Distributed Voltage Research Articles

Robust distributed cooperative control for DC mircogrids with time delays, noise disturbances, and switching topologies

This paper develops a robust consensus-based distributed cooperative control scheme for DC microgrids with asymmetric time delays and switching topologies in noisy environments. The proposed distributed cooperative control scheme, consisting of a leader-following consensus-based distributed voltage controller and a consensus-based distributed load current controller, is to respectively regulate the voltage of DC microgrids to the desired value and achieve the cost-based load current sharing through a sparse communication network (i.e., a distributed low bandwidth communication network) with asymmetric communication delays, switching topologies and noise disturbances. Moreover, the proposed controllers are implemented through sparse communication networks and thus meet the plug-and-play feature of microgrid power systems. Based on the Lyapunov–Krasovskii functional method and stochastic differential equation theory, the criteria for the stability analysis and delays boundedness to maintain the system stable are derived. The effectiveness of the proposed control methods are verified by the simulation of a DC microgrid system in MATLAB/SimPowerSystems.

A distributed non-Lipschitz control framework for self-organizing microgrids with uncooperative and renewable generations

This paper investigates the design of robust distributed voltage and frequency control for a self-organized microgrid. A multiagent distributed secondary hierarchy is proposed using control Lyapunov function. Power resources are categorized as controllable and uncontrollable distributed generations (DG). Controllable DGs are exchanging information with neighbor DGs through agents at communication layer. The agents communicate to restore the voltage and frequency to their nominal references. Furthermore, the proposed scheme is robust against the insufficient data from uncontrollable DGs, since it provides an improved and stable operation even when there is no communication with uncontrollable DGs and loads. It can actively compensate for the random unknown demand and generation, by sharing the power mismatch in distributed droop architecture. It is shown that the suggested controller is capable of stabilizing an uncooperative microgrid in which not all DGs are cooperating. Also, the convergence speed of the system is improved using the finite-time controller. The performance and finite-time stability of a microgrid with partially-cooperative DGs is proved using Lyapunov theorem and is validated through numerical simulation. The results show improved transients, accurate steady state values for voltage and frequency control of a microgrid, and robustness against communication architecture variations. The impact of communication delays, the uncertainty in coupling gains of the communication links, and the time-interval between updating the controller and the states through communication are investigated.

Evaluation of an enhanced power dispatch control scheme for multi-terminal HVDC grids using Monte-Carlo simulation

This paper presents a new multi-objective optimization technique for multi-terminal DC (MTDC) networks to enhance power dispatch control under stochastic operating conditions. The proposed method utilizes the DC voltage droop control concept to achieve distributed DC voltage control of the MTDC grid, while a centralized power dispatch controller monitors system operation and updates the voltage droop settings of the onshore converters in order for them to comply with scheduled power set-points dispatched by the transmission system operator, maintaining at the same time low system losses. The overall optimization problem is formulated and its effectiveness is assessed applying the Monte-Carlo simulation method. A five-terminal MTDC grid is selected as a study-case system, which corresponds to the planning for the future interconnection of Aegean Sea islands with significant wind potential to the mainland grid.

A radio-frequency time-of-flight mass analyzer of ions with planar discrete electrodes

The focusing properties of a linear radio-frequency (RF) electric field and the results of their use for time-of-flight mass separation of polyenergetic ions are considered. A method for forming 2D linear RF fields by planar discrete electrodes with multiple distributed capacitive voltage dividers is proposed. An experimental prototype of an RF mass reflectron with planar discrete electrodes was created and investigated. The results of analytical calculations, computer simulations, and experiments are presented.

Online Coordinated Voltage Control in Distribution Systems Subjected to Structural Changes and DG Availability

The responses of multiple distributed generation (DG) units and voltage regulating devices, such as tap changers and capacitor banks, for correcting the voltage may lead to operational conflicts and oscillatory transients, where distribution systems are subjected to network reconfiguration and availability of the DG units. Therefore, coordinated voltage control is required to minimize control interactions, while accounting for the impact of structural changes associated with the network. This paper proposes a strategy for coordinating the operation of multiple voltage regulating devices and DG units in medium voltage (MV) distribution systems, under structural changes and DG availability, for effective voltage control. The proposed strategy aids to minimize the operational conflicts by allowing voltage regulating devices to operate in accordance with the priority scheme designed based on the electrical-distance between voltage regulating devices and DG units, while maximizing the voltage support by the DG units. The proposed coordination scheme is designed to enact with an aid of a substation centered distribution management system for online voltage control. The control actions of proposed coordination strategy are tested on a MV distribution system, derived from the state of New South Wales, Australia, through simulations, and results are reported.

