Sensitive Bus Research Articles

An integrated approach for multi-objective differential algorithm based event constrained optimal power flow for power system resiliency enhancement

ABSTRACT Due to climatic changes, the probability of occurrence and the intensity of extreme weather events increase day by day which leads to power outages. The probability of failure events is calculated using Monte Carlo simulation technique which is used to identify the most frequent failure events. The least eigenvalues of the inverse reduced Jacobian matrix decide the sensitive buses for load shedding using V-Q sensitivity analysis. This work presents the multi-objective differential evolution (MODE) algorithm for solving resilient constrained optimal power flow (RCOPF) in a deregulated power system. The control variables namely the real power of generators in a base case and under event, generator bus voltage magnitude, the real and reactive power demand of the selected load buses, tap settings and capacitor bank ratings. This algorithm is validated in IEEE 30 bus test system and the Indian 62 bus utility test system to show the effectiveness in four different cases including tie lines and distributed generation.

Optimal Placement and Sizing of DG for Loss Reduction,Voltage Profile Improvement and Voltage Sag Mitigation

Increasing trend in using distributed generation has motivated power sector planners to consider approaches that result in benefiting the most from investments in this field. Meanwhile subjects such as power loss reduction, voltage profile improvement and voltage sag mitigation has significant role in lessoning imposed expenditures to utility companies. Loss reduction is important for utility companies as it directly increases company benefit in a competitive electricity market, beside reaching power quality standards is too important as it has vital effect on customer orientation. In this paper an optimization algorithm is developed to gain these goals all together. In order to evaluate sag mitigation capability of the proposed algorithm, voltage in voltage sensitive buses is investigated. An existing 20KV network has been chosen as test network. Results show the efficiency of the proposed algorithm in reducing power loss, improving voltage profile and mitigating voltage sags in voltage sensitive buses.

Optimal Allocation and Sizing of Capacitor Banks in Distribution System to Reduce the Power Loss Using Beluga Whale Optimization

One portion of the distribution system is the distribution feeder. Buses carrying more loads and having long‐distance route lines are significant problems due to the presence of power loss and the increase in the overall cost of the transportation process. Hence, the overall power loss minimization is taken as the major objective. The best sizing and allocation of capacitors in a bank in the distribution line are used to minimize the total loss. BWO technique is utilized in this optimization process. The backward‐forward sweep load flow is used for the computation of the power flow in MATLAB. The sensitive buses have been chosen according to the factor of loss sensitivity (LSF) and using BWO. The validity of the test has been made on the standard IEEE 34 and 85 bus radial distribution system. The simulation results in the 34‐bus radial system are much different from the results of PSO, GWO, WO, and IWO. In the 85‐bus radial system, the results are seen with the outcomes of PSO, WO, and BFOA. In both cases, the results of the proposed technique are found to be better than the existing methods. Therefore, the result shows that BWO can be effective for future selection to improve large distribution networks by sizing and locating the capacitors optimally.

Impact of DSTATCOM penetration level on technical benefits in radial distribution network

This paper investigates the impact of DSTATCOM on the losses, voltage stability, and voltage deviation of the radial distribution networks (RDNs) at different DSTATCOM penetration levels (DPLs). A novel voltage stability improvement index (VSII) is modeled to assign an index value to represent the proximity of the voltage stability index (VSI) of all the network buses to the ideal value. The VSII allows a fair comparison of the VSI profile obtained for different events of DSTATCOM penetration levels. Due to the numerous buses of the RDN, the new voltage stability index (NVSI) selects the most sensitive buses to reactive compensation for DSTATCOM integration after performing the load flow for the base case before integration of DSTATCOM. The DSTATCOM is placed on the selected bus, turn by turn, and DPL increases from zero to the maximum reactive load of the RDN in the step of 1 %. This methodology was implemented on the standard 33–bus and Nigerian Imalefalafia 32–bus RDNs. The outcome establishes that a DPL of 30–55 % and 70–100 % were attained for standard 33–bus and Imalefalafia 32–bus RDNs respectively without increasing the power loss. The VSII was continually improved, and average voltage deviation index (AVDI) was reduced with increasing DPL.

