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A novel approach to synchronization of shore and ship power systems is presented in this paper, providing a blackout-free supply from the shore. An application of the shore-to-ship synchronization strategy, proposed in the paper, instead of the commonly used ship-to-shore synchronization, enables a fuller exploitation of the high dynamic offered by power electronic converters. Converters are increasingly being used in shore-to-ship supply arrangements in order to ensure the required levels of voltages and frequencies, specified in shore-supply related standards. Simulation results, supported by preliminary tests in small-scale experimental arrangements, have confirmed that shore-to-ship applications might significantly improve the dynamics of the synchronization as well as the parameters of the load transferring process, especially under distorted ship voltage conditions. [ABSTRACT FROM AUTHOR]

Due to the anticipated proliferation of HVDC links up to and beyond 2020 into transmission systems, it is expected that in some locations, two or more HVDC links will be installed with a short electrical distance between them and will form a multiinfeed (MI)-HVDC scenario for the system. The control and operation of MI-HVDC systems are of particular concern for weak grids such as that likely to be found in the North of Scotland network. It is shown that the ac voltage regulation in the VSC-HVDC link may adversely affect the dynamic performance of the host weak ac system under the MI-HVDC scenario. To overcome this identified limitation associated with the ac voltage controller in the VSC-HVDC link, a new controller modification conforming to the grid code is proposed in this paper. Furthermore, this paper presents a robust control design method for ac voltage control using the fractional order (FO) control design theory. The influences of the proposed FO-based ac voltage controller are assessed alongside various voltage controllers for the representative North Scotland system. It is shown that the FO-based ac voltage controller has favorable effects on the dynamic behavior of weak ac systems with MI-HVDC. [ABSTRACT FROM AUTHOR]

Stand-alone microhydro systems based on the self-exited induction generator (SEIG) are popular in developing countries. However, an electronic based controller is required to maintain the quality (voltage and frequency) of the generated power within an acceptable range. Conventionally, this controller is designed using a phase-controlled thyristor circuit (or more recently using a dc chopper circuit) and a fixed resistance dump load to receive the excess generated power. Generally, in small communities the total dissipated power in the dump load is greater than the consumed power by all the households. This problem of inefficient power usage can be solved by distributing the controller among households. The objective of this paper is to improve the distributed electronic load controller (DELC). As with the original DELC, the proposed improved DELC is used for two purposes: First, consuming the excess generated power individually by each household; and second, operating as a complementary device for voltage and frequency regulation of the SEIG. The detailed design and experimental verifications of the proposed improved DELC including the design of an appropriate input filter to minimize the network current distortion are presented here. Additionally, MATLAB simulations are used to study the interaction between the proposed improved DELC and the powerhouse controller (the ELC). [ABSTRACT FROM AUTHOR]

This paper sets forth a new magnetic core loss model to predict core loss in electric machines and power electronic magnetic components. It introduces an alternative method to model magnetic relaxation using a continuous waveform formulation, which significantly improves the accuracy of core loss prediction for arbitrarily complex flux density waveforms. The proposed method is experimentally validated for ferrites and silicon steels. [ABSTRACT FROM AUTHOR]

When two or more electrical machines are electrically and mechanically interconnected, the implementation of a single two-dimensional finite element analysis (2D-FEA) of the whole system is complex or even impossible. This is mainly due to the feature of commercially available 2D-FEA software to use a domain depth equal for all the electrical machines drawn in the geometrical 2-D model. For any typology of rotating electrical machines, the proposed “virtual material method” easily consents to change the actual axial stack length to an arbitrary value, opening the way to describe all the machines in a single geometrical model. In the paper, the complete theory of this original approach is reported and validated on permanent magnet, induction, and field-wound synchronous machines. The cases of study with two and three interconnected machines are also presented and the results compared with the cosimulation technique of their separated bidimensional models. The perfect agreements observed in the comparisons definitely prove the feasibility of the proposed solution. [ABSTRACT FROM AUTHOR]

With the rapid increase of renewable energy sources and power electronic converters in the power system, the inertia of the power system is declined and the stability problem is more serious than ever before. In this paper, a virtual synchronous generator (VSG) control strategy is proposed to enable the voltage-source converter-based multiterminal high-voltage direct current (VSC-MTDC) system to damp the low-frequency oscillation modes. Both rotational inertia part and governor part are modeled in the VSG controller. The $V^2-P-\omega$ characteristic is developed based on the $V^2-P$ droop control to emulate the action of the speed governor when the frequency of ac grid deviates from the nominal value. The virtual inertia part is used to emulate the inertia response of the synchronous generator. The communication between VSC stations is unnecessary with the autonomous power allocation ability of the $V^2-P-\omega$ characteristic. Modal analysis is utilized to test the system stability and optimize the controller parameters. Two test systems which include offshore wind farms, VSC-MTDC systems, and onshore power grids are built in the DIgSIENT/PowerFactory. The simulation results verify the effectiveness of the proposed VSG strategy. [ABSTRACT FROM AUTHOR]

