dawit teshome | National Taiwan University of Science and Technology (original) (raw)

Papers by dawit teshome

Iet Generation Transmission & Distribution, Oct 3, 2018

Distribution system reconfiguration (DSR) is a critical process that improves the power transfer ... more Distribution system reconfiguration (DSR) is a critical process that improves the power transfer efficiency and reduces the overall operational cost. There have been various methods for addressing the DSR problems. Recently, DSR problems formulated in mixed-integer linear programming (MILP) has gained popularity as they generally can be solved by the state-ofthe-art commercially accessible linear programming solvers, and is able to solve the system with thousands of unknown variables within a reasonable time. However, in some MILP formulations, the distribution line losses are omitted in the nodal power injections for the sake of simplicity. This compromises the accuracy of the linearised model and contributes to the disparity between the MILP and the true non-linear model. Hence, in this study, new formulations are introduced for embedding the expressions of line losses inside load flow equations so that the deviations between the modelled and exact losses notably reduce. Moreover, other novel formulations have also been presented for simultaneously optimising distributed generation (DG) locations and sizes, while at the same time considering various DG's modes of connection to the distribution grid. The validity and effectiveness of the proposed MILP model is tested on standard IEEE systems and actual distribution network. Nomenclature Indices i/ j, N node (bus), number of nodes (buses) k, D i , D s node (bus), set of downstream nodes connected to node i, set of feeder (substation) nodes s, S segment, set of segments l, L PV , L PQ DG index, set of PV type DGs, set of PQ type DGs Parameters R j, i , X j, i resistance and reactance of branch connecting nodes i and j PD i , QD j active and reactive power demands at node i SB j, i MAX line capacities SG l MIN , SG l MAX DG size limits PS j, i s , QS j, i s parameters known prior to optimisation for determining the maximum active and reactive power flows of the sth segment mp j, i s , mq j, i s slopes of the sth segment for real and reactive power flows pl MAX maximum allowable DG penetration level n g maximum number of DGs that can be connected to any bus V i MIN , V i MAX upper and lower boundaries of voltage magnitude V i SP specified voltage magnitude for PV bus pf l power factor of the lth DG Variables PB j, i , QB j, i active and reactive power flows from bus i to bus j PL j, i , QL j, i active and reactive losses of a branch from node j to node i PG l, i , QG l, i active and reactive power outputs of the lth DG located at ith bus V i voltage magnitude of the bus i V i s square of voltage magnitude of the bus i SW j, i branch status (OPEN/CLOSED) of the line connecting node j to node i XW j, i binary variable which is equal to 1 if i is an upstream (parent) node connected to j LC l binary variable that takes a value of 1 if the lth DG is connected to the ith bus

IEEE Open Journal of the Industrial Electronics Society

A partial shading condition (PSC) is one of the most common problems in the photovoltaic (PV) sys... more A partial shading condition (PSC) is one of the most common problems in the photovoltaic (PV) system. It causes the output power of a PV system drastically decrease. Meta-heuristic algorithms (MHA) can track the maximum power point in a power-voltage (P-V) curve with multiple peaks. Grey wolf optimization (GWO) algorithm is a new optimization algorithm based on MHA. It has been used to solve optimization problems in many applications including MPPT for a PV system. However, the accuracy and tracking time in the original GWO (OGWO) can still be further improved for various PSCs. Therefore, there have been some modified grey wolf optimization (MGWO) algorithms proposed to improve the GWO. Nevertheless, only incremental improvement has been made. Therefore, a modified GWO, named enhanced grey wolf optimization (EGWO) is proposed in this paper. The proposed method adds the weighting average, the pouncing behavior and nonlinear convergence factor in the OGWO. In particular, since real wolves may engage in pouncing action when they are hunting, inclusion of pouncing completes the GWO algorithm and yields great improvements. As will be shown via simulation and experiment, the EGWO can drastically reduce the tracking time (up to 45.5% of the OGWO) and the dynamic tracking efficiency can be improved by more than 2%, compared to the OGWO. Moreover, the EGWO achieves the highest maximum power point compared to some of the existing GWO and other swarm based algorithms. INDEX TERMS Maximum power point tracking (MPPT), modified grey wolf optimizer (MGWO), partial shading condition (PSC), photovoltaic (PV) array.

2018 IEEE Power & Energy Society General Meeting (PESGM), 2018

This paper investigates the overvoltage problem caused by micro-generators (MGs) in secondary dis... more This paper investigates the overvoltage problem caused by micro-generators (MGs) in secondary distribution feeders. The allowable MG active power injection into a particular feeder essentially depends on the system R/X ratio, supply impedance (system fault level) and feeder topology. Different from transmission systems, distribution systems exhibit a high R/X ratio, involving large amount of reactive power for voltage regulation which cannot be entirely provided by MGs alone. Hence, a limit exists on the allowable MG power injection within acceptable voltage rise tolerances. This paper presents analytical and case studies, clarifying the relation between MG power, feeder characteristics (R/X ratio and fault level) and voltage rise. It also provides some useful charts and equations to estimate voltage rise, maximum allowable MG power and required reactive power for typical R/X ratios and fault levels. The application of switchable shunt inductors as means of voltage rise mitigation in secondary distribution systems with high R/X ratios is also demonstrated in this paper.

