be derived, which indicates that the instability mechanism of VSC-HVDC links under DC-side perturbations is that the DC-voltage-controlled converter and the transmission line cannot provide sufficient positive damping to offset the negative damping induced by the power-controlled inverter. It is also interesting to find that increasing the proportional gain of the DC voltage control diminishes the damping of the converter, thereby endangering system stability. The maximum value of the proportional gain is further determined to guarantee sufficient system stability margins under various operating points. Finally, simulation studies validate the proposed DC-side stabilizing conditions for two-terminal VSC-HVDC systems.

High-precision bus voltage control based on NLESO and TSMC predicted load current and grid voltage differential feedforward

Power battery test equipment is widely used to produce and test new energy vehicles and storage containers. To address the problem of DC bus voltage fluctuations that affect the accuracy of output voltage and current, a high-accuracy bus voltage control strategy is based on nonlinear extended state observation (NLESO) and terminal silding mode controller (TSMC) load current estimation. Simulation and experimental results show that the control strategy has a good suppression effect on the DC bus voltage fluctuation and can effectively improve the accuracy of the DC side output voltage and current. Grid voltage differential feedforward is adopted, which can achieve fast suppression of DC bus voltage fluctuations in power battery test equipment and meet the high precision output requirements of the system DC bus.

Limit‐cycle‐oscillation in DC bus system and its death through heterogeneous coupling

AbstractStability of a complex DC bus system (DBS) is a significant design consideration because of its constant power load (CPL) characteristics of the tightly‐regulated load converter. In this paper, the dynamic properties of a stand‐alone buck‐type DBS are investigated based upon the closed‐form large‐signal‐averaged model. The stability‐analysis‐in‐large around the operation point shows that CPLs create a destabilizing effect on the system that can lead to severe voltage oscillation caused by discontinuity‐induced Hopf bifurcations, which are qualitatively different from the bifurcations we know for smooth dynamical systems. Instead, this paper also explores the application of “amplitude death (AD) technique” to stabilize the coupled oscillatory DBSs and show that how this technique with its necessary modifications, for example, the heterogeneity‐induced AD technique characterized by two or more coupled DBSs with mismatched frequency of oscillations can provide an efficient open‐loop control solution for stabilizing the coupled DBSs. Finally, simulations and experimental results are provided to validate all these concepts.

Integration of a storage device to the DC bus of a grid-forming controlled HVDC interconnection

This paper assesses the performance of a high-voltage direct-current (HVDC) interconnection for providing virtual inertia to the power system. The impact of inertia provision on the DC bus dynamics and system frequency when one or both converter terminals are controlled with a virtual synchronous machine (VSM) based grid-forming strategy is evaluated. It has been demonstrated that an identical inertial support cannot be provided to both terminals due to a fundamental conflict between the DC voltage control and inertia emulation tasks. Therefore, it has been proposed to integrate a storage device (e.g. flywheel energy storage system (FESS)) with an additional converter to the DC link in order to control the DC voltage. Doing so, the DC voltage control is not couple with the inertia emulation at each substation and the obtained results have shown that a good performance in the DC voltage control as well as a proper inertia support provision are achieved. Finally, a discussion on a simplified approach to size the storage system is presented.

Balancing of Common DC-Bus Parallel-Connected Modular Inductive Power Transfer Systems

The aim of this article is to design a modular, fault-tolerant multi-transmitter (Tx)/multi-receiver (Rx) parallel-connected common dc-bus inductive power transfer (IPT) system to replace slip rings in wind turbines or brushless exciters. In parallel-connected common dc-bus systems, current unbalance is a major issue that results in thermal stresses and over current or voltages. In this article, two different new current balancing methods are proposed: cross-coupled Rx modules and intentional detuning of Rx-side resonant frequency. These methods are investigated both analytically and experimentally for a single Tx and two Rx system for a 500-W prototype. The proposed methods are tested independently, and then, the combined current balancing method is also investigated. For the same misalignment case, cross coupled/detuned has a 55.8% current balancing improvement compared with decoupled/fully tuned topology.

An Investigative Analysis of the Protection Performance of Unbalanced Distribution Networks With Higher Concentration of Distributed Energy Resources

Despite the substantial reliability and power quality improvements, the proliferation of distributed energy resources can introduce many protection complexities in distribution networks (DNs). This research article presents a comprehensive investigative analysis of the distributed generation (DG) impacts on the protection performance of the DN. Various protection coordination case studies have been analyzed under different operating conditions by varying the DG penetration level or the fault conditions to highlight the potential risks of the protection networks. The severity of the risks is evaluated by considering the DG locations, protection settings, and fault types/impedance parameters on a standardized IEEE 13 node test feeder in DIgSILENT Power Factory/MATLAB softwares. The subsequent protection hazards are examined for the mutual coordination of the overcurrent relays, auto-reclosers, and series fuses in DNs along with the differential protection issues for dc bus system. Furthermore, the impacts of DGs/PDs types are assessed on the nuisance tripping of the protection networks and results are reported.