This paper proposes an enhanced control scheme for a direct drive variable speed wind turbine with an interior permanent magnet (IPM) synchronous generator. The proposed control scheme incorporates maximum torque per ampere (MTPA) trajectory and maximum power extraction, which ensures the generation of required torque for maximum power extraction with minimum stator current. This in turn minimizes stator copper loss and excessive heat generated in the IPM synchronous generator. The performance of the proposed control scheme has been validated through rigours simulation and experimental studies under varying wind speed conditions. The simulation and experimental results demonstrate the efficacy of the proposed control method. [ABSTRACT FROM AUTHOR]

This paper proposes a method to directly compute controller parameter values in a synchronverter augmented with a so-called damping correction loop, and in so doing, achieve desired transient and steady-state response. The proposed approach is grounded in a reduced third-order system model that captures pertinent dynamic characteristics of the synchronverter active-power loop (APL), particularly those of the dominant mode. This reduced-order model helps to identify and explain a shortcoming in a previous parameter tuning method. Central to the proposed parameter computation method is to express APL parameters of the original system as closed-form functions of the poles of the reduced-order system. Since the reduced-order model retains dominant-mode dynamic behaviors of the original system, APL parameters can be directly computed according to specified APL dominant mode. Time-domain simulations are provided to validate the accuracy of the reduced-order model and the proposed direct-computation parameter tuning method. [ABSTRACT FROM AUTHOR]

This paper presents a generalized method for converting multi-input and multi-output (MIMO) $dq$ impedance model of a grid-tied voltage source converter system into its sequence domain single-input and single-output (SISO) equivalents. As a result, two types of SISO impedance models were derived, one of which was derived from relatively strong and dq$ symmetric grid assumption (reduced SISO model) and the other was based on closed-loop equivalent (accurate SISO model). It was proven that the accurate SISO model has the same marginal stability condition as the MIMO model. Accuracy of these models is assessed with respect to the measured impedances in PSCAD/EMTDC simulations, their effects on stability are analyzed as well. Findings show that the accurate SISO model presents identical stability conclusions as the MIMO model. However, the reduced SISO model may lead to inaccurate results if the system is highly {\rm{dq}} asymmetric, e.g., VSC with fast phase-locked loop or an actively controlled grid. [ABSTRACT FROM AUTHOR]

This paper first derives a usable formula for frequency shift islanding detection methods on the basis of the parallel R, L, C load and the conclusions in current literature: the angle by which the total output current of the distributed resources (DR) units leads the point of common coupling (PCC) voltage must be conducted to have the same shifting direction as the load admittance angle during the variation of the frequency. According to the formula and multi-DR operation, the scenarios in which the classic frequency shift methods are applied to energy storage converters are analyzed. The results indicate that the setting of the angle by which the energy storage converter current leads the PCC voltage may need to be modified when running state changes. It results in the problems that the classic methods are not applicable for non-unity power factor (non-UPF) control and have to distinguish between generation mode and consumption mode for UPF control. On account of the problems, a coping strategy, i.e., an improved method, is proposed. The analyses indicate that the improved method is applicable in every state. The last simulations and experiments confirm the preceding conclusions. [ABSTRACT FROM AUTHOR]

In this paper, we present a scalable approach for real-time simulation of ship power systems with high-frequency power electronics converters (100–200 kHz). The proposed approach is based on the latency-based linear multistep compound method and relies on field-programmable gate array (FPGA) execution. Several examples of increasing dimension and complexity are used to evaluate the scalability—both of in terms of computational delay and of resources usage—of the proposed approach. Real-time execution with a 50 ns time step is achieved for all the examples considered. [ABSTRACT FROM PUBLISHER]

Future shipboard power systems using Medium Voltage Direct (MVDC) technology will be based on a widespread use of power converters for interfacing generating systems and loads with the main DC bus. Such a heavy exploitation makes the voltage control challenging in the presence of tightly controlled converters. By modeling the latter as constant power loads (CPLs), one possibility to ensure the bus voltage stability is offered by the linearizing via state feedback technique, whose aim is to regulate the generating DC-DC power converters to compensate for the destabilizing effect of the CPLs. Although this method has been shown to be effective when system parameters are perfectly known, only a partial linearization can be ensured in case of parameter mismatch, thus, jeopardizing the system stability. In order to improve the linearization, therefore, guaranteeing the voltage stability, an estimation method is proposed in this paper. To this aim, offline tests are performed to provide the input data for the estimation of model parameters. Such estimated values are subsequently used for correctly tuning the linearizing function of the DC-DC converters. Simulation results for bus voltage transients show that in this way converters become sources of stabilizing power. [ABSTRACT FROM PUBLISHER]