IEEE Transactions on Sustainable Energy, 2019

Distributed energy resources (DERs) are a new class of disruptive technologies with rapidly incre... more Distributed energy resources (DERs) are a new class of disruptive technologies with rapidly increasing adoption levels due to favorable government policies and subsidies. However, these emerging technologies come with technical challenges for utilities and system operators; for instance, voltage rise issues in residential secondary distribution systems with high penetration of DERs. One of the low-cost mitigation options to alleviate the overvoltage problem is reactive power absorption. Nevertheless, secondary feeders exhibit a high R/X ratio more noticeably than primary distribution systems, requiring large amount of reactive power for voltage regulation that cannot be entirely provided by the DERs alone. It is also necessary to minimize the reactive power drawn from the primary distribution system to prevent any stress on the network and reduce extra system losses, while at the same time ensuring the voltage within admissible limits. To address these critical issues, this paper proposes a distributed reactive power management, where additional source is provided from inexpensive devices such as switchable shunt reactors. The proposed overvoltage mitigation is accompanied by detailed analytical investigation that estimates the minimum amount of required reactive power to manage the voltage with user specified voltage rise tolerances. Case studies have also been conducted on real residential distribution systems subjected to severe voltage rise issues provoked by large adoption of DERs.

IEEJ Transactions on Electrical and Electronic Engineering, 2016

This paper presents an efficient way of solving the distribution system reconfiguration (DSR) pro... more This paper presents an efficient way of solving the distribution system reconfiguration (DSR) problem in electrical power systems with consideration of different types of distributed generators (DGs). The objective of a DSR is to minimize the system power loss while satisfying the system constraints and keeping the topology of the system radial. In this paper, a new DSR algorithm based on a modified particle swarm optimization (PSO) is proposed to incorporate DGs with the constant voltage control mode. The proposed method is very efficient because it avoids an extra iteration loop for computing the reactive power at PV buses in order to keep the voltage at a specified magnitude. Furthermore, if the reactive power requirement is not met in between the extreme limits, the proposed algorithm strictly searches for the best possible tie switch combination to simultaneously reduce the power loss and ensure that the DGs operate in PV mode within acceptable reactive power limit. The propose...

IEEE Access, 2018

There are, in general, two methods of load monitoring which are intrusive load monitoring and non... more There are, in general, two methods of load monitoring which are intrusive load monitoring and non-intrusive load monitoring (NILM). The NILM method has attracted considerable research interests, since it only requires a set of voltage and current sensors to be installed at the electrical service entry (ESE) for load disaggregation. However, the main challenge of NILM is to accurately analyze data from the ESE and determine the electrical consumption of each appliance. A single load signature (LS) has some limitations and may not be used for the load disaggregation under all circumstances. Thus, the methods such as committee decision mechanism (CDM), which employ multiple LSs for load disaggregation, have been proposed. However, the CDM requires extensive calculations. This paper presents a new NILM method that combines a cascade-filtering approach with the CDM. The proposed method enhances the load identification capability of the NILM. A platform is built to validate the proposed method. The experimental results indicate that the identification accuracy of the proposed method is higher compared with the existing NILM methods. Moreover, the computation burden is much less when compared with the CDM method, demonstrating the high computational efficiency of the proposed method. INDEX TERMS Non-intrusive load monitoring, cascade-filtering, committee decision mechanism, load disaggregation.

IEEE Power and Energy Technology Systems Journal, 2018

This paper presents an investigation on the performance of voltage regulators (VRs) in mitigating... more This paper presents an investigation on the performance of voltage regulators (VRs) in mitigating overvoltage problems caused by distributed energy resources (DERs) in medium-voltage (MV) distribution systems. The control method of VRs is found to be a crucial factor. Studies reveal that even advanced control modes of commercial VRs cannot be relied upon as effective solutions to manage every scenario. The main problems associated with local control methods are identified. A supplementary voltage control scheme is proposed to enhance the capability of VRs as a solution option. The proposed scheme addresses the problems due to local control methods with a minimal investment. The studies are accompanied by several simulations on IEEE 123 nodes system as well as an actual feeder facing such overvoltage problems. Merits of the proposed supplementary control scheme are also demonstrated through simulation results.

