Qiuyu Lu

Nonlinear decentralized excitation and governor coordinated control for hydraulic power plants

In this paper, a nonlinear decentralized excitation and governor coordinated controller design for hydraulic power plants is proposed to enhance power system transient stability. First, the excitation system and hydro-governor system, considering non-elastic water hammer effect, is modeled as a whole. Then, based on differential geometric theory, the original nonlinear system for multi machines is exactly linearized by appropriate coordinate transformation. After that, linear optimization control is applied such that the final optimized nonlinear excitation and governor coordinated control law can be obtained. To demonstrate the efficiency and analyze the coordination mechanism of the proposed controller, simulations on an OMIB system and the EPRI-36 system are performed. Comparison with classical excitation and governor control, nonlinear optimal excitation control, nonlinear robust governor control, the suggested decentralized and coordinated control can achieve pretty better performance in improving the transient stability of power systems.

Wind power uncertainty modeling considering spatial dependence based on Pair-copula theory

Wind power uncertainty modeling forms the foundation of stochastic optimization problems in wind power integration. Due to the similarity of meteorological conditions, outputs of adjacent wind farms have a natural consistency, as well as the forecast errors. Therefore, spatial dependence is imperative for joint wind power uncertainty model, especially for power flow optimizations and transmission risk assessments. The Pair-copula theory is introduced in this paper to construct the spatial relevance for multiple wind farms. The detailed modeling procedure, including model selection, parameter fitting, goodness-of-fit testing and random scenario generation, are explicitly presented. Simulation results show that Pair-copula is flexible in high dimension correlation analyses and can effectively improve the model accuracy.

Research on frequency simulation model and control strategy of hydropower islands

When send end hydropower islands isolated from interconnected grid in large disturbance, frequency of the island will fluctuate markedly. Regular prime mover and governor transient models are not accurate enough in simulating the frequency performance. In this paper, considering the nonlinear character of hydraulic turbine and the influence of no-load gate opening, hydraulic turbine and governor models feasible for long term frequency simulation involving large variation are established. The feasibility and accuracy of the models are verified by the load rejection test data of hydropower plant in Sichuan. Further simulations and analyses of hydropower islands with the above models are performed. For the over frequency problem of the islands, generator tripping scheme and its evaluated index are proposed which will be updated along with the changing of system operation points. The advantages of proposed methods are proved by simulations on hydropower islands in Sichuan.

Coordinated optimizing control strategy between power generators and power grid in Inner Mongolia

With the rapid development of the Inner Mongolia power grid, especially wind power capacity continuing to increase, its randomness and volatility put forward higher requirements on the grid to run scheduling. faced of the multi-level, multi-scale, multi-object complex grid, it is the problem to be solved - how to make full use of adjustable system resources and means of automation equipment, optimizing the operating status of the grid to achieve the coordination of the active and reactive optimization and distribution to ensure the safety of the grid, stability, economic operation. In view of the existing operating and scheduling technologies of Inner Mongolia power grid and drawing on the idea of hybrid control system, this article proposes a control strategy of machine net coordination and optimization based on layered event-driven control. This strategy takes into account indicators as economy, safety and quality of the system. It establishes a layered event driven control model to realize layered management and regulation of the whole system. It can automatically judge and select the optimal (or quasi optimal or appropriate) control mode, thus ensuring the sound dynamic quality of the entire power system while improving its stability and reactive power flow to reduce the network loss. Based on the control theory system, we conducted simulation analysis of Inner Mongolia power grid. The result reveals that the control strategy can not only keep contact line exchange power and central node voltage within permitted range, but also improve the economy and safety of the system. The simulation analysis proves that our control strategy can guarantee the safe, sound and economic operation of the system. It can elevate the automatic control level of Inner Mongolia power grid and guide fine adjustment of active and reactive power.

Online Evaluation of Primary Frequency Regulation Based on WAMS

Primary frequency regulation plays a significant role in power system frequency control. As a result of the separation of plant and grid, it becomes necessary for the grid to monitor the primary frequency performance of generators. This paper designs an online evaluation system of primary frequency regulation based on WAMS. Firstly, the evaluation indices system is proposed, which assesses the primary frequency performance of units from perspectives of static performance, dynamic performance and the regulating process. And the responding algorithms are designed for each index. In this part, a method of Variance Comparison, which helps to find the frequency changing point accurately, is presented to solve the key problem in calculation process. Besides, the impact of electromechanical transient process is taken into account when calculating the contribution electric quantity index and a practical modified method is presented. Computer simulations based on the large frequency disturbance in Hubei Grid are conducted, and the results illustrate the feasibility and efficiency of the proposed algorithms.

Research on Online Evaluation of AGC Performance Based on WAMS

In this paper, an online evaluation method for AGC regulation based on WAMS is proposed. Firstly, we put forwards the evaluation index system which integrates the indices in time scale and state dimension, thus make a comprehensive appraisal for AGC units. Then responding to the high sampling rate and high precision character of WAMS data, the control process of AGC regulation is divided into three segments: fast segment, assessment segment and time-out segment. Different methods are applied in different segments, so the calculation amounts and data storage can be efficiently declined to meet the requirements of online evaluation. The evaluation system is applied in Hubei Power Grid and the results verify the feasibility and efficiency of proposed method.