Power System Regulation Research Articles

An Online Simplified Nonlinear Controller for Transient Stabilization Enhancement of DFIG in Multi-Machine Power Systems

An adaptive nonlinear controller for transient stability and voltage regulation of power systems based DFIG in multimachine configuration is presented using a standard third order dynamical model of the DFIG. Finite time estimators for the unmeasurable time derivative of the quadrature component of the DFIG stator current, mechanical input, unknown direct axis transient open circuit time constant (function of the rotor resistance) are presented. The main feature of the proposed control scheme is its robustness with respect to large perturbations and parameter variations. Numerical results are presented to illustrate the performance of the proposed control scheme and its robustness properties.

Contribution of VSC-HVDC to Frequency Regulation of Power Systems With Offshore Wind Generation

Modern large wind farms are required to provide frequency regulation service like conventional synchronous generation units. The frequency support capability of modern wind farms has been widely investigated and implemented. Remotely located large offshore wind farms are probably connected to the onshore system grid through voltage-source converter-based–high voltage direct current (VSC-HVdc) transmission systems. Due to the decoupling of VSC-HVdc and signal transmission delay, offshore wind farms may not be able to respond to the onshore grid frequency excursion in time and, consequently, the stability and security of the power system will be put at risk, especially for those with high wind penetration. This paper proposes a coordinated control scheme to allow VSC-HVdc link to contribute to the system frequency regulation by adjusting its dc-link voltage. By means of this approach, the dc capacitors of VSC-HVdc are controlled to absorb or release energy so as to provide frequency support. To further enhance the system frequency response, the frequency support from VSC-HVdc is also finely coordinated with that from offshore wind farm according to the latency of offshore wind farm responding to onshore grid frequency excursion. The control scheme is evaluated for both underfrequency and overfrequency events, and results are presented to demonstrate its effectiveness.

Calculation of excore detector weighting functions for a sodium-cooled TRU burner mockup using MCNP5

Power regulation systems of fast reactors are based on the signals of excore detectors. The excore detector weighting functions, which establish correspondence between the core power distribution and detector signal, are very useful for detector response analyses, e.g., in rod drop experiments. This paper presents the calculation of the weighting functions for a TRU burner mockup of the Korean Prototype Generation-IV Sodium-cooled Fast Reactor (named BFS-76-1A) using the MCNP5 multi-group adjoint capability. For generation of the weighting functions, all fuel assemblies were considered and each of them was divided into ten horizontal layers. Then the weighting functions for individual fuel assembly horizontal layers, the assembly weighting functions, and the shape annealing functions at RCP (Reactor Critical Point) and at conditions under which a control rod group was fully inserted into the core while other control rods at RCP were determined and evaluated. The results indicate that the weighting functions can be considered relatively insensitive to the control rods position during the rod drop experiments and therefore those weighting values at RCP can be applied to the dynamic rod worth simulation for the BFS-76-1A.

Hierarchical reactive power regulation strategies for high-penetration photovoltaic distribution systems

This paper proposes a hierarchical reactive power regulation system for distribution systems with photovoltaics (PV) connected. The proposed approach includes both central control level and local control level for decisions involving optimal reactive power compensation and dynamic control of reactive power regulation, respectively. Through local control level, based on the PV inverter controllers and central control level compensation command, the overvoltage and voltage variation problems can be highly relieved. In addition to possible reductions in PV generation curtailment, the grid voltage can also be well regulated with minimal line loss via the proposed PV system operation strategies. Accordingly, added value for PV systems is created, conferring win-win solutions for both PV system owners and utilities. Numerical results tested on a practical Taipower company distribution system verified the proposed approach. Copyright © 2015 John Wiley & Sons, Ltd.

