Constant Impedance Load Model Research Articles

Integration of Distributed Generations and electric vehicles in the distribution system

Power quality challenges are a major problem these days because of the significant increase in load demand and the existence of various reasons for disruptions in the distribution system. A voltage sag or a decrease in the magnitude of the line voltage can be brought on by rapid fluctuations in load or distribution system issues. Enhancing the grid current profile, reducing grid voltage sag, and improving other performances can all be achieved through the combination of electric vehicles with distribution generation systems. In this paper, the integration of Distributed Generation with Electric Vehicles in the distribution system has been done to enhance system performances such as true power loss index, imaginary power loss index, voltage deviation index, short circuit current index, cost function, and environmental impact reduction index for 16 bus distribution system in constant impedance, constant current, and constant power load models, or ZIP load models through proper location, sizing, coordinated controlling, and types of Distributed Generation and Electric Vehicle pairs for both charging and discharging modes by adopting Hybrid Genetic Algorithm - Monte Carlo Simulation optimization methodologies. This study's primary goal is to determine the optimal distribution generation and electric vehicle pairing to improve the aforementioned parameters, which will assist researchers in their future planning. Researchers, industry professionals, scientists, and individuals working with Distributed Generation and Electric vehicles in the smart grid will find this statement to be of great use.

A Power Flow Calculation Method Considering High-order Load Models

Given the popularity of new energy and the connection between large power electronic equipment and power system, the operation of power system becomes more complex and requires higher accuracy of power flow calculation. Therefore, a power flow calculation method considering high-order load model is proposed. On the basis of the Newton-Raphson method, when considering the load voltage characteristics, it is necessary to change the variables in the Newton-Raphson method power flow. Therefore, the established polynomial load model is introduced into the Newton-Raphson method, and the effect becomes more obvious with the increase of the order. Finally, constant power, constant current, constant impedance load and fifth order load models are tested in IEEE14-bus system respectively to verify the good accuracy and robustness of the proposed method.

Impact of Passive-Components’ Models on the Stability Assessment of Inverter-Dominated Power Grids

Power systems are experiencing some profound changes, which are posing new challenges in many different ways. One of the most significant of such challenges is the increasing presence of inverter-based resources (ibrs), both as loads and generators. This calls for new approaches and a wide reconsideration of the most commonly established practices in almost all the levels of power systems’ analysis, operation, and planning. This paper focuses specifically on the impacts on stability analyses of the numerical models of power system passive components (e.g., lines, transformers, along with their on-load tap changers). Traditionally, loads have been modelled as constant power loads, being this both a conservative option for what concerns stability results and a computationally convenient simplification. However, compared to their counterparts above, in some operating conditions ibrs can effectively be considered real constant power loads, whose behaviour is much more complex in terms of the equivalent impedance seen by the network. This has an impact on the way passive network components should be modelled to attain results and conclusions consistent with the real power system behaviour. In this paper, we investigate these issues on the ieee14 bus test network. To begin with, we assess the effects of constant-power and constant-impedance load models. Then, we replace a transmission line with a dc line connected to the network through two modular multilevel converters (mmcs), which account for the presence of ibrs in modern grids. Lastly, we analyse how and to which extent inaccurate modelling of mmcs and other passive components can lead to wrong stability analyses and transient simulations.

A comparative analysis for impact of distributed generations with electric vehicles planning

