Realistic Load Model Research Articles

Optimal dynamic multi-microgrid structuring for improving distribution system resiliency considering time-varying voltage-dependent load models

This paper presents an innovative approach for enhancing distribution network resiliency against severe weather-related faults. Given the importance of loads in the resiliency concept, an exact and realistic load model is developed along with the consumption pattern and voltage-dependency of each load type. By defining two technical and economic objective functions, a unique method is used to combine and optimize the objective functions through Imperialist Competitive Algorithm (ICA). Two main strategies, namely the dynamic arrangement of microgrid regions via hourly network reconfiguration as well as grid voltage control through Automatic Voltage Regulation (AVR) of distributed generation facilities, are utilized for increased load restoration. The effect of each of these strategies on grid resiliency is evaluated along with the overall approach efficiency based on simulations on a sample 33-bus network comprising renewable and non-renewable resources and commercial, residential and industrial loads. Using this approach, the strategy to encounter each particular type of failure is obtained.

Impact of Electric Vehicle Load Demand and Energy Storage Device in Integrated Renewable Energy Sources

ABSTRACT The intermittent nature of renewable-based generation may cause the dip or rise generation and load imbalances. Besides, the higher penetration of Electric Vehicles can affect the voltage profile and imbalances. The main contribution of the proposed work is to determine (i) the realistic load model of electric vehicle (EV) charging station (ii) the size of battery energy storage (BES) considering the EV load demand with the most realistic ZIP load. (iii) the cost-benefit analysis and the probabilistic modeling of EV load demand are considered for BES sizing. (iv) minimization of the daily energy loss (v), maximizing the total benefit of the system, (vi) the nature of the electric vehicle load demand has been modeled for size determination of energy storage devices. The fuel cost of the thermal generator has been minimized, and the operating and maintenance cost of the Solar Photovoltaic (PV), and Wind Turbine (WT) have been considered in the objective function. The daily energy loss has been reduced to 30.085%. The voltage deviation has been reduced to 1.165%. The analysis has been carried out for the IEEE-33 bus test system. The iterative Monte Carlo Simulation and Nonlinear Programming have been used to solve the multi-objective problem.

Voltage Regulation and Loss Minimization in Reconfigured Distribution Systems with Capacitors and OLTC in the Presence of PV Penetration

Optimal reactive power management is one of the key operational aspects for efficient planning of distribution system. This study has become more challenging with renewable energy sources integration into the system. Objective of this paper is to address optimal reactive power planning in distribution system using hybrid optimization. This paper presents a comprehensive model for solving capacitor allocation, PV penetration and feeder reconfiguration simultaneously. The objective function considered in this paper includes cost of capacitor, PV and energy loss. The proposed work includes: (i) capacitor allocation using ant lion optimization, (ii) capacitor rating determination using general algebraic modeling system, (iii) reconfiguration of distribution system using genetic algorithm, (iv) investigated different case studies to realize the impact of various load models and load growth factors on reactive power compensation and network reconfiguration, (v) real-time procedure to determine rating of capacitor banks for practical distribution systems, (vi) reactive power dispatch for realistic time-varying load model considering coordination among capacitors, on-load tap changer and photo-voltaic (PV) penetration. The analysis is carried out considering uncertainty of load demand and PV power generation. The proposed methodology is implemented on IEEE 33-bus distribution system and real-time existing Indian distribution network to demonstrate effectiveness of the proposed methodology. It is observed that voltage-dependent load models have a significant impact on system performance and rating of capacitor banks. The proposed strategy ensures optimal solution compared to other existing techniques.

Decentralized Additive Increase and Multiplicative Decrease-Based Electric Vehicle Charging

Electric vehicle (EV) transition and low-cost renewable energy generation are putting power grid under a challenging transformation. Number of power electronics actuators connected to the grid is increasing, and the legacy control methods employed on the grid are not responsive to this growing demand. Thus, the grid integration of EVs and their charging management requires a system-wide solution that is scalable, autonomous, and stable. In this article, we investigate two very complex networks: Internet and power grid in the context of controlling mass-scale EV charging problem. We adapt the well-known additive increase-multiplicative decrease (AIMD) algorithm used in the Internet congestion control to EV charging in a distributed fashion. We develop an adaptation of the Internet's congestion control method for power grid considering the unique grid constraints using a decentralized concept. The advantage of the proposed method lies in its low-cost (memory-less) congestion detection mechanism based on only local voltage measurements. Results show that decentralized AIMD can successfully help flatten the peak loading caused by high EV penetration. To test the algorithm, a distribution grid model is designed based on IEEE 37-node test feeder with realistic load modeling. Finally, the results are presented in comparison with two other control architectures.