Expected Range of Cooperation Between Transmission System Operators and Distribution System Operators After Implementation of ENTSO-E Grid Codes

The authors present the prospects of cooperation between transmission system operators (TSO) and distribution system operators (DSO) after entry into force ENTSO-E (European Network of Transmission System Operators for Electricity) grid codes. New areas of DSO activities, associated with offering TSO aggregated services for national power system regulation based on the regulation resources connected to the distribution grid, and services on the distribution system level as part of the creation of local balancing areas (LBA) are presented. The paper also presents the possibilities of providing ancillary services by different types of distributed generation sources in the distribution network. The LBA concept, which involves integrated management of local regulation resources including generation, demand, and energy storage is described. The options of the renewable energy sources (RES) using for voltage and reactive power control in the distribution network with the use of wind farms (WF) connected to the distribution system are characterized. DOI: 10.12736/issn.2300-3022.2015202

Decentralized Vehicle-to-Grid Design for Frequency Regulation within Price-based Operation

The utilization of electric vehicles has been suggested to support the frequency regulation of power system. Assuming that an intermediate aggregator exists, this study suggests a decentralized vehicle-to-grid operation scheme in which each vehicle-to-grid aggregator can behave independently of the power system operator. To implement this type of decentralized operation, this study adopts a price-based operation that has been proposed by many researches as an alternative operation scheme for the power system. In this environment, each vehicle-to-grid aggregator can determine its participation in vehicle-to-grid service in consideration of its residual energy of aggregated system and real-time market price. Consequently, the main purpose of this study is to verify whether or not the vehicle-to-grid power can effectively support the current frequency regulation function within the price-based operation scheme. Specifically, a frequency regulation method is proposed based on the real-time price signal, and a feedback controller for battery management is designed for decentralized vehicle-to-grid operation.

Improved synergetic excitation control for transient stability enhancement and voltage regulation of power systems

Abstract This paper proposes decentralized improved synergetic excitation controllers (ISEC) for synchronous generators to enhance transient stability and obtain satisfactory voltage regulation performance of power systems. Each generator is considered as a subsystem, for which an ISEC is designed. According to the control objectives, a manifold, which is a linear combination of the deviation of generator terminal voltage, rotor speed and active power, is chosen for the design of ISEC. Compared with the conventional synergetic excitation controller (CSEC), a parameter adaptation scheme is proposed for updating the controller parameter online in order to improve the transient stability and voltage regulation performance simultaneously under various operating conditions. Case studies are undertaken on a single-machine infinite-bus power system and a two-area four-machine power system, respectively. Simulation results show the ISEC can provide better damping and voltage regulation performance, compared with the CSEC without parameter adaptation scheme and the conventional power system stabilizer.

The Mesh-Up: ENTSO-E and European TSO Cooperation in Operations, Planning, and R&D

The 41 European electricity transmission system operators (TSOs) from 34 countries across Europe are gathered under the umbrella of the European Network Transmission System Operators for Electricity (ENTSO-E) cooperative association to support security of supply, sustainability, and the development of a European internal energy market. Together they provide transmission service to 534 million citizens. Their cooperation is regulated by European Union (EU) Regulation (EC) 714/2009 on cross-border exchanges of electricity. As such, ENTSO-E is the focal point for all technical, market, and policy issues relating to TSOs and the European network; it interfaces with power system users, EU institutions, regulators, and national governments.

Wavelet Packet Transform Based Parameter for the Analysis of Short Duration Power Quality Disturbances

The nature of today’s power system has become highly dynamic due to the increased use of nonlinear loads, power electronics based equipment and changed power system regulations. Conventionally, the Fourier transform (FT) is used for the power quality (PQ) analysis with parameters such as; THD and TDD. These parameters are suitable for stationary disturbances only. The recent state of power system demands to analyze the PQ disturbances on the basis of magnitude, time and frequency. In this paper, a new parameter based on Wavelet Packet Transform (WPT) is defined and tested for the short duration PQ disturbances such as; voltage sag, voltage swell, momentary interruptions, oscillatory transients and harmonics, simulated as per their broad definitions provided by the IEEE 1159-2009 standards.

