Impedance Response Characteristics of Synchronizer under Wide Frequency

Dry-coupling ultrasonic technology is applied to detecting oil-level of oil-filled equipment in power grid. Vinyl silicone rubber is used to substitute liquid coupling agent to fabricate dry-coupling ultrasonic probe, which makes the ultrasonic directly enter the oil-filled equipment through the special structure of dry-coupling probe and detect oil-level of oil-filled equipment accurately and rapidly. Omitting the step that smearing liquid coupling agent on the probe can avoid the contamination on the surface of equipment and significantly improve the detection efficiency.

The proportion of renewable energy units in East China Power Grid increases year by year, and the renewable energy units without modification generally do not have the primary Frequency Modulation (FM) capability. Although the modification of renewable energy units in East China Power Grid have been started and some of them have frequency support capability, the actual frequency response capability in the regional power grid is still uncertain. Consequently, the State Grid East China sets up the plan in east China power grid to test the renewable-energy active frequency support ability. The test includes wind power, photovoltaic (PV), energy storage, wind storage and thermal storage, 5 types of frequency modulation unit combinations. The test results show that the modified renewable energy unit generally has a good ability of fast frequency modulation, and the error between test and simulation results is small. This test verifies that the coordinated combination of multiform FM resources with renewable energy as the main body is beneficial to the construction of east China Power grid to actively support the primary FM system, which provides valuable practical experience for the subsequent primary FM modification of renewable energy units, and has strong promotion and application value for East China and surrounding areas.

The purpose of this paper is to improve the fault early warning effect of smart grid equipment through multi-sensor information fusion technology. Therefore, based on the analytical model of power grid fault diagnosis, this paper considers the influence of distributed generation in distribution network on fault diagnosis, as well as the misoperation or refusal of protection and switch, and the false alarm or leakage of alarm signal. At the same time, in order to display the results of fault diagnosis accurately and intuitively, an analytical model of fault diagnosis of distribution network based on multi-source information fusion is proposed. Finally, this paper verifies the effectiveness of this method through an example application. This article uses the PEDL dataset for experimental research, Through the comparison of fault data, it can be seen that compared with existing methods, the method proposed in this paper achieves the highest goodness of fit for warning, indicating the best fault warning effect.When there is enough training set, the prediction accuracy of the fault set can reach over 99%, Based on experimental analysis, it can be concluded that the proposed power grid equipment model has higher accuracy and reliability compared to traditional models. And the model in this article integrates the real-time monitoring function of power grid equipment and the equipment fault warning function, which improves the practicality of the power grid equipment monitoring system.

State grid Tianjin electric power company carries out lean grid management research based on grid management statistical analysis based on power grid equipment operation efficiency analysis platform. Firstly, this paper introduces the construction process of power grid equipment operation efficiency analysis platform. Secondly, this paper introduces lean management strategy of power grid, based on the constructed operation efficiency analysis platform of power grid equipment, which deepens its application in power grid management. Finally, this paper analyzes the effect of the project results, from the aspects of economic benefit and social benefit. This project can realize lean analysis of grid equipment running efficiency and asset efficiency, and to play a better role for data statistics, on supporting effect of operation and management decision making.

With the integration of power grid developing further, some demand such as power grid analyses decisions centrally has become more and more urgent. At present, the information resources for the use of Power grid equipment monitoring analysis is becoming abundant, but these information, which exists in every professional system independently, is lack of connection and meets the demand of big data analysis on power equipment monitoring hardly. In this paper, a unified information model, modeled by IEC61970 common information model and IEC61850 hierarchical model, is proposed for the analysis of big data monitoring in power grid equipment, which can establish the first and second Equipment Association within the scope of the grid equipment monitoring data, as well as realize centralized access to all measurement information in the method of extending measurement model. This is significant to promote the process of deepening application of power grid equipment monitoring.

