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02516 Design optimization of a large scale rooftop photovoltaic system
06 Electrical power supply and utilization (scientific, technical)
06
ELECTRICAL POWER SUPPLY A N D UTILIZATION
Scientific, technical 05102512 A comparative study of adaptive load frequency controller designs in a power system with dynamic neural network models Oysal, Y. Energy Conversion and Management, 2005, 46, (15-16), 2656 2668. This paper investigates applications of dynamic neural network (DNN) models for adaptive load frequency controller designs in power systems. The proposed dynamic neural network models have lag dynamics and dynamical elements such as delayers or integrators in their processing units. They only differ in activation functions. The first uses sigmoid functions, the second uses standard fuzzy systems and the third uses non-orthogonal mother wavelets as activation functions. Each DNN model is connected between two area power systems. The input signals of the DNN models are the area control errors (ACE). The outputs are the control signals for two area load frequency control. Adaptation is based on adjusting the parameters of each for load frequency control. This is done by minimizing the cost functional of load frequency deviations. In simulations for each DNN model, comparative results are obtained for damping the frequency due to a load disturbance effect applied to a two area power system.
05102513 A new control scheme of a cascaded transformer type multilevel PWM inverter for a residential photovoltaic power conditioning system Kang, F.-S. et al. Solar Energy, 2005, 78, (6), 727-738. From the viewpoint of high quality output voltage generation in a residential photovoltaic system, a multilevel inverter employing cascaded transformers can become a good substitute for the conventional pulse width modulated inverters and other multilevel counterparts. However, to obtain more sinusoidal output voltage waves, it should increase the number of switching devices and transformers resulting in a cost increase. To alleviate this problem, an efficient switching pattern is proposed and applied to a multilevel inverter equipped with two cascaded transformers, which have a seriesconnected secondary. Operational principle and analysis are illustrated focusing on a change of the switching pattern. High-performance of the proposed multilevel scheme embedded in a photovoltaic power conditioning system is verified by computer-aided simulations and experimental results.
05/02514 A robust damping controller for SMES using loop-shaping technique Rahim, A. H. M. A. and Nowicki, E. P. International Journal of Electrical Power & Energy Systems, 2005, 27, (5 6), 465-471. A robust damping controller for a power system installed with superconducting magnetic energy storage (SMES) has been designed using a simple graphical loop-shaping technique. The graphical method starts by selection of a nominal plant function satisfying the robust stability and performance criterion. The variations in operating conditions from the nominal values are modelled as multiplicative structured uncertainty. The generator-SMES system has been represented with a detailed dynamic model for the control design. The robust design, with generator speed variation as the controller input, was tested for a range of operating points considering various disturbances. It is observed that the fixed parameter robust controller provides very good damping for a wide range of operating conditions.
05102515 Combination of thermochemical recuperative coal gasification cycle and fuel cell for power generation Kuchonthara, P. et al. Fuel, 2005, 84, (7-8), 1019-1021. An integrated power generation cycle combining thermochemical recuperation, brown coal gasification and a solid oxide fuel cell (SOFC) was proposed based on the concept of thermochemical recuperative energy. Process simulation combining the coal gasifier, gas turbine cycle, and SOFC module was conducted using the ASPEN Plus process simulation tool. The simulation indicated that the cycle efficiency increases from 39.5% (HHV) without the SOFC to about 45% (HHV) with the SOFC.
370
Fuel and Energy Abstracts
November 2005
05•02516 Design optimization of a large scale rooftop photovoltaic system Gong, X. and Kulkarni, M. Solar Energy, 2005, 78, (3), 362 374. This paper presents the optimization process of a grid connected photovoltaic (PV) system, which is intended to replace a large-scale thermal solar system on the rooftop of a Federal office building. A PV energy conversion model is described. Based on this model, array surface tilt angle and array size are optimized. The optimization method is based on maximizing the utilization of the array output energy, and, at the same time, minimizing the electricity power sold to grid. An effectiveness factor is introduced that takes into account both of these parameters. The array configuration and the output parameters are determined by comparing several PV modules. A 43.2 kW PV system is designed and operational problems such as harmonic effects and anti-islanding are discussed. Finally, the system performance is simulated and through economic analysis it has shown that the cost of PV system can be recouped in 13 years under the current renewable energy incentive program by the state of Illinois.
05102517 Detection of inrush current in distribution transformer using wavelet transform Sedighi, A.-R. and Haghifam, M.-R. International Journal of Electrical Power & Energy Systems, 2005, 27, (5-6), 361-370. Inrush currents in transformers are non-sinusoidal, high magnitude currents generated due to flux saturation in the core during energization. For protection purpose, in this paper an efficient method for detection of inrush current in distribution transformer based on wavelet transform is presented. Using this method inrush current can be discriminated from the other switching transients such as: load switching, capacitor switching and single phase to ground fault. Inrush current and other events for feature extraction and discrimination are simulated using an electromagnetic transient programme. Results in all cases show the effectiveness of proposed procedure in identifying inrush current from other transients.