Short term load forecasting using a hybrid intelligent method

Due to the regulation of electrical power systems, electricity market players need precise information of electrical energy consumption and generation in order to maximize their benefit based on appropriate decisions. In this paper a new hybrid intelligent method is proposed for short term load forecasting. In this method, load and temperature of previous days are used for prediction of the next hour electrical load consumption. Since electrical load signals are non-stationary, Wavelet Transform (WT) as a powerful signal analyzer is applied for the signal decomposing. For elimination of redundant data from input matrices, the Feature Selection (FS) method based on Gram–Schmidt (GS) is used for selection of more valuable features. The elimination of redundant data can speed up learning process and improve the generalization capability of the prediction scheme. Support Vector Machine (SVM) with simple structure and few tuning parameters is applied as a powerful regression tool. Two separate structures are considered for prediction of weekday and weekend electrical load consumption. Besides, in order to increase the forecasting accuracy, indices are determined for each day. The simulation results reveal that the Coiflet wavelet function with 2 decomposition levels lead to the best detection accuracy. Moreover, 30 dominant features of previous 50days should be used to obtain minimum forecasting error. Comparative results show the priority of the proposed method in aspect of prediction accuracy as compared to some reported algorithms.

Simulation of the Volt/Var Control in Distribution Feeders by Means of a Networked Multiagent System

The adoption of networked multiagent systems (MAS) has been recently proposed for the solution of the volt/var control (VVC) problem in distribution feeders. However, constraints and limitations due to the communication network, to the dynamic behavior of power system components and regulators, as well as to the measurement uncertainties of the adopted sensors need to be specifically analyzed for the design of the MAS. For this purpose, a cosimulation platform has been built by the integration of two simulation tools: 1) the electromagnetic transient program EMTP-rv; and 2) the communication network simulator Riverbed-OPNET Modeler. This paper presents the modeling and simulation of an asynchronous leaderless MAS-based approach that coordinates the reactive power outputs of a set of power compensators equipped with phasor measurement units via a shared band-limited packet-switched digital communication network. The effects of communication network latency and packet loss on the VVC performances are analyzed for two unbalanced IEEE Test feeders equipped with on-load tap changer transformers. The paper compares the results obtained by using a transmission control protocol (TCP) and a user datagram protocol (UDP), for different levels of background traffic (BT) and different packet discard ratios (PDRs) in the communication links.

The Impact of Power System Frequency Regulation Caused by Wind Disturbance

The impacts of wind disturbance on voltage regulation and frequency regulation of power system were studied. The opinion that the regulation of power flow on the tie lines between the grids constrains the integrated capacity of wind power was put forward. Based on the real condition of Inner Mongolia power grid, an engineering practical method was put forward to calculate the integrated capacity of wind power under this constraint. The relationship between wind power and spinning reserve and the impacts of other related factors on the capacity of wind power were studied as well. The impact of wind disturbance on voltage stability where the wind farms are located was studied.

Frequency Regulation of Power System Considering PEVs

As a distributed controllable loads, Plug-in electric vehicles (PEVs) connecting to the smart grid and participating in frequency regulation is drawing more and more attention. Depending on Vehicle-to-Grid (V2G) technology to realize the energy interaction between PEVs and the power grid, a dynamic control model of PEVs is proposed by considering the dynamic characteristics of the battery charging/discharging, and the dynamic model consider PEVs participating in frequency regulation is established. Finally, through the SIMULINK simulation based on the model, it demonstrates that the model responds well to the system frequency deviation, and it is important to improve frequency stability and realize the rapid recovery of power system.

Improvements of a Numerical Methodology for Computing Near-Field Parasitic Electromagnetic Emissions of Solar Panels

Improvements of a methodology [1] able to compute the parasitic electromagnetic emissions of a solar panel are presented in this paper in order to handle real solar panels. Thus, the method is able to take into account solar panels with triple-junction solar cells, series or shunt power regulation system, and honeycomb composite panels. This numerical method is validated experimentally by comparing the near magnetic field emitted by a real solar panel and calculated by the method.

