Power Fluctuation Problem Research Articles

Research on secondary power allocation strategy of two types of energy storage units considering dual SOC

Abstract Against the problem of power fluctuation in the photovoltaic microgrid system, the power fluctuation can be smoothed out by hybrid energy storage technology. Still, the limited capacity of two energy storage units will cause safety problems, such as overcharging and over-discharging in two types of energy storage units and reduce the life of the energy storage device. Therefore, a secondary power distribution control strategy for two types of energy storage units considering dual SOC is proposed. Firstly, the system unbalanced power is calculated. The system unbalanced power is divided through the second-order low-pass filter to obtain the primary distribution power. Then, the SOC of the battery and supercapacitor is divided into nine regions. Finally, the power demand and the SOC in the nine regions are considered simultaneously. Then, the secondary power allocation is carried out for two types of energy storage units. In Matlab/Simulink, the modeling of Photovoltaic microgrids is established, and the simulation results verify the feasibility of the control strategy.

Two-stage decision-dependent demand response driven by TCLs for distribution system resilience enhancement

Service restoration is a critical function of the self-healing distribution system to cope with extreme events. Cold load pickup (CLPU) caused by thermostatically controlled loads (TCLs) requires extra generation power to retore loads, slowing down the distribution system restoration process. Meanwhile, increasing renewable energy brings the supply-demand imbalance because of the power variability and may cause voltage or current violations. Accordingly, a two-stage decision-dependent demand response (DR) methodology is proposed to address the two barriers to distribution system resilience enhancement. Specifically, two load control strategies are developed in the first-stage DR to regulate TCLs for CLPU mitigation, which reduces the additional power requirement when re-energized. In the second-stage DR, the restored TCLs that can be controlled to provide flexibility are characterized as virtual energy storage (VES) for managing renewable energy variability. In this way, the required power generation is reduced, and the power fluctuation problem caused by renewable energy can be well addressed. It helps to speed up the load restoration and keep the distribution system operating securely. Moreover, the load profiles with CLPU mitigation control, VES parameters and VES availability time, depend on the re-energization time. In other words, load restoration decisions determine the two-stage DR. This is the most important finding of this paper and explicitly formulated in the load restoration model for accurate load characterization. The load restoration model is described by a mixed integer second-order cone programming (MISOCP) problem and solved using MATLAB 2021 with Gurobi solver. Case studies show that the proposed methodology can significantly mitigate CLPU and restore more loads. The decision-dependent behaviors of the two-stage DR are also validated.

Polarization Controller Based on Variable-Step Greedy Linear Descent for Self-Homodyne Coherent Transmission Systems

A self-homodyne coherent (SHC) transmission system that has a good prospect in terms of short-reach interconnections can simplify digital signal processing (DSP) and reduce the power consumption of laser diodes. However, the polarization control of the carrier becomes a pivotal part of these systems, and different from the traditional polarization control on a certain state of polarization (SOP), it only needs to lock the two polarization lights after the polarization beam splitter (PBS) in a state of equal power. Half-wave plates or Mach–Zehnder interferometers can accomplish the above goals. In order to evaluate the performance of these polarization control structures in the SHC system, we modeled them on the basis of theoretical analysis. Furthermore, a variable-step greedy linear descent (GLD) algorithm is proposed to solve the power fluctuation problem caused by the accelerated change of SOP near the pole of the Poincaré sphere. The simulation results indicate that the variable-step GLD algorithm can effectively improve the tracking ability of the polarization control loop up to approximately 1.5 times of the GLD algorithm and the gradient descent (GD) algorithm.

Fault Ride Through and Intermittency Improvement of Renewable Energy Integrated MMC-HVDC System Employing Flywheel Energy Storage

