The Research On Active Power Balance Of Power System Under Large-scale Integration Of Wind Power

With more wind power being integrated into the power grid, its random and intermittent output has brought great impact on various aspects of active power balances. Among them, the main problem at present is massive wind power curtailment during valley periods due to lack of regulating abilities. Also, frequency control issues caused by trip-off of wind farms from grid are worth concern. The paper probes and discusses the above two issues systematically and in-depth. The main work and the results are as follows.1. All the CHP plants have been operated full load in winter to satisfy the heat demand, giving limited space for wind power to access the grid especially in the off-peak hours at night, which would result in large wind power curtailment when output of wind power is larger than the limited space. Based on the experience of Denmark, the conception of CHP plants reducing their electric outputs to offer more space for wind power in load valley periods is proposed. Then the benefits of accommodating wind power by applying this conception in Northeast China grid are analyzed and the results show its validity. Furthermore, three feasible technical schemes of decoupling heat-power constraints of CHP plants are analyzed, and the key issues of implementing CHP plants to regulate for wind power are discussed.2. To encourage generation companies fully exploiting their potentials of peak load regulation, the marketing pricing mode for unconventional peak load regulation service is suggested under the current power system operation environment of China, especially the current generation price regime. The mode intents to inspire generation companies regulating peak load voluntarily and to lead the wind farm developing rationally with the ability of peak load regulation of system. By anatomizing the mechanism of limiting the wind farms’ outputs, based on the current management pattern of peak load regulation services, the basic trading framework of unconventional peak load regulation service with participation of wind farms is designed, and then the core issues and corresponding possible solutions are discussed. Analysis shows that the wind farm participated peak load regulation service market has several merits. It can generate price signal for active peak load regulation and rational expansion of wind power with the system acceptance ability, and can ensure the economic operation of system, and is also compatible with the current policy for supporting wind power development. 3. To smooth the large fluctuations of wind power output on the inter-day scale, ensure the stabilization of daily peak load for thermal power, and reduce the inter-day start-up and shut-down times of thermal units, a new operation strategy, combining the hydropower with wind power to regulate the peak of load, is advised with a weekly rolling decision framework. The theoretical analyses and numerical examples show that the combined operation of hydro and wind power generation system can not only smooth the large inter-day fluctuations of wind power output in daily peak hours and thus ensure the stabilization of daily peak load and start-up and shut-down operations for thermal power, but also improve the system peak-load regulating ability by utilizing the energy of wind power and the unused capacity of hydropower sufficiently and thus reduce the start-up capacity of thermal units and improve the operation economy.4. With the large-scale wind power integration, the original under--frequency load shedding scheme cannot meet design requirements any more. Thus, the impacts of fluctuating wind power and low frequency protection for wind turbine generator on under-frequency load shedding scheme are analyzed. And then the under-frequency load shedding scheme under large-scale wind power integration is designed. The analyses show that it is necessary to improve the traditional single machine model into multiple machines model. By considering the impact of wind turbines on the system model, a method of modifying the model parameters is proposed. Finally, the improved scheme is compared with the traditional scheme. The simulation results show that the improvement scheme can restrain the frequency falling effectively, and the effect of the recovery of frequency is better.The study shows that for the peak load regulation problem, the participation of CHP plants is an effective way to solve the wind power curtailments in future. The key is to have a good incentive mechanism, while the market is the most effective means. The combination operation of the hydropower with wind power can improve the peak load regulating ability of the system to some extent; thereby enhance the wind power accommodation level of the system. For the frequency control problem, the impact of wind turbines must be taken full consideration in the design of under-frequency load shedding scheme to ensure its reliability. The study would provide a useful reference for the solution of active power balance problem after the large-scale wind power integration in China.