Designing of Higher-Order Series-Parallel resonant converter with improved ZVS under variable source condition for constant DC-bus System

Every Renewable based energy source requires an additional buffer unit to deliver power to either a standalone system or a grid system. Most of the time unit buffer either provides constant voltage DC-power or AC-power. Higher efficiency in the conversion process can only be achieved if ongoing losses of the buffer system are low. Square sine control approach for Higher-Order Series-Parallel resonant DC-DC Converter is presented in the paper which provides excellent results in both highly and lightly loaded conditions. This control also provides stable bandwidth for input voltage source acceptance which is mostly to be considered as a PV-based source. The strategy also enhances the reliability of the converter by providing a stable and most delightful way of soft switching triggering so as to maintain the output voltage by un-affecting the switching cycle of the Solid-State Semi-conducting Device (SSSD). Selection for the components used in converter design was also studied with a susceptive case study. Further to this control for the entire converter unit is maintained to single variable control so as to reduce the complexity of the system and enhance efficiency. The simulated results of the programmable single variable square sine-wave control is presented for the higher-order resonant converter operating under variable input condition.

Modelling and Analysis of Microcontroller Based MPPT Method Using FPGA

Now days, the renewable energy sources (RES) are the most accomplished system for power generation. In this paper, focus on FPGA based digital controller for the grid connected DG system. The study and performance analysis of grid-connected PV system as follows to improve the efficiency of the grid system and to extract the maximum power. This work is designed & development of FPGA. The DC power and battery capture on the DC bus system we have maintained the unity power factor and harmonics current in the DG system. The bi-directional battery systems also provide quick response & the performance under the variable DC voltage. Then, to develop the effectiveness control strategy is to manage the power flow equally AC & DC sides. This system simulated in MTTLAB Tools and FPGA System.

A multi-star synchronous machine model for real-time digital simulation and its applications

Poly-phase electric machines have the advantages of low ripple in torque, better fault tolerance and high reliability in operation. Such properties make them attractive for applications in renewable energies, electric ship propulsion, traction, aircraft systems and electric vehicles [1,2]. Failure of the drive system through a few phases could be tolerated by operating the remaining phases of the machine. One popular group amongst poly-phase electric machines is the category of multi-star machines.This paper presents development and validation of a multi-star synchronous machine model for a real-time digital simulator. The paper starts with the introduction and analysis of multi-star machines. A generalized method of Vector-Space Decomposition (VSD) is introduced for analyzing machines with an arbitrary number of stars. The method of incorporating the model into the network solution of real-time electromagnetic transient program is described. For the purpose of demonstration, a typical circuit of a marine electric vessel, containing poly-phase generators, power electronic converters, DC bus, hotel load, battery, and poly-phase propulsion systems is simulated in real time.

DC-link voltage compensation with fuzzy-based MMC to mitigate the low-order circulating current

ABSTRACT In this paper, a novel fuzzy controller-based technique is used to control the harmonics of the circulating currents in Pulse width modulation (PWM) based modular multilevel converters (MMC). This technique is based on average model circuit of MMC, which recognises the cross-relation in between the sub-module and system-level elements using dependent sources. In addition to improving the damping of the system, the main superiority of this technique is that it maintains the natural balancing property of DC bus system in a PWM-based MMC by combining upper and lower arms together, instead of considering separately like in existing schemes. Fuzzy controller is most suitable controller for the decision-making. Fuzzy gives more accuracy, for the nonlinear loads or heavy industrial applications. Fuzzy controller allows the reduction of the harmonics of the circulating current in the dc-link system and works effectively during the unbalanced AC grid conditions also. Therefore, it is suitable for multi-frequency AC systems. The accuracy of the proposed method is verified using simulation results which include the arm currents, common mode (circulating) currents and DC-link voltages along with AC grid voltage and currents.

