Distribution feeder phase balancing using Newton-Raphson algorithm-based controlled active filter

Abnstract: The distribution system problems, such as planning, loss minimization, and energy restoration, usually involve the phase balancing or network reconfiguration procedures. The determination of an optimal phase balance is, in general, a combinatorial optimization problem. This paper proposes a novel reconfiguration of the phase balancing using the active power filter control and the combinatorial optimization-based Newton-Raphson algorithm to solve the unbalance problem. By utilizing the load switches as state variable, a constant Jacobian matrix can be obtained. The model developed in this paper uses combinatorial optimization techniques to translate the change values (kVA) into a number of load points and then selects the specific load points. It also performs the inter-changing of the load points between the releasing and the receiving phases in an optimal fashion. Application results balancing a distribution feeder network in South Africa for domestic loads are presented in this paper

Pelaksanaan pembelajaran melalui buku teks digital dalam memperkasakan pengajaran guru di sekolah

Kajian ini dijalankan untuk mengkaji persepsi guru dan cabaran dalam pelaksanaan pembelajaran melalui buku teks digital dalam memperkasakan pengajaran guru di sekolah. Selain itu, untuk mengetahui kecenderungan guru untuk melibatkan diri dalam pembelajaran melalui buku teks digital. Kajian ini berbentuk kuantitatif dan melibatkan guru-guru di sekolah yang melaksanakan pembelajaran melalui buku teks digital. Borang soal selidik telah disebarkan kepada 75 sampel kajian yang terlibat. Terdapat tiga buah sekolah yang terlibat dalam kajian ini iaitu Sekolah Kebangsaan Telok Kalong, Sekolah Kebangsaan Paya Bunga dan Sekolah Kebangsaan Kompleks Seberang Takir. Data kajian telah dianalisis menggunakan perisian Statistical Packages For The Social Sciences 20.0 (SPSS) dengan menjalankan analisis deskriptif iaitu nilai min dan sisihan piawai bagi persoalan kajian pertama, kedua dan ketiga. Manakala bagi persoalan kajian keempat dianalisis menggunakan analisis korelasi Spearman untuk mengetahui hubungan antara persepsi guru bagi aspek kesediaan, penggunaan dan kemahuan dengan kecenderungan guru untuk melibatkan diri dalam pembelajaran melalui buku teks digital. Hasil analisis mendapati pekali korelasi menunjukkan terdapat hubungan yang signifikan, sekaligus menunjukkan HO tidak diterima. Kesimpulannya, kajian ini telah berjaya mencapai objektif yang ditetapkan tetapi pelaksanaannya masih ditahap kurang memuaskan dan masih memerlukan penambahbaikan pada masa akan datang

Load flow calculation for droop-controlled islanded microgrids based on direct Newton-Raphson method with step size optimisation

Load flow calculation for droop-controlled islanded microgrids (IMGs) is different from that of transmission or distribution systems due to the absence of slack bus and the variation of frequency. Meanwhile considering the common three-phase imbalance condition in low-voltage systems, a load flow algorithm based on the direct Newton-Raphson (NR) method with step size optimisation for both three-phase balanced and unbalanced droop-controlled IMGs is proposed in this study. First, the steady-state models for balanced and unbalanced droop-controlled IMGs are established based on their operational mechanisms. Then taking frequency as one of the unknowns, the non-linear load flow equations are solved iteratively by the NR method. Generally, iterative load flow algorithms are faced with challenges of convergence performance, especially for unbalanced systems. To tackle this problem, a step-size-optimisation scheme is employed to improve the convergence performance for three-phase unbalanced IMGs. In each iteration, a multiplier is deduced from the sum of higher-order terms of Taylor expansion of the load flow equations. Then the step size is optimised by the multiplier, which can help smooth the iterative process and obtain the solutions. The proposed method is performed on several balanced and unbalanced IMGs. Numerical results demonstrate the correctness and effectiveness of the proposed algorithm

ELECTRICAL POWER SYSTEM MODELING AND SIMULATION OF UNIVERSITI TEKNOLOGI PETRONAS GAS DISTRICT COOLING PLANT

This document is the final report of Final Year Project entitled "Electrical Power System Modeling and Simulation of Universiti Teknologi PETRONAS Gas District Cooling Plant". MatLab with Power System Analysis Toolbox (PSAT) is used to develop the model and to come out with load flow result. Load flow is important to analyze whether the system is reliable and effective to cater the demand from the customer. In the first chapter, an introduction of the Gas District Cooling (GDC) plant and load flow analysis is included as well as the problem statement and the objectives of this project. The second part is the literature review where the author wrote down the detailed research that has been done in order to execute the project. The information is important for the readers as well for the basic understanding of the project. The methodology which comes in the third part is the explanation of the process and activities the author done along the journey in completing the project. In the fifth part, the results are shown and discussion based on the results. The last part is conclusion and recommendations where the author wrote down the summary of the project and recommended how the project can be improve

Electrical Power System Modeling And Simulation Of Universiti Teknologi Petronas Gas District Cooling Plant

