Load Reactive Demand Research Articles

Optimal capacitor planning for power factor improvement using hybrid particle swarm and harmony search optimization

Industrial loads reduce the Power Factor (PF) of supply systems, causing increases in power losses, damaging equipment and higher utility bills. Optimization techniques are used in planning reactive sources to improve PF of power systems. However, conventional techniques suffer difficulties in passing over local optimal, divergence risk, constraints handling or computing higher order derivatives. Herein, the hybridization of Particle Swarm and Harmony Search Algorithm (PS – HSA) is developed for optimal capacitor planning to improve PF, and comparison is made with the Enhanced Particle Swarm Optimization (EPSO) and Improved Adaptive Harmony Search Algorithm (IAHSA). The test systems are the Modified IEEE 6 and 16 buses and nodes respectively. To create semblance of industrial load dominated power systems, the test networks were modified by increasing the reactive load demand at all buses of the IEEE 6 and 16 by 50% and 70% respectively. The capacitor is modelled as static shunt-controlled element deployed to inject reactive power at buses/nodes. Results show that for IEEE 6 buses, PF improved from 0.68 to 0.8983, 0.8986 and 0.8992 with EPSO, IAHSA and hybrid PS – HSA respectively. Similarly, in IEEE 16 nodes, PF improved from 0.76 to 0.9439, 0.943, and 0.944 with EPSO, IAHSA and hybrid PS – HSA respectively. Furthermore, real power losses reduced from 16.94 MW to 14.03 MW in IEEE 6 buses, translating to 17.2% reduction with the hybrid PS - HSA. While in IEEE 16 nodes, reduction is from 0.719 MW to 0.69 MW accounting for 4% reduction, also with the hybrid PS - HSA.

Control of grid-connected residential solar-PV system using novel adaptive linear combiner filter for power quality improvement

ABSTRACT A grid-connected residential photovoltaic (PV) system has been proposed using novel adaptive linear combiner filter-based control for power quality (PQ) improvement. In the present work, novel adaptive linear combiner (ALC) filter-based control-based control has been proposed to generate reference current. MATLAB/Simulink software is used to develop the two-stage grid-connected residential PV. The proposed control is tested in MATLAB/Simulink2018(a) under nonlinear, linear load and variable input and validated experimentally on prototype hardware. The performance of the proposed ALC filter-based control has been analyzed and compared with that of conventional synchronous d-q control. It has been observed from results that THD in grid current using proposed control is 3.74% whereas using conventional d-q control THD is 4.75%. Proposed control provides more efficient performance by improving the PQ of the system by compensating the harmonics and reactive load demand. Harmonic distortion in the grid current is within the limits as per IEEE-1547. Furthermore, proposed control has better transient response viz. settling time, under shoot and overshoot in DC link voltage during grid connection of rooftop PV system and provides, reduced complexity due to absence of phase lock loop (PLL), thus less sampling time, better accuracy, ease of implementation, and adaptability.

Hierarchical distributed control approach for multiple on-site DERs coordinated operation in microgrid

Micro grid (MG) is a self-controllable small-scale network developed to flexibly manage distributed energy resources (DERs). In this paper, an interlinked three-layer distributed control framework is proposed for the coordinated operation of multiple DERs in MG. In the bottom layer, an inner double-loop voltage and current controller is incorporated with a power droop controller for DER primary voltage and frequency regulation, which explores the fast response capability of DERs to counterbalance load fluctuations in MG. In the middle layer, a distributed secondary frequency and voltage control strategy based on the finite-time discrete consensus theory is implemented to correct the DER frequency and voltage offset in the bottom layer, and the proportional allocation of MG reactive load demands among multiple DERs is also achieved. In the upper layer, a distributed economic dispatch algorithm based on finite-time discrete consensus is implemented to minimize DERs total generation cost by optimizing DER active power reference coupled with the middle and bottom layers. Simulation results demonstrated that the proposed three-layer hierarchical distributed control approach is flexible for the plug-and-play behaviors of DERs and can achieve satisfactory reactive power share among multiple DERs; in addition, the approach effectively regulates DER voltage and frequency and ensures their low-cost operation.

Performance of Type-4 Direct Driven PMSG Based Wind Energy Conversion System under Nonlinear Load Demand

The wind power installed capacity in wind power generation increasing day by day and having a substantial amount of share in total electrical power generation. As a result, there is lot of research going on in wind power generation system for the improvement in its steady-state and transient operation by choosing better controllers. In this paper, the control schemes have been developed for the switching of power converters which interfaced with common back-to-back dc-link in Type-4 PMSG based WECS configuration. The proposed system has been tested under non-linear reactive load demand, the controllers of generator-side and grid-side converters operates independently to fulfill the active and reactive power demand, by maintaining the DC link voltage constant. The performance of proposed Type-4 PMSG based WECS system has been evaluated in MATLAB/SIMULINK software under dynamic operation and simulation results verify the proposed control scheme.

