| With the advocating of environment protection and energy saving on a global scale,variable-speed constant-frequency generation technology is highly developed, and is promoted in wind power and other new energy power generation field. Due to the unique design of ontology, the widely studied brushless doubly-fed generator(BDFG) not only has the advantages of other variable-speed constant-frequency electric system, but also shows a series of unique characteristics. Like other ac excitation doubly-fed generator system, brushless doubly-fed generation system not only can significantly save the size and capacity of frequency conversion device, and can effectively adjust the active and reactive power output when connected to the grid, but also saves the cost and it is convenient for later use and maintenance since the slip ring and brush are took out, which means BDFG system is more adaptive to the brutal environment of wind farm.Before the BDFG come into use on a large scale, many issues need to be studied.This paper is about the operation strategy of the connecting-to-grid and the synchronization phase-locked loop. Differing from synchronous generator interconnection methods, the BDFG system does not require the speed synchronization due to the characteristic of variable speed constant frequency. The paper adopts a similar scalar control method to fulfill the synchronizing of the voltage, which avoids the complex parameters of BDFG ontology. Meanwhile, when connected to the grid, the network voltage, especially the phase of it needs to be measured accurately and rapidly. And when the voltage is unbalanced or sudden changed, a common PLL may not work well. This paper proposes a special-designed PLL based on a dual d-q coordinate system to meet the demand.The project at last complete the construction of the experimental platform and verify the feasibility of the control strategy. And the method of phase locked loops is verified through simulation. |
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