This paper describes the implementation of a distributed coordinating control system for power electronic converters in a shipboard distribution system that ensures system optimization dynamically. Multiple agents take part in the process to determine optimal power sharing for the converters. A distributable optimization method suitable for real-time coordination of converters is developed for deployment in multi-agent system type frameworks. The presented optimal power-sharing method ensures minimum distribution losses and economic dispatch of sources while enforcing constraints such as source ramp rates and capacity limits. [ABSTRACT FROM PUBLISHER]

This paper proposes a nonlinear controller to mitigate subsynchronous control interaction (SSCI) in series-compensated doubly fed induction generator (DFIG)-based wind farms. The controller is designed based on partial feedback linearization (PFL) and the proposed design approach involves scrutinizing the partial feedback linearizability of the system. The stability of the internal dynamics, which is not transformed into linear autonomous subsystems by PFL, is also analyzed in the process of deriving the control laws. The frequency scanning method is used to evaluate the performance of the proposed PFL controller, and the performance is compared to that of a finely tuned conventional proportional integral controller. A grid-connected series-compensated 100-MW DFIG-based offshore wind farm is used to demonstrate the performance of the proposed scheme through the identification and mitigation of subsynchronous resonance. An analysis of the power system reveals that the resistance is negative across the entire subsynchronous frequency range, while the reactance becomes negative around 42 Hz. The proposed controller effectively mitigates SSCI, and it can be observed that it results in positive resistance and reactance values across the entire subsynchronous frequency range. Results from the eigenvalue (modal) analysis and electromagnetic transient simulation also confirm the results obtained from frequency scanning. [ABSTRACT FROM PUBLISHER]

Transient simulation programs, either nodal analysis-based electromagnetic transient program (EMTP-like) or state-variable-based, are used very extensively for modeling and simulation of various power and energy systems with electrical machines. It has been shown in the literature that the method of interfacing machine models with the external electrical network plays an important role in numerical accuracy and computational performance of the overall simulation. This paper considers the state-variable-based simulation packages, and provides a constant-parameter decoupled RL-branch equivalent circuit for interfacing the ac induction and synchronous machine models with the external electrical network. The proposed interfacing circuit is based on the voltage-behind-reactance formulation which has been shown to have advantageous properties. For the synchronous machines, this paper describes both implicit and explicit (approximate) interfacing methods. The presented case studies demonstrate the advantages of using the proposed interfacing method over the traditional qd-models that are conventionally used in many simulation packages. [ABSTRACT FROM AUTHOR]

Electric drive systems, which include electric machines and power electronics, are a key enabling technology for advanced vehicle propulsion systems that reduce the petroleum dependence of the ground transportation sector. To have significant effect, electric drive technologies must be economical in terms of cost, weight, and size while meeting performance and reliability expectations. This paper will provide details of the design, analysis, and testing of two permanent magnet (PM) machines that were developed to meet the FreedomCar 2020 specifications. The first machine is an interior PM (IPM) machine and the second machine is a surface PM (SPM) machine. Both machines are equipped with fractional-slot concentrated windings (FSCW). The goal of this paper is to provide a quantitative assessment of how achievable this set of specifications is, as well as a comparison with the state of the art. This paper will also quantitatively highlight the tradeoffs between IPM and SPM FSCW machines especially in the context of traction applications. [ABSTRACT FROM AUTHOR]

In this paper, an analytical approach for the reliability modeling of large wind farms is presented. A systematic method based on frequency and duration approach is utilized to model a wind farm like a multistate conventional unit, where the probability, frequency of occurrence, and departure rate of each state can be obtained using the regional wind regime of wind farm and wind turbine characteristics. The proposed method is capable of finding both annual frequency and average time of load curtailment analytically in the presence of wind power. A wind farm in the northern region of Iran with the wind speed registration of one year is studied in this paper. To accommodate time-varying patterns of wind speed, reliability analysis considering seasonal patterns of wind speed is also carried out. The results show that seasonal patterns significantly affect the reliability indexes. A reliability analysis is also performed using a load profile similar to that of Iran power network. It will be shown that the coincidence of high-load-demand and high-wind-speed periods makes the North Iran wind farm projects highly attractive from a reliability point of view. [ABSTRACT FROM AUTHOR]

Wind energy is considered to be a very promising alternative for power generation because of its tremendous environmental, social, and economic benefits. Electrical power generation from wind energy behaves quite differently from that of conventional sources. The fundamentally different operating characteristics of those facilities, therefore, affect the power system reliability in a manner different from that of the conventional systems. This paper is focused on the development of suitable models for wind energy conversion systems, in adequacy assessments of generating systems, using wind energy. These analytical models can be used in the conventional generating system adequacy assessment utilizing analytical or Monte Carlo state-sampling techniques. This paper shows that a five-state wind energy conversion system model can be used to provide a reasonable assessment of the practical power system adequacy studies, using an analytical method, or a state-sampling simulation approach. [ABSTRACT FROM AUTHOR]