IET Generation, Transmission & Distribution, 2018

Distribution system reconfiguration (DSR) is a critical process that improves the power transfer ... more Distribution system reconfiguration (DSR) is a critical process that improves the power transfer efficiency and reduces the overall operational cost. There have been various methods for addressing the DSR problems. Recently, DSR problems formulated in mixed-integer linear programming (MILP) has gained popularity as they generally can be solved by the state-ofthe-art commercially accessible linear programming solvers, and is able to solve the system with thousands of unknown variables within a reasonable time. However, in some MILP formulations, the distribution line losses are omitted in the nodal power injections for the sake of simplicity. This compromises the accuracy of the linearised model and contributes to the disparity between the MILP and the true non-linear model. Hence, in this study, new formulations are introduced for embedding the expressions of line losses inside load flow equations so that the deviations between the modelled and exact losses notably reduce. Moreover, other novel formulations have also been presented for simultaneously optimising distributed generation (DG) locations and sizes, while at the same time considering various DG's modes of connection to the distribution grid. The validity and effectiveness of the proposed MILP model is tested on standard IEEE systems and actual distribution network. Nomenclature Indices i/ j, N node (bus), number of nodes (buses) k, D i , D s node (bus), set of downstream nodes connected to node i, set of feeder (substation) nodes s, S segment, set of segments l, L PV , L PQ DG index, set of PV type DGs, set of PQ type DGs Parameters R j, i , X j, i resistance and reactance of branch connecting nodes i and j PD i , QD j active and reactive power demands at node i SB j, i MAX line capacities SG l MIN , SG l MAX DG size limits PS j, i s , QS j, i s parameters known prior to optimisation for determining the maximum active and reactive power flows of the sth segment mp j, i s , mq j, i s slopes of the sth segment for real and reactive power flows pl MAX maximum allowable DG penetration level n g maximum number of DGs that can be connected to any bus V i MIN , V i MAX upper and lower boundaries of voltage magnitude V i SP specified voltage magnitude for PV bus pf l power factor of the lth DG Variables PB j, i , QB j, i active and reactive power flows from bus i to bus j PL j, i , QL j, i active and reactive losses of a branch from node j to node i PG l, i , QG l, i active and reactive power outputs of the lth DG located at ith bus V i voltage magnitude of the bus i V i s square of voltage magnitude of the bus i SW j, i branch status (OPEN/CLOSED) of the line connecting node j to node i XW j, i binary variable which is equal to 1 if i is an upstream (parent) node connected to j LC l binary variable that takes a value of 1 if the lth DG is connected to the ith bus

IEEE Journal of Emerging and Selected Topics in Power Electronics, 2017

Photovoltaic (PV) modules subjected to partial shading conditions (PSC) can drastically decrease ... more Photovoltaic (PV) modules subjected to partial shading conditions (PSC) can drastically decrease their power output. Hence, there have been various maximum power point tracking (MPPT) control algorithms developed to reduce or counteract the shading effects. Recently, a new meta-heuristic algorithm known as firefly algorithm (FA) was developed, which, under PSC, has been shown to successfully track the GMP. Nevertheless, the FA still has some inherent problems, which may hinder the performance of the MPPT. This paper modifies the existing FA to counteract these problems. As will be demonstrated in the paper, the proposed modified FA (MFA) method can reduce the number of computation operations and the time for converging to the GMP that the existing FA requires. Experimental results show that the proposed method can track the global point under various PSC, has a faster convergence time, compared to the FA, and can effectively suppress the power and voltage fluctuations. Index Terms Maximum power point tracking (MPPT), photovoltaic (PV) array, partial shading, global optimization, firefly algorithm I. INTRODUCTION Partial shading on a photovoltaic (PV) string comprising multiple modules or substrings is known as a serious problem that significantly decreases the energy utilization. Under partially shading conditions (PSC), the shaded cells in a module become reverse biased and behave as a load, leading to the hot spot problem. To avoid this, bypass diodes are used to conduct the current generated by the non-shaded cells within a module. However, the connection of bypass diodes will change the uniform current-voltage (I-V) and power-voltage (P-V) characteristics of the module, resulting in multiple peaks [1]. To maximize the efficiency of the module, it is necessary to track the global maximum point (GMP).

IEEE Power and Energy Technology Systems Journal, 2016

The performance of a non-intrusive load monitoring (NILM) system heavily depends on the uniquenes... more The performance of a non-intrusive load monitoring (NILM) system heavily depends on the uniqueness of the preferred load signature (LS) extracted from each appliance. Some electrical characteristics such as instantaneous current waveform (CW), instantaneous power waveform (IPW), current harmonic (CH) and voltage-current (V-I) trajectory have been proposed as appliance features in the literature. However, in some situations, these LSs cannot effectively distinguish different loads apart. In this paper, a time-domain based advanced power theory is used to decompose the load current into active and non-active orthogonal components. Then, two new LSs have been established based on the non-active component of the load current, namely the non-active current waveform (i f) and the voltage-non-active current (V-I f) characteristics curve. Simulation and experimental tests show that both of these features can distinguish different appliances. Hence, the proposed LSs can significantly enhance the existing NILM systems.