This document is the final report of Final Year Project entitled "Electrical Power System Modeling and Simulation of Universiti Teknologi PETRONAS Gas District Cooling Plant". MatLab with Power System Analysis Toolbox (PSAT) is used to develop the model and to come out with load flow result. Load flow is important to analyze whether the system is reliable and effective to cater the demand from the customer

Improving Accuracy and Computational Efficiency of the Load Flow Computation of an Active/Passive Distribution Network

Over the last couple of decades, there has been a growing trend to make a paradigm shift from the passive distribution network to the active distribution network. With the rapid enlargement of network and installation of distributed generation (DG) units into distribution network, new technical challenges have arisen for load flow computation. The available techniques for the active distribution load flow calculation have limited scope of application and, sometimes, suffer from computational complexity. The complexity level of the distribution system power flow calculation is higher because of the issues of phase imbalance and high R/X ratios of feeder lines. The phase-imbalance increases computational complexity, whereas, the high R/X ratio makes time-consuming derivative based solver such as Newton-Raphson inviable for such large system. The motivation behind this work is to propose distinct mathematical approach for accurate modeling of network components, and loads to reduce computational time with improve accuracy. The applicability of an existing technique remains limited either by DG control modes, or by transformer configurations. The objective of this work is basically to develop an active distribution load flow (ADLF) algorithm with the following features. • Improved computational efficiency. • Applicability to any feeder network. • Accurate modeling of loads. • Applicability to different mode of operations of distributed generators (DGs). Typically, distributed generators are power-electronically interfaced sources that can be operated either in the current-balanced or in the voltage-balanced mode. The integration of DGs to the feeder network enables the distribution system to have bidirectional power exchange with the transmission grid. Which, also improve the voltage profile of the distribution network by providing additional sources of reactive power compensation. The contribution of the first work is to carry out the load flow analysis of a distribution network in the case of the dominant presence of induction motor loads. For a given operating condition, the load representation of an induction motor on the distribution network is made by analyzing its exact equivalent circuit. Thus, the induction motor is precisely represented as a voltage and frequency dependent load. The necessity of representing an induction motor by means of its precise load model is verified through a detailed case study. The convergence of the load flow solution with the precise modeling of induction motor loads is ensured by carrying out the load flow analysis over a complex distribution network containing several loops and distributed generations. The specific contribution of the second work is to improve the accuracy of the results obtained from the load flow analysis of a distribution network via forwardbackward sweeps. Specific attention is paid to the two-port modeling of a transformer with precise consideration for the zero sequence components of its port voltages. The zero sequence voltages at transformer ports are often ignored in the conventional load flow analyses. A new two-port network model is derived, which is generalized enough for the accurate representation of a transformer in the cascaded connection. Based upon the novel two-port representation made, a new set of iteration rules is established to carry out the forward-backward sweeps for solving the load flow results. All possible transformer configurations are taken into account. It is shown that the load flow analysis technique proposed is suitable for both active and passive distribution networks. The accuracy analysis of the load flow results is also carried out. For a given load flow result, by assessing the nodal current imbalances are evaluated based upon the admittance matrix representation of the network. Extensive case studies are performed to demonstrate the utility of the proposed load flow analysis technique. The contribution of the third work is to develop a computationally efficient and generalised algorithm for the load flow calculation in an active distribution network. The available techniques for the active distribution load flow calculation have limited scope of application and, sometimes, suffer from computational complexity. The applicability of an existing technique remains limited either by DG control modes or by transformer configurations. In this chapter, the load flow calculation is carried out by using the concept of Gauss-Zbus iterations, wherein the DG buses are modeled via the technique of power/current compensation. The specific distinctness of the proposed Gauss-Zbus formulation lies in overcoming the limitations imposed by DG control modes for the chosen DG bus modeling as well as in having optimized computational performance. The entire load flow calculation is carried out in the symmetrical component domain by decoupling all the sequence networks. Furthermore, a generalised network modeling is carried out to define decoupled and tap-invariant sequence networks along with maintaining the integrity of the zero sequence network under any transformer configurations.The computational efficiency and accuracy of the methodology proposed are verified through extensive case studies. The contribution of the fourth work is to identify and eliminate unnecessary itvii eration loops in the load flow analysis of an active distribution network so as to improve its overall computational efficiency. The number of iteration loops is minimized through the integrated modeling of a distributed generator (DG) and the associated coupling transformer. The DG bus is not preserved in the load flow calculation and the aforementioned DG-transformer assembly is represented in the form of a voltage dependent negative load at the point of connection to the main distribution network. Thus, the iteration stage that is involved in indirectly preserving the DG in the form of a voltage source or negative constant power load can be got rid of. This, in turn, eliminates the need for multiple rounds of forward-backward sweep iterations to determine the bus voltages. The power characteristics of the DG-transformer assembly are thoroughly investigated through a carefully performed case study so as to assess the potential convergence performance of the proposed

Using Distributed Energy Resources to Improve Power System Stability and Voltage Unbalance