Renewable energy sources, especially wind turbine generators, are considered as important generation alternatives in electric power systems due to their nonexhausted nature and benign environmental effects. The fact that wind power penetration continues to increase has motivated a need to develop more widely applicable methodologies for evaluating the actual benefits of adding wind turbines to conventional generating systems. Reliability evaluation of generating systems with wind energy sources is a complex process. It requires an accurate wind speed forecasting technique for the wind farm site. The method requires historical wind speed data collected over many years for the wind farm location to determine the necessary parameters of the wind speed models for the particular site. The evaluation process should also accurately model the intermittent nature of power output from the wind farm. A sequential Monte Carlo simulation or a multistate wind farm representation approach is often used. This paper presents a simplified method for reliability evaluation of power systems with wind power. The development of a common wind speed model applicable to multiple wind farm locations is presented and illustrated with an example. The method is further simplified by determining the minimum multistate representation for a wind farm generation model in reliability evaluation. The paper presents a six-step common wind speed model applicable to multiple geographic locations and adequate for reliability evaluation of power systems containing significant wind penetration. Case studies on a test system are presented using wind data from Canadian geographic locations. [ABSTRACT FROM AUTHOR]

The basic idea of the fractional frequency transmission system (FFTS) is to use lower frequency to reduce the effective electrical length of the ac transmission line, thus increasing its transmission capacity. Because the rotational speeds of the generators in hydro and wind power generation systems are very low, the FFTS is particularly suitable for transmitting electricity produced by renewable energy sources. The fractional frequency wind power system (FFWPS) provides an effective approach for integrating the large-scale and long-distance wind power into the grid. A novel method of the integration of the wind turbines in direct-driven FFWPS is introduced in this paper. A full-power ac–dc–ac converter is used as the grid-connection device in the experiment, and the experiment results verify the feasibility and effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In electric power systems, it is very common to find problems of power quality. The flow of harmonics significantly affect the operation of three-phase induction motors, and its energy characterization becomes difficult. There are different methods in situ to estimate motor efficiency. However, it is necessary to deepen the in situ efficiency analysis under nonsinusoidal voltage conditions. In this paper, a procedure is presented based on the equivalent circuits with losses segregation and using a bacterial foraging algorithm (BFA). It allows induction motors’ energy efficiency determination in field conditions with low invasiveness and working under harmonic distortion. The method was successfully tested on a 1.5 kW motor fed with significant levels of voltage harmonic. [ABSTRACT FROM AUTHOR]

Power system operates close to its operational limit to achieve a higher level of utilization of the grid infrastructure. As a result, its transient behavior is of great importance to prevent violation of the operation limits. This paper proposes an internal model control (IMC)-based approach for voltage-sourced converters (VSC) to improve their dynamic behavior. This IMC controller is designed based on a detailed model of the VSC. The proposed control approach has superior performance, i.e., faster step response and less overshoot, and higher axes decoupling than the conventional dq-current control method. The proposed IMC-based controller has a straightforward design procedure, and can be implemented using simple PI and PID controllers. Several case studies are presented to evaluate and compare the transient performance of the IMC-based controller with conventional dq current control subsequent to step changes in the set points of direct and quadrature axes current, single-phase fault, and three-phase fault. [ABSTRACT FROM AUTHOR]

The traditional stator single-phase-to-ground fault protective schemes are hard to completely satisfy the requirement of selectivity for bus-connected Powerformers. In order to overcome the aforementioned problem, a new stator single-phase-to-ground fault protective scheme based on the hierarchical clustering algorithm is proposed in this paper. The direction and magnitude of zero-sequence current and leakage current are discussed and selected as feature vectors. Then, the data set are divided into two groups by hierarchical clustering algorithm, and cluster center of each group is calculated. Finally, the space relative distance among detected pattern and two cluster centers is calculated to discriminate the faulty Powerformer. The fundamental component and the third harmonic component of the data set are combined to realize 100% coverage of fault detection for the stator windings of Powerformer. Simulation results have shown that, under different fault conditions, the new scheme can distinguish internal faults from external faults reliably, and can detect in which machine a stator single-phase-to-ground fault is occurring even if the fault resistance is at 5 kΩ. [ABSTRACT FROM PUBLISHER]

This paper presents a stator ground protection scheme based on the fault current flowing in the breakdown channel. It trips only if the fault current exceeds the fault current tolerance capacity of the generator. Otherwise, it will just emit alarm signals. Thereby, the unnecessary trip-out of large generator can be avoided. The stability of the power system and the generator security can then be ensured. To achieve the scheme, methods of calculating the fault current in real time are proposed for three common generator neutral grounding methods based on the zero-sequence equivalent circuits. In addition, a ground fault location algorithm is presented which can automatically identify the faulted coil in a large generator with multicircuit stator winding. It greatly reduces the workload of repair. An implementation scheme is given on the basis of the subharmonic injection protection device. Simulation results show the validity of the protection scheme and the accuracy of the fault location algorithm. [ABSTRACT FROM PUBLISHER]

