Improved power system stabilizers

The authors propose three novel approaches to improve a conventional power system stabilizer (PSS) in a single machine to infinite bus system. These improved stabilizers use the conventional PSS in the usual manner plus modification of the terminal voltage feedback signal to the excitation system as a function of the accelerating power on the unit. This nonlinear action increase the power system stability greatly. Also, since these improved stabilizers are based on the conventional stabilizers, they are simple to implement. Simulation results show that these three kinds of improved stabilizer can improve power system stability much more than the conventional PSS which has been used widely in power systems since the 1970s     

Robustness of fuzzy logic power system stabilizers applied tomultimachine power system

This paper investigates the robustness of fuzzy logic power system stabilizers using the information of speed and acceleration states of a study unit. The input signals are the real power output and/or the speed of the study unit. Nonlinear simulations show the robustness of the fuzzy logic power system stabilizers. Experiments are also performed by using a micro-machine system. The results show the feasibility of the proposed fuzzy logic stabilizer     

Artificial neural network power system stabilizers in multi-machinepower system environment

The effectiveness of an artificial neural network (ANN), functioning as a power system stabilizer (PSS), in damping multi-mode oscillations in a five-machine power system environment is investigated in this paper. Accelerating power of the generating unit is used as the input to the ANN PSS. The proposed ANN PSS using a multilayer neural network with error-backpropagation training method was trained over the full working range of the generating unit with a large variety of disturbances. The ANN was trained to memorize the reverse input/output mapping of the synchronous machine. Results show that the proposed ANN PSS can provide good damping for both local and inter-area modes of oscillations     

Tuning of power system stabilizers using an artificial neuralnetwork

A new approach using an artificial neural network is proposed to adapt power system stabilizer (PSS) parameters in real time. A pair of online measurements i.e., generator real-power output and power factor which are representative of the generator's operating condition, are chosen as the input signals to the neural net. The outputs of the neural net are the desired PSS parameters. The neural net, once trained by a set of input-output patterns in the training set, can yield proper PSS parameters under any generator loading condition. Digital simulations of a synchronous machine subject to a major disturbance of a three-phase fault under different operating conditions are performed to demonstrate the effectiveness of the proposed neural network     

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 evolutionary programming

The optimal design of power system stabilizers (PSSs) using evolutionary programming (EP) optimization technique is presented in this paper. The proposed approach employs EP to search for optimal settings of PSS parameters that shift the system eigenvalues associated with the electromechanical modes to the left in the s-plane. Incorporation of EP algorithm in the design of PSSs significantly reduces the computational burden. The performance of the proposed PSSs under different disturbances, loading conditions, and system configurations is investigated for a multimachine power system. The eigenvalue analysis and the nonlinear simulation results show the effectiveness and robustness of the proposed PSSs to damp out the local as well as the interarea modes of oscillations and work effectively over a wide range of loading conditions and system configurations.     

Analysis of the damping contribution of power system stabilizers driving wind power plants

Recently, the concept of wind power plant has been introduced as a result of the increment of wind power penetration in power systems. A wind power plant can be defined as a wind farm, which is expected to behave similar to a conventional power plant in terms of power generation, control and ancillary services. Transmission system operators are requiring wind power generation to help to power system with some ancillary services such as fault ride through or power system stabilizer capability. Therefore, it is important to study the power system stabilizer capability of wind power plants. In this paper, a comparison of various power system stabilizer schemes is presented. The effect of the distance from the tie line to the wind farm on the controller response and the influence of wind power plants proximity to synchronous generators are also evaluated. These studies show that wind power plants have promising power system stabilizer capability even using local input signals. However, the location of the wind power plant on the power system is a critical factor. Copyright © 2012 John Wiley & Sons, Ltd.     

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     

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 of augmented fuzzy logic power system stabilizers to enhancepower systems stability

This paper presents an augmented fuzzy logic power system stabilizer (PSS) for stability enhancement of multimachine power systems. In order to accomplish a satisfactory damping characteristic over a wide range of operating points, speed deviation (Δω) and acceleration (Δω) of a synchronous generator were taken as the input signals to the fuzzy controller. It is well known that these variables have significant effects on damping the generators' shaft mechanical oscillations. A modification of the terminal voltage feedback signal to the excitation system as a function of the accelerating power on the unit, is also used to enhance the stability of the system. The stabilizing signals are computed using the standard fuzzy membership function depending on these variables. The performance of the proposed augmented fuzzy controller is compared to an optimal controller and its effectiveness is demonstrated by a detailed digital computer simulation of a single machine infinite bus and a multimachine power systems     

