DC Load Research Articles

On the modelling, analysis, and design of a suboptimal controller for a class of wind/PV/battery based DC microgrid

This study deals with the comprehensive modelling, analysis, and control of a DC microgrid (MG) in islanded mode. The proposed DC MG comprises a wind turbine, a photovoltaic (PV) source, battery storage, DC/DC source, and load side converters with DC loads. To this aim, a circuit-oriented modelling of the whole system is developed. The PV source is modelled with a single-diode electrical circuit. Afterward, a mathematical model of the system with state-space representation was derived. A detailed analysis of PV system design is performed because the parameters of PV are appearing in the dynamic model of DC MG. For the purpose of controller development, the dynamic model of the DC MG, which is modelled by a non-linear-non-affine eight-order system, is linearized around an equilibrium point using the Jacobian matrix framework, while stability using eigenvalue is carried out showing that the stability is guaranteed under operating condition. Finally, for the first time, the state-dependent Riccati equation (SDRE) technique is proposed to find the optimal regulation problem for the DC MG with non-linear-non-affine dynamics. The numerical simulation studies first confirm the validity of the performed mathematical, then the effectiveness of the proposed non-linear controller is evaluated under illumination and load change.

Possibility of Power Electronics-Based Control Analysis of a Self-Excited Induction Generator (SEIG) for Wind Turbine and Electrolyzer Application

A self-excited induction generator (SEIG) is very simple and robust, has a reduced unit size, is easy to implement and simple to control, and requires very little maintenance compared to other types of generators. In variable operating conditions, the SEIG requires a power electronics interface to transform from the variable frequency voltage output of the generator to a battery voltage output or the related applications. In our study, we tied the SEIG to the power electronics system comprising a diode rectifier and DC/DC converter, and then a final DC load for fuel cell applications was connected. An example of such an application is an electrolyzer where an equivalent circuit is modeled for use in this study. To accomplish the proposed system, we utilized PSCAD and MATLAB for its simulation, control, and analysis. A new system configuration considering three different wind speeds and breaker conditions is modeled and analyzed. The results show that the suggested strategies in this study would contribute to designing and analyzing a more practical power electronics interface system for a wind turbine generator with a DC load.

A Techno-Economic Sizing Approach for Medium-Low Voltage DC Distribution System

DC distribution system (DCDS) has many preferable advantages to integrate renewable energy sources and native-DC loads than AC distribution system (ACDS), and the benefits of higher power density, greater energy conversion and wider supply radius can be obtained. In this paper, a methodology of sizing the techno-economic of a medium-low voltage DCDS is proposed. Firstly, the system framework and its equipment composition are stated. Then, considering the distribution capacity, supply ability, operation loss and reliability, the technical indicators of the demonstrated DCDS are analyzed and quantified. In regards to the DCDS's distribution-level and consumer-level, the calculation models of the annual costs are presented. Further, different scenarios are imitated to verify the efficacy of the proposed sizing approach, and the techno-economic comparison is implemented in the DCDS and ACDS with similar structure configurations. The calculation results reveal that the DCDS shows a visible economic performance at the consumer-level, and for the scenario of accessing high proportion DC loads, it is more cost-effective than the ACDS. Finally, the correctness of the cost models is proven, and this study can offer a reliable reference for building the medium-low voltage DCDS.

Analysis and Design Based on the Operation Mode of Power Electronic Transformer in Smart Grid

Power electronic transformers(PET) are the key energy conversion equipment in the operation of modern smart grids, the main function of PET is to achieve the conversion of AC voltage to AC voltage, while taking into account the DC ports. This article mainly studies three-stage power electronic transformers based on three-phase uncontrolled rectifier, full-bridge isolated DC-DC converter and three-phase inverter. The operation mechanism and actual working process of the three parts of the PET are analyzed respectively, and the transformer is simulated and analyzed based on the Matlab/Simulink simulation platform. The rectifier converts the AC voltage on the grid side into a rippled DC voltage; the DC-DC converter transforms the obtained DC voltage, taking into account the access of the DC ports; the inverter converts the obtained DC voltage into AC voltage through unipolar modulation and connects to the grid. The experimental results show that the PET constructed in this way can operate safely and stably, which has good voltage conversion and electrical isolation functions, and can be connected to DC loads.

