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With the wide application of power electronic technologies in power system, such as HVDC, new energy power stations and FACTS, the dynamic characteristics of the interconnected power grid have changed dramatically, and the traditional quasi steady model based electromechanical transient program cannot simulate the fast switching process of the power electronic components and its non-fundamental frequency or asymmetry characteristic, which is important to the accuracy of HVDC and FACTS models. Because of the limitation of calculation load and computing speed, traditional electromagnetic transient program cannot replace electromechanical transient program in large-scale power system stability analysis. FEMTP should be redesigned for transient stability analysis of large-scale electronic power system. Then the generator and transmission line’s electromagnetic models are discussed in this paper, and the discussion and simulation shows the adequation of their electromechanical transient model in FEMTP. Afterwards, the implementation of FEMTP was discussed in detail, and the example of China East power grid shows the appropriation of simplified electromechanical models and proposed technologies.

The construction of Jiangsu UPFC project has put forward higher requirements for the simulation and modeling of large-scale power electronics equipment. In order to deeply analyze the dynamic response of unified power flow controller based on modular multilevel converter(MMC-UPFC). The study of this paper is based on the MMC-UPFC operation principle and control strategy. We established the electromagnetic transient model framework and conducted a research of IEEE 39 case and South Jiangsu 500kV UPFC project in electromagnetic transient and electromechanical transient hybrid simulation program. Besides, a basic model framework of UPFC is also development in independent designed large-scale power system analysis software package called PSD-PSModel hybrid simulation platform and the MMC-UPFC hybrid simulation capabilities is realized. At the same time, the basic functions of the model are verified by simulation results. The achievement can provide strong technical support for further MMC-UPFC project and educational theory.

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.

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.

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.

Special protection systems (SPSs) are very important for the safety and stability of large-scale power systems. A more accurate assessment of system security can be achieved if SPS models are constructed to conform to the actual situation of power grids. However, it is difficult to realistically simulate the performance of SPSs for a large-scale power system. Based on virtual relays and ladder diagrams, this paper proposes a general modelling method for SPSs that conforms to their actual characteristics. Moreover, the full dynamic calculations including these models can be realized using this approach. The modelling process is significantly simplified and the computing work is considerably reduced using the new method. The results show that the simulation program, including the SPS models, can more accurately represent the dynamic performance of a power system after a disturbance, especially during cascading outages caused by power flow transfers. The method can be a useful tool for accurately analyzing the dynamic stability of power systems.

VSC-HVDC (Voltage Source Converter High Voltage Direct Current) transmission system is a recent HVDC technology. The paper presents a new way of VSC-HVDC electromechanical transient modeling and simulation, which is based on the theory of equivalent sources. This method uses equivalent sources to substitute for voltage source converter, in addition, there are no simulation of IGBTs or PWM trigger modular, so it is more appropriate for electromechanical transient modeling and simulation. By this way, the detailed dynamic model for VSC-HVCD is developed. This model includes four parts, i.e. the normal ac system, the VSC-HVDC inner dc system, the interface between ac and dc system and the VSC-HVDC control system. Then a case of VSC-HVDC transmission system is established in PSCAD, the results show that by using this method for VSC-HVDC electromechanical transient modeling and simulation, not only the steady-state power flow can be controlled, but the system can achieve ideal dynamic response.

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 it's 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.

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.

This paper proposes a method to perform electromechanical and electromagnetic transient hybrid simulation, including the interface location, the mutual equivalence solution of the electromechanical system and the electromagnetic system, which can perform excellently when the positive and negative sequence parameters of the equivalent circuit are different. The least square method is adopted to obtain the fundamental frequency current as the equivalent solution of the electromagnetic system. The method was demonstrated to be effective and feasible through two cases. It solves hybrid simulation problems when variable faults (including asymmetric faults) occur in an electromechanical network.

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.

Fault simulation is one of the main components of dynamic electric power system simulation programs. In this work, a fault-branch based admittance matrix was used to simulate a variety of multiple symmetrical or asymmetrical faults in unified dynamic power system simulation software. Admittance matrix contraction was employed to process multiple faults and random faults. An important feature of this method is its ability to process any faults in a branch without the addition of new branches or nodes, which improves the calculation efficiency and the usability of the software.