Efficient Energy Management and Reliability Assessment by Optimal Placement of Renewable Energy Sources with Pump Storage Plant

Deteriorating environment conditions due to global warming and depleting fossil fuels, has forced mankind to shift towards renewable energy sources (RES). The integration of RES in existing power system is challenging due to its intermittent nature. This study formulates novel sensitivity index i.e. nodal price of energy index (NPEI) to assist the location of sensitive buses for optimal placement of RES. Firstly, the proposed approach subjects power system to (N-1) contingency including both loss of generator and line outage. The NPEI is computed for every bus in various contingency conditions. The most severe contingency is identified based on highest value of sensitivity index in peak load period. The buses with highest values of NPEI is the optimal location for RES placement in the most critical contingency scenario. Secondly, the proposed approach focuses on efficient and cost-effective energy management by optimally scheduling disparate energy generation sources. The system incorporates pumped storage plant (PSP) based energy storage devices to effectively utilize wind and solar energy. The objective of this study is to minimize the total generation cost which includes the generation cost associated with conventional generators, its emission cost and valve-point loading effect, generation cost of RES, and the cost associated with energy supplied by PSP. The partial shading of PV modules is also implemented and its impact on system parameters are observed. The penetration of RES and energy storage effects system reliability hence, the proposed approach computes reliability indices expected energy not supplied (EENS) and loss of load expected (LOLE) for both presence and absence of RES and PSP. Finally, the proposed approach results in optimal placement of RES and optimal energy scheduling of disparate energy sources along with analyzing its effect on system reliability. The study is performed on IEEE 30 bus system.

Impact of shunt capacitor penetration level in radial distribution system considering techno-economic benefits

Shunt Capacitor (SC) integration in radial distribution networks is a method utilized to minimize power losses and huge voltage drops. In other to obtain these maximum benefits, they should be optimally allocated. To this effect, researchers have used various optimization methods for solving SC allocation problems but most have not considered how the penetration level of SC into the radial distribution system affects these benefits. The goal of the paper, therefore, is to determine the most sensitive buses to reactive compensation and investigate the effect of the penetration level of SC on the techno-economic benefits. Load flow was performed for the base case to determine the steady-state performance of the system and the most sensitive buses were selected using New Voltage Stability Index (NVSI) technique. The size of the SC was increased in step of these buses, in turn, to determine SC penetration level impact on the techno-economic benefits. The approach was implemented on IEEE 33-bus and practical Nigerian radial distribution networks. The results showed that appropriate penetration of SC on networks leads to reduction of power losses, voltage profile improvement as well cost reduction resulting in high net savings.

A secondary strategy for unbalance consensus in an islanded voltage source converter-based microgrid using cooperative gain control

It is common for industrial and commercial microgrids to experience high levels of load unbalance when operating in islanded mode, which degrades the real output power capability of inverters, causes power quality problems, and impacts on the protection regime. Conventional droop control methods are not designed for sharing of unbalance power where multiple inverters are used, and existing proposals for negative sequence power sharing have several practical disadvantages which are identified. This paper proposes a novel secondary scheme for cooperative adjustment of negative sequence droop gains for voltage source converters. The new design provides an option for sharing of unbalance power, while also correcting voltage unbalance at sensitive buses. In contrast to other designs, the scheme proposes hierarchical unbalance control using a fully distributed architecture. It is robust to communication network failure and adapts to impedance changes in the electrical network. A simulation model of the proposed scheme is demonstrated using MATLAB/Simulink for a reference case.

A Joint Scheduling Strategy for Wind and Solar Photovoltaic Systems to Grasp Imbalance Cost in Competitive Market