Multi-Objective Demand Side Management at Distribution Network Level in Support of Transmission Network Operation

This paper proposes a methodology for advanced demand side management (DSM) in the distribution network (DN), catering at the same time for the requirements of the network operator, transmission or distribution, the available flexibility of the demand side, and the preservation of network performance. The basic premise of the study is that the distribution network operator is providing flexibility to the transmission system operator through load shaping. Different, one or more, indicators can be chosen to assess preservation of network performance. In this paper, for illustrative purposes of the methodology, the steady state voltage stability index, namely the load margin, is chosen as the network performance indicator. This is evaluated before and after a DSM action, in order to analyse the possible effect of DSM on network loadability. Load at each DN bus is represented using a realistic composite load model comprising controllable and uncontrollable loads. The DSM is initially performed based on optimal power flow calculation to ensure that the distribution system load profile at the grid supply point follows the required (pre-specified) load profile during a 24 hour period. Following this, a particle swarm optimisation is used to modify DSM program in those time steps of the planning horizon where load margin is reduced. The methodology is illustrated on a number of case studies using modified IEEE 33 bus distribution network model. The results illustrate the extent to which the available flexibility of demand can be used in support of transmission network operation when the preservation of network performance and appropriate load modeling are considered.

Information extraction from effective descriptor variables in reconstruction of power system security region by considering correlation between loads

Summary In a power network, timely and accurate security assessment has been noted as the major concern of operators in secure operation of the power system. In this paper, power system security region has been constructed by using the retrieval of power system's hidden information. In fact, variables of a power system contain information regarding the status of power system security. Therefore, in order to overcome the complexity and experience-based selection problems, descriptor variables of the power system security have been extracted by using feature extraction techniques. Also, taking the correlation between the load busses of power system into account, a realistic load modeling has been considered based on the copula modeling technique. These methods have been analyzed to opt the most effective approach, based on the mutual information index, average correlation coefficient index, and generalization error rate. The simulation results for the IEEE 9-bus, IEEE 118-bus, and IEEE 300-bus test systems have demonstrated the effectiveness of the proposed method in the security region reconstruction with high information content (HIC). Rigorous analyses have also shown the interdependency of load correlation towards the complexity of implementation, which as a result, achieving a lower-dimensional dataset with a lower classification error and a more obvious separation among the security classes is attainable.

Energy Saving Using D-STATCOM Placement in Radial Distribution System under Reconfigured Network

Abstract High R/X ratio and significant voltage drop causes substantial power losses along the distribution network. In this paper optimal location and size for D-STATCOM is determined for radial distribution networks under reconfigured network to reduce the power loss which in turns save the energy and environment. The main contribution of the paper is: • D-STATCOM allocation using index vector method for radial distribution network with and without reconfiguration, • D-STATCOM size calculation using variational techniques for RDS with and without reconfiguration, • Impact of CP, CI, CZ, and realistic ZIP load model including load growth on D-STATCOM placement, • Energy Saving with improvement in voltage profile, reduction in power losses with D-STATCOM placement under reconfigured network, • Cost analysis with and without D-STATCOM Placement under reconfigured network, • Results are compared with existing technique proposed in literature. The proposed method is tested for D-STATCOM allocation in IEEE 69-bus radial distribution systems. Results show the considerable improvement in voltage profile, reduction in losses and, energy saving under reconfigured network.

Optimizing energy and demand response programs using multi-objective optimization

This paper proposes a new multi-objective day-ahead market clearing (DAMC) mechanism with demand response offers, considering realistic voltage-dependent load modeling. This paper presents several objectives such as Social Welfare Maximization including demand response offers (SWM), Load reduction Minimization ( $${P}_{\mathrm{red}}{M}$$ ), and Load Served Error (LSE) minimization. Energy and demand-side reserves are cleared through co-optimization process. The proposed approach is particularly suitable for stressed system conditions, where demand elasticity alone cannot yield a feasible optimal solution. The feasible solution is obtained by invoking demand-response offers. Here, multi-objective Strength Pareto Evolutionary Algorithm 2+ (SPEA 2+) has been used to solve the proposed DAMC problem. This paper emphasizes the requirement for selecting judiciously, a combination of objectives best suitable for the DAMC. The effectiveness of proposed DAMC scheme is confirmed with the results obtained from IEEE 30 bus system. It is assumed that all the generators and loads participate in DAMC. Two different cases—one with constant load modeling and the other with the voltage-dependent load modeling—have been simulated at stressed loading conditions. When loads are modeled as the voltage dependent, then it is shown that SWM and $${P}_{\mathrm{red}}{M}$$ are not valid single or multiple objectives with this load model, due to reduction in load served. With voltage-dependent load modeling, SWM and LSE minimization are best suited objectives to be optimized simultaneously. The obtained Pareto optimal front allows system operator to make a better decision regarding compromise between the conflicting objective functions.

