Voltage instability problems come out especially when there are not enough fast reacting reactive resources exist. Beijing-Tianjin-Tangshan is the load center area in the North China Power Grid. The power supply in this region has a heavy reliance on external power grid, thus, there is not enough dynamic reactive support in this area and the voltage stability problems may be much more serious than the angle stability problem. In order to solve the above problems and improve the power system stability, this paper discusses a kind of control strategy for practical power grid. All the issues are studied with full scale transient simulation. The methods proposed for the mitigation of voltage instability by using Controllable HV Reactor are flexible and its coordination with other conventional measurements is convenient. Simulation results with serious faults show the effectiveness of the control method. Finally, some suggestions are given, which will make a significant contribution to the stability of power grid as well as reduce the load shedding capacity under some supposed fault conditions.
Distributed generation resources are widely connected to the distribution network, which has great influences on synthesis load characteristics. In order to study the composite load modeling of distribution network with microturbine generation (MTG) system, the models of each function module and its control strategy were expounded. A complete MTG system had been developed and set up in the Matlab/Simulink environment and its operating characteristics had been analyzed through the simulation. The results show that MT generating system can not guarantee constant power output when external voltage disturbance occurs, and the dynamic characteristics can't be ignored. The analysis of the dynamic performance of an MTG system in transient shows that the MTG system can be considered as a generalized dynamic load that consumes negative power. Then a third-order differential state equation was proposed to describe the dynamic characteristics of the MTG system. The self-description ability, parametric stability and generalization ability of this description model were validated by comparison of simulations under different disturbance levels. This paper lays the foundation for synthesis load modeling of distribution network considering MTG system.
A protection relay for a wind turbine generator (WTG) based on positive- and negative-sequence fault components is proposed in the paper. The relay uses the magnitude of the positive-sequence component in the fault current to detect a fault on a parallel WTG, connected to the same power collection feeder, or a fault on an adjacent feeder; but for these faults, the relay remains stable and inoperative. A fault on the power collection feeder or a fault on the collection bus, both of which require an instantaneous tripping response, are distinguished from an inter-tie fault or a grid fault, which require a delayed tripping, using the magnitude of the positive-sequence component in the fault current. The fault type is first evaluated using the relationships between the positive- and negative-sequence fault components depending on type of fault. Then the magnitude of the positive-sequence component in the fault current is used to decide on either instantaneous or delayed operation. The operating performance of the relay is then verified using various fault scenarios modelled using EMTP-RV. The scenarios involve changes in the position and type of fault, and the faulted phases. Results confirm that the relay can successfully distinguish between faults that require an instantaneous, delayed or non-operation response.
The application of PMU measurements and collocated control to damp inter-area oscillations with coordinated DC lines and static var compensators (SVCs) is investigated. The closed loop eigenvalues are excluded from a region of the complex plane guaranteeing that low frequency modes must be damped. A 16-machine, 68-bus study system reinforced with four DC lines or two DC lines and two SVCs is considered. The damping performance of the controllers is examined in the frequency and time domains. The simulation results show that the control scheme is able to robustly damp out inter-area oscillations following possible disturbances.
I For the situation that the traditional switched reluctance motor exists output torque ripple, this article changes the motor structure, adding permanent magnets in the stator, which changes the motor into the hybrid-excitation motor and changes the magnetic circuit into the axial magnetic circuit. As a result, the magnetic circuit becomes shorter and the output torque becomes greater. Besides, because of changes in the structure, the control method using double complementary conduction suppresses torque ripple. At the same time there is no mutual inductance existing between each phases. We also discuss the speed structure and the hardware structure of the new switched reluctance motor.
Based on generation rescheduling, we can damp low-frequency oscillation effectively. In this paper, the authors calculate the three kinds of sensitivities used later in this paper with both analytic method and numerical method. Then the authors give a brief introduction on static HAGVC system as well as static damping HAGVC system, and draw a control diagram of the system. Static damping HAGVC system can not only eliminate some weak damping modes, but also overcome the negative interaction between traditional AGC and AVC control, as the coupling between active and reactive power become much stronger, to coordinate AGC and AVC control systems effectively. As to the top level of the static damping HAGVC system, a diagram about control flow as well as the function of each control module based on cross iteration optimization algorithm is given in this paper. Finally, the simulations of the IEEE 5-machine 14-bus system in five situations indicate the validity of the proposed theory.