Mathematical Problems in Engineering, 2015

The stochastic nature of demand and wind generation has a considerable effect on solving the sche... more The stochastic nature of demand and wind generation has a considerable effect on solving the scheduling problem of a modern power system. Network constraints such as power flow equations and transmission capacities also need to be considered for a comprehensive approach to model renewable energy integration and analyze generation system flexibility. Firstly, this paper accounts for the stochastic inputs in such a way that the uncertainties are modeled as normally distributed forecast errors. The forecast errors are then superimposed on the outputs of load and wind forecasting tools. Secondly, it efficiently models the network constraints and tests an iterative algorithm and a piecewise linear approximation for representing transmission losses in mixed integer linear programming (MILP). It also integrates load shedding according to priority factors set by the system operator. Moreover, the different interactions among stochastic programming, network constraints, and prioritized load ...

2016 IEEE International Conference on Advanced Intelligent Mechatronics (AIM), 2016

A detailed traction model for the Taipei Mass Rapid Traction system is developed, and a new speed... more A detailed traction model for the Taipei Mass Rapid Traction system is developed, and a new speed controller based on Neural Network and PID (NN-based PID) is proposed. The model, which is developed in MATLAB/ Simulink, has three main parts: traction system, third rail voltage system, and load. The train model characterizes the traction motor and the coupling effect of mechanical and electrical parts of the train system. Moreover, the efficiency changes and switching transitions can be observed. An NN-based PID controller is used because of its self-adaptive capability. A case study of an actual track is presented to demonstrate the robustness of the proposed controller.

2015 IEEE 15th International Conference on Environment and Electrical Engineering (EEEIC), 2015

This paper presents an efficient and accurate way of solving radial distribution system reconfigu... more This paper presents an efficient and accurate way of solving radial distribution system reconfiguration (DSR), which plays an important role in distribution automation for realizing smart grids. It deploys different heuristic optimization approaches to resolve the desired optimum configuration and to efficiently reconfigure the connectivity of the distribution networks. The objective is to minimize the system power loss while the voltage in each bus is limited to some allowable range, and the topology of the system is kept radial. In this paper, a hybrid algorithm consisting of particle swarm optimization (PSO) and genetic algorithm (GA) is proposed. The first part of the hybrid approach is based on a modified PSO where the initial swarm of particles fit the radiality constraint and it introduces external randomness to velocities and locations with certain probabilities when particles are in equilibrium or close to equilibrium state. The second part is a modified GA which receives its initial population from best solutions of the modified PSO and uses adaptive mutation for introducing population diversity. In addition, the particle's location in PSO and each chromosome in GA are repaired in such a way that the radiality constraint is always satisfied. The validity and the effectiveness of the proposed method has been tested using the standard IEEE 33-bus distribution network. The results show that the proposed method is robust and delivers a minimal average power loss of independent runs with reduced computational time.

2015 International Conference on Advanced Robotics and Intelligent Systems (ARIS), 2015

This paper presents a new robust methodology for solving radial distribution system reconfigurati... more This paper presents a new robust methodology for solving radial distribution system reconfiguration (DSR) problem based on the concept of cooperative multi-thread strategy and hybrid meta-heuristics. The parallel cooperative meta-heuristics (PCMH) method deploys multiple concurrent explorations of the solution space using genetic algorithm (GA), particle swarm optimization (PSO) and ant colony system (ACS) running in parallel on independent processors. The meta-heuristics are subjected to communicate and cooperate with each other synchronously at a specified interval in the course of iteration. Dynamically at each interval, the best solution so far found is exchanged among all the three processors. In addition, the worst individuals of GA are replaced by the best particles of PSO if the current optimum is delivered by PSO; otherwise the best ants from ACS replace these individuals. The proposed method is applied to the standard IEEE 33-bus distribution network with the objective of minimizing the overall power loss while at the same time accounting for the operational constraints within allowable limits. The results demonstrate the validity and the effectiveness of the proposed approach in terms of accuracy and robustness.

2018 IEEE Power & Energy Society General Meeting (PESGM), 2018

Increased environmental concerns, changing regulations, and government subsidies have played a ke... more Increased environmental concerns, changing regulations, and government subsidies have played a key role in incenting renewable generation. Solar generation has been increasingly proliferating among residential customers in many US states and Canadian provinces. Photovoltaic generation is connected through DC-AC inverters. The operation of these inverters has been a focal point of discussion in recent years. The California Independent System Operator has chaired the development of Rule 21, which was the base for the subsequent UL1741SA standard, paving the way for the upcoming revision of IEEE 1547. Canadian standards are following suit, with upcoming revisions to CSA C22.3 No 9 and C22.2 No 257. These standards require new inverters to feature autonomous functions such as Volt-Watt and Volt-VAR, as well as provision for compatibility with centralized management systems. This paper analyzes the impact of PV curtailment through the Volt-Watt function, as compared with the installation of a Battery Energy Storage System, on voltage management of one feeder of a Canadian electric utility. Technical constraints and economic factors are considered.

