Buhan Zhang

Probabilistic dynamic load flow algorithm considering static security risk of the power system

Nowadays, the stable and secure operation of power system has attach more and more attention. The traditional static security analysis is based on deterministic load flow, which cannot reflect the uncertainty of load and the probability of branch outage. In addition, the conventional load flow model does not consider the static power-frequency characteristic of generators and load, which is not in accordance with the real operating condition of power system. In order to provide comprehensive static security risk assessment for the power system, so that the potential dangerous and vulnerable part of power system can be recognized before serious outage happens, a Probabilistic Dynamic Load Flow considering Static Security Risk (PDLF-SSR) algorithm is proposed, in which a new state variable - system frequency is added. And the loss is no longer undertook by balancing generator only but by all generators having speed controllers. In addition, this paper also considers the contingency set of power system by calculating the probability of each contingency happening and then obtaining the PDLF of each contingency. Thus, the overall PDLF considering contingency set can be obtained by combining the full probability theory and PDLF based on cumulants. The algorithm can provide valuable information for power system planning, reliability analysis and static security risk assessment.

Economic benefits evaluating of wind power integration considering transmission congestion

In this paper, a model of evaluating the economic benefits brought by wind power integration considering transmission congestion is proposed, in which the Probabilistic Load Flow based on Cumulants Method (PLF-CM) is applied to calculate the probability distribution of section power flow. According to the case study, the transmission congestion is the main factor that limits the utilization of wind power, which also limits the economic benefits of wind power. Moreover, the different penetration of wind power and different integration places of wind farms also bring different benefits to the grid, which can provide some references of choosing appropriate wind power integrating places and deciding the best integrating wind power capacity for power grid plan-makers.

Distribution network energy loss calculation method considering wind power integration

Grid energy loss is one of the key factors affecting the economic operation of power systems. Accurate calculation of electric energy consumption, will have a great positive effect on the planning, operation and management of all aspects of the grid. Due to the randomness of wind power resources, wind power is likely to increase access or may reduce power system losses. Therefore, study on grid energy loss calculation method containing wind integration has very important practical significance. Currently there are many grid theoretical line loss calculation method, but these methods have some limitation such as, less considering the load curve changes. This paper presents an improved method of equivalent power to calculate energy loss of wind power integration, through considering the impact of the load curve, and the random fluctuations of wind power, making use of load shape coefficient to correct the average power, computing power flow calculation by using equivalent power, calculate the energy loss more accurately.

A peak load regulation scheme for Hubei power grid with UHVDC integration

Under the background of transmitting thermal power via UHV transmission line from Mengxi to Hubei in the long-term planning, this paper analyzed Hubei power grids peak load regulation scheme which Mengxi UHVDC involved in. Based on the energy-efficient power generation scheduling approach and multiple constraints of units, a peak load regulation scheme under the coordinated operation of thermal power, hydropower, pumped-storage and UHVDC power in a calculating level year was given. It is indicated that the peak regulation capacity shortage problem in Hubei is solved effectively with Mengxi UHVDC integration.

A research of D-FSC technology for improving voltage quality in distribution networks

The series capacitor can improve the transmission capacity and voltage stability effectively. The fixed series capacitor (FSC) applied to the distribution networks can improve the voltage quality and reduce the system losses. This paper presents the analysis methods of D-FSC used to regulate the distribution network voltage. For a typical radial 110kV high voltage distribution grid, we selected the compensation position and calculated the compensation capacity of single-point and multi-point compensation methods, then do the research of the relationship between the compensation capacity and compensation effects. In the scheme proposed, the D-FSC can effectively improve the voltage quality and reduce system losses.

Dynamic stability analysis of the interconnected power system with Mengxi UHVDC integration

Due to the mismatch between power supply and demand, in addition with the increasingly prominent problem of environmental pollution, UHV AC/DC power transmission over long distance obtains rapid development in our country. With the expansion of the power grid, regional low frequency oscillation has become one of the major problems that endanger safe and stable operation of power system. In this paper, taking a large-area interconnected system integrated with Mengxi UHVDC transmission line as the background, dynamic stability of the system is analyzed using small signal analysis method and time-domain simulation based on PSASP under different load and UHVDC operating conditions. The results show that when DC out of running, weak damping will appear in the interconnected power grid. PSS is the most economical and effective equipment for damping low frequency oscillation, which can perform well to both the local mode and the inter-area one. In view of the existing weak damping mode, PSS parameters are optimized which effectively improve the system damping, thus insuring the safe and stable operation of the system after the UHVDC line access.