Investigation Of New Variable-Speed Constant-Frequency Wind Power Generating System Operation

Variable-speed constant-frequency (VSCF) operation is a new high efficient technology for power generation, which has a good future in the field of wind power generating. In this paper, several scheme of VSCF is compared firstly, of which gets doubly-fed generating mode. Doubly-fed VSCF wind power generating system uses a doubly-fed induction generator, which rotate speed can be able to change with wind turbine, and it ensures a constant-frequency output, by controlling the frequency of current input into rotor windings. In vector trans control system, the control of stator active power and the control of stator reactive power can be essentially decoupled, and the former is via torque component and the latter is via exciting component of stator current.After analyzing the mathematical model of wind turbine and doubly-fed induction generator, a schematic is given about the power flow in the wind turbine and generator and a static equivalent circuit is shown as well. Then, through the reference frame transform, the electromagnetic equation, dynamic equivalent circuit, and vectorgraph of doubly-fed generator can be gotten in the dq reference frame. In virtue of the general dynamic equivalent circuit, it produces a asymmetry equivalent.Furthermore, under the vector control strategy of stator field-orient, a vector control model will derive from the generator, which form a close control system with the generator model.About the transducer between rotor and power source, the paper uses a cycloconverters, comprising 36 thyristors, and analyzes the control of circumfluence, the method of cosine crossing, the producing of trigger pulse, zero current detecting, commutating logic control and its mathematical model.In the simulation experiment, the whole system model is founded by the software Matlab/Simulink. Using the stator active power computed from the maximal output power of the wind turbine as the reference value of vector control system, the result of experiment approves that the control strategy is true. Not only the frequency of stator current is constant, but the control of stator active and reactive are decoupled, and the output power tracks the maximal power of wind turbine.