Power Flow Balance Research Articles

電力需要・供給バランスを実現する車載型蓄電池の分散型充電管理方策に関する考察

This paper investigates the distributed energy management strategy for the community consists of households equipped with EV/PHEV storage. We consider the power flow balancing between a prediction based power supply and an actual demand of the community. Each agent, a household, is allowed to determine its own storage charging set-point. On the other hand, the utility, which corresponds to the management office of the community, tries to realize a socially optimal solution that fulfills steady state power flow balancing. In order to align the individual decision making of each agent with the socially optimal solution, the utility is allowed to provide an additional price,which conceptually represents tax or subsidy for the agents. By examining the problem structures of EV/PHEV storage charging, we propose a management strategy that consists of the real-time pricing and distributed optimizations. Effectiveness of the proposed price based distributed management strategy is evaluated through numerical experiments.

Efficient energy control strategies for a Standalone Renewable/Fuel Cell Hybrid Power Source

In this paper, four energy control strategies are proposed and analyzed for the standalone Renewable/Fuel Cell Hybrid Power Source (RES/FC HPS). The concept of the load following (LF) and Maximum Efficiency Point Tracking (MEPT) is used to control the fueling rates. A standalone RES/FC HPS uses at least one Renewable Energy Sources (RES) and a Polymer Electrolyte Membrane (PEM) Fuel Cell (FC) as backup source. Photovoltaic (PV) array and wind turbines (WT) farm are used as RES and the surplus of energy during light load stages is stored in hydrogen tank via water electrolysis to fuel the PEMFC. Small-scale RESs and commercially available PEMFCs are interfaced to the common DC bus via power converters and then to the single-phase distribution grid through a voltage source inverter. RES/FC HPS seem to be an efficient alternative for supplying smart houses and isolated sites. This paper proposes a new supervision strategy of the Energy Management Unit (EMU) based on the LF control approach that assures a charge-sustaining (CS) mode for the Energy Storage System (ESS). So, the capacity of the batteries stack can be reduced at minimum if it is directly connected to the DC bus. The ultracapacitors stack compensates dynamically the power flow balance on the DC bus, regulating the DC voltage via a bidirectional buck-boost power converter. Thus, a semi-active hybrid topology is adopted for the ESS having the batteries stack. The MEPT loops ensure an optimized energy management of the RES/FC HPS. The LF strategy designed based on the power flow balance guarantees the load demand through the efficient management of the power flow from RES, FC and ESS, adapting FC energy production to load profile. The FC energy production is controlled via the fueling rates (one is controlled in the LF loop and the other is controlled in the MEPT loop) to maximize the energy consumption indicator: the ratio of the produced energy and the fuel consumed by the FC system during a load cycle. Thus, this paper evaluates the control performances of the four control topologies to fuel the FC stack during an variable RES and load profile. The MATLAB-Simulink® software package is used to model the RES/FC HPS and develop the four EMU strategies. Simulation results shown comparatively the performance of the EMU strategies proposed under different scenarios of RES power generation and load demand.

Fault Recovery of Distribution Network Based on Genetic Algorithm

Fault recovery of distribution network is realized by operating switches to change topological structure of the network. The final destination of fault recovery is power loss minimization, fault isolation and power load transfer. This article has built the mathematical model of fault recovery considering constraints of node voltage, line capacity and power flow balance. The objective function is power loss reduction. Further, the genetic algorithm is used to solve the proposed model. The optimal network structure and recovered power load could be derived through calculation. Finally, the author complied the program with Matlab and tested it on the IEEE33 bus system. The simulation and analysis results have verified the effectiveness of the proposed method. DOI : http://dx.doi.org/10.11591/telkomnika.v12i3.4567 Full Text: PDF

Research on battery storage system configuration in active distribution networks

In this paper, an optimizing model of battery energy storage system (BESS) capacity configuration for active distribution networks (ADNs) is proposed to mitigate the negative effect of distribution systems with distributed generations (DGs), in stability, economy and reliability perspectives. In details, this model involved the charging and discharging limitation and the operation constrains of BESS, as well as the power flow balance of distribution system. Moreover, three optimizing objectives have been presented for the optimal power profile of BESS, including minimizing the voltage fluctuation, reducing the feeder loss and maximizing the consecutive supplied power of ADN, respectively. After the optimization, the BESS capacity is calculated by estimation of the maximum charging and discharging energy. Finally, the simulation results are shown to illustrate the procedure of capacity configuration.

