Direct Current Bus Research Articles

Energy management in DC microgrid with an efficient voltage compensation mechanism

Direct current (DC) microgrid facilitates the integration of renewable energy sources as a form of distributed generators (DGs), DC loads, and energy storage system (ESS) devices. A new voltage compensation mechanism is presented in this study to resolve the control issues of DC microgrid in a distributed manner. In this mechanism, a fractional-order voltage compensation term is used in the outer controller loop which eliminates the voltage deviation in the steady-state condition. A detailed mathematical model is developed for the ESS along with the new voltage compensation controller to facilitate proper tuning of the control parameters. Since the proposed voltage compensation term guarantees autonomous bus voltage restoration, the supercapacitor state of charge (SoC) remains at nominal value without violation while it only buffers fluctuating power. However, the battery only compensates for the nominal power demand. The DG power control algorithm strictly maintains the battery SoC within lower and upper bounds. A DC microgrid comprising hybrid ESS, DC load, constant power load (CPL), and distributed generator is implemented with real time digital simulator (RTDS). The results show that the proposed controller is reliable, leading to excellent ESS performance and power management within the microgrid, without any DC bus voltage deviation.

Mitigation effect of flywheel energy storage on the performance of marine gas turbine DC microgrid under high-power load mutation

Due to the slow response of output power of the traditional marine micro gas turbine, the directly connecting of high-power load to a shipboard micro gas turbine power generation system usually causes large power imbalance and instability instantly. To address this issue, a flywheel energy storage system (FESS) is applied to compensate the transient power changes, mitigate load fluctuations and maintain the voltage of the shipboard direct current (DC) bus. Based on a practical 100 kW micro gas turbine generator set, a detailed model of DC microgrid for the micro gas turbine generation system including micro gas turbine, FESS, synchronous generator, excitation system and load is established. The coordinated control strategy of micro gas turbine, FESS and load system is designed. The mitigation effects of FESS on marine gas turbine DC microgrid under high-power load mutation are explored by performing simulation with sudden load changes of 25%, 50% and 75% rated power and comparing the performance with and without FESS. The effectiveness of the control strategy has been verified by simulation analysis. The simulation results show that by reasonably designing the coordinated control strategy, the fluctuation of the power system can be effectively mitigated when sudden load, especially high-power sudden load is considered. The stability of the marine gas turbine microgrid has been greatly improved.

Defense Strategy against False Data Injection Attacks in Ship DC Microgrids

False Data Injection Attacks (FDIA) on ship Direct Current (DC) microgrids may result in the priority trip of a large load, a black-out, and serious accidents of ship collisions when maneuvering in the port. The key of the prevention of FDIA is the detection of and countermeasures to false data. In this paper, a defense strategy is developed to detect and mitigate against FDIA on ship DC microgrids. First, a DC bus voltage estimator is trained with an Artificial Neural Network (ANN) model. The error between the estimate value and the measure value is compared with a threshold generated from history data to detect the occurrence of FDIA. Combined with the correlation of artificial neural network inputs, bad data are identified and recovered. The method is tested under six cases with different network and physical disturbances in Matlab/Simulink. The results show that the method can identify and mitigate the FDIA effectively; the error of identifying FDIA by ANN is less than 0.5 V. Therefore, the deviation between the actual bus voltage and the reference voltage is less than 0.5 V.

Fault Tolerant Control of Advanced Power Generation Center for More-Electric Aircraft Applications

This article presents a control scheme for a recently reported aircraft advanced power generation center (APGC) during postfault operation conditions. Within the APGC, two electrical generators extract power from two separate engine shafts and supply electrical power to a common high-voltage direct current (HVDC) bus through their dedicated main ac/dc power converters. An extra back-to-back (BTB) converter is also used to connect the ac terminals of the two generators. This architecture provides merits of fault tolerance capabilities of the APGC. In the case of main ac/dc power converter failure, the system can be reconfigured and the BTB converter provides an extra power flow path from the generators to the HVDC bus. This ensures electrical power generation capabilities onboard. This article discusses in detail about the control of the APGC under fault conditions with one main ac/dc converter failure. A seamless transition scheme from normal operation to postfault conditions is proposed using a voltage command initialization technique within the BTB converter. Both experimental and simulation results have verified the fault tolerance improvement and control performances of the APGC.

