University of South Wales Master of Sciences Thesis
Standalone hybrid generation system for the remote area of Thar, Pakistan
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- 2.4.2. PMSG Controller Modeling
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Standalone hybrid generation system for the remote area of Thar, Pakistan Fig. 2.14. Cross sectional view of rotor design of a) SPMSG and b) IPMSG. 2.4.1. Operating Principle of PMSG In permanent magnet synchronous machines, magnets are placed on the rotor as alternate N and S poles. These magnets cause the development of magnetic flux in the air gap. When the stator windings are excited, they develop their own magnetic flux, and the close interaction between rotor and stator magnetic fields produces electromagnetic torque in the rotor. Fig. 2.15 shows a simplified cross-section view of 3-phase, 2-pole PMSG with symmetrical stator windings, displaced from each other at a 120° electrical angle. The relative motion between rotor and stator induces sinusoidal MMF waves on the magnetic axes of the respective phases. The phase difference between rotor magnetic flux and the magnetic axis of stator phase-a winding is known as rotor position angle (θr). The rate of change of rotor position angle further calculates the angular rotor speed (ωr )[27, 28]. Fig. 2.15. Cross-section view of 3-phase, 2-pole PMSG. 2.4.2. PMSG Controller Modeling The primary objective of the PMSG control is to extract optimum power from varying wind and ensures efficient operation of the PMSG 2.4.2.1. Optimum power control The optimum power extraction concept can be defined as the extraction of required power from a wind turbine under varying wind conditions [26]-[29]. In a variable speed wind turbine, the relationship between rotor speed and the output power for a given wind speed is shown in Fig. 2.13. Standalone hybrid generation system for the remote area of Thar, Pakistan The detailed relationship between the rotor speed and the output power for a given wind speed is discussed in the variable speed wind turbine model section. From (2.13) and (2.14), the applied torque or the extracted power from the wind can be controlled by regulating the rotor speed. By rearranging, the relationship between the applied torque and the rotor speed can be defined as follows: 2.23 where K opt is given by 2.24 The optimum power can be as follows: - 2.25 The rotor speed at optimum power point can be expressed as follows: 2.26 Optimum power can be extracted by controlling the rotor speed. Fig. 2.16 demonstrates the power generated by a turbine as a function of the rotor speed for different wind speeds. As an example, for a particular wind speed (v6), the optimum power (PWopt) can be generated by keeping the rotor speed either equal to ω1 or ω3. However, as ω3 is higher than the base rotor speed, the control system must choose the rotor speed ω1. If the wind speed drops to v5 from v6, the control system sets the rotor speed to ω2 to extract the required power. Fig. 2.16. Power generation of wind turbine in different rotor and wind speeds. tải về 6.62 Mb. Chia sẻ với bạn bè của bạn:
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