In recent years, the subsynchronous oscillation (SSO), which occurs in direct-drive permanent magnetic synchronous generators (D-PMSGs)-based wind farm, has great impact on the stability of power system. The different parameters and operation conditions of D-PMSGs lead to the subsynchronous interaction (SSI) among D-PMSGs. What is more, the SSI will influence the SSO characteristics of the system of D-PMSGs-based wind farm integrated to AC network. Here, considering the difference of parameters or operation conditions among D-PMSGs in the wind farm, eigenvalue analysis, based on the smallsignal state-space model of two aggregated D-PMSGs which are equivalent to wind farm, is carried out. Then the stability and the SSI between D-PMSGs of the equivalent system can be studied, and the dominant D-PMSG can be determined based on the participation factors. Lastly, the detailed electromagnetic transient simulation model of D-PMSGs equivalent system is built in PSCAD/EMTDC. The simulation is conducted to corroborate the eigenvalue analysis. The result shows that an obvious SSI exists between two aggregated D-PMSGs. Furthermore, the different SSO characteristics among D-PMSGs in the wind farm indicate the study of SSO problem based on an aggregated D-PMSGs model may leave out some useful information.
Three attributes relevant to a specific project, including the number of activities in chain, the uncertainty of activities duration and the flexibility of activities start time, were introduced into critical chain project management for sizing buffer. By means of simulation research, the impact of these three attributes on project scheduling in terms of two performance indicators: project duration and on time completion was evaluated. Based on the analyses of simulation experiment, a revised method for sizing buffer was proposed. The case indicates that the performance of project scheduling is significantly improved by using the revised method.
This paper presents the controller design and a simple method to identify the aerodynamic performance for an installed vertical axis wind turbine (VAWT). The hardware realization of the wind energy conversion system consists of a 1.5kW VAWT-driven permanent magnet synchronous generator (PMSG), a PWM rectifier and a grid-tied PWM inverter. The PWM inverter is mandatory to maintain the dc capacitor voltage mainly adapted for operating in parallel with the power grid. The PWM rectifier, serving as a speed governor, is employed to modulate the revolution speed of the VAWT according to the desired power-speed curve so as to extract maximum power from the wind. To guarantee the aerodynamic performance of the VAWT, a simple method, based on the long-term recorded energy efficiency, can determine the optimum power-speed curve for the VAWT. The effectiveness of the proposed strategy is assessed experimentally by examining the closed-loop system response to various wind speeds.
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