提高短期频率稳定性的紧急需求响应分散协调控制方法

短期频率稳定问题是多(特)高压直流馈入受端电网面临的重大安全隐患,紧急需求响应(emergency demand response,EDR)为解决该问题提供了一种思路。针对此前集中式EDR控制依赖高速专网、实现成本高而分散式EDR控制精度低的问题,提出一种多EDR资源的分散协调控制方法,将分散决策与集中决策通过慢速通信互联起来,利用全网惯性中心频率变化率的一致性,解决了无高速专用信道条件下多EDR控制的协同优化问题。在典型受端电网仿真模型上应用该方法,验证了其在馈入直流双极闭锁等场景下提高系统短期频率稳定性的良好控制性能。

Research on resonance fault caused by dc magnetic biasing in ultra high voltage transformer with parallel static var compensator

For dealing with the resonance fault of ultra-high voltage transformers(UHVTs)with the parallel thyristor controlled reactor(TCR)+the filter compensator(FC)type static var compensator(SVC)caused by dc magnetic biasing,a simulation model of UHVT with parallel SVC for the frequency analysis of the impedance characteristics and a magnetic-field coupling model for UHVT based on classic Jiles-Atherton hysteresis theories are constructed based on the MATLAB/Simulink platform.Both the theoretical and simulation results prove that the resonance fault is caused by the resonance point on the low-voltage side of the transformer,which will approach the 4th harmonic point under magnetic biasing.Based on the fault analysis,a new resonance control method is proposed by adding reactance with by-pass switches in series with FC branches.Under dc magnetic biasing,the cutoff of the by-pass switch will increase the series reactance rate of the FC branches and change the resonance point.In order to avoid the 7th harmonic increasement caused by this method,the firing angle of the TCR branches is locked between 130°and 180°.The effect of the proposed method is validated by the simulation model of a 750 kV UHVT and the results show that the mechanism analysis of the resonance fault is correct and the resonance control method is valid.

Study on Transmission Planning of Cascade Hydropower Stations along Lancang River Basin

Most of the hydropower projects in Southwest China and the adjacent foreign regions will be put into operation between 2015 and 2020, which will bring some difficulties for reasonable accommodation and delivery of electric energy. In this paper the author studies the development scale, development schedule, accommodation and transmission schemes of the cascade hydropower stations along the Lancang River basin, one of the five large basins in China, based on the load characteristics of grids at both the sending end and the receiving end, the strategy of complementary utilization of thermal power and hydropower, the advanced transmission technologies, and the optimal economic performance. The study results show that, the cascade hydropower stations on the upper reaches of the Lancang River in Yunnan should mainly serve Guangdong Province, with proper planning of partly serving Yunnan Province during dry seasons. The transmission schemes should adopt UHVDC, UHVAC, and single-tower double-circuited HVDC transmission scheme according to the transmission capacity and distance.

Safe Distance for Inspection of 1 000 kV UHVAC Lines with Helicopter

Helicopter inspection of ultra high voltage （UHV） transmission lines has unmatched advantages compared to manual work due to the inspection angle and high-tech equipment on board, especially in detailed inspections of tower heads and defect-detections in virtue of infrared/ultraviolet techniques. This paper deals with some key technical problems in the inspections of i 000 kV UHVAC lines with a helicopter, such as the safe distance of live-line working, electromagnetic field intensity and flight control. Based on the study results, a set of UHV line inspection methods was worked out and applied to the inspection of live UHV lines.

Oscillation analysis of a DFIG-based wind farm interfaced with LCC-HVDC

With the increasing capacity of wind farm, HVDC technology has become a promising transmission scheme for long distance transportation of large-scale wind power. However oscillation caused by this system will have a great influence on the security and stability of power system operation. In this paper, the oscillation of a doubly-fed induction generator(DFIG)-based wind farm interfaced with line commutated converter(LCC) based HVDC is discussed. Low-frequency oscillation and subsynchronous oscillation(SSO) are studied since these two oscillations are the particularly concerned oscillations in the stability study of power system in recent years. The model of a DFIG-based wind farm interconnected with LCC-HVDC is developed. The impact of drive train model's structure and parameters on the oscillation characteristics is analyzed. Eigenvalue and participation factor analysis are used to identify the three main modes, which include controller mode, electromechanical mode, and shaft mode. The effects of DFIG controller's parameters, wind speed and operating conditions of HVDC on those modes are studied. Electromagnetic transient simulations are performed to verify the results of the eigenvalue analysis.