Miniaturization of spacecraft electrical power systems with solar-hydrogen power supply system

The concept of solar-hydrogen systems for spacecraft, orbital stations, lunar and Martian bases is currently receiving a new impetus. The supply of solar energy to energy receivers aboard space vehicles is limited. The number of everyday tasks and energy-intensive experiments on board space objects is growing with the development of astronautics. To perform energy-intensive work and experiments, energy consumption exceeds the incoming solar fluxes. The modern solar-hydrogen system ensures the reception, conversion and accumulation of excess incoming energy in the form of chemical energy - hydrogen. Cryogenics makes it possible to miniaturize the solar-hydrogen system. The safety of the cryogenic solar-hydrogen energy system is ensured by hydrogen concentration and leakage sensors.The article proposes a comprehensive solution for miniaturization of Power Conversion Unit (PCU) of Energy Power System (EPS) of spacecrafts (SC), which consists in a joint solution of four key problems of miniaturization of power devices: energy, structural, design and technological, system. Miniaturization of the solar-hydrogen energy system (SHES) is achieved by installing onboard hydrogen and oxygen microcryogenic refrigerators, as well as hydrogen and oxygen cryogenic tanks, water tank, electrolyzer and hydrogen fuel cells (FC). The accumulation of chemical hydrogen energy on board the orbiting spacecraft ensures reliable operation when entering the shadow. Storage of hydrogen in cryogenic form significantly reduces the volume required. A cryocooler based on the Stirling cycle provides the process of liquefying hydrogen after the electrolysis of distilled water. In addition, cryogenic temperatures of 20.2 K can be used to thermostat precision instruments placed on board the spacecraft, For example, to ensure the operation of the SQUID. A 3D - model of a voltage stabilization module (VSM), on the basis of which EEC can be produced with different output power and redundancy depth. We give an example of a complete structural scheme of the EEC, which allows implementing all the fulfillment of all the tasks, assigned to the EEC of the PCU SC.     

Application of an inverse input/output mapped ANN as a power systemstabilizer

An artificial neural network (ANN), trained as an inverse of the controlled plant, to function as a power system stabilizer (PSS) is presented in this paper. In order to make the proposed ANN PSS work properly, it was trained over the full working range of the generating unit with a large variety of disturbances. Data used to train the ANN PSS consisted of the control input and the synchronous machine response with an adaptive PSS (APSS) controlling the generator. During training, the ANN was required to memorize the reverse input/output mapping of the synchronous machine. After the training, the output of the synchronous machine was applied as the input of the ANN PSS and the output of the ANN PSS was used as the control signal. Simulation results show that the proposed ANN PSS can provide good damping of the power system over a wide operating range and significantly improve the system performance     

Harmonic control using matrix converter of unbalanced input voltage supplied from solar power system

Most of the renewable energy sources are not distributed directly to consumer. It gone through several section to get optimum output voltage and current with the almost zero distortion. Direct Matrix converters are well known of its better power quality and low power distortion to the reactive loads. Conversely, multilevel H bridge inverters are broadly used to attain a sinusoidal output voltage in solar photovoltaic application. Reactive power is subject to high importance for the operation of alternating current (AC) power systems. Moreover there is always a challenge to obtain the balance current control from an unbalanced supply voltage with minimum harmonic distortion for reactive load application from solar power system. The main objective of the proposed system is to maximize the power usage by maintaining the current and power factor nearby unity. There are many different optimization techniques are used so far in matrix converter, a novel method of optimization BAT algorithm is proposed for the power quality to get the best result. This work mainly deals with the compensation of reactive power used in Solar Photovoltaic Power System. Bidirectional energy flow is possible with matrix converter for battery charging. Simulation results are presented to confirm the appropriate operation of the system under different of operating conditions. Also, in the proposed method the percentage of the higher order harmonics can reduced less than 9% of matrix converter for solar photovoltaic application.     

Distributed generation system with PEM fuel cell for electrical power quality improvement

In this paper, a physical model for a distributed generation (DG) system with power quality improvement capability is presented. The generating system consists of a 5 kW PEM fuel cell, a natural gas reformer, hydrogen storage bottles and a bank of ultra-capacitors. Additional power quality functions are implemented with a vector-controlled electronic converter for regulating the injected power.     