Dynamic load model is of great value in analysis and simulation of power grid, while the composition of load has an important influence on the characteristic and accuracy of load model. There is mass of load equipment in power grid, so it is usually necessary to classify the load equipment according to their different characteristic first, then establish a suitable load model separately, and synthesize them into a composite model according to their proportion. Only the power value of load can be measured when power grid operates in a normal and steady state, and their dynamic response characteristics are unknown. Therefore, it is difficult to obtain sufficient information for load classification. However, frequency characteristics of load are distinguished and easy to obtain, so it is useful for load classification indirectly. Firstly, several elector-magnetism models of typical load are established, and their harmonic curves and frequency characteristic are simulated and analyzed separately. Then, cluster analysis is carried out to obtain the typical characteristics and the membership degree which can represent the contents of load overall. Finally, a classification method combined with Neural Network is adopted, and the computation speed is also improved.

With the application and popularization of distributed power supply and power electronic equipment in power grid, AC distribution is faced with problems such as low efficiency and low power quality. At the same time, due to the advantages of large power supply capacity, long power supply radius, high efficiency, good controllability and adaptability to renewable energy access, DC power distribution has become a crucial development direction of the future distribution system. Reasonable and systematic analysis of power quality problems of DC distribution network plays an important role in its construction and application. Firstly, this paper introduces the background, significance and status of the research on DC distribution network and its power quality. Then introduces the three main topology of DC distribution network structure and connection mode. After selecting pseudo bipolar structure to build the simulation circuit, the power quality phenomena such as voltage sag are simulated and analyzed by PSCAD. The results obtained are consistent with theoretical analysis.

Together with the daily variation of load demand in power grids, the continuous integration of offshore and onshore wind farms to feed the grid with green energy has recently led to a severe frequency stability issue due to the extra variation in the generation side. Hence, wind turbines (WTs), among other renewable energy units are required to regulate their output power to mitigate the fluctuation in generated power and support frequency stability. In this paper, model predictive control (MPC) is implemented in an adaptive way to operate WT in de-loading mode under wind disturbances. In addition, to get comprehensive operation of WTs and meet grid code requirements; we present a new grid-forming controller in the WT rotor side converter to emulate the inherent synchronizing and load sharing property of conventional generators. The limitations of rotor speed and rotor side converter are considered in the proposed control approach.

In recent years, countries around the world have been vigorously developing new energy and electrifying new energy sources. As a result an increasing number of power electronic devices appear in the grid which makes the power grid develop toward low inertia and low damping. The Virtual Synchronous Generator (VSG) control strategy can simulate the working state of the synchronous generator and provide the grid with inertia and damping, which has become a research hotspot for scholars. Due to the unbalanced load distribution and the random change of power load, the grid voltage may become unbalanced during the actual operation process. The three-phase output current of the VSG would be unbalanced and a fluctuation of output power appears. To solve this problem, a new current and power quality control strategy based on VSG is proposed in this paper, in which the current balancing or constant power is achieved without changing the basic characteristics of the inverters using VSG control strategy.

Aiming at the problem that the traditional fault monitoring method of mine power supply equipment is single and can not effectively reflect the real-time working state of equipment and cables, this project studies a comprehensive intelligent fault diagnosis and monitoring early warning technology method. Through the research of two key technologies, power quality analysis technology based on harmonic method and insulation condition monitoring technology of electrical equipment, an intelligent diagnosis system for the health condition of mine power supply equipment is designed and formed. Through real-time monitoring of power grid harmonic parameters, power grid operation parameters, insulation parameters, and temperature parameters, the system can comprehensively analyze and judge the working status of various equipment and connecting cables in the underground power grid to comprehensively judge the faults of high explosive switches, transformers, and connecting cables, and achieve the purpose of fault location and early warning.