Analysis of SiC and SiC-Cascode MOSFET in the design of power electronics converters for more electric aircrafts

<span>Wideband gap (WBG) semiconductors have developed rapidly in recent years, enabling greater efficiency and power density in the design of power electronics converters for several areas of application. In this sense, this work analyzes the efficiency and specificities of silicon carbide (SiC) technologies and their cascode topology (SiC-Cascode), operating at high switching frequencies. The analyzes are performed using a Boost converter designed for conversion systems in the more-electric aircraft (MEA) context, where the alternating current (AC) power systems can operate at fixed frequency (115V/400Hz), or at variable frequency (115V/360-800Hz), such as observe in Boeing 787, and the direct current (DC) power system can operate with a DC bus of 400 V and +/-270 V are normally used. To validate the project, computer simulations were performed and a 1.0kW prototype was built in the laboratory. The performance analyses demonstrates that 97.5% of efficiency is achieved at 500 kHz switching frequency.</span>

ANFIS based AZSPWM methods for reduction common mode voltage in asynchronous motor drive

<div class="keywords">Space vector pulse width modulation (SVPWM) is a popular technique in the field of variable frequency induction motor drives. It gives better working and good direct current bus utilization in comparison to the sinusoidal PWM (SPWM) method. However, it decreases harmonic fluctuations and generates high common mode voltage (CMV) fluctuations, which results in common mode currents inside the motor. Hence, the performance of the motor may be deteriorated. To reduce the CMV, this paper presents a family of active zero state PWM (AZSPWM) methods using an adaptive neuro-fuzzy interference system (ANFIS). The proposed approach uses a five-layer hybrid learning algorithm for training the network. The training data is obtained from the classical SVPWM method. To analyze the proposed PWM methods, simulation is carried out using MATLAB and evaluated.</div>

Parameterization of indicators for interleaved converters design in photovoltaic applications

The design of power converters for photovoltaic systems is a challenging issue to be addressed. This challenge lies on the need of considering efficiency, thermal and volume requirements at the same time; with the added drawback that these indicators have different behaviors depending on the operation conduction mode and also have opposing effects according to the switching frequency. The complexity increases when interleaved converters are selected, since the relationship among indicators is also affected by the number of phases. Many attempts have been made in the literature to address this issue; however, they have all reached partial strategies, focusing on some of the indicators and without taking into consideration the interactions among them. In this sense, this work proposes a mechanism to obtain indicators of total efficiency, thermal dissipation in inductors and semiconductors, as well as the volume of magnetic devices and sinks, as a function of switching frequency and number of phases, for continuous and discontinuous conduction modes. This information is crucial to study the interaction among the performance indicators, and to determine the most suitable values for the mentioned parameters. In order to show the proposal contribution, the parameters for an interleaved converter that connects a photovoltaic array with a direct current bus of 450V are obtained

An efficient energy-management strategy for a DC microgrid powered by a photovoltaic/fuel cell/battery/supercapacitor

Abstract The outcome of this paper is to suggest an efficient energy-management strategy (EMS) for a direct-current (DC) microgrid (MG). The typical MG is composed of two renewable energy sources [photovoltaic (PV) systems and fuel cells (FCs)] and two energy-storage elements (lithium-ion battery and supercapacitor). An EMS was proposed to ensure optimal bus voltage with a power-sharing arrangement between the load and the sources. As a result, in the suggested DC MG, non-linear flatness control theory was used instead of the traditional proportional-integral control approach. The suggested EMS is intended to supply high power quality to the load under varying load conditions with fluctuating solar irradiation while considering the FC status. To validate and prove the effectiveness of the proposed EMS, a MATLAB® environment was used. In addition, the output power of the PV system was maximized using the particle swarm optimization algorithm as a maximum power point tracking (MPPT) technique to track the MPP of the 3000-W PV system under different irradiance conditions. The results show that the suggested EMS delivers a stable and smooth DC bus voltage with minimum overshoot value (0.1%) and improved ripple content (0.1%). As a result, the performance of the DC MG was enhanced by employing the flatness control theory, which provides higher power quality by stabilizing the bus voltage.