Travelling-wave starting element is an integral part of the ultra high-speed protection. Existing design method depends on engineering experience, low accuracy in travelling-wave signal recognition, easy to trip frequently or refuse to trip. To solve these problems, through mass of starting signal simulation and analysis under different fault conditions, this paper focuses on the travelling-wave starting element and figures out the travelling-wave identification method. This paper summarizes the frequency and voltage characteristics of travelling-wave head, puts forward a new method in real-time travelling-wave fault identification. In addition, the analysis course included in this paper is a useful attempt that can be used in similar fault travelling-wave analysis.
With the rapid development of power system, the capacity of generator unit results in an increasing impact on the power grid. Therefore, coordinated control of generator and grid become a research hotspot. In order to put the optimal coordinated control strategy into practice, this paper designs and implements the software structure and hardware apparatuses of the Coordination System of Generator and Grid (CSGG) in Hubei Province. Two fundamental concepts, which are “hierarchical” and “event-driven”, are adopted and applied in the process of implementing. Based on the principle of expandability, modularity and standardization, this paper designs the software architecture and flow chart for the CSGG. Also, the internal software modules and their inter-relations are given out in detail. With standard data interface and command interface, the CSGG is connected with the existing Automatic Dispatching System and Wide Area Measurement System (WAMS), which can ensure the practicability and reliability of the CSGG. With the field data of Hubei Province Power Grid, the CSGG has carried out the simulation examinations. The results have verified the usability and effectiveness of the System.
When fault occurs in outbound channel, isolated hydropower group will face the problem of high frequency pressure and other special issues in security and stability. Self-excitation of the hydroelectric generator is the main reason for the resonance over-voltage of the isolated hydropower group. This paper research the conditions for the self-excitation and the dynamic characteristics in the isolated hydropower group with MATLAB software, and an example of a typical isolated hydropower group in Sichuan province is used to illustrate the theory of self-excitation in the situation of isolated hydropower group.
The paper proposes faulted feeder selector in power distribution system with neutral non-effectively grounded. At first, the paper presents basic principle of single-phase-to-ground fault feeder selection based on traveling waves, which compares amplitude and polarity of the initial current traveling waves in all feeders. Then the implementation scheme, including hardware design and software flowchart is presented. At last field application of faulted feeder selector is introduced. The field operation results validated the correctness of faulted feeder selector based on transient traveling wave.
To meet the need of high performance and high efficiency, cascaded H-bridge grid-connected PV inverter is investigated. The cascaded multilevel inverter features several advantages such as lower voltage harmonics, smaller filters, reduced switching frequency, and the capacity to solve the problems of the partial shades and the mismatching of photovoltaic array, all of which is able to improve efficiency. However it requires a more sophisticated control method due to a non-integer ratio among the dc-link voltages. In this paper the proposed control method is based on traditional voltage oriented control with a cascaded dc-link voltage control and grid current control loop. Two extra stages are added to this traditional control scheme, one to introduce maximum power point tracking for each power cell, and another to control the dc-link voltages balancing due to unequal power in each power cell. The latter is performed by the addition of a simple feedforward control strategy directly in the modulation stage. Performance of the cascaded inverter and the corresponding controllers are evaluated based on the digital time domain simulation studies in the PSCAD/EMTDC environment.
Some clients request the stability study of a protection system in designing power system to evaluate whether protection relays properly operate in case of an internal fault and if they do not function in the events of severe external fault. High fault currents could cause Current Transformers (CTs) to be saturated. A critical concern is the performance of fast protective relay (instantaneous or differential elements) during severe saturation of CTs. Time domain transient simulation software is widely used for the study of these types of works. In this paper, a relay stability study of 115 kV and 34.5 kV transmission and distribution systems was carried out and evaluated utilizing the PSCAD software, which provides several modeling methodologies for various electrical equipment such as transmission line, power transformer, current transformer and protective relays. For the purpose of this study, the modeling method of CT is the most important factor because it influences heavily on the protection relay operation. It is very important to model CT as close as the real characteristics of the CT. Two types of CT models provided by the PSCAD were discussed and compared with each other and an appropriate CT modeling methods were covered in this study. This study is mainly based on digital relays, which prevail recently in the relay market. Digital relay characteristics like anti-aliasing filter, digital filter and various setting function are embedded into PSCAD.