Iet Generation Transmission & Distribution, Oct 3, 2018

Distribution system reconfiguration (DSR) is a critical process that improves the power transfer ... more Distribution system reconfiguration (DSR) is a critical process that improves the power transfer efficiency and reduces the overall operational cost. There have been various methods for addressing the DSR problems. Recently, DSR problems formulated in mixed-integer linear programming (MILP) has gained popularity as they generally can be solved by the state-ofthe-art commercially accessible linear programming solvers, and is able to solve the system with thousands of unknown variables within a reasonable time. However, in some MILP formulations, the distribution line losses are omitted in the nodal power injections for the sake of simplicity. This compromises the accuracy of the linearised model and contributes to the disparity between the MILP and the true non-linear model. Hence, in this study, new formulations are introduced for embedding the expressions of line losses inside load flow equations so that the deviations between the modelled and exact losses notably reduce. Moreover, other novel formulations have also been presented for simultaneously optimising distributed generation (DG) locations and sizes, while at the same time considering various DG's modes of connection to the distribution grid. The validity and effectiveness of the proposed MILP model is tested on standard IEEE systems and actual distribution network. Nomenclature Indices i/ j, N node (bus), number of nodes (buses) k, D i , D s node (bus), set of downstream nodes connected to node i, set of feeder (substation) nodes s, S segment, set of segments l, L PV , L PQ DG index, set of PV type DGs, set of PQ type DGs Parameters R j, i , X j, i resistance and reactance of branch connecting nodes i and j PD i , QD j active and reactive power demands at node i SB j, i MAX line capacities SG l MIN , SG l MAX DG size limits PS j, i s , QS j, i s parameters known prior to optimisation for determining the maximum active and reactive power flows of the sth segment mp j, i s , mq j, i s slopes of the sth segment for real and reactive power flows pl MAX maximum allowable DG penetration level n g maximum number of DGs that can be connected to any bus V i MIN , V i MAX upper and lower boundaries of voltage magnitude V i SP specified voltage magnitude for PV bus pf l power factor of the lth DG Variables PB j, i , QB j, i active and reactive power flows from bus i to bus j PL j, i , QL j, i active and reactive losses of a branch from node j to node i PG l, i , QG l, i active and reactive power outputs of the lth DG located at ith bus V i voltage magnitude of the bus i V i s square of voltage magnitude of the bus i SW j, i branch status (OPEN/CLOSED) of the line connecting node j to node i XW j, i binary variable which is equal to 1 if i is an upstream (parent) node connected to j LC l binary variable that takes a value of 1 if the lth DG is connected to the ith bus

IEEE Open Journal of the Industrial Electronics Society

A partial shading condition (PSC) is one of the most common problems in the photovoltaic (PV) sys... more A partial shading condition (PSC) is one of the most common problems in the photovoltaic (PV) system. It causes the output power of a PV system drastically decrease. Meta-heuristic algorithms (MHA) can track the maximum power point in a power-voltage (P-V) curve with multiple peaks. Grey wolf optimization (GWO) algorithm is a new optimization algorithm based on MHA. It has been used to solve optimization problems in many applications including MPPT for a PV system. However, the accuracy and tracking time in the original GWO (OGWO) can still be further improved for various PSCs. Therefore, there have been some modified grey wolf optimization (MGWO) algorithms proposed to improve the GWO. Nevertheless, only incremental improvement has been made. Therefore, a modified GWO, named enhanced grey wolf optimization (EGWO) is proposed in this paper. The proposed method adds the weighting average, the pouncing behavior and nonlinear convergence factor in the OGWO. In particular, since real wolves may engage in pouncing action when they are hunting, inclusion of pouncing completes the GWO algorithm and yields great improvements. As will be shown via simulation and experiment, the EGWO can drastically reduce the tracking time (up to 45.5% of the OGWO) and the dynamic tracking efficiency can be improved by more than 2%, compared to the OGWO. Moreover, the EGWO achieves the highest maximum power point compared to some of the existing GWO and other swarm based algorithms. INDEX TERMS Maximum power point tracking (MPPT), modified grey wolf optimizer (MGWO), partial shading condition (PSC), photovoltaic (PV) array.

2018 IEEE Power & Energy Society General Meeting (PESGM), 2018

This paper investigates the overvoltage problem caused by micro-generators (MGs) in secondary dis... more This paper investigates the overvoltage problem caused by micro-generators (MGs) in secondary distribution feeders. The allowable MG active power injection into a particular feeder essentially depends on the system R/X ratio, supply impedance (system fault level) and feeder topology. Different from transmission systems, distribution systems exhibit a high R/X ratio, involving large amount of reactive power for voltage regulation which cannot be entirely provided by MGs alone. Hence, a limit exists on the allowable MG power injection within acceptable voltage rise tolerances. This paper presents analytical and case studies, clarifying the relation between MG power, feeder characteristics (R/X ratio and fault level) and voltage rise. It also provides some useful charts and equations to estimate voltage rise, maximum allowable MG power and required reactive power for typical R/X ratios and fault levels. The application of switchable shunt inductors as means of voltage rise mitigation in secondary distribution systems with high R/X ratios is also demonstrated in this paper.

