tailieunhanh - Fundamentals of Electrical Drivess - Chapter 4

Chapter 4 THREE-PHASE CIRCUITS Đa số các hệ thống truyền động điện sử dụng được hỗ trợ bởi một giai đoạn ba được gọi là (ba dây) cung cấp. Lý do chính của việc này là chuyển giao năng lượng hiệu quả hơn từ cung cấp cho tải, chẳng hạn như một máy AC ba giai đoạn, có thể so sánh với một mạch AC (hai dây). Tải, máy hoạt động như một động cơ, được hình thành bởi ba giai đoạn. Mấu Mỗi giai đoạn trong đó có hai thiết bị đầu cuối, năng suất tổng cộng sáu thiết bị. | Chapter 4 THREE-PHASE CIRCUITS Introduction The majority of electrical drive systems in use are powered by a so-called three-phase three wire supply. The main reason for this is that a more efficient energy transfer from supply to the load such as a three-phase AC machine is possible in comparison with a single two wire AC circuit. The load being the machine acting as a motor is formed by three phases. Each phase-winding of which has two terminals yieldingatotalof six terminal-bolts usually configured as sketched in figure . The phase impedances are assumed to be equal. Figure . Connector on a tlựee phmemachịne with a total of six terminals The terminal lay-out as shown in figure has been purposely chosen to allow the user to readily connect the machine s phase windings in two distinct configurations. The star and delta configurations are depicted in figure and figure respectively. Voltages and currents in the different conhgurationsare identified by the subscripts SI S2 S3 when the machine is in star wye or Y-configuration. Subscripts DI D2 D3 apply to the delta or A configuration. The voltages currents identified by the subscripts R s T are linked to the supply source which iuusuahy ecpowcr electigmcconvhrtesor tho thip c-phasi grid. Figure shows an euampte oi alhrpp-pianp vohagptiicp y svhich gcnai c ates three voltages-of ívtóha-yohcpep up. Us UT dia-civwlahicidwhh aps ccc1 to the ov neutralloffihis sye-pm. hl this chupgpo wc win pc o mtomodlp lpcu 76 FUNDAMENTALS OF ELECTRICAL DRIVES Figure . Supply convention voltage sources shown three-phase circuits and in this context introduce a new set of building blocks as required to move in both directions from machine phase variables to supply variables for either star or delta connected machines. So-called space vectors are introduced as an important tool to simplify the dynamic analysis of three-phase circuits. In the sequel to this chapter the link between phasors and space vectors is