The majority of the fixed-speed wind turbines are equipped with squirrel-cage induction generators (IG) and ac-connected to the power system. During a fault in power system, voltage and rotor speed instability may occur, especially when the strength of the system compared to the power delivered by the IG is relatively low. This paper investigates a new method for improving the transient stability of power systems equipped with squirrel cage IGs. For stability improvement, the unique property of the induction machines which is the possibility of reversing the direction of the rotating flux is employed. In this method, after clearing the fault, operating mode of the induction machine is changed from the generating to the plugging mode for a short time. This leads to opposition between the rotating flux and mechanical torques, thus preventing the generator from further acceleration. Simulation results show that the proposed method can be effective in enhancing the transient stability. Since in this method, there is no need for accessory equipment, the proposed method is more attractive than the previous ones, from economic point of view. [ABSTRACT FROM AUTHOR]

The novel scenario of power systems with massive utilization of distributed generation (DG) imposes that islanding detection methods for voltage source inverter (VSI)-interfaced DGs must be evaluated taking into account multi-inverter configurations. This paper presents the experimental validation of an active islanding detection algorithm for multi-inverter systems proposed by the authors in previous work. Field programmable gate array implementation of power control and islanding detection algorithms has been used to test this proposition in a multi-inverter system based on grid-connected insulated gate bipolar transistor VSIs. The proposed islanding detection algorithm offers a very low impact on power quality and rapid and efficient islanding confirmation which is demonstrated by simulation and experimentation. The performance of the algorithm was tested under critical conditions as resonant load with high quality factor and unity power factor and also for cases where load and VSI powers are matched. [ABSTRACT FROM PUBLISHER]

This paper presents a dynamical model for simulating combined cycle power plants to be used for assessing the plant behavior during large transients and for restoration procedures. The 80th dynamic order model considers the complex structure of the heat recovery steam generator and calculates the main variables that are critical during these transients. The model has the double purpose of studying both the plant behavior under the usual control systems as well as innovative logics and control strategies for increasing its performances in terms of regulation and emergency services. The possible use of combined cycle power plants for supplying a restoration area is finally investigated adopting different control strategies that also involve the regulating capacity of the steam turbine. [ABSTRACT FROM PUBLISHER]

This paper presents an integration algorithm for stator flux estimation of direct torque control (DTC). This algorithm only contains a fifth-order low-pass filter (LPF), a high-pass (HP) filter, and a simple logical calculation part, where the fifth-order LPF and the HP filter can effectively filter out HF harmonics and the dc drift in the back EMF, respectively. The α- and β-axis back EMFs passing through the two filters will obtain β-axis stator flux linkage and opposite polarity α-axis stator flux linkage, respectively, and then by the logical calculation part can finally achieve α- and β-axis stator flux linkages. At any synchronous angular frequency, the amplitude- and phase-frequency characteristics of this algorithm are same as those of the pure integrator, and meanwhile its dc gain is zero. The proposed algorithm with high estimation accuracy behaves well in both steady state and dynamic performance when used in a DTC-based electrical excitation flux-switching generator dc power system, which is verified by experimental results. [ABSTRACT FROM PUBLISHER]

A parallel hybrid excitation flux-switching (PHEFS) generator dc power system is presented in this paper. The PHEFS topology is proposed to achieve good flux regulation capability of the system as well as capability of deexcitation at fault and avoid permanent magnet (PM) magnetic shortcircuit and demagnetization. In order to improve the system's steady state and dynamic performance, a direct torque linear control (DTLC) scheme is proposed then. This DTLC scheme, which contains a voltage loop only and develops the direct linear relationship between the torque and sinusoidal value of the torque angle, can regulate the instantaneous torque directly and smoothly without current loop. The flux-weakening control of the DTLC scheme is also studied; the PHEFS generator system with excellent dynamic performance and lower flux and torque ripple has been achieved experimentally. [ABSTRACT FROM PUBLISHER]

The most important reference quantities for monitoring and controlling transient stability in real time are the rotor angle and speed of the synchronous generators. If these quantities can be estimated with sufficient accuracy, they can be used in global and local control methods. In the classic state estimation methods, such as the extended Kalman filter (EKF) technique, the linear approximations of the system at a given moment in time may introduce errors in the states. In order to overcome the drawbacks of the EKF, the authors of this paper have applied the unscented Kalman filter (UKF) to estimating and predicting the states of a synchronous machine, including rotor angle and rotor speed, using phasor measurement unit (PMU) quantities. The UKF algorithm propagates the pdf of a random variable in a simple and effective way and is accurate up to the second order in estimating the mean and covariance. The overall impression is that the performance of the UKF is better than the EKF in terms of robustness, speed of convergence, and also different levels of noise. Simulation results including saturation effects and grid faults show the accuracy and efficiency of the UKF method in state estimation of the system, especially at higher noise ratios. [ABSTRACT FROM AUTHOR]