Modular multilevel converter (MMC)-based high voltage direct current (HVDC) transmission networks integrate remotely located distributed renewable energy resources (RER). The intermittent nature of RER and symmetrical and asymmetrical AC-side low-voltage faults produce operational difficulties. It reduces the MMC’s ability to transfer the rated power, which raises the voltage of the HVDC link. Therefore, the MMC-HVDC network’s fault ride-through (FRT) capabilities and the power fluctuation brought on by RER intermittency are potential challenges to the efficient integration of renewable energy resources. In response, this article suggests an energy control scheme for the flywheel energy storage of the PV-wind-MMC-HVDC system in order to regulate the HVDC-link voltage during low voltage faults at the point of common coupling (PCC) of the AC grids and to address the problem of power fluctuation caused by intermittent RER and sudden load changes. The suggested method eliminates the dynamic braking resistor (DBR) from the HVDC link and seamlessly integrates the RER without actively reducing renewable energy power during low voltage faults. To test the effectiveness of the proposed control method for the flywheel energy storage in reducing excess energy in the HVDC link, symmetrical and asymmetrical low voltage faults have been conducted. In addition, changes in wind speed, solar radiation, and temperature have been made to validate the flywheel energy management system’s performance. A real-time digital simulator (RTDS) and dSPACE-based controller hardware in loop (CHIL) configuration with a complete system have been used to simulate and evaluate the entire system.

Refractive Index Measurement Based on Thin-Core Fiber In-Line Mach-Zehnder Interferometer and Differential Intensity Demodulation

A compact and reliable thin-core fiber (TCF) based in-line Mach-Zehnder interferometric (MZI) sensor for refractive index (RI) measurement is proposed and experimentally demonstrated. A section of TCF is sandwiched between a multi-mode fiber (MMF) and a single-mode fiber (SMF) to form the sensing head. In addition, the use of the differential intensity demodulation method not only greatly reduces the system cost, but also solves the problem of power fluctuation in the RI interrogation system. Three samples with different sensing lengths have been made, and the maximum sensitivity of 59.9 dB/RIU has been obtained in the range of 1.332–1.411 RIU, which means the measurement resolution is about 1.669 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−4</sup> RIU. Besides, the proposed MZI-based RI sensor is less sensitive to temperature, thus the cross-sensitivity effect can be greatly weakened.

An Improved Hydraulic Power Take-Off Unit Based on Dual Fluid Energy Storage for Reducing the Power Fluctuation Problem in the Wave Energy Conversion System

The power take-off (PTO) stability is one of the most important concerns for wave energy converters (WECs). The PTO unit converts the mechanical energy produced by the wave absorber (WA) unit into useful electrical energy. Due to the drastic input energy variation of real wave motions, the generated electrical power from the PTO unit significantly fluctuates and is potentially harmful to electrical and electronic appliances. This paper proposes an improved hydraulic PTO (HPTO) for the WECs. An improved HPTO unit comprises a dual high-pressure accumulator (HPA) module and fluid energy control (FEC) module, which significantly enhances the generated electrical power from the generator under irregular wave circumstances. A complete model of wave absorber device with conventional and improved HPTO units was built in MATLAB/Simulink using a Simscape fluids toolbox. The parameters of the FEC control strategy were optimized using a genetic algorithm. The improved HPTO unit model was simulated with five irregular wave inputs to evaluate its performance in irregular conditions. The effects of the HPA pressure constraints on the improved HPTO unit performance were also investigated. Overall, the simulation results indicate that the improved HPTO unit was able to generate a stable power up to 87.3% of WECs in an irregular sea state.

Two-level model predictive control energy management strategy for hybrid power ships with hybrid energy storage system

Compared with the load power characteristics of ground power systems, the intermittent and random fluctuation of ship load power demand brings challenges to the energy management system of ship power systems. To achieve fuel economy and solve the problem of power fluctuation, the hybrid energy storage system (HESS) composed of the battery pack and ultra-capacitor is applied to the diesel-electric hybrid ship. A two-level model predictive control (MPC) strategy consisting of two optimization stages is proposed. The first stage aims to determine the power distribution solution of the diesel generator and battery at a large time-scale. In the second stage, the operation strategy of the ultracapacitor is determined at a small time-scale based on the power distribution solution of the first stage. The conventional MPC-based strategy and global optimization strategy based on dynamic programming (DP) are compared with the proposed strategy. The simulation results show that the proposed strategy has better fuel saving ability, and realizes the clear power frequency division between the supercapacitor and battery. In addition, the proposed strategy can also approach the performance of global optimization.