IEEE Transactions on Sustainable Energy, 2019

Distributed energy resources (DERs) are a new class of disruptive technologies with rapidly incre... more Distributed energy resources (DERs) are a new class of disruptive technologies with rapidly increasing adoption levels due to favorable government policies and subsidies. However, these emerging technologies come with technical challenges for utilities and system operators; for instance, voltage rise issues in residential secondary distribution systems with high penetration of DERs. One of the low-cost mitigation options to alleviate the overvoltage problem is reactive power absorption. Nevertheless, secondary feeders exhibit a high R/X ratio more noticeably than primary distribution systems, requiring large amount of reactive power for voltage regulation that cannot be entirely provided by the DERs alone. It is also necessary to minimize the reactive power drawn from the primary distribution system to prevent any stress on the network and reduce extra system losses, while at the same time ensuring the voltage within admissible limits. To address these critical issues, this paper proposes a distributed reactive power management, where additional source is provided from inexpensive devices such as switchable shunt reactors. The proposed overvoltage mitigation is accompanied by detailed analytical investigation that estimates the minimum amount of required reactive power to manage the voltage with user specified voltage rise tolerances. Case studies have also been conducted on real residential distribution systems subjected to severe voltage rise issues provoked by large adoption of DERs.

IEEJ Transactions on Electrical and Electronic Engineering, 2016

This paper presents an efficient way of solving the distribution system reconfiguration (DSR) pro... more This paper presents an efficient way of solving the distribution system reconfiguration (DSR) problem in electrical power systems with consideration of different types of distributed generators (DGs). The objective of a DSR is to minimize the system power loss while satisfying the system constraints and keeping the topology of the system radial. In this paper, a new DSR algorithm based on a modified particle swarm optimization (PSO) is proposed to incorporate DGs with the constant voltage control mode. The proposed method is very efficient because it avoids an extra iteration loop for computing the reactive power at PV buses in order to keep the voltage at a specified magnitude. Furthermore, if the reactive power requirement is not met in between the extreme limits, the proposed algorithm strictly searches for the best possible tie switch combination to simultaneously reduce the power loss and ensure that the DGs operate in PV mode within acceptable reactive power limit. The propose...

IEEE Access, 2018

There are, in general, two methods of load monitoring which are intrusive load monitoring and non... more There are, in general, two methods of load monitoring which are intrusive load monitoring and non-intrusive load monitoring (NILM). The NILM method has attracted considerable research interests, since it only requires a set of voltage and current sensors to be installed at the electrical service entry (ESE) for load disaggregation. However, the main challenge of NILM is to accurately analyze data from the ESE and determine the electrical consumption of each appliance. A single load signature (LS) has some limitations and may not be used for the load disaggregation under all circumstances. Thus, the methods such as committee decision mechanism (CDM), which employ multiple LSs for load disaggregation, have been proposed. However, the CDM requires extensive calculations. This paper presents a new NILM method that combines a cascade-filtering approach with the CDM. The proposed method enhances the load identification capability of the NILM. A platform is built to validate the proposed method. The experimental results indicate that the identification accuracy of the proposed method is higher compared with the existing NILM methods. Moreover, the computation burden is much less when compared with the CDM method, demonstrating the high computational efficiency of the proposed method. INDEX TERMS Non-intrusive load monitoring, cascade-filtering, committee decision mechanism, load disaggregation.

IEEE Power and Energy Technology Systems Journal, 2018

This paper presents an investigation on the performance of voltage regulators (VRs) in mitigating... more This paper presents an investigation on the performance of voltage regulators (VRs) in mitigating overvoltage problems caused by distributed energy resources (DERs) in medium-voltage (MV) distribution systems. The control method of VRs is found to be a crucial factor. Studies reveal that even advanced control modes of commercial VRs cannot be relied upon as effective solutions to manage every scenario. The main problems associated with local control methods are identified. A supplementary voltage control scheme is proposed to enhance the capability of VRs as a solution option. The proposed scheme addresses the problems due to local control methods with a minimal investment. The studies are accompanied by several simulations on IEEE 123 nodes system as well as an actual feeder facing such overvoltage problems. Merits of the proposed supplementary control scheme are also demonstrated through simulation results.