In the approaching years, the utilization of Distributed Generations (DGs) with Electric Vehicles (EVs) will accelerate. Future issues will be exacerbated by the relationship between the distribution system of DGs solely, DGs with Fuel Cell Electric Vehicle (FCEV), and DGs with Extended Plug-in Hybrid Electric Vehicles (Ex-PHEV). This paper discusses the use of a multi-tasking Genetic Algorithm to optimize DGs with EVs planning in distribution systems for load models for rating and placement determination. From a system perspective, the goal of this research is to reduce total real power loss. The various types of DGs with EVs are taken into account from the standpoint of the analysis. Photovoltaic, diesel engines, synchronous condensers, and doubly-fed induction generators are examples of various types of DGs. In this analysis, EV types such as FCEV and Ex-PHEV are considered. Different forms of constant impedance (Z), constant current (I), and constant power (P) load models are included in DGs with EVs planning for improving system performance indices, such as Light-emitting diode, Laptop charger, Personal computer, Tungsten light, and Vacuum tube. The real power loss index (%ILP), the reactive power loss index (%ILQ), the voltage deviation index (%IVD), the short circuit current reduction (%IC), the active power DGs with EVs penetration (% PPWDGs & EVs), and the reactive power DGs with EVs penetration (%PQWDGs & EVs) are all measured in this paper. On the 37-bus test distribution system, the effectiveness of the listed approach was verified.This article is very much useful for researchers, industrial, scientific persons, and those who are working in the smart grid with DGs and EVs.

Volt–Var Optimization and Reconfiguration: Reducing Power Demand and Losses in a Droop-Based Microgrid

Optimal planning and dispatch for satisfying peak demand are challenging, especially for microgrids with significant penetration of renewable energy. In extreme cases such as weather contingencies, microgrid operators may resort to load shedding. Alternatively, conservation voltage reduction (CVR) can be used to decrease the power and energy demand across the network. In this article, a mixed-integer linear programming problem has been formulated for a droop-based microgrid to implement network-wide CVR along with minimal line losses. For planning purpose, optimal sizing and placement of distributed generators (DG) is performed initially. Afterwards, a day-ahead dispatch is generated for these DGs for a realistic hourly load profile considering residential and industrial loads. Besides, network reconfiguration concept has been explored to boost the demand reduction. Furthermore, the effect of using a constant impedance-current-power (ZIP) load model instead of considering the classic constant impedance load model has been tested. The effectiveness of the proposed optimization has been tested on 33 and 69 bus islanded microgrids. The obtained results demonstrate the accuracy of the proposed planning and dispatch formulation, and validate its utility in reducing the power and energy consumption while attracting very low line losses.

Linear Power Flow Method Improved With Numerical Analysis Techniques Applied to a Very Large Network

In this paper, we propose a fast linear power flow method using a constant impedance load model to simulate both the entire Low Voltage (LV) and Medium Voltage (MV) networks in a single simulation. Accuracy and efficiency of this linear approach are validated by comparing it with the Newton power flow algorithm and a commercial network design tool Vision on various distribution networks including real network data. Results show that our method can be as accurate as classical Nonlinear Power Flow (NPF) methods using a constant power load model and additionally, it is much faster than NPF computations. In our research, it is shown that voltage problems can be identified more efficiently when MV and LV are integrally evaluated. Moreover, Numerical Analysis (NA) techniques are applied to the Large Linear Power Flow (LLPF) problem with 27 million nonzeros in order to improve the computation time by studying the properties of the linear system. Finally, the original computation times of LLPF problems with real and complex components are reduced by 2.8 times and 5.7 times, respectively.

Low voltage power grid congestion reduction using a community battery: Design principles, control and experimental validation

By installing a battery storage system in the power grid, Distribution Network Operators (DNOs) can solve congestion problems caused by decentralized renewable generation. This paper provides the necessary theory to use such a community battery for grid congestion reduction, backed up by experimental results. A simple network model was constructed by linearizing the load flow equations using a constant impedance load model. Using this model, an accurate estimate of voltage and overload problems is fed into a receding horizon charge path optimizer. The charge path optimization problem is posed as a linear problem and subsequently solved by an LP solver. The algorithms have been applied and validated on a real-world community battery installation. It was found that the voltages and currents can be controlled to a great degree, increasing the grid capacity significantly. The proposed control framework can be used to safeguard network constraints and is compatible with other battery control goals, such as energy trading or energy independence. Network design formulas are described with which a DNO can quickly estimate the potential (de) stabilization of a community battery on the steady-state voltages and currents in the grid.