Hybrid Data-Driven and Model-Based Distribution Network Reconfiguration With Lossless Model Reduction

Distribution network reconfiguration is an effective method to face the problem of power fluctuation in the power system. Previous studies have focused on mathematical optimization techniques with complex modeling processes and heuristic algorithms with time-consuming solving processes to obtain the optimal reconfiguration strategy. In this article, a hybrid data-driven and model-based distribution network reconfiguration (HDNR) framework is proposed, where the model-based module includes model reduction and goal-oriented clustering to cluster the identical reconfiguration strategies. Here, the data-driven module is implemented through a long short-term memory network to learn the mapping mechanism between load distribution and optimal reconfiguration strategies. The model-driven module and the data-driven module are coupled through the proposed hierarchical network recovery process, which presents the reconfiguration results layer by layer. Finally, the numerical case study on the IEEE 33-bus, IEEE 119-bus, and IEEE 123-bus network shows the validity of the proposed HDNR framework. It is shown that the solution space is reduced, which contributes to reducing computation time and resources. Moreover, the obtained accuracy of the reconfiguration strategy is higher than most existing research even with limited data samples.

Smart hybrid microgrid for effective distributed renewable energy sharing of PV prosumers

In this research article, a Distributed Energy Sharing Program (DESP) is proposed to share energy among PV prosumers in a smart hybrid microgrid (SHM), making the PV prosumer utilize the energy efficiently. The difficulties faced by the PV prosumers include the intermittent nature of Renewable Energy Sources (RESs), and PV prosumers who consume their own PV power face a power fluctuation problem. PV prosumer have one-time slot with excess PV power generation (power loss) and another slot with insufficient PV power generation (shortage). Moreover, sometimes, a total absence of PV power (affecting the prosumer day to day life). PV prosumers directly connect to the utility grid, resulting in moderate PV power selling prices, but PV prosumers purchase power from the utility grid at high prices at a time slot t. PV prosumers only earn the smallest profit under this plan. As a consequence, the DESP is proposed. SHM needs a DESP to manage the Battery Storage System (BSS) and minimize the PV prosumer electricity tariff using an internal pricing scheme to utilize RES efficiently. The Internet of Things (IoT) communicates SHM to PV prosumers or vice versa, enabling efficient and cost-effective PV energy exchange. This approach enhances PV utilization and maximizes PV prosumer’s profit through DESP.

Research on the method of suppressing power fluctuation of hydro generator unit based on vortex elimination technology

Hydro power is a clean and renewable energy source, and it is one of the important ways to realize “carbon peak” and “carbon neutrality”. With the reform of the power system structure, the Central China Power Grid covering the four provinces of Hubei, Hunan, Jiangxi and Henan and the Southwest Power Grid covering the three regions of Sichuan, Chongqing and Tibet have realized asynchronous operation. In terms of stable operation of the power grid, the Power Grid, which accounts for a large proportion of hydro power, is facing severe challenges. Aiming at the power fluctuation problem of a hydro power station in Southwest China, the mechanism that caused the active power fluctuation problem was explored from the aspects of water, machinery, and electricity. Combined with an example of active power fluctuation of a hydro power station, it was found out that the active power fluctuation was caused by the water inlet vortex caused by large fluctuations in shell inlet pressure. A method of installing a vortex eliminator at the water inlet is proposed to reduce the pressure fluctuation at the inlet of the volute. Numerical simulation and field data measurement prove that this method is effective in reducing the fluctuation of active power, and the problem of power fluctuation has been well solved. It provides an important reference for similar problems of hydroelectric generating units.

A day-ahead energy management and reserve declaration strategy for parking lot based on electric vehicle accessing guidance

Electric vehicle (EV) could realize the role transformation between mobile load and energy storage by adjusting charging and discharging status, which is a promising reserve resource for power grid to cope with the power fluctuation problem. However, due to the quantity limit of charging equipment, the reserve capacity of EVs will be undermined as their accessing process become stunted. To this end, an accessing guidance model is established to alleviate the congestion of parking lot (PL), and a day-ahead energy management and reserve declaration strategy for PL operator is formulated with the goal of daily operation profit maximization. In this paper, the conception of electricity fluctuation feasible region is suggested to achieve the reliable evaluation of reserve declaration capacity. And the EV guidance feasibility between different PLs, as well as the asynchronous problem of EV appointment interval and reserve market time scale is also considered. Simulation verification is carried out to examine the effectiveness of our proposed model, where the results show that the congestion of PLs is effectively relieved after the guidance model is introduced, and the reserve declaration capacity, as well as the operation profit of PLs is enhanced accordingly.

