Frequency Regulation of Power Systems With a Wind Farm by Sliding-Mode-Based Design

Load frequency regulation is an essential auxiliary service used in dealing with the challenge of frequency stability in power systems that utilize an increasing proportion of wind power. We investigate a load frequency control method for multi-area interconnected power systems integrated with wind farms, aimed to eliminate the frequency deviation in each area and the tie-line power deviation between different areas. The method explores the derivative and integral terminal sliding mode control technology to solve the problem of load frequency regulation. Such technology employs the concept of relative degrees. However, the subsystems of wind-integrated interconnected power systems have different relative degrees, complicating the control design. This study develops the derivative and integral terminal sliding-mode-based controllers for these subsystems, realizing the load frequency regulation. Meanwhile, closed-loop stability is guaranteed with the theory of Lyapunov stability. Moreover, both a thermal power system and a wind power system are applied to provide frequency support in this study. Considering both constant and variable external disturbances, several numerical simulations were carried out in a two-area thermal power system with a wind farm. The results demonstrate the validity and feasibility of the developed method.      

Neural-Network-Based Terminal Sliding Mode Control for Frequency Stabilization of Renewable Power Systems

This paper addresses a terminal sliding mode control (T-SMC) method for load frequency control (LFC) in renewable power systems with generation rate constraints (GRC). A two-area interconnected power system with wind turbines is taken into account for simulation studies. The terminal sliding mode controllers are assigned in each area to achieve the LFC goal. The increasing complexity of the nonlinear power system aggravates the effects of system uncertainties. Radial basis function neural networks (RBF NNs) are designed to approximate the entire uncertainties. The terminal sliding mode controllers and the RBF NNs work in parallel to solve the LFC problem for the renewable power system. Some simulation results illustrate the feasibility and validity of the presented scheme.      

Robust H∞ Load Frequency Control of Multi-area Power System With Time Delay: A Sliding Mode Control Approach

This paper is devoted to investigate the robust H_∞ sliding mode load frequency control (SMLFC) of multi-area power system with time delay. By taking into account stochastic disturbances induced by the integration of renewable energies, a new sliding surface function is constructed to guarantee the fast response and robust performance, then the sliding mode control law is designed to guarantee the reach ability of the sliding surface in a finite-time interval. The sufficient robust frequency stabilization result for multi-area power system with time delay is presented in terms of linear matrix inequalities (LMIs). Finally, a two-area power system is provided to illustrate the usefulness and effectiveness of the obtained results.      

Developing a new 2D model for heat transfer and foam degradation in EPS lost foam casting (LFC) process

In this study, a 2D model is developed for heat transfer, foam degradation and gas diffusion at the interfaces of the liquid metal, foam pattern and gaseous gap in between, for EPS lost foam casting process. In this model based on mass and energy balance between gas and molten metal, radiation and conduction between foam and molten metal and convection between gas and molten metal are considered, both metal and foam surfaces are tracked and gap volume and pressure are calculated. A combination of energy balance and geometric correlations is used to define receding foam surface during mold filling. Gas flow in the gap is considered as wedge flow and Nusselt number for a laminar incompressible wedge flow is used for it. To apply our model to an example case, SOLA-VOF algorithm was used to simulate the flow of molten metal with free boundaries. Model results are compared with some data reported in the literature which show acceptable agreement. It is found that besides radiation in the gaseous area between foam and molten metal, conduction also plays an important role in foam degradation and control of molten metal velocity. This model can acceptably predict the effect of some parameters like foam density, coating permeability and foam degradation temperature.     

试样壁厚对振动消失模铸造球墨铸铁组织的影响

采用振动消失模铸造的方法制得阶梯形球墨铸铁,利用光学显微镜对球墨铸铁中的石墨形态及基体组织进行观察,借助图像分析软件对石墨球的数量进行定量分析。通过比较分析的方法,研究了试样壁厚对球墨铸铁的石墨形态及基体组织的影响。结果表明,随着试样壁厚的增大,石墨球的个数先减少后增多,基体组织则先变得粗大,尔后变得细小,并且在壁厚为60mm的试样中石墨球数较30mm厚的试样增加了69.5%。石墨形态及基体组织的变化主要应归因于试样壁厚的增大降低了试样的冷却 速度,延长了振动对凝固组织的作用时间,增强了振动力对结晶组织的“黏性剪切”作用。     

ALFC of hybrid multi-generation power system using UC and TCPS by ANFIS control technique

ABSTRACT

This paper reveals the impact of an ultra-capacitor (UC) and thyristor control phase shifter (TCPS) on frequency stability of large hybrid interconnected power system. The impact of UC and TCPS has been studied for general purpose hybrid generated multi areas power system. Further to this, an adaptive neuro fuzzy inference system (ANFIS) is is proposed for automatic load frequency control (ALFC). Thermal and reheat thermal plants are connected in Area-1 and area-2, whereas area-3 has hydro plant and area-4, 5, 6 consists of nuclear power plant, diesel power and gas turbine plant, respectively. A micro grid based on Solar Photovoltaic (PV) system and fleet of electric vehicle (EV) system is developed and integrated with load side of area-1 for load management in interconnected grid. Effect of Small load change and large load change are discussed in separate cases. The controllers are tuned by adding sliding surface to enhance the performance. A comparison between ANFIS and PI-based control approaches with and without UC and TCPS exhibits the superiority of ANFIS controller by integrating UC and TCPS. The results of the proposed control technique are compared with already published results.     