Construction Method of Electrical Vehicle Fast Charging Load Model

Electric vehicle (EV) has been increasing recent years, which brings more challenge to power grids, especially impacting on voltage stability. Building accurate EV model is important to evaluate voltage stability. Firstly, EV charging configuration is analyzed. Secondly, a static load model for EV is developed based on charging configuration. Finally, simulations analyze that Rs and Rl in the rectifier impact on voltage stability. The EV load model is developed and constant power, current and impedance (P, Z, I ) load model impacting on voltage stability are compared, and results reveal that loading margin with EV load model is more lower than other load models such as P, Z, I.

GA for enhancement of system performance by DG incorporated with D-STATCOM in distribution power networks

This paper presents the enhancement of voltage profile using distributed generation (DG) incorporated with distribution static synchronous compensator (D-STATCOM) with different load models (DLMs) such as constant power, constant current, constant impedance, composite and reference load models in distribution power networks by using genetic algorithm (GA) from minimization of total real power loss of the system. In this paper, considered the different size of D-STATCOM such as −50 to +50MVAR, −75 to +75MVAR, −100 to +100MVAR, −125 to +125MVAR and −150 to +150MVAR are taken for evaluation of voltage profile of the system buses. The proposed methodology illustrated for IEEE-75 bus test system. This work is very useful for researchers and scientific persons in conjunction with enhancement of voltage profile using distributed generation (DG) incorporated with distribution static synchronous compensator (D-STATCOM) with different load models in distribution power networks.

Balancing distribution systems with three‐phase active front end rectifiers: field experiment results

This study describes field tests of alternative methods to control three-phase active rectifiers to reduce voltage unbalance in low-voltage (LV) distribution systems. The tests show that per-phase control of active power of two residential loads can significantly reduce unbalance throughout an LV feeder shared by 25 homes. Different algorithms, designed to either reduce negative sequence voltage, or phase–neutral (P–N) voltage unbalance using active or reactive power (four algorithms in all), were tested. The algorithm designed to reduce P–N voltage unbalance using active power showed the greatest reduction in median P–N voltage unbalance at the prototypes terminals (up to 87%), the greatest reduction in median current unbalance at the feeder's substation (38%), and was also effective at reducing negative sequence voltage in the feeder. The algorithms controlling reactive power reduced negative sequence voltage, but did not show significant effects on P–N voltage unbalance. Two prototypes were tested at different locations on the same feeder, and the average combined effect of the two prototypes was well predicted by the sum of their individual effects. Some of the results are inconsistent with earlier simulations and laboratory tests which used simple constant impedance load models, highlighting the importance of field trials to validate controller designs.

Congestion management with generic load model in hybrid electricity markets with FACTS devices

The load variations during the entire day specially during the peak hours have substantial impact on the loading pattern of the transmission system. The voltage profile become poor during such situation of peak loading of the network and can lead to congestion during such events. This paper attempts congestion management considering the impact of constant impedance, current, and power (ZIP) load model along with the load variation pattern in a day-a-head hybrid electricity market. The main contribution of the proposed work is: (i) Optimal rescheduling based congestion management for a hybrid market model with three bid offer from generators, (ii) study of the impact of ZIP load model and load variations on rescheduling and congestion cost, (iii) impact of third generation FACTS devices on congestion management, (iv) comparison of results obtained for hybrid market model without and with ZIP load model. The generators offer three block bid structure to the ISO in a day-a-head market for congestion management. The base case economic load dispatch has been obtained for generators and is taken as base case generation output data during the congestion management to obtain new generation schedule. The three block bid structure submitted to the ISO has been modeled as a linear bid curve which is a function of increment/decrement (inc./dec.) of generation within the upper and lower bounds offered for congestion management. The results have been obtained for IEEE 24 bus test systems.