05•02518 Development and testing of a domestic woodstove thermoelectric generator with natural convection cooling Nuwayhid, R. Y. et al. Energy Conversion and Management, 2005, 46, (9 10), 1631-1643. A thermoelectric generator was fitted to the side of a domestic woodstove. The generator was driven using one or more thermoelectric modules designed to give significant power at a reasonable cost. The thermoelectric generator was air cooled by natural convection using a commercially available heat sink. Testing was undertaken under a controlled woodstove firing rate and temperatures, and open circuit voltages were monitored over extended periods. The maximum steady state matched load power was 4.2 W using a single module. The use of multiple modules with a single heat sink was found to reduce the total power output relative to the single module case as a result of reduced hot to cold surface temperature differences.
05/02519 Distributed grid-connected photovoitaic power system emission offset assessment: statistical test of simulated- and measured-based data Spiegel, R. J. et al. Solar Energy, 2005, 78, (6), 717-726. This study assesses the pollutant emission offset potential of distributed grid-connected photovoltaic (PV) power systems. Computer-simulated performance results were utilized for 214 PV systems located across the US. The PV systems' monthly electrical energy outputs were based on a performance calculator called PVWATTS. Offset emissions of sulfur dioxide (SO2), carbon dioxide (CO2), and nitrogen oxides (NO y) were determined from PV system outputs and average utility emissions data from each state. For validation, the simulated monthly results were statistically compared with measurement-based data (both production and corresponding emissions data) from 29 PV systems installed at different sites across the US. While the data shows high (geographic) variability, the substantial number of measurements allows reliable statistical analysis. The methods are found to give consistent results in spite of the necessity to employ some even quite crude input approximations - such as the use of statewide rather than specific emissions data for the systems. No significant differences between simulated and measured monthly means for any of the pollutants were noted on the basis of individual monthly analyses, though the results for NOx suggest the possible existence of some difference in that case. A more detailed statistical modelling using all monthly data in one combined analysis (allowing improved variability estimation) confirms these conclusions. Even the shorter confidence intervals for expected offsets obtained through the combined analysis show no significant differences between simulated and measured methods for SO2 and CO2. The differences for NOx are statistically significant but consistent-suggesting useful prediction by the simulations via a constant correction factor. As expected, significant differences between months are evident for both simulated and measured offsets.
06
ELECTRICAL POWER SUPPLY A N D UTILIZATION
Scientific, technical 05102512 A comparative study of adaptive load frequency controller designs in a power system with dynamic neural network models Oysal, Y. Energy Conversion and Management, 2005, 46, (15-16), 2656 2668. This paper investigates applications of dynamic neural network (DNN) models for adaptive load frequency controller designs in power systems. The proposed dynamic neural network models have lag dynamics and dynamical elements such as delayers or integrators in their processing units. They only differ in activation functions. The first uses sigmoid functions, the second uses standard fuzzy systems and the third uses non-orthogonal mother wavelets as activation functions. Each DNN model is connected between two area power systems. The input signals of the DNN models are the area control errors (ACE). The outputs are the control signals for two area load frequency control. Adaptation is based on adjusting the parameters of each for load frequency control. This is done by minimizing the cost functional of load frequency deviations. In simulations for each DNN model, comparative results are obtained for damping the frequency due to a load disturbance effect applied to a two area power system.
05102513 A new control scheme of a cascaded transformer type multilevel PWM inverter for a residential photovoltaic power conditioning system Kang, F.-S. et al. Solar Energy, 2005, 78, (6), 727-738. From the viewpoint of high quality output voltage generation in a residential photovoltaic system, a multilevel inverter employing cascaded transformers can become a good substitute for the conventional pulse width modulated inverters and other multilevel counterparts. However, to obtain more sinusoidal output voltage waves, it should increase the number of switching devices and transformers resulting in a cost increase. To alleviate this problem, an efficient switching pattern is proposed and applied to a multilevel inverter equipped with two cascaded transformers, which have a seriesconnected secondary. Operational principle and analysis are illustrated focusing on a change of the switching pattern. High-performance of the proposed multilevel scheme embedded in a photovoltaic power conditioning system is verified by computer-aided simulations and experimental results.
05/02514 A robust damping controller for SMES using loop-shaping technique Rahim, A. H. M. A. and Nowicki, E. P. International Journal of Electrical Power & Energy Systems, 2005, 27, (5 6), 465-471. A robust damping controller for a power system installed with superconducting magnetic energy storage (SMES) has been designed using a simple graphical loop-shaping technique. The graphical method starts by selection of a nominal plant function satisfying the robust stability and performance criterion. The variations in operating conditions from the nominal values are modelled as multiplicative structured uncertainty. The generator-SMES system has been represented with a detailed dynamic model for the control design. The robust design, with generator speed variation as the controller input, was tested for a range of operating points considering various disturbances. It is observed that the fixed parameter robust controller provides very good damping for a wide range of operating conditions.