Hybrid stochastic/robust scheduling of the grid-connected microgrid based on the linear coordinated power management strategy

It can be predicted that the future power system, especially microgrids (MGs) will consist of many different sources and storages. In this regard, many researches have been conducted on different energy management strategies to improve power system adequacy indices. This paper presents a hybrid stochastic/robust coordinated power management strategy (CPMS) to simultaneously improve the flexibility, reliability and security indices of MG in the presence of electric vehicles (EVs), energy storage system (ESS), distributed generation (DG) and demand response programming (DRP). At first, this paper models the original problem which minimizes the difference between MG operation and reliability costs and its flexibility and security benefits considering MG optimal power flow constraints. This problem is non-linear programming (NLP) that is generally resulted in the local optimal, hence, this formulation is converted into linear programming (LP) using the first-order expansion of Taylor’s series for linearization of power flow equations and a polygon for linearization of circular inequalities. In addition, the active and reactive load demand, energy price, active power of renewable energy source (RES), different parameters of EVs, and availability/unavailability of MG equipment are considered as uncertain parameters. Hence, the hybrid stochastic/robust optimization with coupling the bounded uncertainty-based robust optimization (BURO) and scenario-based stochastic programming (SBSP) is used for the presented problem for modeling of uncertain parameters. Finally, the proposed method is applied to 32-bus MG using GAMS software. The numerical results show the capabilities of the proposed strategy to improve power system adequacy indices determining the optimal power scheduling for MG devices.

Distributed Consensus for Output Power Regulation of DFIGs With On-Site Energy Storage

This paper proposes a novel distributed control architecture for output power regulation of doubly fed induction generator (DFIG) based wind turbines (WTs) with on-site battery energy storage systems (BESSs). The proposed distributed control architecture receives information from adjacent WTs+BESSs to control the DFIG's grid side converter (GSC) and the storage unit for output active/reactive power regulation and energy management purposes. The proposed method guarantees the equal active power sharing and energy management of WTs+BESSs in various wind speed conditions. A distributed controller is also designed to respond to the reactive power demand and share the reactive load demand between the GSC and BESS controllers based on their capacities. Furthermore, a controller is designed to account for the communication delays caused by the communication systems based on the IEEE standards. The proposed method is tested on the modified IEEE 14-bus power system with 10 WTs+BESSs.

A Reliability-Oriented Fuzzy Stochastic Framework in Automated Distribution Grids to Allocate $\mu$ -PMUs

This paper proposes a reliability-oriented stochastic aggregated integer linear framework for full observability of the automated distributed systems based on the $\mu $ -synchrophasor units. The $\mu $ -synchrophasor unit as a newly introduced high-tech device makes it possible for an accurate and high-speed measurement of the voltage and current waveforms in the distribution systems. This paper proposes a multi-stage strategy for the $\mu $ -synchrophasor unit placement together with the communication system requirements in the reconfigurable distribution systems, considering the zero-injection constraints in the model. To determine the optimal topology at the end of each phase, a reliability-based cost function is developed to optimize the customer interruption costs and power losses simultaneously. In order to model the uncertainties of forecast error in the active and reactive load demands as well as the failure rate and repair rate parameters, a stochastic framework based on the fuzzy cloud theory is employed. The proposed bi-level mixed integer linear programing approach is used to co-optimize the network switching scheme as well as the optimal $\mu $ -synchrophasor positions and communication infrastructure costs in the same framework. The simulation results on a practical test system verify the observability of the automated reconfigurable distribution system during the reconfiguration process.

A Unique Concept of Limited Grid Capacity and Voltage-Frequency Control of an RES Based Rural Electrification System

Abstract This paper presents dynamic performance analysis of a PV-biogas-biodiesel-grid based hybrid power system designed for rural electrification. The linear small signal model of the system using power balance equations is developed and small step change in solar incident power and active and reactive load demand of the system are applied. The objective of this work is to control the system voltage (magnitude and angle), frequency and to operate the grid for controlled supply. The voltage source inverter (VSI) used for photovoltaic (PV) system provides active and reactive support and controlled to maintain system voltage and frequency constant. The biogas and bio-diesel engine are equipped with electronic governor control, uses synchronous generator (SG) with automatic voltage regulator (AVR). The variation in load demand is balanced by the biogas, bio-diesel generator and by PV system keeping grid supply constant. The system is simulated in MATLAB and the performance is analyzed for variable loads and input solar power. The PI controllers are applied and their gains are optimized using ISE method. The state variables are plotted and their oscillations are stabilized within few seconds. The system voltage, frequency and grid are controlled effectively.

