John T. Agee

Optimal location of network devices using a novel inherent network topology based technique

A new approach for the identification of the best node for the injection of bulk power is proposed. The proposed approach can also be used to determine the minimum numbers of static var compensator devices that can ensure the operation of power system network within the specified voltage limits. The proposed approach is based on the inherent topology of networks and application of singular value decomposition technique. The results of numerical examples show that buses with the smallest singular values can serve as indicators of the best locations for static var compensators and best node for injection of bulk power without the need for additional transmission lines.

Viability and economic analysis of wind energy resource for power generation in Johannesburg, South Africa

In this study, wind characteristics and wind power potential of Johannesburg are investigated using 5-min average time series wind speed collected between 2005 and 2009 at anemometer height of 10 m. The statistical distribution that best fits the empirical wind speed data at the site of study is first determined based on the coefficient of determination and root mean square error criteria. The statistical parameters and wind power density based on this model are estimated for different months of the year using standard deviation method. Economic analyses of some wind turbines are also carried out. Some of the key results show that the site is only suitable for small wind turbines in a standalone application. A 10 kW wind turbine with cut-in wind speed of 3.5 m/s, rated wind speed of 9 m/s, and cut-out wind speed of 25 m/s seems most appropriate in Johannesburg with the lowest cost that varies from 0.25 to 0.33

Voltage profile improvement based on network structural characteristics

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A Statistical Analysis of Wind Distribution and Wind Power Potential in the Coastal Region of South Africa

This paper demonstrates voltage profile improvement by partitioning the Y-admittance and the application of circuit theory on power system networks. The partitioned Y-admittance matrix and eigenvalue decomposition technique were used to identify the suitable locations for reactive power compensators. The proposed approach was applied to the 40-bus Southwest England network and the results were compared with the classical Q-V sensitivity approach. The proposed approach improves the overall voltage profile towards the nominal voltage limit.

Solar Tracker Technologies: Market Trends and Field Applications

This article investigates the wind characteristics and the wind power potential for electricity generation in the coastal regions of South Africa through the analysis of local wind regime of ten different sites. The data used consist of 10-min average time series wind speeds, temperatures, and standard deviation measured at anemometer height of 20 and 60 m for a period of 1 year. First, the statistical distribution model that best fits the empirical wind speed data in the areas of study is determined based on the coefficient of determination and root mean square error, which are used to test the goodness of fit. The parameters and the wind power density based on this model are estimated for each of the months and season of the year. For a realistic result in estimating the power density, the stochastic nature of the site air density based on the local temperature and the site altitude above the sea level is taken into consideration. The diurnal (day and night), electricity peak periods wind characteristic, and the turbulence intensity of the sites are calculated. The optimum wind speed, most probable wind speed and shear exponential which are important pieces of information in the selection of wind turbines are evaluated. Some of the key results show that at 60 m anemometer height, site WM05 has an exceptional wind power potential with annual power density of 694 W/m2, while site WM02 shows a poor wind power potential with annual power density of 216.29 W/m2.

Tip trajectory control of a flexible-link manipulator using an intelligent proportional integral (iPI) controller

Solar energy is increasingly becoming a significant component in the energy profiles of several tropical nations. This paper discusses trends in solar tracking technologies: analyzing the cost of acquisition, domains of application, maintenance costs and efficiency improvements. The paper concludes that hydraulic-based tracking systems are suitable for low capacity installations with low pay loads while polar axis tracking systems offer a performance nearly equal to that of two-axis tracking systems, at the cost of single axis trackers.

Classification of networks based on inherent structural characteristics

This paper presents the development, stability analysis and validation of an intelligent proportional integral (iPI) controller for the tip position control of a flexible-link manipulator. A stability analysis included in the paper shows that the iPI controller is equivalent to the proportional integral-squared controller. In order to verify the performance of the iPI controller, several experiments were conducted. In these experiments, step and square-wave inputs and two other trajectories were applied to the flexible-link manipulator. Also, the performance of the iPI controller was compared with those of classical PI and PID controllers. The results obtained from the comparison experiments showed that, the PI and PID controllers produced better performance in step and square-wave inputs, but the iPI controller yielded better trajectory tracking performance. All of the controllers were tested for disturbance and noise rejection capability. The iPI controller eliminated disturbance and noise better than the classical controllers. Considering all of the results, the iPI controller has great potential in trajectory tracking control of flexible-link manipulators.

Intelligent proportional-integral (iPI) control of a single link flexible joint manipulator

This paper seeks to identify and classify power system networks based on their inherent definitive structural property. The participation between the load buses is observable from the eigenvectors obtained from a Schur complement of the Y-admittance matrix. This is used to classify power system networks as either topologically strong or weak. Results show that in a topologically weak network, load voltages are below the nominal voltage limit. Conversely, in a topologically strong network they are above the nominal limit.

Higher-order differential feedback control of a flexible-joint manipulator

This paper presents the design, stability analysis and experimental validation of a computationally non-intensive, model-free, intelligent proportional-integral (iPI) controller for flexible joint manipulators. In order to show the performance of the iPI controller, it is compared with classical proportional-integral and proportional-integral-derivative controllers. Based on this comparison, the iPI-controlled system achieved a better than 60% tracking accuracy for both kane trajectory and sine input tracking. The iPI controller also significantly reduced transient swings in the flexible joint of the manipulator, when tracking a train of pulses. Moreover, the iPI controlled system successfully eliminated both disturbances and noise effects from the dynamics of the manipulator.

Relationship between generator affinity and voltage profile improvement

This paper presents a new control scheme for a flexible-joint manipulator using a higher-order differential feedback controller (HODFC). Two higher-order differential operators were designed and used to perform observations of both the reference input and the output of the manipulator, together with the requisite state derivatives. An error-based state-space model was then derived from the observed states. A pole-placement procedure with filtering was then used to drive the system error to zero. Practical controller implementation was carried out using the dSPACE real-time prototyping system. For the comparative validation of the performance of the HODFC with respect to a classical proportional-integral and proportional-integral-derivative (PID) controller, several experiments were undertaken. In these experiments, the step input, sine waves, kane trajectories, and external disturbances were applied to the controlled flexible-joint manipulator. The results showed that the HODFC controller eliminated disturbances within one second of occurrence, and produced superior kane trajectory tracking. Moreover, based on the root-mean-square tracking error criterion, the HODFC was observed to track both the sine and kane function trajectories with one-fourth the tracking error obtained with classical PID control.