05102515 Combination of thermochemical recuperative coal gasification cycle and fuel cell for power generation Kuchonthara, P. et al. Fuel, 2005, 84, (7-8), 1019-1021. An integrated power generation cycle combining thermochemical recuperation, brown coal gasification and a solid oxide fuel cell (SOFC) was proposed based on the concept of thermochemical recuperative energy. Process simulation combining the coal gasifier, gas turbine cycle, and SOFC module was conducted using the ASPEN Plus process simulation tool. The simulation indicated that the cycle efficiency increases from 39.5% (HHV) without the SOFC to about 45% (HHV) with the SOFC.
370
Fuel and Energy Abstracts
November 2005
05•02516 Design optimization of a large scale rooftop photovoltaic system Gong, X. and Kulkarni, M. Solar Energy, 2005, 78, (3), 362 374. This paper presents the optimization process of a grid connected photovoltaic (PV) system, which is intended to replace a large-scale thermal solar system on the rooftop of a Federal office building. A PV energy conversion model is described. Based on this model, array surface tilt angle and array size are optimized. The optimization method is based on maximizing the utilization of the array output energy, and, at the same time, minimizing the electricity power sold to grid. An effectiveness factor is introduced that takes into account both of these parameters. The array configuration and the output parameters are determined by comparing several PV modules. A 43.2 kW PV system is designed and operational problems such as harmonic effects and anti-islanding are discussed. Finally, the system performance is simulated and through economic analysis it has shown that the cost of PV system can be recouped in 13 years under the current renewable energy incentive program by the state of Illinois.
05102517 Detection of inrush current in distribution transformer using wavelet transform Sedighi, A.-R. and Haghifam, M.-R. International Journal of Electrical Power & Energy Systems, 2005, 27, (5-6), 361-370. Inrush currents in transformers are non-sinusoidal, high magnitude currents generated due to flux saturation in the core during energization. For protection purpose, in this paper an efficient method for detection of inrush current in distribution transformer based on wavelet transform is presented. Using this method inrush current can be discriminated from the other switching transients such as: load switching, capacitor switching and single phase to ground fault. Inrush current and other events for feature extraction and discrimination are simulated using an electromagnetic transient programme. Results in all cases show the effectiveness of proposed procedure in identifying inrush current from other transients.
05•02518 Development and testing of a domestic woodstove thermoelectric generator with natural convection cooling Nuwayhid, R. Y. et al. Energy Conversion and Management, 2005, 46, (9 10), 1631-1643. A thermoelectric generator was fitted to the side of a domestic woodstove. The generator was driven using one or more thermoelectric modules designed to give significant power at a reasonable cost. The thermoelectric generator was air cooled by natural convection using a commercially available heat sink. Testing was undertaken under a controlled woodstove firing rate and temperatures, and open circuit voltages were monitored over extended periods. The maximum steady state matched load power was 4.2 W using a single module. The use of multiple modules with a single heat sink was found to reduce the total power output relative to the single module case as a result of reduced hot to cold surface temperature differences.
05/02519 Distributed grid-connected photovoitaic power system emission offset assessment: statistical test of simulated- and measured-based data Spiegel, R. J. et al. Solar Energy, 2005, 78, (6), 717-726. This study assesses the pollutant emission offset potential of distributed grid-connected photovoltaic (PV) power systems. Computer-simulated performance results were utilized for 214 PV systems located across the US. The PV systems' monthly electrical energy outputs were based on a performance calculator called PVWATTS. Offset emissions of sulfur dioxide (SO2), carbon dioxide (CO2), and nitrogen oxides (NO y) were determined from PV system outputs and average utility emissions data from each state. For validation, the simulated monthly results were statistically compared with measurement-based data (both production and corresponding emissions data) from 29 PV systems installed at different sites across the US. While the data shows high (geographic) variability, the substantial number of measurements allows reliable statistical analysis. The methods are found to give consistent results in spite of the necessity to employ some even quite crude input approximations - such as the use of statewide rather than specific emissions data for the systems. No significant differences between simulated and measured monthly means for any of the pollutants were noted on the basis of individual monthly analyses, though the results for NOx suggest the possible existence of some difference in that case. A more detailed statistical modelling using all monthly data in one combined analysis (allowing improved variability estimation) confirms these conclusions. Even the shorter confidence intervals for expected offsets obtained through the combined analysis show no significant differences between simulated and measured methods for SO2 and CO2. The differences for NOx are statistically significant but consistent-suggesting useful prediction by the simulations via a constant correction factor. As expected, significant differences between months are evident for both simulated and measured offsets.