To improve the processing ability of asymmetrical eletromechanical side fault as well as the flexibility of electromechanical and electromagnetic transient hybrid simulation, a calculation method of complex asymmetrical fault in the electromechanical and electromagnetic side at the same time is proposed.This method obtains the fault circuit admittance matrix according to the type of asymmetric fault.By modifying the admittance element associated with the faulty node, the fault circuit admittance matrix is superimposed on the normal admittance matrix to obtain the admittance matrix after fault.The network solution is finally achieved by solving the network equation after fault.Based on the linear circuit superposition theorem, the Thevenin equivalent voltage of the interface node is calculated.To reduce the modeling scale of the electromagnetic side, positive sequence equivalent conductance of the interface is used for the conversion of the Thevenin equivalent voltage into Norton equivalent current.At last, through the electromechanical and electromagnetic transient hybrid simulation platform of a IEEE 39 system containing a HVDC line based on PSCAD+C frame, the simulation accuracy and effectiveness of the method is validated.

Power quality problems could cause enormous amounts of economic cost to electricity consumers. Taking voltage dips as an example, this paper presents a general overview of methods to quantify economic impact of power quality problems. It also presents in detail several ways how to collect power quality economic data. At last, suggestions on how such researches could be done in China are represented.

The information model is an abstract description of existing physical objects and their relationship in a system, such as the common information model(CIM) in IEC61970, which is provided with broad applicability in power system. In order to track the real-time operation state of the system, this paper proposes a novel method for the analysis of the area of vulnerability based on CIM, which is widely adopted in standardization for power dispatching automation system, and programs it. Firstly, the design scheme and CIM parse method are introduced in detail. Then a new fault positions method based on interpolation is proposed to calculate the area of vulnerability, which has higher precision and faster computation speed and could overcome the blindness of setting fault points. Finally, the graphic and data-based result of the area of vulnerability is provided.

The area of vulnerability (AOV) of point of common coupling (PCC) can directly reflect the issue of voltage sag caused by faults in power system. In order to calculate the area of vulnerability more accurately and faster, this paper proposes a new fault positions method based on interpolation, which overcomes the blindness of setting fault points. The influence of transformer winding connections on voltage sag is also taken into account. Short-circuit calculation is adopted and transfer matrix representing the transfer law of transformer on voltage sag is deduced firstly. Then, the principle and implementation flow of the new method are presented in detail. Finally, the new method is applied to a regional power system of China, and graphic result of the area of vulnerability is displayed under balanced and unbalanced faults.

As the traditional reliability indexes are no longer to meet the needs of more complicated power quality demands for end-users, this paper introduces the concept of voltage availability to describe how the operation conditions are influenced by different voltage disturbances based on the traditional reliability. Besides outages in the traditional reliability, voltage dips, swells, short interruptions are also considered to assess the voltage availability.The severity index of voltage availability is evaluated with the help of technical characteristics of various disturbances, such as energy index. Moreover, combining severity index with the frequency of disturbances in different sites, the method is able to get the final voltage availability index, based on which the levels of voltage availability are determined. An example is made with the data of 27 sites, which confirms the usefulness of this method.

Voltage dips(VDs)(including voltage momentary interruption) could cause interruptions of the producing processes,which brings significant economic loss to end-users.The evaluation of the economic loss of voltage dips provides a solid foundation for reasonable investments on power quality mitigation measures,and could be used by the end-users to make production plans.Few relative researches have been done so far in China.In order to get an evaluation model of plant-level economic loss due to voltage dips,this paper presents a detailed discussion in two dimensions,including the characteristics of a producing process interruption and the composition of cost during voltage dips.At last,an evaluation example is presented to testify this model,according to the results of one power quality economic survey in China.The calculation result presents a precise prediction of the plant-level lost caused by voltage dips for one single user.

In recent years, power end-users are more and more demanding on the power distribution reliability and power quality, as even some small disturbances in power supply could lead to production process interruptions, which cause enormous costs to power users. Based on a one-year-long survey comprised of 37 face-to-face interviews in a coastal and industrial city in China, this paper presents the evaluation results of costs of power disturbances to different industrial categories. The annual costs of voltage dips, short-duration interruptions and outages for per end-user are investigated. With the data from the survey samples, it is shown that there is statistically significant correlation between the costs of power disturbances and the annual output value of end-users, which makes the evaluation of the whole costs in China possible.

The power energy of photovoltaic cells changes according to the external environment. In order to get high-efficient photovoltaic array power, it is necessary for the photovoltaic grid-connected system to conduct maximum power point tracking system. This paper came up with a perturbation and observation method based on hysteresis comparison and optimal gradient method to overcome the problems of oscillation and erroneous judgement. To test the effectiveness of the new algorithm, a three-phase single-stage photovoltaic system based on the PSCAD/EMTDC software was built. On the basis, a comparable analysis was provided for the regular perturbation and observation method with fixed step and the improved one respectively. Simulation results show that the improved MPPT algorithm can effectively eliminate the ripples of DC side voltage caused by the disturbance; when there is a mutation of the external environment, the grid system can stabilize quickly at a new maximum power point.

Power quality problems can cause enormous economic losses to electricity consumers.Based on a number of studies and articles,this paper presents a general overview of methods and processes to quantify economic impact of power quality problems.It also introduces in detail several ways to collect power quality economic data.Moreover,Net Present Value(NPV) method is introduced here to access power quality solutions.At last,the study scheme of power quality economic losses is proposed based on China’s actual conditions.