Robust design of multimachine power system stabilizers usingsimulated annealing

Robust design of multimachine power system stabilizers (PSSs) using simulated annealing (SA) optimization technique is presented in this paper. The proposed approach employs SA to search for optimal parameter settings of a widely used conventional fixed-structure lead-lag PSS (CPSS). The parameters of the proposed simulated annealing based power system stabilizer (SAPSS) are optimized in order to shift the system electromechanical modes at different loading conditions and system configurations simultaneously to the left in the s-plane. Incorporation of SA as a derivative-free optimization technique in PSS design significantly reduces the computational burden. One of the main advantages of the proposed approach is its robustness to the initial parameter settings. In addition, the quality of the optimal solution does not rely on the initial guess. The performance of the proposed SAPSS under different disturbances and loading conditions is investigated for two multimachine power systems. The eigenvalue analysis and the nonlinear simulation results show the effectiveness of the proposed SAPSS's to damp out the local as well as the interarea modes and enhance greatly the system stability over a wide range of loading conditions and system configurations     

Optimal design of power-system stabilizers using particle swarm optimization

In this paper, a novel evolutionary algorithm-based approach to optimal design of multimachine power-system stabilizers (PSSs) is proposed. The proposed approach employs a particle-swarm-optimization (PSO) technique to search for optimal settings of PSS parameters. Two eigenvalue-based objective functions to enhance system damping of electromechanical modes are considered. The robustness of the proposed approach to the initial guess is demonstrated. The performance of the proposed PSO-based PSS (PSOPSS) under different disturbances, loading conditions, and system configurations is tested and examined for different multimachine power systems. Eigenvalue analysis and nonlinear simulation results show the effectiveness of the proposed PSOPSSs to damp out the local and interarea modes of oscillations and work effectively over a wide range of loading conditions and system configurations. In addition, the potential and superiority of the proposed approach over the conventional approaches is demonstrated.     

Robust tuning of power system stabilisers to install in wind energy conversion systems

This paper addresses the problem of robustly tuning power system stabilisers (PSSs) in systems with large wind power integration. PSSs installed in wind energy conversion systems, namely in doubly fed induction generators, are used in this research to provide additional damping to the electromechanical modes of oscillation. A new method that aims to reduce the computational effort required to find a robust solution that is suitable for a very large set of operating conditions is also proposed.     

Stability investigation of a longitudinal power system and itsstabilization by a coordinated application of power system stabilizers

This paper presents the results of a stability investigation of a power system with longitudinal structure and its stabilization by coordinated power system stabilizers (PSSs). The effects of the existing controllers on system stability are studied. If no PSSs are present, the damping of various swing modes in the system will be very poor and low frequency oscillations present. Eigenvalue analysis shows that the undamped modes are sensitive to excitation control while speed governors have little influence on damping. In order to enhance the overall system stability through excitation control, a coordinated design procedure for power system stabilizers has been developed based on generation coherency, total coupling factor and nonlinear simulation. A PSS designed using this procedure is robust to different operating conditions and very effective for damping oscillations. Comprehensive simulation studies were conducted and results are presented     

Experimental verification of fuzzy excitation control system formulti-machine power system

A fuzzy excitation control system (FECS), based on the fuzzy theorem and having the function of both AVR and PSS, was established to improve power system stability. This paper includes the results of experiments of the FECS on the AC/DC power system simulator of the CRIEPI. The FECS is compared with the conventional quick-response excitation system with optimized PSSs on a 4-machine long distance fish-bone type power system and various system configurations. The results show that the FECS increases the power transfer limit more than 20 (%) without any parameter tuning     

Experience with digital power system stabilizers at steam and hydrogenerating stations

Test results from installations of digital power system stabilizers (DPSSs) at steam and hydro generating stations by two electric utilities in Western Canada are described. Reasons for selecting digital versus analog PSSs are outlined, stabilizer design objectives are listed, and commissioning and test results are included. It is concluded that DPSS has decided advantages over analog types and should be seriously considered as a replacement for existing analog PSSs or for new installations     

