Zeng Yuan

An improved power system stability criterion with multiple time delays

Since there exist significant time delays in the data of phasor measurement unit (PMU) and wide-area measurement system (WAMS), to evaluate their impact is very important for power system online stability assessment and controller design in the wide-area environment. In this paper, we use Lyapunov stability theory and linear matrix inequality (LMI) method to analyze the impact of time delays on power system stability. An improved delay-dependent stability criterion for power system stability analysis with multiple time delays is presented. Based on Lyapunov-Krasovskii theory, a proper Lyapunov functional is firstly constructed. And, in deduction of its derivative function along the system trajectory, some necessary slack variables are introduced so as to reduce the method conservativeness. Then the derivative function is expressed as a set of linear matrix inequalities, which can be easily solved with LMI toolboxes in Matlab or Scilab. Finally, a typical two-dimension time-delayed system and WSCC 3-generator-9-bus system with two time delays are employed to validate the method effectiveness. It is revealed that the presented method is correct, effective and with less conservativeness. Work of this paper is helpful for power system stability assessment and control with considering time delays under wide-area environment.

Network reconfiguration for distribution system with micro-grids

Nowadays, technologies of distributed generation (DG) and distributed energy resource (DER) are developing rapidly. It has been demonstrated to be more reliable and economical that DGs or DERs are integrated into the traditional power grid based on micro-grid. So, more and more micro-grids will occur in distribution system in the future. In this paper, we mainly concern and discuss the impact of micro-grids on the distribution network reconfiguration. A model suitable for reconfiguration of distribution system with micro-grids is presented in this paper. Once a fault occurs in a distribution system, it can be applied to construct some islands so as to guarantee the power supply for some important customers and to reduce the system power loss at the same time. The problem is decomposed into a capacity subproblem and a reconfiguration sub-problem. The former is used to determine the optimal capacity for each island, and the latter is used to find the optimal reconfiguration with less power loss. They are called iteratively to get the optimal solution. Finally, some typical systems are employed to validate the effectiveness of the presented method.

Interface control based on power flow tracing and generator re-dispatching

In recent years, economical and environmental reasons have forced the transmission systems to be operated closer to their security limits. Power utilities world-wide have become even more concerned with various power system stability problems. In this paper, we mainly concern power flow control strategy on some system critical interfaces. A control method based on power flow tracing and generator re-dispatching is presented. It can effectively control the power flow on some critical interfaces in a relatively large range. Power flow on the interface is first traced backward to locate generators to be adjusted in the sending-end subsystem. And then, it is traced forward to determine loads to be affected. Power flow tracing is adopted again from such loads to determine their supplying generators in the receiving-end subsystem, which is then used to compensate the load fluctuation on the interface. Since power flow tracing is mainly used in the congestion management, power loss allocation, node pricing in deregulation study, the presented method can not only be used in the traditional and monopolistic environment to enhance power system stability, but also can be used to mitigate power system congestion under deregulation environment. Finally, New England 39-bus system, 57-bus system and 118 bus system are employed to verify the effectiveness of the presented method.

Fast assessment of regional voltage stability based on WAMS

Voltage stability margin of regional network is not a fixed quantity but closely related to operation condition and operation constrains. This paper proposes an effective method to estimate the real-time voltage stability margin based on some locally synchrophasor measurements. A Radial Basis Functions (RBF) neural network is employed to estimate the regional margin. The validity of the method is illustrated by case studies on the IEEE 30-bus system.

Improvements on economic analysis of coal transportation and power transmission

The economic analysis of coal transportation and power transmission in traditional studies do not consider the reliability and environmental factors and their influences on the critical distance. In this paper, the assessment method based on system operation simulation can evaluate the fuel cost, environmental cost and reliability cost in each time period. Economic analysis of the instance for coal transportation and power transmission is comparatively studied from the point of total social cost of unit electricity. Moreover, the sensitivity analysis of railway cost, environmental cost and reliability cost on critical distance is studied. The results show that the environmental cost and reliability cost have a great influence on the critical distance and cannot be ignored in the economic analysis of coal transportation and power transmission.

Visualization tool for transient stability monitoring of bulk power systems based on DSR

Dynamic security region (DSR) gives power system engineers systematic and global information about the feasible operation region. This paper is a result of an investigation into the use of DSR concept and its effective application in bulk power systems. It particularly concerns with developing a software-based tool for the transient stability monitoring in the on-line operation environment. A practical DSR solving method based on massively parallel computer clusters is described, and a new software package, named power system dynamic security region (PSDSR) is developed. Following a brief discussion about the main requirements, the paper gives a summary of the development of PSDSR from both the software architecture and the function implementation. A most distinctive character, the practical application in monitoring the cut-set power flows, with result visualization is emphasized.