Fourth Generation Neutron Source in Dubna, ‘‘Solution of Pulse Power Fluctuation Problem’’

Fourth Generation Neutron Source in Dubna, ‘‘Solution of Pulse Power Fluctuation Problem’’

BMI-Based Load Frequency Control in Microgrids Under False Data Injection Attacks

In this article, the power fluctuation problem caused by adding renewable energy sources to microgrids (MGs) is addressed. These power fluctuations which can cause several adverse effects, including system instability, load shedding, and eventually blackouts are attenuated by designing a load frequency controller (LFC) to provide a constant and uniform frequency in different operation cases of MGs. This article designs a dynamic output feedback controller (DOFC) for LFC in MGs while considering the contraction observer for attack mitigation. We suggest a new formulation of the sufficient conditions for the DOFC design problem in the form of bilinear matrix inequalities (BMIs) and try to minimize the frequency deviation subject to load, solar, and wind energy changes. The proposed formulation effectively changes the problem to a new BMI model which can easily be divided into two problems, one is a convex optimization problem and the remained part is a quadratic matrix inequality problem which is linearized around the feasible solution of the linear matrix inequality part by a Taylor-like expansion. This leads to a more exact and less conservative solution as compared to the previous methods suggested in the literature. To illustrate the merits of the developed approach, numerical simulations on a sample ac–MG are carried out. Comparing norms of the frequency variations in the closed-loop system with multiple prominent methods in previous works, including <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${{\boldsymbol{H}}_\infty }, \ {\boldsymbol{\mu }}$</tex-math></inline-formula> , fuzzy type-1, and intelligent-PI, shows that our proposed method reduces the two and infinity norms of frequency fluctuations by 84% and 80%, respectively compared to the traditional <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${{\boldsymbol{H}}_\infty }$</tex-math></inline-formula> method which is the best among the analyzed approaches. This further verifies the efficacy of the designed DOFC in our article.

Power stabilisation scheme design using spatial rotating coil based on magnetic field aggregation

The power fluctuation problem has been a key issue in dynamic wireless power transfer (WPT) systems. In the past research studies, the power fluctuation problem at low-transmission distance has been solved, but existing solutions often involve complex control strategies and cannot realise power stabilisation for dynamic WPT systems under high-transmission distance. As a remedy, the spatial rotating coil design scheme is proposed based on magnetic field aggregation to solve the power fluctuation problem without control strategy for high distance dynamic WPT system. Firstly, the crucial parameters affecting power fluctuations are analysed. Then the relative optimisation backgrounds are introduced. Afterwards, the mechanism of power sag is analysed based on magnetic field analysis. Subsequently, the spatial rotating double D (DD) coil design is proposed inspired by omnidirectional WPT coil, and various different DD coil schemes are optimised utilising magnetic field aggregation method to acquire the optimal scheme. Compared with the original coil scheme, the proposed design scheme improves fluctuation of system mutual inductance without complicated control strategies according to simulation results. Finally, a physical coil system consistent with the simulation system is constructed, which verifies the improvement effect of the proposed scheme and effectively confirm feasibility of the optimal scheme.

Power-friendly Primary Frequency Control Method and System of Receiving-end Grid

With the rapid development of new energy sources such as wind power and photovoltaics, and the intensification of interconnected power grids, power fluctuation problem brings adverse influence on power grid frequency control. The stability of power grid frequency mainly depends on primary frequency compensation (PFC) of thermal power units. How to control and improve the PFC ability is the precondition to realize the safe and stable operation of power grid. By analyzing the PFC assessment system and standard of power grid, the problems in the current unit’s PFC were pointed out. By dynamically correcting the current rotation difference according to the actual main steam pressure measurement value of the unit, it can fully compensate the grid power gap by using the unit’s heat storage. The application results show that the power-friendly PFC method and system of receiving-end grid can effectively control the thermal power units to achieve the stability of power grid frequency.

Hierarchical and distributed demand response control strategy for thermostatically controlled appliances in smart grid

Thermostatically controlled appliances (TCAs) have great thermal storage capability and are therefore excellent demand response (DR) resources to solve the problem of power fluctuation caused by renewable energy. Traditional centralized management is affected by communication quality severely and thus usually has poor real-time control performance. To tackle this problem, a hierarchical and distributed control strategy for TCAs is established. In the proposed control strategy, target assignment has the feature of self-regulating, owing to the designed target assignment and compensating algorithm which can utilize DR resources maximally in the controlled regions and get better control effects. Besides, the model prediction strategy and customers’ responsive behavior model are integrated into the original optimal temperature regulation (OTR-O), and OTR-O will be evolved into improved optimal temperature regulation. A series of case studies have been given to demonstrate the control effectiveness of the proposed control strategy.