On the snap-through buckling analysis of electrostatic shallow arch micro-actuator via meshless Galerkin decomposition technique

Micromechanical systems (MEMS) based on electrostatic actuators are commonly involved in driving and actuating high-speed micro-structures. For this to be efficient, these micro-actuators must produce sufficient actuating force in order to achieve the required large strokes for such operations (usually in the order of tens of microns). However, this larger amount of displacement will require high actuation electrostatic voltages (typically in the order of hundreds of volts) or larger actuator dimensions, resulting in a bulky and inefficient design. To overcome these challenges, this paper examines the possible use of the snap-through instability in an electrostatically actuated and initially curved (shallow arch) clamped-clamped microbeam actuator arrangement. An extended version of the variational Hamilton principle is applied to derive nonlinear equations governing the steady-state behavior of the structure under step DC load. These equations are solved by effectiveness meshless numerical Galerkin decomposition technique. A convergence study is performed to show the effectiveness and advantages of the applied numerical approach to the formulated nonlinear problem. The investigation inspects different initial curvature profiles (first three symmetric buckled modes: first, third, and fifth modes) for the shallow arch. It was reported that the presence of the snap-through instability, for all investigated initial profiles, in the structural behavior of the micro-actuator produces a non-trivial order of magnitude increase in its resultant displacement as compared to the classical parallel-plate actuator with identical geometrical dimensions and operating conditions. In addition, out of the assumed first three symmetric buckled modes to outline the initial curvature of the shallow arch microbeam, only the first and fifth modes showed a strong impact on the micro-actuator performances.

Designing of Lithium - Ion Battery Pack Rechargeable on a Hybrid System with Battery Management System (BMS) for DC Loads of Low Power Applications – A Prototype Model

Now a days, Li-ion batteries are quite possibly the most exceptional battery-powered batteries; these are drawing in much consideration from recent many years. M Whittingham first proposed lithium-ion battery technology in the 1970s, using titanium sulphide for the cathode and lithium metal for the anode. Li-ion batteries are the force to be reckoned with for the advanced electronic upset in this cutting-edge versatile society, solely utilized in cell phones and PC computers. A battery is a Pack of cells organized in an arrangement/equal association so the voltage can be raised to the craving levels. Lithium-ion batteries, which are completely utilised in portable gadgets & electric vehicles, are the driving force behind the digital technological revolution in today’s mobile societies. In order to protect and maintain voltage and current of the battery with in safe limit Battery Management System (BMS) should be used. BMS provides thermal management to the battery, safeguarding it against over and under temperature and also during short circuit conditions. The battery pack is designed with series and parallel connected cells of 3.7v to produce 12v. The charging and releasing levels of the battery pack is indicated by interfacing the Arduino microcontroller. The entire equipment is placed in a fiber glass case (looks like aquarium) in order to protect the battery from external hazards to design an efficient Lithium-ion battery by using Battery Management System (BMS). We give the supply to the battery from solar panel and in the absence of this, from a regular AC supply.

Performance Analysis of VRLA Battery for DC Load at Telecommunication Base Station

The high level of power outage in Sukabumi-Cianjur area has influenced the operations of telecommunication industry in the vicinity. This has shortened the battery life at the Base Station (BTS). This study aims to analyze the performance of a (new) VRLA battery against a DC load (BTS) to support the continuity of BTS operation in case of a power outage. The research method used is a (new) battery charge-discharge procedure. Parameters are analyzed by determining the on-site battery discharge duration, the pressure at the battery terminals between cells during backup, and the capacity of the rectifier module to support fast charging. To support fast charging, the rectifier with the formula N+1 and C-rate is 10% and C15 is 15% of the battery capacity. The internal impedance value is 3.4 mΩ and the battery terminal pressure (torque) is 9-11 N/m. The battery performance analysis of the four BTS shows that two of them managed to do a backup, while the other two did not provide good performance.

Improving the stability of hybrid microgrids by nonlinear centralized control in island performance

In this paper, based on the nonlinear controller, a new structure is presented for centralized control of hybrid microgrids. In the proposed model, AC and DC buses are used to connect AC and DC sources and loads respectively. A bidirectional interface converter (BIC) is provided for the electrical and control connection of these two buses. Here, based on the generalized backstepping method (GBM), a new method is presented for integrated and simultaneous controlling of AC bus frequency and DC bus voltage. The advantages of this method are the centralized control of the hybrid microgrid, taking into account the dynamics of the whole system and the interaction of its state variables with each other. Harmonized and optimal exchange of power and precise regulation of control signals in this structure has led to improved stability and thus improved system performance. The comparative results of centralized and decentralized control show the efficiency of the proposed model to reduce fluctuations and improve the stability of the system.