A Multiobjective Minimax Regret Robust VAr Planning Model

This paper proposes a risk-based mixed integer quadratically-constrained programming model for the long-term VAr planning problem. Risk aversion is included in the proposed model by means of regret-based optimization to quantify the load shedding risk because of a reactive power deficit. The expected operation and expansion costs of new installed reactive power sources and load shedding risk are jointly minimized. Uncertainty in the active and reactive load demands has been included in the model. An $\epsilon$ -constraint approach is used to characterize the optimal efficient frontier. Also, discrete tap settings of tap-changing transformers are modeled as a set of mixed integer linear equations which are embedded into an ac optimal convex power flow. Computational results are obtained from a realistic South and South–East Brazilian power system to illustrate the proposed methodology. Finally, conclusions are duly drawn.

Voltage control through reactive power support for WECS based hybrid power system

This paper presents a novel technique for voltage and reactive power control a multi wind generator based hybrid power system. The proposed configuration consists of wind energy conversion system (WECS) comprising number of wind turbines each having doubly fed induction generator (DFIG), and power generation from biomass source using synchronous generator (SG). The dynamics of the system is analyzed with the step change in inputs applied in both reactive load demand and wind speed. The analysis is focused on the voltage and reactive power control of the hybrid power system using reactive capability of the load side converter (LSC) of DFIG. When the reactive load and thereby the terminal voltage deviates by a small amount, the LSC works as a reactive power generator. A PI control is used in LSC and it provides the effective control of system voltage.

Electricity market equilibrium of nonlinear power systems with reactive power control

The impact of reactive power control on the electricity market equilibrium is investigated. The effects of limitations on the reactive power generation and absorption, and load power factor adjustments, are examined using a novel electricity market equilibrium model that solves large-scale nonlinear power systems with asymmetric strategic firms. The algorithm implemented employs the linear supply function theory for bid-based pool markets. AC power flow analysis is used to represent the electricity network, incorporating variable price-responsive active and reactive load demands. The significance of the reactive power modeling in the electricity market equilibrium is demonstrated using the IEEE 14-bus and IEEE 118-bus systems. It is shown that variations on the reactive power in the system result in different market outcomes, as incentives are given to the strategic generating firms to alter their bidding strategies. The convergence characteristics of the IEEE 118-bus system are graphically presented and discussed to demonstrate the superior computational performance of the proposed algorithm in producing results under strict binding constraints and heavy transmission congestion conditions.

Neural networks-based control of active and reactive power of a stand-alone PEM fuel cell power plant

This paper presents a neural networks (NN)-based active and reactive power controller of a stand-alone proton exchange membrane (PEM) fuel cell power plant (FCPP). The controller modifies the inverter modulation index and the phase angle of the ac output voltage to control the active and reactive power output from an FCPP to match the terminal load. The control actions are based on feedback signals from the terminal load, output voltage and hydrogen input. The validity of the controller is verified when the FCPP model is used in conjunction with the NN controller to predict the response of the power plant to: (a) computer-simulated step changes in the load active and reactive power demand, and (b) actual active and reactive load demand of a single family residence. The response curves indicate the load following characteristics of the model and the predicted changes in the analytical parameters highlighted by the analysis.

New tool for reactive power planning

A new tool for planning reactive power compensation is presented. It is based on the capability chart of the power system, which describes the domain of allowable operation of the system in the plane of total active and reactive load demand. Reliability concepts are used to describe the ability of the power system to face the load; the stochastic approach is adopted because load demand is fundamentally uncertain. Results for the AEP 14 bus test system are presented.

Maximal load demand allocation

The authors address the problem of determining the maximum amount of active and reactive unserved load demand that can be connected to each bus in an electric power system without violation of its operating constraints. This maximal load demand allocation problem, which is associated with each electrical island of a power system operating in a restorative state, is formulated as a mixed nonlinear-integer programming problem. A decoupling procedure partitions the overall allocation problem into a maximal active load demand allocation subproblem and a minimal reactive load demand deallocation subproblem. The approach has been implemented in the form of a computer program and tested using power system models of up to 118 buses. Details of the implementation procedure and some illustrative test results are presented. >

Power systems economic dispatch by a rearranged active-reactive power loss model

The economic dispatch conditions of a power system are evaluated using a rearranged active-reactive power loss model. The active-reactive power loss model is divided into two separate submodels. In this formulation, the network total active and reactive power losses are expressed in terms of the active and reactive powers of the generation buses. The network purely reactive sources are modeled in terms of the total reactive load demand. The advantages gained by this separation are discussed. The parameters of the network submodels are estimated by least squares with a high degree of accuracy from a set of load flow results. Based on the above submodels, the constrained fuel cost function is then minimized to obtain the economic dispatch solutions of the power system under consideration. Results are presented for a standard IEEE test system for a wide range of system load levels. The results obtained by the proposed method are also compared to the economic dispatch solutions based on the active power loss model.