Yue Yuan

Research on transmission congestion of power system containing wind farms based on genetic algorithm

With large-scale integration of wind power, load flow distribution is highly uncertain. It is unrealistic to adopt traditional deterministic load flow calculation for system operation. What is more, load flow in some transmission lines may be increased to a level where a random event could cause the network collapse. A method of combined cumulants and Gram-Charlier expansion (CCGCE) to calculate probabilistic load flow distribution and a research on relieving transmission congestion by FACTS are proposed in this paper. On the basis of a thorough analysis of the international and domestic researches, this thesis firstly introduces mathematical models, including wind power, FACTS and system models. There are two typical FACTS instruments. One is the SVC, modeled with two ideal switched elements in parallel: a capacitance and an inductance. The other is the TCSC, modeled with three ideal switched elements in parallel: a capacitance, an inductance and a simple wire, which permits the value zero. Secondly, it discusses the procedures of Genetic Algorithm, which includes forming initial population, defining fitness function, and application of crossover, mutation and so on. Thirdly, it carries out two simulations. The first simulation demonstrates the accuracy and computational efficiency of CCGCE method by comparing to Monte Carlo method. The second simulation is composed of two parts. The first part is to find out the appropriate location and capacity of FACTS, and the second part is to check the congestion relieving after the installment of FACTS by CCGCE method. Finally, it suggests that the CCGCE method can significantly reduce the computational time, while maintaining a high degree of accuracy on probabilistic load flow calculation, and concludes that after the installment of FACTS, the transmission congestion of power system containing wind farms can be relieved well.

A novel algorithm for power system planning associated with large-scale wind farms in deregulated environment

In recent years, more and more inter connected large-scale wind farms and ongoing deregulated environment take many challenges to transmission network expansion planning (TNEP). These challenges lie not only on more uncertainties of power flow in network but also on difficulty to compromise behalf of all new key stakeholders of power utilities. A novel algorithm is proposed in this paper. Firstly the power flow distribution and overload probability of network is calculated based on WTG output distribution and trade mechanism of power market. On this basis a new index which is introduced to evaluate the economic efficiency of all lines in candidate pool is proposed. Then low efficient lines are removed from the candidate pool step by step until optimum expansion scheme is obtained. Several experiments are carried out to demonstrate the performance of proposed algorithm on the modified Garver six-bus test system, then impacts of wind farm capacity and wind regime on TNEP are also discussed here.

A comprehensive pole control unit design for HVDC converter station

As the core control unit, the pole control unit of converter station determines the performance of the whole HVDC system. Aimed the back-to-back converter station, the control strategies are analyzed and discussed in this paper; characteristic curve for converter station control is patterned. On the basis of above work, the pole control unit is designed. Through the fast control for fire angle of converter valves and the slow control for taps of converter transformer, the projected control strategies are implemented. At last, the simulation results verified that this designed pole control unit can realize expected functions.

Design of energy storage scheme for the smoothing and dispatch planning of large-scale wind power generation

The paper examines the use of energy storage system to smoothen the output power from wind farms, and to make dispatch planning from the wind power generators possible. Firstly wind power is segregated into components through the use of filters designed from the application of empirical mode decomposition technique. Buffering of the high- and mid-frequency components of the wind power is then effected through the use of battery-supercapacitor banks, while the low-frequency components of the wind power are used in conjunction with a pumped-hydroelectric storage system to realize short-term dispatch planning. The proposed method is illustrated using data obtained from an existing wind farm.

A new method for analyzing the influence of the impact load in steel plant on grid

Electric arc furnace (EAF) and other non-linear impact load are equivalent to the pollution source for power quality of grid, which will cause the device in grid to be heated and vibrated, that will increase loss, condense the life of the device and even damage it, interfere with communication, cause the relay protection to misoperate, and cause flick that will have the eyes more tired. In this paper, a new method for simulation of the impact of electric arc furnace reactive impact load on grid is presented. The voltage fluctuation at PCC (i.e. point of common coupling), caused by the reactive impact load, will be simulated by the transient short circuit, which will solve the problem that the change time of the impact load is uncertain. The proposed method will be applied to the analysis of the impact of the reactive impact load in one steel plant on grid. Comparisons of simulation and measured values of the voltage fluctuations and flicker have confirmed that the proposed method is reasonable. By analyzing the results, this paper has put forward the requirement to compensation capacity and corresponding time of the dynamic reactive power compensator device for reducing the impact of the steel plant on grid, which will make contribution for the safe and stable operation of grid and the use of the power with high quality for millions of households.

A study on value compensation of SVC Ancillary Service based on power market

So far, the issue on active power pricing has been preliminarily settled, but the research on reactive power pricing is still in its infancy. Studies in this field are mainly focused on three aspects: marginal reactive power pricing without considering reactive power producing cost, marginal reactive power pricing taking reactive power producing cost into account, and the reactive power pricing theory on non-marginal cost. However, there is still no consensus on how to calculate and compensate the value of reactive power ancillary service (RPAS), such as static VAR compensator (SVC) and so on. The thesis firstly introduces the domestic and foreign studies on compensating the value of RPAS. Then, it presents the mathematical model of SVC, and gives a brief account on the contributions made by installing SVC, such as increasing the active power transmission capacity of power line, restraining low- frequency oscillation and enhancing the transient stability of power system, and so on. Based on a power system model, the thesis puts its emphasis on analyzing the value compensation mechanism of reactive power ancillary service of static VAR Compensator. Finally, it points out that the mechanism can embody the essence of power market fairly well.

A novel method for the analysis of the impact of the high-power motor starting on grid

The starting current in high-power motor is very high, which will cause the voltage drop during start. Especially, with the smaller capacity of the source, the voltage drop in the grid is even more. In this paper, a new method for the simulation of the voltage drop in grid, caused by motor starting, is presented. Depending on the different start-up methods, the method determines the equivalent circuit of the motor at start up time. With the use of the transient simulation and the full consideration of the transient regulation of the grid, this method has solved the limitations of the traditional simulation, and is more accurate. Then, the proposed method will be applied to the high-power motor in one steel plant. Comparison between the simulation and the measured curves has confirmed that the results of simulation are accurate and reasonable. The proposed method could be extensively used to the analysis of the voltage drop in grid caused by the motor starting in the future, for the choice of the reasonable start-up method.