The economic and reliability benefits of adding a wind energy conversion system (WECS) to a power system are highly dependent on the wind turbine generator (WTG) installation design, i.e., the type and number of WTG. This paper presents an approach to determine the optimum installation design at each wind site considering the WTG parameters, the total cost of WECS and the power system reliability performance. The model is formulated as a combinatorial constrained optimization problem with a nonlinear, nondifferentiable objective function, which consists of the capital, maintenance and operating costs, and the costumer interruption costs. A number of constraints, including the total installed capacity at a specific wind site and the capital cost, are considered in the model. The model is solved using a genetic algorithm with adaptive crossover and mutation probabilities based on the standard deviation of chromosome fitness in a generation population. The proposed model and algorithm are tested on two power systems. The results show that the proposed approach can be used to obtain the maximum economic and reliability benefits associated with a WECS installation and is a powerful search technique for determining the optimum number and type of WTG considering reliability performance and costs. [ABSTRACT FROM PUBLISHER]

In this paper, a multiphysical proton exchange membrane fuel cell stack model, which is suitable for real-time emulation is presented. The model covers three physical domains: electrical, fluidic, and thermal. A Ballard 1.2 kW 47 cells fuel cell stack model is introduced. The corresponding fuel cell system auxiliary models are given based on experimental tests. Based on the modeling equations, the fuel cell dynamic phenomena in different physical domains are analyzed and the corresponding time constant expressions are given. Using the real-time stack model, a fuel cell stack emulator based on a buck converter is used to emulate the fuel cell stack electrical part. The experimental results show that the emulator can reproduce the real-stack behavior with a great agreement. Such a fuel cell stack emulator can be used for hardware-in-the-loop applications, in order to test and validate the fuel cell system design. [ABSTRACT FROM PUBLISHER]

Sequential wind simulation models have been developed to forecast effective load-carrying capability (ELCC), but they produce data that follow a Gaussian distribution, which can be considerably different from real wind-speed distributions, and they do not explicitly model the influence of temperature on the evolution of wind speed. The latter issue is of significant importance considering the strength of correlation between electricity load and temperature and the influence electricity load shapes have on system reliability. This paper presents a new approach to reliability estimation of wind facilities that models wind-speed distributions nonparametrically and includes the effect of temperature on the evolution of wind speed. A relatively long tall tower anemometer dataset is then used to test whether or not the model output produces ELCC distributions that are statistically similar to observed distributions. Results indicate that, relative to temperature independent models, temperature-dependent time-series models are better at both short-term wind-speed forecasting and long-term reliability forecasting. Results also show that reliability forecasts are relatively unaffected by the shape of the wind-speed distribution. Finally, it is apparent that model performance is robust to variation in the average wind power in the years used for model parameterization. [ABSTRACT FROM AUTHOR]

A sensorless internal temperature monitoring method for induction motors is proposed in this paper. This method can be embedded in standard motor drives, and is based on the stator windings resistance variation with temperature. A small ac signal is injected to the motor, superimposed to the power supply current, in order to measure the stator resistance online. The proposed method has the advantage of requiring a very low-level monitoring signal, hence the motor torque perturbations and additional power losses are negligible. Furthermore, temperature estimations do not depend on the knowledge of any other motor parameter, since the method is not based on a model. This makes the proposed method more robust than model-based methods. Experimental results that validate the proposal are also presented. [ABSTRACT FROM AUTHOR]

This paper describes power modulation of a photovoltaic (PV) generator for frequency regulation. The generator has a small electric double-layer capacitor. The capacitor absorbs rapid fluctuations of PV generation, and allows the generator to change its output at a limited ramp rate. The capacitor voltage is kept at a specified value to maintain adequate energy storage. The generator output is modulated in proportion to the frequency deviation. The responses to step and periodic changes of the frequency are examined. The voltage control is modified so as not to affect the frequency control. It is shown by numerical simulations that the PV generator cooperates well with conventional generators. Some experimental results are demonstrated to validate the proposed method. [ABSTRACT FROM AUTHOR]

The problem of establishing maximum size of a wind farm (WF) when it joins a WF cluster (WFC) is examined. It is shown that the clustering effect can be quantified by detailed simulation of system dynamics, using appropriate models for wind events, wind facilities, and power system equipment. The paper points out the inevitability of WFC formations and draws attention to their operational impacts. A case study is used to demonstrate how location and layout of a WF can influence system dynamics, and thus, restrict the WF size. [ABSTRACT FROM AUTHOR]