A Distributed Two-Level Control Strategy for DC Microgrid Considering Safety of Charging Equipment

A direct current (DC) microgrid containing a photovoltaic (PV) system, energy storage and charging reduces the electric energy conversion link and improves the operational efficiency of the system, which has a broad development prospect. The instability and randomness of PV and charging loads pose a challenge to the safe operation of DC microgrid systems. The safety of grid operation and charging need to be taken into account. However, few studies have integrated the safety of charging devices with grid operation. In this paper, a two-level control strategy is used for the DC microgrid equipped with hybrid energy storage systems (ESSs) with the charging equipment’s safety as the entry point. The primary control strategy combines the health of the charging equipment with droop control to effectively solve the problem of common DC bus voltage deviation and power distribution. The consistency the control algorithm for multiple groups of hybrid ESSs ensures the local side DC bus voltage level and ensures reasonable power distribution among the ESSs. The simulation results in MATLAB/Simulink show that the control strategy can achieve power allocation with stable voltage levels in the case of fluctuating health of the charging equipment, which guarantees the safe operation of the microgrid and charging equipment.

Distributed Secondary Control for Voltage Regulation and Optimal Power Sharing in DC Microgrids

In this article, a novel distributed secondary control scheme is proposed to solve the voltage regulation and power sharing problems of an islanded direct current (DC) microgrid. It not only eliminates the voltage deviation caused by droop control but also minimizes the total generation cost of the DC microgrid. The proposed secondary control of distributed generators (DGs) does not require global information, but only current information of neighbors and the DC bus voltage. Different from the existing secondary frequency control, the corresponding closed-loop system of the DC microgrid under the proposed scheme is a nonlinear networked system. With the help of the properties of cascade systems and the input-to-state stability theory, it is found that the DC microgrid under the proposed scheme can achieve voltage regulation and minimization of the total generation cost if the corresponding communication graph of DGs is connected. A simulation model is established to verify the proposed scheme. Finally, a DC microgrid platform with two DGs in parallel is used for the experimental verification.

Optimized servo-speed control of wind turbine coupled to doubly fed induction generator

<p>Optimal control of any variable speed wind turbine needs maximum power point tracking (MPPT) coupled to doubly fed induction generator (DFIG) for better power generation. This paper offers a novel direct power servo-speed control of wind turbine. This latter is based on DFIG optimal hysteresis MPPT inverter current control combined with space voltage modulation (SVM) inverter voltage technique, thus providing a stable and continuous energy flow to power grid. In this design, the asynchronous machine stator is directly connected to the grid. Bidirectional power converter, acting as frequency converter, is rotor circuit located. Rectifier supplies rotor windings with voltages and reference frequency resulting from control procedure of the power exchange between the stator and grid. Inverter is directly controlled by means of SVM technique to maintain direct current (DC) bus voltage constant. Simulation results show that the proposed configuration improves power converters efficiency due that rotor circuit needs less power than stator circuit which is injected into the grid.</p>

Model Control and Digital Implementation of the Three Phase Interleaved Parallel Bidirectional Buck–Boost Converter for New Energy Electric Vehicles

In recent years, the imminent environmental problems and increasing attention to the global energy crisis have prompted the need for new opportunities and technologies to meet higher demands for clean and sustainable energy systems. As a result, new energy electric vehicles have been developed to replace fossil fuel cars. Therefore, this paper presents a three-phase interleaved parallel bidirectional buck–boost converter, which is the core factor of electrical energy flow regulation and management between the battery pack and motor drive inverter within the high voltage direct current bus and converts the voltage from two directions. Corresponding circuit topology, mathematical model, and control strategy are analyzed in three operation states: charge buck, discharge boost, and electric energy interaction modes. The digital implementation with double closed loop, power feedforward compensation, and bidirectional switching logic are realized by XDPTM Digital Power Controllers XDPP1100-Q040 of Infineon Technologies AG. Finally, the experimental results of the proposed converter clearly show that it achieves the objectives, namely, the feasibility and practicality of the system.