Design and techno-economical optimization for stand-alone hybrid power systems with multi-objective evolutionary algorithms

The optimal design of the hybrid energy system can significantly improve the economical and technical performance of power supply. However, the problem is formidable because of the uncertain renewable energy supplies, the uncertain load demand, the nonlinear characteristics of some components, and the conflicting techno-economical objectives. In this work, the optimal design of the hybrid energy system has been formulated as a multi-objective optimization problem. We optimize the techno-economical performance of the hybrid energy system and analyse the trade-offs between the multi-objectives using multi-objective genetic algorithms. The proposed method is tested on the widely researched hybrid PV-wind power system design problem. The optimization seeks the compromise system configurations with reference to three incommensurable techno-economical criteria, and uses an hourly time-step simulation procedure to determine the design criteria with the weather resources and the load demand for one reference year. The well-known efficient multi-objective genetic algorithm, called NGAS-II (the fast elitist non-dominated sorting genetic algorithm), is applied on this problem. A hybrid PV-wind power system has been designed with this method and several methods in the literature. The numerical results demonstrate that the proposed method is superior to the other methods. It can handle the optimal design of the hybrid energy system effectively and facilitate the designer with a range of the design solutions and the trade-off information. For this particular application, the hybrid PV-wind power system using more solar panels achieves better technical performance while the one using more wind power is more economical. Copyright © 2006 John Wiley & Sons, Ltd.     

A novel methodology for scrutiny of autonomous hybrid renewable energy system

The optimal design of a hybrid system with different configurations including renewable generation is presented in this paper. A novel multi‐objective function consisting of 6 different objectives of hybrid system is reported using GA, PSO, and TLBO to decide the optimal configurations of parameters. The technical (loss of power supply probability, renewable factor), economical (cost of energy, penalty and fuel consumption), and social (job creation, human development index, and particular matter) features are investigated as objectives simultaneously for optimal design of hybrid system. The different objective indices namely cost of energy, loss of power supply probability, particular matter, human development index, job creation, and renewable factor indices are considered. The newly invented particular matter factor for design consideration of hybrid system directly shows the human health impacts, while pollutant emission is measured in the hybrid system design. The optimum values of objective indices are decided on the basis of the minimum value of multi‐objective function. The distinct cases from I to VI of hybrid system are examined for optimal configuration including different combinations of PV, wind, biomass, diesel generator, and battery bank. The resulting analysis of each case reveals that the performance of TLBO is better than PSO, and PSO is better than GA in all respect through new multi‐objective function and found case I is more efficient solution.     

Stabilizing torsional oscillations using a hunt reactor controller

Results of a study on the application of shunt reactors for the damping of torsional oscillations that occur in a power system containing series-capacitor compensation are presented. The IEEE Second Benchmark Model, system-1 is used to investigate the benefits of the utilization of modulated reactive power in suppressing unstable subsynchronous resonance (SSR) modal interactions. A set of shunt reactors is connected to the generator bus of the affected synchronous machine whose shaft is directly coupled to the turbine system of the benchmark model. In order to stabilize all the torsional modes, a unified approach based on modal control theory is proposed for the design of a shunt reactor controller, which is essentially a dynamic output compensator. To demonstrate the effectiveness of the damping enhanced by the proposed scheme, eigenvalue analysis for different loading conditions and sensitivity analysis for controller parameters are performed     

Optimal sizing method for stand-alone hybrid solar–wind system with LPSP technology by using genetic algorithm

System power reliability under varying weather conditions and the corresponding system cost are the two main concerns for designing hybrid solar–wind power generation systems. This paper recommends an optimal sizing method to optimize the configurations of a hybrid solar–wind system employing battery banks. Based on a genetic algorithm (GA), which has the ability to attain the global optimum with relative computational simplicity, one optimal sizing method was developed to calculate the optimum system configuration that can achieve the customers required loss of power supply probability (LPSP) with a minimum annualized cost of system (ACS). The decision variables included in the optimization process are the PV module number, wind turbine number, battery number, PV module slope angle and wind turbine installation height. The proposed method has been applied to the analysis of a hybrid system which supplies power for a telecommunication relay station, and good optimization performance has been found. Furthermore, the relationships between system power reliability and system configurations were also given.     