In this paper, dynamic models of main micro-generation sources are described and built based on their mathematical model, in particular, the models of Micro-turbine, Wind turbine with full rated converter, Photovoltaic Systems and Battery Energy Storage System (BESS). In addition, control mode of their power electronic interfaces are given and analyzed based on the characteristic of Distributed Generations (DGS). A micro-grid adopting peer-to-peer control mode is then built comprising these micro-generation source and a battery energy storage system. Dynamic characteristics of frequency response and voltage response are made under operating mode switch of micro-grid between grid connected mode and islanded mode. According to the simulation case study, the battery energy storage system using droop control is essential to the micro-grid in islanded, which can increase the speed of response of micro-grid efficiently.
Partial discharge (PD) is a common reason that causes electrical breakdown in high voltage underground XLPE cables. This paper proposes a concept of how to build an on-line, on-site system that is able to diagnose the severity of PD activities in XLPE cable as well as differentiate different types of PD signals. The system consists of magnetic probes, low noise amplifier, 3GSPS analog to digital converter (ADC) and a field programmable gate array (FPGA) board. The energy of PD signals is used to assess the severity of PD activities and artificial neural network (ANN) is used to classify different types of PD waveforms. In addition, wavelet transform is used to clean the time-resolved input signals and statistical method is used to extract important features of PD signals to fetch into neural network. The training of ANN is done on personal computer. The prototype and results of the research is elaborated in this paper.
The monitoring and control of smart power transmission grid represents active infrastructure capable of obtaining increased transfer and distribution of electrical energy, with considerable rate of generation from renewable energy sources without compromising the stability, security and reliability of power grid in different operating conditions. The development concept of intelligent protection and control systems of the entire smart power transmission grid defines: • use of complex information and communication technology (ICT) system, • sending selected local information to a remote location where this information is processed and • implementation of accurately defined automated actions to neutralize and stop the spreading of major system disturbances. Wide area monitoring of electrical power system, which is the initial step in developing the smart power transmission grid has found its place around the world and it's expected increase of use in the daily work of system operators will result in more efficient and reliable use of ancillary functions during large scale disturbances. The intention of this paper is to point out the needs and developing possibilities of monitoring and control systems of the entire smart power transmission grid based on the System Integrity Protection Schemes (SIPS) and synchronized measurements technologies, to summarize accomplishments within ongoing projects and experience gathered worldwide, and to emphasize the need for making practical roadmap towards greater deployment of the technology. This paper will give the scheme of automatic transmission control system that aims to mitigate the possible overloading of existing transmission lines while maintaining the same rate of generation.
There are many papers that propose diagnosis and fault detection in hybrid electric vehicles. However just a few of them con-cern in short circuit fault. In HEVs battery is one of the most crucial pars and can failure because of the short circuit due to several causes. In this paper, Matlab/Simulink Environment based hybrid powertrain system modeling and simulation for Toy-ota Prius HEV including short circuit case in DC bus system that is developed under SimPowerSystems and Sim- Driveline toolboxes is proposed. This is a multi-domain system which is composed of control system, electric power subsystem, and driving force subsystem. As for the short circuit model, it is developed according to the data collected from investigation report of Prius fire forensics. This hybrid powertrain is of series-parallel type and in order to increase drivetrain efficiency and reduce air pollution, It has two kinds of motive power sources: Internal Combustion Engine and Electric Motor. This system has the advantage of high dynamic performance and low pollution at low speeds coming from internal combustion engine and the ad-vantage of no-pollution and high available power at low speeds coming from electric motor drive. We present the short circuit analysis in DC electric supply system of HEV. The effect of short circuit to the HEV performance is analyzed.
It is urgent to cognize grid operation state along with complication of electric power characteristic. First, database structure was expounded in this paper. Secondly, Grid state judge Procedures was introduced detailed. Last, the concept of Grid Operation State Cognition Flag which was used to represent indexes group state and grid state was advanced in the end of this paper.
IP/MPLS is the technology of choice for utilities wanting to implement converged Smart Grid networks. By introducing the demand from utility, especially for smart grid, the article introduced utility's evolution to converged network, addressed teleprotection as key application and its design consideration, demonstrated the reliability in utility company in Northern America.
Utilizing Distributed Generation (DG) is greatly increasing in recent years. This is mostly because of simple installation, environmental effects and loss reduction due to closeness to the load centers. However, DG installation, especially in distribution networks, raises some problems. One of these problems is over-current (OC) relays coordination. In this paper, DGs' effects on OC relays in distribution network are studied. An IEEE 8-bus standard system is simulated in MATLAB software. A new method is proposed to optimize the operating time of OC relays in such a way that using DGs in any bus will not affect on the main and backup protection relays operation and coordination. In this method, optimized relays settings are obtained by linear programming approach.