Modeling and Estimation of Break Arc Extinction Distance in Low Voltage DC Systems

Recently, as DC power generation and DC loads such as renewable energy and EVs increase, the need for a low-voltage direct current (LVDC) distribution system has gradually emerged. The DC system has various advantages, such as system stability, transmission efficiency, and connectivity to renewable power generation compared to AC distribution systems. One of the important technical issues for commercialization of DC distribution system is safety. Since the DC system does not have a current zero point, unlike the AC system, a breaking arc accompanied by a high-temperature plasma is easily generated when the circuit is cut off. The arc can cause fire accidents that threaten people and facilities. In order to prevent customers and facilities from the accidents caused by the arc in the DC system, a study on the characteristics of the DC breaking arc is necessary. An important factor of characteristics for the DC breaking arc fault is an arc extinction distance at which the DC breaking arc is completely extinguished. There are two major behaviors in DC breaking arc; one is active behavior where the arc voltage is inversely related with the arc current for a given gap distance, the other is passive behavior where the arc voltage is negatively proportional to the arc current according to Kirchhoff’s voltage rule. This paper combines the two arc characteristics together to establish a DC breaking arc model, and proposes a method to estimate the arc extinction distance. Experiment results verify the method under various power and load conditions.

Development of prototype battery management system for PV system

An energy and battery management systems (EMS/BMS) have a great importance in PV-battery system to increase the system efficiency and battery life. In this study, a prototype battery management system (BMS) has been designed and implemented for grid-connected residential-PV system with lithium-ion battery (LIB). Besides the main function of the all BMS which is to keep the LIBs within the safe-operation condition, by measuring/monitoring and controlling the battery parameters during the charge/discharge cycles, this designed BMS manages also the energy flow between PV system, battery, grid and load. In the designed BMS, there is a measuring unit (to measure current, voltage and temperatures), a control unit (to control the energy flows in the system), balancing circuit (capable of balancing in each of the four modules with 7LIB connected in series), the battery circuit (to fix the batteries well and measure the charge/discharge currents on the battery module).The proposed prototype system includes the designed BMS, 400Wp PV modules, 18650 type lithium-ion batteries (LIB) block with a capacity of 353 Wh, the programmable 300 W electronic DC load for modelling the various load profiles by reducing the real home energy consumption by 1/15, 300 W power supply for supplying the energy from the grid and 24 V light bulbs for the sale of excess energy to the grid. For retired and working household power consumption profiles, various scenarios were created for 24-h power consumption on different days on weekdays/weekends to test the proposed prototype system. These scenarios were uploaded on the electronic load, the operation of the designed battery and energy management system was tested with these experiments by using proposed prototype set-up. The battery management system ensured that the batteries operate in safe working conditions. Due to the energy management function of BMS, when the PV-batteries system is not sufficient, the energy will be taken from the grid; when the PVs charged batteries fully, the excess energy will be sold to the grid. Therefore, the designed prototype system, providing a flexible manner with various load profiles, will be useful tool in the investigation of the optimum conditions for a grid connected PV-battery system designed.

A Comprehensive Study on Magnetoelectric Transducers for Wireless Power Transfer Using Low-Frequency Magnetic Fields

Magnetoelectric (ME) transducers, comprising of layered magnetostrictive and piezoelectric materials, are more efficient than inductive coils in converting low-frequency magnetic fields into electric fields, particularly in applications that require miniaturized devices such as biomedical implants. Therefore, ME transducers are an attractive candidate for wireless power transfer (WPT) using low-frequency magnetic fields, which are less harmful to the human body and can penetrate easily through different lossy media. The literature lacks a comprehensive study on the ME transducer as a power receiver in a WPT link. This paper studies the impact of different ME design parameters on the WPT link performance. An accurate analytical model of the ME transducer, operating in the longitudinal-transverse mode, is presented, describing both temporal and spatial deformations. Nine ME transducers with different sizes (ME volume: 5-150 mm3) were fabricated with Galfenol and PZT-5A as magnetostrictive and piezoelectric layers, respectively. Through the modeling and measurement of these ME transducers, the effects of the ME transducer dimension, DC bias magnetic field, loading (RL), and operation frequency on the resonance frequency, quality factor, and received power (PL) of the ME transducer are determined. In measurements, a 150 mm3 ME transducer achieved > 10-fold higher PL for a wide RL range of 500 Ω to 1 MΩ at 95.5 kHz, compared to an optimized coil with comparable size and operation frequency.

