Mei Shengwei

Advanced EMS and its trial operation in Shanghai power system

To meet the demand of high stability, high quality, and low losses of power systems, the advanced energy management system (AEMS) is established and revealed in this bulletin, which has been put into trial operation in Shanghai power system for almost half a year. The AEMS is novel from all aspects covering idea, theory, method, software, and engineering. The essence of AEMS is exercising the hybrid automatic control theory and technology to realize multi-objective optimal closed-loop control of power systems. Based on an “event-driven” strategy, the AEMS transforms multi-objective optimal control problems into event identification and elimination by defining the unsatisfactory states of a power system as events. This bulletin concisely presents the theory and main advantages of AEMS, as well as its implementation in Shanghai power system.

On power system blackout modeling and analysis based on self-organized criticality

This paper makes a comprehensive survey on power system blackout modeling and analysis based on SOC (self-organized criticality). Firstly, a generalized SOC theory from the viewpoint of cybernetics is introduced. Then the evolution model of power system and its relative mathematical description, which serves as a concrete example of the proposed generalized SOC, are given. Secondly, five blackout models capturing various critical properties of power systems in different time-scales are listed. Finally, this paper analyzes SOC in power systems, such as, the revelation of criticalities of proposed models in both micro-scale and macro-scale which can be used to assess the security of power system, and cascading failures process.

On global controllability of affine nonlinear systems with a triangular-like structure

In this paper, we investigate a class of affine nonlinear systems with a triangular-like structure and present its necessary and sufficient condition for global controllability, by using the techniques developed by Sun Yimin and Guo Lei recently. Furthermore, we will give two examples to illustrate its application.

Identification of key transmission lines in power grid using modified K-core decomposition

Power grid today has been more interconnected than it used to be, resulting in frequent occurrence of cascading failure in the power system. According to historical data, many major cascading failures are caused by the outage of certain transmission lines. The transmission lines with potential to cause large scale cascading failure are called key transmission lines (KTL). To find out the KTL, this paper first proposes a correlation network which characterized the interaction between different lines in the system. Then, based on this new network, we identify the KTL in power system using the modified K-core decomposition, which has been amended to better suit the power systems inherit features. Finally, case studies utilizing cascading failure simulation on New England System and IEEE-118 system are conducted to substantiate the effectiveness and efficiency of the proposed approach.

Research on Self-Power Supply System of Inspection Robot for High-Voltage Power Transmission Lines

Inspection robot is a promising technique in automatic fault detecting for high-voltage power transmission lines. However, the small energy capacity and poor life of the battery hold back the application of inspection robots. To solve this problem, a self-power supply system is designed to realize the online battery charging by utilizing the voltage induced from the current on the transmission line in this paper. The key issues in the optimal design and practical implementation are discussed in details, including the induction module, the power conversion module. Experiments have been carried on to demonstrate the validity and effectiveness of the designed self-power supply system for inspection robots.

Modeling collapse and blackout of power system via AC-based model

The collapse and blackout caused by cascading failures in power system is a difficult problem. This work is concerned with the mechanism of collapse in large power systems. Firstly, a AC model for blackout is employed with OPF, which can describe the whole process of power system accurately; second, an algorithm is given to model the cascading failures with overloads and outages; thirdly, simulation performed on IEEE-30 bus system has verified that the proposed model and algorithm can reveal some collapse characteristics such as load level, outage lines and network structure

Effect of Sudden Increase of Dynamic Loads on Voltage Stability

With more and more dynamic loads, mainly induction motors, the associated voltage stability has become a growing concern in modern power system. This paper focuses on induction motor starting up. Firstly, a failure starting-up example of a 12 MW induction motor in China SINOPEC Yanshan chemical is given and analyzed through Lyapunovs first method and time-domain simulation. Then, from the viewpoint of static voltage stability, small-signal stability and acceptable voltage level, this paper classifies the starting-up situations into 6 categories. This classification can be used to analyze the above example. Furthermore, this paper points out that load rate and node voltage sensitivity should be considered in order to prevent cascaded voltage collapse in multi-motor situation. Finally, an index is proposed to forecast voltage stability during the starting up process.

Nonlinear stabilizing of multi-machine power systems based on Feedback Domination Method

Nonlinear turbo-generator valve control law for enhancing transient stability in multi-machine power systems is constructed based on feedback domination method (FDM). The nonlinear valve control based on FDM is simple and has robustness to some kinds of unknown disturbances. Different from the basic idea of feedback linearization method (FLM) which is to transform a nonlinear system into a linear system through nonlinear feedback, the basic idea of FDM is to transform a nonlinear system into another nonlinear system which is of particular form through nonlinear feedback. The dynamics of the transformed nonlinear system is dominated by the nonlinear part introduced by the feedback control law. In some sense, FLM can be considered as a simplified version of FDM. Digital simulations show that the nonlinear valve control based on FDM can improve power system transient stability greatly.

Blackout risk analysis and control of power system integrated with wind farm

With the increase of wind power penetration, the characteristics of the wind farm have brought a significant impact on the security of power system. It is urgent to study how to reduce the risk of cascading failures while improving the environmental benefits. In this paper, a cascading failure model containing wind farm is proposed, which considers wind power characteristics, such as the structure of wind farm, the randomness of power of wind farm, the virtual inertia control of wind turbine, and the disconnection response of wind turbine after short-circuit faults. In order to identify the key factors of blackout, decision tree is used to analyze results generated from this blackout model. Preventive control is adopted to decrease the probability or effect of critical attributes that can be found in decision tree. The blackout risk of IEEE 30 test system integrated with wind farm is analyzed. Several key factors, such as disconnection of wind turbines from the grid and certain transmission lines, are identified by decision tree. Besides, the effectiveness of the virtual inertial control of wind turbine, reactive power compensation and line construction is verified by simulation.

Power oscillation damping controller based on active disturbance rejection control technique for DFIG-based wind turbine generators

With large-scale integration of wind power in power systems, the impact of wind generation on power system stability has become an important issue. In this paper, a new power oscillation damping controller based on active disturbance rejection control technique for DFIG-based wind turbine generators is presented. The proposed power oscillation damping controller utilizes the grid frequency at the point of common coupling to generate the active power modulation, so as to damp power system oscillations. The kinetic energy of the rotating masses of wind turbine generators is utilized to provide the required damping active power. Case study on a two-area system verifies the effectiveness of the proposed power oscillation damping controller.