Economic viability analysis of planned WEC system installations for electrical power production

The aim of this investigation is the development and implementation of a general and systematic procedure for the evaluation of the economic viability of planned installations of wind energy converters (WEC) for the purpose of electrical power production. The procedure is based on: the assessment of wind energy potential of an area (of interest); the limitations involved in selecting specific locations/sites for system installation in this area; the technical specification of a candidate WEC system; and the assessment of the economic viability of such electrical power production systems by applying suitable economic/financial analysis techniques. The proposed procedure was illustrated by applying it in the Thrace area of Greece, taking into consideration the national legislative frame for the exploitation of wind energy resources, and the associated subsidy provided for developing private enterprises with respect to the purchase and installation of the relevant technical equipment. The obtained computational results favor by comparison the installation of medium size WECs (150–500 kW) for the case of independent producers over the case of auto-producers.     

Reducing the effect of penstock pressure pulsations on hydroelectric plant power system stabilizer signals

A characteristic trait of Francis turbines operating at low-head is pressure pulsations that occur during certain load levels of the generator. These stem from pressure variations across the turbine due to pulsating flow in the draft tube. This surging action of the water column is related to draft tube geometry and flow rate of water in the penstock. The pressure pulsations cause torque variations on the turbine and corresponding electric power pulsations. If electric power is used as a feedback signal to the power system stabilizer (PSS), then MVAr and terminal voltage pulsations will occur when the generator is operating in the "rough zone". This paper describes field test results for investigating feedforward control from the penstock, draft tube and spiral case pressure to reduce the effects of MW pulsations on PSS output signals. This investigation involved a PSS with generator power as the feedback signal and the PSS tuned for local and inter-area damping     

Modeling electrical arcs for power circuit-breakers

Measuring and predicting the interrupting limits of modern circuit breakers by means of modeling is discussed. The operation of SF₆ -insulated breakers is described. Post-arc-current measurement and extraction are addressed. Once post-arc current and voltage recordings are available from a test, they may be used to analytically extract the two main parameters, arc time constant and nozzle cooling power. These can be used in the Mayr model to represent the dynamic arc resistance as a circuit component and will predict, by modeling, whether current interruption occurs or not for different testing stress levels or test circuit configurations     

An integrated system for thermal power generation,electrical energy storage and CO2 capture

This work reports a newly proposed system for electrical energy storage. The new system combines a direct open nitrogen (cryogen) expansion cycle with a natural gas‐fuelled closed Brayton cycle and the CO₂ produced in the system is captured in the form of dry ice. Thermodynamic analyses are carried out on the system under the baseline conditions of 1 kg s^?1 natural gas, a combustor operating pressure of 8 bars and a cryogen topping pressure of 100 bars. The results show that the exergy efficiency of the proposed system is as high as 64% under the baseline conditions, whereas the corresponding electricity storage efficiency is about 54%. A sensitivity analysis has also been carried out on the main operating conditions. The results indicate that the baseline performance can be enhanced by increasing the gas turbine (GT) inlet temperature, decreasing the approach temperature of the heat exchange processes, operating the combustor at an optimal pressure of ～7 bars and operating the cryogen topping pressure at ～90 bars. Further enhancement can be achieved by increasing the isentropic efficiency of the GT and the liquefaction process. The results of this work also suggest that the power capacity installation of peak‐load units and fuel consumption could be reduced by as much as 50% by using the newly proposed system. Further work is suggested for an economic analysis of the system. Copyright © 2010 John Wiley & Sons, Ltd.     

考虑风电消纳能力的含风电场电力系统多目标优化调度研究

针对含风电场的电力系统调度中存在的风电消纳问题,提出一种基于第二代非劣支配排序遗传算法(Non-dominated Sorting Genetic Algorithm II,NSGA-II)的多目标优化调度方法。为使电力系统在消纳尽可能多的风电同时,兼顾经济性、安全性和环保性,分别以风电消纳、发电成本和污染物排放量为目标建立了含风电场电力系统双目标及三目标调度模型,采用NSGA-II进行优化求解,并详细分析了不同目标组合策略下电力负荷、机组组合和优化目标对风电消纳的影响程度,同时引入伪权向量法为决策者提供非劣解信息,辅助决策者完成优化调度。分析结果表明,该方法有助于评估机组组合、目标组合等因素对电力系统优化调度的影响程度,对合理提高含风电场电力系统的风电消纳能力有一定的指导意义。