PEMFC分布式发电系统动态协调控制仿真

符号表m-质量/kg W-质量流量/kg·s-1N-电池个数I-电流/AM-摩尔分子质量F-法拉第常数/kg·mol-1/9.6 487×104C·mol-1R-气体常数/J·(mol·K)-1T-温度/KV-体积/m3A-反应面积/m2nd-电渗透系数Dw-扩散系数/m2·s-1cwa、cwc-膜阳极侧和阴极tm-膜厚度/m侧的水浓度/mol·m-2kp-水力     

How to select regenerative configurations of CO2 transcritical Rankine cycle based on the temperature matching analysis

CO₂ transcritical Rankine cycle is regarded as a potential technology for internal combustion engines waste heat recovery, and its regenerative configurations present great prospect to increase the power output capacity. This paper proposed different regenerator layout configurations based on the temperature matching analysis, including low temperature regenerative transcritical Rankine cycle (LR-TRC), high temperature regenerative transcritical Rankine cycle (HR-TRC), dual regenerative transcritical Rankine cycle (DR-TRC) and split dual regenerative transcritical Rankine cycle (SR-TRC). Afterward, the thermodynamics, electricity production cost (EPC) and miniaturization performance are implemented. The results show that regenerative configurations have an effect on improving net power output and SR-TRC obtained optimal value of net power output. For the perspective of economic performance, the greatest value is obtained for HR-TRC among four regenerative configurations. As for the miniaturization performance, the total heat transfer area increment of LR-TRC is the lowest. The comparative analysis results offer guidance for selecting optimal regenerative configurations.     

Off‐design performance and operation strategy of expansion process in compressed air energy systems

Compressed air energy storage (CAES) systems usually operate under off‐design conditions due to load fluctuations, environmental factors, and performance characteristics of the system. In order to optimize design and operation of CAES systems, it is significant to study off‐design performance. The expansion process plays an important role in the whole system. The main objective of this study is to explore the off‐design characteristics and optimization strategy of the multistage expansion process of CAES systems with thermal storage. Two kinds of off‐design operating modes, which are equal‐power‐ratio (EPR) operation and optimizing variable stator vane rotation angle (OVRA) operation, are proposed and compared for the first time. Correlation between key parameters such as total output power ratio, exergy efficiency, outlet air/water temperature versus mass flow rate ratio, and inlet pressure are revealed. Furthermore, optimal operation principles are obtained. The primary optimizing operation principle is to optimize the isentropic efficiencies of low‐pressure stages to improve the whole efficiency of expansion process. Lastly, the optimized regulating law for variable stator vane is expressed in a polynomial form.     

Energy production of photovoltaic systems: Fixed, tracking, and concentrating

This work compares the energy production (EP) of four photovoltaic system configurations: fixed, 1-axis and 2-axis tracking flat plate, and concentrating photovoltaics (CPV). The EP comparison is based on real performance data from systems installed in Spain in 2009. These systems are located close to each other but house different configurations. Many of the systems analyzed are new installations in 2008, including two of the largest CPV systems in the world that together have 9.3 MW and represent more than 50% of the world's total CPV. The EP analysis shows: (1) compared with the fixed flat plate systems, 1-axis and 2-axis tracking flat plate systems have 22.3% and 25.2% gain in the annual EP, respectively. These real EP gains are less than 32.1% for 1-axis and 38.7% for 2-axis tracking, which are the predicted gains when only considering the difference of captured illumination by these configurations (based on the data from Photovoltaic Geographical Information System (PVGIS)). (2) The EP from CPV systems is quite close to that from fixed flat plate systems. This differs from the predicted 16.1% gain from CPV when only considering the illumination difference. Besides comparing the energy production, the performance ratio (PR) is also estimated and analyzed for the different configurations, based on the best available irradiation data. PR measures the agreement between the operation of a real system and of an ideal system that only considers the nominal module efficiency loss. The analysis shows the PR decreases in the order: fixed, 1-axis, 2-axis tracking flat plate, CPV.     