The integration of renewable energy sources with active thermal power plants contributes to the green environment all over the globe. To achieve maximum reliability and sustainability of the renewable-thermal hybrid system, plentiful constraints need to be considered for minimizing the situation, which creates due to the unpredictable nature of renewable energy. In wind integrated deregulated system, wind farms need to submit the power generation scenario for future days to Independent System Operator (ISO) before the date of operation. Based on their submitted bid, ISO scheduled the power generation from different generating stations, including thermal and renewable. Due to the uncertain nature of the wind flow, there is always a chance of not fulfilling the scheduling amount of power from the wind farm. This violation in the market can impose an economic burden (i.e., imbalance cost) on the generating companies. The solar photovoltaic cell can be used to decrease the adverse economic effects of unpredicted wind saturation in the deregulated system. This paper presents consistent, competent, and effective operating schemes for the hybrid operation of solar PV and wind farms to maximize the economic profit by minimizing the imbalance cost, which occurs due to the mismatch between the actual and predicted wind speed. Modified IEEE 14-bus and modified IEEE 30-bus test systems have been used to check the usefulness of the proposed approach. Three optimization techniques (i.e., Sequential Quadratic Programming (SQP), Smart Flower Optimization Algorithm (SFOA), Honey Badger Algorithm (HBA)) have been used in this work for the comparative study. Bus Loading Factor (BLF) has been proposed here to identify the most sensitive bus in the system, used to place wind farms. The SFOA and HBA optimization technique has been used first time in this type of economic assessment problem, which is the novelty of this paper. The Bus Loading Factor (BLF) has been introduced here to identify the most sensitive bus in the system. After implementing the work, it has been seen that the operation of the solar PV system has reduced the adverse effect of imbalance cost on the renewable integrated deregulated power system.

Efficient Hybrid Algorithm Solution for Optimal Reactive Power Flow Using the Sensitive Bus Approach

This paper presents the design and application of an efficient hybrid algorithm for solving the Optimal Reactive Power Flow (ORPF) problem. The ORPF is formulated as a nonlinear constrained optimization problem where the active power losses must be minimized. The proposed approach is based on the hybridization of Particle Swarm Optimization (PSO) and Tabu-Search (TS) technique. The proposed PSO-TS approach is used to find the settings of the control variables (i.e. generation bus voltages, transformer taps, and shunt capacitor sizes) which minimize transmission active power losses. The bus locations of the shunt capacitors are identified according to sensitive buses. To show the effectiveness of the proposed method, it is applied to the IEEE 30 bus benchmark test system and is compared with PSO and TS without hybridization, along with some other published approaches. The obtained results reveal the effectiveness of the proposed method in dealing with the highly nonlinear constrained nature of the ORPF problem.

An optimisation model based approach for power systems voltage stability and harmonic analysis

This paper presents a novel optimisation problem formulation for power systems voltage stability and harmonic analysis. The purpose is to evaluate the maximum loadability of an electrical power system considering voltage magnitudes, active/reactive powers, total and individual harmonic distortion limits as inequality constraints. The impact of power quality on the maximum loadability margin is evaluated based on the results of the optimisation problem solved by interior-point method and the proposed indices in which Lagrange multipliers are used to identify sensitive buses of electrical systems due to power quality degradation and voltage instability. Simulations are carried out using IEEE 30-bus power system assuming the insertion of non-linear loads to validate the use of the proposed method and show the applicability of the indices based on Lagrange multipliers for the assessment of both voltage stability and harmonic distortion. Results are compared with the traditional modal analysis to validate the ability of the proposed method for identifying the most critical buses of the system.

Photovoltaic Placement for Losses Reduction and Voltage Stability Enhancement in the Port Moresby System, Papua New Guinea

The power grid in the capital city of Papua New Guinea, Port Moresby, still experiences problems of voltage stability and power losses due to many factors which is the common problem that most power systems continue to mitigate until today. The factors that give rise to these problems are the imbalance between generation and load and the long-distance of transmission lines. A possible solution to counteract these problems is to integrate photovoltaic systems into the power grid, especially at the load distribution network. This paper presents PV placement for Port Moresby system by using two stages, which are (1) identification of location with good irradiance then (2) determination of PV location by minimizing power losses and improving the voltage profile. This alternative approach is considered because Port Moresby city is situated in a location that is exposed to a significant amount of solar radiation of about 1976 kWh/m2 GHI annually. Therefore, this makes Port Moresby a suitable location to utilize this type of renewable energy technology. This research provides an analysis of the power flow within the Port Moresby grid through simulation using the Newton-Raphson method. The analysis and simulations are performed to identify the most sensitive buses within the system. Based on their high irradiance levels, these specific areas are identified as the best possible areas for integrating the photovoltaic system.