Research on the Multilevel STATCOM based on the H-bridge Cascaded

This paper mainly studies the main circuit topology, the working principle, modulation technique and control strategy of the STATCOM based on H-bridge. The STATCOM direct power control algorithm based on the virtual flux is used to control the AC side reactive power compensation, and in accordance with the principle of conservation of power, the DC side voltage imbalance factors are analyzed, and a distributed DC voltage control algorithm is also introduced. The DC side control algorithm is divided into upper and lower control parts, of which the upper control section is aimed at the average of DC side capacitor voltage of the sub-module unit for the STATCOM device, the lower control part is mainly for each sub-module DC side capacitor voltage. Finally, the control strategy is verified in a three level chain STATCOM system with VME control box as its core controller, and the experimental results show that the algorithm is feasible.

Operation and Power Flow Control of Multi-Terminal DC Networks for Grid Integration of Offshore Wind Farms Using Genetic Algorithms

For achieving the European renewable electricity targets, a significant contribution is foreseen to come from offshore wind energy. Considering the large scale of the future planned offshore wind farms and the increasing distances to shore, grid integration through a transnational DC network is desirable for several reasons. This article investigates a nine-node DC grid connecting three northern European countries — namely UK, The Netherlands and Germany. The power-flow control inside the multi-terminal DC grid based on voltage-source converters is achieved through a novel method, called distributed voltage control (DVC). In this method, an optimal power flow (OPF) is solved in order to minimize the transmission losses in the network. The main contribution of the paper is the utilization of a genetic algorithm (GA) to solve the OPF problem while maintaining an N-1 security constraint. After describing main DC network component models, several case studies illustrate the dynamic behavior of the proposed control method.

A distributed DC voltage control method for VSC MTDC systems

Abstract With the development of VSC HVDC transmission, the realization of the first VSC MTDC grid is coming within reach. An outstanding issue is DC voltage control in MTDC systems. The easiest way to maintain stable operation is to assign the task of DC voltage regulation to one converter. This paper discusses a control strategy for an extended VSC MTDC grid using a typical DC voltage control on one DC bus, combined with a DC voltage droop characteristic on the other DC buses. The impact of the proposed control structure on the stability of the AC and DC grid is investigated by numeric simulations using the MatDyn software package.

A DC micro‐grid for superhigh‐quality electric power distribution

AbstractThe “DC Micro‐grid” is a novel power system using DC distribution in order to provide superhigh‐quality electric power. The DC distribution system is suitable for DC output distributed generation techniques such as photovoltaic and fuel cells, and energy storage forms such as batteries and electric double‐layer capacitors. The power is distributed through a DC distribution line and converted to the required AC or DC voltage by converters placed near loads. The load‐side converters do not need transformers due to the choice of the proper distributed DC voltage. The spread converter scheme helps to assure high‐quality power supply. Even if a short circuit occurs on one load side, it does not affect other loads. In this paper, we propose a DC micro‐grid configuration and converter control methods for generation and energy storage. Computer simulation results demonstrate seamless operation during turn‐on and turn‐off of distributed generation, transients at the times of connecting and disconnecting operation with the bulk power system, and stability against sudden large load variations. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(1): 34–42, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20641

Stability of piezoelectric FGM rectangular plates subjected to non-uniformly distributed load, heat and voltage

This paper employs the element free Galerkin (EFG) method to analyze buckling of piezoelectric functionally graded material (FGM) rectangular plates subjected to non-uniformly distributed loads, heat and voltage. A two-step solution procedure is implemented. In the first step, based on a two-dimensional (2D) plane stress problem, pre-buckling stresses of plates subjected to non-uniformly distributed loads are calculated. In the second step, based on the Mindlin plate assumption, buckling load and temperature parameters of the plates are obtained using the EFG method with penalty coefficients. Numerical examples are presented to validate the proposed numerical method. Some useful results for the FGM plates are presented.

Centralized and Distributed Voltage Control: Impact on Distributed Generation Penetration

With the rapid increase in distributed generation (DG), the issue of voltage regulation in the distribution network becomes more significant, and centralized voltage control (or active network management) is one of the proposed methods. Alternative work on intelligent distributed voltage and reactive power control of DG has also demonstrated benefits in terms of the minimization of voltage variation and violations as well as the ability to connect larger generators to the distribution network. This paper uses optimal power flow to compare the two methods and shows that intelligent distributed voltage and reactive power control of the DG gives similar results to those obtained by centralized management in terms of the potential for connecting increased capacities within existing networks

Coarse–fine, wideband distributed voltage controlled oscillator for wireless applications

A new distributed voltage controlled oscillator (DVCO) is presented. The proposed topology allows a very wide tuning range VCO and fine-coarse tuning. The design of a prototype DVCO is discussed and measurements are reported showing improved performance in terms of phase noise, tuning range and power consumption.

