Smooth Power Research Articles

Multi-Timescale Active Distribution Network Optimal Dispatching Based on SMPC

Smoothing power fluctuations and arranging reserves play a more crucial role in the secure and economic operation of the active distribution network (ADN), as the high penetration rate of uncertain renewable energy sources (RES) increases. In this article, a multitimescale ADN optimal dispatching model based on stochastic model predictive control (SMPC) is proposed to track the random fluctuation of RES and address the operation risk. First, load shedding and RES curtailment risk are quantified by a conditional value at risk based on the probability distribution and a reserve arrangement strategy considering the tradeoff between reserve cost and operation risk is further proposed. Second, the copula theory is introduced to establish a high-dimensional RES prediction error model for the purpose of capturing its spatial–temporal characteristics. Furthermore, according to prediction error distribution, based on the scenario method, typical RES output scenarios for the day-ahead, intraday, and real-time stages are generated. Then, a multitimescale optimal dispatching framework based on SMPC is established in which the outputs of units are optimized and coordinated under different time scales. Finally, simulation results on a modified IEEE 33-bus power system demonstrated the superiority of the proposed method in tracking the fluctuation of RES and also verify the effectiveness of the method to improve the economy of system operation.

A Control Strategy to Smooth Power Ripple of a Single-Stage Bidirectional and Isolated AC-DC Converter for Electric Vehicles Chargers

This paper proposes a single-stage AC-DC rectifier with power factor correction (PFC), high-frequency isolation and bidirectional power conversion capability for on-board battery charger (OBC) applications. The proposed converter is based on the interleaving technique and the Dual Active Bridge (DAB) operation, applying the phase-shift control to regulate the power flow. In addition to topology, this article presents a control strategy for reducing low-frequency power ripples transferred to the secondary side without any additional component and hence maintaining overall size and cost. The single-phase OBC can interchange active power with the grid to charge batteries while performing grid-to-vehicle (G2V) functionality or transferring energy back to the grid via vehicle-to-grid (V2G) mode. The theoretical analysis of the converter including modulation strategy and feedback control scheme are presented. The proposed topology and control strategy have been verified by experimental results of a 650 W SiC-based prototype.

Assessing the Effectiveness of a Novel WEC Concept as a Co-Located Solution for Offshore Wind Farms

The combined exploitation of wave and offshore wind energy resources is expected to improve the cost competitiveness of the wave energy industry as a result of shared capital and operational costs. In this context, the objective of this work is to explore the potential benefits of co-locating CECO, an innovative wave energy converter, with the commercial WindFloat Atlantic wind farm, located on the northern coast of Portugal. For this purpose, the performance of the combined farm was assessed in terms of energy production, power smoothing and levelised cost of energy (LCoE). Overall, the co-located farm would increase the annual energy production by approximately 19% in comparison with the stand-alone wind farm. However, the benefits in terms of power output smoothing would be negligible due to the strong seasonal behaviour of the wave resource in the area of study. Finally, the LCoE of the co-located farm would be drastically reduced in comparison with the stand-alone wave farm, presenting a value of 0.115 per USD/kWh, which is similar to the levels of the offshore wind industry as of five years ago. Consequently, it becomes apparent that CECO could progress more rapidly towards commercialisation when combined with offshore wind farms.

Configuration Design and Screening of Multi-Mode Double-Planetary-Gears Hybrid Powertrains

Abstract Hybrid powertrains with planetary gearset (PG) have been widely used. However, there are few types of powertrains in use, and more powertrains have not been found. Based on the principle of organic chemistry, a design and screening method of multi-mode 2-PGs hybrid powertrain is proposed, which is divided into five stages. First, powertrains are expressed in the form of molecules. Second, powertrains split into the libraries of PGs and power sources. The power sources can be mutually identified to construct new library. Third, the mode switching rules are defined to screen power source group. Fourth, two libraries interact with each other to promote the generation of new molecules, namely, new powertrains. And the more modes, the greater the potential for performance. Powertrains are screened with mode richness theory firstly. Finally, taking the comprehensive evaluation of power performance and fuel economy as the optimal standard, powertrains are screened and evaluated twice. Through the method, hybrid powertrains with smooth mode switching, simpler structure, and optimal power and economy can be obtained.

