Modeling and small-signal stability analysis of doubly-fed induction generator integrated system

Owing to their stability,doubly-fed induction generator(DFIG)integrated systems have gained considerable interest and are the most widely implemented type of wind turbines and due to the increasing escalation of the wind generation penetration rate in power systems.In this study,we investigate a DFIG integrated system comprising four modules:(1)a wind turbine that considers the maximum power point tracking and pitch-angle control,(2)induction generator,(3)rotor/grid-side converter with the corresponding control strategy,and(4)AC power grid.The detailed small-signal modeling of the entire system is performed by linearizing the dynamic characteristic equation at the steady-state value.Furthermore,a dichotomy method is proposed based on the maximum eigenvalue real part function to obtain the critical value of the parameters.Root-locus analysis is employed to analyze the impact of changes in the phase-locked loop,short-circuit ratio,and blade inertia on the system stability.Lastly,the accuracy of the small-signal model and the real and imaginary parts of the calculated dominant poles in the theoretical analysis are verified using PSCAD/EMTDC.

The Method of the SiC MOSFET Replacing the Si IGBT in the Traditional Power Electronics Converter without Redesigning the Main Circuit and the Driver Circuit

As a wide bandgap power electronics device,the SiC MOSFET has a lot of advantages over the traditional Si IGBT.Replacing the Si IGBT with the SiC MOSFET in the existing power electronics converter is an effective means to improve the performance and promote the upgrading of the traditional converter.Generally,in order to make full use of its advantages of the SiC MOSFET,the Si IGBT in the traditional power electronics circuit cannot be simply replaced by the SiC MOSFET,but the main circuit and the driver circuit need to be redesigned because the oscillation problem and the cross-talk problem caused by the parasitic parameter are very serious when the SiC MOSFET switches.However,considering the low cost and the short cycle requirement of the equipment development,it is often difficult to redesign the circuit hardware structure of all converters.In order to resolve this contradiction,a ferrite bead based method is proposed in this paper.Through this method,without redesigning the hardware structure of the main circuit and the driver circuit,the SiC MOSFET can be used to replace the Si-based power electronics device directly,and the loss of the converter can be reduced with small oscillation.Finally,the effectiveness of the proposed method is proved by experiments.

Research on the Impacts of the Inertia and Droop Control Gains from a Variable-Speed Wind Turbine Generator on the Frequency Response

System frequency must be kept very close to its nominal range to ensure the stability of an electric power grid.Excessive system frequency variations are able to result in load shedding,frequency instability,and even generator damage.With increasing wind power penetration,there is rising concern about the reduction in inertia response and primary frequency control in the electric power grid.Converter-based wind generation is capable of providing inertia response and primary frequency response;nevertheless,the primary frequency and inertia responses of wind generation are different from those of conventional synchronous fleets;it is not completely understood how the primary frequency and inertia responses affect the given system under various disturbances and available kinetic energy levels.Simulations are used to investigate the influences of inertia and droop control strategies on the dynamic frequency responses,particularly the index of the second frequency drop under various disturbance and wind conditions.A quantitative analysis provides insight into setting of inertia and droop control coefficients for various wind and disturbance conditions to facilitate adequate dynamic frequency responses during frequency events.

How to manage a task-oriented virtual assistant software project:an experience report

Task-oriented virtual assistants are software systems that provide users with a natural language interface to complete domain-specific tasks.With the recent technological advances in natural language processing and machine learning,an increasing number of task-oriented virtual assistants have been developed.However,due to the well-known complexity and difficulties of the natural language understanding problem,it is challenging to manage a task-oriented virtual assistant software project.Meanwhile,the management and experience related to the development of virtual assistants are hardly studied or shared in the research community or industry,to the best of our knowledge.To bridge this knowledge gap,in this paper,we share our experience and the lessons that we have learned at managing a task-oriented virtual assistant software project at Microsoft.We believe that our practices and the lessons learned can provide a useful reference for other researchers and practitioners who aim to develop a virtual assistant system.Finally,we have developed a requirement management tool,named SpecSpace,which can facilitate the management of virtual assistant projects.