超高品質電力供給システム「DCマイクログリッド」

“DC Micro-grid" is a novel power system using dc distribution in order to provide a super high quality electric power. The dc distribution system is suitable for dc output type distributed generations such as photovoltaic and fuel cells, and energy storages such as batteries and electric double layer capacitors. Power is distributed through dc distribution line and converted to required ac or dc voltage by converters placed near loads. The load side converters do not need transformers by choosing proper distributed dc voltage. The spread scheme of converters contributes to provide a high quality power supplying. Even if a short circuit occurs at one load side, it does not effect other loads. In this paper, we propose a configuration of DC micro-grid and control methods of converters for generations and energy storages. Computer simulation results demonstrated the seamless operation during turn-on and turn-off of a distributed generation, the transient of connecting and disconnecting operation with bulk power system, and the stability against a sudden large load variation.

Field‐excited multiconductor transmission lines: a wavelet approach

The analysis of multiconductor transmission lines excited by an electromagnetic field is investigated here by the use of the wavelet expansion. The exciting field is taken into account considering its contribution in terms of equivalent distributed voltage and current along the line. The resulting equations are expanded in the wavelet domain on both the variables (space and time), leading to an algebraic system in a Lyapunov form which is solved by the use of standard techniques.

New Reduction Technique for Distribution Feeders

A unique method is developed for reducing the distribution feeders, both for series and parallel configurations, by combining the discrete distributed load voltage drop solutions and discrete distributed line losses solutions. The reduction method may be applied to represent a feeder or few feeders with distributed loads by a point load and a fictitious section connected at an equivalent length. To match both voltage drop and line losses, fictitious section represents a load or generation. The suggested method herein, while preserving the accuracy of Vempati's method for series configuration when dealing with distribution feeders containing parallel laterals, gives a higher degree of accuracy compared with other methods, including Vempati et al. [10].

A CMOS high voltage controller integrated circuit

The MHV 100 is a custom CMOS integrated circuit, developed for the AMS experiment. It provides complete control for a single channel high voltage (HV) generator and integrates all the required digital communications, D to A and A to D converters, the analog feedback loop and output drivers. This chip has been designed for use in both distributed high voltage systems and low cost single channel high voltage systems. The output voltage and the maximum current are determined by the external components.

95/06087 Utilities sign to support Mescalero storage project

This paper presents a new multi-objective optimization technique for multi-terminal DC (MTDC) networks to enhance power dispatch control under stochastic operating conditions. The proposed method utilizes the DC voltage droop control concept to achieve distributed DC voltage control of the MTDC grid, while a centralized power dispatch controller monitors system operation and updates the voltage droop settings of the onshore converters in order for them to comply with scheduled power set-points dispatched by the transmission system operator, maintaining at the same time low system losses. The overall optimization problem is formulated and its effectiveness is assessed applying the Monte-Carlo simulation method. A five-terminal MTDC grid is selected as a study-case system, which corresponds to the planning for the future interconnection of Aegean Sea islands with significant wind potential to the mainland grid.

Simplified Feeder Modeling for Loadflow Calculations

Three models of a distribution system are developed in this paper. Included are descriptions of simulation models of the diverse components of a typical distribution system. The three system models are illustrated by examples. They are applied to an actual feeder and the results are analyzed to show the advantages and disadvantages of each model. A unique method is developed for combining the discrete distributed load voltage drop solution with the discrete distributed load losses solution. The development of this combined method is in the form of a tutorial , as are the developments of the components of this method. The conclusion is reached that it is possible to reduce many complex feeders to simple models in the study of feeder voltage profiles and losses with negligible error.

Discrete Models of Slow Voltage Dynamics for under Load Tap-Changing Transformer Coordination

In this paper, an approach to modeling, analysis, and design of slow distributed voltage control schemes is proposed. In particular, a dynamical voltage model governed by the under load tap-changing transformers as control tools is studied. Rigorous conditions are derived to predict when the LTC based scheme may be poorly coordinated and not able to maintain voltages within the limits. The proposition is that nonconvergence of LTC control scheme is one of the causes of a systemwide voltage collapse.