Review of Single-Phase Bidirectional Inverter Topologies for Renewable Energy Systems with DC Distribution

Recent developments in renewable energy installations in buildings have highlighted the potential improvement in energy efficiency provided by direct current (DC) distribution over traditional alternating current (AC) distribution. This is explained by the increase in DC load types and energy storage systems such as batteries, while renewable energy sources such as photovoltaics (PVs) produce electricity in DC form. In order to connect a DC distribution system to the alternating current grid (e.g., for backup, delivering energy storage to the grid) there is a need for a bidirectional inverter, which needs to operate over a wide range of source and load conditions and is therefore critical to the overall system performance. However, DC distribution in buildings is relatively new, with much of the research focused on the control of the DC bus connection between sources and loads, rather than on the grid connection. Therefore, this review aims to explore recent developments in bidirectional inverter technologies and the associated challenges imposed on grid-connected DC distribution systems. The focus is on small-scale building applications powered by photovoltaic (PV) installations, which may include energy storage in the form of batteries. An evaluation of existing inverter topologies is presented, focusing on semiconductor technologies, control techniques, and efficiency under variable source and load conditions. Challenges are identified, as are optimal solutions based on available technologies. The work provides a basis for future developments to address current shortcomings so that the full benefits of DC distribution can be achieved.

Voltage Regulation and Current Sharing in DC Microgrids With Different Information Scenarios

We present a general framework for the control of a direct current (DC) microgrid with star topology (a common DC bus) consisting of renewable sources of energy, loads, and storage devices connected via step-up and step-down DC/DC converters. The control objective is guaranteeing voltage stability in the DC microgrid while delivering power to the loads and extracting energy efficiently from renewable sources. To verify grid voltage regulation among a number of devices via current sharing, we use Lyapunov-based Input-to-State Stability (ISS) analysis. We consider three control scenarios: distributed, partially distributed, and decentralized according to the amount of information available to the controllers.

An improved energy management control strategy for a standalone solar photovoltaic/battery system

This <span>paper proposes efficient energy management in hybrid microgrid-comprising of photovoltaic (PV) and battery storage systems. The proposed technique. The hybrid system's power balance is based on smart control to meet the demands of isolated off-grid direct current (DC) loads as well as to stabilize the voltage to DC Bus. The Perturb and Observe technique (P&O) is used to achieve maximum power point tracking by adjusting the duty cycle of the Bidirectional converter, which links the Li-ion battery to the DC Bus of stand-alone power systems (SPS). The proposed controller regulates the power flow of the battery for efficiency voltage control in a microgrid. The energy management system proposed has been approved using MATLAB/Simulink under variable solar irradiation conditions. The simulation results show that the technique used increases the battery cycle-life and better energy management and voltage control performance compared with previous examples</span>.

Research on the strategy of lithium-ion battery-supercapacitor hybrid energy storage to suppress power fluctuation of DC microgrid

Abstract The wide application of clean energy has promoted the development of microgrids. For direct current (DC) microgrids, power fluctuations are inevitable, because photovoltaics, wind power and other clean energy sources are very unstable, which will bring great trouble to DC microgrids. Hybrid energy storage systems (HESS) are an effective solution to suppress power fluctuations. For a HESS composed of battery and supercapacitor (SC), a low-pass filter is usually used to allocate energy and power requirements to each energy storage unit, but the filter constant of the filter cannot be dynamically adjusted to adapt to different situations. The low-pass filter compensation coefficient used in this paper will change with the state of charge and discharge, and dynamically change and allocate different power requirements to the battery and SC according to the actual operating conditions of the HESS. The objective function of DC bus power fluctuation is established, and the optimized particle swarm algorithm (PSO) is used to obtain the output power coefficient of each energy storage unit. The output coefficient of the HESS control strategy has the characteristics of fast convergence speed and high computational efficiency in the optimization process, and it will not fall into the local optimal solution. Through the design experiment, the SC can withstand more high-frequency components, fully utilize the advantages of SC with fast response to power fluctuations, improve the performance of HESS, and have great engineering application value.