Multi-Objective based Congestion Management using Generation Rescheduling and Load Shedding

This paper proposes a new congestion management (CM) approach by using the generation rescheduling and load shedding, with the realistic voltage-dependent load modeling. The paper presents several objective functions such as generation and load shedding cost minimization (GLCM)/social welfare maximization including demand response offers (SWM), load shedding minimization ( $P_{\rm shd}$ M), load served maximization (LSM), and load served error minimization. To the best of our knowledge, all previous CM efforts considered constant load models. Using voltage-dependent load models, the paper clearly brings out the inappropriateness of conventional single objectives for CM, such as GLCM/SWM and $P_{\rm shd}$ M, due to the reduction of amount of load served. Therefore, multi-objective optimization is required and the objectives can be judiciously combined depending on the loading condition. Multi-objective strength pareto evolutionary algorithm 2+ has been employed to solve the proposed CM problem. The effectiveness of the developed approach is confirmed from the simulation results on IEEE 30 bus test system.

Co-optimization of Energy and Demand-Side Reserves in Day-Ahead Electricity Markets

Abstract This paper presents a new multi-objective day-ahead market clearing (DAMC) mechanism with demand-side reserves/demand response (DR) offers, considering realistic voltage-dependent load modeling. The paper proposes objectives such as social welfare maximization (SWM) including demand-side reserves, and load served error (LSE) minimization. In this paper, energy and demand-side reserves are cleared simultaneously through co-optimization process. The paper clearly brings out the unsuitability of conventional SWM for DAMC in the presence of voltage-dependent loads, due to reduction of load served (LS). Under such circumstances multi-objective DAMC with DR offers is essential. Multi-objective Strength Pareto Evolutionary Algorithm 2+ (SPEA 2+) has been used to solve the optimization problem. The effectiveness of the proposed scheme is confirmed with results obtained from IEEE 30 bus system.

Capacitor Allocation in Radial Distribution System with Time Varying ZIP Load Model and Energy Savings

Abstract In this paper, novel method based on loss sensitivity approach is utilized to determine optimal locations and size of the capacitors in radial distribution system to reduce power losses and improve voltage profile. Reduction in power loss enhances energy efficiency in distribution system also releases feeder capacity. Distribution system has combination of different type of loads (Industrial, commercial and Residential). Load models have significant impact on selecting capacitor size for better deployment of reactive power support. The main contribution of the paper is: (i) Capacitor allocation for radial distribution network using sensitivity approach, (ii) capacitor allocation and sizes calculation for radial distribution system with load growth and winter load variations, (iii) comparison of the results obtained with single and multi-capacitors placement with load growth and load variations, (iv) The loss savings and overall cost savings per annum with capacitors placement. In this paper we considered the impact of time varying load flow with realistic load model. The load growth factor is considered in the study which is essential for the planning and expansion of the existing systems. The impact of the realistic load model as ZIP load model has been considered for study of the systems. The results have been obtained for the distribution network of UK Distribution Corporation consisting of 38 buses.

Analysis of Mesh Distribution Systems Considering Load Models and Load Growth Impact with Loops on System Performance

The distribution system is the final link between bulk power system and consumer end. A distinctive load flow solution method is used for analysis of the load flow of radial and weakly meshed network based on Kirchhoff’s Current Law (KCL) and KVL. This method has excellent convergence characteristics for both radial as well as weakly meshed structure and is based on bus injection to branch current and branch-current to bus-voltage matrix. The main contribution of the paper is: (i) an analysis has been carried out for a weekly mesh network considering number of loops addition and its impact on the losses, kW and kVAr requirements from a system, and voltage profile, (ii) different load models, realistic ZIP load model and load growth impact on losses, voltage profile, kVA and kVAr requirements, (iii) impact of addition of loops on losses, voltage profile, kVA and kVAr requirements from substation, and (iv) comparison of system performance with radial distribution system. Voltage stability is a major concern in planning and operation of power systems. This paper also includes identifying the closeness critical bus which is the most sensitive to the voltage collapse in radial distribution networks. Node having minimum value of voltage stability index is the most sensitive node. Voltage stability index values are computed for meshed network with number of loops added in the system. The results have been obtained for IEEE 33 and 69 bus test system. The results have also been obtained for radial distribution system for comparison.

