In order to identify weaknesses in distribution network planning alternatives, providing a scientific basis for grid investment decisions, effective and comprehensive evaluation is needed. According to the related principles and objectives, this paper establishes a comprehensive evaluation index system based on hierarchy. This system is guided by the long-term development strategy of China southern power grid, including six strategic layer indices as safety and reliability, economic efficiency, coordination and flexible, smart and green, controllable risk and social benefits. The meaning and classification of every index is listed in details. According to different technical characteristics of every index different fuzzy membership functions are structured. Furthermore, in accordance with the relevant guidelines and specifications, this paper gives specific values of the membership function parameters to achieve standardization of indexes of different dimensions, laying the foundation for a comprehensive assessment.

Doubly fed induction generator (DFIG) is now becoming one of most widely used wind turbines in global market for wind power generation, due to its outstanding advantages. However, the DFIG is sensitive to grid faults. The DFIG will have to be removed from the grid if there’s no protection appliance in it. Therefore, the crowbar protection is widely used in the world for improving the low voltage ride-through ability of wind turbines. This paper analysed the operating characteristics and short-circuit current of DFIG under symmetrical short-circuit fault with respect to different sags to grid voltage, which on the basis of DFIG wind turbine with crowbar protection. And the expressions of short-circuit current under symmetrical short-circuit fault for DFIG were derived. The effectiveness of the expression was simulated in PSCAD/EMTDC.

This paper presents a stochastic programming method that can assess the impact of wind generation uncertainties on unit comment (UC) problem. To model the uncertainty of wind genration, scenarios of wind speed are generated based on the known probability interval of forecasted wind speed and a scenario reduction technique limits the number of scenarios. The UC problem is modeled as a stochastic programming problem based on chance-constrained programming, and is decomposed into two embedded optimization sub-problems: the unit on/off status schedule problem and the load economic dispatch problem. Discrete particle swarm optimization (DPSO) and the equal incremental principle are used to solve the stochastic UC problem. The numerical results indicate that the proposed stochastic model is more suitable for wind integrated system with uncertainty.

Wind power is the most fast growing energy source in the world while its intermittency and uncertainty generate stability, reliability and power quality problems in the electric grid. A battery/supercapacitor Hybrid Energy Storage System (HESS) is integrated to the directly driven Wind Turbine Generation (WTG) system to achieve a better wind power output characteristic. When integrated to a grid connected WTG, the supercapacitor and battery respectively absorbs the high frequency part and low frequency part of the wind fluctuations. Feedback elements are added to achieve a better performance of this management algorithm. While for a HESS applied to the stand-alone WTG system, the supercapacitor supports the frequency of the isolated system after the islanded operation and PI controllers are used. The control models are developed by the User Definition (UD) module on Power System Analysis Software Package (PSASP). Simulations are carried out to verify the control strategies effective and feasible.

Research of power flow evenness has great significance for grid steady state analysis. This paper researched for a method for power flow evenness analysis through entropy theory. According to current power flow distribution and branch power limits, the branch load ratio distribution could be obtained, and the power flow entropy was calculated based on discrete information entropy theory. The study case indicates that the power flow entropy effectively describes the power flow evenness. With certain system load level, the system security level will be dramatically declined when power flow evenness reduces to a certain level, which is demonstrated in the case meanwhile. Power flow evenness analysis based on entropy theory is applicable in power system static security assessment.