Integration and Operation of a Single-Phase Bidirectional Inverter With Two Buck/Boost MPPTs for DC-Distribution Applications

This study is focused on integration and operation of a single-phase bidirectional inverter with two buck/boost maximum power point trackers (MPPTs) for dc-distribution applications. In a dc-distribution system, a bidirectional inverter is required to control the power flow between dc bus and ac grid, and to regulate the dc bus to a certain range of voltages. A droop regulation mechanism according to the inverter inductor current levels to reduce capacitor size, balance power flow, and accommodate load variation is proposed. Since the photovoltaic (PV) array voltage can vary from 0 to 600 V, especially with thin-film PV panels, the MPPT topology is formed with buck and boost converters to operate at the dc-bus voltage around 380 V, reducing the voltage stress of its followed inverter. Additionally, the controller can online check the input configuration of the two MPPTs, equally distribute the PV-array output current to the two MPPTs in parallel operation, and switch control laws to smooth out mode transition. A comparison between the conventional boost MPPT and the proposed buck/boost MPPT integrated with a PV inverter is also presented. Experimental results obtained from a 5-kW system have verified the discussion and feasibility.

Dynamic stability study of an isolated wind-diesel hybrid power system with wind power generation using IG, PMIG and PMSG: A comparison

This paper presents a comparative study of reactive power control for isolated wind-diesel hybrid power system in three different cases with wind power generation by induction generator (IG), permanent-magnet induction generator (PMIG) and permanent-magnet synchronous generator. The synchronous generator (SG) is used with diesel engine set. A mathematical model of the system based on small signal analysis, is developed considering reactive power flow balance equations. The variable reactive power needed by the system is provided by a static synchronous compensator (STATCOM) when wind power generation is done by IG and PMIG. When permanent-magnet synchronous generator (PMSG) is used for wind power generation, the variable reactive power demand is fulfilled by a voltage source converter (VSC) which is on the load side. A new mathematical approximation model for VSC connected with PMSG is proposed such that the voltage source converter fulfills the increased reactive power requirement of load and also increases its active power equal to the increased input wind power. Proportional and integral (PI) gains of the STATCOM and VSC controllers are optimized using integral square error criterion (ISE). The dynamic responses of the system for small (1%) step increase in load reactive power with and without 1% step increase in input wind power are shown. The paper also shows the dynamic responses of the system for random step change in load reactive power plus random step change in input wind power. The MATLAB/SIMULINK environment is used for simulation.

A scaling approach for high-frequency vibration analysis of line-coupled plates

A scaling approach is proposed for the vibration analysis of line-coupled plates at high frequencies. It extends earlier scaling approaches for an isolated system to coupled systems. Based on the power flow balance in the plate assembly, a general scaling law is derived and a scaled model is built accordingly. Due to the dynamic similitude in a statistical sense, the scaled model is able to simulate the dynamics of the original system at high frequencies. Numerical examples validate the efficiency of the approach and suggest the application of finite element methods in the high-frequency vibration analysis.

Damage identification using combined transient power flow balance and acceleration matching technique

This paper presents a multiobjective optimization formulation to detect and quantify crack damage in beam structures at variable locations. It is implemented at the substructure level where the concept is to balance the instantaneous power flow by equating the input power to the dissipated power and the time rate of change of kinetic and strain energies and power transferred to adjacent substructures. This imbalance is reduced to zero to identify the structural parameters or damages. For improved results, the power balance method is combined with conventional acceleration matching method where the objective is to minimize the deviation between measured and estimated accelerations—no additional sensors are required to incorporate the extra power flow balance criteria. Numerical simulations are performed for a lumped mass system, a planar truss structure, and a cantilever beam of 20 elements with multiple damages to evaluate the accuracy of the proposed method. Effects of noise are also taken into account by contaminating the measured responses with 3%, 5%, and 10% Gaussian noise. The particle swarm optimization is used as the optimization algorithm, and normalized fitness functions are defined for both power flow and acceleration components with weighted aggregation multiobjective optimization technique. The effects of various weighting factors for the combined objective function are also studied. The results demonstrate that improvement in accuracy of damage detection is achieved by the combined method, when compared with previous acceleration only matching method as well as other methods. Copyright © 2013 John Wiley & Sons, Ltd.