Mesh distribution system analysis in presence of distributed generation with time varying load model

With the implementation of competitive electricity supply system all over the world, there is the need of optimal utilization of the existing generation sources at the same time to curtail the generation from the conventional power plants and add the renewable sources generation looking into the environmental concern and limitation of the fossil fuels. This has lead to the motivation for the studies on the integration of distributed resources to the grid. In this paper optimal locations and sizes for DG is determined for weakly meshed distribution networks based on the sensitivity method. Novel method based on loss sensitivity is used in this paper to determine optimal size and location of DGs. The modified Novel method is proposed for DG allocation. The main contribution of the paper is: (i) distributed generation allocation for mesh network using sensitivity approach, (ii) modified Novel method for DG allocation and sizes calculation for meshed distribution system with load variations, (iii) comparison of the results obtained with single and two DG placement with load variations, (iv) the loss savings and overall cost savings per annum with single and two DGs placement with load variations. In this paper we considered the impact of time varying load flow with realistic load model. The realistic ZIP load model has been considered for study. The results have been obtained for a distribution network of UK Distribution Corporation consisting of 38 buses. The results have also been obtained for radial distribution system for comparison.

Demand Response for Residential Appliances via Customer Reward Scheme

This paper proposes a reward based demand response algorithm for residential customers to shave network peaks. Customer survey information is used to calculate various criteria indices reflecting their priority and flexibility. Criteria indices and sensitivity based house ranking is used for appropriate load selection in the feeder for demand response. Customer Rewards (CR) are paid based on load shift and voltage improvement due to load adjustment. The proposed algorithm can be deployed in residential distribution networks using a two-level hierarchical control scheme. Realistic residential load model consisting of non-controllable and controllable appliances is considered in this study. The effectiveness of the proposed demand response scheme on the annual load growth of the feeder is also investigated. Simulation results show that reduced peak demand, improved network voltage performance, and customer satisfaction can be achieved.

Capacitor Allocation in Unbalanced Distribution System under Unbalances and Loading Conditions

It is well known fact that distribution systems can operate under unbalanced loading conditions, means that the distribution system planner have to account for any unbalances in the system for reliable operation of the system. In this paper optimal sizes and locations of capacitors is determined using Index Vector method in unbalanced radial distribution system (ubds). In this paper two types of load unbalances and different loading conditions are considered to investigate its impact on optimal capacitor sizes and locations. The main objective of this paper is:•Finding optimal size and locations of capacitors in ubds.•Impact of different loading conditions (low, medium and high loading) on optimal placement of capacitors in ubds is evaluated.•Impact of type-A and type-B unbalances on voltage profile, voltage unbalance, total power losses and cost of energy losses in ubds is determined.•Impact of type-A and type-B unbalances on optimal capacitor allocation problem is addressed.•Impact of realistic load model as ZIP load model has been considered in optimal capacitor placement problem.•Computing required amount of capacitive reactive power to minimise total power losses and improve voltage profile under different load unbalances, different loading conditions and realistic ZIP load model.

Comparison of optimal capacitor placement methods in radial distribution system with load growth and ZIP load model

In this paper, a combined power loss sensitivity (PLS) index-based approach is proposed to determine the optimal location of the capacitors in the radial distribution system (RDS) based on the real and reactive combined loss sensitivity index, as capacitor placement not only reduces real power loss with voltage profile improvement but also reduces reactive power loss due to the reactive power compensation in the network. The results have been obtained with the existing methods of power loss index (PLI) and index vector (IV) method for comparison. Besides, the optimal placement has been obtained with the proposed method as well as existing methods and the total kVar support has been obtained. In addition, the results of net cost savings for the 10-, 34-, and 69-bus systems are obtained for comparison. Moreover, the results have been obtained for a large system of 85 buses to validate the results with combined sensitivity based approach. Furthermore, the load growth factor has been considered in the study which is essential for the planning and expansion of the existing systems, whereas the impact of the realistic load model as ZIP load model has been considered for the study of all the systems.

