Yutian Liu

Optimal VAr planning in area power system

This paper combines the theory of decomposition and coordination with improved tabu search (TS) technique and applies them to reactive power planning in area power systems. Based on the theory of decomposition and coordination, the complex problem is decomposed into several sub-problems under different load conditions. Each sub-problem is solved by the tabu search which is a heuristic optimal technique characterized by avoiding local optimal solutions in high probability. Sensitivity analysis and expert knowledge are used to aid the initial solution generation and improve the search process. Compared with the conventional single load condition and stochastic search method, the proposed algorithms make the complex optimization feasible and can find optimal solutions effectively. Such advantages are demonstrated through the Jinan area power system with 137 buses and 162 transmission lines in Shandong province of China.

Network Partition for Distributed Reactive Power Optimization in Power Systems

Reactive power optimization is an important measure to improve the secure and economic performance of power systems. To reduce the dimension of solution space and solve the time-consuming problem more effectively, a network partition method for distributed reactive power optimization is introduced to divide a large-scale power system into several small-scale subsystems. The voltage response of nodes to the perturbation of various reactive power resources is calculated in the partition method. And a new electrical distance is worked out in the method, which combines the network topology information with the voltage response. The alpha decomposition algorithm is used to cluster nodes in power systems. Some supplements based on divided subsystems for distributed reactive power optimization are represented after network partition. The simulation of a practical system verifies that the reasonable and effective results can be obtained using the proposed partition method.

Padé approximation based method for computation of eigenvalues for time delay power system

Transcendental terms appear in the characteristic equation of a power system and results in an infinite number of eigenvalues, when time delays in the feedback signals of power system wide-area damping controllers are considered. This makes it very difficult to obtain system eigenvalues via direct solution of the equation. In this paper, a method for computing a reduced set of eigenvalues of a time delay power system is proposed by using Padé rational polynomials to approximate the delays. The Padé polynomials are firstly transformed into their equivalent state space representations. By interconnecting the models of the open-loop power system, wide-area damping controllers and the state space representations of time delays, the linearized model for the closed-loop power system is then established and a reduced set of eignevalues of the system can be computed. The method has been tested on the New England 10-machine 39-bus test systems and compared with the eigenvalue computation method in the software package DDE-BIFTOOL. It shows that the proposed Padé approximation-based method can accurately obtain nearly all of the eigenvalues relating to system dynamic devices. The number of eigenvalues relating to time delays that can be correctly computed and their accuracy strongly relates to the orders of the Padé rational polynomials.

Generator field overvoltages due to energizing lines

The field current transient characteristics are studied in the paper when generators energize transmission lines under no-load. The tendency of reverse current induced in field circuit is explained. Taking into account the effect of rotor eddy currents, a transient equivalent circuit of generator is presented. A generator energizing a 500 kV long line under no-load is simulated using the EMTDC program. The simulation results demonstrate that large reverse voltages may occur in field circuit and happen easier than the phenomena of self-excitation and switching surge overvoltages, and that the 4-quadrant excitation system can avoid the large reverse voltages.

A new method for incorporating load pickup as a control means for standing phase angle reduction in power system restoration

A mixed-integer nonlinear programming model is proposed in this paper for reducing excessive standing phase angle difference (SPA) across open circuit breakers in transmission loop paralleling operation. The model adopts both the active power generation increment and the load switch as control variables and takes the relative importance of the loads to be restored into account, resulting in fewer rescheduled generators and less adjustment of active power generation. The condition for transmission loop paralleling operation can be reached from two ways of reducing generator adjustment time and optimally restoring load. The method can improve power restoration efficiency, speed up restoration progress, and hence reduce the loss of outage. Simulation results of New England 10-machine 39-bus test system demonstrate the effectiveness of the method.

Power Transmission Path Analysis of Voltage Stability in Shandong Power System

Voltage stability of Shandong power system is analyzed by power transmission path analysis. Weak buses are decided by local voltage stability index. Voltage stability indices of both active power transmission paths from the west to the east and local reactive power transmission paths are computed with load increasing. The reactive power reserve indicator is also calculated and key factors that have great influence on voltage stability are summarized. Results of the software VAST prove the feasibility of power transmission path analysis applied to Shandong power system. Schemes to improve the voltage stability by SVC are compared and the optimal position is determined.

Distributed reactive power optimization and programming for area power system

A distributed reactive power optimization method for area power system is presented in this paper. Considering the difference of network structure and the characteristics for reactive power optimization, area power system is divided into a subtransmission sub-system and distribution sub-systems according to layers and regions. So the optimization problem of large-scale area power system is decomposed into several optimization sub-problems of small-scale systems, which can reduce the difficulty of reactive power optimization problem significantly. The subtransmission sub-system and distribution sub-systems are independent relatively in power flow algorithms, objective functions and optimization algorithms. The optimization of the whole area power system is solved synthetically in the distributed computing way. Based on the proposed approach, a Client/Server software package is also introduced. The simulation results, greatly improved voltage profiles and reduced power losses, show that this method is feasible and effective.

Network development plan in reconstructed Philippines electric power industry

For the restructured electric power industry, transmission planning had become increasingly complicated with both economic and engineering considerations, and many new issues have surfaced. Significant challenges arising from the reconstruction for transmission planner are extensively analyzed from the views of transmission, generation, uncertainties, regulatory risks, and market needs, etc in this paper. Then, a specific long term transmission development plan for restructured electric power industry in Philippines is introduced. Long term transmission development plan of Philippines covers 2010 to 2030. For Luzon Grid, the long term transmission plan mainly focuses on the 500 kV and major 230kV transmission backbone, which is the major highway for bulk power transmission and the Metro Manila transmission configuration that serves the grids load center. For Visayas grid, the plan mainly focuses on the 230kV transmission backbone from Samar, Leyte, Cebu, Negro, and Panay Island, which is almost 900 km. For Mindanao grid, it focuses on upgrading transmission backbone from north part to the south part from 138kV to 230kV and on improving its transmission capacity.

Wide-area model predictive damping controller based on online recursive closed-loop subspace identification

This paper proposes an adaptive damping controller design method by integrating online recursive closed-loop subspace model identification with model predictive control theory. The reduced order state space model which contains dominant low frequency oscillation modes was firstly identified. According to model prediction and optimization with the current state of power system as the initial state, an infinite horizon closed-loop optimal control was obtained. Online model identification and control optimization were repeated in each time interval. The strategy overcomes the inherent shortcomings of controllers with fixed parameters based on offline identification thus solves the problem of the control performance degradation due to variation of the complex operation conditions and time-varying and uncertain characteristic of system parameters. Simulation results demonstrate the effectiveness and robustness of the proposed controller in damping inter-area low frequency oscillations. The strategy to coordinate the proposed controller with PSSs and other similar controllers in multi-machine power systems is also discussed.

Monitoring and Analysis of Power Supply Reliability of Low Voltage Consumers

Power supply reliability can reflect the overall quality and safety management of power system. But statistical analysis for low voltage power supply reliability is still difficult mainly due to the limit of investment. In this paper, a monitoring and statistical analysis system for power supply reliability estimation of low voltage consumers is developed. In this method, it is proposed to set some suitable low voltage reliability monitoring points according to measurement precision requirement. The operation data collected by the monitoring points was transmitted to monitoring center for automatic computation and analysis. By setting suitable monitoring points scientifically and analyzing the collected data statistically, it is possible to control statistical error to a reasonable range with a much lower investment. Practical application results of the low voltage network in Jinan illustrate that this method is valid and feasible for the current low voltage system and technical equipment condition in China.