Research on distributed networked unbalanced harmonic control combined with APF

In order to solve the unbalanced harmonics problem of multi-source and multi-inverter system, a networked hierarchical control approach is proposed, based on the structure of hierarchical control and combined with active parallel filters (APF). In the control approach, the distributed generator (DG) consists of primary and secondary control. In the primary controller and the secondary controller, some basic controls are proposed and modified, which maintain the stable operation of the system. Similarly, a DG compensation and APF-coordinated compensation controller are designed, which coordinate with each other to control the power quality of the system. When the DG compensator cannot fully compensate the sensitive load bus (SLB) by itself, the APF controller can calculate compensation through coordinated control management, then using the APF auxiliary compensator for compensation. Not only does the proposed approach compensate the voltage unbalanced harmonic at SLB, but it also improves the precision of power distribution and load current sharing. Finally, simulation results can validate the effectiveness and feasibility of the proposed approach.

Secondary‐control‐based harmonics compensation scheme for voltage‐ and current‐controlled inverters in islanded microgrids

In this study, a coordinated control scheme is proposed for sharing harmonics compensation effort among voltage and current controlled mode (VCM and CCM) inverters in islanded microgrids. In this method, the voltage harmonics compensation of sensitive bus (SB) is achieved by using secondary control as well as virtual impedance and admittance loops in primary control of VCM and CCM units. The limited capacity of the inverter is taken into account for harmonics compensation. Photovoltaic (PV) systems are considered as CCM units. The harmonics compensation is mainly performed by VCM inverters. However, in order to prevent these units from overloading, the PV interfacing inverters (CCM units) are called to collaborate in harmonics compensation whenever needed. The results of simulation study in Matlab/Simulink show the effectiveness of this method in coordination of CCM and VCM units.

Weighted Multi-Objective Index-Based Placement of Power Quality Disturbance Mitigating Devices in DG Environment

In recent years, the Electrical Distribution system is operated with the integration of various Distributed Generators close to its working limits. Some of the D-facts devices such as D-STATCOM, DVR, and UPQC are placed in the Distribution system to enhance the power quality and to improve the overall stability of the system but the placement of these D-Facts devices in DG environment is essential for the overall power quality improvement. In this paper, a novel technique is introduced based on weighted multi-objective function with power quality indicators for finding the most sensitive bus concerning power quality disturbance in the Distribution system. The optimal sensitive bus is identified for integration of Power quality disturbance mitigating devices with Rotating and Static Distributed Generators

Estimation of Dynamic Compensation for Renewable-Based Hybrid DG in Radial Distribution System Using Least Error Iterative Method

In this paper, wind diesel-based hybrid electrical system is proposed as distributed generator (DG) for radial distribution system (RDS). Since renewable-based DGs and especially wind operated electric generating system requires reactive power for its excitation along with the reactive power demand for maintaining the voltage profile at all buses in RDS, a fast and adequate dynamic compensation is required along with DG. The main contribution of this paper is to optimize the amount of reactive power supplied by dynamic compensator using new proposed approach of least error voltage constraint iterative approach. The paper is starting with the selection procedure of most sensitive bus satisfying three voltage stability indices fast voltage security index, line quality factor and voltage stability index followed by the selection of DG optimal size using optimization approach with multiconstraints all together, namely total real and reactive power loss, voltage limits voltage stability indices and voltage stability indices. The result shows how the dynamic compensator can maintain voltage level by releasing additional reactive power with the adjustment of firing angle for different levels for multidynamic load changes.

A probabilistic approach for assessment of financial loss due to equipment outage caused by voltage sag using cost matrix

In the industrial sector, poor power quality (PQ) can malfunction or shut down the processes or equipment, which leads to excessive loss in revenue. During a visit to a chemical industry, it has been observed that equipment ceases operation frequently due to PQ issues, which hinders the completion of consignment within the stipulated time. It has made the industrial authority to feel the need for quantifying the loss of economy due to frequent equipment trip to provide proper immunity to the system against PQ issues. This paper deals with the assessment of financial losses in industrial loads due to voltage sag. Analytical methods considering Monte Carlo simulation technique is implemented for the evaluation of voltage sag due to the occurrence of symmetrical and unsymmetrical faults. Depending on the characteristics of sensitive equipment towards voltage sag, the process trips were evaluated using probabilistic methods for a chemical industry's distribution system. In this paper, a concept of sag score is used to find out the most sensitive buses for the evaluation of the cost of the equipment trip. An energy index is given for the industrial system to find out how much energy is being unused during a voltage sag event. Factors like variable cost, restart cost and hidden cost are influenced by the tripping of sensitive equipment due to voltage sag. The data are collected from the industrial personnel for the evaluation of the proposed methodology.

