5715ch2 - 2 Wound Rotor Induction Generators: Transients...

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2 -1 2 Wound Rotor Induction Generators: Transients and Control 2.1 Introduction . ...................................................................... 2 -1 2.2 The WRIG Phase Coordinate Model. ............................... 2 -2 2.3 The Space-Phasor Model of WRIG . ................................. 2 -5 2.4 Space-Phasor Equivalent Circuits and Diagrams . ........... 2 -7 2.5 Approaches to WRIG Transients. .................................... 2 -12 2.6 Static Power Converters for WRIGs . .............................. 2 -13 Direct AC–AC Converters DC Voltage Link AC–AC Converters 2.7 Vector Control of WRIG at Power Grid. ........................ 2 -18 Principles of Vector Control of Machine (Rotor)-Side Converter Vector Control of Source-Side Converter Wind Power WRIG Vector Control at the Power Grid 2.8 Direct Power Control (DPC) of WRIG at Power Grid. ....................................................................... 2 -34 The Concept of DPC 2.9 Independent Vector Control of Positive and Negative Sequence Currents. ........................................... 2 -39 2.10 Motion-Sensorless Control. ............................................. 2 -41 2.11 Vector Control in Stand-Alone Operation. .................... 2 -44 2.12 Self-Starting, Synchronization, and Loading at the Power Grid. ............................................................ 2 -45 2.13 Voltage and Current Low-Frequency Harmonics of WRIG. ........................................................................... 2 -49 2.14 Summary. .......................................................................... 2 -51 References. ................................................................................... 2 -53 2.1 Introduction Wound rotor induction generators (WRIGs) are used as variable-speed generators connected to a strong or a weak power grid or as motors in the same conditions. Moreover, WRIGs may operate as stand-alone generators for variable speed. In all these operational modes, WRIGs undergo transients. Transients may be caused by the following: • Prime mover torque variations for generator mode • Load machine torque variations for motor mode © 2006 by Taylor & Francis Group, LLC
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2 -2 Variable Speed Generators • Power grid faults for generator mode • Electric load variations in stand-alone generator mode During transients, in general, speed and voltage, current amplitudes, power, torque, and frequency vary in time, until eventually, they stabilize to a new steady state. Dynamic models for typical prime movers (Chapter 3, Synchronous Generators ), such as hydraulic, wind, or steam (gas) turbines or internal combustion engines, are needed to investigate the complete transients of WRIGs. An adequate WRIG model for transients is imperative, along with close-loop control systems to provide stability in speed, voltage, and frequency response when the active and reactive power demands are varied. Typical static power converters capable of up to four-quadrant operation (super- and undersynchro- nous speed) also need to be investigated as a means for WRIG control for constant stator voltage and frequency, for limited variable speed range. Vector or direct power control methods with and without motion sensors are described, and sample transient response results are given. Behavior during power grid faults is also explored, as, in some applications, WRIGs are not to be disconnected during faults, in order to contribute quickly to power balance in the power grid right after fault clearing. Let us now proceed to tackle the above-mentioned issues one by one.
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5715ch2 - 2 Wound Rotor Induction Generators: Transients...

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