Feasibility Analysis of a DC Distribution System for a 6 kW Photovoltaic Installation in Ireland

Recent developments in micro-grids have led to increased interest in DC distribution due to its high efficiency in distributing energy from renewable energy sources to DC loads. This paper seeks to analyse the performance of AC and DC systems in a relatively large-sized 6 kW PV installation to determine the level of improvement in efficiency provided by DC distribution and to identify methods for further improvement. Baseline annual data for the AC system were collected from a live installation on a national school in Inis Oirr, an island off the west coast of Ireland. The results indicate that usage of a DC distribution system has the potential to reduce system losses by up to 50% as well as the ability for an annual saving in grid energy of 5% compared to the existing AC system. Moreover, the analysis reveals that DC outperforms AC distribution more in spring and autumn, when power consumption is comparable to the system production, but there is less impact in summer, when PV production is significantly higher than demand. These findings provide insights into the benefits of future DC distribution systems in individual buildings and in larger-scale micro-grids.

Multifunction Capability of SiC Bidirectional Portable Chargers for Electric Vehicles

A SiC bidirectional portable charger is proposed to realize both bidirectional ac–dc and bidirectional dc–dc high-efficiency power conversion by multiplexing the same powertrain. Control strategies for different operation modes are proposed to realize the comprehensive functions of the portable charger. The proposed portable charger enables the EV to interact with the ac grid, dc microgrid, other EVs, and off-line loads efficiently and conveniently. The SiC portable charger adopts 300-kHz high-frequency isolation to improve the power density. The proposed vehicle-to-vehicle (V2V) mode adopts two-stage direct dc–dc power conversion so that it achieves higher efficiency compared with conventional V2V mode using an on-board charger (OBC). A 6.6-kW SiC bidirectional portable charger is built and the power density is 14.7 W/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . The full-load efficiency of V2V mode is 96.1%, which is 4.7% improved compared with the conventional V2V mode. Bidirectional energy interaction between EV and the 380-V dc microgrid is also verified. The portable charger provides 36–400-V wide output voltage for dc loads with the efficiency above 95.7% at 6.6 kW.

Efficiency evaluation of the microgrid for selection of common bus using copula function-based efficiency curves of the converters

Due to the increase in load growth, construction of renewable energy-based microgrids (MG) has been seen as the most economical and viable solution in the recent past. It leads to the need for feasibility investigation at the planning and design stage for appropriate selection of common bus (CB) type. One of the critical factors to determine the suitable CB is efficiency analysis. This paper proposes an efficiency evaluation method by using the copula function-based efficiency curves of the converters. The degree of association between percentage loading and efficiency of the converters is defined using best-fitted copula estimation, and a large number of iterations are performed using Monte Carlo simulations to generate the efficiency for each time instant. A variety of scenarios are simulated to determine when and which type of CB is most favourable. The efficiency of the MG is strongly dependent on the converter efficiency, number of converters in the MG, and seasonal variations, both in generation and load demand. The results indicate that DC CB has superior performance with the net efficiency gain ranging from 8.26% to 5.63% in all scenarios considered in this study. Moreover, DC CB is most advantageous in the MG with the DC load only. It will bring greater advantages in the future with the continuous development of renewable energy-based MGs and the increasing penetration of DC loads.

Effects of coordinated operation management of HVDC links and PSTs on the redispatch in a Central European case study

In this paper, the effects of coordinated operation management of embedded HVDC links and phase shifting transformers on the optimal redispatch costs and volumes are examined. The underlying optimization problem, including these power flow controlling devices, is formulated for linear optimization using DC load flow equations. The evaluation is based on the results of a year-round simulation of the expected energy market and network situation of the ENTSO-E region of the year 2025. The results highlight the need for coordinated operation management of PFCs since uncoordinated operation management increases the accruing redispatch costs.

Power Management and Control of Smart Microgrid Including Renewable Energy and Energy Storage Systems

Hybrid AC/DC microgrid is getting common nowadays as a result of increasing DC-compatible loads, renewable energy resources and energy storage systems. The hybrid AC/DC systems with AC and DC loads and energy sources are considered to be the structure of the future smart grids. Strategies of controlling the process of energy conversions and power management are considered from the most critical aspects. The suggested hybrid grid consists of AC loads and wind generator in the AC side and DC loads with energy storage elements and PV generator in the DC side. Bidirectional AC/DC converter is used to link between AC side and DC side to maintain balance and stability of the system under different generation and load conditions. In this paper we present an overview of power management strategy of hybrid AC/DC microgrid with energy storage elements. Control strategy and Maximum power point tracking for the bidirectional converter to maximize power harvesting are also presented. MATLAB/Simulink model for the hybrid microgrid is developed to verify that the proposed model can maintain balance of the system.