Protocol for characterizing the molar mass distribution and oxidized functionality profiles of aged transformer papers by gel permeation chromatography (GPC)

Oil-immersed paper insulation and paper pressboards for structural support are widely used in electrical power transformers. Cellulose thus fulfills an essential task for the smooth power supply of our societies. However, the prevailing temperatures in such equipment, combined with a targeted service life of several decades, pose a serious challenge to the long-term integrity of cellulosic paper insulation. Therefore, numerous studies have been conducted to obtain kinetic data on the degradation processes that contribute to the thermally induced decomposition of cellulose. These studies usually rely on the assessment of the average degree of polymerization by viscosity measurements. In this work, we applied and optimized more advanced methods for the characterization of cellulosic materials based on gel permeation chromatography for the special case of thermally stressed unbleached Kraft paper samples. This allowed studying the molar mass distributions of paper polymers upon exposure to heat, as well as the investigation of changes in their conformation in solution and the observation of thermally induced cross-linking. In combination with group-selective fluorescence labeling, it was possible to track over time the changes in molar mass-dependent profiles of carbonyl and carboxyl groups of authentic Kraft insulator paper samples under thermal stress. In addition, changes of the hemicellulose composition were quantified. We hope that this analytical approach to the in-depth characterization of thermally stressed insulator paper will prove useful for future studies of this important cellulose product, and that our findings will contribute to a better understanding of the thermal decomposition of paper in general.Graphical abstract

Comparative study of power smoothing techniques produced by a wind energy conversion system

This paper aims to present and compare two techniques used to smooth the injected power in the grid from a doubly-fed induction generator (DFIG) based conversion system. The first technique based on an inertial storage system while the second is founded on limiting the power captured by the wind turbine. The overall system composed of a wind energy conversion system (WECS) allowing to convert a wind power into electric power. It is controlled by two converters, grid side converter and a rotor side converter, both are controlled by sliding mode. The storage system is used to consume power which exceeds the setpoint due to storing it or producing more in the event of a lack, the system is controlled through the flywheel side converter by the sliding mode. Numerical simulations were carried out using Matlab/Simulink software.

Design and Implementation of the Bidirectional DC-DC Converter with Rapid Energy Conversion

The bidirectional DC-DC converters are widely used in the energy storage system (ESS) and DC distribution system. The power capacity is limited when the converter is operated with smooth power transfer. In addition, the directions of the inductor current and the capacitor voltage cannot change instantaneously. In this study, a rapid energy conversion technique for smoothing and accelerating the energy transfer under the same specification of the main components in steady state is proposed. Moreover, a bidirectional DC-DC converter with a high conversion ratio is proposed to overcome the commonly low voltage input from renewable energy sources. The operating principles of the proposed converter’s step-down and step-up modes are discussed in this study. Furthermore, to achieve rapid energy conversion, digital control is a crucial component in the converter system. A digital signal processor is used as the control platform, and a control strategy is formulated to achieve rapid energy conversion. The bidirectional DC-DC prototype converter with a 24 V battery, a DC bus of 200 V, and an output power of 500 W is constructed to confirm the feasibility of rapid energy conversion. The proposed converter can be operated in CCM, BCM, and DCM conditions. The transfer period can be completed within one switching cycle when the proposed converter is operated in BCM or DCM. The energy is freewheeled before energy conversion when the proposed converter is operated in CCM condition. In the experiment, the minimum transfer period is 6.29 µs on the DCM stage.

Battery Sizing Optimization in Power Smoothing Applications

The main objective of this work was to determine the worth of installing an electrical battery in order to reduce peak power consumption. The importance of this question resides in the expensive terms of energy bills when using the maximum power level. If maximum power consumption decreases, it affects not only the revenues of maximum power level bills, but also results in important reductions at the source of the power. This way, the power of the transformer decreases, and other electrical elements can be removed from electrical installations. The authors studied the Spanish electrical system, and a particle swarm optimization (PSO) algorithm was used to model battery sizing in peak power smoothing applications for an electrical consumption point. This study proves that, despite not being entirely profitable at present due to current kWh prices, implanting a battery will definitely be an option to consider in the future when these prices come down.

Comparison of SPS and FA methods for Blind Carrier Frequency Offset Estimation in OFDM systems

In orthogonal frequency-division multiplexing (OFDM) systems, synchronization issues are of great importance since synchronization errors might destroy the orthogonality among all subcarriers and, therefore, introduce intercarrier interference (ICI) and intersymbol interference (ISI). Several schemes of frequency offset estimation in OFDM systems have been investigated. This paper compares performance and computational complexity of Smoothing Power Spectrum (SPS) and Frequency Analysis (FA) methods for blind carrier frequency offset (CFO) estimation in OFDM systems.