Inspired by observing the similarity between adaptive control systems and recurrent neural networks (RNNs), a new control scheme, the recurrent adaptive control (RAC), is presented in this paper. Back propagation through time (BPTT), a learning algorithm for RNNs, can be exploited in RAC. Application of truncated BPTT to RAC is also discussed. Further, a new control algorithm for RAC, termed recursive gradient (RG), is developed to improve the performance of the original and truncated BPTT algorithms. Effectiveness of the RG control algorithm as a power system stabilizer is demonstrated. [ABSTRACT FROM AUTHOR]

This paper uses the data from seven wind farms at Muppandal, Tamil Nadu, India, collected for three years from April 2002 to March 2005 for the estimation of energy yield from wind farms. The model is developed with the help of neural network methodology, and it involves three input variables-wind speed, relative humidity, and generation hours-and one output variable, which give the energy output from wind farms. The modeling is done using MATLAB software. The most appropriate neural network configuration after trial and error is found to be 3-5-1 (3 input layer neurons, 5 hidden layer neurons, 1 output layer neuron). The mean square error for the estimated values with respect to the measured data is 7.6 × 10-3. The results demonstrate that this work is an efficient energy yield estimation tool for wind farms. [ABSTRACT FROM AUTHOR]

The effective load carrying capability (ELCC) is considered the preferred metric to evaluate the capacity value of added wind generation. However, the classical method of computing this metric requires substantial reliability modeling and an iterative process that is quite computationally intensive. Consequently, a noniterative method of estimating a wind plant's ELCC is proposed in this paper. Inspired by Garver's approximation and derived based on well-known reliability concepts, the proposed method provides an excellent approximation while requiring only minimal reliability modeling and no computationally-intensive iterative process. It computes ELCC estimates from a single function using only the wind plant's multistate probabilistic representation and a graphically determined parameter that characterizes the existing power system. After presenting the complete mathematical derivation of this function, the method is applied to compute the ELCC estimates of various wind plants at different penetration levels. It is shown that the resultant ELCC estimates only slightly overestimate the classically computed values by relative errors of 2.5% or less. Furthermore, the proposed method yields more accurate ELCC estimates than the capacity factor approximation, which is commonly used to approximate the ELCC of a wind plant. [ABSTRACT FROM AUTHOR]

The aim of the paper is to demonstrate the way in which mechanical power variations, due to tower shadow and wind turbulence, influence control performance of power system stabilizer (PSS) loops for doubly-fed induction generators (DFIGs). The PSS auxiliary loops are applied on a specific DFIG control scheme, the flux magnitude and angle controller (FMAC). However, since the PSS signal is applied at the output of the basic controller, the PSS performance characteristics displayed are deemed typical for DFIG control schemes in general. The relative capabilities of PSS controllers based on stator power, rotor speed, and network frequency, when the DFIG turbine is subjected to aerodynamic torque variations, are investigated via simulation studies. A two-generator aggregate model of a wind farm is introduced, which enables the influence of tower shadow and wind turbulence on both an individual turbine and on the overall wind farm itself to be assessed. [ABSTRACT FROM AUTHOR]

This paper deals with control of voltage and frequency of an autonomous wind energy conversion system (AWECS) based on capacitor-excited asynchronous generator and feeding threephase four-wire loads. The proposed controller consists of three single-phase insulated gate bipolar junction transistor (IGBT)based voltage source converters (VSCs) and a battery at dc link. These three single-phase VSCs are connected to each phase of the generator through three single-phase transformers. The proposed controller is having bidirectional flow capability of active and reactive powers by which it controls the system voltage and frequency with variation of consumer loads and the speed of the wind. VSCs along with transformer function as a voltage regulator, a harmonic eliminator, a load balancer, and a neutral current compensator while the battery is used to control the active power flow which, in turn, maintains the constant system frequency. The complete electromechanical system is modeled and simulated in the MATLAB using the Simulink and the power system blockset (PSB) toolboxes. The simulated results are presented to demonstrate the capability of the proposed controller as a voltage and frequency regulator, harmonic eliminator, load balancer, and neutral current compensator for different electrical (varying consumer loads) and mechanical (varying wind speed) dynamic conditions in an autonomous wind energy conversion system. [ABSTRACT FROM AUTHOR]

Nowadays, tethnology evolution and deregulation of the electric utility industry enable distributed generation (DG) to play an increasing role in locally satisfying the expanding power demand. In this paper, the islanded operation of an electrical grid supplied by wind turbines, which belong to the most rapidly expanding DG technologies, is studied. Control strategies for power electronics interface of variable speed wind turbines, ensuring fast control of frequency and voltage, are proposed. [ABSTRACT FROM AUTHOR]

This paper presents a cost analysis of grid-connected electric energy storage. Various energy storage technologies are considered in the analysis. Life-cycle cost analysis is used. The results are presented in terms of the cost added to electricity stored and discharged, in US dollar per kilowatt hour. Results are compared with wholesale and retail electricity costs and with the cost of conventional pumped hydro storage. [ABSTRACT FROM AUTHOR]