由于电网中大量电力电子器件的应用，导致电网中谐波问题严重。解决电网谐波问题，首先是对电网中谐波成分的检测，将三相三线制的电力系统中瞬时无功理论的基本原理，推广到三相四线制系统，验证在存在零序电流的情况下，低压配电网系统对检测负载电流谐波含量的实用性。在检测谐波含量的过程中，为有效解决传统方法中跟踪精度和响应速度无法兼备的问题，利用引入电流平均值法模块来代替传统LPF模块。通过Matlab搭建仿真模型，分析优化后算法的适用性及其高效性能。证明改进后的方法可以有效的解决精度和响应速度之间的问题，更有效的完成对谐波电流的检测，从而计算出指令电流，以便于实现对电网电流的补偿。 Due to the application of a large number of power electronic devices in the grid, the harmonics problem is serious. The first to solve the harmonics problem is detection of harmonic components in power grid. The basic principle of the instantaneous power system of three-phase-three-wire system in reactive power theory is extended to three-phase-four-wire system by examining the practicability for harmonic detection in low voltage distribution network system with zero sequence current. In the process, for solving a tradeoff between maladjustment and the speed of dynamic response in the conventional detection method, the low-pass filter is substituted by current average method. By using the platform of Matlab to prove its applicability and highly active ability, it aims to prove that the improved method can resolve problems between accuracy and response speed and be more efficient detection of current harmonics. Thus we can calculate the referential current to complete the compensation of grid current.

Renewable energy units are required to have reliable fault ride-through capability to prevent large-scale disconnection of renewable energy plants due to grid faults. Since synchronous generators have better voltage and current resistance capabilities, one of the advantages of renewable energy connected to the grid through the motor-generator Pair (MGP) system is the isolation of grid faults, which is totally different from existing fault ride-through methods. First, the structure and mathematical model of the MGP system are introduced in this paper. Then, a novel control method for the MGP system based on DC link voltage feedback is given, which is very important for fault ride-through in the control power balance on both sides of the DC bus. The isolation mechanism, damping and reactive power support functions of the MGP system on grid faults are analyzed by means of the rotor motion equation and phasor diagram of synchronous machine. A 5-kW MGP simulation and experimental platforms are built to verify the isolation and protection effects of the MGP system on a renewable energy generation system during the transient processes of grid voltage sag, overvoltage and multiple voltage sags. The results demonstrate that the MGP system can isolate grid faults on the generator side, while the oscillation amplitude on the motor side is much smaller, and the generator can provide strong reactive power support to the grid during three grid faults.

Pervasive computing emphasizes the integration of computing and the environment. In this computing model, people can get information and process knowledge at any time, in any way. But the traditional knowledge representation methods can not be applied to pervasive computing directly. Agent technology is originated from the research of distribution in artificial intelligence, and the BDI theoretical model of Agent is considered one of the foundations of distributed artificial intelligence theories. BDI agent can sense environment, get information, store, use, exchange knowledge. This paper proposed a agent-based knowledge representation, focusing on basic concepts, basic framework and the key points of the agent-based knowledge representation. Taking power grid as an illustration, it describes how to use agent-based knowledge representation to represent the diverse equipments in power grid, applying the knowledge to pervasive computing. We can find that the agent-based knowledge representation has advantages in the pervasive computing.

The virtual synchronous generator (VSG) technique is used to simulate the external characteristics of a synchronous generator (SG) to provide certain damping and inertia to power systems. However, it may easily cause low-frequency oscillation of the power system. We studied the small-signal stability of a grid-connected virtual synchronous generator. Firstly, the small-signal models of single-VSG and multi-VSG grid-connected systems were established. Subsequently, the system eigenvalues were obtained by solving the state matrix, and the system oscillation modes were analyzed. The eigenvalue analysis method was used to analyze the impacts of parameter changes, such as virtual moment of inertia, virtual damping coefficient, line resistance, and line inductance, on system stability. Finally, our conclusions were verified by numerous simulation models.

Since the 500 kV DC transmission project was put into service by monopolar link in Dec. 2002, noises of the 500 kV main transformers around WuNan increase significantly (about 21 db). This article discussed the impact of ground direct current produced by DC monopolar link upon equipment in AC system. It includes the impact of DC magnetic biasing on transformers and current transformers, the impact of power grid harmonic on protection relay devices and the corrosion impact of ground DC magnetic biasing on the earthing network in substations. It also proposed the measures of injecting reverse direct current to neutral point of transformers to limit the DC magnetic biasing in transformers