Decentralized Controls and Communications for Autonomous Distribution Networks in Smart Grid

The traditional power grid system was constructed in a centralized and radial topology where power is generated and delivered from one end to the other. Conventional methods for unidirectional power flow analysis will no longer be effective to control renewable energy sources implemented at the consumption sector efficiently; new strategies are called for to facilitate the bidirectional flow incurred by power production of the distributed energy resource units. The transformation will require intelligent distribution automation by means of decentralized power management as well as information and communications technologies to actualize smart grid modernization. In this paper, we design autonomous distribution networks that take scalability into account by dividing the legacy distribution network into a set of subnetworks. We tackle the power flow and power balance issues individually in parallel to optimize the global distribution operation by our proposed power-control method. Meanwhile, we propose an overlay multi-tier communications infrastructure for the underlying power network to analyze the traffic of data information and control message required for associated power flow operation. Based on the proposed schemes, we show that we can potentially improve the utilization of renewable energy production and achieve data traffic reduction under decentralized operations as compared to legacy centralized management.

Microgrid Test-Beds and Its Control Strategies

The scares of conventional energy resources and negative environmental impact of non renewable energy recourses are accelerating the technologies for new non conventional environment friendly energy options. Most of utility the grids are saturated with bulk energy resources but there are plenty of available small scale energy resources distributed around regions. Most of them are identified as wind, photo voltaic (PV), solar thermal and waste heat from industries and cooling tower of combined cycle power plants. It is difficult to gain full potential from these renewable energy resources as when they are connected to the power system individually, it leads to hindering the system stability. Microgrid is an attractive option to harness the benefits offered by distributed generation, eliminating constraints on high penetration of Distributed Energy Resources (DER). The microgrid provides an interface between central grid and micro devices to overcome these individual integration issues. So microgrid should capable to address those issues to optimize grid stability and power quality. Control system of the microgrid can be discriminated as voltage and frequency control, power flow balancing, load sharing, and protection as well as islanding and resynchronization. This research is focused on design and development of a microgrid test-bed for experimenting several kinds of microgrid topologies and coordination of individual components with a well defined energy management scheme.

A Resonant Switched-Capacitor IC and Embedded System for Sub-Module Photovoltaic Power Management

The viability of grid-connected photovoltaic (PV) energy has improved dramatically in recent years: large increases in manufacturing capacity have driven reductions in cost and higher efficiencies, improving lifetime cost of energy (LCOE). Mismatch loss remains an important consideration in PV systems and a range of power electronic solutions have been proposed to recover losses due to shading, dust/debris, factory mismatch and aging. This paper presents a high-voltage CMOS IC and embedded system based on a resonant switched-capacitor converter. The solution is integrated into the junction box to balance power flow in parallel with sub-module strings of PV cells. A custom dual-core cable and connector extend the balancing function to multiple PV modules connected in series, improving energy production of large-scale PV arrays in the case of shading or mismatch. The converter is based on a resonant switched-capacitor (ReSC) topology that achieves effective conversion efficiency over 99% for a wide range of mismatch, insertion loss below 0.1%, a vertical footprint less than 6 mm, and weight less than 1 Oz.

Structural Identification Based on Transient Power Flows using Particle Swarm Optimization

This paper presents a transient power flow balance formulation for identifying structural parameters from time domain responses. It is implemented at the substructure level where the concept is to balance the instantaneous powers by equating the input power to the dissipated power and the time rate of change of kinetic and strain energies. This imbalance is reduced to zero to identify the structural parameters. For better results the power balance method is combined with the conventional acceleration matching method where the objective is to minimize the deviation between measured and estimated accelerations - no additional sensors are required to incorporate the extra power flow balance criteria. Numerical simulations are performed for substructures taken from a lumped mass system, a planar truss and a cantilever beam. In numerical simulations, noise free and 3% noise contaminated response measurements are considered. The Particle Swarm approach is used as the optimization method with weighted aggregation multi-objective optimization (MO). The results demonstrate that the proposed combined method is more accurate in identifying the structural parameters of a system compared to previous methods.

Crack identification using combined power flow and acceleration matching technique

This article presents a multi-objective optimization (MO) formulation to detect cracks in structures using time-domain acceleration responses combined with power flow balance conditions. No additional sensors are required to ensure power flow balance. This is an application of inverse problem formulation whereby the unknown structural stiffnesses are estimated by minimizing the difference between the measured and theoretically predicted accelerations; simultaneously ensuring the net power flow balance in the substructure is zero. Numerical simulations are performed for identifying a lumped mass system and damage detection in a cantilever beam of 20 elements with single crack. Effects of noise are also taken into account by contaminating the measured responses with up to 5% Gaussian noise. The particle swarm approach is used as the optimization algorithm, and the objective function is defined to minimize the error with weighted contribution of both acceleration and power flow parameters. The effects of various weighting factors are studied. It is shown that significant improvement in accuracy of damage detection is achieved by the combined method, when compared to previous methods. The enhanced accuracy of identification could imply the use of fewer sensors for this method.