Using a spatially realistic load model to assess impacts of Alaskan glacier ice loss on sea level

[1] Ice loss from glaciers results in highly nonuniform patterns of sea level change due to the effects of self-attraction and loading. To quantify these spatial effects, it is necessary to obtain an ice load model that is both spatially realistic and regionally complete. We demonstrate a technique to produce such a model for the Alaskan glaciers by combining mass balance rates from a Gravity Recovery and Climate Experiment (GRACE) mascon solution with realistic glacier geometries. This load model can be used to solve the “sea level equation” to determine gravitationally self-consistent sea level and gravity rates. The model predicts a significant drop in relative sea level in the near field of the glaciers, with coastal rates of around −9 mm/yr (compared to a global average rise of 0.2 mm/yr) and significant differences to those predicted by a coarser model. The magnitude and sensitivity of these near-field rates imply that the near-field tide gauge records could contain significant information about the spatial distribution of ice loss. Comparison of model gravity rates with an independently produced, spherical harmonic, GRACE solution verifies that our technique can successfully capture the mass changes estimated in the mascon solution within our higher-resolution model. Finally, we use our ice load model to examine the possibility of detecting the effects of ice loss in estimates of ocean bottom pressure (OBP) from GRACE. We use the model to simulate the effects of GRACE signal leakage and show that the OBP signal from leakage has a similar pattern to, but larger amplitude than, the sea level “fingerprint” expected from ice loss.

Investigation of local load introduction methods in aircraft pre-design

Accurate mass estimation of aircraft structures plays an important role during the preliminary design phase. A widespread method for mass estimation is based on the combination of computational structural analysis and a structural sizing algorithm. Based on the results of the structural analysis, the sizing algorithm adjusts the local properties of the aircraft structure (e.g. the local sheet thickness) according to a number of predefined sizing criteria. In case of the often used fully stressed design criterion, a direct relationship between the local stress levels and local sheet thickness is assumed. As the stress distribution is driven by the loads acting on the structure, it is clear that realistic load modeling and load introduction are crucial for accurate mass estimation.This publication presents a comparison of two different load introduction methods used for the mass estimation of transport aircraft wingbox structures. The first method uses low-fidelity SMT (shear, moment, torsion) loads introduced into the wingbox structure at the wing rib stations. The second method features high-fidelity nodal loads that allow for the realistic modeling of all wing load types: Aerodynamic and fuel loads are represented as surface distributed pressure loads, engine and landing gear loads are modeled as local loads introduced through dedicated load interfaces. The wingbox of a generic long range aircraft based on the DLR-F11 configuration served as a test model for the qualitative and quantitative comparison between the two load introduction methods. The switch from SMT to nodal loads resulted in a small but significant increase of 4% in wingbox mass. Subsequent analyses revealed that this increase was mainly caused by the use of nodal loads modeling for fuel loads, landing gear loads and engine loads. Surprisingly, the use of nodal aerodynamic loads instead of SMT loads did not have a significant impact on the structural mass of the wingbox. This suggests that aerodynamic loads, which are the predominant driver for the wingbox mass, are accurately represented by SMT loads.

Adaptive Transfer Function Estimation of a Notional High-Temperature Superconducting Propulsion Motor

In this paper, the application of a novel time-frequency analysis tool for the online estimation of the transfer functions of a notional high-temperature superconducting (HTS) marine propulsion motor is demonstrated. A detailed simulation model of the notional HTS motor with a realistic load modeling of sea states to produce torque oscillations is utilized for the analysis. A method is presented for the online near real-time estimation of transfer functions between the torque oscillations and the concomitant variations in the field current and mechanical speed of the HTS motor. The transfer functions, obtained by using the novel method, are compared with the results from a traditional offline transfer function estimation technique.

A parametric study of composite footbridges under pedestrian walking loads

This paper presents a realistic load model developed to incorporate the effects induced by people walking in the dynamical response of footbridges. The effect of the human heel was also incorporated in the dynamical load representation. The investigated structural model was based on several footbridges, with main spans varying from 10 to 35 m. The proposed computational model adopted the usual mesh refinement techniques present in finite element method simulations. The results obtained throughout the investigation showed that the design standards could produce unsafe values since they are based on excessively simplified load models. Hence it was detected that this type of structure can reach high vibration levels that can compromise the footbridge user’s comfort and especially its safety.