Zhong Wuzhi

Mechanism Research of Short-Term Large-Disturbance Voltage Stability

The right understanding of mechanism of short-term large-disturbance voltage stability is very important for further research of voltage stability. In this paper, the actuality of voltage instability research are summarized, the concepts of voltage stability and voltage collapse are expounded. The influence of load on short-term large-disturbance voltage stability is analyzed on a simple power system. The results show that the dynamic characters of load must be considered in analysis of short-term large-disturbance voltage stability. Through research of voltage stability and voltage collapse, a new mechanism of short-term large-disturbance voltage instability is presented from the engineering point of view. In the end, some solution measures preventing short-term large-disturbance voltage instability are given.

A frequency-domain parallel eigenvalue search algorithm of power systems based on multi-processing

With the rapid development of large-scale interconnected power systems, inter-area low frequency oscillation phenomena occasionally occur; thus, the small signal stability problem has become a serious issue affecting power system stability. When analyzing the small signal stability of a large-scale power grid (in particular, on-line dynamic security early warning systems), given the high rank of the differential algebra equations (DAEs), the serial eigenvalue algorithm cannot meet the requirements of computation speed. In recent years, the development of multi-core CPU technology has been very rapid. By fully using the hardware resources of multi-core CPU computers, the small signal stability calculation speed problem can be effectively solved in parallel computing technology. In this paper, a frequency-domain parallel eigenvalue search algorithm of power systems based on multi-processing is described, with the algorithm realized in the PSD-SSAP system, which is widely used in China. The calculation is accurate, the realization of the algorithm is simple, and the parallel computing efficiency is very high. Numerical simulation results of actual large-scale power systems show that the proposed algorithm is correct and efficient.

New mixed integral algorithm for unified dynamic power system simulations of transient, medium-term and long-term stabilities

This paper discusses a new mixed numerical integral algorithm for unified dynamic simulations of power systems in which the electro-mechanical transient, medium-term and long-term dynamic phenomena are united. The main problems were analyzed using the existing Gear integral algorithm for the dynamic simulation of power systems. The new mixed integral algorithm integrates the advantages of the implicit trapezoidal integration algorithm with a fixed time step and the Gear algorithm with a variable time step. The proposed algorithm was found to achieve a great computational efficiency in the transient stability stage of unified dynamic simulation and can easily deal with discontinuous equations in control system models. The simulation results of two actual large-scale power systems show that the proposed algorithm is effective and feasible.

Modeling of protective relay systems for power system dynamic simulations

To solve the problem of lacking of accurate protection relay models in power system dynamic simulation, a general modeling method of protection relay based on “virtual relay” is proposed. A “virtual relay” is a kind of simulation for real relay and defined with rules of logic operation. With hierarchical structure and object-oriented modeling strategy, this method has the advantages of clean logic and convenient modeling, and its easy for the users to correct models and expand functions. An open and transparent protective relay model library is developed and dynamic simulation calculation including protection relay models is realized. The simulation results revealed that the dynamic simulation program including protection relay models can represent the dynamic performance of electric power system after disturbance more actually. It can be used to analyze cascading failures caused by incorrect operation of protective relays, replay the accident in a long time after a disturbance in power system, study the essence cause of accident and find the correct fault prevention measures.

Power system risk assessment method based on dynamic power flow

Risk assessment theory is paid more and more attention to consider the random characteristics of power system, but traditional method could not consider the operating factors as frequency response of generators and loads, various emergency control measures. In this paper, a dynamic contingency analysis method base on dynamic load flow is proposed considering the above factors. The dynamic contingency analysis is a less time-consuming approach, but could simulate as well the detailed load shedding relay model, and the time-varying reliability model. So the proposed dynamic contingency analysis gives a good tool for cascading failure simulation.

Review on power system cascading failure thoeries and studies

A large number of blackouts have happened in power system recently, and most of them are cascading outages. Because of their severe consequences, a variety of methods are proposed to study the mechanism of cascading outages. These methods can be divided into four categories: self-organized critical theory, complex network theory, operational reliability theory, and power system simulation theory. This article reviewed the researches on cascading outages, and pointed out some important research achievements and their drawbacks.

Study of Credibility Evaluation of Dynamic Models and their Parameters

The time-domain simulation plays an important role in planning, designing and operation of the power system, but mismatches between its results and the actual system response show that the credibility evaluation of dynamic models is critical in all the above aspects of power systems. This paper discusses the technologies of credibility evaluation, including hybrid dynamic simulation with PMU measurements, error analysis and the calculated indices. Moreover, a phase shift method is presented to implement hybrid dynamic simulation in PSD-FDS. Then the paper proposes a credibility evaluation scheme to provide solution for the evaluation. At last, one sample is used to validate the implementation of hybrid dynamic simulation, while the other sample illustrates the effectiveness of the credibility evaluation approach.