Study on Load Model of PV Generation Planning

In distribution system planning with photovoltaic generations (PVGs), if load is not properly modeled in the simulation, the accuracy of results will be affected. A large number of studies show that load characteristics play a impotrant role in the system analysis. This paper presented the resultant load model, and on this basis, studied the impacts of the constant power load model and constant impedance load model on PV generation planning. Simulation results show that the selection of load models has an important impact on PV generation planning.

An Approach to Determine a Pair of Power-Flow Solutions Related to the Voltage Stability of Unbalanced Three-Phase Networks

This paper proposes an approach to determine a pair of power-flow solutions associated with the voltage stability of unbalanced three-phase networks. The approach is derived from the observations of the multiple three-phase power-flow solutions of a two-bus network. It is found that there are two pairs of solutions at the load bus. The plot of the voltage magnitude of each pair against the power demand at the load bus shows that two possible PV curves can be constructed for each phase. Each of the two curves is a combination of the two pairs of solutions. One of these curves is associated with the voltage stability of the system whereas the other is associated with the imbalance of the three-phase network. Based on the above observations, a constant impedance load model is utilized to calculate the solution associated with the voltage stability of the study system. Then the equivalent complex power load demand is used to calculate the two pairs of solutions, i.e., the multiple three-phase power-flow solutions. Simulation studies have been carried out for the multiple solutions. The results show that there is a point which is directly proportional to the imbalance in the power demand at the load bus. This point is used to set a criterion to differentiate between the two PV curves. Hence, the PV curve which is related to the voltage stability can be determined without the assumption of the linear load model at the start of the study.

Voltage Stability Analysis of Radial Distribution Networks

The paper presents voltage stability analysis of radial distribution networks. A new stability index is proposed to identify the nodes that are on the verge of voltage collapse. The value of the proposed voltage stability index is calculated at each node of the network. A modified load flow method is used for voltage stability analysis. The modified load flow method incorporates composite load modeling and variations in load pattern at each node. The results are compared with the other known methods of voltage sensitivity indices and found satisfactory. A comprehensive comparison with the recently proposed voltage stability index by Chakravorty and Das [1] is presented in this paper. A detailed analysis of effects of different load models on voltage computation and voltage stability are carried out, and it is observed that for voltage stability analysis, a constant impedance load model can be used without losing the sensitivity of load modeling.

Investigation of impacts of different three-phase transformer connections and load models on unbalance in power systems by optimization

This paper investigates the impacts of different three-phase transformer connections and load models on unbalance in power systems. New three-phase transformer models are presented. These models are derived from a new primitive impedance matrix incorporated with positive, negative and zero sequence elements. The constant power and constant impedance load models are discussed. The three-phase models are implemented in a general-purpose optimization software package. Two power systems are used to illustrate the test results. The test results provide assistance to engineers in understanding the effect of different connections on the transformers. This paper also emphasizes that a proper load model should be used; otherwise, an incorrect solution will be obtained.

Effect of Load Models on AC/DC System Stability and Modulation Control Design

This paper investigates important aspects related to the effect of load models on the modulation control design and stability of a modulated ac/dc system. Static load is modeled as a nonlinear function of load bus voltage and dynamic load is modeled by an equivalent induction motor. DC power and reactive power modulations are considered for the modulation controllers. A method for eigenvalue sensitivity calculation is developed to predict the effect of load characteristics on system stability. Eigenvalue sensitivity and simulation results show that static and dynamic load characteristics may have a considerable effect on the system stability. Figure 1 shows an ac/dc power system model used for studying the effect of nonlinear load on system stability. Reactive power modulation gain is obtained via optimal control theory. Figure 2 shows speed response of synchronous generator for a 5% change in reference current (Iref) of the rectifier terminal. Reactive power modulation by static var compensator improves system stability with constant impedance load model. However, reactive power modulation makes the system unstable when the modulation gain is based on constant impedance load model and the actual load is represented by induction motor. Important conclusions resulting from the computations and simulations performed for an integrated ac/dc system are listed below. 1. The dynamic behavior of induction motor load has a significant effect on the system stability. Induction motor in most cases reduces the overall system damping.