IET Generation, Transmission & Distribution, 2018

Distribution system reconfiguration (DSR) is a critical process that improves the power transfer ... more Distribution system reconfiguration (DSR) is a critical process that improves the power transfer efficiency and reduces the overall operational cost. There have been various methods for addressing the DSR problems. Recently, DSR problems formulated in mixed-integer linear programming (MILP) has gained popularity as they generally can be solved by the state-ofthe-art commercially accessible linear programming solvers, and is able to solve the system with thousands of unknown variables within a reasonable time. However, in some MILP formulations, the distribution line losses are omitted in the nodal power injections for the sake of simplicity. This compromises the accuracy of the linearised model and contributes to the disparity between the MILP and the true non-linear model. Hence, in this study, new formulations are introduced for embedding the expressions of line losses inside load flow equations so that the deviations between the modelled and exact losses notably reduce. Moreover, other novel formulations have also been presented for simultaneously optimising distributed generation (DG) locations and sizes, while at the same time considering various DG's modes of connection to the distribution grid. The validity and effectiveness of the proposed MILP model is tested on standard IEEE systems and actual distribution network. Nomenclature Indices i/ j, N node (bus), number of nodes (buses) k, D i , D s node (bus), set of downstream nodes connected to node i, set of feeder (substation) nodes s, S segment, set of segments l, L PV , L PQ DG index, set of PV type DGs, set of PQ type DGs Parameters R j, i , X j, i resistance and reactance of branch connecting nodes i and j PD i , QD j active and reactive power demands at node i SB j, i MAX line capacities SG l MIN , SG l MAX DG size limits PS j, i s , QS j, i s parameters known prior to optimisation for determining the maximum active and reactive power flows of the sth segment mp j, i s , mq j, i s slopes of the sth segment for real and reactive power flows pl MAX maximum allowable DG penetration level n g maximum number of DGs that can be connected to any bus V i MIN , V i MAX upper and lower boundaries of voltage magnitude V i SP specified voltage magnitude for PV bus pf l power factor of the lth DG Variables PB j, i , QB j, i active and reactive power flows from bus i to bus j PL j, i , QL j, i active and reactive losses of a branch from node j to node i PG l, i , QG l, i active and reactive power outputs of the lth DG located at ith bus V i voltage magnitude of the bus i V i s square of voltage magnitude of the bus i SW j, i branch status (OPEN/CLOSED) of the line connecting node j to node i XW j, i binary variable which is equal to 1 if i is an upstream (parent) node connected to j LC l binary variable that takes a value of 1 if the lth DG is connected to the ith bus

IEEE Journal of Emerging and Selected Topics in Power Electronics, 2017

Photovoltaic (PV) modules subjected to partial shading conditions (PSC) can drastically decrease ... more Photovoltaic (PV) modules subjected to partial shading conditions (PSC) can drastically decrease their power output. Hence, there have been various maximum power point tracking (MPPT) control algorithms developed to reduce or counteract the shading effects. Recently, a new meta-heuristic algorithm known as firefly algorithm (FA) was developed, which, under PSC, has been shown to successfully track the GMP. Nevertheless, the FA still has some inherent problems, which may hinder the performance of the MPPT. This paper modifies the existing FA to counteract these problems. As will be demonstrated in the paper, the proposed modified FA (MFA) method can reduce the number of computation operations and the time for converging to the GMP that the existing FA requires. Experimental results show that the proposed method can track the global point under various PSC, has a faster convergence time, compared to the FA, and can effectively suppress the power and voltage fluctuations. Index Terms Maximum power point tracking (MPPT), photovoltaic (PV) array, partial shading, global optimization, firefly algorithm I. INTRODUCTION Partial shading on a photovoltaic (PV) string comprising multiple modules or substrings is known as a serious problem that significantly decreases the energy utilization. Under partially shading conditions (PSC), the shaded cells in a module become reverse biased and behave as a load, leading to the hot spot problem. To avoid this, bypass diodes are used to conduct the current generated by the non-shaded cells within a module. However, the connection of bypass diodes will change the uniform current-voltage (I-V) and power-voltage (P-V) characteristics of the module, resulting in multiple peaks [1]. To maximize the efficiency of the module, it is necessary to track the global maximum point (GMP).

IEEE Power and Energy Technology Systems Journal, 2016

The performance of a non-intrusive load monitoring (NILM) system heavily depends on the uniquenes... more The performance of a non-intrusive load monitoring (NILM) system heavily depends on the uniqueness of the preferred load signature (LS) extracted from each appliance. Some electrical characteristics such as instantaneous current waveform (CW), instantaneous power waveform (IPW), current harmonic (CH) and voltage-current (V-I) trajectory have been proposed as appliance features in the literature. However, in some situations, these LSs cannot effectively distinguish different loads apart. In this paper, a time-domain based advanced power theory is used to decompose the load current into active and non-active orthogonal components. Then, two new LSs have been established based on the non-active component of the load current, namely the non-active current waveform (i f) and the voltage-non-active current (V-I f) characteristics curve. Simulation and experimental tests show that both of these features can distinguish different appliances. Hence, the proposed LSs can significantly enhance the existing NILM systems.

