Tip Leakage in a Centrifugal ImpellerThe effects of tip leakage have been studied using a 1-m-dia shrouded impeller where a leakage gap is left between the inside of the shroud and the impeller blades. A comparison is made with results for the same impeller where the leakage gap is closed. The static pressure distribution is found to be almost unaltered by the tip leakage, but significant changes in the secondary velocities alter the size and position of the passage wake. Low-momentum fluid from the suction-side boundary layer of the measurement passage and tip leakage fluid from the neighboring passage contribute to the formation of a wake in the suction-side shroud corner region. The inertia of the tip leakage flow then moves this wake to a position close to the center of the shroud at the impeller outlet.
A comparison is made between the flow in two impellers, one with radially ending blades and one with blades backswept by 30°. The two impellers have identical inducers. Measurements are made of the three velocity components and total pressures across five measurement stations within each impeller. The flow in the backswept impeller is dominated by a counter-clockwise vortex which reduces the severity of the shroud boundary layer separation and hence leads to a higher impeller efficiency. The wake is consequently smaller in the backswept impeller but adopts a similar position on the shroud surface at the impeller exit. Analysis of the secondary flow generation reveals the mechanisms responsible for the differences in the flow fields in the two impellers.
Double Fed Induction Generators (DFIG) has been widely used for the past two decades in large wind farms. This paper presents control and analysis of the doubly fed induction generator (DFIG) connected to variable speed horizontal axis wind turbine (HAWT). The detailed wind turbine (WT) model, DFIG dynamic model in d-q-synchronous reference frame, power electronic converters, and controllers are presented. The reactive and active power of the DFIG can be precisely decoupled by controlling the rotor side converter (RSC). The field-oriented control (FOC) strategy and the proportional-integral (PI) controllers were used to control the RSC of the DFIG. Furthermore, a space vector pulse width modulation (SVPWM) was utilized to generate pulsing signals required to drive three phases DC-AC converter (inverter). The proposed control method of DFIG based on HAWT was verified by simulation in MATLAB-SIMULINK software. The obtained simulation results showed the capability and effectiveness of the proposed control method.
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