A Detection Mechanism Against Load-Redistribution Attacks in Smart Grids

This paper presents a real-time non-probabilistic detection mechanism to detect load-redistribution (LR) attacks against energy management systems (EMSs). Prior studies have shown that certain LR attacks can bypass conventional bad data detectors (BDDs) and remain undetectable, which implies that presence of a reliable and intelligent detection mechanism to flag LR attacks, is imperative. Therefore, in this study a detection mechanism to enhance the existing BDDs is proposed based on the fundamental knowledge of the physics laws in the electric grid. A greedy algorithm, which can optimize the core LR attack problems, is presented to enable a fast mechanism to identify the most sensitive locations for critical assets. The main contribution of this detection mechanism is leveraging of power systems domain insight to identify an underlying exploitable structure for the core problem of LR attack problems, which enables the prediction of the attackers' behavior. Additional contribution includes the ability to combine this approach with other detection mechanisms to increase their likelihood of detection. The proposed approach is applied to 2383-bus Polish test system to demonstrate the scalability of the greedy algorithm, and it solved the attacker's problem more than 10x faster than a traditional linear optimization approach.

Probabilistic assessment of static voltage stability in distribution systems considering wind generation using catastrophe theory

With increasing penetration of distributed generations, the importance of the voltage stability assessment of distribution networks has been increased. Considering this situation, a probabilistic model is proposed to evaluate the voltage stability of distribution network integrating wind turbine (WT) units. With this intention, a probabilistic voltage stability index (PVSI) of a radial distribution system with wind power generation is presented. This index investigates the probabilistic risk of voltage collapse for all the buses of system considering uncertainty of WTs. Therefore, the most sensitive bus to the voltage collapse can be identified. The problem model is based on the catastrophe theory that can find the bifurcation point of system. Three-point estimation method is employed to calculate the statistical moments of voltage and PVSI of nodes. Moreover, to estimate the cumulative distribution function of output random variables, the Cornish−Fisher series are used. The performance of the probabilistic index is tested on the IEEE 69-bus radial distribution system where different load models are considered. The results demonstrate that the PVSI can accurately predict the voltage instability condition of the system.

Identification of the Area of Vulnerability to Voltage Sags Based on Galerkin Method

A novel method is proposed to calculate the area of vulnerability (AOV) to voltage sags, which can reflect the relationship between the position of fault occurrence and voltage sags at sensitive buses. Previous methods based on interpolation approach are mainly based on the assumption that the fault voltage magnitude curve has a unimodal shape, which does not hold in all cases. Moreover, the accuracy of polynomial interpolation is largely affected by the selection strategy of sample points, and inappropriate initial points will lead to divergence. To overcome these drawbacks, an effective approach which does not rely on sample results is proposed, where the fault voltage magnitude curve could be any arbitrary shapes. The AOV is derived by solving the parametric fault voltage equations, where Galerkin method is used to identify the polynomial approximation coefficients. With the order of polynomial approximation increased, an iteration scheme is applied, where the results in each iteration are selected as the initial points of the next iteration. Case studies show that the proposed method can provide very accurate results with high efficiency.

Selection of Sensitive Buses using the Firefly Algorithm for Optimal Multiple Types of Distributed Generations Allocation

Power loss is one aspect of an electric power system performance indicator. Loss of power can have an impact on poor voltage performance at the receiving end. DG integration in the network has become one of the more powerful methods. To get the maximum benefit from synchronizing the system with DG, it is necessary to ascertain the size, location, and type of DG. This study aims to determine the capacity and location of DG connections for DG type I and type II. To address the aim of this paper, a metaheuristic solution based on a firefly algorithm is used. FA can cover up the lack of metaheuristic algorithms that require a long computational time. To ensure that the load bus location solution is selected as the best DG connection location, the input of the load bus candidate has been filtered based on stability sensitivity. The proposed method is tested on IEEE 30 buses. The optimization results show a decrease in power loss and an increase in bus voltage, which affects an increase in system stability by integrating three DG units. FA validation of the evolution-based algorithm shows a significant reduction in computational time.