Mathematical Problems in Engineering, 2015

The stochastic nature of demand and wind generation has a considerable effect on solving the sche... more The stochastic nature of demand and wind generation has a considerable effect on solving the scheduling problem of a modern power system. Network constraints such as power flow equations and transmission capacities also need to be considered for a comprehensive approach to model renewable energy integration and analyze generation system flexibility. Firstly, this paper accounts for the stochastic inputs in such a way that the uncertainties are modeled as normally distributed forecast errors. The forecast errors are then superimposed on the outputs of load and wind forecasting tools. Secondly, it efficiently models the network constraints and tests an iterative algorithm and a piecewise linear approximation for representing transmission losses in mixed integer linear programming (MILP). It also integrates load shedding according to priority factors set by the system operator. Moreover, the different interactions among stochastic programming, network constraints, and prioritized load ...

2016 IEEE International Conference on Advanced Intelligent Mechatronics (AIM), 2016

A detailed traction model for the Taipei Mass Rapid Traction system is developed, and a new speed... more A detailed traction model for the Taipei Mass Rapid Traction system is developed, and a new speed controller based on Neural Network and PID (NN-based PID) is proposed. The model, which is developed in MATLAB/ Simulink, has three main parts: traction system, third rail voltage system, and load. The train model characterizes the traction motor and the coupling effect of mechanical and electrical parts of the train system. Moreover, the efficiency changes and switching transitions can be observed. An NN-based PID controller is used because of its self-adaptive capability. A case study of an actual track is presented to demonstrate the robustness of the proposed controller.

2015 IEEE 15th International Conference on Environment and Electrical Engineering (EEEIC), 2015

This paper presents an efficient and accurate way of solving radial distribution system reconfigu... more This paper presents an efficient and accurate way of solving radial distribution system reconfiguration (DSR), which plays an important role in distribution automation for realizing smart grids. It deploys different heuristic optimization approaches to resolve the desired optimum configuration and to efficiently reconfigure the connectivity of the distribution networks. The objective is to minimize the system power loss while the voltage in each bus is limited to some allowable range, and the topology of the system is kept radial. In this paper, a hybrid algorithm consisting of particle swarm optimization (PSO) and genetic algorithm (GA) is proposed. The first part of the hybrid approach is based on a modified PSO where the initial swarm of particles fit the radiality constraint and it introduces external randomness to velocities and locations with certain probabilities when particles are in equilibrium or close to equilibrium state. The second part is a modified GA which receives its initial population from best solutions of the modified PSO and uses adaptive mutation for introducing population diversity. In addition, the particle's location in PSO and each chromosome in GA are repaired in such a way that the radiality constraint is always satisfied. The validity and the effectiveness of the proposed method has been tested using the standard IEEE 33-bus distribution network. The results show that the proposed method is robust and delivers a minimal average power loss of independent runs with reduced computational time.

2015 International Conference on Advanced Robotics and Intelligent Systems (ARIS), 2015

This paper presents a new robust methodology for solving radial distribution system reconfigurati... more This paper presents a new robust methodology for solving radial distribution system reconfiguration (DSR) problem based on the concept of cooperative multi-thread strategy and hybrid meta-heuristics. The parallel cooperative meta-heuristics (PCMH) method deploys multiple concurrent explorations of the solution space using genetic algorithm (GA), particle swarm optimization (PSO) and ant colony system (ACS) running in parallel on independent processors. The meta-heuristics are subjected to communicate and cooperate with each other synchronously at a specified interval in the course of iteration. Dynamically at each interval, the best solution so far found is exchanged among all the three processors. In addition, the worst individuals of GA are replaced by the best particles of PSO if the current optimum is delivered by PSO; otherwise the best ants from ACS replace these individuals. The proposed method is applied to the standard IEEE 33-bus distribution network with the objective of minimizing the overall power loss while at the same time accounting for the operational constraints within allowable limits. The results demonstrate the validity and the effectiveness of the proposed approach in terms of accuracy and robustness.

2018 IEEE Power & Energy Society General Meeting (PESGM), 2018

Increased environmental concerns, changing regulations, and government subsidies have played a ke... more Increased environmental concerns, changing regulations, and government subsidies have played a key role in incenting renewable generation. Solar generation has been increasingly proliferating among residential customers in many US states and Canadian provinces. Photovoltaic generation is connected through DC-AC inverters. The operation of these inverters has been a focal point of discussion in recent years. The California Independent System Operator has chaired the development of Rule 21, which was the base for the subsequent UL1741SA standard, paving the way for the upcoming revision of IEEE 1547. Canadian standards are following suit, with upcoming revisions to CSA C22.3 No 9 and C22.2 No 257. These standards require new inverters to feature autonomous functions such as Volt-Watt and Volt-VAR, as well as provision for compatibility with centralized management systems. This paper analyzes the impact of PV curtailment through the Volt-Watt function, as compared with the installation of a Battery Energy Storage System, on voltage management of one feeder of a Canadian electric utility. Technical constraints and economic factors are considered.