A study of a solar PV and wind-based residential DC NanoGrid with dual energy storage system under islanded/ interconnected/grid-tied modes

Progress in Direct Current (DC) power technologies has paved way for the emergence of DC Nano Grid (NG) as a new research area drawing international attention. This paper aims to design a simple and cohesive control algorithm for a solar PV and wind generator coupled low power residential DC NG with electrical and thermal energy storage systems. The envisaged NG control architecture extracts maximum power from solar PV, effects maximum active power transfer from wind generator with voltage regulation of the DC bus, draws/delivers balanced sinusoidal currents at Unity Power Factor (UPF) from/to the grid and monitors power scheduling to DC and thermal loads. The maximum solar PV power is extracted through incremental conductance algorithm and maximum wind power is tracked using a polynomial curve fit equation derived from the wind power curves without implementation of any speed/torque control loops. The maximum active power transfer from wind and UPF operation of the grid is achieved using a reference current generation method based on symmetrical components theory of equal current strategy with no complex transformations. A power factor of 0.99 with generation of balanced sinusoidal currents during both grid power import and export is achieved. Further, the operation of the proposed DC NG in all possible modes such as islanded/grid-tied/interconnected modes are monitored through a supervisory controller implemented in OPAL-4510 Real Time Digital Simulator (RTDS) under varying solar irradiation, wind velocity and load conditions, which projects the suitability of the system to be implemented in any geographical location (hilly terrain/rural/urban) either with limited availability of renewable sources or grid supply. The successful operation of the system is validated through experimentation on a 120 W scaled-down hardware prototype.

Design and Implementation of a Four-Quadrant DC-DC Converter Based Adaptive Fuzzy Control for Electric Vehicle Application

Electric vehicles (EVs) provide an excellent opportunity for limiting the emission of a variety of environmentally hazardous gases caused by gasoline and diesel-based vehicles. These propelled vehicles require a forward and backward motion as well as a variable speed operation. Hence, the use of a four-quadrant (4-Q) direct current (DC) converter becomes a necessity. This paper aims to analyse the traction system of an electric automobile along with the improvement of energy efficiency. Inserting a bi-directional DC-DC converter between the battery and the four quadrant-DC chopper assembly allows the power flow from the battery to the motor and the other way around during regenerative braking. Therefore, increasing the limited driving range of the EV. This paper also focused on the application of model reference adaptive fuzzy control (MRAFC) in order to adjust the direct current bus voltage and the DC motor speed. The proposed system has been tested on an experimental bench and the results have been analysed.

Kalman Filter-based DC Bus Voltage Control for Autonomous DC Microgrid System with PV, Wind and EVs Integration

ABSTRACT The power system network is complex and diverse in nature because of the random and irregular existence of renewable sources, various types of varying and constant loads. Under these circumstances, the stabilization of DC link voltage and obtaining reduced power fluctuations are the main control aspect of DC microgrid (MG) system. This paper explores a Kalman filter (KF) based voltage–current control algorithm for the battery unit to control the medium voltage direct current (MVDC) bus voltage accurately with trivial oscillations as compared to the traditional VI algorithm. The stability and monitoring of DC microgrids are greatly influenced by gathering sufficient and precise information. Since installing several sensors on DC MGs is costly and increases DC MG ripple. In this work, an extended Kalman filter (KF) is used to estimate the current of the lead-acid battery. Hence the current represents an important factor in guaranteeing safe operations. Where the Kalman Filter, which improves the estimation efficiency, to reach a good performance in the current prediction. By updating the proposed approach provides smooth and noise-less operation from the measured DC voltage. The control strategy established for electric vehicle (EV) in this paper is to improve the overall charging ability of the EV only if the system’s total power is greater than the load level by means of the current loop management technique. The feasibility of the designed MG system with the established battery management mechanism and the Escape Ford EV performance is studied using MATLAB/Simulink platform.

Optimal Control Virtual Inertia of Optical Storage Microgrid Based on Improved Sailfish Algorithm

The optical storage microgrid system composed of power electronic converters is a small inertia system. Load switching and power supply intermittent will affect the stability of the direct current (DC) bus voltage. Aiming at this problem, a virtual inertia optimal control strategy applied to optical storage microgrid is proposed. Firstly, a small signal model of the system is established to theoretically analyze the influence of virtual inertia and damping coefficient on DC bus voltage and to obtain the constraint range of virtual inertia and damping coefficient; Secondly, aiming at the defect that the Sailfish optimization algorithm is easy to premature maturity, a Sailfish optimization algorithm based on the leak-proof net and the cross-mutation propagation mechanism is proposed; Finally, the virtual inertia and damping coefficient of the system are optimized by the improved Sailfish algorithm to obtain the best control parameters. The simulation results in Matlab/Simulink show that the virtual inertia control optimized by the improved Sailfish algorithm improves the system inertia as well as the dynamic response and robustness of the DC bus voltage.