In this paper, a novel autotransformer for a 40-pulse ac-dc converter configuration is designed, modeled, simulated, and implemented to feed vector-controlled induction motor drive (VCIMD). The proposed converter consists of two paralleled tenpulse ac-dc converters along with pulse doubling circuit at dc bus. Each ten-pulse ac-dc converter involves five-phase diode bridge rectifiers. It improves power quality at ac mains, and it meets IEEE-519 standard requirements at varying loads. A set of power quality indexes on input ac mains and dc bus for a VCLMD fed from 20-pulse and 6-pulse converters is also given to compare their performance. It is observed that input current total harmonic distortion (THD) of much less than 5% is possible with the proposed topology at varying loads. [ABSTRACT FROM AUTHOR]

Over the past several years, there has been renewed interest in modeling electrical machines using phase (abc) variables. This paper considers modeling induction machines using phase variables in a voltage-behind-reactance (VBR) formulation. Specifically, three VBR models are proposed wherein the rotor. electrical subsystem is modeled using flux linkages as state variables expressed in the qd reference frame. The stator electrical dynamics are represented in abc phase coordinates that enable direct interface of the machine model to an external network. Such a direct interface is advantageous when the machine is fed from a power electronic converter and/or when the modeling is carried out using circuit-based simulators. Computer studies of an induction machine demonstrate that the proposed VBR models achieve a 740% improvement in computational efficiency as compared with the traditional coupled-circuit phase-domain model. [ABSTRACT FROM AUTHOR]

This paper aims to determine the optimal capacitors required for maximum output power of a single-phase self-excited induction generator (SEIG), using a three-phase machine feeding inductive as well as capacitive loads. The generator consists of a three-phase star-connected induction machine with three capacitors and a single-phase load. The algorithm, which gives directly the values of the optimal capacitors for the maximum power output and the maximum power available, has been developed using the steady-state model of the SEIG and sequential unconstrained minimization technique (SUMT). The variations of the maximum power output with power factor (pf) of loads (both inductive and capacitive) and speed of the SEIG have been presented. The voltage regulation of the generator is small due to the effect of the two series capacitors. Experimental results have shown the effectiveness and accuracy of the developed algorithm. [ABSTRACT FROM AUTHOR]

A new criterion to detect the stator single phase-to. ground fault for Powerformer is proposed in this paper, which is based on the direction of zero-sequence compositive power flow. By virtue of the analysis of new fault characteristics of Powerformer and the comparison with conventional methods, a novel identification scheme is put forward. The proposed approach detects the ground fault by analyzing the power direction. Only zero-sequence current from the terminal of Powerformer and zero-sequence voltage from the busbar are used in this scheme. Combined with third-harmonic principle, it can provide a 100% coverage of fault detection for the stator windings of Powerformer. The effectiveness of this scheme is validated with the Matlab simulation results. [ABSTRACT FROM AUTHOR]

Microgrids are low-voltage (LV) distribution networks comprising various distributed generators (DGs), storage devices, and controllable loads that can operate either interconnected or isolated from the main distribution grid as a controlled entity. This paper describes the operation of a central controller for microgrids. The controller aims to optimize the operation of the microgrid during interconnected operation, i.e., maximize its value by optimizing the production of the local DGs and power exchanges with the main distribution grid. Two market policies are assumed including demand-side bidding options for controllable loads. The developed optimization algorithms are applied on a typical LV study case network operating under various market policies and assuming realistic spot market prices and DG bids reflecting realistic operational costs. The effects on the microgrid and the distribution network operation are presented and discussed. [ABSTRACT FROM AUTHOR]

This paper presents system modeling, modified space vector PWM implementation (MSVPWM), and control system design of a Z-source converter. For an electrical analysis of the fuel cell powered systems, the fuel cell system is modeled by an R-C circuit including its voltage—current polarization characteristics. A discrete-time state space equation is given to implement digital control and a space vector pulse-width modulation technique is modified to realize the shoot-through zero vectors that boost the dc-link voltage. Three discrete-time controllers and an asymptotic observer are designed. [ABSTRACT FROM AUTHOR]

A novel nonlinear control scheme for disturbance attenuation of structure preserving multimachine power systems based on Hamiltonian theory is proposed in this paper. The proposed control scheme includes two steps: first, the dissipative Hamiltonian realization of structure preserving power system is completed using the singular perturbation approach in which the algebraic equations are considered as a limit of fast dynamics; second, a nonlinear decentralized disturbance attenuation excitation controller is designed without linearization to improve transient stability of power system as well as the robustness with respect to unknown exogenous disturbance in the sense of L2-gain. Simulation on a two-area system demonstrates that the proposed scheme can enhance transient stability of the system regardless of the exogenous disturbance. [ABSTRACT FROM AUTHOR]