A Single-Objective Modulated Model Predictive Control for a Multilevel Flying Capacitor Converter in a DC Microgrid

This paper presents a single-objective modulated model predictive control for a bi-directional DC-DC flying capacitor (FC) converter in a microgrid. The presence of FC facilitates the converter to integrate a low-voltage battery to a high-voltage DC bus at reduced voltage stress on its power switches. The converter in such a configuration demands a multi-objective controller to accomplish DC bus and FC voltage regulations, and bi-directional power flow. The proposed controller realizes these multiple control objectives by determining optimum duty ratio for the power switches using a single-objective cost function based on battery current. In doing so, the converter realizes its multiple control objectives without weighting factors in the cost function and operates its power switches at a fixed switching frequency. The proposed controller also eliminates an additional control loop by utilizing an improved dynamic reference model to generate appropriate battery current reference for the DC bus voltage regulation and bi-directional power flow. Finally, the proposed system is validated experimentally under step-response of DC bus voltage, load, PV power, and system parameter variations, and compared with a finite control set model predictive control to prove its effectiveness.

Smart protection system for identification and localisation of faults in multi‐terminal DC microgrid

DC microgrid provides the horizontal infrastructures to integrate distributed generation (DG) and loads. Unlike traditional AC systems, DC systems cannot survive or sustain high magnitude fault currents. It makes locating faults very difficult. The conventional protection techniques completely de-energies the DC link in the DC microgrid. A new protection scheme for multi-terminal DC microgrid against line-to-line fault and the low resistance earth fault is presented in this study. The scheme isolates the faulted section from the DC microgrid. Healthy sections are operated without any disturbance and supply continuity is maintained in a ring main DC bus system. The current sensors are mounted at DC bus segments to monitor the entering and outgoing current at different nodes. Further, the current sensors are also mounted at both ends of service mains to monitor their current difference at both ends of the service mains. The controller detects this current difference and opens circuit breakers. To meet the requirement of fast interrupting time and high short-circuit current withstanding capability, insulated-gate bipolar transistors used as circuit breakers. The fault location scheme gives the fault location in various sections (service mains) and faults resistance in the microgrid. The proposed concepts have been verified by computer simulation.

DC Bus Systems for Electrical Ships: Recent Advances and Analysis of a Real Case

The maritime industry accounts for a significant share of global emissions of CO2, nitrogen oxides (NOx), and sulfur oxides (SOx), giving it a substantial environmental footprint. According to research conducted by the Lloyds Register and University College London on global marine fuel trends, if no actions are taken, exhaust gas emissions from shipping will double by 2030 and remain on an upward trajectory. Ships also contribute to local problems of poor air quality, constituting a significant threat to global health. Through chemical reactions in the air, NOx and SOx are converted into fine particles of sulfate and nitrate aerosols.

Analysis of fuzzy logic controller based bi-directional DC-DC converter for battery energy management in hybrid solar/wind micro grid system

This paper proposes a fuzzy logic-based battery energy management system in hybrid renewable system. The novel topology consists of solar and wind energy system-based input sources and a battery bank to store the energy when in excess. The PV-Wind source is equipped with unidirectional boost converter whereas, the battery storage system is connected to the system with a bi-directional DC/DC converter. The main novelty of this research is the fuzzy logic-based battery management system which charges and discharges into the DC bus system based on the supply-load demand. The fuzzy logic controller (FLC) based maximum power point tracking (MPPT) is used in the PV and wind energy conversion system (WECS) to track the maximum available power for the different irradiance and wind velocity respectively. The obtained results are compared to conventional P&O MPPT control algorithm to find the effectiveness of the system. A 500 W PV system and a 500 W Permanent magnet synchronous generator (PMSG) based WECS is implemented for its simplicity and high efficiency. The proposed control topology is designed and tested using MATLAB/Simulink

Impedance-based Stability Analysis of Servo Drive DC Bus Systems

Impedance-based Stability Analysis of Servo Drive DC Bus Systems

A New Multilevel AC/DC Topology Based H-Bridge Alternate Arm Converter

The current popular modular multilevel converter topology (MMC) needs a large number of cascaded sub modules and switches, a high voltage level of DC bus and a large loss. Based on these problems, a new multilevel converter topology with H-bridge alternate arm is proposed. This topology combines two structures of H-bridge sub module cascade and H-bridge switch series arm. In high-voltage and high-power applications, on the premise of outputting the same AC voltage level, this topology reduces the DC bus voltage level, system loss and cost, and the number of components, simplifies the control method, and improves the system reliability compared with the MMC structure. In this paper, the working mechanism of the topology is described in detail. On this basis, the control strategy of sub module capacitor voltage balancing is proposed. Finally, the PSIM simulation of the topology is carried out, and a single-phase prototype is made in the laboratory. The simulation and experimental waveforms are obtained, which verify the correctness and feasibility of the topology structure.