A novel hybrid gravitational search and pattern search algorithm for load frequency control of nonlinear power system

In this paper, a hybrid gravitational search algorithm (GSA) and pattern search (PS) technique is proposed for load frequency control (LFC) of multi-area power system. Initially, various conventional error criterions are considered, the PI controller parameters for a two-area power system are optimized employing GSA and the effect of objective function on system performance is analyzed. Then GSA control parameters are tuned by carrying out multiple runs of algorithm for each control parameter variation. After that PS is employed to fine tune the best solution provided by GSA. Further, modifications in the objective function and controller structure are introduced and the controller parameters are optimized employing the proposed hybrid GSA and PS (hGSA-PS) approach. The superiority of the proposed approach is demonstrated by comparing the results with some recently published modern heuristic optimization techniques such as firefly algorithm (FA), differential evolution (DE), bacteria foraging optimization algorithm (BFOA), particle swarm optimization (PSO), hybrid BFOA-PSO, NSGA-II and genetic algorithm (GA) for the same interconnected power system. Additionally, sensitivity analysis is performed by varying the system parameters and operating load conditions from their nominal values. Also, the proposed approach is extended to two-area reheat thermal power system by considering the physical constraints such as reheat turbine, generation rate constraint (GRC) and governor dead band (GDB) nonlinearity. Finally, to demonstrate the ability of the proposed algorithm to cope with nonlinear and unequal interconnected areas with different controller coefficients, the study is extended to a nonlinear three unequal area power system and the controller parameters of each area are optimized using proposed hGSA-PS technique.     

Bat inspired algorithm based optimal design of model predictive load frequency control

Bat inspired algorithm (BIA) has recently been explored to develop a novel algorithm for distributed optimization and control. In this paper, BIA-based design of model predictive controllers (MPCs) is proposed for load frequency control (LFC) to enhance the damping of oscillations in power systems. The proposed model predictive load frequency controllers are termed as MPLFCs. Two-area hydro-thermal system, equipped with MPLFCs, is considered to accomplish this study. The suggested power system model considers generation rate constraint (GRC) and governor dead band (GDB). Time delays imposed to the power system by governor-turbine, thermodynamic process, and communication channels are accounted for as well. BIA is utilized to search for optimal controller parameters by minimizing a candidate time-domain based objective function. The performance of the proposed controller has been compared to those of the conventional PI controller based on integral square error (ISE) technique and the PI controller optimized by genetic algorithms (GA), in order to demonstrate the superior efficiency of the BIA-based MPLFCs. Simulation results emphasis on the better performance of the proposed MPLFCs compared to conventional and GA-based PI controllers over a wide range of operating conditions and system parameters uncertainties.     

Load frequency control in deregulated environments via active disturbance rejection

Linear active disturbance rejection control (LADRC) method is investigated for the load frequency control (LFC) of power systems in deregulated environments. The connections between one area and the rest of the system and the effects of possible contracts are treated as a set of new disturbances besides the system load. LADRC uses an extended state observer (ESO) to estimate the disturbances and compensates them quickly. Thus it can achieve good disturbance rejection performance and is a good candidate for LFC design. The proposed method is tested on two power systems. Simulation results show that the LADRC is simple to tune for load frequency control systems, and good performance can be achieved.     

A Method for Presuming Total Output Fluctuation of Highly Penetrated Photovoltaic Generation Considering Mutual Smoothing Effect

Mutual smoothing effect of renewable energy (RE) is quite important because the amount and cost of countermeasures for maintaining soundness of power systems highly depend on evaluation of the effect. In spite of its importance, there is as yet no established method to evaluate the effect. The authors present a method for presuming the total output fluctuations of highly penetrated RE from a few measured data considering the effect. By analyzing the measured data, existing photovoltaic (PV) output fluctuations are revealed to be coherent at slower swing periods and random at faster swing periods. To represent the PV’s output fluctuation tendencies, a “Transfer Hypothesis” is introduced. A “Constant Transfer Swing Period Hypothesis” and “–20 dB/dec Slope Hypothesis” are also introduced. These hypotheses are verified by direct and indirect methods using the measured data. Only 3 sites’ data are able to presume total fluctuation of 15 sites successfully. The relationship between distance and the transfer swing period for every 2 sites out of the 15 sites agrees with these hypotheses. Finally, the authors show the total fluctuation presumption of highly penetrated PV deployment in the Hokuriku region using the proposed methods. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 186(3): 31–42, 2014; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.22327