Stand-Alone Solar PV System using MPPT Technique in Simscape

the stand-alone solar photovoltaic (PV) system mostly used by the islanded power electricity needed for rural area that located far away and unreachable from the national grid. Due to operate the system, the multiple power point tracker (MPPT) technique is used to support PV system to operate at its maximum power. The way the MPPT algorithm works is by calculating the output of PV module, then compares it to battery voltage then fixes what is the optimum power that PV module can produce to charge the battery and converts it to the optimum voltage to get maximum current into battery. It can also supply power to a DC load, which is connected directly to the battery. MPPT is very useful in cloudy days. This paper deploys the use of MPPT technique within the stand-alone solar PV system by simulating the designed Simscape model. Two MPPT techniques, which are the incremental conductance and perturbation and observation (PO) have been chosen to be run as the system simulated. The parameters that have been observed are DC bus voltage, the PV power, the PV voltage, and the PV current, respectively. The results showed that the DC bus voltage raised and steady at the 377.3 V, the solar power increased to 2 kW, and the PV current decreased to approximately 7 A. The DC load is connected across the boost converter output. The solar PV system operates in both maximum power point tracking and de-rated voltage control modes. To track the maximum power point (MPP) of the solar PV, the two MPPT techniques incremental conductance and PO might have been chosen.

The Impact of Different Operation Conditions on the Plasma Extraction Transit Time Oscillation in High-Voltage Insulated Gate Bipolar Transistor Devices

During the tailing current period when the bipolar device is turned off, plasma extraction transit time (PETT) oscillation will occur, and the electromagnetic interference caused by it will have a negative effect on the driver circuit and the surrounding electronic components. Therefore, it is necessary to investigate the factors that affect the characteristics of PETT oscillation. In this paper, the relationship between the characteristics of PETT oscillation and the operation conditions of high-voltage insulated gate bipolar transistor (IGBT) device is studied experimentally. When the DC link voltage, load current and gate driver resistance are changed, and the peak value and duration of PETT oscillation under different operation conditions are recorded. The results show that the PETT oscillation characteristics have a strong dependence on the voltage and current of IGBT device, as well as the gate driver resistance. The experimental results in this paper can provide the guidance for suppressing the PETT oscillation of high-voltage IGBT devices.

Power Management of AC/DC Hybrid Distribution Network With Multi-Port PET Considering Reliability of Power Supply System

In the current distribution network, photovoltaic, wind power, energy storage, and other distributed energy are widely connected, and the proportion of generalized DC load is rapidly increasing. With the development of power electronics technology, using multi-port power electronic transformer (PET) to achieve high-efficiency access of large-capacity AC/DC source and load is the current research hotspot, and AC / DC hybrid power supply is inevitable. The introduction of a large number of power electronics and the flexible coordinated control and complementary fault-tolerant advantages of PET bring challenges to the operation and maintenance management of the AC/DC hybrid power system. In this paper, the structure of the AC/DC hybrid power system with the multi-port PET cluster is introduced. Based on the idea of hierarchical and partitioned control, a three-layer and multi-time scale control mode of integrated automation system, PET cluster and PET controller is proposed; Aiming at the problem of reliability evaluation, a sequential Monte Carlo simulation method is proposed to simulate the AC/DC hybrid power system with the multi-port PET cluster. The influence of multi-port PET parallel cluster mode and port capacity limitation on the reliability of the power system is analyzed, and the effectiveness of the model and algorithm is verified. Finally, an example is given to verify that the proposed structure is conducive to improving the utilization level of renewable energy in the distribution network.

Design of Buck Converter and PV Module for Solar Powered Sailing Boat

The main intention of this work is to minimize the operating cost and increase the power generation of solar photovoltaic (PV) power-driven sailing boat with buck converter. The design of dc-dc converter for solar powered sailing boat is presented here. The entire PV source output power is taken and given to the solar boat through buck converter. The entire output power from the PV source which is given to the dc load is enough to drive a boat. The Buck converter model and solar PV module has been designed and simulated with the use of Matlab Simulink and compared with theoretical predictions.