Optimal design and techno-economic analysis of a hybrid solar–wind power generation system

Solar energy and wind energy are the two most viable renewable energy resources in the world. Good compensation characters are usually found between solar energy and wind energy. This paper recommend an optimal design model for designing hybrid solar–wind systems employing battery banks for calculating the system optimum configurations and ensuring that the annualized cost of the systems is minimized while satisfying the custom required loss of power supply probability (LPSP). The five decision variables included in the optimization process are the PV module number, PV module slope angle, wind turbine number, wind turbine installation height and battery capacity. The proposed method has been applied to design a hybrid system to supply power for a telecommunication relay station along south-east coast of China. The research and project monitoring results of the hybrid project were reported, good complementary characteristics between the solar and wind energy were found, and the hybrid system turned out to be able to perform very well as expected throughout the year with the battery over-discharge situations seldom occurred.     

Optimal analysis of a space solar dynamic power system

The major purpose of the present study is the theoretical modeling, numerical simulation and optimal analysis of a space solar dynamic power system. Using the method of system analysis, a mathematical and physical model is developed to describe the process of energy transfer and conversion in a space solar dynamic power system. As a new assessing criterion for total launch mass, it is proposed to combine the system mass and aerodynamic drag area into a unified criterion. The effects of the configurations and operating parameters on the system performance are analyzed and the optimal scheme of a space solar dynamic power system is obtained by numerical simulation.     

Analysis, dimensional sizing and configuration comparison of switched-reluctance motors operating under multiphase excitation

The paper presents a simple approach for analyzing switched reluctance motors (SRMs) operating under multiphase excitation. The analysis results in specific design coefficients [derived from the SRM flux and magnetomotive force (MMF) distributions that can be used in a methodology] to calculate the SRMs initial dimensions while taking into account the magnetic loading and electric loading. Finally, the approach enables comparison of SRM configurations for an application without performing complete designs. The magnetic loading (i.e., saturation) and torque of various SRM configurations designed using the proposed approach are verified through finite-element analysis (FEA).     

Optimal chiller sequencing by branch and bound method for saving energy

This paper proposes a method for using the branch and bound (B&B) method to solve the optimal chiller sequencing (OCS) problem and to eliminate the deficiencies of conventional methods. The coefficient of performance (COP) of the chiller is adopted as the objective function because it is concave. The Lagrangian method determines the optimal chiller loading (OCL) in each feasible state. The potential performance of the proposed method is examined with reference to an example system. The proposed method consumes much less power than the conventional method and is very appropriate for application in air conditioning systems.     

Numerical analysis of limit load and reference stress of defective pipelines under multi-loading systems

The concepts of limit load and reference stress have been widely used in structural engineering design and component integrity assessment, especially in Nuclear Electric's (formerly CEGB) R5 and R6 procedures. The reference stress method has been proven to be successful in problems pertaining to creep growth, rupture damage, creep buckling, and more recently, elastic–plastic fracture toughness. An approximate method of reference stress determination relies on prior knowledge of limit loads for various configurations and loadings. However, determination of the limit loads for the problems with complicated geometric forms and loading conditions is not a simple task. In the present paper, a numerical solution method for radial loading is presented, the mathematical programming formulation is derived for the kinematic limit analysis of 3D structures under multi-loading systems, and moreover, a direct iterative algorithm used to determine the reference stress is proposed which depends on the evaluation of limit load. The numerical procedure is applied to determine the limit load and reference stress of defective pipelines under multi-loading systems. The effects of four kinds of typical part-through slots on the collapse loads of pipelines are investigated and evaluated in detail. Some typical failure modes corresponding to different configurations of slots and loading forms are studied.