Design of Optimal SMES Controller Considering SOC and Robustness for Microgrid Stabilization

The microgrid with wind and photovoltaic (PV) power sources unavoidably encounters the power fluctuation problem. To solve this problem, the superconducting magnetic energy storage (SMES) can be used. Nevertheless, large power fluctuation from wind and PV sources, and severe system faults may cause the overcharge or deep-discharge state of SMES. These abnormal states highly degrade the dynamic performance of the SMES. To handle these situations, this paper concentrates on the new SMES power controller design considering state-of-charge (SOC), robustness, and optimal inductance of the superconducting coil for microgrid stabilization. The active and reactive power controllers of SMES are represented by the proportional-integral (PI) control. The SOC deviation control and the mixed H 2 /H ∞ control are proposed to optimize the SMES coil inductance and PI parameters. Simulation study is performed to signify the control effect of the proposed SMES.

Comparison of optical, structural, morphological, vibrational and thermal analysis of V2O5 nanobelts prepared with and without the application of constant current source from renewable energy

Investigating the optical and vibrational properties of a material plays a vital role in the materials applicability. One dimensional nanostructures of V2O5 are used as applications in the field of desalination, microelectronics, optoelectronics, sensors, lithium batteries, etc. The synthesis parameters play a vital role on the properties of the prepared nanostructured materials. Especially the problem of power fluctuation during the synthesis has a very predominant effect in the synthesis of Nanomaterials. Hence a constant and continuous power from a renewable energy-constant current source incorporating solar and wind energy has been applied for the preparation of uniform and smooth surfaced V2O5 nanobelts by simple hydrothermal method. Therefore the resulting nanobelts proved to be successful outcome of material science and renewable technology. The prepared nanobelts were found to be uniform surfaced with narrow size distribution. The samples have been characterized by UV-vis, XRD, SEM, FTIR and TG/DTA in order to investigate the optical, structural, morphological, Vibrational and thermal properties.

Day Dispatch Strategy for Integrated System Based on Time-frequency Scales of PWP

A day dispatch strategy for the integrated system (IS) of wind/photovoltaic/pumped-storage/gas-turbine-power/energy-storage plant is proposed in this paper based on the time-frequency scales of power of wind/photovoltaic (PWP). Based on the day-ahead dispatch strategy, the day dispatch optimization model of the IS is first established, and then according to the patulous short-time prediction (PSP) and ultra-short-time prediction (UP) of PWP, the day rolling and real-time scheduling strategies are put forward based on the time-frequency scales of PWP. Finally, the cone programming method is applied to optimize the day dispatch schedule. Simulation results show that the proposed strategy can compensate for the error in the day-ahead dispatch strategy based on short-time prediction (SP) of PWP. Thus, as an important supplement to the day-ahead dispatch strategy, this method is proved to be an effective solution to the power fluctuation problem in large-scale wind/photovoltaic integration, realizing a smooth power output, as well as guaranteeing the economical, efficient, and environmentally friendly operation of the system.

Application of electrolyzer to alleviate power fluctuation in a stand alone microgrid based on an optimal fuzzy PID control

Due to the high intermittent power generations from wind and photovoltaic in the microgrid (MG) system, these result in the severe power fluctuation. When the fuel cell (FC) equipped with the aqua electrolyzer (AE) has been installed in the MG, in addition to hydrogen production for FC, the absorbed power by AE can be controlled to alleviate the power fluctuation. This paper proposes the coordinated control of AE and FC to solve the power fluctuation problem in the MG. By control of the power absorption by AE and the power production by FC, the power fluctuation in the MG can be suppressed. The optimal fuzzy logic based-proportional-integral-derivative (FLPID) is used to design the controllers of AE and FC. Without trial and error as in the conventional FLPID controller design, scale factors, membership functions and control rules of the optimal FLPID controller are automatically and simultaneously tuned by a bee colony optimization. Simulation results confirm the superior stabilizing effect of the proposed optimal FLPID controller in comparison with the conventional FLPID controller under several system disturbances.