Design and performance analyses of thermoelectric coolers and power generators for automobiles

In this paper, a thermoelectric cooler applicable to automobiles and a thermoelectric generator using exhaust heat were developed and integrated. Typically, car air conditioning systems are driver-oriented due to space limitations. We designed a thermoelectric cooler that delivers cool air from the ceiling of the rear seat. The cooler is simple to install; it is small and does not generate any noise or vibration. The cooler takes less than three minutes to cool a space the size of an average adult’s head from 45 to 26 °C. The power required for the cooler was produced by a thermoelectric generator that can be attached to an automobile exhaust pipe. Twelve thermoelectric generators generated 90.715 W of power at an average temperature of 90.37 °C. A storage device was designed to integrate the thermoelectric cooler and generator, thereby achieving a smooth power supply from the thermoelectric generator to the thermoelectric cooler. This study established a practical thermoelectric system for upgrading automobile systems.

An Active and Reactive Power Controller for Battery Energy Storage System in Microgrids

Battery energy storage systems (BESS) are widely used for renewable energy applications, especially in stabilizing the power system with ancillary services. The objective of this paper is to propose an active and reactive power controller for a BESS in microgrids. The proposed controller can operate the BESS with active and reactive power conditions and realize power smoothing and voltage regulation. The demanded active power flow generated through a low pass filter (LPF) is used to control the power smoothing for microgrids. LPF design is presented based on the BESS sizing and genetic algorithm (GA). The demanded reactive power flow generated according to the reactive current calculation is used to compensate the microgrid voltage to fulfill the voltage regulation. The analysis of the vector diagram is adopted to validate the proposed controller and to explain the applicability and functionality of the voltage regulation for microgrids. To verify the validity of the proposed controller, a 1-kW grid-connected inverter is built to demonstrate the ability of power smoothing and voltage regulation. Both simulations and hardware experimental results agree well with the theoretical analysis.

Grid-connected photovoltaic system with power smoothing

This paper analyzes the power smoothing of grid-connected photovoltaic (PV) systems under fast irradiance changes. The analyzed converter is composed of a triple active bridge series-resonant (TABSR) DC-DC converter cascaded with a voltage source inverter (VSI). Two controlled variables are considered: battery current and the PV voltage. The TABSR DC-DC converter is modeled as controlled current sources for the battery and the PV ports. The ramp rate (RR) control algorithm is used to smooth the PV output power profile enhancing the power delivered to the grid. Four ramp rates (10%, 5%, 2% and 1%) are used to evaluate the RR control algorithm and the battery state of charge (SOC) response. Therefore, the battery can be sized appropriately. Real data for irradiance and temperature in an overcast day is used to verify the effectiveness of the proposed system.

Optimal Capacity Configuration of Hybrid Energy Storage System Considering Smoothing Wind Power Fluctuations and Economy

After comparing the economic advantages of different methods for energy storage system capacity configuration and hybrid energy storage system (HESS) over single energy storage system, a method based on improved moving average and ensemble empirical mode decomposition (EEMD) to smooth wind power fluctuations is proposed aiming at the optimal capacity configuration of HESS. Firstly, EEMD was used to decompose the HESS reference power which was derived by improved moving average filtering, and then several intrinsic mode functions (IMFs) were obtained. Each IMF instantaneous frequency-time profile was processed by Hilbert transform, the so- call gap frequency was identified, and then reconstruct the high and low frequency components to obtain the HESS reference power. Subsequently, taken the energy storage system charge-discharge efficiency and state of charge (SOC) into account, the rated power and capacities of each scheme was determined. Finally, based on Life Cycle Cost (LCC) theory, an energy storage system economic cost calculation model was established to compare the costs of each scheme and select the optimal one.

A Power Management Scheme for Grid-connected PV Integrated with Hybrid Energy Storage System

The penetration of renewable energy sources (RESs) in the distribution system becomes a challenge for the reliable and safe operation of the existing power system. The sporadic characteristics of sustainable energy sources along with the random load variations greatly affect the power quality and stability of the system. Hence, it requires storage Systems with both high energy and high power handling capacity to coexist in microgrids. An efficient energy management structure is designed in this paper for a grid-connected PV system combined with hybrid storage of supercapacitor and battery. The combined supercapacitor and battery storage system grips the average and transient power changes, which provides a quick control for the DC-link voltage, i. e., it stabilizes the system and helps achieve the PV power smoothing. The average power distribution between the power grid and battery is done by checking the state of charge (SOC) of a battery, and an effective and efficient energy management scheme is proposed. Additionally, the use of a supercapacitor lessens the current stress on the battery system during unexpected disparity in the generated power and load requirement. The performance and efficacy of the proposed energy management scheme are justified by simulation studies.