Energy and provision management study: A research activity on fuel cell design and breadboarding for lunar surface applications supported by European Space Agency

This paper addresses the findings of the European Space Agency (ESA) study (Energy and Provision Management Study), performed by an Italian consortium, aimed at designing and breadboarding of an Energy Provision and Management system (EPM), based on Polymer Electrolyte Fuel Cell (PEFC) technology. The EPM has been developed for supporting space exploration applications, specifically for lunar surface missions. The fuel cell technology has been selected through a trade-off activity, and the power requirements of a Lunar Base (LB) power plant and a Pressurized Lunar Rover (PLR) have been identified. A synergetic design of EPM has been proposed for both the LB and the PLR. Finally three technological demonstrators have been designed, manufactured and tested: i) a 1 kW PEFC stack, ii) a stand-alone power system based on the developed stack, iii) a regenerative power system based on the stand-alone stack connected with a commercial electrolyser. The tests carried out on breadboards, have demonstrated the ability of fuel cell power systems to meet the requirements of future space missions.

A Research Summary on Combined Peaking Load Strategies of Nuclear Power Plant

Based on extensive research, introduced the peak load regulation characteristics and capacity of different nuclear power plant (NPP) in this paper. The running mode of NPP participating in peak load regulation of power system, combined operation tactics of NPP with other peaking power source and synergistic scheduling of an integrated power generation system with wind, photovoltaic, energy storage unit and NPP were summarized, technology development trend of NPP participating in peak load regulation of power system was analyzed and forecasted.

Optimized Integral Gain Controllers for Price Based Frequency Regulation of Single Area Multi-Unit Power System

This Paper deals with the Price Based Load Frequency Control (PBLFC) using optimizedgain of integralcontroller with three different system marginal cost cases of single area four generator schemes. Case one having System Marginal Cost (SMC) value more than the nominal Unscheduled Interchange (UI) rate. Case two having system marginal cost value less than the nominal UI rate. Case three illustrates about the peak load condition following sudden loss of large generation to see whether PBLFC can handle such event or not. Particle Swarm Optimization (PSO) technique has been used to optimize gain of integral controllers in case one and two. An attempt has been made to achieve effective system frequency response using optimized gain controllers and also to explore the change in profit earned by Generation Companies (Gencos) in both the cases. For the analysis, UI rate of the year 2012, issued by Central Electricity Regulation Commission (CERC, INDIA) is used.

Analytical evaluation of control strategies for participation of doubly fed induction generator‐based wind farms in power system short‐term frequency regulation

Increase in doubly fed induction generator (DFIG)-based wind farms degrades the short-term frequency regulation of power systems. However, such wind farms may have large amount of kinetic energy which can be rapidly injected into the power system to support system frequency by using an appropriate supplementary control loop. This study first analyses the impacts of DFIGs and their supplementary loop on power system short-term frequency regulation. Then, the average power system frequency model is modified to include the participation of wind farms in frequency control. Moreover, a new method is proposed to derive an analytical expression for minimum frequency of a power system, as an important index of frequency regulation, after a power imbalance occurrence. This analytical expression provides a tool for better insight into frequency behaviour of power systems with high levels of wind generation. The results of the analysis are verified by simulation of the nine-bus test system, using MATLAB/SIMULINK.

Features of establishing regimes of limited speed in power-regulation systems

Features of setting up regimes of limited speed in power-regulation systems in which there is no feedback regarding speed and position are considered. It is suggested to introduce feedback regarding speed and position when the coordinates of an electric motor exceed maximum allowable values. Results of mathematical modeling and an example of practical implementation of the proposed control system are stated.

Dynamic participation of doubly fed induction generators in multi-control area load frequency control

Summary This paper proposes a new control strategy to consider the doubly fed induction generator (DFIG) wind generation contribution in frequency control and regulation of multi-area interconnected power system when the wind power is the main generation of one area. Based on frequency requirements and system conditions, the proposed control approach determines whether to switch the wind generation into the maximum power tracking mode or the frequency regulation mode. In the frequency regulation mode, the output power of the wind power plant is controlled through a PID controller. At this mode of operation, the input signal of the PID controller is the system frequency. Finally, the PID performance is optimized by tuning its parameters through fuzzy and Zigler–Nicholes methods. The proposed control strategy is applied to a multi-area control system including thermal and wind power generations. The simulation results indicate that the proposed control scheme works desirably and thereby wind generation can effectively participate in load frequency control (LFC). Copyright © 2014 John Wiley & Sons, Ltd.