The increasing penetration of renewables has driven power systems to operate closer to their stability boundaries and makes maintaining power quality more difficult. The goals of this dissertation are to develop methods to control distributed energy resources to improve power system stability and voltage unbalance. Specifically, demand response (DR) is used to realize the former goal, and solar photovoltaic (PV) systems are used to achieve the latter. We present a new DR strategy to change the consumption of flexible loads while keeping the total load constant, improving voltage or small-signal stability without affecting frequency stability. The new loading pattern is only maintained temporarily until the generators can be re-dispatched. Additionally, an energy payback period maintains the total energy consumption of each load at its nominal value. Multiple optimization problems are proposed for determining the optimal loading pattern to improve different voltage or small-signal stability margins. The impact of different system models on the optimal solution is also investigated. To quantify voltage stability, we choose the smallest singular value (SSV) of the power flow Jacobian matrix and the distance to the closest saddle-node bifurcation (SNB) of the power flow as the stability margins. We develop an iterative linear programming (ILP) algorithm using singular value sensitivities to obtain the loading pattern with the maximum SSV. We also compare our algorithm's performance to that of an iterative nonlinear programming algorithm from the literature. Results show that our ILP algorithm is more computationally scalable. We formulate another problem to maximize the distance to the closest SNB, derive the Karush–Kuhn–Tucker conditions, and solve them using the Newton-Raphson method. We also explore the possibility of using DR to improve small-signal stability. The results indicate that DR actions can improve small-signal characteristics and sometimes achieve better performance than generation actions. Renewables can also cause power quality problems in distribution systems. To address this issue, we develop a reactive power compensation strategy that uses distributed PV systems to mitigate voltage unbalance. The proposed strategy takes advantage of Steinmetz design and is implemented via both decentralized and distributed control. We demonstrate the performance of the controllers on the IEEE 13-node feeder and a much larger feeder, considering different connections of loads and PV systems. Simulation results demonstrate the trade-offs between the controllers. It is observed that the distributed controller achieves greater voltage unbalance reduction than the decentralized controller, but requires communication infrastructure. Furthermore, we extend our distributed controller to handle inverter reactive power limits, noisy/erroneous measurements, and delayed inputs. We find that the Steinmetz controller can sometimes have adverse impacts on feeder voltages and unbalance at noncritical nodes. A centralized controller from the literature can explicitly account for these factors, but requires significantly more information from the system and longer computational times. We compare the performance of the Steinmetz controller to that of the centralized controller and propose a new controller that integrates centralized controller results into the Steinmetz controller. Results show that the integrated controller achieves better unbalance improvement compared with that of the centralized controller running infrequently. In summary, this dissertation presents two demand-side strategies to deal with the issues caused by the renewables and contributes to the growing body of literature that shows that distributed energy resources have the potential to play a key role in improving the operation of the future power system.PHDElectrical and Computer EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/162969/1/mqyao_1.pd

Symmetry in Renewable Energy and Power Systems

This book includes original research papers related to renewable energy and power systems in which theoretical or practical issues of symmetry are considered. The book includes contributions on voltage stability analysis in DC networks, optimal dispatch of islanded microgrid systems, reactive power compensation, direct power compensation, optimal location and sizing of photovoltaic sources in DC networks, layout of parabolic trough solar collectors, topologic analysis of high-voltage transmission grids, geometric algebra and power systems, filter design for harmonic current compensation. The contributions included in this book describe the state of the art in this field and shed light on the possibilities that the study of symmetry has in power grids and renewable energy systems

Reverse Engineering of Short Circuit Analyses

The electrical distribution system has evolved with embedded computer systems that can better manage the electrical fault that occurred around the feeders. Such random events can affect the reliability indices of overall systems. Computerized management system for distribution operation has been improving with the advanced sensing technologies. The general research question is here to articulate is the responsiveness for utility crew to pinpoint the exact location of a fault based on the SCADA fault indicators from pole-mounted feeder remote terminal units (FRTUs). This has been a tricky question because it relies on the information received from the sensors that can conclude fault with logic\u27s of over currents. The merit of this work can benefit at large the grid reliability because of time-saving in searching the exact location of a fault. The main contribution of this thesis is to utilize the 3-phase unbalanced power flow method to incrementally search for narrowing the localization of electrical short circuits. This is known as the reversal of the typical short circuit approach where a location of the fault is presumed. The 3 topological configurations of simulation studied in this thesis exhibit the typical radial configuration of a distribution feeder have been researched based on unidirectional and bidirectional power flow simulation. The exact fault location is carried in two steps. Firstly, a bisection search algorithm has been employed. Secondly, an incremental adjustment to match the simulated currents of fault with the measurements is conducted. Finally, the sensitivity analysis of a search can be improved with the proposed algorithm that leads to matching of telemetered and calculated values. The analysis of exact fault location is carried in unidirectional and bidirectional flow of power. Distributed energy resources (DER) such as residential PV at a household level as well the wind energy changes affect the protective relaying within a feeder as well as the reconfigurability of the switching sequences. Furthermost, the bidirectionality of power flow in an unbalanced manner would also be a challenging issue to deal with the power quality in automation. Finally, the simulation results based on unidirectional and bidirectional power flow are extensively discussed along with the future scope