Solar Power Generation System With Power Smoothing Function

The output power from a solar power generation system (SPGS) changes significantly because of environmental factors, which affects the stability and reliability of a power distribution system. This study proposes a SPGS with the power smoothing function. The proposed SPGS consists of a solar cell array, a battery set, a dual-input buck-boost DC-AC inverter (DIBBDAI) and a boost power converter (BPC). The DIBBDAI combines the functions of voltage boost, voltage buck and DC-AC power conversion. The BPC acts as a battery charger between the solar cell array and the battery set. For the proposed SPGS, the DC power that is provided by the solar cell array or the battery set is converted into AC power through only one power stage. The solar cell array also charges the battery set through only one power stage. This increases the power conversion efficiency for the solar cell array, the battery set and the utility. The battery set is charged/discharged when the output power of the solar cell array changes drastically, in order to smooth the output power from the SPGS. In addition, the DIBBDAI can suppress the leakage current that is induced by the parasitic capacitance of the solar cell array. The proposed power conversion interface increases power efficiency, smooths power fluctuation and decreases leakage current for a SPGS. A hardware prototype is completed to verify the performance of the proposed SPGS.

Transient power smoothing control strategy for battery of pure electric bus

Transient power smoothing control strategy for battery of pure electric bus

Transient power smoothing control strategy for battery of pure electric bus

Transient power smoothing control strategy for battery of pure electric bus

Development of EMS for Hybrid Electric Two-Wheeler

Rising the emission level from conventional vehicles (CV) is a major concern of today’s world. Electric vehicle (EV) and hybrid electric vehicles (HEV) technology are two ways to deal with it. EV technology is an emerging technology but they have some challenges in adopting the EV technology. So, this paper deals with modelling and simulation of a hybrid electric vehicle such as series hybrid electric vehicle and parallel hybrid electric vehicle with different energy management strategies. The heart of HEV development is energy management strategy (EMS), on which vehicle’s performance and fuel consumption can be optimized. For series HEV charge depleting charge sustaining (CDCS) EMS has been used and for parallel HEV rule-based (RB) EMS has been used. Supervisory control algorithms play important role to allow smooth power flow between the engine and electric source. There are different EMSs such as rule-based, optimization-based (OB), and learning-based (LB). These EMSs are used to split the power flow. In this paper, fuzzy logic controller (FLC) as an energy management strategy is proposed for a parallel hybrid electric vehicle, further this strategy is compared with RBEMS. The simulation results are compared and analyzed which shows there is improvement in range and reduction fuel consumption. In this study, MATLAB/Simulink and QSS toolbox are used for the simulation.

A Holistic Methodology to Identify Cost-Effective Smooth Routes for Power Transmission Lines

The design of cost-effective power line routes is a critical step towards elaborating a consistent network expansion plan. Although several attributes are considered by planning agents, the impact of sharp curvatures is typically neglected within the route design process, thus not accounting for the need for more expensive structures to support the power line. In this work, we tackle this issue by developing a holistic methodology that combines geoprocessing technologies with a novel combinatorial optimization technique to assist practitioners in identifying cost-effective smooth power line routes. For the latter, since the fundamental mathematical structure of the proposed tool falls into the class of a Quadratic Shortest Path Problem, an efficient dynamic programming algorithm is designed to handle the typical large-scale instances of power line tracing applications. The effectiveness of the proposed methodology is illustrated with a case study based on a real-world project of the Brazilian transmission sector.

Internal Model-Based Cascaded Control Approach for Multi-Functional Grid Interactive Converters

The concept of distributed generators (DG) and their control has been evolved as a key area of research, to ensure the sustainability of a microgrid (MG). Design and implementation of a proactive cascaded control strategy is an effective method to make the MG more sustainable and resilient towards uncertainties. In this paper, a novel cascaded control strategy consisting of two degree of freedom (2DOF) PI and an internal model controller (IMC) is proposed to effectively control the grid interactive converter (GIC). The proposed control strategy exploits the combined benefits of 2DOF-PI and IMC in improving the steady-state and dynamic performance of the GIC. The primary function of the proposed control strategy is to effectively control the GIC to facilitate smooth power flow between MG and utility. In addition to this, the proposed control strategy enables the GIC to offer different ancillary services that include unbalanced load current compensation, reactive power compensation, and harmonic current reduction. To achieve this multi-functional feature, appropriate reference currents are extracted, and a control strategy is implemented in a synchronous reference ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq0</i> ) frame. An evaporation rate-based water cycle algorithm (ERWCA) optimization technique is employed to estimate the optimal design parameters of the cascaded controller. The closed-loop stability of the system is verified using frequency and time domain analyses for the estimated optimal design parameters. To show the effectiveness of the proposed control strategy, various case studies are considered, and results are compared with existing methods.