Analysis Of BDFG Control Strategy With Unbalanced Loads Basd On Wave Power Generation

Brushless doubly-fed motor or BDFM is a new type of AC motor which is developingrapidly in recent years. It has two separate stator windings and one rotor winding with specialstructure. By using a converter to control the frequency of the voltage of stator control winding,the rotor speed of BDFM can be controlled. BDFM has many advantages. Unlike common ACmotor, BDFM doesn’t have brush and its structure is simple and robust, the converter capacitylinked to is smaller and the power factor of BDFM is adjustable. So, BDFM is a strongcompetitor with custom AC motor and DC motor. In the application field of large pump, windpower generation, wave power generation and so on, BDFM has a vast potential for futuredevelopment.This paper is written under the background of wave power generation. And do somesimulation reserach to BDFG and its control strategy. Firstly, by using coordinatetransformation theory, the dynamic mathematical models of BDFM are built, includingthree-phase static model, two-phase synchronous rotating model and bisynchronous rotatingmodel. On the basis of two-phase rotor speed dq model, the simulation model of BDFM is builtin MATLAB/SIMULINK simulation environment. To test the dynamic performance of BDFM,the model of BDFM is set to run in single feed asychronous mode, doubly-fed synchronousmode, doubly-fed subsynchronous mode and hepersynchronous mode.Based on the simulation results of the test of BDFM dynamic performance, various kindsof control strategies for BDFM are introduced. Specially, power control strategy for BDFGbased on the rotor speed dq model has been studied. And then build the simulation model ofBDFG using power control strategy in the MATLAB/SIMULINK software environment,analyze the wave form of active power,negative power and electromagnetic torque of BDFG.It is found that when the voltage of power grid is normal and three-phase balanced, the BDFGgeneration system runs fine; and when the voltage of power grid is three-phase unbalanced, thewave form of active power, reactive power and electromagnetic torque of BDFG wouldfluctuate severely. To eliminate the impact of the unbalancement of power grid to BDFGgeneration system, an unbalanced control method of BDFG based on internal model control isproposed. And then a simulation of BDFG generation system based on this control strategy isbuilt in the MATLAB/SIMULINK software environment. Simulation results show that thefluctuations of active power, reactive power and electromagnetic torque of BDFG are improvedand they could be floating controlled in this new method. The simulation results also show the correntness of the proposed control strategy.