A novel scheme design of UC banks based on series-parallel connections switchover for internal combustion-linear generator integrated power system

In order to meet the requirements of bi-directional high efficiency energy flow for internal combustion-linear generator integrated power system (ICLGIPS), a novel programme using UC banks as power source is designed, and non-isolated bi-directional DC-DC power converter (BDPC) converts and transfers energy between power source and linear electric generator (LEG). An alternative way of applying UC banks that are switched over between series and parallel modes accomplish several voltage outputs of UC banks so wide range continuous terminal voltage and back electromotive force (EMF) of LEG are divided into several small zones. Each voltage output of UC banks is corresponding to a small zone, satisfying the voltage ratio which is not larger than two as demanded by BDPC. This programme accomplishes power flow balance among UC banks, and improves energy conversion efficiency and transfer efficiency. The simulation results are shown. This provides a theoretical guidance and practical application for the system which has wide range variational voltage and power convert requirements.

An Explicit Solution of the Power Balance Equations of Structure Preserving Power System Models

In this paper, we consider the widely popular structure-preserving models used to describe the dynamic behavior of multimachine power systems. These models consist of differential-algebraic equations, where the algebraic constraints stem from the power flow balance between generators, loads, and lines. Our main contribution is the explicit computation of a solution for these algebraic equations under the assumption that the loads are constant impedances. This result is of interest for transient stabilization problems where, to estimate the domain of attraction of a given control law, it is sometimes necessary to explicitly solve the algebraic constraints. Besides this application, we believe this result may be of interest in other problems of power systems analysis.

A parallel dual-type algorithm for a class of quadratic programming problems and applications

In this paper, we present a parallel dual-type (PDT) algorithm for solving a strictly convex quadratic programming problem with equality and box constraints. The PDT algorithm is suitable for distributed implementation and can be used as a basic optimization module for handling optimization problems of large distributed systems. Besides, combining the proposed algorithm with a successive quadratic programming (SQP) method, we can solve constrained nonlinear programming problems such as power-system state estimation with power-flow balance constraints on no generation and no-load buses. We have demonstrated the computational efficiency of our method, by comparing with the benchmark commercial NCONF and QPROG routines and the state-of-the-art parallel algorithm through the implementation in the sequential version of Sparc workstation and the parallel version of PC network in solving constrained state estimation problems within IEEE 30-bus and IEEE 118-bus systems.

Double-Input PWM DC/DC Converter for High-/Low-Voltage Sources

A novel double-input pulsewidth-modulation (PWM) dc/dc converter for high-/low-voltage sources is proposed in this paper. With a PWM control scheme, the proposed double-input dc/dc converter can draw power from two different voltage sources simultaneously or individually. The operation modes and the steady-state analysis of the proposed double-input dc/dc converter are introduced in detail. The PWM control scheme for the power flow balancing is also presented. By using a single passive lossless soft-switching cell, switching losses of all power switches can be reduced significantly. Finally, experimental measurements are demonstrated to verify the performance of the proposed converter

The similitude research on underwater complex shell-structure based on SEA

In this paper, the vibration and sound radiation of the underwater complex shell-structure which is the cylindrical shell with hemi-spherical shell on the ends are studied by statistical energy analysis (SEA). The whole shell-structure is divided into the four subsystems, and the SEA physical model and power flow balance equations among these subsystems are established. The similitude relations of input power, coupling loss factor and modal density of the subsystems between the complex shell-structure and its scaled-down model are analyzed. According to the similitude theory and power flow balance equations, when the immerged shell-structures are excited, the similar relations of spatially averaged vibration response and underwater radiating sound power are established for the complex shell-structure and its scaled-down model.

Investigating an LCL Load Resonant Inverter for Inductive Power Transfer Applications

A inductor/capacitor/inductor load resonant inverter is investigated for inductive power transfer applications. The inverter uses a variable frequency controller and operates in discontinuous current mode. The steady state operation of this system is determined by a power flow balance between the inverter and the resonant tank. The results are used to design a system to achieve maximum power transfer.

High-voltage multicellular converters applied to ac/ac conversion

This paper considers arrangements for multilevel, multicellular power converters with emphasis on applications in the field of transmission and distribution. A classification system for such converter structures is proposed which allows the many possible topological variations to be individually identified. A description and analysis of the power flow and energy balance characteristics of multicellular converters is presented. This analysis is applied to specific multilevel multicellular topologies and switching strategies. Two methods of achieving power balance in the case of multiple dc energy storage elements are presented, along with both stimulation and experimental results.